Flat Cabling

An alternative to flexible cabling in some motion applications are flat cables. These cables can incorporate any variety of power, signal, and video conductors in a single compact cable. In addition to every type of electrical conductor, flat cables can also include tubing for air or liquids, and even fiber optics. By incorporating all these elements into a single flat cable, motion equipment can be significantly smaller, quieter, and more energy efficient.

Most industrial automation equipment today operates continuously, with robots that execute rigorous motions repeatedly, sometimes thousands of times a day. These applications stress not only the moving parts of the machine, but also the electrical cabling. All too often, designers spend more time sizing components like motors, actuators, and controllers and give little thought to the cabling needed. The result is that if standard cabling is used in these applications, the cables, not being designed to flex continuously, can’t handle the rigors of the application and can result in costly premature failures. Flat cables are best for continuous flexing. Their wire conductors can individually flex in a single plane, which provides optimum flex life.

Some motion control systems may encase separate wires, cables, and tubes in a carrier track to contain and manage the separate elements and to constrain their motion. These tracks are usually made of plastic and they usually have a rather large bend radius due to their size and the rolling link element design. These tracks do not add performance to the motion device or machine, as they are simply cable management devices. Cable tracks can add bulk, mass and inertia to the motion system, and moving this extra mass requires more energy. While certain motion systems such as robotic applications may require this type of cabling design, other designs may not and can use standard flat cabling instead to save weight and cost.

Some flat cable manufacturers offer cables with silicone jacketing. These types of flat cables are durable and need no external armor for protection. They resist abrasion and will even self-heal minor nicks. Silicone encapsulation also provides protection against oils, acids, ozone, steam, and extreme temperatures.

When specifying flat cables in motion control applications, four considerations are key; the bend radius, life cycles under constant flexing, any packaging constraints, and environmental factors.

The bend radius ultimately depends on the gauge of the wire and the kind of conductors used in the cable. As a general rule, the finer the conductor gauge the smaller the allowable bend radius. Flat cables with PTFE jackets can have a larger bend radius than cables with silicone jacketing, given that each cable contains the same conductors.

For cabling used in flexing applications, two key factors are the wire conductors and the cable jacket. With continuous flexing, conductors containing multiple strands of fine-gauge wire generally last the longest.

Chief environmental factors include exposure to harsh conditions such as temperature and humidity, and resistance to environmental contaminants such as any oil or corrosive materials.

Flexible cabling

Flexible cables, or continuous-flex cables, are cables specially designed to cope with the tight bending radii and physical stress associated with motion control applications. These highly flexible cables were developed with unique characteristics to differentiate them from standard designs. These are sometimes called chain-suitable, high-flex, or continuous flex cables.

A higher level of flexibility translates into an increase in service life for a cable inside a cable carrier. A regular cable typically manages 50,000 cycles, but a flexible cable can complete between one and three million cycles.

Flexible cables can be divided into two types; those with conductors stranded in layers inside the cable, and those that have bundled or braided conductors.

Stranding in layers is easier to produce, and therefore usually less expensive. The cable cores are stranded firmly and left relatively long in several layers around the center and are then enclosed in an extruded tube-shaped jacket. In the case of shielded cables, the cores are wrapped up with fleece or foils.

However, this type of construction means that during the bending process the inner radius compresses and the outer radius stretches as the cable core moves. This can work quite well because the elasticity of the material is still sufficient, but material fatigue can set in and cause permanent deformations. The cores move and begin to make their own compressing and stretching zones, which can lead to a “corkscrew” shape, and ultimately, core rupture.

The other construction technique involves braiding conductors around a tension-proof center instead of layering them. Eliminating multi-layers guarantees a uniform bend radius across each conductor. At any point where the cable flexes, the path of any core moves quickly from the inside to the outside of the cable. The result is that no single core compresses near the inside of the bend or stretches near the outside of the bend, which reduces overall stresses. An outer jacket is still required to prevent the cores untwisting. A pressure filled jacket fills all the gussets around the cores and ensures that the cores cannot untwist. The resulting flexible cable is often stiffer than a standard cable, but lasts longer in applications where it must constantly flex.

Selecting the right flexible cable for an application starts with a few fundamental parameters. First, determine the application type. Will the cable be stationary or will it be moving? If the latter, is the motion mainly flexing or is there torsional motion involved? Or does the application call for both flexing and torsion? Different applications have specifically designed cables for that application.

Next, consider the wiring itself; that is, the number of conductors needed, the size of the conductors, and the operating voltage. In addition, are there special insulation or jacket materials required? Also, are there any special shielding requirements? And don’t forget to check for any special approvals that may be required such as UL, CSA, CE, and so forth.

