Units of Measure

My first semester of physics was a disaster.  I really didn’t get it.  The basic forces of motion made sense, but I always had difficulty solving the problems.  I was interpreting all sorts of other issues that weren’t really solving the problem in question.

A major lesson that I came away with was imparted during one of my attempts to repeat the course with a passing grade. (It took me 3 tries before I passed)  ”Always pay attention to the units of measure when you are trying to analyze a problem”.  In the problem solving arena, trying to figure out the relationships is sometimes a little easier when you just look at the units of measure.

In energy its really important to understand the units of measure.  Electrical power is measured as Watts.  Watts can be used as a measure of electric light, electric heat or any form of energy which can be directly derived from electricity.   As we seek to conserve power it is important to consider how efficient it is to convert electricity to another form of power.

The often ignored unit of measure is time.  It is especially important in energy measurements because the ratings of equipment can vary dramatically between starting conditions and running conditions.  Most motors and heaters have a significant inrush current when they are first switched on and then settle over time.   The ratings need to be examined more closely to get this information.

So a 100 Watt light bulb left on for 10 hours is one kilowatt hour.  The cost of a kilowatt hour varies around the US, but here in Texas its around 11 cents.  A computer with a high resolution video card can use 400 Watts.  In this case we are exploring the “dollars per kilowatt hour” for various appliances.  A large refrigerator can use 500 Watts, which is substantially better than older units with ratings over 1000 Watts.  And a central air conditioner rated at 5 tons can run as high as 17,585 watts or $2.00 an hour when running at full load.

When comparing electric motors, regardless of type, Wattage and duty cycle are consistent units of measure for the power that can be produced by the motors.  In this arena what is really being measured is the amount of work that can be performed within the thermal limitations of the motor and drive.  This is really important to keep in mind because at the end of the day it’s all about the amount of work required and the cost of the solution.  The units of measure might be $/kW or $/inch pound of torque.

When comparing motor and drive hardware from various suppliers, make sure the units of measure are the same (which they usually aren’t) and the thermodynamic basis for the ratings is similar.  The exact size of the cooling plate, what material its made of and how long the motor is run for thermal testing is all part of the rating system.

Some years ago I was confronted with a torque comparison between a 4″ servo from one vendor that claimed to put out the same torque as a 5″ servo from another vendor.  After considerable effort, an associate came up with the real answer.  The smaller servo was rated at a thermal limit 50 degrees higher than the larger one.  Although ratings are generally not so disparate in today’s market, there is still plenty of variation that has to be considered.  So make sure you know the units of measure.

Changing Landscape

Over the last few years there have been a number of changes in the cost of technology that are impacting the motion control marketplace.

The first is the cost of microcontroller technology that is dedicated to electric motor applications.  Up until recently, the Digital Signal Processor was the “de facto” standard for motor control.  Not because it was the the ideal solution for motor control, but because it was the only processor with sufficient bandwidth to handle the analog input and output requirements representing 3 phase motor voltages and currents and math calculations needed to regulate the motor as needed.

Doing motor control is one of the toughest applications for a variety of reasons.  The rate of change of motor data is 16 milleseconds at 60 hertz.  If the motor has 3 phases that are staggered at 120 degrees from each other, then three channels of 12 bit analog waveform data are being monitored as inputs in order to control a motor and the information must be handled with absolute precision at 5 millesecond timing.  That’s a lot of data before any control calculations are begun.

Recent generations of microcontrollers have emerged with the processing bandwidth, 50 megahertz processor speeds, 8 channel a/d and d/a, dedicated pulse width modulation channels for controlling power semiconductors, quadrature encoder inputs and even families with embedded network communications.  The communications capability does not impact processing speed of the code dedicated to the motor regulation algorithms.  This is because the communications are handled as interrupts and scheduled.  Which is also a weakness with a DSP.  DSP’s do not like to answer requests for information.

And the really good news is that some of the new processor technology is available at the $3 level at 10k pieces for controllers without communications.  Processors with communications are typically in the $5 to $6 level for comparable volumes.

At the same time power semiconductor prices are declining.  Power mosfets and IGBTs have dropped to half the price of five years ago.  The performance specifications have improved as well.  Typical peak currents are 200% of continuous rating.  So the overall performance is excellent compared to the power semiconductors in the past.

Thermal management is also getting good attention.  Some of the newer mosfets include thermal pads on both the top and bottom of the chip.  This can potentially double the thermal performance of the fets in a motor control application.

