A lot of it is precisely ‘doing more with less’.  How do we make the same quality of parts at prices low enough to compete with foreign competition?  It’s not easy when the typical pay scale for manufacturing labor is $8 a day in some parts of the world.

There are a couple of obvious components to price competition that don’t get a lot of attention.  Scrap rates and delivered cost.  When a US company buys parts from offshore, any defective parts are very costly.  The direct shipping cost, duties and processing fees are additional and can be 10-15%.

During my years at Rockwell Automation, we investigated the cost of selling US products in different parts of the world.  Depending on where in the world we are talking about, the shipping and logistics can accumulate between 25 and 40% additional cost to the product being sold.

So the cost of scraps and logistics are the minimum cost hurdles for companies seeking to export their products to the US.  Low cost producers have to make parts cheaply enough that the landed cost and scrap rates cost out less than the price of producing them in the US.

Doing more manufacturing in the US requires finding creative ways to lower costs.  That is the second area that is undergoing change.  American manufacturing technology is finding ways to reduce machinery and process costs.  And this area of effort may provide key strategies that will help the US gain back ground in the pursuit of more world class manufacturing.

Innovation processes like additive manufacturing allow fabrication of metal parts with no machining.  For higher levels of precision there are new machine tools that can do final machining to less than 0.001″ accuracy and the costs of machine tools are lower than ever.  These are the keys to producing high quality parts at lower costs.

There are unique mechatronic solutions that can improve machinery performance across a wide range of applications.  The Acme screw which is very inexpensive, has limited accuracy but plenty of torque handling capability.  What happens if you can add a very inexpensive linear feedback technology to the simple low cost Acme screw?  You get a really high resolution linear motion system that is very inexpensive.

The great news is that these products are currently available.  And that means that making better machines that make better parts at lower cost is practical, achievable and there are no technical challenges.  Common off the shelf parts will get it done.

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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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Alternative energy in the US has failed to produce the return on investment or to create new jobs in any significant numbers.  Car sales have picked up significantly over 2011, but not nearly at the rate of 16 million cars/year as in the heyday of that industry.  The real estate bubble has burst after a decade of speculation and bad lending practices that continue to depress new construction.

The second industrial revolution, Henry Ford’s industrial revolution, was about mass production and cost reduction.  For almost 100 years we have been perfecting the centralized manufacture of almost everything around us.  Economies of scale that enable volume manufacturing of consumer electronics at lower cost year after year are the result of the Ford approach to manufacturing.

So where do we go from here?  We start re-inventing the industrial revolution.

The new wave of manufacturing has begun with the advent of the Maker Bot and a family of low-cost fabrication tools that can manufacture based on 3D printing techniques.  While solid model prototyping has been around for some time, the magic ingredient is a new family of machines that cost less than $2000. and some recent new entries around the $1000 mark.  At these price points, it doesn’t take a lot of volume to justify the purchase of one of these machines.

There are advanced processes that are becoming available to generate sintered metal parts, even titanium parts, using processes resembling the additive manufacturing process.

Amortization cost is the secret.  Lowering amortization costs and minimum order quantity at the same time results in a fantastic breakthrough in productivity.  It also lowers the barrier to entry into new markets.  So if you have an idea for something that’s never been done before, the cost for development may be a lot lower than you think.  And thousands of people have begun to jump into the mainstream economy because of the availability of these new tools.

While the “maker” tools are limited to plastics, there is progress in the metals arena as well.  The computer numerically controlled (CNC) machine tools have traditionally been the domain of 6 figure costs, HAAS has been making $50,000 machines and last year Tormach entered the market with the “Personal CNC”, a high quality machine that is priced at $10,000.

My prediction?  There is going to be a lot of activity at the $10,000 and below price point to come up with low cost machine tools as a complement to the “maker” bot 3D printer technology.  Additive manufacturing will require a complementary subtractive manufacturing infrastructure at a comparable price point.

And creative American engineers and tinkerers will be leading the way.

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This was the case when a friend of mine was designing a material handling system for newspaper bundles.  A very exotic conveyor system with 8 servo driven belts and a design that involved 10 pages of hand calculations of inertia.  We shipped the servos and sent out a field engineer to start up the project only to find out that the motors and drives were too small.  The designer had forgotten to account for friction.  In this case the frictional load was 3 times the mechanical load due to the unique belt and roller configuration.

