The electric light, for example, which was coveted 100 years ago as the great solution to night time darkness, making obsolete the candle or gas lamp.  Mass production has made the light bulb an inexpensive  commodity on the verge of extinction at about 25 cents per bulb.  The desire to reduce energy consumption is ushering in the age of the light emitting diode (LED) as the replacement technology for electric light.  Every effort is under way to reduce LED costs by any means possible so that illumination will be available that is even cheaper than incandescent lighting when the energy cost over ten years is factored into the new technology.

Even generating and delivering electricity is the result of applying the principles of mass production.  Large generating facilities are able to generate power cost effectively through economy of scale, selling the power profitably at 4.5 cents per kilowatt hour.  Wire, cable, switching systems and other infrastructure are generally costed in at an additional 2 cents per kilowatt hour to deliver the power to your door.  This is an incredible deal, trillion of dollars of resources at your disposal for pennies.

But mass production is not the answer for every aspect of modern society.  Lowering the cost of mass-produced goods implies that there is a requirement for the sufficient numbers of a product to warrant the investment in the necessary processes and tooling to accomplish the task.

Enter 3D printing technology.  Also known as “Maker bots”, this new class of tools is making fabrication a  new American pastime at incredibly low cost.  Where 3D printing equipment has recently been the domain of well-funded large corporations , selling at $10,000 to $20,000 each, 3D printer kits are available at less than $1000.  And lest you think that these are only toys for boys, the additive manufacturing paradigm has taken hold in the metals industry producing high quality parts in various steel alloys and even in titanium.

Why does it matter?  Because anything that lowers the barrier to market entry for new products creates the opportunity for people to enter a market that was previously inaccessible.  The hidden relationship is financial, it is the cost of amortizing the manufacturing resources across a given number of products that makes startup of a new product impractical.  So barriers to entry in new product development are primarily the result of amortization costs.

What happens when a new technology introduces a significant reduction in the amortization cost?  You get the opportunity to experiment with things because the cost of iterating the design is low.  New products can be test marketed and improvements made because there is no major investment in tooling that would have to be modified in order to change the design.  You don’t have to get it right the first time.

And that means that anything is possible.

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The traditional metal cutting machine tool has been around since the 1800′s and was entirely manually operated.  Since the machines were manually operated, the dexterity of the operator became a major factor in accuracy and repeatability of part manufacturing.  Because of the skill required, we still have the term “master machinist” in circulation, even though most machining today is automated.

During the Second World War, the Air Force was confronting the difficulty of manufacturing airplane parts.  Through the work of John Parsons and MIT, the first “punch card” controlled machine tool was built.  Parsons’ company was using early punch card computers to generate a larger number of points along the curve of a wing brace.  The numerical information was then used directly by machinists as a look up table for manually positioning a milling tool.  Parsons realized that if they could motorized the manual process, it could greatly increase the speed of the machining process, lowering costs dramatically and increasing accuracy at the same time.

Gordon Brown’s Servomechanisms group at MIT has recently been working on early forms of closed loop dc motor control for the gun turret on B-29 bombers.  By combining these recent technologies to numerical punch card calculation approach the first Computer Numerical Controlled Machine Tool was demonstrated.

The rest, as they say, is history.  The lessons learned in computer numerical control have been instrumental in every major field of manufacturing.  Cars, electronics, robotics, would not be feasible or cost effective without the underlying control technology of CNC.

Which brings me to a 2 major points as we contemplate the next generation of manufacturing.

Additive manufacturing is maturing rapidly with a wide range of materials, steels and titanium are now available, and precision is improving at the same time.   The surface finish requirements for a large number of parts cannot be achieved with a strictly additive process.  The new wave of additive manufacturing requires a complementary subtractive technology at complementary prices.

Secondly, while there are an increasing number of machine tools at low cost, they are not CNC.  This will likely be the next “breakout” technology.  There are a number of technical hurdles that have to be addressed in terms of reducing the cost to a level comparable with the Makerbot.  With the current generation of dedicated motion controller chips, lower cost step motors and low cost feedback technology, this should be a slam dunk.

Get your pencils out and get after it!  There’s some serious money to be made here.

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In the wind energy arena the biggest change has been the shift to direct drive permanent magnet generators.  By eliminating the gear “increaser” to convert the low RPM of the propeller system to a high RPM for a standard high power generator.  This is crucial step in bringing the cost of wind power down. Current systems are weighing in at 100 tons and have to be suspended above water or land 165 feet in order to pick up sufficient wind currents to be economically practical.

