Mechanical PT - Motion Control Tips

Geared stepper motors drive movements of Breakfast Brixel moving architectural wall

November 13, 2018 By Lisa Eitel Leave a Comment

A new architectural wall called the Breakfast Brixel is making some installations more dynamic. The system is built from dozens of digitally controlled rotating bricks that act as pixels to create waves, stripes, and undulating shapes on the moving walls. Brixel installations can even run customizable artwork and facades to evolve in response to real-time data and software commands.

Breakfast engineers designed everything from scratch — PCBs included — and employ geared stepper motors to rotate the bricks.

In addition, the center support shaft of each Brixel column allows each brick to spin endlessly in either direction without tangled wires or the use of slip rings.

“A computer runs a fully featured application in the background. It sends data to the Brixels with movement commands that include speed and direction. We can also set custom acceleration and deceleration curves at any time on the fly when the Brixels are moving. This lets us create beautiful and organic displays — such as wind animations,” explained Breakfast CTO and cofounder Mattias Gunneras.

For high-level programming of animations and interactive movements, controls were dynamically scripted was Python, OpenCV-Python, and Numpy. In addition, for Brixel Silhouette — a Brixels mode that causes the wall to rotate bricks to mirror the shapes and movements of people in front of the installation — Breakfast engineers used 3D simulation for testing through a VR headset. That let the team get a feel for the displays before a prototype physical installation was ready.

“We’re using stitched-together 3D depth cameras to create a point cloud of the scene in front of the installation,” said Gunneras. With this technique, we can create the mirroring effect to map a person … regardless of how close they stand to the installation.”

Breakfast Brixel walls are customizable to work as facades, railings, dividers, and fences. The design allows an unlimited number of rows and columns.

When there’s nobody standing in front of the installation, kinetic animations and relevant information can play across the installation in the form of letters created by positive and negative colors and space.

Brixel walls can display an array of digitally programmed visuals and movements. The bricks come in an array of sizes, shapes, materials, and colors.

A Linux controller sits at the heart of each installation to execute programs that process visual data and pass high-level data to the bricks. Data goes via RS-485 connections to controller PCBs at the bottom of each column. Each controller PCB then sends the data over serial lines up the columns to each individual brick. Brixel installations are controllable and updated via a web-based app running off the Linux controller — for access from any mobile device. Users can upload content, create playlists, and set schedules.

Strain-wave gearing core to one exoskeleton for logistics-plant work

November 13, 2018 By Lisa Eitel Leave a Comment

Consider a specific example of how strain-wave gearing gets used — in the German Bionic Systems Cray X exoskeleton. This 7.9-kg design assists plant personnel with manual handling of tools and heavy goods while reducing lower-back compression pressure. The exoskeleton joints use strain-wave gearing to reduce their brushless motors’ high rpm for an output of low rotational speed with high torque.

On a related note, at 2018 Consumer Electronics Show harmonic-gearing manufacturer Harmonic Drive exhibited with a team from suitX, designer of the Phoenix walking-assist exoskeleton … which also uses strain-wave gearing.

Exoskeletons are most useful where human work cannot be fully replaced by robotics — in industrial production for automotive, logistics, or and healthcare industries. BIS Research predicts that the market for wearable robotics could grow to U.S. $4.65 billion by 2026.

The Cray X has a battery life of about eight hours give its wearer 15 kg of assist. Worn like a backpack, the Cray X extends down the legs and straps to the user’s thighs. Battery-driven electric motors at the joints then help the user with lifting or (in another mode) stand up straight with a constant vertical force (for core support) after bending down for a task. The Cray X begins actuation when an armband tracking forearm-muscle tension sends feedback to a processor indicating that on object is being lifted. Then the exoskeleton’s strain-wave-gearing-fitted motors go into action.

Production Cray X models are now available for order. “After testing with several industrial companies, we made the first models available. Now, scaling production and further technological development are top priorities for us,” said German Bionic Systems CEO Peter Heiligensetzer.

Heiligensetzer predicts his company’s technology will help trim healthcare costs and (in manufacturing and logistics settings) raise productivity levels. “This technology could solve pressing societal issues now — a time of broad demographic shifts and reported shortages of skilled workers … and exoskeletons may also help workplaces avoid age discrimination.”