The other big cost factor in motors and controls is the number of connectors needed. Brushless servos require power, hall effect sensors and feedback devices.  This puts a huge cost burden on the system, sometimes as much as 10 to 20% of the total price. Which has lead to a significant number of motor, drive combinations which eliminate the cabling costs.  The tradeoff is the overall peak torque, but for many applications, this is fine.

More choices, better prices mean more options for the motion control enthusiast.

Re-Manufacturing the USA

For about 20 years that I can remember most candidates for the Presidency of the United States have disrespected manufacturing.  Most people who are running for the office of President don’t have manufacturing in their background.  So it shouldn’t be a surprise that after years of manufacturing being attacked from a political standpont that we have a huge decline in the manufacturing base of the American economy.  Yes, there are certainly other factors at work here, but our political perspective is one among many which need correction.

Since the Second World War, manufacturing employment has dropped steadily from 33% of all employment to about 10% of all employment.  What is really interesting about this trend is that the total output of manufactured goods has remained roughly constant.  What accounts for this is increasing productivity.  And in recent years a lot of that productivity has been from automation.

The same Department of Commerce research shows agricultural employment, typically a very high labor area, dropping from 33% to 2-1/2% from the turn of the century, 1900′s, to the present.  And similarly, agricultural output in the US has remained constant.  The main force behind the reduction in labor has been the mechanization of agriculture, or as I would like to refer to it, the “mechatronic-ization” of agriculture, if that doesn’t butcher the English language too severely.

Mechatronics is that elastic term that takes into account so many disparate technologies.  Putting a hydraulic system on a power take off from the gasoline engine on a tractor in order to power a variety of farm implements is mechatronics at its finest.  And the dawn of factory robotics in the 1980′s has lead to production welding robots that cost less than $50,000.  So people are being freed from some of the more repetitive tasks required at the factory level, and, I suppose, being replaced by automation.

The dilemma becomes, how do we create new jobs.  Many people believe that the “Green Revolution” will create a lot of new employment.  Personally, and after much review of industry studies, there are jobs there, but not enough to turn the economy around anytime soon.  And frankly, most of the green power generation technologies have failed to meet their economic burdens, so it’s a work in progress.

On the other hand, the same ingenuity that led to robots on the assembly line in Detroit has also provided us with 3D solid printers that produce very high quality parts in small batches at very low cost.  Another mechatronic triumph.  Three axes of stepping motors using belt drives and rod bearings to move a print head in 3D that dispenses a variety of hot melt plastic materials into solid shapes following a computer program for a 3D part.

This technology drastically reduces the major hurdle of new product development, which is the cost of prototyping.  Hmmm.  Sounds like an opportunity.  And it is.

So maybe the key to increasing employment is new solutions to old problems.  Reinventing the means of production in every industry should be a powerful stimulus to innovation, invention and economic growth.  Let’s hope so.

Motion Paradox

Mechatronics is a field made up of paradoxes.  It can be inclusive of so many different technologies that its hard to define what it is and what it isn’t.  Primarily mechanical in nature, as the name suggests, it is incredibly ironic that there are no actual sensors for some of the major physical properties of the motion control system.  How do you measure the physical dynamics of mechanical motion?

This is especially ironic since most mechanical components in the load can be characterized to 3 or 4 decimal places of accuracy.  More than enough information to define things very precisely.  Yet, little information actually flows into the control system model.

There are obviously plenty of ways to sense velocity or position.  The old school solution was a tachometer generator puts out a voltage that is proportional to velocity.  Although the voltage type feedback closely matches the velocity command signal sent to the motor, using a tach to get position requires some fancy integration of the voltage over time to get decent accuracy.

The most popular modern technology for position is the encoder.  It’s great because it’s digital, it’s simple, low cost and very reliable.  But the digital data flows as pulses and must be counted.  So in order to get a velocity measurement you have to add up the number of pulses and divide by the unit of time, which can result in latency since you are trying to measure something in real time.  Not so easy as it would seem at first glance. The update rates for encoders are now measured in nanoseconds in order to deal with this problem.

There is a sensor that helps in motion, the accelerometer.  The accelerometer is a silicon strain device that outputs a voltage that is proportional to the rate of displacement and actual force produced by a moving part.  This is an unprecedented opportunity to gain real control over the motion because there is typically no sensor that can give precise feedback about the moving parts.  But there is a difficulty in implementing accelerometers, you need wires, which makes it difficult since motion control involves stuff that is moving.

