Out Of The Gait: Robot Sets Untethered ‘Walking’ Record

The loneliness of the long-distance robot: A Cornell University robot named Ranger walked 14.3 miles in about 11 hours, setting an unofficial world record at Cornell’s Barton Hall early on July 6. A human – armed with nothing more than a standard remote control for toys – steered the untethered robot. Ranger navigated 108.5 times around the indoor track in Cornell’s Barton Hall – about 212 meters per lap, and made about 70,000 steps before it had to stop and recharge its battery. The 14.3-mile record beats the former world record set by Boston Dynamics’ BigDog, which had claimed the record at 12.8 miles.

A group of engineering students, led by Andy Ruina, Cornell professor of theoretical and applied mechanics, announced the robotic record at the Dynamic Walking 2010 meeting on July 9, in Cambridge, Mass.  Ruina leads the Biorobotics and Locomotion Laboratory at Cornell. The National Science Foundation funds this research.

Previously, students in Ruina’s lab set a record for an untethered walking robot in April 2008, when Ranger strode about 5.6 miles around the Barton Hall. Boston Dynamics’ BigDog subsequently beat that record.

One goal for robotic research is to show off the machine’s energy efficiency. Unlike other walking robots that use motors to control every movement, the Ranger appears more relaxed and in a way emulates human walking, using gravity and momentum to help swing its legs forward.

Standing still, the robot looks a bit like a tall sawhorse and its gait suggests a human on crutches, alternately swinging forward two outside legs and then two inside ones. There are no knees, but its feet can flip up – and out of the way, while it swings its legs – so that the robot can finish its step.

Ruina says that this record not only advances robotics, but helps undergraduate students learn about the mechanics of walking. The information could be applied to rehabilitation, prosthetics for humans and improving athletic performance.

Cornell University
www.cornell.edu

Igus Develops A Simpler Robotic Bionic Joint

When it comes to robotic joints, engineers have had to put together complex custom configurations out of multiple components, which involved considerable development time with the mechanisms. This time requirement often reduced the amount of time artificial-intelligence programmers had with the system. So, two goals of robotics developers were to enable the programmers to be involved with the process earlier and develop a straightforward modular system. The realization of these goals is closer, thanks to a recently introduced innovative robot joint module system from igus. The company is currently looking for beta testers for this new product.

The robot unit, known as Robolink, was primarily designed for robot developers and laboratories that work with humanoid systems, as well as with lightweight engineering systems for handling and automation. The design was inspired by Dr. Rudolf Bannasch, Managing Director at the Berlin-based company EvoLogics, a high-tech company working in the field of bionics and humanoid robots. He provided both the motivation and developmental support behind this Robolink component.

It consists of a drive-and-control unit, joints in different lengths, and arms in different sizes, including a duct for additional control cables. The jointed arms are made from carbon fiber reinforced plastic and other lightweight materials. At the end of the jointed system is the option to connect to different types of tools.

The drive-and-control unit was purposely designed as a black box. Robot developers have the option to work with pneumatics, electro technology, or hydraulics.

The bionic core of the robot’s skeletal parts is the injection-molded plastic joints. They are controlled through cable pulls that transfer tensile forces, similar to the way tendons function in humans. The cable sheath is held and the inner cable moved. This way, the gripper, shovel, hook—or whichever tool the developer chooses—is moved and operated.

All data cables are routed safely through the jointed arms. The cable pulls are routed through from one joint to the next—just as joints are connected in humans. Only four cables are required for each plastic joint to rotate and swivel freely. These cables convey images, acoustics and forces, which are the artificial senses of humanoid robots.

The cables themselves are made from technical synthetic fibers. The fibers are extremely strong, hardly stretch at all, are resistant to chemicals, and are lubrication-free and wear resistant. When compared to steel, their lighter weight also makes them much more energy efficient.

Since the system is modular, it can be constructed with all kinds of humanoid robot configurations. This ranges from jointed arms, moving ‘digger’ arms, through to four-legged ‘creatures.’ The joints can be easily combined as required.

igus’ development objective was to keep the moving mass as low as possible, so that the actuators can be separated from functioning tools, such as grippers, hands, suction cups, and so on. Particular attention was given to enable quick assembly, as well as the use of tribo-optimized plastics to reduce lubrication needs and weight.

igus
www.igus.com

Torque, Control and Adaptive Gain

Torque is a very important aspect of motion control.  Torque in a car (electric or combustion powered) is what turns the tires.  Torque control is the ability to control the amount of torque needed based on conditions of the application.

