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.

Mechatronic Tips

Which is saying a lot.

Some of that economic activity is the obvious stuff.  Jobs.  Making things that are important to the industry.  Like all the silicon ingot, water treatment, chip encapsulation compounds, chemical solvents, and gases that are needed.  And all of those feedstocks require people in their respective industries.

There is also the capital equipment market.  Companies that make machines that make chips.  Machines that grow silicon ingots, machines that slice silicon into thin wafers.  Polishing machines that make the surface smooth enough to create the nanometer sized features that become semiconductors.  Wafer probing machines that do functional testing, dicing machines that slice the wafer into the single chips, wire bonding the bare die into lead frames to we can attach the circuits.  Encapsulation, labeling, testing and packaging the final products.

The Semiconductor Industry Machinery business is estimated to be an $11B activity separate from the sale of chips.  The semiconductor equipment market is still the largest target market for motion control products and mechatronics of any market I know of.  At a close second place would be the electronic assembly machinery market  with it’s pick and place, adhesive dispensers and inspection machinery.

Interestingly, the semiconductor industry also provides trickle down technology.  Hard disk drive spindle motors require the exact same 3 phase brushless drive and control as industrial servo motors.  The difference is that the spindle motor is manufactured in quantities of tens of millions of units.  This allows disk drive manufacturers to explore the ultimate boundaries of cost reducing the technology and introducing new techniques to improve performance.  Much of this technology has migrated to the motion control industry in the way of integrated motor control chips.

The semiconductor industry is now made up of two major markets.  Chips and Solar Cells. The solar cell market is counted separately and does not overlap with traditional semiconductor business.  Many of the companies that make semiconductor machinery have extended their capabilities to the solar industry as a way of diversifying into new markets and making up the lost ground that was experienced in the machinery business.

While Solar is still an emerging industry to some extent, it will continue to drive large segments of the economy. Solar photovoltaics and solar hot water drive a lot of jobs in manufacturing and installation of systems.

What we need in the public policy sector is better understanding of the business needs that these industries require.  Generating enough electricity for these industries to thrive is one requirement.  And most states in the US have failed to bring any new capacity on line over the last 30 years. States that recognize these needs and are willing to meet them are going to be the States that prosper with low unemployment and thriving economies.  And that’s where we all want to be.

Mechatronic Tips

The contrast between InterSolar 2010 and 2008 was very noticeable.  This year’s trade show reflected the growth and sophistication.  Tremendous effort is being put into every aspect of the photovoltaic technology, tandem junction semiconductors that produce the photovoltaic effect at 2 different light frequencies, enhanced surface texturing of the surface glass to improve transmission of light and reduce the problem of incident angle of light, new chemistries like Copper-Indium based photovoltaics which are now “printable” as ink coatings, and ongoing development of thin film silicon, concentrated light focusing on silicon, recycling of the silicon itself, and a host of improvements all targeted at reducing the cost of producing electricity from sunlight.  As you might expect, incredible support from semiconductor equipment makers to provide new equipment to make the technology scalable in production and cost effective in the marketplace.  Solar is the new growth engine in semiconductor equipment.

Solar Panels, like other types of semiconductors, are subject to decreasing cost with increasing volume.  In typical Semiconductor Industry fashion, a lot of capacity has been ramping up since early 2000 which led to a 40% correction (read “drop”) in the price of solar panels during 2009 which played havoc with project bids and created serious difficulties for distributors with inventories or contracts for solar panels at the higher prices of early 2009.  However, now that prices are lower, more demand is expected, and hopefully, companies that had a tough time during 2008-2009 will find business conditions in 2010 and 2011 more favorable.

There is continued optimism that the US solar market will continue to grow at 30%+ per year for the next couple of years, some forecasts are 50% per year and one forecast from Europe suggests 100% growth in the US market next year.  Huge growth forecasts combined with caution on the manufacturing side has created shortages and long lead times for new deliveries.

But we should note, with caution, that this market is largely subsidized by State Renewable Energy Portfolios mandating the alternative energy systems, Utility Company Rebates and Federal Tax Incentives.  Solar energy technology is generally sold on the basis of avoiding future increases in energy costs, not on the basis of eliminating energy costs.

