Motion Control Tips Editor - Motion Control Tips

CC-Link Partner Association Announces ASCO CC-Link IE Field Certification

September 28, 2016 By Motion Control Tips Editor Leave a Comment

Continuing to strengthen CC-Link’s position as a leading global open automation network technology, the CC-Link Partner Association (CLPA) announced today that ASCO has received CC-Link IE Field Network Certification for their Numatics valve manifold with G3 Fieldbus Electronics.

ASCO introduces its CC-Link IE Field certified Numatics valve manifold with G3 Fieldbus Electronics with integrated scalable I/O that is designed to work as a complete pneumatic valve manifold and I/O solution interfacing with CC-Link IE Field Industrial Ethernet Network applications:
• Numatics G3 CC-Link IE Field Communications Module (P/N: 240-362)

CC-Link is a high-speed, high-performance family of open automation network technologies that enable devices from numerous manufacturers to communicate, resulting in a fast, deterministic control system. CC-Link is managed by the CLPA, an organization comprised of manufacturers and users of CC-Link technology, academics and other interested parties.

ASCO is a global innovation leader in fluid automation technology. The ASCO product line has a history of technological breakthroughs. ASCO offers a broad range of 2, 3, and 4-way air-piloted and solenoid-operated directional control valves with fieldbus and I/O capabilities, along with a full offering of fluid power and fluid control products.

As a part of their fluid power line up, ASCO offers ISO & NFPA cylinders, ISO compliant valves, line-mounted valves, poppet valves for compressed air or vacuum service, lock-out and shutoff valves that prevent unauthorized pressurization, and valves designed for specific industries, such as SAE-compliant automotive valves. For applications that require rapid response and tight control over pressure and flow, ASCO has the automation industry’s most complete line of proportional valves!

CC-Link IE Field is a 1 Gbit/s Ethernet-based network that provides exceptional data bandwidth and transaction rates. It unifies the best of present technologies with an easy construction and a flexible network topology. ASCO is a proud member of CC-Link Partner Association (CLPA). You can learn more about ASCO.com.

About the CC-Link Partner Association (CLPA)
Established in 2000, the CC-Link Partner Association (CLPA) is an international organization with more than 2,600 member companies worldwide.

TEL: (847) 478-2647
E-Mail info@CCLinkAmerica.org
CCLinkAmerica.org 

Designing motors with safety in mind

September 9, 2016 By Motion Control Tips Editor Leave a Comment

by Hilary Whiting, Manufacturing Engineer, Advanced Manufacturing, Kollmorgen

With scientifically verified hygienic design principles, motor manufacturers are designing motors for food and beverage applications that dramatically improve safety.

The food and beverage industry is one where safety is paramount. That’s why food and beverage companies and their machine suppliers are battling constantly to keep their products safe. These microscopic battles are fought with large quantities of water and chemical sanitation processes. Hygienic machine design is critical even down to the sub-component level in order to allow these processes to be effective in removing product residues as well as pathogens, and destroying bacterial intruders.

Motor H does not have any metal to metal joints. Instead, all joints are mated with gaskets. The gaskets are bright blue in color to contrast against food products.

Both the North American Meat Institute (NAMI) and the European Hygienic Engineering Design Group (EHEDG) have published lists of Hygienic Machine guidelines (See Table 1). One of the challenges in meeting these guidelines is the design of components such as motors, gearboxes, and sensors.

Table 1: NAMI guidelines table of continence *referenced from Fact Sheet, Sanitary Equipment Design, American Meat Institute, 2012

Kollmorgen set out to verify the benefits of hygienic machine design by partnering with the Virginia Tech Department of Food Science and Technology (VT FST). These hygienic design principles could then be applied to the design of servomotors used in the food and beverage industry.

Test motors were a representation of commonly used motors on food and beverage equipment.

Scientific testing
A series of tests were conducted to determine the sanitizability of three servomotor designs. The three motors tested were an industry standard IP67 wash down servomotor designated as Motor W, a stainless steel motor used in the food and beverage industry designated Motor C, and a stainless steel servomotor designed to comply with the NAMI hygienic design checklist and EHEDG design parameters designated Motor H. These motors represent the most common types used in food and beverage equipment.

Each motor was inoculated with ATCC 25922 strain of E. coli. The study focused on determining the sanitizability at areas of concern on the motor’s surfaces including labels and surface finish, seals and fasteners, and cabling. The team focused on these areas to see how design features affected the ability of the servomotor to be sanitized of E. coli. These areas were marked and isolated, then put in contact with 10 μl of E. coli for one hour. During this time, the motors were run at amperage that kept their surface temperatures between 33 °C and 38 °C, non-lethal temperatures for E. coli.

Sites were inoculated with E. coli and sampled prior to the cleaning and sanitation procedure (pre-wash) to determine a baseline. A typical industry cleaning and sanitation procedure supplied by a leading food production company was used to clean and sanitize each of the motors. The marked sites were sampled again post-wash to determine if the area was successfully sanitized. The test included three repetitions of this process to provide an appropriate data sample size. The reported study findings can be seen compiled in Table 3. This data could then be used to draw conclusions about the impact of design features on the sanitizability of the three motors.

Table 3: Pre-wash and post-wash E.coli sampling.

Label and surface finish testing results
The first sets of locations to be evaluated are those pertaining directly to labeling and surface finish on the motors. Motor W has labels etched onto the surface of the aluminum housing (Figure 1) and the surface is covered with food grade paint. The rough finish of the etched label was identified as high risk to harbor bacteria. Motor C has stamped labeling with a brushed surface finish on its housing (Figure 2). The brushed surface finish of Motor C was identified as an area of concern due to the textured surface finish, so was targeted as a sampling location by the test team. Motor H has a smooth stainless steel housing that holds a 32 μ-in. surface finish or better, even across the annealed label face (Figure 3). In the NAMI guidelines Principal 6.1 states; “It is recommended product contact surfaces textures shall not exceed 32 μ-inches…” The housings and labeling methods of Motor W and Motor C do not comply with this guideline, but Motor H is compliant. Both Motor W and Motor C were found to have E. coli present on their surfaces post-wash, whereas Motor H was not found to have any. So the lack of bacterial recovery post-wash from Motor H supports the NAMI design guidelines regarding surface finish and external materials as verified through the scientific testing.

Fig. 1: Motor W has an etched label covered with paint. The etching process creates a rough uneven surface that can create niches where bacteria and food product may be harbored.

Fig. 2: Motor C has a high-risk texture surface for product trapping and bacteria harboring. The uneven surface finish creates niches where microorganisms can hide.

Fig. 3: Motor H features an annealed label with a 32 μ- inch surface finish. Unlike etching, the annealed label preserves the metal’s surface finish. This smooth label was designed to avoid trapping bacteria or food.

Seal and fastener testing results
Seals and fasteners were the second group of test locations investigated. The NAMI guidelines caution against the use of fasteners above product areas in Principle 7 as well as stating that seals and O-rings must be designed to minimize product contact, Principle 2.9. Most standard fasteners create niches or spaces where microorganisms and product can be harbored. Principle 6 of the NAMI guidelines explicitly outlines the need for elimination of niches. Both Motor W and Motor C have external screws, a shaft seal, and several metal-to-metal joints (Figures 4 and 5) while Motor H has hygienically designed gasket joints instead of metal-to-metal joints, as well as a shaft seal, and does not use any external screws or fasteners. Motor W was found to have bacteria present post-wash on all of its junctures except the seal surface where the shaft was spinning. Motor C was found to have E. coli present on the outer juncture of the shaft seal. However, on the surface of Motor H, E. coli bacteria were not found to be present on any external sealing surface after sanitation. So here again, the lack of E. coli recovery supports the NAMI design guidelines regarding fasteners and junctures.

Fig. 4: Motor W has metal to metal joints that are covered by a layer of paint. The motor has eight screws in total.

Fig. 5: Motor C has metal to metal joints at both ends of the motor body. The end cover joint is secured with six screws as seen in Figure 2.

Cable and hardware testing results
The third area examined on the test motors was the cables and hardware. The NAMI guidelines do not explicitly address cables, but the general material guidelines can be applied in addition to Principle 6, the elimination of niches. Both Motor W and Motor C were found to have bacterial colonies on the cable and both cable fitting interfaces. The VT FST test team was not able to recover any E. coli on the cable or the cable junctures for Motor H, post-wash. The cable of Motor H was specifically designed to not harbor bacteria and withstand harsh wash down procedures. The cable connection to the motor is also sealed using a bushing interface instead of a metal to metal interface like Motor W and Motor C. Here, too, the lack of post-wash bacterial recovery on Motor H supports the NAMI guidelines regarding material specifications and niche elimination.

