Motion, Measurement and Control

Motion control is all about control.  But you cannot control what you cannot measure.  So there is an important measurement component to the control of moving systems.  The difficulty lies in knowing what to measure, how to measure and what to do about things you can’t measure.

The obvious thing to measure is motor speed.  That part is easy.  Servo motors have built in feedback devices. In the old days, the preferred feedback device was a small generator that produced a voltage proportional to the speed.  In the digital age feedback is by quadrature encoder that outputs a digital pulse that is primarily used for position control.  Most control systems are able to easily integrate the pulse train to derive the speed of the motor.

Unfortunately, most applications require relatively low speed.  Most motors are engineered for high speed.  This is in an effort to package more work related power in a smaller physical package.  Often, the motor is connected by pulleys or gear reducers to get the speed of the motor to more closely match the desired speed of the load.

Some of the important attributes of motion cannot be easily measured.  In addition to speed, torque is extremely important to controlling motion.  Torque can be measured directly from the drive electronics, but this is rarely used for control.

Torque and current are direct equivalents with a slight variation due to the temperature of the motor winding. As the temperature of the motor goes up, the resistance goes up and the current required goes up at the same time.  Since high performance motors have fairly high internal temperatures, this swing can be in excess of 100 degrees centigrade, and should be considered in the control scheme.

Most of the emphasis on current control is in terms of protecting the motor and drive electronics.  The first derivative of current over time  is the limiting parameter of the power electronic devices and is an important boundary condition in safe operation of the electronics.

More important information can be derived by considering the region of the motion profile and the current or torque requirements that are presented.  In order to accelerate a load, a lot of current is needed to overcome the mass of the load.  But once the load is moving the torque requirement drops off.  This creates an opportunity to profile the current requirement while using the conventional error detection scheme of the traditional control.

Other variable that are part of the mechanical system are things like momentum and center of mass.  In multi-axis mechanisms, there is usually a dependency of one axis upon another.  The idea that the mass of one axis is changing it’s center of mass and momentum with respect to the other axis is generally ignored.  This too is an opportunity to gain increased stability in the control and possibly improve throughput by having a better model of the application from which to create the ideal control.

Looks to me like there is a lot of room for improvement.  Let me know if you agree or disagree.

Japan, Nuclear Power, Real Challenges

The earthquake in Japan brings us face to face with another challenge to the engineering community.  The earthquake is certainly a disaster, and we hope and pray that the loss of life in Japan will be small.  But the emerging crisis of radiation leaking from nuclear powerplants that have been damaged by the quake and tsunami waves are pause for serious reflection about the future of energy.

The damage is the result of natural forces that are beyond the ability of designers to engineer against.  And how we take heed of these events, or even if we take heed, may be the real measure of progress in western civilization.  The future of nuclear power plants is going to have include choices and alternative technology.

A nuclear power plant is a complex system, mostly controlled by technology from the process industry because it creates steam to drive a turbine which turns a generator.  The generator is a classic electric motor run in reverse to create electricity from torque.  So there is mechatronic technology involved in the process itself.

Even more mechatronics content is involved in the creation of the fuel and the operation of the control rods in water cooled reactors.  Robots are also frequently used in the processing of the fuel into the final shape for use in a reactor.

But the bigger question is what are the technology choices for nuclear power generated electricity that can survive the forces of natural disasters?  Interestingly, there are a number of mini reactor technologies that because of their small size, are much more likely to withstand the forces of nature.  Just Google mini nuclear reactors and you will find pages of information.  And discussions of numerous technologies that are competing for use in the power industry.

Large water cooled reactor have been producing electricity for 40 years or more.  But these designs are massive and susceptible to failure when the water flow is interrupted.  Which is what we have going on in Japan.

There are wave reactors, Thorium reactors, small water cooled designs and pebble bed reactors.  Each technology working its way through the torturous process of qualification for use by federal regulators.

Some of the technology is unproven and controversial.  But since I have seen the pebble bed reactor demonstrated, for me this is a leading edge technology.  The pebble fuel is a small .5mm diameter pebble of uranium contained in layers of graphite and ceramic.  By spacing the fuel apart in small bits, it cannot reach thermal runaway, and in fact, using helium coolant, the system can reach thermal equilibrium at 800 degrees.  Since the ceramic insulator is designed to withstand temperatures of 3000 degrees, there is little chance of the fuel melting the insulator and creating a runaway chain reaction.  Safe, small.  The American Nuclear Regulatory Commission attended a demonstration of this technology years ago.  I saw the video.

So the question is, when are we going to see some progress?  At the rate our government chooses to do things, it will take years.  At the risk of being redundant, providing electricity shouldn’t be about politics, it should be about free markets, and doing things right.  If the electric power industry is going to be regulated by politicians, then politicians need to be doing the people’s business and getting it done.