The environmental conditions in which the cable will operate are also important in the selection process. For instance, what is the operating temperature for the application; will the cables be in low-temperature (freezing and below freezing) or high-tempearature environments? Also, will the cables need to be oil resistant? In this case, there are cables that provide minimal protection which may be sufficient for low-level exposure and cables that provide full immersion protection over a period of days. Lastly, consider flame resistance. Options can range from minimal protection to higher levels or protection as the application calls for them.

Cable Carriers

Motion control systems can vary from simple, straightforward single-axis direct-drive systems with little wiring to large and complex multi-axis robotic systems with a hornet’s nest of cables. This is usually where cabling, which was an afterthought, now takes center stage.

Especially where there are lots of cables and wiring, cable management becomes an issue. A simple form of cable management uses twist-tie type bundlers that tie together groups of wires and cables. These are low cost and easy to use. The problem is that with more and more cabling, they become impractical. Also, if the wiring and cabling have to be suspended, bundling them together may pose weight problems which cause sagging and put undue strain on the cables.

Using cable carriers is another option. Cable carriers are essentially structures designed to house cables. The structures themselves can be made of many materials such as plastic, steel, or a metal alloy. Cable carriers are used to protect cables and hoses on moving machinery. They prevent tangling and increase safety by not having cables susceptible to getting caught in moving parts of a machine. Applications for cable carriers can range from machine tools and robotics to cleanroom applications and large industrial equipment like cranes and other construction machinery.

Carriers can house a large volume of cables and wires and support the weight of them all without sagging or putting stress on the cabling. They also make managing and routing the cables through a machine or factory much simpler and provide easy access for troubleshooting or maintenance as well.

Selecting the right kind of cable carrier for an application starts with a few simple guidelines. The most important points to consider are the specifics of the application. These include the length of travel, the number of cables or hoses, the size and weight of the cables, the required speed and acceleration and environmental factors such as exposure to any debris, excessive heat or chemicals. Knowing the weight of the cables ensures that the carrier won’t fail by snapping in two.

Cable carrier styles can be either open or closed. Open varieties allow for easy access to the cables and visible access as well, whereas closed carriers seal off the cables from the environment to protect from environmental contaminants such as metal filings.

Environmental conditions play a large part in selecting a cable carrier. If the application is in a dirty or contaminated area, an enclosed carrier is the best choice. An open carrier is lightweight and makes inspecting and replacing cables easier.

Another important consideration is the bend radius of the cable carrier. Bend radius is measured from the center of the curve loop to the center of the pivot pin on the side link. A larger bend radius means less stress on the cable and a longer service life.

Pharmaceutical equipment wire and cable product offering from Alpha Wire

Alpha Wire (www.alphawire.com) is proud to unveil the new wire and cable product offering for pharmaceutical equipment. Multi-functional cable components are very essential with pharmaceutical processing equipment becoming more precise and automated. The new pharmaceutical processing wire and cable from Alpha Wire increase the equipment’s reliability and capability in conditions from cleanrooms to factory floor. With full solution set, the company solves the problems of complex drive systems, continuous flexing applications and signal interference.

“As the pharmaceutical industry grows, the manufacturing demands have kept pace,” said Mike Dugar, Alpha Wire’s Director of Marketing. “Component failure can halt an entire production process, causing backorders and possibly the scrapping of an entire production run. Not only are our products designed for maximum reliability, our short lead times ensure that you won’t have to wait for your order.”

Additional to the custom cable for unique designs, the company is offering the following products for pharmaceutical equipments:

• Industrial Series XM Flexible Control Cable made for continuous flexibility in processing tray-rated applications and equipment control systems.

• Xtra-Guard 1 Performance Cable features a specially formulated PVC jacket, which prevents heat build-up for unstoppable reliability in a control and communication cable.

• Flexible Motor Supply Cable has a premium PVC jacket for resistance against oil in an MTW-rated cable for any motor-driven component system, which requires flexibility and tight clearances.

• Industrial Series SF Flexible Servo Cable specifically designed for dynamic braking systems on conveyors, multi-axis mixing systems, encoder and resolver feedback and other servo motor-driven applications.

• Industrial Series V VFD Cable made for variable-frequency drives designed particularly extended duty cycles typical in conveying and mixing.

GORE High Flex Cables

GORE High Flex Cables provide superior flex life performance and maximum resistance to severe mechanical and environmental stresses. With more than 45 years of experience in the wire and cable industry and extensive knowledge of unique materials, Gore provides reliable solutions to your most demanding cable and assembly needs.

GORE™ On-Line Design Tool…
For quick lead times and small order quantities try Gore’s interactive design guide. Design GORE™ Trackless Cable, GORE™ High Flex Round Cable, or GORE™ High Flex Flat Cable (Spooled Cable for larger quantities and Discrete Length Cable for cut to length cable).