In the car, starting torque requirements can be very high, depending on how fast you want to accelerate.  Running torque, the amount of torque needed to overcome air drag, is very small.   If you want to reach 60 miles an hour in 4 seconds or less, like a Corvette, you will probably need around 450 horsepower.   Cruising on the freeway at 65 miles an hour, constant speed, will probably only require 5 horsepower.

So the power requirements for what appears to be “the same” application can vary wildly, 100 times the power, depending on the circumstances.  That’s where control and regulation come in.   The question being, how fast is the rate of power being dissipated over a small instant in time.  This is the domain of calculus, the first derivative of power over time.  This will determine how fast the control system monitors and updates the value of the power being controlled.  This can also be referred to is as the dynamic rate of the control system, the change in time for the power rate to be measured.

In AC drives, the dynamic response of the drive is a crucial parameter in order to specify the right drive for the application.  Large systems like paper rolls, which can weigh hundreds of pound, have a very slow dynamic rate and a drive for this application should have a dynamic response that is comparable.

Hard disk spindle drives, which have tiny loads and must regulate speed and acceleration based on 2 millisecond seek times, must have extremely fast dynamic response.  The high rate of acceleration requires that torque is regulated in the microsecond range.  Regulating a paper drive with a control designed for hard disks would not only be a waste, but the high response rate in the control would probably lead to instability in the control.

But more complex conditions exist in the real world that must be considered.  What happens when the load is changing?  When you have to palletize beer bottles, every ten cases of beer completes a layer on the pallet.  There are 8 layers to the pallet.  So you start with an empty pallet and end up after 8 identical moves with 3800 pounds of beer.  How do you set the gain?

Either you use an average value equivalent to half the payload weight and live with the results, or you need something that reloads the gain value as the load changes.  Both techniques can be done, both work, but the ideal solution is the second, adaptive gain.  Something that is adaptive, however will require some pretty advanced programming to consider all possible conditions.

And that is the new frontier in robotics.  If robots are to work in human service, they have to be able to operate in a reduced torque mode so that they cannot produce forces that exceed human strength and frailties.  But there are other conditions where the robot’s superior strength can be extremely helpful.  So the current generation of drives will have to incorporate increasingly complex adaptive gain controls in order to make human service robots safe and practical.

Adaptive gain is a discipline that has been talked about for at least a decade in the control community, but it’s been somewhat of a technology looking for an application.  There are the occasional situations where adaptive gain would really be “cool”, but not any widespread applications.  Well, the next great application for adaptive gain will likely be human service robots.  Coming soon to a neighborhood near you.

Air Bearings

Most things that turn, do so on bearings.  Over the years, much attention has been paid to the bearing.  The basic ball bearing has been mastered to reduce friction to incredibly low levels.  The automotive drivetrain would not be possible without the friction reducing ability of the ball bearing.

Accuracy in machining of the bearing parts and lubrication technologies have become incredibly sophisticated.  Some of the latest innovations include the use of  ceramics rolling elements instead of metal on metal contact, and whole new classes of fluorine based lubricants that survive incredible temperatures.

There are a number of applications where conventional bearings are not usable.   The inherent vibration of bearings may be unacceptable.  Creation of particulates can be a problem in some situations.  The alternative is fluidized bearings.  Fluidized bearings are designed using precision flat surfaces with grooves that allow oil to form a film between the moving parts.  So the parts are literally riding on a layer of oil, no contact between moving parts.

Fluidized bearings have successfully taken over the spindle drive motors on hard disk drives, which is a really tough application, 10,000 rpm and starting and stopping in 2ms.  On the opposite end of the power spectrum, I worked with a company that makes machines that make the cans for beer.  The machines form the can body using impact extrusion with a 75 horsepower drive and a massive inertia flywheel.  The linear motion of the forming tool runs on fluidized bearings.  Very cool stuff!

But what do you do when conventional bearings won’t do it, and even a fluidized bearing won’t work?  The ideal fluid is air.  And thanks to some really creative engineering at New Way Air Bearings, the superior performance of air bearing is available as an off the shelf technology.

New Way Air Bearings are based on a porous carbon media that allow air to flow through it at a controlled rate so that a cushion of air is formed on the face of the media.  Parts are suspended on 5 millionths of an inch.  And there is no contact, so there is no wear, no particulates, no lubricant.  Pretty awesome stuff.