In summary, the hygienically designed Motor H outperformed Motor W and Motor C with regards to hygienic design. The VT FST team could not detect E. coli colonies on the exterior surfaces of Motor H post-wash while Motor W and C both had multiple positive sites after the sanitation procedure. The problem sites can be directly correlated to areas where hygienic design criteria were not strictly followed. Each bacterium that survives a wash down procedure may be a risk to food safety or quality, not only to food and beverage companies, but most importantly to the end consumers.

The data collected through this study points to the importance of system-wide hygienic design including purchased components. The importance of careful design on the servomotor component level can only be magnified when applied to entire machines and production lines.

The data also show that deviating from hygienic design standards corresponds to decreased motor sanitizability leading to increased contamination risk and the need for additional costly and time-consuming interventions. These risks translate to real world costs, whether it’s added sanitation time, increased numbers of cleaning interventions, reduced production time or increased risk of consumer harm when safeguards fail.

Reprint info >>

Kollmorgen
www.kollmorgen.com

Select the right machine controller for your application

July 25, 2016 By Motion Control Tips Editor Leave a Comment

by Don Pham, Product Manager, IDEC

Picking the right type of machine controller will minimize costs and complexity, while still providing the performance required for the application.

Many different controller options are available for machine automation, giving you the opportunity to select a controller closely matched to the application. All those choices can cause confusion. The Controller Comparison Table lists some of the leading characteristics of each type of controller to help guide your selection.

Let’s start with a class of controller often used in simple applications due to its low cost, small form factor and ease of implementation.

Educated relays
Relay-based controllers were very basic when first introduced and only suitable for use in place of a few relays and timers. But now, the capabilities of these smart relays are approaching those of micro PLCs, making them a good choice for control of simple machines. These expanded capabilities have led to increased demand with more than a million units purchased per year and an annual projected growth rate of 6%.

Most smart relays come with an integral front panel alphanumeric display (Figure 1), and some also feature an optional external text display panel. Typically, both displays show the same information, with the external display used when the base unit is mounted inside a control enclosure and thus not visible during normal operation.

Figure 1. Smart relays are typically supplied with an integral display, and often with an external display mimicking the same information.
All images courtesy of IDEC.

Although most smart relays can be programmed through their display, it’s more common to use PC-based programming software, which is usually supplied free of charge with the relay. Once programmed, at least some of the smart relay’s settings, such as alarm settings and other values, can typically be modified with its display.

Newer smart relays have an Ethernet port in addition to a serial or proprietary communication protocol port. This Ethernet port can be used for connection to the PC for initial programming, and then for connection to other devices once programming is complete. These other devices might include the external text display panel, other smart relays or an Ethernet switch.

Some newer smart relays have built-in web server capability, allowing web pages to be programmed and stored in the unit for remote access with any web browser. This feature connects the smart relay to the world through the internet, useful for remote access. Some suppliers are also writing smartphone apps to enable communications with their smart relays with Apple and Android phones, which greatly increases speed and ease of remote access.

Ladder logic or function block are the programming languages of choice, which makes it easy to write efficient programs for simple operations. Internal program storage is limited, so operations can’t be overly complex. Smart relay I/O used to be strictly discrete, but analog I/O is now becoming available on some newer units.

With respect to maximum allowable I/O, IDEC’s FL1F SmartRelay can handle up to 60 I/O with its base unit and expansion model. These 60 I/O consist of a maximum of 24 discrete inputs, 20 discrete outputs, 8 analog inputs and 8 analog outputs.

When this amount of I/O isn’t sufficient, or when other features are required such as a graphic display or more sophisticated control, the next step up is a PLC or a PAC.

Is it a PLC or a PAC?
Programmable logic controllers (PLCs) and programmable automation controllers (PACs) are the main engines driving machine control worldwide, and with good reason. Starting with the introduction of the PLC as a relay replacement in the 1960s, these controllers have grown to dominate the machine control market. Annual purchases exceed 8 million units with a growth rate of about 7%.

Although there is no clear line defining the difference between a PLC and PAC, in general PACs add more capabilities than PLCs, particularly for control of very complex systems. PACs can handle advanced motion control, incorporate vision systems and perform advanced control of analog loops—a set of tasks that might unduly burden a PLC.

These controllers run the range from micro PLCs with about 32 built-in I/O points, to full-featured PACs capable of handling tens of thousands of I/O. For example, the Micro PLC pictured in Figure 2 can handle up to 520 I/O total, and 126 of these I/O points can be analog. Although this controller is labeled as a Micro PLC, it approaches PAC power in many respects including execution speed and program memory.

Figure 2. Newer micro PLCs are approaching the capabilities of older model PACs, putting pressure on PACs to add new features and capabilities.
All images courtesy of IDEC.

Multiple operator interface options can be used for PLCs and PACs. The first is the supplier’s operator interface graphics terminal, often connected to the controller with a proprietary interface. The second is an embedded HMI, which consists of third-party HMI software running on some type of embedded platform. The third is a PC-based HMI.

PLCs and PACs are programmed using PC-based software, and any changes to the program typically require a PC. The programming PC typically connects to the PLC or PAC through an Ethernet port. Although the program usually can’t be changed without a PC, many parameters can be adjusted with the operator interface device such as setpoints and alarm values. When the operator interface device is a PC-based HMI, the PC can also be used for programming.

PLCs and PACs are capable of controlling almost any machine, and many now have built-in PID and motion control. Copious on-board memory allows real-time and high-speed control of many I/O points and control loops, even for sophisticated applications like multi-axis motion control.

I/O can range up to tens of thousands of points, and can include many types of local and remote I/O modules. Very high-speed applications can be addressed with special I/O modules with quick scan times, and high-resolution modules are available when precision is required. Remote I/O modules are often available in machine mount versions, with no cabinet mounting required.

Networking options are numerous, with almost all PLCs and PACs equipped with multiple Ethernet ports and support for various Ethernet protocols. Communications with these ports can typically be programmed in scripting languages, which are much more powerful and easier to use than ladder logic for these types of tasks.

Speaking of programming, many of these controllers support the IEC 61131 suite of languages that includes ladder diagram, function block diagram, structured text, instruction list and sequential function chart.

Even with all these options, some applications demand even more performance, making an industrial PC the best fit.

Figure 3. Combining the operator interface and the PLC into one unit is an attractive option for many OEMs building simple machines and looking to keep costs down.
All images courtesy of IDEC.

PC performance
Industrial PCs (IPCs) are at the top of heap in terms of machine control, combining the power and connectivity of a PC with the ruggedness of a PLC. As one would expect, costs are correspondingly high, making these controllers economical only for the most demanding applications.

Many modern industrial PCs now come in rack-mount versions, giving them an appearance and form factor similar to a PLC or PAC. IPC I/O also looks similar, with local rack mount and remote options, easily expandable to tens of thousands of I/O points. IPCs are the most open of all controllers, so adding almost any type of I/O is possible, often through the addition of a plug-in card to handle a particular protocol.

And because IPCs are so open, connectivity is easy, with the ability to connect to virtually any type of HMI, controller, vision system or upper-level computing platform such as a database, ERP system or a manufacturing execution system.

Like PCs, IPCs can be configured as virtual machines, meaning they can host multiple operating systems simultaneously. For example, a real-time operating system could be used for control, a Windows operating system for running an HMI, and a third operating system for a dedicated task such as machine vision.

In terms of programming languages, expect an IPC to accommodate all the IEC 61131 languages, as well as PC-based languages like C++ and Virtual Basic. Because so many different languages can be used, the cost of IPC programming software is typically quite high.

Program and data storage memory can be expanded as required, allowing both execution of large real-time control programs and storage of manufacturing data. There are also many options for storing data including internal disk drives, CDs and jump drives.

One way to get more bang for the buck with an IPC is to combine control with HMI functionality. When this is done, all that’s needed to create a powerful graphical interface is an industrial monitor. This concept is also trickling down to more applications in the form of combo PLC+HMI units, as discussed in the Combo Controllers sidebar.

Your three main options for machine control are smart relays, PLCs/PACs and IPCs. Each option has its place, and making the right choice will help keep costs and complexity down while providing the required level of performance for your specific application.

Combo Controllers

Specialty controllers include combo, motion and hydraulic controllers.

Combo PLC+HMI controllers combine the operator interface, controller and I/O into one unit (Figure 3). When compared to a separate controller and operator interface, combo units cut costs, reduce required footprint and simplify integration.

Costs are reduced because upfront purchase price is less, there are fewer components to install and wire, and there are fewer components to stock. Integration is easier because there’s no need to establish a connection between the controller and the operator interface device.

Although combo units traditionally weren’t as powerful as PLCs or PACs, their capabilities have expanded over the past few years to include analog I/O and control, Ethernet connectivity and web server functionality.

Motion controllers are a good fit for machines with lots of motion functions, but with few other real-time control requirements. Although these units excel primarily at motion control, many also include I/O and logic capability to control a limited number of discrete and analog inputs and outputs.

