Archive for January, 2008

Mechatronics Training

Steve Meyer
January 31st, 2008.

If mechatronics wasn’t difficult enough to define (concisely), try and get a degree in it!  Interestingly, with the increased attention that mechatronics is receiving around the globe there are established degree programs in Europe and Australia.  Some schools in the US are picking up on the trend.  The electric car races, Darpa Challenge and battling robot competitions, with some very hefty cash prizes, have stimulated interest from thousands of participants and spectators alike.

The latest innovation is the partnering of schools, automation equipment suppliers and funding from the Department of Labor.  DOL (Department of Labor) estimates that 10 million technical factory jobs could go unfilled by the year 2020 without an aggressive effort to train students and teachers.  The assessment of American labor’s capability to deal with emerging technology trends on the factory floor has lead DOL to contribute millions of dollars in cooperation with schools and equipment companies to make state-of-the-art training available on a large scale.

Festo Corporation is partnering with community colleges and universities around the US to provide sophisticated training simulation equipment in pneumatics and control, hydraulics, programmable controls, sensors and electric actuators.  These systems are designed to provide students with real-world experience in robotics and complex material handling applications that will impart the kinds of skills needed in the emerging technical markets.

These trends lead to increased American competitiveness in world markets.  Let’s hope it continues.

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Actuators

Steve Meyer
January 30th, 2008.

Another area of Mechatronics that is very confusing is the area of actuators. The problem is that you can buy actuators that are assemblies of several components, or you can buy the components, and they’re all called actuators. This is traditionally an ambiguous area of mechatronics and I will try to add a little definition to help clarify things a bit.

An actuator assembly is made up of 5 different technologies integrated into a package. These 5 are;

• motive power source
• means of transmission
• bearing or guidance
• frame or support structure
• position feedback (in most cases)

So an actuator assembly can have many components. Each one needs to be understood in terms of its contribution to the overall result. But with actuator assemblies, the integration engineering has been done by the supplier so that you don’t have to. Most of the time this is the most cost effective and convenient way to deal with the requirement of a specific application.

But many times the pre-engineered solution involves some compromises. That’s totally fair since the solution offered by a supplier must be suitable to a number of different requirements. If an off the shelf solution fits, or you can make it fit, then you’re “good to go”.

But if you are having trouble finding an “off-the-shelf” solution, navigating the technology solutions that exist can be a daunting task. Actuator technology is an excellent example of the intersection of many diverse technologies that is characteristic and challenging in mechatronics.

Motive Power can be electric motors, air and hydraulic motors or air and hydraulic cylinders.

The Means of Transmission in the motor cases will require a mechanical rotary to linear conversion, either belt and pulley, leadscrew and nut, or rack and pinion. Cylinder actuators do not require the conversion, but cannot take mechanical advantage as the rotary systems do, so as the force needed increases the size of the cylinder increases with it.

Bearings are a big topic on their own, but in the actuator linear bearings are usually ground rod with ball cages or square cross roller types.

The frame or support structure is whatever is needed to mount the parts together. Leadscrew systems are fairly simple as they pose no particular stress components, just passive weight loading. Belts and pulleys must be tensioned and the support system must be able to handle the tensioning load without deflection.

Feedback requirements are another broad topic because the feedback device must interface to a controller. Typically the focus of feedback is accuracy but sometimes too much accuracy can cause problems. The other major consideration is the operating environment. High temperature or harsh atmospheres will restrict what technology solutions are appropriate.

More to come on each of these topics.

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Common Terms are Not So Common

Steve Meyer
January 22nd, 2008.

I have worked around electric motors for a long time. It still blows my mind that we can’t seem to settle on common terms and definitions of things we work with on a daily basis. When is a motor AC Synchronous or DC Brushless? They are identical. Same motor.

So you have to start from the beginning of the motor family tree and work your way through it. What makes a motor AC versus DC. The only definition I know of that makes any sense is this;

An AC motor has only one magnetic field, in the stator, and induces a second magnetic field through induction, into the rotor. The rotor becomes magnetized and follows the circulating magnetic field in the stator by passive attraction. This is why most AC motors are referred to as induction motors, because the magnetic polarity in the rotor is induces. AC motors as a result are constant speed machine based on the frequency of the electrical excitation. Since that’s mostly 60 hertz in the USA, its usually some multiple of 60, most commonly 1800 RPM (minus some rotor slip). AC machines require an inverter to change AC into DC and then DC into variable frequency AC in order to achieve variable speed performance. Due to decreasing costs for the AC motor and recent cost breakthroughs in inverter technology, AC variable speed is the dominant solution.