However, there are some excellent devices on the market.  two and three axis models, some with wireless interfaces.  But best of all, prices are falling.  All of the iPods and Ouii user interface devices use accelerometers.  This is fueling mass production of the devices and lowering costs.  So we should expect to see an increase in the use of accelerometers in motion control applications in the future.

This new opportunity for superior control system performance should be approached with a moment’s pause to consider the implications.  Most trajectory planning is done based on manipulating the velocity command to the servo motor.  But the forces involved are torques which create momentum in the moving parts.  And the forces are changing in relation to time, the rate of change of force is very important in controlling the loads.  A more complete control environment has to be created, and a lot of software innovation will be required to take fullest advantage of the implications.

The Language of Control

Language is what we use to describe reality. When we design machinery and write control programs, we use specialized languages to describe the desired behavior we are trying to achieve. And this is the beginning of problems. There is no single solution that describes everything in the control domain. And this condition is aggravated by the fact that each of the many unique disciplines of control has grown within its respective area of expert knowledge.

Ultimately, machine control is about translating the high level language of the programming into the correct manipulation of zero’s and one’s in the control system electronics. And this fact has numerous implications that are not obvious. The biggest issue being, the person that wrote the original executable code or firmware that the processor is executing, probably was not a domain expert in the application that was being programmed.

This should not be a surprise. Being expert in how a microprocessor language is structured, how to write code for that processor, and the infrastructure tools that go with it is a big enough task. Being expert in the application at the same time is not a likely combination. As a result, some of the nuances of things like motion control can get lost in the “translation”. Which means that there needs to be more teamwork between the people writing the code and the people who are actual experts in the application.

There are many descriptive languages that have developed over the years. Ladder logic is a result of describing the large relay cabinets of that were the primary means of control in the 1960′s. With the availability of inexpensive microprocessors, it became more cost effective and reliable to create an electronic representation that mimics the behavior of those systems.

So when we talk about control systems, we are talking about behavior. And every field of control, PLC, CNC, Process Control, you name it. It’s all about behavior. So there is a lot of effort required to make control systems that truly embody the behaviors required from a given discipline. The complexity of trying describe many different control disciplines is evidenced by the number of programming languages. Ladder diagram editors have had to expand their capability to incorporate function block diagrams that can deal with functions that are not native to the PLC, for example. And PLC’s have had to re-invent themselves to handle the ever increasing need for interface with data systems where massive amounts of data are required by other applications.

Most of the executing power is a by-product of the massive speed of the microprocessor. With 50 million instructions per second, you can get a lot of work done with efficient languages, even if everything has to be converted to zero’s and one’s. But the proliferation of cheap silicon also leads to lots of options about what device to use, what language and what support systems.

And at the end of the day, the real question is; “Is there any one language that can support all control applications?”

Read Part Two Here

3D for Better Control

If you can’t describe it you can’t control it.  And control is what its all about.  So we need to get better at describing what it is that our control system projects are going to do.

This has some serious implications.

First, if the programming language is not well suited to the task this will create a number of issues.  Ladder logic was never intended to deal with real time control. So blending Ladder logic with motion control, which can be the most demanding of real time control applications, doesn’t alway turn out well.  The precise coding of the control system processor now becomes an element of the control system behavior.  And often anomalies occur that are difficult to diagnose and which may be impossible to modify to achieve the desired results.

Maybe this is why embedded controls are gaining in popularity.  The computing power and connectivity of embedded controls has increased at least 10 fold in recent years making real time applications relatively straightforward.    But embedded controllers involve complex programming languages and require very exotic programming capability, often with expensive supporting “tool chains” are needed to develop and debug applications.  These costs make developing embedded applications suited to high volume products and not to one-of-a-kind machine control systems.

Control systems have become more interactive with data intensive applications like Excel Spreadsheet and higher level resource management applications.  So network connectivity and precise transaction capability with Windows applications becomes more appealing. It sounds more and more like a computer and not a control system.  And Windows isn’t really suited to the real time control or the hardware specific I/O that goes along with motion control applications.

PID as a control language for motion seems equally unsuited.  Its a great way to manage current and voltage relationships dynamically between motor and amplifier, but poorly equipped for managing the mechanical relationships between axes or mechanical properties like time and momentum.