So there is still a big gap in bringing electricity costs down using solar power.  Modern coal plants produce electricity that the utility company can sell at a profit for 6 cents per kilowatt/hour.  By comparison, a 300 watt solar panel will cost at least $1500 installed and functioning.  It can only produce about 756 kilowatt hours per year, and even at 12 cents per kilowatt/hour, won’t break even for about 16 years without government incentives.  So you’re not eliminating your electric bill, you’re prepaying it with a bank loan for a bunch of equipment that doesn’t burn coal.

That’s OK if you can afford it, just don’t make the mistake of thinking you are getting rid of your electric bill.   But be on the lookout for the next breakthroughs in solar.  They are coming.

Mechatronic Tips

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

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

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

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

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

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

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

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

Mechatronic Tips

Occasionally the line between mechatronics as the design of mechanisms in discrete manufacturing and applications that are more process oriented blur the neat categories of the major control disciplines. More and more control system requirements involve the blending of 2 or 3 different types of control into a single architecture.  This creates subtle problems in order to properly architect the system so that the final effects are achieved.

Polishing and grinding, for example, appear to be positioning applications.  A grinding wheel or buffing wheel must be brought into position to make contact with a workpiece.  So the normal control system behaviors must be dealt with in order to achieve position.  But positioning the tool is only the beginning of the process.

How do we measure the process of grinding or polishing?

And most importantly, how do we know when it is done?

The process of grinding or polishing is a matter of torque in the application of the working tool to the workpiece it is in contact with.  Generally through an electric motor that is turning the tool.  By measuring the torque, which is current in the motor, we can know that the actual process is being achieved.  It may require empirical measurement to determine how much torque is required to achieve the proper surface finish, but there is a direct correlation.  Too much current means the tool is buried in the part, too little current and there is no work being done.

But at this point, there is a process that can be controlled.  If the proper torque level is applied through the motor the runs the tool, there is also a corresponding value as the contact is reduced that indicates the completion of the process.

This behavior is completely separate from the position of the tool.  However, if there is reduced contact with the workpiece due to the tool wearing out, that is, the size of the tool has decreased slightly, then the positioning system has to be updated to compensate.

These are simple concepts, but they are often overlooked.  Ironically, there are many applications that require close consideration of the mixed control methods.  Chemical mechanical planarization of silicon wafers suffers from similar difficulties with the need for extraordinary precision in polishing the surface of the wafer.  Do we really know when the process is done or do we just leave it running an extra 20 minutes just in case?

There’s always room for improvement.  And some of the recent control system innovations are delivering significant performance that should be considered as we pursue new applications.

Mechatronic Tips

Or so the story goes.

We’ve been trying to reach grid parity for some time.  Without much success.  And not because we aren’t trying.  Billions of dollars of government subsidies, R&D funding and private investment are being poured into the pursuit.

Energy independence!  Both as a Nation and as individuals.  It would be great to be able to say, personally, we don’t have pay any utility bills.

The first great fallacy is that either solar power and wind power can cause energy independence for the US.  This is because the energy we depend on is not electricity, it is Middle East Oil for gasoline.  We are dependent because of our cars and the choice to not make our own gasoline, even though we can at lower cost than importing it.

But on top of that, almost none of the electricity generated in the US uses Oil.  It’s all coal, natural gas, or nuclear.  So the idea that the US will reduce it’s foreign oil imports by generating electricity with solar power or wind power, is completely ridiculous.  There is no connection between the two.

There is a theoretical energy equivalency that can be expressed.  But there is no real connection.  So people who make this claim are intentionally misleading anyone who listens.

How are we doing with respect to the cost of electricity generated by solar power?  It’s been an interesting couple of years.  The industry experienced a brief shortage of raw silicon which kept prices fairly high.  More recently there was a precipitous drop in panel prices.

Opinions vary as to the cause of this drop, but with the massive increase in manufacturing capacity worldwide, I would guess that the price drop is strictly a matter of oversupply.

Economies of Scale will fix the problem according to some.  After all, look how well we’ve done with computers, hard drives and flat screens. Flat screens that were $10,000 to $50,000 a decade ago are now affordable to the point where the CRT has become obsolete.

Since the biggest component cost of the solar panel is silicon wafer, we should expect similar results in the solar market.  The stampede to build more solar panel manufacturing plants resulted in oversupply.

Now the race continues to drive costs down.  Panels that were selling for $3.50/Watt a year ago are down to $2./Watt and prices are expected to continue to fall. And some manufacturers will not be able to keep up with falling prices using older technology.