Most efficient vehicle in the world uses brushless motor in drivetrain

November 8, 2018 By Lisa Eitel Leave a Comment

One little hydrogen fuel-cell vehicle holds the Guinness world record for the most efficient vehicle … and uses a slotless brushless 60L-H-175-A from Koford Motors to drive its rear power wheel. This year, the tiny car from the Duke Electric Vehicles team beat the 12,600-mpg efficiency of the PAC CAR 2, in turn designed by a student team at the Eidgenössische Technische Hochschule (ETH) in Zürich, Switzerland.

The Duke vehicle’s conversion of chemical energy (stored in hydrogen gas) to mechanical energy is maximally efficient.

According to Patrick Grady (president of the Duke Electric Vehicles team until he graduated this year) their fuel-cell vehicle Maxwell (in its final World Record iteration) has a 15-mph design speed and 40.8 W of total power (sourced from hydrogen chemical energy). During redesign based of a Maxwell predecessor, the team saw that with a nominal fuel-cell efficiency of 58% average electrical energy from the fuel cell (used by the motor) couldn’t exceed 23.6 W. With a motor and drivetrain efficiency of 87% or so, mechanical power dissipation couldn’t exceed 20.6 W.

The Duke team used the 23-W target extensively to make quick decisions on what components to swap for better.

“For Maxwell prototypes, our Teensy 3.2 microcontroller of choice drew about 300 mW when powered from 5 V … so had we used the Teensy in the final Maxwell design, we would’ve lost 1.3% efficiency just powering the microcontroller,” explained Grady.

Another key to ensuring efficiency was calculating the average power level and then optimizing the fuel-cell system for top efficiency there. But average motor load over a representative race is 23 W … and the Duke team’s original design used a motor most efficient at 80 W.

Yet another wrinkle: To maintain speed during races, the driver cycles the motor on and off. So to allow this mode of operation, the team considered a few system architectures:

No load levelling — with the motor controller directly connected to fuel-cell output with no energy storage between the two

Passive load levelling — with a large supercapacitor bank connected to the fuel-cell output

Active load levelling — with a custom DC/DC converter between fuel cell and supercapacitor bank for total fuel-cell control

Fuel cells are more efficient under constant load than dynamic load. This fact (and how a larger fuel-cell stack to output 80 W has higher leakage and auxiliary losses than a stack sized for 23 W) meant the Duke team needed something to modulate draw from motor off stack.

The first approach would’ve required the fuel cell to supply full motor power … and optimization around 80-W motor power instead of the car’s nominal 23 W. Making matters worse, such a design would’ve necessitated “optimization” for 0-W conditions — requiring low gas leakage and latent current draw in such situations. So the team vetoed this design.

The second method was one the Duke team used on their Gemini car — for a 2018 Shell Eco-Marathon race. This setup employs a dc/dc converter to actively control power with software to stepup fuel-cell voltage to higher supercapacitor and motor voltage. The configurable converter drew constant power from the fuel cell and into a supercapacitor bank for efficiency. This entirely decoupled the fuel cell from the motor and was the theoretically cleanest option. But in the 2018 Eco-Marathon, the Duke team only got 96% efficiency from the converter. Plus it (and associated software and hardware) introduced complexity and design issues.

So for Maxwell’s world-record run, the Duke team employed passive load levelling. Here, a supercapacitor bank connects in parallel to the fuel cell and motor controller. The fuel cell continuously trickles power into the supercapacitors … and then motor discharges the bank in high-power bursts. Supercapacitor size was chosen to hold voltage and power draw off the fuel cell constant over a lap. The supercapacitors added about 2 kg to the vehicle weight, but their simplicity made the car design more robust — and losses from the dynamics of the fuel cell were smaller than the losses from dc/dc converter to boot.

Shown here is the energy flow on Maxwell’s powertrain.

More specifically, supercapacitors run at better than 99% efficiency (with losses from internal resistance) … and that of Maxwell vehicle’s supercapacitor bank is only about 10 mOhm — far lower than that of comparable lithium-ion solutions.

Shown here is Maxwell’s 1200F supercapacitors next to a lithium polymer (LiPo) unit of comparable capacity.

Electric motors do their part maintaining the car’s efficiency

Critical to Maxwell’s efficiency is having an efficient electric motor that’s also light and reconfigurable to myriad input voltages.