Although many PLCs, most PACs and all IPCs can perform motion control, using a dedicated motion controller can simplify programming, startup and maintenance.

Another type of specialty controller is dedicated to hydraulic systems, making them the right choice to control hydraulic machines. As engineers like to say, given enough time and budget virtually any controller can be programmed to accomplish any task, including control of a complex hydraulic system. But, using a controller dedicated to this specific function provides the best tool for the job, reducing design and programming time and costs, and simplifying startup.

Like motion controllers, most hydraulic controllers contain logic and additional I/O for control of other points in addition to hydraulic systems.

Expanding options to include specialty units such as combo PLCs+HMIs, motion controllers and hydraulic controllers gives designers increased flexibility, allowing them to match machine requirements more closely to controller capabilities.

Reprint info >>

IDEC
www.idec.com

Open-loop stepper motor versus closed-loop stepper motor systems

July 6, 2016 By Motion Control Tips Editor Leave a Comment

By Jeff Kordik, CTO • Applied Motion Products Inc. || Step motor systems are a bedrock of the motion control industry. We’ll look at the differences between open-loop system vs. closed-loop system and also explain the latest developments making step motor systems even faster, quieter, and more energy efficient than ever before.

Step motor systems have come a long way from the early days of voltage drives and full stepping. First came PWM drives and microstepping and then digital signal processors (DSPs) and anti-resonance algorithms. Now, new closed-loop stepper technology is ensuring that step motors continue to be a cornerstone of the motion control industry for years to come.

This is a cutaway of a StepSERVO closed-loop integrated stepper motor from Applied Motion Products.

Whether the motion is linear or rotary, two top considerations that dictate which motor and drive systems are most suitable are torque and efficiency. This applies whether the final application is an automated assembly system, a material handling machine, a 3D printer, a Cartesian positioner, a peristaltic pump, or one of countless other applications in which step motors are a preferred technology.

The latest development in stepper systems is the application of low cost, high resolution feedback devices and advanced DSPs to close the loop on stepper motion. Such controls boost closed-loop stepper performance to outperform open-loop systems. As we’ll see, one such closed-loop system implements on an integrated motor design that includes a feedback device, driver and controller boards, power, communication and I/O electronics, and system connectors on the motor’s side and back.

Open-loop vs. closed-loop stepper systems
First let’s explore how high performance closed-loop stepper systems compare to traditional open-loop stepper systems in terms of torque and efficiency.

There’s superior performance from closed-loop stepper systems over open-loop setups as demonstrated in laboratory test results comparing the two systems’ acceleration (torque), efficiency (power consumption), position error (accuracy), heat generation, and noise levels. Just consider the relationship between torque and acceleration. Torque-speed curves show the peak and continuous torque ranges of a closed-loop stepper system alongside the usable torque range of an open-loop stepper system. Very often, torque in the real world translates into acceleration — so motors with greater torque can accelerate a given load faster.

To test this difference in torque performance in the lab, equally sized open-loop and closed-loop step motor systems get identical inertial loads. Programming commands the two systems to perform identical move profiles, except that acceleration rate and top speed are slowly increased in each system until they make positioning errors.

Here we have a move profile comparison between a open-loop vs. closed-loop system. This is a comparison between that from a StepSERVO closed-loop system and that from an open-loop system. The closed-loop system (due to its higher torque producing capability) gets a maximum acceleration rate of 2,000 rev/sec² and a top speed of 20 rev/sec (1,200 rpm)
as seen here.

Say that the open-loop system gets a maximum acceleration rate of 1,000 rev/sec² and a top speed of 10 rev/sec (600 rpm). This top speed of 10 rev/sec correlates to where the flat portion of the torque-speed curve ends. The closed-loop system (due to its higher torque producing capability) gets a maximum acceleration rate of 2,000 rev/sec² and a top speed of 20 rev/sec (1,200 rpm). This is double the performance of the open-loop system and cuts the move time nearly in half — from 110 msec down to 60 msec.

For applications requiring high throughput (such as indexing, edge guide positioning and pick-and-place systems) the closed-loop system provides a clear performance advantage.

Open-loop vs. Closed-loop efficiency

To measure the relative efficiency of an open-loop vs. closed-loop system, assume we repeat the same test with the same two motors of equal size. This time we have the closed-loop and open-loop motors run side by side with the same inertial loads but run programming that holds the move profiles constant and equal, so that both systems perform the same amount of work.

This is a Relative Comparison Chart for StepSERVO closed-loop systems versus open-loop systems. Note the superior performance of the closed-loop stepper system as demonstrated in the results of laboratory testing that compare two systems for acceleration (torque), efficiency (power consumption), position error (accuracy), heat generation, and noise levels.

While the two motors index the same move profile repeatedly, current draw from the dc power supply feeding the two systems is measured and power consumption is calculated. As can be seen in value plots, average power consumption of the open-loop stepper system is 43.8 watts, while that of the closed-loop system is only one third as much — 14.2 watts on average. This dramatic difference in power consumption clearly shows the higher efficiency operation of the closed-loop system. Any user looking to increase the system efficiency of their open-loop stepper system can now consider a simple upgrade to a closed-loop system and expect significantly lower consumption.

This comparison of power consumption by the StepSERVO closed-loop system and an open-loop system shows the StepSERVO’s
higher efficiency.

How to address motor heating

A natural extension of the power consumption tests is the investigation of motor heating. Open-loop stepper systems are simple beasts. One simply sets the drive for the motor’s rated current and the drive will do its best to supply that current to the motor at all times, whether the resulting torque is needed or not. This often causes the generation of heat instead of energy towards the application function — and is the reason why open-loop stepper systems typically run hotter than closed-loop counterparts. It also means that machine designers must take additional steps to deal with this heat, often by including special guarding around step motors that will run in the vicinity of human operators, or by installing additional cooling systems such as fans.

Consider the results of a motor heating test conducted in a laboratory using the same open-loop and closed-loop systems as above. In this test, the two systems again produce the same amount of work driving the same inertial loads, and are allowed to operate until they reach thermal equilibrium. The open-loop system reaches a case temperature of 76.0° C, whereas the closed-loop system reaches thermal equilibrium at a case temperate of only 36.9° C — less than half that of the open-loop system. This significant reduction in motor heating can mean lower component costs for machine builders, because they can omit extra guarding and cooling subsystems.

This is a laboratory test temperature comparison of a StepSERVO closed-loop system and an open-loop system. It shows the results of a motor heating test using the same open-loop and closed-loop
systems as in the other tests detailed in this article.

Noisy motors no more

Another common complaint about open-loop stepper systems is that they are known to make quite a bit of audible noise. In certain environments, such as laboratories, hospitals, and offices, this noise can pose a real problem for machine designers.

The noise emitted by step motors arises from high electrical frequency and rapid flux changes in the stator teeth, and because open-loop systems are operated at full rated current regardless of load. Closed-loop stepper systems, on the other hand, supply the motor with just enough current to control the load and this results in much less audible noise.

Shown here is the audible noise plotted against the speed of for an open-loop system and a StepSERVO closed-loop system. Closed-loop stepper systems supply the motor with just enough current to control the load, and this results in much less audible noise than open-loop setups.

To produce the test results shown in the plot of acoustic noise accompanying this article, the acoustic noise of each system is measured in a soundproof chamber. The closed-loop system is dramatically quieter than the open-loop option at speeds from 0 to 20 rev/sec. This speed range coincides with the real-world speed range of applications where step motor systems are most often used, meaning that the vast majority of step motor applications could benefit from reduced motor noise if switched to closed-loop systems.

Better motor accuracy to eliminate position errors

Open-loop step motor systems are prized for their ability to precisely position loads without a feedback mechanism or closed-loop control system, but only if the open-loop system has sufficient torque margin such that position errors will not occur during normal operation. For improved accuracy, and for a more robust system design, closing the servo position loop around feedback from the high resolution encoder allows closed-loop systems to compensate automatically for increases in torque demand that would otherwise lead to position errors in open-loop systems. This greatly improves overall system accuracy, particularly for highly dynamic applications such as pick-and-place systems and 3D printers where short, fast moves and frequent changes of direction are needed.

Dynamic torque comparison between StepSERVO closed-loop (peak torque), StepSERVO closed-loop (continuous torque), and open-loop (useable torque). These plots show the peak and continuous torque ranges of a closed-loop stepper system alongside the useable torque range of an openloop stepper system. The open-loop system outputs a maximum acceleration rate of 1,000 rev/sec² and a top speed of 10 rev/sec (600 rpm). This top speed of 10 rev/sec correlates to where the flat portion of the torque-speed curve ends.