But are we getting to grid parity?  Is Solar power cheap enough to compete with utility power?  Nope. Because even at today’s bargain pricing, a 225 Watt panel will only produce 900 kilowatt hours in a year at maximum efficiency.  At market cost for electricity, $.05/kW, it’s only $45 worth a year.  And it currently costs about $1125 pay for the panel, installation and balance of system components.  That means it will be around 25 years, the end of the useful life of the system, before it breaks even.  Yes, in California where consumers pay $.23/kW the payback is better, but it’s still very expensive to convert to solar.

We have got to do better than that.  And we will.  The technology is coming along.  But economies of scale by themselves can’t quite get us there.

Mechatronic Tips

In addition, the Magnetics 2010 Conference will be running concurrently at the same venue.  Magnets are a strategic material without which many motors would simply not operate.  In the ever-changing motor industry, there is always a new design that seeks to make an enhancement over previous solutions, or introduce a new solution to old problems.  Declining prices for Neodymium Iron Boron magnets over the last few years have created a number of novel design shifts which have been instrumental in bringing more varieties of permanent magnet machines into the forefront of motion control and mechatronic technology.  To the point where over the last two years a resurgance of permanent magnet rotor designs have been created to improve the energy denisty and lower the cost of specialty motors in washing machines and air conditioning compressors.

This last development, combined with the forecast increase of hybrid electric car sales coming this year, are expected to increase the sale of permanent magnets by 10-15 percent by 2011.  That’s a staggering jump in a market that is almost exclusively supplied by China.  And there is no assurance that China can meet the forecast production.

The US Department of Commerce usually has a say in the sale of products or businesses to foreign countries that are deemed to be strategic or sensitive technology.  In fact, I got stuck in a situation where my employer was told specifically that we could not sell a CNC controller to a Korean customer.  That’s pretty small potatoes compared to controlling the supply of permanent magnets which influences billions of dollars worth of electric motors manufactured and sold all over the world.  So it strikes me as a little odd that the sale of Magnequench to its current owners, Neo Materials, was completed without a much discussion. leaving the US without a domestic magnet supplier.

There will surely be a lot of discussion about this situation at the conference, and I will be in attendance to get the latest information on the subject.  So look forward to a review of the conference in an upcoming post.

Mechatronic Tips

And there are so many technologies, all focused on solving application problems but balancing the economics of development cost and manufacturing scalability.  Where would the Oui or iPhone be without accelerometers that are really inexpensive?  Fax machines without G3 communications chips,  or $49 printers without stepping motor chips and ink jet controls?  All benefits of high volume economy of scale.

Industrial control systems have generally required chip technology, but in numbers of chips considered too small to merit custom designed solutions.  But the Rockwell Control Logix concept breaks the partitioning of applications by applying the same control processor to all kinds of control equipment, variable frequency drives, programmable controllers, HMI’s, you name it.

Is there an ultimate chip?  A chip solution that does everything?  Not really.  But the wizards of the microcircuitry world keep coming up with new architectures.  New approaches to existing applications that offer price or performance attributes that will hopefully trigger lots of new designs that result in breakthrough products.

Recent trade press is buzzing about a new processor that combines the logic solving capability of FPGA (Field Programmable Gate Arrays) with ARM (Advanced Risc Machines).

FPGA excels in the ability solve logic, and has scaled up to massive numbers of gates and tremendous processor speeds to solve enormously complex applications.  Even applications requiring real time operation like motor control can be solved through FPGA with proper attention to detail.   Applications that were considered impossible a few years ago are now within the range of these processors.

But using gate arrays may not be the most efficient way to do motor control.  Hard real time motor control requires a great deal of analog processing to monitor conditions in the real world (like voltage and current) and the ability to respond to dynamic changes through complex programming and mathematical models.  Much easier for ARM processors with super efficient instruction sets and single cycle multiplication and division.  In some designs 16 channels of high resolution A to D converters and direct PWM capabilities.

So combining the two technologies seems like the ideal solution for a huge range of industrial control applications.  And if you get it all in one processor, wouldn’t that be great?

I  can’t wait to see what new product developments take place in the next few years with this kind of processing power available.

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And, in fact, the industry is getting there. The current estimates are that solar power is costing about the same as peak demand consumer power, $.23/kWh. And with the current wave of investment and scale up, something which the semiconductor industry has always done well, there is serious forecasting that the cost of solar electricity will continue to fall.