There is no single solution that is ideal for wind applications.  One supplier has a generator that is made up of 4 smaller units on a single large ring gear.  This system seems to have significant advantages in reducing the size and weight of the generator and makes maintenance more simple in the event of a failure.

Among the major mechatronic challenges driving change in the motor industry, electric vehicle applications are continually pushing the boundary for energy density and efficiency.  The performance demands of electric vehicles and other mobility applications make every percentage point of efficiency crucial to the range of the target vehicle.  This has led to a rash of new motor and drivetrain designs with a variety performance capabilities.

Each new innovation seeks to organize the basic materials of the electric motor in a new way to improve some aspect of performance.  Electric motors are copper conductors, “soft” magnetic steels and many times, permanent magnets.  The basic costs for copper wire at $5-6 a pound, commodity strip steel is about $.50 per pound but has to be punched in precise shapes, coated with insulation and stacked into larger assemblies, and $16. per pound for permanent magnets.  Complex processes associated with motor manufacturing make motor costs considerable.

In a recent development teams in academia in Australia and the US have developed simple low RPM motor structures based on polymer actuators referred to as “artificial muscle”.  While this development is in its early phases, the simplicity and low cost are significant and very appealing.  A demonstration of the new technology can be seen on YouTube at;  www.youtube.com/watch?v=ZcCPNJR5PCMand it is very much worth the watch.

The only sure thing is that we continue to meet the challenge of new market needs with innovation.

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American buyers will be able to buy American hybrid cars.  The Chevy Volt will be flanked by the Ford Fusion Electric scheduled to be released for sale in 19 US markets in March of 2012.  The Nissan Leaf might be the first production electric, so most commentators will make comparisons regarding driving range, speed and recharge time based on the performance of the Leaf.  At present, the claimed performance of the vehicles is very comparable.

It’s all speculation until there are a few units out there and the actual life cycle of the batteries can be measured.  100′s to 1000′s of vehicles will have to be built and consumer experiences cataloged in order to get a handle on how the batteries really work.  With all due respect to the development and testing efforts, it’s educated guesswork until there is real world experience.

Will the batteries be able to cycle enough times to make them cost effective?  When will they require replacement?  What will the price tag be for the battery pack?  Hopefully less than the $13,000 Tesla battery pack.

EV’s are coming.  But they are, like all the alternative energy technologies, still not cost competitive with Internal Combustion engines.  Most vehicles carry a $39,995 starting price tag with a $7,500 Federal rebate.  The basic purchase price puts EV’s out of the price range for many people, which fundamentally defeats the purpose.  The point of alternative energy technology is that it must become widespread in order for any impact on the environment to take place.  High prices are a major barrier to broad adoption.

Meanwhile the internal combustion engine is seeing some revival.  New approaches are being built and tested that offer dramatic improvements in efficiency and engine weight.  The EcoMotors opposing piston engine has been under DARPA development since 2007.  EcoMotors technology has been demonstrated to 40% efficiency, more than double that of traditional ICE.  In addition, it weighs less, takes up less space and gives of dramatically less heat.

Recently, the University of Michigan announced a new breakthrough called the wave engine that is expected to increase combustion efficiency to 60%.  And the rotor only turns in one direction like a scroll compressor instead of a piston, so there are no reciprocating motions to deal with.  This will also lower vehicle weight substantially, so the engine efficiency improvement leads to further overall efficiency in fuel required per transportation mile.

If these ICE improvements translate directly into miles-per gallon, then based on average 20 mpg cars today, we are talking about 53+ mile per gallon in town and possibly 70 mpg highway for EcoMotors solution.  At these levels, the equivalent energy cost per transportation mile is at parity with electricity.  If the wave engine proves successful, in town ratings of 80 mpg and 100 mpg highway become feasible, making electric options more expensive.

The future is what we make it.  Let’s make it the best we can with choices that make sense economically and environmentally.

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Many of the constraints of the work are environmental.  If work is being done outdoors, then temperature and humidity are a factor.  Felling trees and in the forest requires extremely high forces due to the work needed to cut through a tree and drag it to a truck to be hauled off for processing.  Processing trees, even in a plant environment, requires some serious hardware, 125 horsepower band saws are not unusual.

Doing work on a ship or oil rig has additional constraints because of the presence of explosive fumes and fuels.  Often the need to avoid any possibility of igniting a combustible atmosphere causes engineers to apply pneumatic control systems.  Yes, there is still a compressor somewhere to generate the compressed air supply, but that is usually remote or contained to avoid exposure to the volatile atmosphere.

Environmental constraints come in many forms.  Extremely high temperatures push the limits of what is possible.  Making glass, semiconductors, and primary metal processing are all high temperature environments where engineers have developed whole technologies in order to bring us the materials we use in everyday life.