So the first lesson is; don’t forget to look at friction as 1 of 3 components of the torque load.  The three being; steady state torque, torque of acceleration and friction.

Then there is the fanciful wishing that there wasn’t any friction to worry about.  Kind of like doing experiments in the space station and having no gravity.  It’s fun to think about, but there are few real world situations where this is likely to work.  The only exception is air bearings.  Of which there are a few.

If you have ever played air hockey, air bearings are like that.  Parts in motion tend to stay in motion when there is no friction to worry about.  And that would be good in a lot of applications.  No friction will generally result in smaller servos, so there are savings in the hardware requirement.  No friction means no mechanical wear, nothing to service as the machine runs up cycles.  No friction also means high speed motion is a lot easier to achieve.

Cars coast to a stop because of friction.  That’s a good thing.  Without friction, parts would end up flying off the conveyor instead of going where you want them to go.  In conveyor belt applications there is usually a lot of friction and that helps the system slow down and stop.

So the second lesson is; friction can be your friend.

In between systems with friction and systems with no friction, there are rolling bearings.  Systems like the Bishop Wisecarver “Vee Guide” are among many products on the market are examples of this.  Rolling element bearings have very low coefficients of friction, so losses are low and therefore the energy needed to overcome them is very low.  This also results in very low wear, so maintenance on this type of mechanism is also low.

The are dozens of linear actuators on the market and each vendor has developed unique bearing solutions, whether sliding or rolling, that perform well at varying price points.  There are no universal rules for selection.  The typical criteria are move speed, positioning accuracy, life expectancy and cost.

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A few weeks ago, I had the opportunity to write a couple of small “C” programs in a training class and re-discovered why I don’t like to write control software.  I don’t have much background in C programming.  It’s not that C programming is inherently good or bad, it’s just another language.  What is difficult to deal with is each controller having it’s own library of C language instructions.

It’s not that any particular language difficult, it’s that every language is iterated on different controllers and the instruction set and programming quirks have to be learned on each platform.  Ladder Logic instructions have become largely standardized and the difference from one platform to another are becoming less and less significant.  Turning discrete inputs and outputs on and off is pretty straightforward.  Reading analog signals, doing some mathematical operations and setting analog outputs is also fairly straightforward.   Even when there a lot of I/O to deal with, the knowledge base required to understand the applications of the technology are ultimately very repeatable.

The variations of how to do motion control on different platforms are very significant.  Each controller company has to come up with a complete programming environment that defines how to command the controller to execute motion tasks.  The creation of commands and processor executables requires coding and testing the code over man years of development.  This is a complex form of knowledge capture and there are a lot of nuances as programmers come up the learning curve before good effective programming environments can be created.

This is part of the reason why the motion control field hasn’t progressed as much as other control disciplines.  There is no agreement on any standard programming methods past trapezoidal move profiles.  The situation becomes more complex because each motion control vendor develops its own programming environment based on the selection of processor platforms and what its programmers come up with for the programming suite.  This creates a barrier to entry for new companies, and makes improved code solutions problematic.

Many of the PLC programming suites include dialog boxes that provide scripting for the motion commands in the ladder logic program.  The technology is readily available to make a high level motion programming suite that is processor independent and capable of addressing 80-90% of all motion control applications.  This will make motion more accessible to a wider audience and simplify the programming aspects of motion and machine control.

We need to bring the industry into the 21st century and make everyone’s lives a little easier.

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Considering the possibilities of improved personal transportation, the consequences of a major change in transportation technology are significant and should be carefully considered as we move forward.

The major impact of all the technology being promoted these days is increased efficiency and reduced fuel consumption.  Whether your motivation is reducing emissions and cleaning the air, or you are interested in reducing your cost of transportation, the requirement is the same; get more miles out of a gallon of gasoline or eliminate gasoline usage altogether, as is the case for a pure electric vehicle.

Across the entire population of cars in the US, the average fuel efficiency is around 20 miles per gallon. Despite the demand for higher fuel mileage from consumers, this situation hasn’t improved much in the last few decades.  A dismal thought in contrast to the claims being made these days for the new solutions.