GORE™ Trackless Cable and Assemblies…
GORE Trackless Cable Solutions allow automated equipment manufacturers to eliminate cable track and avoid many of the problems associated with cable track such as particulation, vibration, size and weight.

GORE™ High Flex Flat Cables
GORE High Flex Cables are used in any energy chain or cable track reducing particulation and eliminating the need for dividers.

GORE™ High Flex Round Cables
GORE™ High Flex Cables are used in applications where flex life reliability is critical. GORE High Flex Cables will provide your application with reliable performance reducing expensive equipment downtime and field repair due to cable failure.

www.gore.com

Reduce the Number of Cables

by Alexander Bromme, Managing Director, Steinmeyer FMD and George Jaffe, Executive VP, Steinmeyer Inc.

The use of new, miniature single axis motion controllers enables an innovative cabling concept. Each axis carries its own peripheral controller connected with motor, encoder and sensors by means of short, stationary cables. The peripheral controllers are connected by a high throughput data bus system that allows interpolated movements between different axes. Thus, the number of moving cables (one power, one data bus) is independent of the number of axes in a system.

Cable reduction can be especially useful in wafer inspection systems, which typically consist of a stack of XYZ linear stages plus a theta rotary unit. There can easily be 16 connectors at the final electrical terminal with over 100 wires, many of which are in constant motion during system operation. The disadvantages and potential problems of this many cables include:
1. All moving cables must be accelerated, moved, and bent by the stage system itself, which raises driving force, causing an undesirable temperature rise.
2. The bend resistance of the cables is not constant. The result is stick-slip plus randomly distributed effects that complicate precision positioning.
3. Moving cables generate particles and tend to outgas, which is undesirable in clean room applications.
4. Stage system reliability is reduced in proportion to the number of moving electrical lines. The higher the number of moving cables the higher the risk of a failure or defect.
5. Electromagnetic interference between cables may cause crosstalk, creating problems in system integration.
6. A multi-axis moving cable system requires additional space, so the motion system becomes larger to accommodate the many cable carriers. With the extra carriers, total system cost
increases.

A better solution is to reduce the number of moving cables!

How? Replace central multi-axis motion controllers with single separate control modules mounted directly to the axes.

These modules, connected by a high-speed bus interface, even allow interpolated movements between different stages.

In the system developed by Steinmeyer, the bus-interface is Controller Area Network (CAN).

As an example, the model DAC1005 (manufactured by LPKF) is a universal motor controller for one axis. It complies with the CANopen standards (DS 301 and DSP 402) and is certified by the CAN in Automation e. V. It can control DC-, 2- and 3-phase servo-, stepper- and linear motors. Powerful algorithms and high sampling rates guarantee high quality control. The interfaces for limit switches, digital and analog inputs and outputs, and encoders are integrated.  Alternatively to CANopen, the communication with a master computer may be executed via a serial port (RS232).

By miniaturizing the electronic PCBs, the size and mass of the individual control boxes is smaller than a comparable cabling system. For a 3-axis XYZ system, instead of a huge number of moving wires, there are three moving control modules, a tiny three wire shielded CAN-bus cable in a daisy chain configuration and two wires for power.

In total, the complete system needs just two separate cables with diameters of 7 mm and 12 mm independent of how many axes the stage system includes. The five electrical leads are easy to handle in one moving cable carrier.

Each axis carries its own motion controller independently. All leads to motor, sensors, and encoder systems have a length of typically less than 20 cm. More important, all the electrical connections to the upper axes are static, which means there is no bending or relative movement of the cables.

With a single linear motor driven stage, each axis can require up to 4 separate cables with diameters of 8 to 14 mm.  That means up to 27 electrical wires must be connected. But, replacing a central multi-axis motion controller with single separate control modules mounted directly to the axes can significantly reduce the number of cables in the system.

By shortening the cable length, the main concerns of crosstalk and radiation are eliminated.  Instead of a bulky central motion controller, only an external power supply is needed which is usually available in the machine anyway.

The use of separate control modules is an innovative way to reduce the number of cables in a system.

And in case axis replacement is necessary, the complete stage-controller combination is exchanged. So individual stage related information, like PID-controller tuning, is hardware-connected to the mechanical structure. These parameters can be made as a factory setting so the system integrator saves time and money.

Such a configuration was exactly what Scienion AG, located in Berlin, Germany, was searching for its line of ultra-low volume liquid handling systems used in such applications as DNA microarrays, protein microarrays, reversed phase protein microarrays, cell transfection arrays, and Glycan microarrays.

The company’s leading product is the sciFLEXARRAYER, a state-of-the-art non-contact dispensing system for ultra-low volume liquid handling.

The company recently introduced a novel high throughput instrument for array and biosensor production, the model S100 – which includes 3-axis motion platforms designed and manufactured by Steinmeyer FMD.

Steinmeyer Inc.
www.steinmeyer.com