Re-Manufacturing the USA

For about 20 years that I can remember most candidates for the Presidency of the United States have disrespected manufacturing.  Most people who are running for the office of President don’t have manufacturing in their background.  So it shouldn’t be a surprise that after years of manufacturing being attacked from a political standpont that we have a huge decline in the manufacturing base of the American economy.  Yes, there are certainly other factors at work here, but our political perspective is one among many which need correction.

Since the Second World War, manufacturing employment has dropped steadily from 33% of all employment to about 10% of all employment.  What is really interesting about this trend is that the total output of manufactured goods has remained roughly constant.  What accounts for this is increasing productivity.  And in recent years a lot of that productivity has been from automation.

The same Department of Commerce research shows agricultural employment, typically a very high labor area, dropping from 33% to 2-1/2% from the turn of the century, 1900′s, to the present.  And similarly, agricultural output in the US has remained constant.  The main force behind the reduction in labor has been the mechanization of agriculture, or as I would like to refer to it, the “mechatronic-ization” of agriculture, if that doesn’t butcher the English language too severely.

Mechatronics is that elastic term that takes into account so many disparate technologies.  Putting a hydraulic system on a power take off from the gasoline engine on a tractor in order to power a variety of farm implements is mechatronics at its finest.  And the dawn of factory robotics in the 1980′s has lead to production welding robots that cost less than $50,000.  So people are being freed from some of the more repetitive tasks required at the factory level, and, I suppose, being replaced by automation.

The dilemma becomes, how do we create new jobs.  Many people believe that the “Green Revolution” will create a lot of new employment.  Personally, and after much review of industry studies, there are jobs there, but not enough to turn the economy around anytime soon.  And frankly, most of the green power generation technologies have failed to meet their economic burdens, so it’s a work in progress.

On the other hand, the same ingenuity that led to robots on the assembly line in Detroit has also provided us with 3D solid printers that produce very high quality parts in small batches at very low cost.  Another mechatronic triumph.  Three axes of stepping motors using belt drives and rod bearings to move a print head in 3D that dispenses a variety of hot melt plastic materials into solid shapes following a computer program for a 3D part.

This technology drastically reduces the major hurdle of new product development, which is the cost of prototyping.  Hmmm.  Sounds like an opportunity.  And it is.

So maybe the key to increasing employment is new solutions to old problems.  Reinventing the means of production in every industry should be a powerful stimulus to innovation, invention and economic growth.  Let’s hope so.

Landcrawler Robot Wobbles But Doesn’t Fall

This funny lookin’ fella weighs just 27 pounds, has 12 legs, and can carry you around on its back if you let it.

The Land Crawler xTreme robot offers its master a ride on top of  its square platform top, provided you don’t weigh more than 175 pounds. As it ambles around, it definitely doesn’t look like the smoothest or speediest way to get around the place, but it sure has got plenty of style doing it.

Funny thing is the maker of the robot says he made the Land Crawler eXtreme as a toy for his 2-year old son because he told him that he wanted to ride on a robot. Why couldn’t we all have dads who were that handy with robotics?

technabob.com

Universal Gripper Utilizes Coffee Bean-Filled Balloon

Gripping and holding of objects are key tasks for robotic manipulators. The development of universal grippers able to pick up unfamiliar objects of widely varying shape and surface properties remains, however, challenging. Most current designs are based on the multifingered hand, but this approach introduces hardware and software complexities. These include large numbers of controllable joints, the need for force sensing if objects are to be handled securely without crushing them, and the computational overhead to decide how much stress each finger should apply and where.

Here we find a completely different approach to a universal gripper. Individual fingers are replaced by a single mass of granular material that, when pressed onto a target object, flows around it and conforms to its shape. Upon application of a vacuum the granular material contracts and hardens quickly to pinch and hold the object without requiring sensory feedback.  The volume changes less than 0.5% suffice to grip objects reliably and hold them with forces exceeding many times their weight.

The universal gripper utilizes ground coffee beans inside of a balloon.  The coffee beans offer an interlocking grain that proved better than other materials tested that ranged from sand to ground rubber tires.

The Universal Gripper uses ground coffee beans inside of a balloon

Veiw full photo gallery here

The operating principle is the ability of granular materials to transition between an unjammed, deformable state and a jammed state with solid-like rigidity. They delineate three separate mechanisms, friction, suction, and interlocking, that contribute to the gripping force. Using a simple model we relate each of them to the mechanical strength of the jammed state. This advance opens up new possibilities for the design of simple, yet highly adaptive systems that excel at fast gripping of complex objects.