“Few motor manufacturers list their motors’ theoretical efficiency, and still fewer have measured dyno results. Unfortunately, most vendors focus on optimizing power density or cost … so we struggled to find resources focused on efficiency,” said Grady. “Our team ultimately chose Koford Motors to power Maxwell. Their data sheets very helpful and their motors highly efficient — with dyno results to quantify that efficiency.”

More specifically, the team picked a Koford 60L-H-175-A motor — with a peak efficiency of about 92% and well-suited sizewise for Maxwell.

Shown here (black, in background) is a Koford 60L-H-175-A motor with a sprocket to engage a chain — which ultimately propels the power wheel on the world’s most efficient vehicle.

Paired to the brushless motor is a chain transmission — to transfer power from the motor shaft to Maxwell’s rear wheel. On the final record-setting Maxwell powertrain, a #25 chain runs on a 14T sprocket coupled to the Koford motor …and then a 120T sprocket drives a freewheel on Maxwell’s rear wheel. The chain transmission let the Duke team easily change gear ratios to let the motor run at peak efficiency … which was helpful, as the motor and drive are most efficient at 100% duty cycle (near top speed).

The Duke students built an inertial dynamometer to measure the efficiency of purchased motors themselves. Results partially masked in red here cover inaccurate results due to an incorrectly programmed motor controller misreporting low-speed efficiency. True efficiency curves are flatter … and the high speed results shown here are more accurate. The students got their efficiency results after the chain transmission (which taxes peak efficiency by 3 to 4%).

Direct-drive option? Not for this efficient design

The Duke team considered using a direct-drive hub motor in Maxwell, as such motors are theoretically more efficient than electric motors connected to power-transmission components. But the team only found hub motors that were heavy, poorly documented, or designed for low-cost electric bikes.

Maxwell’s motor controller uses Hall-sensor feedback for simple block commutation. The team tried out a blended Hall and back-EMF commutation for more accurate timing but found its implementation didn’t match the performance of classic Hall commutation.

To save power, Maxwell was programmed to shut off most electrical systems when the motor wasn’t running. The car’s driver was given just a button control the motor — not the more standard throttle potentiometer. Upon depression, the button triggers a wake-up sequence and throttles the motor at constant current. Removing the driver’s throttle control boosts consistency and performance by keeping the electric motor running near its optimal point.

Visit this blog deep link on duke-ev.org for more information from Patrick Grady about the Maxwell fuel-cell vehicle — and on challenges related to getting top performance out of Maxwell’s off-the-shelf Horizon H-100 PEM fuel cell. At the blog, Grady also explains the advanced analysis the team performed on various racetracks to pick one that would give Maxwell the best odds of beating the world record for vehicle efficiency.

New rail gearbox lubricant from Klüber Lubrication enhances cold-weather operation

November 8, 2018 By Miles Budimir Leave a Comment

Klüber Lubrication’s new Klübersynth LEG 4 75 W 90 is a synthetic high-performance gear oil for rail vehicle gearboxes. Even in the cold, trains need to run smoothly and these vehicle gearboxes often operate under high loads. The new polyalphaolefin-based oil technology of Klübersynth LEG 4 75 W 90 provides a wide service temperature range, including excellent low-temperature characteristics. Compared to conventional synthetic gear oils, its VI (viscosity index) enables a higher viscosity at lower temperatures.

Additionally, the good shear stability of Klubersynth LEG 4 75 W 90 prevents a decrease of the lubricant film thickness, even during long-term operation at high loads. The high micro pitting resistance protects gearboxes operating under high loads that are susceptible to this damage. Its low foaming tendency and anticorrosive properties make possible problem-free gear operation.

The high scuffing load capacity enables this gear oil to be used in gearboxes that require API GL-4 or API Gl-5. Its excellent wear protection of both gears and rolling bearings extends the life of lubricated components. The excellent aging and oxidation stability permit longer oil change intervals compared to mineral or other synthetic oils. Both of these characteristics reduce maintenance costs.

For maximum benefit, especially for the low-temperature range, Klübersynth LEG 4 75 W 90 can be paired with Klübersynth GE 4 75 W 90.

For more information, visit www.klueber.com.

