Energy Saving and Automation

In an era where energy costs have become a focus of attention, many people have authored articles with reducing energy as their theme.  Saving money is always a good thing.   Perhaps we can gain a little clarity on where the real savings are.

Start with the big loads.  Plant air handling, building HVAC and lighting are generally a lot more significant in total Watts or equivalent horsepower.  1 Horsepower is equal to 746 Watts.  If you are located in the northern states, winter heating uses a lot more energy than summer air conditioning.  In the southern states, it’s the opposite.  There is one study that puts the northern thermal cycle at a much higher overall cost, so everybody needs to move their manufacturing to the south.

Check all the integral horsepower motors in the plant.  A recent DOE study shows that over time, many motors get replaced with whatever is readily available in the next larger frame size.  This is in reaction to plant failures where the exact replacement motor is not handy or on the shelf.  The result is that the plant power and power factor can be very poor because there is a lot of excess capacity that is not being used efficiently.

Industrial plants also suffer from peak demand billing practices.  The utility company agrees to provide power, but large users get billed extra when they have peaks above their average usage.  Again, look at the large loads, and see if some or all can be put on soft starters or inverters with longer starting profiles.  AC motors try to get to full running speed and spend several seconds at poor power factor and huge inrush currents during starting.  Most motors require at least 4 seconds to get to speed.  So, is there a savings opportunity if you can get by with a 6 to 10 second starting period?  Yes, there absolutely is.

The smaller loads like individual plant floor machines are a little harder to regulate.  Some production machines consist of dozens of individual motors and sub-systems.  In large conveyor installations, newer control system turns off whole zones of equipment if there is no traffic for that section.  Use the same strategy in production equipment.  If there is nothing coming into the machine, turn off as much stuff as possible.

Again, look for the largest loads.  In CNC machines, the spindle is usually the dominant load.  Turning off a 10kW spindle motor will save lots more money than turning off 400 Watt positioning axes.  However, don’t pass up an opportunity if one exists.  If there are a large number of individual axes of motion that have low duty cycles, it may be cost effective to put brakes on the load and turn the motors off when they are not in use.

Prudent planning can be turned into real cash savings.

What is Control – Part 2

While considering the nature of control we tend to focus on the two big issues; hardware and software.  This is very understandable since hardware selection has a lot to do with cost and functionality.  Software has more to do with how we program the hardware to execute the tasks that the control system is intended for.

There is a complex interaction between the two that is often not expressed.  The hardware has “firmware” that defines the exact capabilities of the hardware.  The software is a tool for users to create programs that the hardware executes.  These programs are the embodiment of the useful behavior that the process or machine is intended to accomplish.

So is machine control hardware or software?  It’s both.  The hardware is only capable of executing instructions that we built into it by it’s microprocessor and firmware.  Those instructions are merely a library of possible functions.  The user program calls those firmware functions in an organized manner to accomplish some beneficial result.

There are a couple of really significant issues that are often overlooked.  One is experience.  A lot of experience is required to make good product selections.  The application of control systems involves understanding the application requirements and matching those requirements to specific hardware.  Motion systems that do “high speed registration” for example, require very specific hardware to capture the input signal to define where the registration target is, and then to turn off so that input noise is filtered out.  This is a very specific feature, and if you don’t have it, you generally can’t create it.

Complex control requirements like coordinated motion are both hardware and software dependent.  The simplest example is to draw a circle with two linear axes.  In order to know how to deal with this application the control system must have a dedicated motion controller either as a stand-alone element or embedded within the control architecture.  Most high end PLC’s offer a 4-Axis dedicated controller card that do this.

After all the wrangling is done to get the application and hardware properly scoped out, after all the software development work is done, there is still an aspect of control that is missing from this discussion.  It is the external wiring of power, power protection, and safety systems.  These circuits are separate from the control system hardware and software, and yet embody elements of control that are sometimes necessitated by the hardware itself.

Variable frequency drives and some servomotor drives require time to charge their capacitors.  Most drives has interlocks that will prevent operation until the caps are charged.  PLC processors require a time delay to insure that the I/O devices are powered before the processor “wakes up”.  If not, the processor will immediately fault.  The wiring of emergency stop circuits are physically separate and frequently use reverse power logic, they are energized when “off”, to all detection of broken wires.

All of these behaviors are part of the control system but generally not considered in the early phases of system design.  Yet all are required in order to make safe, working systems.

What is Control?

‘Control’ is a term for the use of binary calculation methods to execute a process or task.  I suspect it is as ambiguous a term as ‘mechatronics’.  I suspect that we cannot even agree on what control is, without getting into some depth on the all the possible definitions of the subject.