Universal Gripper Demonstration

Universal Gripper Pouring Water

www.pnas.org

Clean Room, Clean Robot

The consumer electronics market is expected to generate over $165 billion in revenue within the U.S. in 2010, thanks to cell phones, laptops, digital cameras, DVRs, and MP3 players. The sensitive components such devices contain require precise handling during manufacturing. The consumer electronic supply chain with its clean room requirements is growing and clean room robotics will play a key part in this growth. Following is a quick guide to all things clean when it comes to robots.

Clean rooms are classified according to the number and size of the particles permitted per volume of air. For example, a Class 10 clean room denotes that no more than ten particles of 0.5 µm or larger and zero particles of 5.0 or larger are permitted per square foot of air. Contaminants come from people, process, facilities, and equipment. In order to control contaminants that are invisible to the human eye, the manufacturing cell and in many cases the entire room must be controlled. Robots used in this environment must meet stringent clean room certification requirements to prevent them for acting as a source of contamination.

Much of the hardware used in a clean room robot is the same as any other robot with the important exception of a combination of sealed covers to prevent particles from escaping the robot, stainless steel hardware, proper non-gassing lubricants and vacuum to evacuate any internally generated particles. Robots for clean room processes have special considerations for harnesses, . . . “which can be a serious particulate generator and a major design challenge for clean applications,” said Scott Klimczak president of CHAD Industries, a pioneer in the area of wafer and substrate handling WLP I (Wafer Level Packaging) applications.

As a matter of practice, materials prone to particle generation are substituted or coated to eliminate the potential for contamination.

Certification is done by counting the number of particles generated when the robot is in motion. For this process the industry uses particle counters that are calibrated to meet or exceed the standards set by NIST (National Institute of Standards and Technology). In addition to NIST traceable practices, other standards of particle counter calibration include Japanese Industrial Standard (JIS) B 9921, Light Scattering Automatic Particle Counter, and ASTM F 328-98, Standard Practice for Calibration of an Airborne Particle Counter Using Monodisperse Particles. Adept Technology, Inc. a leading manufacturer of clean room robots tests robots both internally and through third party testing and certification to ensure integrators and end-users deploy their equipment appropriately to meet manufacturing cleanliness requirements.

There are two accepted clean room specifications, the ISO 14644-1 spec and the Fed 209E spec.

Depending on the cell design and the robot style selected, a lower class robot may be used and still meet the overall system requirements if the system is designed appropriately. For example, for a semiconductor wafer application, if a robot can operate under the wafer with a vertical laminar flow of clean air present sweeping the particles away from the product, the ultimate requirement for the robot may be less stringent.

Installing the clean room robot requires attention to cleanliness. “Robots built for Class 1 environments are wrapped in several layers to protect them as they are shipped to the site,” said Kevin Lonie, application sales manager for Clear Automation, a Connecticut based automation integrator specializing in the design, engineering, fabrication and installation of integrated robotic and machine vision systems. “Then at the site the equipment is moved through progressively cleaner spaces as the wrapping is wiped down and finally removed before entering its ultimate clean room destination.”

Once wiped down with clean room wipes to remove any foreign particles, it is a good practice to connect the robot to the plant’s vacuum system and evacuate the robot for several hours to make sure all particles are purged completely.

www.adept.com

Iron Man Suit Becoming A Reality

Raytheon’s second-generation exoskeleton (XOS 2), essentially a wearable robotics suit, was unveiled for the first time recently during an event at the company’s Salt Lake City research facility. XOS 2 is lighter, stronger and faster than its predecessor, yet it uses 50 percent less power, and its new design makes it more resistant to the environment.

View a full photo gallery here

The wearable robotics suit is being designed to help with the many logistics challenges faced by the military both in and out of theater. Repetitive heavy lifting can lead to injuries, orthopedic injuries in particular. The XOS 2 does the lifting for its operator, reducing both strain and exertion. It also does the work faster. One operator in an exoskeleton suit can do the work of two to three soldiers. Deploying exoskeletons would allow military personnel to be reassigned to more strategic tasks. The suit is built from a combination of structures, sensors, actuators and controllers, and it is powered by high pressure hydraulics.

Representatives from Paramount Home Entertainment, including the actor Clark Gregg (aka Agent Phil Coulson of the Marvel® Movie franchise) were in attendance to capture footage of XOS 2 to include in a video that’s being produced to support the release of Iron Man® 2 on DVD and Blu ray.

www.raytheon.com

Festo Turns An Elephant’s Trunk Into A Robotic Arm

Smart engineers copy ideas. Great engineers copy nature. Festo’s Bionic Handling Assistant is a robot arm modeled on an elephant’s trunk (or Dr. Octavius if you’re a Spiderman fan), and it has all the supple flexibility of the original. Using hollow plastic chambers that change size with air pressure, the Bionic Handling Assistant can move through an incredible range of motion in three dimensions. It’s designed to provide gentle forces, and to give when pushed, making it safe for working with humans in a working environment.

