Mechatronic Stepper Motor Drives with CANopen

Hamburg, Germany – TRINAMIC announces new members of the PANdrive™ family. The latest members of the family are the types PD-140-42-SE and PD-116-60-SE. Both feature TRINAMIC’s integrated absolute sensOstep™ encoder which detects and corrects missed stepper-motor turns by examining the absolute posi-tion. This insures correct shaft motion even under heavy motor loads. Reliable high-speed motor operation is assured by TRINAMIC’s patented chopSync™ function which eliminates resonance problems.

The new mechatronic units from TRINAMIC have an integrated absolute sensOstep™ encoder. CANopen firmware lets the PANdrives™ be used in large networks.

Optional CANopen firmware makes it easy to use the PD-140 and PD-116 in large net-worked applications, even with components from various vendors. The advantages of such distributed designs include greater flexibility, reduced wiring expenditure and main-tenance-friendly service.

TRINAMIC also offers its TRINAMIC Motion Control Language (TMCL) which lets engi-neers develop programs easily. Complete programs can be downloaded and run inde-pendently on the PANdrive, or specific commands can be sent to the drive. A selection of different interfaces such as RS-232, RS-485, CAN and USB are supported and a com-plete PC-based Integrated Development Environment (IDE) is available for free.

The new PANdrive™ PD-140-42-SE from TRINAMIC has sensOstep™, which offers recognition and correction of step losses, and allows exact positioning and ’step loss correction’.

Both models have general purpose inputs and outputs as well as additional inputs for limit switches or reference switches. The supply voltage is typically 24V.

The PD-140-42-SE is based on a 42 mm NEMA17-flange stepper motor. There are sev-eral variants, with retaining torque from 0.22 Nm to 0.47 Nm. The larger PD-116-60-SE has a 60 mm NEMA24 flange and retaining torque options from 1.1 Nm to 3.1 Nm. An impact-resistant cover protects the electronics module.

An integrated encoder for position maintenance increases the system reliability at low cost. This is especially important in applications such as laboratory automation, biotech-nology, wafer-handling and chip testers.

www.trinamic.com

Electric Actuator EGC

Festo announces the addition of the Electric Actuator EGC to the family of electromechanical actuators. The EGC is designed for high dynamic speeds and high rigidity. This modular actuator can be used as an individual component adapted to third-party motors or as a complete system provided by one source – Festo.

The EGC offers a broad range of options including:
–Toothed belt or ball screw actuator
–Different screw pitches available
–Sizes 70, 80, 120, 185 (ball screw)
–Sizes 50, 70, 80, 120, 185 (toothed belt)

Performance Highlights
–High speeds and feed forces
–High loads and torques
–Maximum rigidity

In addition to these impressive features, the EGC offers an excellent price-performance ratio. Due to the high performance and rigidity of the EGC, a smaller size actuator can be used to save both space and costs.

www.festo.com/us/egc

Dynamics of Performance

All mechatronic systems, electric, pneumatic and hydraulic, can be evaluated according to thei rdynamics.  The aspect of dynamic performance that is most significant is the bandwidth, the inverse of time or 1/t.  Its not obvious, but once considered, can make the technology decision a lot easier.

1/t can also be expressed as Hertz, the number of cycles per second that a system behavior is changing.  The most familiar domain for Hertz is, of course, sound.  But most mechanical systems have resonant behaviors that can indicate a variety of conditons that are important in that system.

Beyond the mechanics of vibration, the most important issue for mechatronics purposes is the variation in the load.  If a load has a cyclical variation, that is a fundamental property that must be considered to make an appropriate technology selection.  The higher the system throughput, the smaller 1/t becomes tougher to deal with.  

To some extent the technology continuum can be considered as the slowest responding to the fastest responding.  Hydraulics tend to be slower, pneumatics faster and electrical actuators the fastest.  This would be an intuitive assertion just considering the dynamics of the medium, hydraulic fluid power is more viscous than air and takes more time to propagate.  Pneumatics are faster because air is a much lighter fluid.  Electronics are the fastest because electrons travel at almost the speed of light, although it is fascinating to consider how long it takes an AC motor to reach full speed. 