Air bearings are available, from stock, in rectangular pad forms, round journals and radial designs.  You can see a great animation of the radial air bearing used in MRI machines on the company’s website.  Medical imaging depends on extremely precise motion and NO vibration.  A perfect application for air bearings.  New Way has also done a number of applications in the semiconductor arena that combine air bearings and vacuum barriers in the same assembly.

One of the great subtleties of bearings is their concentricity.  There are many applications in cutting and shaping operations where the active tool is rotating at high speed to shape a desired part.  But slight errors in the rotary precision of the tool become exaggerated at high speeds.  But with air gaps of 5 millionths of an inch, and the high stiffness of the air bearing, extraordinary truing of the rotating shaft is built in.

And I suspect there are dozens of other applications possible.  Especially as the standard bearings are very reasonably priced.

Six degrees of freedom and high precision

Parallel kinematics (PKM) precision positioning systems have many advantages over serial kinematics stages, such as lower inertia, improved dynamics, smaller package size and higher stiffness. Hexapods, a type of parallel kinematics positioning system, can move masses of 50, 200 or even 1000 kg with micron accuracy such as that required in medical applications. This particular Hexapod system, the M-810, is built with six, high-resolution electro-mechanical or piezoelectric actuators acting on a common platform. It is the familiar flight simulator design, but considerably more precise: in place of hydraulic cylinders, the Hexapods are driven by accurate, precision-controlled rotary or linear motors.

Different drive principles are used, depending on the application: Hexapods with NEXLINE® drives make a positioning system that is vacuum compatible and non-magnetic.

These Hexapod systems include a controller that lets you set a pivot point anywhere inside or outside the Hexapod working space. The freely definable pivot point stays with the platform, no matter how it moves. Moves are specified in Cartesian coordinates and the PC-based controller transforms them into the required motion-vectors for the individual actuator drives.

The miniature hexapod system delivers more than 10 lb of force and motion in all six degrees of freedom.  This 6-axis robot can be used for manufacturing and part placement that requires high precision for microscopy applications or laser and optical alignment. Its size is 10 cm in diameter and 11.8 cm in height. Minimum incremental motion is 0.2 microns (40 nm resolution). Travel ranges to 40 mm linear and 60° (rotation). Velocity is 10 mm/s.

PI (Physik Instrumente)

www.pi-usa.us

CUI Launches Updated Website for AMT Encoder Series

TUALATIN, OR – CUI Inc announced that it has launched a new version of amtencoder.com, a website dedicated to their proprietary AMT modular encoder series. The site now features detailed product pages, a resource area with technical documents, videos, frequently asked questions, a news section, and an inventor’s bio. CUI’s VP of Marketing Jeff Schnabel commented, “Users of the new amtencoder.com can expect to find a wealth of resources on this exciting technology and the products that utilize it.”

The AMT encoder has been designed with proprietary, capacitive, code-generating technology that represents a breakthrough in cost vs. resolution. Capacitive technology holds numerous advantages over the optical technology typically used in today’s modular encoders. The AMT’s design allows users to select from a range of resolutions via an on-board dip switch, creating flexibility for companies utilizing multiple encoders in their applications. Additionally, common problems associated with optical encoders, including fragility of the optical disk, LED burn-out, limited temperature range, and high current consumption are eliminated by capacitive technology.

The AMT is available immediately through Digi-Key starting at $29.95 for 1 piece. Contact CUI directly for OEM quantities.

CUI Inc
www.cui.com

Motors are Strategic Technology

The 2007 Department of Commerce Census data is just now being released (how’s that for government efficiency?) and the good news is that the sector of the economy that manufactures electric motors and generators, a lot of which is used in industry for motion control applications, was up over 2002.  The increase in total revenue was a whopping $12.37 Bil over $9.08 Bil 2007/2002.  A couple of strange statistics show up in employment figures, total employees declined by 10,872 jobs, a full 20% based on the 2002 employment levels.

So we can register some gains prior to the slowdown in 2008, but there’s a catch.  We have traded in 20% of our employment for about 30% growth in the market over the five year period.  Those two facts cannot be resolved except by the fact that foreign suppliers have established operations in the US and are shipping products into the US for sale.  And we continue to lose manufacturing based employment.

On a happier note, average salaries increased by about $6500 per employee, so the news is not all bad.  And for those keeping score on health care costs, the industry paid an average of $4520. per employee for medical care.

But electric motors are used for all kinds of things.  Putting your favorite beer into a bottle and onto a truck requires millions of dollars of mechatronic equipment to get the job done at the rate of 1-2 million bottles a day.  You wouldn’t believe how much equipment goes into making frozen pizzas.  Missile guidance and a lot of military applications like targeting required high performance motors.  Disk drives are a huge user of brushless dc spindle motors.