The simplest action of rolling or sliding becomes a real challenge when environmental constraints are added to the work statement.  Sawdust becomes a potential abrasive in woodworking environments that can introduce severe wear in moving parts.  Corrosive and explosion proof atmospheres as well as food industry applications introduce all sorts of chemical compatibility problems that require special materials and processes in order to meet strict guidelines for safety.

As always, resourceful engineers have worked out solutions for all of these difficult applications.  One family of solutions to rolling applications is the use of all ceramic bearings.  No steel, no lubrication.  None is needed because the ceramics are extremely high purity to start with and have extremely high precision surfaces eliminating the need for lubrication.  No outgassing or contamination to worry about.

Other solutions take the form of air bearings and non-contact material handling devices.  Air bearings have become more readily available for conventional applications, but are particularly compelling in large machinery applications where precision is required.  Large flat screen display glass  presents unique challenges that successfully addressed using a combination of air bearing regions and vacuum regions to move the glass without actual contact and with overall flatness measured in millionths of an inch.

A unique solution in pneumatic material handling takes compressed air driven into a funnel shaped recess and creates a vacuum in the center and an air cushion at the edges where the air is exiting.  This creates a vacuum pickup that never quite comes in contact with the part, leaving no marks.  Perfect for solar cell and some food and beverage applications.

Engineers continue to meet the unique challenges of industry and create commerce at the same time.  And that’s what it should be about.

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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.

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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.

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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.

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The most important aspect of torque is the proper description of torque from the mechanical perspective.  Torque has three mechanical aspects, the torque needed to overcome the friction of the load, the torque needed to keep the inertia mass moving, and the torque of acceleration.

Each one of these has to be considered.  They also have to be considered in terms of their relationship to the total amount of torque required from the motor and drive combination.  Generally we consider the frictional torque to be a small fraction of the requirement and sometimes we can ignore it altogether.  But this is a mistake.  I have had some complex conveyor and material handling fixtures in which the friction was the most significant part of the load.  And it was ignored and caused all of the servo sizing to have to be increased significantly.  A very expensive mistake.

What makes the torque requirement so critical is that the torque needed to accelerate the  load is a complex calculation that has the change in the time in the denominator of the formula.  This means that as the time required for move decreases, the torque required increases arithmetically.  This is why acceleration is generally the main consideration in sizing servo systems.

The electrical component of torque is that torque is current.  So the amount of current that is required from the drive amplifier must be correctly sized or there won’t be enough torque available to power the load.  The calculation uses the torque constant of the motor which is expressed as ounce inches of torque per ampere of current.  But this calculation doesn’t consider the rate at which torque needs to be applied to the load in order to achieve the desired move times.

Coincidentally, the rate at which power can be added to the load is also the breakdown condition of the power transistors that are used for drive amplifiers.  In very high speed applications, this value also has to be considered in terms of the thermodynamic implications.   Using a bigger amplifier will allow you to push more current through the motor, i.e. more torque, but you have to have dwell time for the motor to dissipate the heat that is generated.  So there’s no free lunch here.

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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.

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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.

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As control technology has progressed over the last few decades, the performance requirements haven’t really changed much in a certain sense.  In the case of Computer Numerical Controls, the basic performance hasn’t really changed.  The big difference has been the cost.  The early CNC at $500,000 has been replaced by today’s production CNC at $50,000.

Certainly, there have been significant advances in capability, larger machine structures for aerospace applications, high precision applications and even the advent of the “maker bot” low end machines.  But the basic relationships required to shape parts in 3 dimensions are the same.

Yes, there are example of industries and applications that simply didn’t exist 50 years ago, like semiconductors, flat panel displays, etc.  Most of the improvements in electronic motor controls and motion control actually derive from the work done to improve the disk drive spindle motor.

But generally speaking, industrial control has migrated from specialized control hardware, to the PLC, a general purpose, high reliability form of controller, to personal computer based solutions.  Primarily due to the low cost and high performance computing power of the PC.

Some of the performance attributes have to do with how a given control is architected.  In the push for high reliability, the PLC goes to great lengths to insure that memory cannot be compromised, input-output hardware is extremely resistant to external electrical interference, and state changes are captured in a rigidly deterministic manner to insure that control code executes consistently.  In the PC there are PLC emulators that have been approved by various agencies that qualify their performance as equal to PLC’s.

Some attributes of performance are not obvious.  The operating system and its performance become part of the control system equation.  If the OS faults, the control system is down.  Hence the advent of Real Time Operating Systems, Linux and a host of other solutions aimed at reliability.