The mechatronic connection is really interesting. It was something I wasn’t really paying attention to. The solar tracking application. You need 2 axes of motion, elevation and azimuth, to follow the sun in its daily course and maximize the electricity coming out of the solar panel. Most vendors claim up to 40% increase in the amount of electricity generated by solar power. But when you get right down to it, this is a very difficult application to do, because even though the duty cycle is very low, it requires decent accuracy and low cost. A very tough combination.

Some solar trackers use two motors and gear reducers to move 12 or 16 solar panels in a large frame. The typical solar panel is 15″ wide and 48″ long and weighs about 33 to 40 pounds. 12 units would be a payload of 480 pounds. Pretty serious amount of load.

The nice thing is, you can use a lot of gear reduction to make a smaller motor do the job. But on average the systems I have seen add more than $200 per solar panel to the installation. And that’s about half again the cost of the solar panel to begin with. So it really impacts the return on investment for solar power.

And that means we need a better mechatronic solution to do this job at a much lower cost. So we need to run a contest for the best solar tracker. You can do it any way you want, 1 panel system or multi-panel system. There are some new solar energy systems where mirrors are used to create solar concentrators to increase the light density on the surface of the silicon photovoltaic device. But we just have get a better solution out into the marketplace.

See? There really is a mechatronic connection in this solar energy stuff.

Now here’s the hard part: It doesn’t matter how good a job you do on the mechatronic part if we don’t get the government to change its policy on home financing. Currently, none of the green energy technologies qualify for FHA lending. This means that you have to do your solar retrofit for cash. You can’t get a second on your house or roll it into a new home finance package. So you have to come up with $20K- $25K to get a system installed. That’s the reason we don’t have a million home off the grid yet. Write your congressman or woman.

Mechatronic Tips

Various stainless steels and nickel alloys are available as sheath materials for specific application requirements. Diameters are available from 0.020 to 0.500 in.

Termination options are application-driven and range from standard male plugs to screw-cover terminal housings. These units are field-bendable for easy installation. Standard calibration types are K, S, T, E, N, R, S and B. Temperature tolerances are available as standard or special limits-of-error. The thermo-element design can either be single or duplex for multiple outputs from the same point.

Durex Industries
www.durexindustries.com

Mechatronic Tips

By Dr. Jens Kummetz,
Marketing Application Development,
Dr. Johannes Heidenhain GmbH

The semiconductor industry continues to demand tighter precision and faster operating speeds from machines in order to satisfy growing demands on quality, production, and size reduction. Linear motors are becoming more important in such highly dynamic applications that use one or more feed axes. The benefits of direct drive technology are low wear, low maintenance, and more throughput.

However, this increase in throughput is possible only if the control, the motor, the machine frame, and the position encoder fit one another. Direct drives place rigorous demands on the quality of the measuring signals. High quality signals reduce vibration in the machine frame, stop excessive noise exposure from velocity-dependent motor sounds, and prevent additional heat generation, allowing the motor to realize its maximum mechanical power rating.

Design of direct drives
The decisive advantage of direct drives is the very stiff coupling of the drive to the feed component without any other mechanical transfer elements. This configuration allows significantly higher gain in the control loop than with a conventional drive.

Direct drives do not need an additional encoder to measure speed. Both position and speed are measured by the position encoder: linear encoders for linear motors, angle encoders for rotating axes. Because there is no mechanical transmission between the speed encoder and the feed unit, the position encoder must have a correspondingly high resolution to enable exact velocity control at slow traversing speeds.

The velocity is calculated from the distance traversed per unit of time. This method—which is also applied to conventional axes—represents a numerical differentiation that amplifies periodic disturbances or noise in the signal. The combination of the significantly higher control loop gain used with direct drives and insufficient encoder signal quality can reduce drive performance.

Signal quality of position encoders
Modern encoders have either an incremental, which means counting, or an absolute method of position measurement. In the encoder, path information is transformed into two sinusoidal signals with 90° phase shift. Both methods require that the sinusoidal scanning signals be interpolated in order to attain a sufficiently high resolution. Inadequate scanning, contamination of the measuring standard, and insufficient signal processing can lead to a deviation from the ideal sinusoidal shape. As a consequence, during interpolation periodic position error occurs within one signal period of the encoder’s output signals. These position errors are referred to as “interpolation error.” On high-quality encoders the error is typically 1% to 2% of the signal period.