In the mechanical realm of describing motion control, there is a similar problem.  Describing the mechanical task as a time-displacement trajectory seems an incredible understatement of the real work that needs to be done.  And there are no descriptive languages that do this well, at least, not yet.

But we are seeing the beginnings of a more comprehensive approach.  3D modeling software would seem to be the ideal environment from which a better description of the actual machine would be able to inform a control system program with valuable information about the performance of the actual mechanism.

Where could you get more perfect information about the changing nature of the reflected load of an actuator from a dependent axis as it creates changes in momentum of a primary axis.  As in a pick-and-place system.  The actual momentum as it changes over the entire motion profile can be extracted directly from the 3D model of the actuator and used as a filter to modify the commanded motion with incredible precision.  And this information can be used over and over, regardless of which location the actuator has to move to.

So we still don’t have the ideal solution.  But maybe that’s coming, soon.  The tools are there.

Electric Motors for Electric Cars

The field of electric motors is always subject to change.  Its always in a state of flux (pun intended).  We keep trying to make up rules about how motor families relate based on their technology, but right about the time you think you know what’s going on, something new changes the rules. And sometimes the rule changes come from seemingly unrelated areas.  The switched reluctance motor that was abandoned 20 years ago due to its high cost of control has re-emerged with the availability of low cost microcontrollers and power semiconductors to control it.

With all the interest in electric cars, the electric motor and the battery are the key components.  And the motor is certainly undergoing some major change.  And as a person with more than average interest in electric motors, the latest innovations continue to amaze.

Among the recent entrants are Apex Drive Labs new axial flux motor that is being used on the Porteon family of electric cars.  Porteon is not in production yet, but they are very close to release of their new family of cars.  Porteon is focused on the neighborhood electric vehicle, 45mph max speed in a small footprint.  The big news is that they are focusing on the manufacturing strategy integrating modular components and applying processes that will reduce cost without compromising safety.

The interesting innovation is the power dense electric motor Apex Drive Labs.  While Axial motors are not new, these guys came up with some interesting variations that radically alter the manufacture of the stator and seem to improve energy density at the same time.    Cranking out 20 HP in a 50 pound motor at low RPM is quite a feat, especially for a motor that is only 11″ in diameter and flat enough to fit inside a wheel.   Which is a great combination and just what is needed in an electric vehicle application.  This kind of power density will create some very exciting 2 wheel and 4 wheel drive options.  And the efficiency at greater than 90%, will enhance battery drive range, the key to successful EVs.

PML Flighlink has changed to Protean Electric and appears to be showing on the new Fiskar sport sedan that is intended to compete with the Tesla. Protean gained some press for a Cooper Mini that was retrofitted with their in wheel drive and really impressive acceleration.  Protean came up with a completely unique in wheel drive with integrated electronics that actually adjust to your driving style and manage all the wheels together to improve vehicle safety and stability.

Truly amazing engineering.  And there is surely more to come.

CUI Inc Expands V-Infinity Power Line

TUALATIN, OR – CUI Inc’s power line, V-Infinity, announced the addition of 10 and 15 W models to their VOF series of low cost open frame ac-dc power supplies. The VOF series has a low no-load power consumption of <0.5 W and efficiencies up to 83%. The combination of efficiency and competitive pricing makes this series ideally suited for use in ITE, industrial, and consumer electronics applications.

The VOF-10 and VOF-15 provide continuous output power, universal input (85-264 Vac), and are offered in 3.3, 5, 12, 15, 24, and 48 Vdc output voltages. The VOF-10 measures 2.6” x 1.8” x 0.9” and the VOF-15 measures 2.8” x 1.9” x 0.9”. Protections for over voltage and over current conditions are included.

CUI Inc
www.cui.com

Linear Actuators

Linear Actuators are a class of mechatronic systems with some unique design constraints.  As a result there are dozens of approaches, dozens of vendors, the option of designing the actuator from scratch, and, frankly, a lot of confusion.  The problem lies in the fact that the actuator as a subassembly is the combination of a number of separate technologies.  This means there are a number of design tradeoffs incorporated into the resulting actuator that must be acceptable in order to use that actuator.

Categorizing linear actuators is not entirely straightforward because many categories overlap.  The “motive power” category can be any type of power source, rotary motor or linear motor powered.  Linear motor solutions are much more commonplace in linear actuators today due to declining costs for this technology choice.  But in a linear motor based actuator, the linear motor is both the motive power and the mechanical transmission at the same time.