Upgrading existing stepper systems

Of the components in an integrated step motor system, the motor, power amplifier and communication costs generally will not increase when going from open-loop to closed loop. The control electronics may require a bit more central processing power or memory to servo control the motor, but these typically don’t have an impact on list prices. Much of the cost difference between open-loop and closed-loop stepper systems lies in the addition of a high resolution feedback device, but refinements in manufacturing have made these devices increasingly affordable. So now, closed-loop stepper systems maintain the cost benefits of open-loop stepper systems over other types of positioning systems — such as a traditional servo — but with greatly increased performance in nearly every way. Typically, the energy savings and increased throughput of a closed-loop system quickly pay for the slight increase in cost of the feedback device.

In addition to a minimal cost increase, upgrading from an open-loop stepper system to a closed-loop system is simplified with NEMA frame size offerings. A closed-loop NEMA 23 step motor has the same frame size, pilot diameter, bolt hole circle and bolt hole diameter as an open-loop NEMA 23 step motor, so mounting brackets stay the same. The greater torque available from the closed-loop system means the shaft diameter of the closed-loop step motor may be larger, but this can usually be solved quite easily with a simple change of the shaft coupling.

StepSERVO closed loop step motor technology is a product of Applied Motion Products. StepSERVO closed loop integrated motors were used in the quantitative examples in this feature. Get full results of the lab tests discussed in this article at www.applied-motion.com/stepservo-white-paper.

Reprint info >> || Applied Motion Products Inc. • www.applied-motion.com

How to choose an industrial lubricant

June 2, 2016 By Motion Control Tips Editor Leave a Comment

by Bill Watson, Director of Application Engineering, Klüber Lubrication NA LP

Choosing the right lubricant for an industrial power-transmission design can be a tricky task, because industrial lubricants come in many varieties and formulations, and many industries require lubricants that adhere to specific regulations and standards. Here are some tips to make the selection easier.

For decades, lubricant suppliers have been developing and manufacturing specialty lubricants tailored to the requirements of industrial applications. There are general technical requirements that all lubricants must meet, including the reduction of friction and wear, protection against corrosion, dissipation of heat and sealing. But, depending on the operating conditions and manufacturing processes in the plant, lubricants may also be expected to provide a host of additional properties.

Before selecting an industrial application, consult a supplier who can help answer key questions about the design. In the case of a chain drive, ask: Will the installation need to survive an outdoor environment? Will the chain be subject to infrequent service? Lubricants exist to help chain and other power-transmission components last for years in even the harshest machine setups.

General purpose or synthetic lubricants?
One of the first questions a lubricant supplier should ask is if the equipment’s lubrication will be maintained at regular intervals or if it must be lubricated for life. The answer to this question helps determine whether the use of a general purpose lubricant or a synthetic specialty lubricant is more appropriate.

Oils, greases, pastes and waxes, and bonded coatings are the most common categories of industrial lubricants. Typically, an oil lubricant contains 95% base oil (most often mineral oils) and 5% additives. In contrast, greases consist of lubricating base oils that are mixed with a soap to form a solid structure. Pastes contain base oils, additives and solid lubricant particles. Finally, lubricating waxes consist of synthetic hydrocarbons, water and an emulsifying agent, which becomes fluid when a certain temperature level is exceeded.

Kluber-bertherm-HB-8-182-lubricant-for-olling-bearing

Greases (as that on this bearing) consist of lubricating base oils that are mixed with a soap to form a solid structure. Pastes contain base oils, additives and solid lubricant particles. In contrast, lubricating waxes consist of synthetic hydrocarbons, water and an emulsifying agent. Work with the supplier to determine which is most appropriate.

The majority of oil lubricants, including many motor oils, are mineral oil distillates of crude oil (petroleum), while synthetic oil lubricants are also used. Synthetic oils such as polyalphaolefins (PAOs) or synthetic esters are produced artificially from other compounds. Because of this, the composition is quite different from petroleum oil. Their higher purity and uniformity provide for several enhanced properties, such as viscosity index, oxidation stability and color.

There are also semi-synthetic oils (also called synthetic blends), which are a blend of mineral and synthetic oil. This class of lubricants provides many of the benefits of synthetic oil at a fraction of the cost.

When synthetic oil is selected, it is generally to provide mechanical and chemical properties superior to those found in traditional mineral oils. When a manufacturer does not stock an appropriate synthetic lubricant with the performance features needed for a given power-transmission application, that design may necessitate a customized specialty or ‘optimized’ lubricant.

If the equipment will be regularly lubricated, synthetic or specialty lubricant designed to last for an extensive period of time is usually unnecessary. In this case, the lubricant needs only to meet basic performance standards and be replenished regularly.

On the other hand, if equipment is lubricated for life, synthetic base oils are often recommended for their many benefits:

• Low and high-temperature viscosity performance
• Decreased evaporative loss
• Reduced friction and reduced wear
• Improved efficiency
• Chemical stability and resistance to oil-sludge problems
• Extended drain intervals

Despite their many benefits, synthetic lubricants are also known for one distinct disadvantage of cost. But the cost may be mitigated by extended change intervals, as synthetic and specialty lubricants can last five times longer or more than non-synthetic lubricants when a high-quality base oil is used.

Some synthetic or specialty lubricants are 50 to 500% more expensive than general-purpose lubricants, but price per pound or kilogram should not be the only determining factor in selection.

Factors that influence selection
The key requirement for selecting the proper lubricant is the base oil viscosity. In order to select the appropriate viscosity, the lubricant supplier will need to gather key information about the application at hand:

• Axis operating speed (variable or fixed)
• Specific type of friction (such as sliding or rolling)
• Load and environmental conditions
• Industry standards

For example, some lubricants such as PAG (polyalkylene glycol) oils are good for sliding friction, but are unsuitable for rolling friction. Likewise, PAO oils are used for rolling friction and can handle some sliding friction, whereas silicon and PFPE lubricants are typically used for extremely high temperatures.

Common mistakes in lubricating power-transmission components
During the information-gathering stage, equipment owners often make the mistake of overlooking some basic application details which can have a significant impact on the resulting lubricant’s performance. It is important to provide as much information as possible and to be specific, as this will help the design-engineering team and supplier identify the lubricant best suited to the task.

Another common mistake equipment owners make is choosing a lubricant based solely on price. Admittedly, there is a vast difference in the price of a synthetic or specialty lubricant and a general purpose lubricant. Some synthetic or specialty lubricants are 50 to 500% more expensive than general-purpose lubricants, but the price per kilogram should not be the only determining factor in selection.

Additional factors to take into consideration are:

• Reduced operating costs resulting from less downtime
• Improved labor utilization (as there’s less time required for re-lubrication and maintenance)
• Measurable energy savings and increased output

Often, when a supplier makes a lubricant recommendation for a particular application, and that application is successful, the customer wants to use the same lubricant in another application. Unfortunately, this is typically not an option. Remember, every application is different, and while one lubricant may work well for a ball bearing application, it likely will not provide the same performance for a different bearing application.

Ultimately, the first step in choosing the right lubricant is choosing the right lubricant supplier. Look for a supplier to provide quality documentation and detailed test data that demonstrate the consistency and quality of the product being recommended. A reputable supplier will spend time educating design teams so they can make qualified decisions about lubricating equipment.

Reprint info >>

Klüber Lubrication
www.klueber.com

HMIs double as edge-of-network gateways

April 26, 2016 By Motion Control Tips Editor Leave a Comment

by Michael Sheldon and Ryan Kelley, Maple Systems

Industrial networks can use operator terminals to handle communications and analytical duties associated with IoT tasks.

The Industrial Internet of Things (IIoT) is here and it’s changing the way manufacturers think about business. These days, everyone wants to be wirelessly connected, synced up and remoted in. You name it, we want to be connected to it. Within the manufacturing industry, there is great need and desire for more connectivity and access to valuable data from our factory machines.

Enter the edge gateway. The edge gateway unlocks valuable data created by existing assets. In the manufacturing sphere, edge gateway devices translate data used by control applications into an IIoT-friendly format, sending that data to the Internet for use by IIoT applications.

An edge gateway device must fulfill key requirements. It must be efficient, reliable and scalable. It must also be easy to configure and put into service. Above all, it must be secure. And it must communicate with a wide range of existing equipment and support emerging IIoT protocols such as MQTT (formerly MQ Telemetry Transport). This is an ISO standard (ISO/IEC PRF 20922) publish-subscribe-based “lightweight” messaging protocol for use on top of the TCP/IP protocol. It is designed for connections with remote locations requiring a small code footprint or a limited network bandwidth.

An HMI is a good candidate for serving as the edge gateway device. The HMI, the operator’s window into the machine, can easily be extended to play the same role in the virtual world. The HMI is the place where data is aggregated, filtered and presented to the operator. This same data can easily be presented to users connecting to the HMI through the IIoT.

An HMI terminal can serve as an edge gateway device for IoT installations. A block diagram of the HMI internals shows the system facilities used for functions such as security and device communications.

A primary requirement of the IIoT is interoperability. The dizzying array of communication protocols used in manufacturing today present a significant barrier. Fortunately, modern HMIs possess extensive libraries of industrial protocol drivers operating on different network architectures. This makes HMIs a means of handling the interoperability challenge.