This is rather ironic considering the billions of dollars that are spent on control systems across all fields. Is control fundamentally any different if it is inside a car, automating lighting and HVAC in a large building, on an automotive manufacturing plant floor, in a biological resesearch laboratory, or in a giant refinery where chemical products are made.  It’s all control.  And the more we try to define it, the more inclusive we make the definition, the more vague and ambiguous the term becomes.

Efforts continue to increase the power of the PLC (programmable logic controller) across many vendors. By increasing processor speed, memory and capability PLC’s are becoming the universal platform of control as a discrete controller, process controller and motion controller.

Simultaneously, motion control specialty companies continue to increase speed, processing power and I/O structures in an effort to expand the dedicated motion controller as a competitive platform to the PLC.  This is a necessary migration to address control applications where an external PLC could be eliminated.

Is there an ideal mix of motion axes and I/O that will help resolve which hardware solution is best?  Not really.  The fact is that the majority of the market is made up of motion control using stand-alone axes that are triggered by logical conditions in the system.  Coordinated axes require the sharing of pulse to pulse position feedback information.  Stand-alone axes do not share data at that low a level in time.  Most PLC controllers are well able to handle stand-alone axes, especially if an intelligent indexer is used.  This off-loads the motion to the servoamplifier and only I/O handshakes are used.

Part of the ambiguity here is that control is the result of hardware and software together.  ’Control’ seeks to generate complex behaviors using digital methods.  The digital methods, processors, depend on programming techniques in order to implement the desired behavior.  So when we talk about Control, we are talking about hardware and software simultaneously.

What matters most to users of automation technology is both logic control and motion control programming exist in a single environment.  It doesn’t matter if the programming environment is a PLC with motion blocks inside it, or a motion controller with logic blocks inside it.  What matters is that all aspects of a control system can be programmed using a single editor.  Controllers from the major electrical companies like Rockwell Automation and others have opted for the logic-centric programming environment with motion blocks in the ladder diagram.

This approach eliminates the complexity of multi-processor solutions, each with their own programming language, that were commonplace a few years ago.  Multiprocessors have their own unique programming environments and a significant amount of programming to create proper interaction between the various platforms.

Missing from this description is the hard wired control that is part of system start up, power management and safety.  More on this in the next installment.

Motion, Measurement and Control

Motion control is all about control.  But you cannot control what you cannot measure.  So there is an important measurement component to the control of moving systems.  The difficulty lies in knowing what to measure, how to measure and what to do about things you can’t measure.

The obvious thing to measure is motor speed.  That part is easy.  Servo motors have built in feedback devices. In the old days, the preferred feedback device was a small generator that produced a voltage proportional to the speed.  In the digital age feedback is by quadrature encoder that outputs a digital pulse that is primarily used for position control.  Most control systems are able to easily integrate the pulse train to derive the speed of the motor.

Unfortunately, most applications require relatively low speed.  Most motors are engineered for high speed.  This is in an effort to package more work related power in a smaller physical package.  Often, the motor is connected by pulleys or gear reducers to get the speed of the motor to more closely match the desired speed of the load.

Some of the important attributes of motion cannot be easily measured.  In addition to speed, torque is extremely important to controlling motion.  Torque can be measured directly from the drive electronics, but this is rarely used for control.

Torque and current are direct equivalents with a slight variation due to the temperature of the motor winding. As the temperature of the motor goes up, the resistance goes up and the current required goes up at the same time.  Since high performance motors have fairly high internal temperatures, this swing can be in excess of 100 degrees centigrade, and should be considered in the control scheme.

Most of the emphasis on current control is in terms of protecting the motor and drive electronics.  The first derivative of current over time  is the limiting parameter of the power electronic devices and is an important boundary condition in safe operation of the electronics.

More important information can be derived by considering the region of the motion profile and the current or torque requirements that are presented.  In order to accelerate a load, a lot of current is needed to overcome the mass of the load.  But once the load is moving the torque requirement drops off.  This creates an opportunity to profile the current requirement while using the conventional error detection scheme of the traditional control.

Other variable that are part of the mechanical system are things like momentum and center of mass.  In multi-axis mechanisms, there is usually a dependency of one axis upon another.  The idea that the mass of one axis is changing it’s center of mass and momentum with respect to the other axis is generally ignored.  This too is an opportunity to gain increased stability in the control and possibly improve throughput by having a better model of the application from which to create the ideal control.