Ogura explains how permanent-magnet brake work with new animation

October 8, 2018 By Lisa Eitel Leave a Comment

Ogura Industrial Corp. has created a new animation showing how permanent magnet brakes work. The animation shows an exploded view of the component parts and how they interact with each other.

In permanent magnet brakes, holding force is created by permanent magnets and released by energizing the magnetic field.

Permanent magnet brakes are higher torque and smaller diameter versus spring applied brakes. Permanent magnet brakes also allow torque to be controlled by varying the offsetting current to the brake. Brakes are used on a wide variety of medical, robotic and other motion control applications.

Check out the video on the manufacturer’s website and on YouTube:

Ogura Industrial Corp. has been producing clutches and brakes since 1938. Over that time, the brakes manufacturer has developed more than 5,000 different models of clutches and brakes. Although Ogura primarily produces electromagnetic clutches and brakes, the brakes manufacturer also produces magnet particle brakes and clutches as well as mechanical, pneumatic, and hydraulic motion components —and a variety of specialty products. Ogura is the world’s largest manufacturer of electromagnetic clutches and brakes … current manufacturing capacity is more than 30 million units per year.

To provide localized support, the brakes and clutches manufacturer has manufacturing plants spread throughout the world — in Asia, The Americas, and Europe. All manufacturing facilities are ISO certified and conform to ISO 9001;2008, ISO 140001, and ISO/TS 16949.

Design engineers seeking a special product or modification to existing standard models should call (732) 271-7361 or visit www.ogura-clutch.com.

ETP shaft-locking device from Zero-Max provides verifiable component installation

October 4, 2018 By Miles Budimir Leave a Comment

Now there’s a better way to mount components on motion control shafts while verifying the installation for quality purposes. It’s the ETP Express shaft-locking bushing that locks into position gears, pulleys, sprockets and other components in automated machinery.

Handling torque ranges from 34 to 12,538 ft-lb (46 to 17,000 Nm), these ETP Express shaft-locking bushings from Zero-Max ensure fast mounting, repositioning and phasing of the components to the shafts. Three key reasons make the ETP Express a superior shaft-locking device:

Fast Installation: Positions in seconds and can be readjusted hundreds of times just as quickly. No axial movement of the bushing or component along the keyless shaft during installation. Much faster installation than other mechanical bushings requiring multiple screws. An Allen wrench is all that is required to mount and lock ETP Express bushings into place. They have sealed, clean lines that resist debris collection and clean easily without any special maintenance.

Minimal Runout: ETP Express provides maximum concentricity with a solid and more precise connection between shaft and hub unlike conventional shaft locking bushings. Its hydraulic design gives even and full contact pressure around the circumference of the bushing. The bushing aligns precisely without axial movement as it is tightened.

Verifiable Installation: With single screw installation, ETP Express locks securely into position, making it a verifiable installation position for maintaining ISO procedures and quality maintenance records. One mounting screw equals one torque value. By comparison, most mechanical bushings require torqueing at multiple locations. With multiple screw mechanical bushings, torqueing at one location easily changes the result at an adjacent location with a loss of concentricity.

Available in 15 through 100 mm and various inch shaft sizes, ETP Express bushings are a great choice for new and retrofit applications particularly in automated machinery applications.

See the video demonstration below:

For complete information, go to www.zero-max.com.

New grinding machines increase quality and productivity at Nixon Gear

September 25, 2018 By Miles Budimir Leave a Comment

Two new grinding machines were recently added to production at Gear Motions’ Nixon Gear Division in Syracuse, NY.

The Studer S121 is a 2-spindle universal cylindrical grinder capable of grinding IDs and faces.

The Studer S121 is a 2-spindle universal cylindrical grinder, one of two new gear grinding machines recently acquires by Gear Motions’ Nixon Gear Division.

It was purchased to accommodate a program for a new customer with Nixon Gear. The machine adds new capabilities to grind small diameters with its 60,000 rpm spindle, while still being able to handle larger gears with its 10-in. chuck and 36,000 rpm spindle. It also vastly improves productivity by offloading work from older, mechanical Heald bore grinders. The S121 is also capable of grinding bores and faces in one setup, saving even more valuable production time.