For example, the Maple Systems HMI5097DXL HMI has three serial ports and a CANbus port that can operate simultaneously using more than 200 different protocols. In addition, two separate Ethernet ports let the device dedicate one port for real-time industrial control network demands while the other is reserved for external network connections and IIoT functions. Distinctly separate Ethernet ports offer added security, because a direct network path does not exist to the machinery itself.

Data transmitted by the edge gateway-enabled HMI must be presented to upstream IT applications in a way that is flexible, modular and efficient. The MQTT feature available on all Maple Systems HMIs exemplifies the power of this protocol. MQTT is organized into topics that can contain single data points or a group of related data. The HMI can be configured to transmit data from a specific topic whenever a change arises, or periodically, lowering the bandwidth needed for connection.

A fundamental advantage of MQTT is that data goes to a central “broker” instead of directly transmitting to multiple clients such as remote interfaces or management software. The MQTT broker is responsible for maintaining client connections and sending/receiving messages. Client devices, edge gateways and IT applications (or publishers/subscribers in MQTT language) are freed up to focus on producing and consuming data. This division of labor greatly enhances scalability. As overall system sizes grow, the CPU resources and bandwidth requirements of the edge gateway remain static.

In addition, MQTT is a lightweight protocol. A widely used broker implementation consumes only about 3 MB of RAM with 1,000 connected clients. This small footprint means the HMI can be configured as both an edge gateway and an MQTT broker, reducing the need for additional hardware.

In one example of using an HMI terminal for edge gateway duties, the HMI connects with an off-site server as a way to interact with distributed clients.

Applications engineers have a lot of flexibility using the data an edge gateway produces as an MQTT publisher. Engineers can assign topic names to the variables or tags they wish to publish to the broker. Topics are the titles, or addresses, used to organize data in the MQTT protocol. MQTT allows topics to be divided in intuitive ways. A single data point can be assigned to multiple topics, and one topic can contain more than one data point. An application can subscribe to all topics on a single HMI, creating an application monitoring one specific machine. Or, if a parameter (say temperature) exists on many machines, the programmer can use a topic “wild card” to instantly subscribe to the same parameter across all machines. This enables efficient and easy detection of abnormal conditions across an entire installed base of machines.

The HMI configuration process is easy for the controls engineer who incorporates an edge gateway into a system. The engineer simply creates an authenticated broker connection, then selects the tags to publish. The engineer organizes tags into topics, then downloads the project to the HMI.

MQTT is one of many Internet-enabled applications available on edge gateway devices, such as Maple HMIs, which offer notable communication and data collection features. HMIs can send emails containing data log and alarm conditions. Remote access applications let remote users monitor and control machines through secure VPN connections. They also enable remote download of project updates. Database integration allows machines to log data directly to database servers over a LAN. Custom server/client applications enable smart device integration (Android/Apple tablets) for machine monitoring and control. Compared to machine replacement, edge gateway-enabled HMIs are an inexpensive option for upgrading machines or adding to new machine builds.

An example shows how the configuration process typically works. Company A wants to offer customers remote access/monitoring, remote email alarms, off-site troubleshooting and configuration, and similar benefits. Company A goes with the MQTT protocol for its extensive use and documentation with Facebook messenger, cloud compatibility, and ability to efficiently transport large amounts of data across networks. MQTT also allows Company A to seamlessly expand its Amazon Web Services without hogging all available network bandwidth at each manufacturing site.

The company’s engineering departments use many different PLC brands, all with different protocols. So Company A decides to use a Maple Systems HMI5097DXL dual-Ethernet HMI, which serves as both an HMI and edge gateway. The HMI5097DXL supports MQTT and more than 200 other control protocols, letting it link existing control networks with the IIoT.

An operator interface without a display can serve as an edge gateway. In this example, the operator interface is an RMI5010. It connects to PLCs on the factory floor using several different communication protocols. It uses MQTT to communicate with management offices.

Dual-Ethernet ports separate networks inside the plant from external information technology networks. This secure connection allows for advanced remote access and monitoring, remote email alarms and remote programming. Dual-Ethernet HMIs let Company A maintain an isolated network dedicated to its machinery, yet still offer access to the internet through the customer’s ISP. The publish/subscribe architecture of the MQTT network means Company A personnel won’t have to bug their customers’ IT departments.

Because their systems are widely distributed, Company A hosts its MQTT broker off-site. The new data stream connects to a web application that customers can log into for real-time machine monitoring.

Remote functions built into the HMI allow Company A to update projects (including off-site MQTT setup) to meet changing customer demands without spending time and money on-site. It can respond faster to software and data demands across deployed equipment without leaving company facilities. Company A uses predictive maintenance instead of preventative maintenance to cut costs, improve troubleshooting and reduce downtime. New machines added to the network send smart data back to the central database for analysis.

Consider another example involving a single-facility food processing company. Like many in the manufacturing industry, Company B’s biggest obstacles for IIoT adoption are budget and interoperability. Its factory hosts both Ethernet and serial control networks unable to share data because of incompatible protocols. The company wants to centralize data without buying a new server and remote hosting. Key requirements for IIoT hardware include support for the MQTT protocol, legacy protocol support and secure remoting. Maple Systems RMI5010 fits Company B’s needs because there’s no requirement for new displays. This unit has a small form factor that fits into existing panels.

Company B creates both a project and the MQTT broker inside its new interfaces using EZware configuration software. They define MQTT topics to bring data from the plant floor to dashboards and analytic programs in use by management. Analytic software now offers a live data stream from operating machinery.

Remote access through the RMI5010 securely connects to laptops, Android phones or Android/iPad tablets, giving floor managers mobile access. The email alarm feature alerts staff immediately when something runs amiss regardless of location. Dual-Ethernet ports plus serial communication offers a safe connection to office networks exposed to the Internet.

The centralizing of data from facility machinery boosts system awareness. Maintenance costs drop thanks to the linking of data about machine wear and usage. Software identifies data patterns that indicate likely failures, so machines can run to full life without risking costly shutdowns.

All in all, Company B can use detailed statistics on both its highest-profit machines and on its process bottlenecks. In the end, the HMI edge gateway performs local machine control while opening up new possibilities in the IIoT.

Maple Systems
www.maplesystems.com/IIoT

Embedded software enables IoT in today’s vehicles

April 22, 2016 By Motion Control Tips Editor Leave a Comment

by Anil Khanna, Andrew Patteron, Mentor Automotive

IoT connectivity for next-generation automotive apps is made possible by new software devised with audio and video networking in mind.

There’s a shifting landscape when it comes to today’s modern automobiles. Automakers face the challenge of satisfying consumer expectations for rich, multimedia experiences within the vehicle cabin. Meanwhile, security has become a big issue as regulations and requirements have begun to apply to external vehicle connectivity.

The electronification of the car generates large amounts of data within and across the vehicle. This data must be integrated, processed and presented, usually in real time, in a format the occupants of the vehicle find actionable.

And finally, cost issues are as critical as ever. The challenge is to innovate while keeping research and development costs down. Embedded systems have taken a lead role in meeting such challenges.

There has been a steady progression in vehicle electronics, from simple electronic control units (ECUs) that had no need for an embedded operating system (OS), to today’s complex multi-function ECUs, which can require multiple operating systems. Once upon a time, an embedded operating system was treated as a separate isolated entity, but for performance and security reasons, this can no longer be the case. The operating system directly influences safety, security and connectivity to devices both inside the vehicle and to the roadside infrastructure, cloud or other vehicles externally.

A high-level view of the Connected OS software platform and development tools.

Connectivity inside the vehicle encompasses communications across a wide range of physical networks. Traditional in-vehicle networking technologies such as CAN, FlexRay, MOST, and LIN are being supplemented by more capable technologies such as Ethernet, Ethernet Audio Video Bridging (eAVB), Automotive Audio Bus (A2B), and wireless solutions. The design of individual networks is typically driven by application needs, with gateway ECUs connecting different vehicle domains. The combination of powerful SoCs and software systems let automakers consider new consolidated system architectures. One example of this would be a joint in-vehicle infotainment (IVI) and driver information cockpit that not only displays infotainment choices, but also overlays vehicle operation data such as speed, engine status, safety pointers, and data from lane departure warning systems (LDWS) and other kinds of warning systems.

The simplified network schematic for a typical eAVB network includes IVI and ADAS applications.

ECU and module consolidation
Luxury vehicles now carry more than 100 ECUs. And ECUs are migrating from 8- and 16-bit microcontrollers to 32-bit microprocessor-based system SoCs and into multicore architectures.

As vehicles sport more electronic features, it becomes obvious that electronic functions need to consolidate into modules. Therein a number of issues arise. The vehicle wiring harness grows more complex and heavier. The growing number of ECUs in the vehicle also forces designers into more standardization. There’s a challenge to reengineer the software and perhaps re-architect the system to move or consolidate functions among modules.

