Nippon Pulse Introduces Green Drive Linear Actuator

Nippon Pulse has announced the introduction of its newest linear servo product, the Green Drive linear actuator. The Green Drive is an all-inclusive linear direct drive actuator suited for high-performance applications requiring high force, accuracy, and precision.

Features of Nippon Pulse’s Green Drive include:

• Acceleration (peak) force of up to 600N for 40 seconds
• Effective stroke lengths between 10mm and 1540mm
• Cooling systems that can increase rated force up to 20%
• Rated force between 13N and 150N
• Position repeatability of ±0.05mm
• T-slots for easy and quick integration into applications
• Position sensors, temperature sensors, interpolation electronics
• Four different feedback output types: analogue SIN/COS, Digital Bus BISS-C, Digital A/B TTL Linedrive Incremental, and Absolute SSI
• Color coded quick connectors
• High-performance slide bearings

The Green Drive currently is available in two sizes, the G16x series and G25x series. The G16x series features a shaft (magnets) with a 16mm diameter and the G25x a 25mm shaft diameter. The G16x series is 66mm wide and high, while the G25x series is 88mm wide and high. Each has varying lengths depending on the required effective stroke.

Nippon Pulse will be highlighting the Green Drive at the ATX West tradeshow in Anaheim, CA in mid-February. Those interested in the Green Drive can visit booth #4348 to learn more about the actuator.

Nippon Pulse America, Inc.
www.nipponpulse.com

Minarik Drives Announces Distribution Agreement with Kaman Industrial Technologies

Minarik Drives is very pleased to announce that it has signed and implemented a National Distribution Agreement with Kaman Industrial Technologies.  This agreement will further enhance a partnership that will provide Minarik Drives with 200 new locations and will provide Kaman Industrial Technologies a premier DC drive and drive systems product line.

“We are very pleased to add Kaman Industrial’s selling capability and the value added approach they brings to their customers to our already strong distribution channel.” said John Hegel, President of Minarik Drives.  “Kaman’s penetration into the user and OEM markets will open doors for us that had been previously inaccessible and will help us serve a greater cross section of business across the U.S.”

Minarik Drives is an independent company that specializes in low to medium power electric drive and power applications.  It has been a standard, and a leader, in the DC drive business for almost 60 years.  With design engineering and manufacturing headquartered in S. Beloit, Illinois, it provides standard and customized solutions at a globally competitive price.  More information about Minarik Drives is available at www.minarikdrives.com or by calling 815-624-5959.

Next Generation Manufacturing

As a follow on to the last post, I have been investigating the cost of manufacturing equipment.  The classic machine tool is the most widely used piece of equipment for fabricating just about anything made out of metal.  The machine tool has been quietly undergoing it’s own revolution since it’s inception in the 1950′s.

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.

Innovation in Motors for Mechatronics

Innovation is the watchword of mechatronics.  The pressure for solutions in alternative energy continue to push the boundaries of design in electromechanical systems.

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.

Friction, Friend or Foe?

Friction is rarely talked about in motion control circles (pun intended for those paying attention).  It is the “waste” energy in mechanical systems.  We spend a lot of time and sometimes cost, trying to eliminate it.  Many times we just ignore it.

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.

Programming Software and Control

Writing software for control applications isn’t the easiest thing.  It’s probably been 15 years since I had to write any actual code for a control application.  I have scripted and taught training classes in PLC programming and am very familiar with ladder logic programming and Boolean instructions, although I am less familiar with the latest editing software which has become very sophisticated.

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.

Control System Theory and Feedback

Control system performance is based on feedback.  Control of electric motors, however, continues to be a bit mysterious because the common conventions associated with motor control are often driven by cost considerations.  The feedback component is often target for elimination in cost constrained systems.

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.

Energy Saving and Automation

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

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

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

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

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

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

Prudent planning can be turned into real cash savings.

What is Control – Part 2

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

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

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

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

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

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

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

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

What is Control?

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

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

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

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

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

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

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

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

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

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