And for every assertion that we make about one technology or the other, there are workarounds.  Fluid power systems can use accumulators and servo valves (with electronic controls) to improve the responsiveness of the system, both in terms of time and in terms of precision.  

In the field of AC drives the responsiveness is the key determinant of what type of drive to use.  Take a simple conveyor application.  If the system has to move 50 pound bags of dog food to a palletizer, things are pretty easy.  Throughput might only be a few bags a minute, lets say 6 a minute.  So every ten seconds a bag gets dropped off changing the load condition on the conveyor by a small fraction.  No big challenge.

But if you are loading cases of beer on a pallet, 10 cases of six packs of glass bottles per pallet layer every six seconds, then there are 100 cases a minute flying through the system and the speeds at which a diverter must sweep to move each case into the correct lane are pretty challenging.  At 30 pounds per case, a 10 case pallet layer is 300 pounds.  8 pallet layers is 2400 pounds of beer bottles.  And when you have to lower the pallet to a precise height to make the next layer slide on smoothly there is a speed issue which is compounded by changing load.  Every 6 seconds the load increases by 300 pounds.  And when the pallet is empty the load change is disproportionately large, when the seond layer is added the change is 100%, and when the next layer is added its 50%, and so on.

So while there is a frequency consideration to the rate at which conditions are changing, there is also a load component.   Factor in the true dynamics of performance in your next project to insure success.

New Software Enhances Robot Simulation

There is now a more accurate way to simulate robots in action before they’re put to work, thanks to new software developed by Microsoft and DS SolidWorks. The new simulation capability helps companies program robots more quickly and effectively.

With Microsoft RDS, you can incorporate 3D CAD models designed in SolidWorks software and simulate robot operation more accurately.

Users of Microsoft Robotics Developer Studio 2008 (Microsoft RDS) will be able to directly incorporate 3D CAD models designed in SolidWorks software into Microsoft’s Visual Simulation Environment (Microsoft VSE) and accurately simulate their operation. Robotics developers can correct any robotic application issues early. The solution takes advantage of the fact that both applications support a common XML format, COLLADA, for rendering 3D objects and motion. A demo of the system is available now at SolidWorks Labs, and for download.

You can download the free SolidWorks/Microsoft RDS integration software, export a SolidWorks robot design into Microsoft VSE, develop the robotic application, then simulate the robots’ operation prior to deployment. The integration preserves dimensions, constraints, mass properties, motors, springs, colors, textures, and more from the SolidWorks model. Download from http://labs.solidworks.com/

“The worlds of machine design, mechatronics, and robotics are converging, and this first-of-its-kind partnership is just one way we’re supporting the convergence,” said Fielder Hiss, director of product management at DS SolidWorks.

Microsoft Corp.
www.microsoft.com

Time – Part 2

Time is the single variable that ties all of motion control and mechatronics together.  And if that is so, its impact on our design work cannot be underestimated.

The most basic feature of time is its relationship to work.  The work done in a mechatronic system is defined through displacement over time.  So a bunch of important variables get picked up.  The force exerted in mechanical terms can be a torque for a rotating load or thrust for a linear load.   The torque of a rotating load is the same as the current through the motor and drive.  And this makes sense of why these performance characteristics are related.

The power rate of electricity usage is the Kilowatt Hour.  The measure of work done over a period of time.

The horsepower is the mechanical unit of measure of work.  One horsepower is the work done to move a 550 pound load 1 foot in one second.  One horsepower is the equivalent of 746 Watts.  Now we have a direct correspondence between the mechanical and electrical definitions.

If electric motors are rated in horsepower, the implied property is the amount of work that can be done using that motor to power a load.  And an interesting anomoly occurs.  In most situations the motor is built based on an arbitraty size, like 10HP, and not based on the load requirement, unless the application has sufficiently high volume to merit a custom design.  A hard disk drive spindle motor is a case in which, because of the millions of units that will be sold, the motor design is unique.  So its construction is specifically designed for the load it is applied to, the hard disk platter turning in a vacuum.