Partnership efforts, such as the Automotive Open System Architecture (Autosar), have done an exceptional job of creating and establishing open standards for various automotive software architectures to address these types of issues. Automotive OEMs, electrical suppliers, chip manufacturers and software companies are all Autosar members.

A modern infotainment system is the cockpit through which the driver and passenger command and control data across the vehicle. The infotainment system must connect with the vehicle network to collect data from multiple ECUs and report on its own status. Externally, there are connections to smart devices, increasingly fulfilled through apps and technologies for car-smartphone connectivity, such as Apple CarPlay, Google Android Auto and MirrorLink.

With the advent of autonomous cars, the infotainment functions must also connect to other vehicles and the outside world. It is not surprising that the OS of the infotainment system, typically in the head-unit, has become the proverbial brain of the car.

Consequently, the embedded system forming the cockpit is a crucial piece of technology. One concept addressing this role is called Connected OS. Devised by Mentor Graphics, it covers the integration and connectivity needed for next-generation in-car experiences.

A mixed-criticality instrument cluster of electronics allows certified safety-critical graphics indicators to combine with 3D graphics on a single display. The safety-critical graphics operate in a secure hardware zone and run on a stand-alone safety certified Nucleus SafetyCert RTOS.

The Connected OS software employs a modular, GENIVI-based Linux platform with a board support package (SuperBSP) and a middleware layer (OPTstack). Out of the box, the software platform delivers technologies such as fast boot, instant-on, and optimized audio/video—all necessary for cutting-edge automotive applications. One example of its use might be enabling a rapid system start-up along with quick turn-on of audio and video, necessary for infotainment systems with back-up cameras.

In addition, Connected OS offers middleware support for emerging networking technologies such as eAVB and A2B. The pre-integration of the eAVB software stack is especially helpful in developing applications that require low-latency, real-time communications, such as those found in Advanced Driver Assistance Systems (ADAS).

Beyond this, the combination of support for protocols, such as eAVB with video processing expertise, allows Connected OS based systems to deliver features such as Rear Seat Entertainment (RSE). The eAVB stack in Connected OS is developed to IEEE AVB standards and complies with AVnu Alliance deterministic networking standards.

Supported IEEE implementations include IEEE 802.1AS (to ensure synchronization for time-sensitive applications such as audio and video); 802.1Qat (protocols, procedures and managed objects that let network resources be reserved for specific traffic streams traversing a bridged LAN); 802.1Qav (lets bridges provide guarantees for time-sensitive, loss-sensitive, real-time AV data transmission); 1722.1 (provides the audio video discovery, enumeration, connection management, and control protocol for AVB devices); and 1733 (protocol, data encapsulations, connection management, and presentation time procedures for interoperability between AV-based stations). Similarly, support for the A2B software stack in Connected OS lets automakers develop less expensive audio networks that still deliver exceptional in-car audio.

Safety and security are always high on car maker priority lists. With the advent of autonomous vehicles, more wireless “attack surfaces” have appeared for hackers to exploit. Security must be at every level of the vehicle architecture, from the hardware to embedded software, through to applications and even human factors. Embedded software protection techniques—such as key-exchange protocols, public-key cryptography, data hashing algorithms, and symmetric-key encryption—can help improve vehicle data security. Further, ECUs that must communicate with each other can exchange manufacturer-assigned security keys before proceeding with any data exchange, so only necessary and authorized data transmits.

On the safety side, minimization of software defects is a must. Strategies for exhaustive testing of safety-critical software continue to evolve. Through careful partitioning, safety-critical elements can be isolated and certified separately from more complex systems that are harder to fully validate line by line.

Mentor Graphics has developed a mixed-criticality instrument cluster solution that combines certified safety-critical graphics indicators with rich 3D graphics on a single display. The safety-critical graphics operate in a secure hardware zone. They run on a stand-alone safety-certified Nucleus SafetyCert RTOS for security from external interference and denial-of-service attacks.

Multi-domain communication in a vehicular automotive system might use RPMsg and VirtIO protocols to handle infotainment, instrument cluster and engine control tasks. The software standards involved might map out in a way similar to that depicted here.

The Connected OS concept covers more than just a foundation Linux operating system. New multicore architectures allow for the hosting of multiple operating systems with tight communication among them. These include, for example, the Autosar basic software (BSW) operating system, real-time operating systems such as Nucleus RTOS, and even links to Android running natively or in a Linux container (LXC).

Once multiple operating systems are used, secure communication is enabled using protocols such as Remote Processor Messaging (RPMsg) and VirtIO, so information generated in one domain can transmit to another. An example could be a phone status message, needed on the secure driver information cluster display. Separating domains on multicore frameworks, or through use of embedded hypervisors, helps manage security and separation while simultaneously optimizing performance.

Mentor Graphics
www.mentor.com/solutions/automotive

Autosar
www.autosar.org

Two positioning components speed OEM product development

February 8, 2016 By Motion Control Tips Editor Leave a Comment

by Robert Gloeckner, Advanced Engineering Group, MICROMO

Innovative components help OEMs revolutionize designs. In fact, some original equipment can now benefit from zero-backlash actuators and integrated gearhead encoders. These give designers multiple options for demanding applications.

Performance, cost and size requirements for motion applications vary widely. In some cases, performance trumps all and the budget must simply tolerate the result. In others, the application demands performance but at reasonable price. As we’ll explore, if an application requires absolute accuracy, a gearhead encoder is an economical and compact solution. For applications that cannot tolerate any backlash, zero-backlash actuators remove it mechanically.

This tiny FDM0620 series FAULHABER stepper motor from MICROMO delivers high performance. All of its components (including connections) are in a housing that measures 9.7 x 6 mm in diameter. It’s an expansion of a stepper-motor family in the 6 to 22 mm diameter range.

Consider a perfect motion system in which the controller sends a signal, and then the hardware delivers the load to the commanded position. In reality, error sources such as mechanical hysteresis and backlash compromise performance. With enough design time, effort and money, it’s possible to minimize these effects. However, motion is an enabling technology rather than an end in itself—which means OEMs generally aim to focus on their product’s unique value proposition, and not on matching gear teeth and damping vibration, for example.

Now, new technology simplifies performance optimization and makes it cheaper, too.

Preventing lost motion with tandem gearing
As mentioned, some zero-backlash actuators ensure stable performance for applications that cannot tolerate lost motion. To remove error caused by vibration, compliance and shock load, the gearhead encoder drives deviation to zero. That frees OEMs to focus on the development of innovative products of their own.

Even the best gearheads have small gaps between the teeth to let them mesh and maintain lubricant between contacting surfaces. The downside is that this space introduces a bit of lost motion called backlash. This shows up as positioning error, especially in precision applications with frequent reversals. Even for high-accuracy or precision gearheads, backlash still amounts to a few degrees of arc-min, and normal wear over the lifetime of the machine only worsens it. This is not a problem for a case packer or palletizer, but even that small amount of error is too much for applications such as robotics, optical positioning and gantries.

Over the years, motion vendors introduced designs to mitigate backlash using plastic spacers, split gears and springs to apply a preload that maintains contact between the gear teeth. But none are ideal, because they still exhibit a few arc minutes of error, and the preload needs adjusting for wear and environmental changes to maintain performance.

To address the problem, some zero-backlash actuators use an integrated assembly. These deliver fast and accurate positioning without backlash, which in turn delivers loads to commanded locations with minimal error. Compact and robust, the plug-and-play actuators also speed assembly and eliminate scrap.

Consider one specific setup with two motors. This design uses a gear flanked by two motor-driven pinions. One pinion positions the axis, and the other engages the opposite tooth flank and takes up backlash. During normal motion, the motors drive the load with combined torque. At the end of the move, the first pinion holds the position while the second pinion reverses to apply the counterforce. This effectively removes backlash mechanically. Such actuator gearheads perform equally well during acceleration, deceleration and reversals. They’re flexible in that the servo controller can adjust the preload to be softer or stiffer. Plus, it’s a scalable design.

In addition to two-motor setups, this design concept also implements with four or even six motors to increase torque while adding redundancy, especially in high-reliability applications.

Zero-backlash actuator options
Design engineers can choose from rotary and linear actuator configurations with myriad performance levels and form factors. For example, through-hole versions are useful for optical systems that operate in space-constrained applications. More specifically, through-hole zero-backlash actuators can position optical components while a laser beam shines through the aperture. The result is precise performance in a compact system. The aperture also lets users run cables through the center as a way to save space and reduce cable fatigue.

Zero-backlash actuators can have a central gear flanked by two pinions. Consider this generic CAD rendering: During normal operation, the pinions (green) drive the motor shaft. When the move completes, one pinion drives forward while the other reverses to introduce a counter force to mechanically remove backlash. Applications for such actuators are optics, photonics, medical devices and small robotics.