The Toyoda GL4Ai-50 OD Grinder is another new addition to Nixon’s fleet of gear manufacturing equipment. It has a Ø12.6-in. swing and 19.6-in. distance between centers. Nixon already uses a model GL4A in production, and the purchase of this newer model adds even more shaft grinding capacity. The GL4Ai-50 includes two part auto-sizer gauges, which is an increase over the older GL4A’s single gauge. The 2nd auto-sizer gauge saves time and increases productivity as two different tight tolerance diameters can now be ground in the same setup.

Gear Motions continues to make investments in new equipment that allow them to meet and exceed customers’ expectations. The purchase of these state-of-the art machines gives the company the tools needed to produce the highest quality products at a lower cost, delivered in a timely manner.

About Gear Motions
Gear Motions, Inc. is an employee-owned company, with gear manufacturing facilities in Syracuse and Buffalo, NY. Specialists in precision ground gears, the company manufactures custom cut and ground gears for OEMs all around the world. Products include precision ground helical gears, spur gears, pump gears, bevel gears and worm gears, as well as multiple types of sprockets, timing pulleys, shafts and splines.

For more information, visit www.gearmotions.com.

What are rotary unions and how are they used in motion applications?

September 25, 2018 By Danielle Collins Leave a Comment

Rotating components are common in motion applications — robot arms, winders, spools, spindles, and rotary tables are just a few examples. And while creating rotary motion is easy, when air or liquids need to be transferred from a stationary supply to a rotating component for cooling, heating, lubricating, or transmitting fluid power, the task becomes more complicated. This is where rotary unions come in.

Rotary unions provide an interface that allows fluid media — air, steam, or liquid — to be transferred between a rotating component and a static component. They’re designed to accommodate a wide variety of media conditions, including very high and low temperatures, flows, and pressures, including vacuum applications. And unlike other fluid transfer mechanisms, rotary unions work for applications involving any combination of rotation angles, including continuous rotation in one direction.

This rotary union can be used for supplying cooling from a stationary source directly to a machine tool spindle.
Image credit: Dublin Company

Rotary unions are referred to by a variety of names, including rotating unions, rotary joints, rotary swivels, and rotary couplings.

There are numerous designs and configurations for rotary unions — in fact, they’re often custom-designed for the application — but all rotary unions are made up of four basic parts: the housing, one or more bearings, the shaft, and one or more seals.

The housing is typically the stationary part and is connected to the media supply. The shaft is independent of the housing and rotates with the connected rotary equipment. Media can flow through the union radially or axially via ports in the housing. The rotating part is supported by radial bearings — typically one or more fully sealed deep groove ball bearings.

The most important component of the rotary union is arguably the sealing mechanism, which prevents or reduces leakage between the rotating and stationary components, and must do so with minimal friction and wear. Seal types range from simple lip seals to more complex spring-loaded mechanical seals that automatically adjust to minimize the pressure on the seal faces, reducing friction and wear.

Of course, the fluid transfer should ideally be leak-free, but in some applications, completely leak-free transfer is not possible. For these cases, the media is prevented from being released into the environment by a collection system that recovers the leaked media, protecting surrounding equipment and personnel.

This video from Dynamic Sealing Technologies Inc. demonstrates how rotary unions transfer fluid between rotating and stationary component, with examples of their use in various industries.

Whether choosing a standard, off-the-shelf rotary union or designing a custom product, the following factors should be considered:

type of media being transferred
speed of rotation
flow rate of media
pressure of media
temperature of media
allowable leakage

The type of media is especially important, since the housing, shaft, and seal materials must be compatible with the fluid flowing through the union. Fluid media can range from water to highly corrosive liquids and steam, and manufacturers address the challenges of each by offering a wide range of materials, not only for the housing and shaft, but also for the seals.

Although single- and dual-flow designs are most common, rotary unions can include multiple independent flow paths that allow different media to be transferred concurrently without mixing. It’s also common for slip rings or fiber optic rotary joints to be integrated with rotary unions, allowing the passage of both fluids and electrical or fiber optic cables.

This cross-section of a two-passage rotary union shows the two separate channels through which different media can pass without mixing.
Image credit: Kadant Inc.

In motion control systems, rotary unions can be found in robot joints, especially for transferring air or fluid to end-of-arm tooling. They’re also used for passing vacuum or air pressure through rotary air bearing stages, and for supplying coolant and lubrication to machine tool spindles.