The DC motor has two active magnetic fields, one of which may be permanent magnet and operates by repulsion and attraction at the polarity of one of the magnetic fields is reversed. Reversing polarity in DC machines is often done mechanically using brushes, but there are many branches of the DC motor family such as Stepping Motors which do not use brushes.

DC motors are intrinsically variable speed and have other characteristics that make them a viable choice in many situations. The cost of permanent magnets has made them more expensive in larger designs. So DC machines are in somewhat declining popularity.

So it becomes possible to create lots of special purpose motors to solve different problems. And as the industry has evolved, navigating the many technology choices has become very difficult.

We have standardized on a 3 phase brushless DC motor for servo systems. We could have any number of phases, but it seems that 3 is very popular, probably as a result of the many 3 phase AC winding machines available. So from an electrical power standpoint, the motor is 3 phase. And the magnetic field in the stator is circulating.

But the rotor is permanent magnet. There are some 3 phase AC motors with buried magnets to increase the flux of the rotor. They are called “salient pole” because of the enhanced magnetic strength of the rotor. And because the rotor follows the stator’s magnetic orientation without slipping, its called AC Synchronous.

So which is it going to be? AC Synchronous or DC Brushless. Call me “Old School”, but I think its DC Brushless every time. Anyone out there agree?

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Energy and Control

Steve Meyer
January 12th, 2008.

Looks like I was mistaken about one thing recently, and its probably not the only thing.  The new clothes washer we got to replace our failing machine does not use a switched reluctance drive.  Its an intelligent inverter drive with a standard AC motor.

As somewhat of a technology freak, this comes as quite a surprise.  I had been involved in a lot of advanced motor R&D during the late 1990’s.  Switched reluctance was touted as the next big thing in motor technology.  In truth, its a permanent magnet machine that uses high energy magnets (neodymium iron boron), which are expensive.  So in the effort to advance technology, we never escape the cost impact.

Where cost is not constrained, anything is possible.  Men on the moon, robots on Mars, telescopes in space that see the edge of the universe.  Superconducting electromagnets that contain the power the of sun, particle accelerators that approach the speed of light.  Almost anything you can think of.

But in normal everyday events, everything is cost constrained. So when customers and engineers ask if something is possible, there is always the follow on question, “How much is it going to cost?” We need to remember to answer that question explicitly, even if its not asked.

As it turns out in the washing machine, it is a lot cheaper to change the mechanical transmission into a simple belt and pulley system. By using a large reduction ratio to give the small ac motor the needed mechanical advantage and adding an intelligent inverter to the standard ac motor the new drive train is transmissionless and lower cost. This new system even includes extra sensors to detect proper motion from the tub (I think its an inductive proximity device tied to a counter on the controller that tells how fast the tub is moving). This machine cost a lot less than its predecessor, runs a lot quieter, and uses less energy over a year’s time.

Yes, the cost of the final solution is lower, and the overall machine performance is better. But the lesson that is most significant from this example is; the biggest improvements in energy reduction are not the result of trying to squeeze the last percentage point of efficiency from the motor. The biggest reduction in energy cost comes from a better mechatronic solution, leveraging the mechanical, electrical and control system together and getting the best overall result.

Coincidentally, this is also the best return on investment for the manufacturer and strengthens GE’s position as an appliance maker and employer.  But the same benefits are available to everyone in manufacturing.

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Motor Industry and the New Year

Steve Meyer
January 03rd, 2008.

Hope everyone had a great holiday and a successful year in 2007.

I was reviewing the Department of Commerce figures for electric motors. Hey, its just something I do.

A few years ago when I was hired to help a young high tech motor company in Denver understand the marketplace, we started with the Department of Commerce data for electric motors and generators. We studied the data and went into an interesting exercise in analyzing the market. At that time the US produced approximately $12B in electric motors. That includes all the industrial and high tech stuff, as well as starter motors on cars, alternators, generators and fractional horsepower fans you find around the house. Big numbers, lots of parts.

I recently had occasion to get the latest census data for the year ending 2006. The same market segments, but the US only made about $7B in electric motors. Not a good thing for America. Less jobs, less steel, copper, insulation, motor housings.

We still buy a lot of products that use electric motors, so we must be getting them from other countries. And if the electric motor is the #1 energy consuming device in the United States, we had better be looking at where and how well those motors are made. How efficient are they, how long will they last, who makes the profit on selling them here.

The business side of the problem gets to be two-fold; do the multi-national companies that were created by the American enterprise system have any responsibilities to the country they originated in? and are there any companies out there with technology and processes that will permit new motor companies to emerge? I say yes to both.

Let’s make 2008 a great year for the electric motor industry.

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