And in order to make motors you have to have copper wire, steel laminations and magnets.  Copper wire and lamination grade steel have become much more expensive in the last few years while Neodymium magnets have declined steadily in cost at the rate of about 7% per year.  This has created a very strange situation where conventional AC motors with small high performance permanent magnets in the rotor have become more cost effective than their standard counterparts.  This is a set of circumstances that no one in the industry expected.  It was assumed that Neodymium magnets would always be expensive.

And the really high strength “exotic” materials are.  But there is this new middle ground where the costs have crossed over.  And high volume appliance manufacturers are jumping on the new platform of price and performance.

In an unrelated event, General Motors, who has been having financial problems for a while, sold it’s Magnequench business unit off to a Chinese owner.  Magnequench held some of the basic Patents for Neodymium magnets and was the largest and only producer of magnet grade Neodymium alloys in North America.

So where does that put us?  There are no US companies that can make motor grade Neodymium magnets.  Yes, the Magnequench factory is still in Indiana.  And I doubt there going anywhere anytime soon.  But still.  Every disk drive motor, every brushless servo, every high performance appliance motor will be using more parts made by Chines and not American companies.

Certainly GM did what it needed to do, but the sale of a US company to a foreign entity normally requires review by Commerce.  If you heard something about this, please let me know.

It’s time for some new ideas in the motor industry.

Electric Vehicles and Electric Motors

A friend of mine finally got delivery of a Tesla Roadster.  This prompted discussion of the drive train and the fact that Tesla has had to go from two speed transmissions which were failing to a transmissionless drive train.  The ultimate mechatronic challenge, the electric car, is also a challenger in terms of the precise  application of electric motor technology.

But it has to be said that the motor and drive solution for the electric car is not where the problem has to be solved.  Any motor can be made to run an electric car.  What is critical is how you apply it.  The starting conditions require high torque at low speed and the running conditions require low torque at high speed.  So, typically, what looks like a small 5 to 15 horsepower running requirement at full speed, becomes a 150 horsepower starting requirement depending on how quickly you would like to start.  If you want to keep up with a Corvette, it uses 450 HP to start.

And this produces a lot of confusion.  Why not use at 2 speed transmission to help the situation.  Fine, but the ones that are available can’t handle the dynamic response of the electric motor.

Can electronics help this situation?  Interestingly, yes.  There is a control algorithm generally called vector control which allows you to manage the rotor torque and stator torque separately.  By varying the phase angle between the two, like advancing and retarding the timing of a mechanical distributor cap on an internal combustion engine, you get different speed torque curves out of the motor.  COOL!  Is there any downside to this?

Yes.  You need more current to produce more torque.  That doesn’t change.  So you have to be able to supply the current, and you have to be able to manage the heat.  The heat is transitory since you only need the high current during starting, but it is best to have sophisticated software running to keep track of the RMS temperature of the motor.  Lower operating temperatures mean longer life and reduced risk of demagnetizing the motor.

So, yes, you can run an electric car with a garden variety AC motor, and with good electronics, you can make it run fairly efficiently.  With higher efficiency motors, the benefit is increased driving range from a given power source.  High efficiency motors are frequently smaller and lighter weigh, but a weight savings in the motor of 50 or even 100 pounds is not that big a factor in the driving range when the curb weight of the vehicle is 3000 pounds.

Basically, its F=ma.  If you can reduce the mass of the vehicle, you reduce the battery payload required to power the car.  Aluminum space frames, like on the Prowler, have been studied by the car industry and can reduce curb weight by 400 pounds and reduce cost by 10% at the same time.  We need to bring all the mechatronic leverage to the situation that we can, if we are going to make electric cars that make sense.  Before its too late for Detroit.

Super Size my Motor?

There is an interesting problem with applying electric motors that is a constant source of difficulty, the nature of peak power versus continuous power.  The problem is that few systems operate at a statistical average power demand.  Frequently, this causes equipment designers to oversize the motor for the application.  At the same time, however, this can put the motor in a very low efficiency operating range.

So what’s the right solution?  Right sizing.  Yes, just like Goldilocks and the Three Bears, not too big, not too small, but just right.