During interpolation, position errors can occur within one signal period of an encoder’s output signals.

The interpolation error can produce several effects:
—Generation of heat and noise. If the frequency of the interpolation error increases, the feed drive can no longer follow the error curve. The current components generated by the interpolation error
increase motor noises and additional heating of the motor.

A comparison of the effects of linear encoders with low and high interpolation error on a linear motor illustrates the significance of high-quality position signals.  The LIDA linear encoder, for example, generates barely noticeable disturbances in the motor current: the motor operates normally and develops little heat.

If at the same controller setting, the interpolation errors of the same encoder are increased through poor adjustment, significant noise arises in the motor current, which can cause more noise and heat generated in the motor.

—Dynamic behavior. Digital filters will smooth the position signals for direct drives. However, the additional phase delay caused by filtering in the speed-control loop must be kept to a minimum, otherwise the dynamic accuracy decreases.
Position encoders with optimum signal quality help to reduce the use of filters, which maintains the control bandwidth.

Position Encoders for direct drives
Linear encoders that generate a high quality position signal with low interpolation errors are essential for optimal direct drive operation in the electronics industry. Encoders that use photoelectric scanning are ideally suited for this task, since they can scan very fine graduations.

The right encoder will generate minimal disturbance in the motor current.

Encoders with optical scanning measure periodic structures known as graduations. The substrate material is glass, steel, or—for large measuring lengths—steel strips. These fine graduations—graduation periods from 40 μm to under 1 μm are typical—are manufactured in a photolithographic process. They have high edge definition and excellent homogeneity—a fundamental prerequisite for low interpolation error, and therefore for smooth operating performance and high control loop gain.

By the nature of their design, the measuring standards of exposed linear encoders are less protected from their environment. The manufacturer should therefore always uses tough gratings made in special processes.

Here’s a look at the heat generation of linear motor contolled with an encoder
TOP: With low interpolation error
BOTTOM: With high interpolation error
In the DIADUR process, hard chrome structures are applied to a glass or steel carrier. The AURODUR process applies gold to a steel strip to produce a scale tape with a hard gold graduation.

In the SUPRADUR process that we use, a transparent layer is applied first over the reflective primary layer. Then an extremely thin, hard chrome layer is applied to produce a grating. Scales with SUPRADUR graduations have proven to be particularly insensitive to contamination because the low height of the structure leaves practically no surface for dust, dirt or water particles to accumulate.

These production technologies ensure an enduringly high signal quality suitable for the use of direct drives in demanding applications.

Optimal scanning
The scanning method and the high quality of the grating share responsibility for low interpolation error. In single-field scanning, the output signals are generated from one scanning field. This large field and the special optical filtering through the structure of the scanning reticle and photosensor
generate scanning signals with constant signal quality over the entire range of traverse. Constant signal quality is necessary for:
—Low signal noise
—Low interpolation error
—High traversing speed
—Good control loop performance for direct drives
—Low motor heat generation

To put it simply, the imaging scanning principle functions by means of projected-light signal generation: two scale gratings with equal grating periods are moved relative to each other—the scale and the scanning reticle. The carrier material of the scanning reticle is transparent, whereas the graduation on the measuring standard may be applied to a transparent or reflective surface.

When parallel light passes through a grating, light and dark surfaces are projected at a certain distance. An index grating with the same grating period is located here. When the two gratings move in relation to each other, the incident light is modulated: if the gaps are aligned, light passes through. If the lines of one grating coincide with the gaps of the other, no light passes through. Photovoltaic cells convert these variations in light intensity into electrical signals. The specially structured grating of the scanning reticle filters the light current to generate nearly sinusoidal output signals.

Linear encoder scales made with SUPRADUR graduations tend to be less sensitive to contamination because they have few surface structures.

In the XY representation on an oscilloscope the signals form a Lissajous figure. Ideal output signals appear as a concentric inner circle. Deviations in the circular form and position are caused by position error within one signal period and therefore go directly into the result of measurement. The size of the circle, which corresponds to the amplitude of the output signal, can vary within certain limits without influencing the measuring accuracy.

In single-field scanning, the output signals are generated from one scanning field. This large scanning field, and the optical filtering through the structure of the scanning reticle and photosensor generate scanning signals with constant signal quality over the entire travel range.