The US consumes 383.25 million gallons of gasoline and diesel fuel per day.  This all goes into transportation.  The only fuel going into electrical generation is in diesel gen-sets for backup and remote power, just in case anyone is thinking about the barrel- of-oil-to-electricity energy equivalency.

Imagining a future in which gasoline usage declines is not difficult.  I drive a Ford Fusion for work which is averaging 30 mpg combined city and highway.    If the US fleet average is 20 mpg, increasing that average to 30 mpg implies decreasing the amount of gasoline sold by 1/3.  Currently, gasoline retails for $3.25/gallon, or $453 Billion annually at the pump.

So a sharp change in usage due to efficiency or an increase in the number of electric vehicles, is cause for concern from oil & gas exploration companies, gasoline refiners, distributors and dealers.  Unless gasoline prices continue to go up.  In which case there would be less gasoline solid at roughly the same total revenue, which suggests that higher profits might be the side effect if the true cost doesn’t go up.

What about tax revenues?  The direct state and federal tax on gasoline is about 40 cents per gallon.  This does not include large excise taxes collected by the states, taxes paid by refiners and distributors, etc.  In fact, it would be hard to calculate how much of gasoline pricing is taxes and how much is the cost of the product.  Regardless, at 40 cents/gallon, the daily revenues are $153 million and the annual is above $55.8 billion.

Given the current economic picture, is there any level of government that is willing to give up the tax revenue from gasoline?  Probably not.  Is this any different than “Dollars for Oil” at the UN a couple of years ago?  Probably not.  But we thought that was a scandal.

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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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Control systems can be described as “open loop” or “closed loop” depending on the whether or not the system being controlled is well characterized.  Many forms of motor control seek to be “open loop”, that is, without the use of a feedback device.   However, this notion should be modified to open loop meaning without an explicit feedback device. This is because great effort is expended to “infer” what is going on in the motor through various means. The most common of which is current.

In the world of electric motors, the alternating current motor of Nicola Tesla is well understood, and rarely requires a feedback device.  Motor speed is derived from the frequency of the power being supplied minus losses depending on the details of rotor construction and how a specific load affects the motor.  The standard ac motor has a small amount of rotor “slip” from 1800 rpm to 1750 rpm which reflects the magnetizing current losses in the motor and magnetic features in the rotor that would be needed to maintain perfect synchronism with the line frequency.

Load variations can be measured by sensing the current in the line going to the motor.  So there is a feedback element available from which a great deal of information can be derived.  This is where the ambiguity about feedback comes in.  The current needed to run the motor with no load is fixed value, so more current read on the motor leads is load, until the motor reaches locked rotor current or stall.

In brushless dc systems a similar approach is used.  Detecting the zero crossing point of the phase current establishes precise timing of the rotor speed and is used to regulate timing of current pulses to all three phases of the motor.  In this way even the brushless dc motor can be operated without an explicit feedback sensor.    However the tradeoff here is very poor low speed regulation of the motor which makes this approach unsuitable for many applications.

From a control system standpoint, feedbacks are the last, slowest loop in the control scheme of the motor.  This makes sense in the context of position control as it is normally executed in a PLC or motion controller.  However, this makes load regulation more of a challenge since the actual error detection of the control system is being done a level removed from the actual load.

A host of mathematical tools from the signal processing domain have traditionally been employed to characterize the lag created by the control system and the interaction of the controls at varying speeds. All of which works well, but has also lead to “rules of thumb” that are not very clearly understood and which are sometimes misleading.

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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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Considering the rules for servo tuning first, the ideas are basically simple.  Based on the use of 0-10V velocity command, the control system is designed to regulate motor speed.  A Proportional, Integral and Derivative gain value is used to “tune” the command signal sensitivity to allow the control system to regulate the motor and load performance.  This strategy has been created over the years and is used by almost all servomotor and drive suppliers in the motion control industry.

The Proportional term is the most important value in this approach.  The proportional value is generally the amount the 0-10V command signal will be increased in response to a following error.  The more gain, the more velocity will be commanded.  This will allow the control system to correct for changes in load conditions.  The proportional gain is how the system responds to current conditions.