Categorizing linear actuators by their mechanical transmission style is another approach.  The most common categories are screw type, belt and linear motor.   But the motive power for a screw based actuator could be a stepping motor or a servo motor.  The stepping motor is predominant because of it’s suitability for positioning, but it may be underpowered for some applications where a servo is needed.   So the linear actuator transmission category can have overlaps because of the different motor types that are used in conjuncion with it.

Price seems to be one means of eliminating the ambiguity.  Stepping motor and lead screw combinations are popular because they are economical and maintaining 0.001″ accuracy is very easy.   Linear motor systems are capable of .5 micron accuracy with little or no friction, acceleration and speed that is incredible, but generally the higher performance comes at a higher price.

But in the end, the selection process is best guided by the criteria of the application.  The list is, thankfully, short.  Load weight or force that must be generated, speed, accuracy and life expectancy or number of cycles of operation.  This last is probably the key determinant in system selection.  Long life or high cycling goals lead to linear motors actuators with little or no friction. You have to familiarize yourself with the overall field because the tendency of confusing the technology and the application needs.

At the recent Semicon gathering of manufacturers involved in semiconductor manufacturing, a lot of attention is given to the mechatronic content of machinery.  And as far as I have been able to determine from many different market research projects, semiconductor manufacturing is one of, if not, the largest market for mechatronics every.   So it’s also not a surprise that a lot of vendors come to the Semicon show with their latest and greatest product offerings.

Among the most interesting, Nanomotion continues to extend the reach of piezoelectric linear motors, yet another technology choice within the linear actuator sphere.  Piezo motors have only one moving part, and meet the high precision, high reliability criteria.  With increasing usage, there has been decreasing cost for this unique solution, along with superior position feedback technology and excellent packaging for space constrained applications.

In addition, IKO has released a number of new linear actuator assemblies, both screw driven and linear motor driven.  They are also showing a number of unique 2-axis configurations one of which is the thickness of a tape reel and is targeted to unloading parts for electronic pick and place machinery.

Brilliant examples of manufacturers continuing to integrate mechatronic technology to make it more convenient for the customer.

The Next Industrial Revolution

The industrial revolution was a period of unprecedented expansion of technology that lead to a huge increase in economic opportunity.  It was a period marked with great inventiveness that transformed the Europe and America.  The power of that inventiveness echoes through today.

Similarly, in recent years, there have been a number of significant breakthroughs that offer great potential for the improvement of many current technologies.  But more subtle transformations are taking place throughout the industrial landscape that offer new opportunities yet to be explored.

In many areas of part production, there are solutions that offer reduced cost per part.  The emergence of new CNC’s that are available at the $10,000 level reduces the amortized cost for producing parts by as much as 500%.  Simply put, it you have to produce 1000 parts on a machine tool, the final cost of the part is significantly impacted by the cost of the machine tool.  A $50,000 machine tool will cost $50 per part across 1000 parts.  A $10,000 machine tool will only cost $10 per part.

This economic shift may make it possible to enter a market with an improved price point for an existing product, or create an opportunity to do something new that wasn’t possible because of cost and volume constraints.

In similar fashion the metals industry has consistently worked to developed processes and technology that allow part cost reductions, and more recently, smaller batch sizes for certain applications.  The smaller batch size has the same effect on cost, it lowers the investment cost for improving old designs or coming up with new ones.

The same trend is in place in the controls arena.  Processor technology that used to cost $20. a few years ago is available now for $2-3 and network versions that permit Internet interface are available for around $5.  This makes it practical to embed intelligence and communications in products even if the application is relatively simple.  The low cost is a compelling value in many products.  And in many arenas there are libraries of application code that already exists that may provide 60% or more of the development code for something you are working on.

Energy is still a bit of a limitation.  We don’t have a “Mr. Fusion” nuclear reactor that runs of kitchen scraps.  But things are looking up in this area with lithium based batteries making great strides in energy density.  And there is substantial improvement on the way.

But the real point here is;  Dust if off and Try it Again.  Take those “back of the napkin” sketches you’ve been tinkering with or thinking about and look at them again from the perspective that there dozens of technology improvements out there that will reduce the cost of the product you were thinking about a couple of years ago.  The change in the economics, as amortized cost, or the cost threshold to get your first batch of parts made, are factors that have a huge impact on the feasibility.

It just may be the time for a breakthrough.  A second industrial revolution.

« Previous Page — Next Page »