So in general application, electric motors are poorly matched to their loads because of the economics that drive motor manufacturing.  The mis-match can be speed matching or power matching.  This impacts energy efficiency more than the inherent efficiency of the motors themselves.  Efficiency data is usually measured at rated power and can fall off dramatically for all load conditions less than maximum power.

The Power Rate of the system is directly related to the specification of the power semiconductors and mechanical contactors that are used to control motors.  So when we think of torque being equal to amperes, the current rate dI/dt is the power rate throught the electronics side of motor control.  In fact, the definition of the failure threshold in the power semiconductor, also called shoot through, is dI/dt.

Thinking about the relationship of torque and time, what happens when we consider acceleration?  Acceleration is measured in units per second squared.  Exponential.  So when we start pushing system performance for a given load, as the allowable time for the motion decreases (cycle time decreases or throughput increases) then the torque requirement goes up exponentially, and the current requirement goes up exponentially as well.  This requires a big increase in motor and drive size and cost, and in some cases reducing cycle times cannot be achieved.

Unless you change the inertia of the load.  Aluminum is one third the mass of steel, and engineering plastics are often half the inertia of aluminum.  So when you have the need for speed, don’t overlook material substitution as part of your strategy.

KUKA Robotics On Display at ProMat 2009

KUKA Robotics will display the KR 500 570-2 PA in a de-palletizing demonstration. The KR 500 570-2 PA , a heavy duty robot with a payload up to 570kg and three different palletizing algorithms for mixed and unmixed palletizing is known for it’s space saving and cost-effective support in a spectrum of palletizing applications. The KR 500 570-2 PA will be tooled with a state-of-the art KUKA designed Servo controlled layer gripper known for the ability to remove entire layers from a pallet of virtually any material in a single cycle.

The Servo layer gripper motors are synchronized with the KR 500 570-2 PA allowing for a more time saving, cost efficient solution for palletizing when mixing different product layers on the same pallet. The KR 500 570-2 PA user friendly interface can communicate directly to a warehouse management system software and is suitable for building rainbow or starter pallets in distribution centers or feeding a layer descrambler for a down stream case buffer. This same system can also be integrated to perform slip sheet handling and empty pallet handling.

www.kuka-robotics.com

DualVee® Washdown Wheels

Pittsburg, CA – - Bishop-Wisecarver Corporation announces its new patent pending washdown wheels, the latest addition to the company’s signature DualVee product line. Designed primarily to meet the extreme demands of food processing equipment linear motion applications, the washdown wheel significantly extends bearing life, and is interchangeable with standard vee wheels for ease of replacement.

Available in sizes 2 and 3, DualVee washdown wheels feature an all stainless steel construction, FDA approved grease, an outer shield, and inner seal for added protection from liquids and debris. The rubberized metallic shield acts as a momentary seal when subjected to a stream of high velocity washdown fluid. The fluid velocity causes the rubberized shield to deflect and conform to the metallic surface of the wheel, sealing against ingress of liquids. The inner seal provides the principal line of defense, ensuring that external fluids are kept out of the wheel while retaining the internal lubrication grease; both important factors affecting the life of the wheel. Once the stream is directed away from the wheel, the deflected shield returns to its original position, allowing any residual fluid that entered the zone between the shield and seal to drain out or be spun out by centrifugal force.

For more information on DualVee washdown wheels visit www.bwc.com/products/dual-vee.html.

www.bwc.com

Time and Motion

What is the one variable in the universe of motion control system variables that ties everything together?

Some time ago a friend of mine, Phd Mathematician, wrote a software program that optimized all the variables required to construct an electric motor.  The obvious ones are simple physical variables like diameter and length of the motor housing.  The issue of motor size can be arbitrary for most applications, but every now and then you get caught in a size constrained application like the well water pump that needs to have a 2″ outside diameter in order to fit inside a 3″ pipe.