Such actuators also excel in gantries for pick-and-place operations, where backlash can cause binding (and compromise performance while making the system wear prematurely). Here, zero-backlash actuators ensure symmetrical motion so carriages can travel faster while handling heavier loads.

Just consider how the position of a solar cell on a satellite can mean the difference between a functioning device and a useless lump of space junk. In one real-world setup, the reliability and functionality of a zero-backlash actuator lets engineers optimize solar cell positioning. The actuator has also maintained solid performance, even under launch and orbital conditions.

Another approach: Driving error toward zero
In standard servo systems, an encoder mounted to the motor shaft monitors the number of rotations to estimate the position of the load. However, compliance, hysteresis and backlash all introduce error between predicted and actual load positions. This error can be as much as 2 to 3° in some cases. While that’s acceptable in many standard designs, demanding OEM applications can’t tolerate such error.

Kessler-Optics-and-Photonics-Solutions-microscope

Shown here is a dual-band fluorescent microscope from Kessler Optics and Photonics Solutions. Actuators with a through-hole design can be useful in similar applications to position optical components while beams shine through an aperture. The result is precise performance in a tight system, and an aperture that lets cables run through the center to save space and reduce cable fatigue.

Precision OEM machines need an encoder mounted to the output shaft of the gearhead, not just the motor shaft. Such systems can operate on a dual control loop. They first close the loop around the motor encoder and then around the gearhead encoder. This configuration lets the controller measure the difference between predicted and actual location of the load (and compensate for the error). This process introduces a small amount of latency, but makes for highly accurate and precise output. It’s particularly effective for ultra-demanding applications such as micro-robotics.

3D printing and aerospace
Dual-control-loop techniques can be challenging, though. Space can be a factor. After all, adding an encoder to the gearhead won’t do much good if the assembly won’t fit. Mounting an encoder to a gearhead shaft involves mechanical, electrical and controls interfaces. That’s a non-trivial task that consumes time that would be better spent working on the actual product being designed.

The new MICROMO MCST 3601 motion controller for steppers fits the FDM 0620 motor.

As one solution, some motion vendors offer magnetic gearhead encoders. These integrated packages are assembled in the factory and fine-tuned to optimize performance. Based on a Hall-effect sensor, they deliver 0.022° resolution—and excel in applications subject to vibration or shock loads, and those that can’t tolerate settling times. It can work as stand-alone feedback for configurations that lack the space around the motor to install a conventional shaft encoder. Coupled with a stainless-steel housing, the encoder makes the gearhead encoder robust enough to handle tough contamination and vibration conditions. It’s also compact—just 15 mm in diameter—so it fits in tight spots.

Such encoder setups work in myriad applications. In robot-guided surgery, even a millimeter of error can drastically impact patient outcome. Using the gearhead encoder in a robot end effector lets surgeons position their equipment with absolute accuracy. 3D printing demands the same level of performance to fabricate parts with fine detail.

In robot-guided surgery, even a
millimeter of error can drastically impact patient outcome. Here, zero-backlash actuators with encoder-equipped gearheads at the robot end effectors let surgeons accurately position equipment.

Consider another example: In electronics assembly, accurate positioning of components during pick-and-place operations can mean the difference between a finished circuit board and expensive pieces of scrap. The gearhead encoder’s accuracy and small size make it suitable for these uses.

Reprint info >>

MICROMO
www.micromo.com

Cost-effective electronic control for brushless dc motors

January 11, 2016 By Motion Control Tips Editor Leave a Comment

by Adriano De Rosa, IC Architect, Micronas || Motor drive solutions using brushless dc motors are increasing, thanks to the declining cost of electronics. Highly integrated, single-chip controllers are helping drive the trend.

Advances in semiconductor integration are spurring new motor drive designs, including more intelligent drives. The various options for semiconductor integration are opening up an ever-growing array of applications for distributed intelligent small motor drive solutions. These include brushless dc (BLDC) motors, permanent magnet synchronous motors (PMSM) and stepper motors. Because of their technical advantages and increased efficiency, these types of motors are replacing brush-type motors in many existing applications.

The automobile industry is just one example. Typically, automotive components must support low system cost, be small, light, reliable and highly efficient. Reducing exhaust emissions and lowering fuel consumption is also important. The need for drive concepts that work with a wide range of motors, and the extreme demands made on efficiency, system design and networking options have a major impact on actuator electronics.

Electronics for the control function are shown integrated into a brushless dc motor. The continuing miniaturization of electronic components, as well as their decreasing cost, is making this a more viable option for control designs

For many applications, the design-in time can be reduced because complete platforms of small motors can be developed using a single-chip solution. Different motor types and properties can be tailored to by adapting the software. Today’s brush-type dc motor system can be replaced by a BLDC motor system that on the outside looks like a conventional motor, but inside provides advantages needed to realize intelligent motion control.

Self-diagnosis and functional safety increasingly play an important role. Drives with “integrated intelligence” by means of electronics can provide this diagnostic feature. For example, changing motor properties can be tracked and stored by the electronics and adjusted to a certain extent.

Adapting the software allows a large number of functions and applications to be addressed. Designers can efficiently equip a complete platform of actuators with just one type of controller. The small number of discrete components and high integration provide a great degree of miniaturization. The high level of reusability of hardware and software permits quick responses to changes in application requirements.

The BLDC motor market
The level of adoption of BLDC motor technology is increasing. Many automotive functions, such as fuel or water pumps, curve light, head-lamp leveling and others, are converting from brush-type dc motors or stepper motors to BLDC motor technology. If nothing else, the old orthodoxy that the electronics to control the motor are too expensive compared to the price of the motor itself is becoming less valid every day. Furthermore, BLDC motor advantages can significantly enhance other system properties.

When looking at motion control systems, including brush-type dc motors, it’s obvious that control is less complex compared to a BLDC motor. Engineers with little experience in BLDC motor control system design often fear that they will have difficulty converting to BLDC motor technology, even though they know about the advantages. Complex electronics and the programming of such a system are often thought to be a barrier.

Shown here is a typical valve actuator system that integrates the control electronics using the HVC 4223F single-chip solution.

However, the transition to BLDC motors is not necessarily difficult. Using a single-chip solution greatly simplifies the electronic circuit.

Benefits of single-chip architecture
The new Micronas High-Voltage Controllers (HVCs) allow systems with highly integrated motor drive electronics to achieve the performance potential of modern, permanently excited dc motors. The HVC 4223F is an integrated microcomputer system with peripheral modules for directly driving PMSM/BLDC motors and bipolar stepper motors. The programming capability of the peripheral modules and the user-defined software allow the best possible adaptation to the properties and attributes of different drive systems.

The increasing integration density in drives, made possible by the low power/weight ratio (W/kg) of PMSM/BLDC motors, affects the power dissipation, the flexibility of driving circuitry, the selected drive, and the diagnostic options. The high integration density of the electronics requires adapting the thermal operating conditions by means of a target-specified power management. The new HVC family provides many functions that allow this adaptation.

The use of different drive concepts in automotive actuators, for instance, requires the easy adaptation of the motor power bridge and how the bridge is activated. The HVC 4223F addresses this issue with a configurable final output stage, fully integrated and programmable peripheral module, and a powerful ARM Cortex-M3 processor.

The EPWM-Module (Enhanced Pulse-Width Modulation) supports passive and active free-wheeling current patterns (Asynchronous/Synchronous Rectification) for different operating modes and types of motors. The integrated current measurement and the D/A converters allow the programming of nominal current values (for current-controlled micro-stepping, for example). In the PMSM/BLDC motor, without using sensors, the feedback signal of the rotor position can be sent using comparators and integrated star-point references or Hall-effect sensors/encoders.

Algorithms for speed and current control can be quickly executed with the ARM Cortex-M3 CPU—supported by the high-speed A/D converter and adjustable signal paths for voltage and current measurements. The output stage includes overload protection (overvoltage/excess current) and diagnostic functions.

Application example: positioning actuator with BLDC motor
A typical application example only requires 13 components, including the HVC 4223F itself. In many cases, a smaller motor can be used due to better efficiency. The actuators can also be smaller, further reducing material cost. What’s more, the BLDC control system can be programmed to behave like a brush dc motor from outside, with only a voltage and ground supply as connections. This means that existing motion control systems can be upgraded without changing the complete system design. And in the long term, the system can be improved with networking and/or diagnostic functions. Designers don’t have to start from scratch with software development because the existing application notes and demo software can provide an adequate level of functionality.

A good example involves positioning actuators. Mechanical actuators for positioning applications usually have to provide a high torque. Typically, a gear is used to obtain low rpm at the load, introducing considerable losses due to friction. In many cases, the actuator must apply a stable holding torque and the actuator shouldn’t lose its last position to avoid calibration runs. Due to weight reduction and space constraints, the motor and electronic geometry plays an important role. The example describes a solution for a single-chip motor actuator with the HVC 4223F driving a BLDC motor in sensor-less six-step commutation with a LIN communication interface.