The Derivative term controls how quickly the control system can add or subtract energy from the load.  The derivative can take the form of dI/dt or dV/dt depending on the specific controller.  This term has two important purposes.  As stated, it defines how quickly the system responds to changes in the load condition, and it exactly parallels the breakdown limit of the power transistors used in the motor amplifier.

The integral term provides correction on a cumulative basis.  All previous error information is integrated over time to provide the system with correction to the control command that “damps” reaction to disturbances.

Notice that all the gains are directly tied to time.  The faster the motion, the more P and D gain is needed to provide adequate response in the control.  Many motion applications have low enough dynamics that servo tuning needs to be very low performance compared to the capability of the equipment.

For most applications, and depending on the gear you are using, the best thing to do is start with I & D gains set to zero.  Use the amplifier autotuning for the motor without the load.  Sometimes these are default settings that are already loaded into the controller.  Tune the motor and amplifier until the P gain seems the best for a step input.  Then add the load and run the autotune again.  If possible, use a step response input that is similar to the type of move you will do in your actual application.

Then gradually add D gain until the leading edge of the step response has no overshoot.  If there was little overshoot without P gain, the motion dynamics are probably very slow and that’s OK.  With D gain set for the application, slowly add I gain and see if the trailing edge of the step response is improved.

If the axis is “hunting” after the motion stops, there is probably too much play in the mechanical system. Using a gearbox with a lot of backlash or a timing belt that is a little loose will produce just enough mechanical error that the servomotor will detect.

Tuning, like everything in motion control, is as unique as each individual application.  There are more complex analytical techniques that can be applied to the subject of tuning.  But I hold to the theory that the majority of applications can be dealt with using simple techniques.

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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.

Mechatronic Tips

Government is not the answer.  Anytime government gets involved there is a very high risk that money will get spent and nothing will change.  Remember stimulus 1?  We were assured that if this money were spent, unemployment would never go above 8%.  And with unemployment at 9.1%, the administration wants to try stimulus 2.  No thanks.

What are the real unemployment numbers?  No one wants to really talk about that because it would mean having to admit that the real number is much higher.  Quoting from the most recent data provided by the Bureau of Labor Statistics (BLS), there are 14 million people unemployed, officially, with a labor force that has increased to 153.6 million in August.  That’s where the 9.1% comes from.

But the BLS also reports 2.6 million people “marginally attached to the labor force”.  This category refers to people who have been out of work over the last 12 months, ready and available for work, but had not looked for a job over the last 4 weeks.  I’m still not sure I understand this categorization, certainly someone who has been out of work for 12 months should qualify as unemployed.  The quibbling over details here is clearly designed to hide the real numbers.

2.6 million plus 14 million is 16.6 million which is 10.8% unemployment.  The psychologically dreaded 10% unemployment number could be easily avoided if one can find a way to finesse the reporting categories.   How bad is it really?  Some commentators have said the real unemployment numbers are 16% or higher.  Donald Trump said it was 20%+ in his interview with Greta van Sustern last week.  Personally, I am quite sure its something above 10.8%.

Sadly, this is not the first time employment data has been misrepresented.  Remember how the “Green Economy” would generate 30,000 jobs?  The report that was quoted by many in Colorado State and Federal government used a number of statistical machinations to “fluff up” the numbers.  Workers who put insulation in your home were counted as part of the “Green Economy” as were a fraction of the appliance manufacturers workforce, since effort to reduce energy consumption is a part of that industry.

Attempts by government to increase employment have been mediocre.  The way government creates jobs is by adding more government workers.  Which this administration did like crazy in its first year.  This is not how we grow the economy.  Every dollar spent by government is at the expense of someone who works for a living.    It robs the consumer of discretionary dollars that can be spent in the real economy.  When things get bad enough, government spending robs people of their ability to pay for necessities.  This isn’t how it’s supposed to work.

More disturbing is the trend in the number of manufacturing jobs added per month.  The manufacturing sector added 14,000 job per month in the second quarter, compared to 35,000 jobs per month added in the first quarter.  Not a good trend.

There are two big lessons here.  One is that manufacturing is where the jobs are. American jobs and American manufacturing.  Our politicians have been running down the manufacturing sector for the last 20 years.  Second is that government is not the answer.  Americans and American ingenuity are.  So let’s agree to let American’s get about the business of inventing the future and get the roadblocks out of the way.

Mechatronic Tips