Looks to me like there is a lot of room for improvement.  Let me know if you agree or disagree.

Inventing the Future

What happens when the cost of technology drops?  Not just the raw cost of something, but the means to produce it.

Semiconductor costs decrease over time as volume increases.  This has been the magic of the industry for decades.  The cellphone, flat screen monitor, tablet computer all represent incredibly low cost of technology as a result of massive volume production.  All of these technologies had incredibly high investment cost.  A typical wafer fab was in excess of 3 billion dollars last time I checked the price.

Lots of different chip technologies have followed the extraordinary shift in pricing as the specific technology matures.  Power semiconductors continue to increase their power handling capability at decreasing costs.  This has been a great advantage for the motor and control industry.  Processor technology that is motor specific has undergone similar cost performance improvement.  Digital signal processors used to be the primary choice for motor control.  DSP’s have been replaced by a number of other technology options, dedicated microcontrollers and FPGA’s being the most cost effective.

What is really startling is that not only has the cost of the chip technology fallen, but the development tools to create new applications has fallen as well.  If you can afford the price of a PC, development software like LabView, you can define a completely new application, program and download executable code in a target processor.  Voila!  Working application!

If your target market is 5oo units of some cool new product, and you can put the development system together for less that $5000., then a $10 amortization is all that is required in the first year to reimburse you for the investment in a development system.  Combine this with $1500 3D printer that can make solid parts and the possibilities are endless.  If you need metal parts, use the 3D printer to make prototypes that can be used for metal casting models.  Even the metal casting industry has learned to decrease it’s volume requirements to gain access to lower volume market requirements.

Economies of scale have been a powerful agent of change in the age of electronics.  But by themselves, economies of scale are not sufficient to create a major change in the dynamics of entering new markets and creating new industries.  The cost to design, program and implement a technology has to be considered as part of the overall economics of new technology.  The latest innovations in development of technology are dramatically addressing the cost of development.

Lower development costs mean lower cost per unit for whatever new product is being considered.  The new revolution in manufacturing will be ongoing developments that change the way new products are designed and brought to market.

Differentiating Motion Control Products

One of the major topics among motion control professionals is the number of applications that are stand-alone, single axis systems with little or no external interaction between other motion systems.  There is great debate about how much of the overall market is single axis and how much is multi-axis.  The industry has always engineered high performance multi-axis controls with 32 or 64 axes capability, with 20 mHz feedback rates to handle linear motors, and computing capability to coordinate as many axes as needed.

With single axis applications, the computing requirements are pretty low and performance requirements are generally simple.  If the application uses a PLC as the main control system, its easy to make the motion control a sub-system that is only connected to the main control by inputs and outputs.  There are lots of “indexing controls” that will provide good motion performance with a variety of motor technologies.

Many folks I know estimate that the motion market is 80-90% “low performance” single axis systems. So why all the focus on the complex, high end control platforms.   In motion control, as with many technology driven markets, the reputation of the brand is built on high performance solutions.

However, this poses a significant problem.  How does the industry create products that satisfy the requirements and still create significant differentiation to sell their solutions.  Motion control suppliers, being the clever types that they are, have proliferated all sorts of solutions over the last few years.  One solution from Animatics combines the motor, drive electronics, controller and communications capabililty all in one package.  This eliminates interconnect cabling between the drive electronics and the motor, which in many servo systems costs between 10 and 20% of the hardware cost.

There are a number of stepping motor companies that supply an integrated stepping motor and control.  Check out the wide variety of products offered by IMS, AMCI, Lin Engineering and others.  The integrated drive and motor are very space efficient and simple to interface with.

All of these products reflect great creativity and value.  But its still difficult to differentiate among the many products.

Sometimes, as you get into the details, there may be specific features that will determine the suitability of one product over another. But for me, it is symptomatic of an emerging problem that proliferates all over the motion control and automation industry.  There are many overlapping products on the market. For example, every major supplier of multi-axis controllers has a PC based control platform and flat screen interface.  So do the PLC companies.

The cost per axis for a motor and drive has fallen steadily.  Power mosfet costs, a significant cost component in most drives, have fallen by half in the last few years.  The next generation of embedded processors for high performance motor control are half the cost of DSPs. Yes, magnet prices have been rising, copper is up, lamination steel is up.  But overall, prices for motion control components are falling.

When there are a number of comparable control platforms available, there can only be differentiation based on some new technology that makes the product clearly superior to other offerings, or based on cost reduction.  With increasing competition within the industry and competitive product offerings from foreign sources, the most likely scenario for the coming few years is declining prices.

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.

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