On direct drives, deviations from the circular form cause acoustic noise, reduce control quality and increase heat generation.

This chart shows a selection of position encoders for direct drives and the maximum values of interpolation error with respect to the signal period.

Lower sensitivity to contamination
Production facilities and handling devices for the semiconductor industry demand high acceleration and compact designs. Such requirements usually mean exposed measuring systems that operate without friction and, because they operate without their own housing, can be designed to be very small and low in mass. Special scanning methods and production techniques provide tough protection against contamination even without sealing the encoder.

The specially structured grating of the scanning reticle  filters the light current to generate nearly sinusoidal output signals. An XY representation of the signals on an oscilloscope takes the form of a Lissajous figure. Ideal output signals appear as a concentric inner circle. Deviations in the circular form and position are caused by position error within one signal period.

Many exposed linear encoders operate with single-field scanning where only one scanning field generates the scanning signals. Local contamination on the measuring standard (such as fingerprints from mounting or oil accumulation from guideways) influences the light intensity of the signal components, and therefore of the scanning signals, in equal measure. The output signals do change in their amplitude, but not in offset and phase positions. They stay highly interpolable, and the interpolation error remains small. The large scanning field additionally reduces sensitivity to contamination. In many cases this can prevent encoder failure.

Thus, optical encoders with low sensitivity to contamination need an optimal scanning method, a large scanning field, and contamination-tolerant graduation.

Very small signal periods usually come with very narrow distance tolerances between the scanning head and scale tape. However, several varieties of encoders provide ample mounting tolerances in spite of the small signal periods. Within the mounting tolerances, therefore, changes in the signal amplitude remain negligible.

HEIDENHAIN Corp.
www.heidenhain.com

Mechatronic Tips

Both inductive sensors use “auto-configure” output technology, which auto-detects if the sensor has been wired for NPN(sinking) or PNP(sourcing), and switches the sensor to the appropriate mode without user intervention.

Eaton Corporation
www.eaton.com

Mechatronic Tips

We don’t have a major position in the display technology arena, most of the flat panel display technology comes from Asia. But organic LED may be the next emerging technology and it is still substantially in American hands.

Battery power storage and fuel cell development is a big technology effort in the US and development of small, power dense battery technology has “fueled” (pun intended) many new product breakthroughs like the iPhone and iPod. Scalable storage technology like the recently improved Lithium Ion battery is going to be the key to short range electric vehicles that operate at a few pennies per mile, unlike the hydrocarbon based vehicles that dominate the road today.

And like the classic economists would predict, all the electronics businesses behave in perfectly linear economies of scale. The more product made, the lower the price. The entry level laptop is now $500 and is far more powerful than the most expensive desktop available five years ago. Now that’s my idea of a great “engine of commerce”.

And the commerce cuts across many fields. Medical imaging would not be possible without PC-like products to calculate the volumetrically correct image to be rendered and manipulated in 3D. Mechanical design workstations that used to cost $50,000 can now be hosted on $1000 PC’s The DaVinci surgical robot, an extraordinary accomplishment of mechatronic excellence, would be impossible without semiconductors to control and power it. In fact, we run all our businesses with computers, because its cheaper and faster.

These are multi-billion dollar market segments that are all closely knit together in an industry infrastructure that requires a lot of support. And the factories of the current era of semiconductors and consumer electronics are multi-billion dollar facilities that host some of the most sophisticated technology ever conceived by man.

So it strikes me as somewhat irresponsible that we can have the megalithic technology structure hobbled by the inability to generate electricity, a business that has been with us for almost 100 years. How can we let the energy infrastructure fall into such a state of disrepair that in the summer in California, when demand for electricity is high because of air conditioning usage, that our semiconductor industry can have brown outs and plant shutdowns.

Its absurd. And it is irresponsible for politicians who hold the power to grant permits to build new powerplants, to deny the industry the ability to supply its customers. There haven’t been powerplant permits granted in the US in 30 years. No wonder we’re in trouble.

A former client of mine is in the power generation business and I have done work for his company. Powerplants in the US are among the cleanest burning anywhere. There are even a handful of plants that burn garbage that is carefully pre-screened, and some of those plants are even cleaner than the cleanest coal fired plants.