The Bionic Handling Assistant was developed through Festo’s Bionic Learning Network, a coordinated group of industrial and academic research partners interested in bringing nature inspired concepts to robotics.  However, all this biology inspired innovation is really only going to be useful if we can find the right applications. Opportunities for the Bionic Handling Assistant in medicine, manufacturing, and mechanical repair are shown below.

For a better idea of how the pressurized air allows the Bionic Handling Assistant to move, here’s a more detailed animation of the robot arm:

No matter where it eventually is applied, the Bionic Handling Assistant is a good sign that engineers have a lot to work with when mimicking natural structures. With all the humanoid robots running shuffling around it’s important to remember that the primate form is only one of many successful architectures we should be copying. Robots that swim like fish, fly like insects, and form colonies like bees could all have crucial applications in the years ahead as we continue to explore the world. It will be interesting to see which animals the Festo Bionic Learning Network pursues next.

www.festo.com

EPSON Expands RS-Series High Performance SCARA Plus Robot Lineup

EPSON Robots has added to their Power of Choice initiative by introducing the NEW RS4 to the RS-Series High Performance SCARA Plus robot lineup.

The new work space design of the RS4 robot provides a pallet size of 778mm x 778mm. A pallet size this large would normally requre a SCARA arm which is more than double the size. Imagine now being able to use a 550mm arm for applications that used to require a much larger 1,200mm arm.

The EPSON RS4 robot offers these features that differentiate it from other SCARA robots available on the market today:

* Industry Leading Work Envelope Usage
* No Lost Space in Center of Work Envelope
* Superior Cycle Throughput
* Zero Footprint Robot
* 450 Degrees Axis Rotation
* Exceptional Flexibility

EPSON Robots
www.robots.epson.com

Biotech Wizards Engineer Electronic Skin

Biotech wizards have engineered electronic skin that can sense touch, in a major step towards next-generation robotics and prosthetic limbs.

The lab-tested material responds to almost the same pressures as human skin and with the same speed, they reported in the British journal Nature Materials.

Important hurdles remain but the exploit is an advance towards replacing today’s clumsy robots and artificial arms with smarter, touch-sensitive upgrades, they believe.

The “e-skin” made by Javey’s team comprises a matrix of nanowires made of germanium and silicon rolled onto a sticky polyimide film.

The team then laid nano-scale transistors on top, followed by a flexible, pressure-sensitive rubber. The prototype, measuring 49 square centimetres (7.6 square inches), can detect pressure ranging from 0 to 15 kilopascals, comparable to the force used for such daily activities as typing on a keyboard or holding an object.

A different approach was taken by a team led by Zhenan Bao, a Chinese-born associate professor at Stanford University in California who has gained a reputation as one of the top women chemists in the United States.

Their approach was to use a rubber film that changes thickness due to pressure, and employs capacitors, integrated into the material, to measure the difference. It cannot be stretched, though.

The achievements are “important milestones” in artificial intelligence, commented John Boland, a nanoscientist at Trinity College Dublin, Ireland, who hailed in particular the use of low-cost processing components.

In the search to substitute the human senses with electronics, good substitutes now exist for sight and sound, but lag for smell and taste.

Touch, though, is widely acknowledged to be the biggest obstacle.

Even routine daily actions, such as brushing one’s teeth, turning the pages of a newspaper or dressing a small child would easily defeat today’s robots.

Bao added important caveats about the challenges ahead.

One is about improving the new sensors. They respond to constant pressure, whereas in human skin more complex sensations are possible.

This is because the pressure-sensing cells in the skin can send different frequencies of signal — for instance, when we feel something painful or sharp, the frequency increases, alerting us to the threat.

In addition, Bao warned, “connecting the artificial skin with the human nerve system will be a very challenging task”.

“Ultimately, in the very distant future, we would like to make a skin which performs really like human skin and to be able to connect it to nerve cells on the arm and thus restore sensation.

“Initially, the prototype that we envision would be more like a handheld device, or maybe a device that connects to other parts of the body that have skin sensation.

“The device would generate a pulse that would stimulate other parts of the skin, giving the kind of signal ‘my (artificial) hand is touching something’, for instance.”

In the future, artificial skin could be studded with sensors that respond to chemicals, biological agents, temperature, humidity, radioactivity or pollutants.

berkeley.edu



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