It can go deeper than that.  Exactly how the OS deals with interrupts can mean the difference between reliable operation and catastrophic failure.  Windows CE has different performance attributes over Windows for industrial control application.

In the PC architecture, how does data move from the disk drive to the operating program?  In the PLC how does the backplane impact the update rate of field I/O?

In the software realm, newer operating systems have made possible multi-threading programs that allow several task to execute simultaneously in the same hardware and software environment with complete coordination between tasks.  Robotic and CNC applications with multiple system operating in a single controller are able to execute separate programs with sophisticated anti-collision detection.

So exactly where the control system performance originates from is not exactly a function of a specific piece of hardware, but rather the result of hardware, OS and software combined to achieve a desired outcome.  Not a simple matter.

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There is a lot that can be done from the control system to improve overall performance.  Some of that improvement takes the form of sophisticated control algorithms.  Some improvement may take the form of increased power electronics to provide added acceleration and deceleration capability.  And sometimes projects get scoped to do things that are marginally impossible.  This is because there is gap between our understanding of the difference between mechanical and electrical properties of the application.

The gap in understanding is partly due to the educational system that teaches mechanics and electronics separately.  With the newer mechatronic programs that are available at many schools this gap is decreasing.

But there is a deeper issue.  The issue is context.  Mechatronics combines electronics and mechanics.  The missing context is that everything we do in the electrtronics, is an  analog for something mechanical.  If you don’t know how the mechanical relationships work, it’s unlikely that you will get the best results in controlling the system.

There are all sorts of examples.  A belt and pulley reducer is a mechanical system that turns a high speed input to a lower speed output.  The analogy in motion control is electronic gearing.  We can arbitrarily program any given motor to follow a speed reference from an encoder, tachometer or other motor, and follow the input signal at a programmed speed or ratio.

Electronic line shafting is a similar application that seeks to operate several independent motors and loads as if they were connected on the same mechanical shaft.  This application requires very high angular precision between the following loads which requires high speed regulation between the motor and associated electronics, but mathematically is very simple.

From the mechanical standpoint moving something from point a to point b seems pretty simple.  But as the time requirement for the motion decreases, the forces acting on the system become very significant.  As the load is accelerated from rest, it gains momentum.  Overshoot at end of the acceleration profile is a property of the momentum or kinetic energy of the system.  Tuning the system properly involves understanding the mechanical properties of the load and specifically how the control systems relates to the mechanics.

Does overshoot even matter?  Not so much if there isn’t a following axis involved.  At the end of travel it may be a concern if the load is positioning under a fixture or a next mechanical operation.  In many systems, there is settling time required for the load to come to a complete stop.  In these applications, the “S Curve” is an ideal solution because it compensates for the mechanical properties of optimizing the acceleration so that little or no overshoot takes place.

Maybe it’s less about the tuning and more about intelligent trajectory planning.

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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.

Mechatronic Tips

Getting it done on time and in budget are basic requirements of the challenge.  Over the years the only thing I have learned is that things always take more time and cost more than what was planned.    Good planning rarely eliminates mistakes or discovering an unforeseen problem late in the project that can jeopardize the whole effort.

The fix, if there is one, is building some slack in the project work plan.  So if it is at all possible, plan for 10 percent of the time and money to be set aside for contingency.  This will allow room for corrections to take place within the project plan and help prevent delays to the project deliverables.

Among many competing priorities in machine development, one that is rarely discussed is life expectancy.  Machine life expectancy is more subjective because component selections are not simple and straightforward.  Many decisions will be based on judgement and experience rather than on an explicit technical basis.

Something simple like a pulley may be perceived to be more durable if made of steel instead of aluminum.  But that component decision will increase the load mass.  The increased load will then require a larger motor and drive to power it.  And there are hundreds of similar choices that have to be made just like this.

Sprocket and chain mechanisms are generally indicated when high loads are being powered.  But in a situation where high life expectancy or reliability are involved, may be preferred over belts and pulleys.

Mechanical components of this type are subject to significant variations in cost versus life expectancy. The basic metallurgy of parts will impacted.  In one project, the balancing of load versus durability lead to the use of titanium.  The increased cost of the material was offset by reduced cost in the motor and drive solution.

Plating and coating of parts can be a significant opportunity for improved life.  Nickel plating has excellent performance in low friction, corrosion resistant coatings.  There are a number of hard Teflon coatings that can be used for reducing friction.

The life expectancy question is also connected to the maintenance cost of equipment.  For new machine designs, the maintenance issues are largely unknown and are part of the learning curve.  But the reliability of any piece of equipment is a huge issue.  And a lot harder to engineer in a systematic way.  But always worth the effort.

Mechatronic Tips