Then there is the nuclear option. 20 years ago the American Nuclear Regulatory Agency participated in demonstrations of the “pebble bed” reactor. The size of a waste paper basket and totally safe. It can’t melt down and it can’t become unstable because each “pebble” of nuclear material is encased in ceramic that is resistant to temperatures of 3000 degrees.

Let’s wake up the sleeping giant of American ingenuity and start putting to work the people, the technologies that will reinvigorate our economy, before its too late.

Mechatronic Tips

Wafer polishing machines must polish the slices of silicon to a flatness and perfection that can’t be measured by conventional means. Multi-axis robots handle silicon wafers in vacuum chambers without putting the tiniest scratch on the surface. Wafer cassettes with $250 to $500K worth of uncut chips have to be shuttled from process machine to process machine inspected and tested for defects.

The materials are among the most exotic in the world; gold interconnects, high purity copper, pure silicon crystals that are grown in furnaces at temperatures in excess of 2600 degrees Fahrenheit. Processes that require chemicals with extraordinary purity, some of which are the most corrosive acids on the planet.

The shiny little sliver of crystalline silicon can embed the intelligence of man-years of programming, sense the position of an actuator to millionths of an inch, measure current in a conductor or regulate lethal amounts of voltage or current in power semiconductor applications. Pretty amazing stuff.

And when it comes to controlling motion, many solutions are available. Digital Signal Processors have been one of the key technologies for controlling motion because of their ability to process mathematical models of analog events. Field Programmable Gate Arrays that host huge arrays of logic gates can read encoder feedback and execute control tasks at incredible speed. Microprocessor based motor controls and servo systems have been around for a decade or more. And the latest generation of microcontrollers offers to integrate the power of the DSP with the flexibility of a microprocessor and multitasking needed to support network communications to other devices.

What’s a bit strange is that we keep solving the same problems over and over using different platforms. Why haven’t we found the ideal solution? At a certain point, its the same mathematical model of a real world phenomenon that we are trying to run. Isn’t it? Or are we solving different problems and needing to find better hardware solutions? Or are the tools evolving to make treatment of the complexities easier?

A little bit of all of these. And maybe that’s what makes it so interesting.

Mechatronic Tips

It is somewhat ironic that as we move into the e-tainment era of the 2010′s, surrounded by e-media delivered by ever more powerful portable electronics, that the US semiconductor industry is at least the size of, and by some accounts, a much larger enterprise than the auto industry.   The Department of Commerce shows semiconductor manufacturing at $90B for 2002 and computer manufacturing at about $88B, some of which of course is overlapping.  If you start adding all the flat screen display, cellphones, well, you get the picture.  Semiconductors enable so many products that we take for granted, it is hard to estimate the impact.

US auto sales have been falling since 2002, but the Department of Commerce data lists auto sales at $90B.  Similarly, to get a better picture of the overall auto industry you have to add in trucks and tractors and all the other gasoline and diesel powered vehicle segments that make up the overall industry.  The largest user of glass and carpet is, you guessed it, the auto industry, not residential construction.  So cars are still important in the US economy.

But when you consider the role of control systems in the manufacture of electronic products, the solutions are not the same. Semiconductor equipment companies are among the largest users of motion control across all industries.  Some motion control companies have made their fortunes supplying board level motion solutions to operate the most sophisticated equipment in the world. Just like 50 years ago in the auto industry.

The odd part is, that the semiconductor industry has not taken to the classical controls solutions of the automotive type suppliers very well.  And it took me a while to get that message.  Partly, I think there is a preference for the PC as a platform of control as a cultural proposition.   Computers are the dominant consumer of the electronic components, so people in the industry tend to use what’s closest, most familiar, and in some cases, lowest cost.

But there are much more compelling issue involved.  The semiconductor industry did not grow up with relays as a control technology, so ladder logic as a programming environment isn’t really significant.  Many people in the industry are more familiar with C language programming or other languages that don’t depend on electrical conventions.

But the biggest challenge to control systems isn’t the control, its the data.  Process data is crucial to finding out if you have a $25,000 wafer of silicon that’s good, and can continue in its manufacturing process, or bad and needs to be scrapped out.  When making the platter for a hard disk drive, it takes many steps to build the magnetic layer on the aluminum disk.  Each step is monitored for temperature, time, chemical concentration and pressure so that the process will operate correctly over hundreds of thousands of operations.  Data is the key to process integrity.   So control systems in the semiconductor world have to be data centric, not control centric.

Its a different world.

Mechatronic Tips