There are some great DOE publications on motor sixing that can be very helpful on the AC motor side, so make sure to give those a look.  But the implications of how to deal with varying loads are complex, each requirement having its own unique conditions that need to be considered.  Is an underpowered application actually safer?  Sometimes, yes.  I recently noticed that a particular orbital sander had been designed so that if the unit became momentarily overloaded, it stalled.  Perfectly safe.  In fact, this design is to be preferred because it prevents accidentally damaging a work piece by burying the sander in the wood and removing too much material.  Who’d have thought of it?  Certainly not Tool Time Tim.  More Power!

In fact, most of us view more as better.  More power means more production.  Or does it.  In an increasingly energy conscious community, more power means more cost.  And that’s really what its all about.  The value of the motor is not just in the purchase price, but also in the operating cost.  Especially if the motor is expected to run for 8 years, 24/7.  (That’s what the life expectancy of large AC motors is)

There’s another trick to the power requirement problem.  How much time is spent at full load and how much time is spent at average power, or, what is the duty cycle?  If the system is starting and stopping frequently it puts different constraints on the motor.  If the system is typically starting only once an hour, then we can consider the thermal duty cycle of the motor.  The momentary peak power requirement is insignificant and the vendor can usually tell from their modeling and testing of their products how much impact the peak current will have on the motor’s average temperature.

After all, its Thermodynamics 101 in the final analysis.  Every energy transformation produces heat as a byproduct.  How much heat a given system can tolerate is the key to its operating life.  In electric motors, the key values are the insulation system’s temperature rating, usually in the range of 150 to 180 C and in the case of steppers, brushless dc and permanent magnet dc motors, the magnet’s ability to resist high temperature and high coercive magnetic fields that can be generated in the motor.  Both sets of limits are generally well considered by suppliers when electrically controller motors are shipped as motor/drive combinations.  This can get a little tricky when pairing motors from one vendor with controls from another vendor.

Top 10 Mechatronic Challenges

I recently wrote on the mechatronic challenge of wind power.  Converting wind into mechanical power that can be harnessed for man’s use has been going on since the 9th Century according to Persian historians.  Certainly wind powered grinding of grains has been around in Europe for several centuries and, lest we forget, wind power pumping of water in the United States.  So there is some irony to the cultural “buzz” about wind power at home and abroad, as if the technology were entirely new.  There’s a lot of history, we’re just updating the technology to produce energy in the age of electricity.

Water has been used for power generation as well.  Following a similar path, we learned during the early part of the industrial revolution how to locate manufacturing plants near waterways so we could convert water flow into mechanical power using the water wheel.  This is, in fact the root of all modern motion control.  All the belts and pulleys, cams, gear reduction systems follow from the work done in mechanical engineering from this period of time.  All of the electronic analogs of the mechanical behaviors found in mechanical systems are the functions which we refer to in mechatronics today.

Wind power and water power gave way in the 1800’s to steam power as the improved steam engine of Watt became the standard of energy efficiency, or should I say “cost effectiveness”.  Because the absolute value of technology is in its cost effectiveness.

Still, wind energy poses a huge technology challenge, as witnessed by the number of vairations that exist and new versions that are emerging.  And hopefully improvements will continue to come from the creativity and  imagination of engineers and inventors all over the world.

But what are the other big mechatronic challenges that come to mind?

Transportation certainly ranks in the top 10.  We have seen hydraulic, pneumatic and electric vehicle solutions touted for a variety of uses, personal transport, delivery vehicles etc.  Ballard Energy and General Motors have both been building hybrid and pure electric buses for city transportation systems for several years with some success.  Interestingly, the electric bus is easier to engineer, which seems unreasonable, but the bus has more interior space to put things like batteries and a methanol converter for generating hydrogen for fuel cells.

But there is a great lesson in what appears to be an almost chaotic string of choices in the transportation arena.  One solution will not work for all requirements.  There are many people for whom a 40 mile per day drive cycle is perfect.  The NEV, Neighborhhod Electric Vehicle, is a golf cart type solution that is rated for street usage, and because of its relatively simple performance requirements, is relatively easy to achieve and lowe cost.  As we categorize cars with greater range, the problems get more difficult, and because of the storage limitations of batteries, have only been achievable as hybrids.  But with some hybrid designs reaching 50 and 60 mpg (estimated), these vehicles may be great solutions for other users.  Although, we must consider their cost effectiveness.  If they cannot be introduced at prices well below $50,000 the absolute value of the technology is not very good.

So forget the 15 second soundbyte that will solve the world’s problems.  It doesn’t presently exist.

I would like to hear from any readers about their picks for the Top Ten Mechatronic Challenge.

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