A typical control solution using
the HVC 4223F can greatly reduce the number of external components needed. In this example, the complete circuit only requires eight capacitors, two resistors, a diode and an inductor.

The efficient interaction of hardware and software inside a motion control system depends on the distribution of the particular functions of the available chip peripherals. A possible approach for a system includes sensor-less six-step commutation, including rpm and current control, functions for diagnostics, and communication stack. The software architecture can be a simple round-robin with interrupts.

A basic circuit solution for such a system can reduce the number of external components for the motor to a minimum of 12 components. In case of special system ESD and/or EMC requirements, some additional components, like ferrite beads, might be required, for instance, in the dc supply link or LIN signal path.

Reprint info >>

Micronas
www.micronas.com/en

A brief introduction to common bus and line regeneration

January 11, 2016 By Motion Control Tips Editor Leave a Comment

by Steven Peterson, Product Training Engineer, Yaskawa America

Deciding which setup is right for a common bus takes research and evaluation, but selecting and implementing the right one significantly improves design performance and efficiency. Here we’ll outline how to prioritize features while accommodating a given design’s potential amount of regenerative energy and harmonic content.

Designers implement VFDs on a variety of applications due to their high performance, reliability and energy savings. However, VFDs are not without shortcomings.

On most VFDs, the input diode bridge consists of six diodes. These diodes make up the converter portion of a VFD and rectify the three-phase ac input to a fixed dc voltage. Current flow in the converter portion is typically unidirectional. This is a non-issue in most applications, but causes problems when an application has regenerative energy present—for example, when a motor is braking or overhauling due to the load. Such situations cause the motor to act as a generator sending energy back into the VFD. Here, the diode bridge stops current from flowing back to the line; that charges the dc bus capacitors and potentially causes faults due to high dc bus voltage.

In this article, we’ll compare various solutions that use line regeneration and common dc bus arrangements. Then we’ll detail solutions with different benefits (including more compact designs, cost reduction, energy savings and reliability improvements).

Common dc bus
Applications consisting of just two VFDs can benefit from a common dc bus, sometimes called a shared bus. Simply interlinking the dc bus between VFDs through a fused connection establishes a common bus.

Linking the dc bus together between two VFDs through fused connections makes one simple form of a common bus. An oversized drive then supplies ac-to-dc rectification.

The key benefit of a common bus is the sharing and balancing of power. For example, consider a system with two VFDs and two motors: One motor may be in a motoring state while the other motor is in a regenerating state. During this condition, the motoring VFD consumes the regenerative power instead of pulling from the grid.

Some notes here: Remember that two common conditions that can cause regeneration are an overhauled motor or when a motor is braking. Also: Regenerative energy is sometimes called braking energy. However, for simplicity in this article, we’ll just use the term regenerative.

There are multiple ways to establish a common dc bus, each with its own strong points. However, there is no sole best method, as applications can vary wildly and all applications feature differing system needs and budgets.

One quick note on terminology: Motoring is when an electric motor is converting electrical energy into mechanical energy to perform work; regenerating is when a motor is overhauling or braking, it acts such as a generator. Mechanical energy generates electrical energy.

In this topology, a common bus exists between the main drive and back drive on a centrifuge. The second VFD is sourcing dc power from the built-in diode rectifier for the first VFD. The main drive can consume regenerative energy from the back drive. When the centrifuge is decelerating, the regenerative converter sends excess regenerative energy back to the grid.

Six-pulse diode bridge rectifier
One option is for the design to use a large stand-alone six-pulse diode bridge rectifier to establish a common bus. The diode bridge serves to rectify the ac input power to dc. The diode bridge must be of an appropriate size to power all connected VFDs and loads. The diode bridge is identical to the converter section of many VFDs. It’s inherently unidirectional, meaning that excess regenerative energy cannot be sent back to the grid.

A six-pulse diode rectifier works for common bussing multiple drives. Regenerating drive-motor setups can power motoring ones (and reduce overall wiring as well).

Motoring loads must be greater than regenerating loads to keep the dc-bus voltage at a safe level. When regenerating loads are greater than motoring loads, the design must implement a common dynamic-braking package or line regeneration. Alternatively, when the amount of regenerative energy present is low, wiring is simple and less complicated than that of a standard ac setup.

Another option: Line regeneration
If an application needs to return excess regenerative energy to the grid, line regeneration is an option. Here, the electrical system sends excess regenerative energy back to the line by line regeneration. To accomplish this, the design must implement a regenerative converter. This converter wires into the common dc bus just like the existing drives. This converter accepts excess dc voltage from the bus and outputs a six-step waveform back to the grid. This reduces operating costs due to recycling of the regenerated power back to the supply. Total regenerative energy present dictates the capacity of the regenerative converter.

Instead of using a stand-alone diode-bridge rectifier to provide a system with dc power, it’s sometimes beneficial to use a larger VFD. A VFD has a built-in rectification circuit on its front end. Engineers can establish a common bus by sizing the VFD to supply dc power onward to connected VFDs and motors.

Note that, compared to a six-pulse diode rectifier, this setup eliminates the stand-alone rectifier, as the second VFD gets power from the dc bus of the first one. This makes one wiring simpler while keeping costs down.

An industrial centrifuge is one design that benefits from a common dc bus.

A centrifuge consists of a main drive, which turns the drum, and a back drive, which turns the auger at a speed slightly slower than the drum to separate fluids or solids. The back drive is typically a smaller capacity than the main drive. In this application, the back drive is in constant regeneration because it is acting as a brake. This braking energy can power the main drive that’s motoring. When the main drive needs to stop, there’s huge inertial load present. This makes regenerative energy excessively high during deceleration and warrants the need to send the power back to the grid through a regenerative converter.

Cost and space requirements are always a top priority. These are directly proportional to the amount of regenerative energy present. So, it’s extremely important that an engineer confirms the amount of regenerative energy on a given application. Knowing this, the engineer can either opt to oversize the larger VFD to increase bus capacity or use a regenerative converter to apply energy back to the grid. If the amount of regeneration taking place is low, a dynamic braking setup is the most cost-effective solution. Dynamic braking simply burns off the excess voltage onto a bank of resistors.

If the design engineer determines that a regenerative converter is necessary, take note of the additional devices when using it. The reactors are necessary to limit current supplied back to the grid and add impedance between the ac source and load devices. There is also a detection circuit, which is wired directly from the converter to the power supply. The converter uses this circuit to detect the power supply phase order and voltage levels. Tip: Whenever designers consider a common dc bus or line regeneration, follow manufacturer wiring requirements for each system device. Pay particularly close attention to fusing recommendations, peripheral devices, power up sequencing and maximum lengths for dc bus lines.

Harmonics and active front ends
The input diode bridge on a VFD conducts the line current in a discontinuous (non-linear) fashion. This is due to the input diodes only conducting during the peak voltage amplitude of each input phase. The result is a rippled voltage waveform, in turn causing input current distortion and harmonics applied back to the supply.

A regenerative converter always wires in parallel to the VFDs on a common bus. The VFD diode bridge is not isolated from the supply, so the converter won’t help mitigate harmonics generated by the diode bridge. Typically, when harmonics are a concern, the design implements passive front ends consisting of various reactors, filters and multi-pulse transformers. These decrease harmonics but cannot handle line regeneration. Additionally, passive front ends tend to be both expensive and bulky.

Here is an example of a passive front-end system diagram compared with an active front-end system diagram using the D1000 regenerative converter.

A regenerative active front end (AFE) is implemented when harmonic mitigation and line regeneration are a concern. A regenerative AFE gets wired in series with the VFDs being powered from it. Harmonics are low due to passive filtering and reactors paired with the AFE in combination with a pulse-width modulated (PWM) switch array on the input of the front end. Fly-back diodes on the insulated gate bipolar transistors (IGBTs) rectify ac-to-dc for powering one or multiple drives. Additionally, the IGBTs use PWM to reconstruct an ac sine wave by switching the dc bus voltage back onto the supply when regenerative energy is present, making the AFE bidirectional.

A regenerative AFE can act as the dc supply source for VFDs
connected to it. This arrangement is useful in that it reduces harmonics, simplifies wiring and offers line regeneration.

Sizing a regenerative AFE is a matter of simple addition. First, add up all VFD capacities to be powered by the AFE. For example, consider an application running four 45-kW VFDs. To determine which size of regenerative AFE to select, we calculate that 45 kW x 4 = 180 kW. So using simple math, we find that the AFE must be rated for at least 180 kW. The application needs this rating because the AFE works as a power supply for all connected VFDs. This differs from the regenerative converter mentioned earlier (sized solely on the amount of regenerative energy present).

Reprint Info >>

Yaskawa
www.yaskawa.com