Feature image credit: Moog

Advanced manufacturing, materials yield new, efficient traction drives

September 21, 2018 By Miles Budimir Leave a Comment

Rolling Motion Industries (RMI) has released two high efficiency traction drives; the MAR-17-1-2.1 Traction Drive and the MAR-23-1-2.1 Traction Drive. These are 1-Way traction drives with only six moving parts and use an engineered traction fluid with a coefficient of friction of just 0.1 to 0.12. These traction drives typically last three times longer than conventional gearboxes and with no metal to metal contact these high efficiency drives generate up to 72% less heat after 24 hours of continuous operation. They also create up to 38% lower dB at 3,000 rpm. Even though there is no metal to metal contact there is no slippage or lost motion between the input and output shafts.

The MAR17-1-2.1 Traction Drive is designed for speeds to 3,600 rpm with 10 to 20 in./lb of torque, and the MAR-23-1-2.1 Traction Drive is rated for 3,600 rpm with 20 to 30 in./lb of torque. Operating at temperatures that are lower than a motor’s, with low vibration, and no torque losses from 10 to 3,000 rpm, these traction drives permit a motor to operate at peak efficiency. Applications for these traction drives which can operate in explosive environments (i.e. Zone 1 and 21) include: Pumps, blowers, fans, turbo and super chargers, conveyers, HVAC systems, medical applications, and other power transmission and motion applications.

The new drives are available with an optional overriding clutch and, incorporating standard NEMA mounting dimensions, can be easily integrated into new and existing applications.

For more information, visit www.RMIDrive.com.

Advanced manufacturing and materials have made an highly efficient traction drive possible

September 14, 2018 By Lisa Eitel Leave a Comment

Rolling Motion Industries (RMI) has released two high-efficiency traction drives — the MAR-17-1-2.1 Traction Drive and the MAR-23-1-2.1 Traction Drive. These are 1-Way traction drives with only six moving parts and use an engineered traction fluid with a coefficient of friction of just 0.1 to 0.12. These traction drives typically last three times longer than conventional gearboxes and with no metal to metal contact these high efficiency drives generate up to 72% less heat after 24 hours of continuous operation, Additionally they create up to 38% lower dB at 3000 rpm (less than a home refrigerator) than conventional gearboxes. Even though there’s no metal to metal contact there’s no slippage or lost motion between the input and output shafts.

The MAR17-1-2.1 Traction Drive is designed for speeds to 3,600 rpm with 10 to 20 in/lb of torque, and the MAR-23-1-2.1 Traction Drive is rated for 3,600 rpm with 20 to 30 in/lb of torque. Operating at temperatures that are lower than a motor’s, with low vibration, and no torque losses from 10 to 3,000 rpm, these traction drives permit a motor to operate at peak efficiency. Applications for these 1-Way traction drives which can operate in explosive environments (ie. zone 1 and 21) include: Pumps, blowers, fans, turbo and super chargers, conveyers, HVAC systems, medical applications, and other power transmission and motion applications.

These revolutionary drives are available with an optional overriding clutch. Incorporating standard NEMA mounting dimensions, these drives can be easily integrated into new and existing applications.

In 1993 John Pawloski and his brother Ray took over the family business, Jewelers Machinist Co. They realized they needed to switch from outdated conventional thread grinders to CNC thread grinders. As a result, Jewelers Machinist Co is a source of some of the most complex thread grinding in the industry. The concept for the RMI traction drive came from John in 2007. Working in that high precision industry aided John in the development of the RMI Traction Drive.

In the years that followed, the design of the individual components and formula of the engineered traction fluid were finalized, testing was completed, a patent granted, and production begun. The RMI Traction Drive is one of the most efficient ways to transmit power from one point to another. Using rolling motion, RMI is able to transfer power at various ratios with minimal energy loss. Tested against V-belt, direct drive, chain, and gearbox setups, RMI Traction Drives offer energy saving benefits through true efficiency rating percentages up to 98%. The high efficiency of the traction drive allows electric motors to run at their peak efficiency ranges.

There are many applications where it can be used from automotive to industrial to medical. The RMI traction drive can be used in the electric vehicle market and precision applications. Offering benefits such as low backlash and no back driving, it set a new standard for high efficiency.

For more information, call (860)846-0530, email info@RMIDrive.com, or visit RMIDrive.com.