Shaft diameter and length, or course, would have to be considered based on the amount of torque that must be transferred.  And even though these are simple physical constraints, you caught in a more complex relationship because there is static torque and dynamic torque.  In the dynamic consideration there are starting and stopping characteristics, each of which is often unique.

The time displacement curve is the cornerstone of all motion control.  You can get pretty fancy with the analysis.  You can refer to the first and second derivatives of the motion, acceleration and jerk, and define a lot of boundary performance issues that a target motor and amplifier must be able to provide or the application will not work.

An interesting side note on the time-displacement curve is that you can consider work done as the area under the curve.  So integral calculus had some value in the situation.

And we haven’t really addressed the magnetic circuit yet.  There are generally 2 magnetic elements in any motor.  Usually one is an electromagnet and the other is a permanent magnet.  So we need to consider all the associated variables of design in an electromagnet are copper windings on ferromagnetic metal cores.  Wire diameter, number of turns, length of turn, length of end turn ( the un-used portion of the copper from a magnetic standpoint), the voltage, current and excitation frequency of the applied current assuming its coming from a PWM based solution.

And we’re just getting started.  The magnetic performance of the core material at varying frequencies and temperatures.  You get the picture.  That nice, neat, simple little starter motor that’s attached to your car engine with two wires from the battery turns out to be pretty complex.

My friend the mathematician said that his program has 23 variables of design that were needed to define the electric motor.   Pretty scary if you have to do tradeoff analysis to find the “perfect” design for a specific requirement.  But it is way too much work to actually do all this analysis unless you are going to produce a whole lot of one design.

So is there any Unified Field Theory that brings all this stuff together?  TIME!  The one thing that unifies all motor considerations is time.  And by looking at the system from this perspective it is sometimes possible to simplify things a bit, in an otherwise very complex system.  We’ll look at this in further detail in the next installment.

FIRST Launches Eighteenth Robotics Competition

Manchester, NH – FIRST (For Inspiration and Recognition of Science and Technology) launched its eighteenth FIRST Robotics Competition season today with a Kickoff of a new robotics game called “Lunacy” at Southern New Hampshire University in Manchester, NH, hometown and headquarters of FIRST.

“Forty years ago, NASA fueled a generation’s imagination with the success of Apollo 11. As we celebrate that remarkable feat of technology and engineering with our 2009 game, “Lunacy,” we are sparking more of that kind of inspiration through the FIRST Robotics Competition,” said FIRST founder, Dean Kamen. “Just as NASA scientists landed a man on the moon and returned him safely to earth in 1969, so too will these young people go on to explore new frontiers and develop breakthrough technologies that will change the world.”

The FIRST Robotics Competition is an annual competition that helps students discover the rewards and excitement of science, engineering, and technology. More than 42,000 high-school students on 1,686 teams from the U.S., Brazil, Canada, Chile, Germany, Israel, Mexico, the Netherlands, the Philippines, Turkey, and the U.K. are participating in this year’s competition.

“In today’s social environment, FIRST has a chance to re-define the larger economic and moral playing field,” noted Dr. Woodie Flowers, FIRST national advisor and Pappalardo professor Emeritus of Mechanical Engineering, Massachusetts Institute of Technology. “Our students can be their own economic stimulus packages by leveraging their skills into self-sustaining careers and help with the issues we face in the 21st century.”

In the “Lunacy” game, robots are designed to pick up 9″ game balls and score them in trailers hitched to their opponents’ robots for points during a 2 minute and 15 second match.  Additional points are awarded for scoring a special game ball, the Super Cell, in the opponents’ trailers during the last 20 seconds of the match. “Lunacy” is played on a low-friction floor, which means teams must contend with the laws of physics.

At today’s Kickoff, teams were shown the game field and received a Kit of Parts made up of motors, batteries, a control system, and a mix of automation components ­ but no instructions. Working with mentors, students have six weeks to design, build, program, and test their robots to meet the season’s engineering challenge. Once these young inventors create a robot, their teams participate in competitions that measure the effectiveness of each robot, the power of
collaboration, and the determination of students.

Sponsored by NASA, PTC, Booz Allen Hamilton, and Worcester Polytechnic Institute, the exciting Kickoff event gave teams the opportunity to see the new game for the first time. Teams across the nation and in Canada, and Israel watched the proceedings via NASA TV broadcast or webcast from 52 local Kickoff sites, many of which also offered workshops and a chance to meet other teams. The agenda included presentations by FIRST founder Dean Kamen; PTC executive vice president and chief product officer James E. Hepplemann; NASA program executive Dave Lavery;
FIRST chairman John Abele; FIRST national advisor Dr. Woodie Flowers; and FIRST president Paul R. Gudonis. The program also featured the premiere of the 2009 FIRST Safety Video, presented by the Fabricators and Manufacturers Association and Underwriters Laboratories.

In 1992, the FIRST Robotics Competition began with 28 teams and a single 14 x 14 foot playing field in a New Hampshire high school gym. This season, 1,686 teams ­ including 322 rookie teams ­ will participate. Forty regional competitions in the U.S., Canada, and Israel, plus seven district competitions and one state championship in Michigan, will lead up to the 2009 FIRST Championship at the Georgia Dome in Atlanta, April 16-18. FIRST programs are operated by over 85,000 dedicated volunteers worldwide, many of them professional engineers and scientists who mentor the next generation of innovators.

usfirst.org

Navigating the Technology

There’s a lot of cool technology available these days.  And one of the problems of having a lot of options is “Navigating the Technology”.  What’s the best solution for a particular mechatronic application?  I think a good understanding of the application and associated constraints goes a long way to making good decisions.

Is the application a “prime mover”, running at a set speed for many hours or a positioning application?  Prime movers run at constant speed for long periods like fans and pumps.  These are best served by AC motors and across the line starters.  When variable frequency drives are used, its usually to eliminate mechanical damping of the load and “tune” the electrical requirement to the mechanical requirement.  This technology option can provide huge cost savings when properly applied.

Positioning applications are completely different.  Most often, they are intermittent in operation and have varying loads.  The goals are completely different and the solutions are different.  But what can make positioning applications difficult is the myriad options for how to do it.

Linear motors are a great option with incredible speed, acceleration and precision.  They are particularly popular in semiconductor manufacturing due to millionth-of-an-inch precision and design for clean room operation.  But if you don’t have those requirements its overkill in performance and probably over cost for what’s needed.

There’s the venerable lead screw and stepping motor combination.  Very cost effective and capable of impressive precision.  Tow ten thousandths (0.0002 inches) accuracy is achievable at low cost.

But positioning applications need not be exclusively electronic.  Pneumatics make great choices where speed and extended life cycles are required.  One of the great attributes of modern pneumatic systems is the integration of the actuator and structural framing that is often a separate requirement in other systems.  And with a wide range actuator options and styles available, the possibilities are endless.

Are there some guidelines that can help make the process more objective?  In the positioning applications, one obvious differentiator is accuracy.  And as a practical matter, it seems that there might be three logical categories; coarse (greater than 15 thousandths) medium (from 15 thousanthds to one ten-thousandth) and fine accuracy from 50 millionths to sub-micron).  By considering a positioning requirement in terms of the accuracy requirement, a lot of technology choices become more clear.

Another attribute of the application is dynamics.  The dynamic requirement considers how quickly the load is varying.  This aspect directly impacts power electronics and control system performance.  The relationship of current over time defines what power transistors will have to handle and correlates directly with variations in the load.  After all, torque and current are the same in electrically based systems.  Dynamic response in ac and dc drives is referred to as the inverse of time so typical performance is expressed in Hertz.  A slow system response might be in the 2 Hertz range, meaning that the system must handle a known load variation and be able to stabilize itself in a half second.  A closed loop ac drive may be capable of 100 Hertz performance.  A high performance servo may have a speed regulation loops of 2 thousand hertz.

Armed with accuracy and dynamic response, we can sort out a lot of options on the way to better mechatronic solutions.