I never learned about pneumatic devices in college, and I never used them in any type of equipment. But they offer interesting alternatives to hydraulic and electronic devices. In sensitive equipment, the use of clean air eliminates problems from a hydraulic-fluid leak, or a short circuit from a broken wire or faulty connection. Air comes in an endless supply, and it seems fairly simple to route it to just about anywhere we need it. If oxygen could create a problem, pneumatic equipment could use an inert gas.
I have seen rotary and linear-slide positioners and two-jaw pneumatic grippers in pick-and-place equipment used to assemble electronic and electromechanical equipment. Pneumatic devices require maintenance, but they don't burn out. They don't dissipate energy (except from a bit of friction). Pressure regulators and fittings are off-the-shelf items, and designers don't face RFI or EMI issues with air lines. Granted, a pneumatic system requires a compressor or source of pressurized gas, valves (probably electric), and some sort of electronic controller.
Where can engineers learn about pneumatic controls and devices? I looked at the undergraduate course offerings at three engineering universities and found nothing that relates to pneumatics except for courses on the theory of compressible fluids. So it might seem like it's anyone's guess where engineers pick up the knowledge to apply pneumatics.
The National Fluid Power Association Website includes a section titled, "What is pneumatics?" It includes information about pneumatics applications, fundamentals, training, and resources. A link on this page goes to a list of companies that offer training and additional information.
The International Fluid Power Society provides an extensive list of books and certification materials. It also certifies fluid-power technicians and engineers at several levels.
Parker-Hannifin Co. has an extensive training program. Look under "Technology Training."
Matrix Multimedia, a company in the UK, will soon have a pneumatics trainer and educational materials with the brand name Airways. This product line comprises about 100 rugged pneumatic components that mount on a stable aluminum platform. Each component has a label with the corresponding industry-standard pneumatic or electrical symbol. Students take the rugged components, mount them to the platform using plastic "t" bolts, and connect the components with nylon tubing to build working pneumatic circuits. They then use the curriculum provided to carry out experiments in pneumatic and electronic control. Sounds like a cool way to start.
You could play hockey with a chop stick too. Maybe you'd do so to handicap a much less capable opponent? But it's a false analogy to the pneumatic - electric - (hydraulic) debate.
In applications with high cycle rates and high masses, pneumatic servos can be 25% the cost of a linear motor solution, and 30-50% of the cost of an electromechanical solution - while requiring less space.
For many applications that require a combination of controlled, rapid translation (12" in 100ms) coupled with a high force joining operation (think resistance welding, hot melt, etc.), servo pneumatics again has a similar big cost advantage.
Generally speaking, if you look into many of the positioning, general automation applications in packaging and similar industries, you can replace a linear electric axis with servo pneumatics with the benefit of 50% less installation cost, and a 50% increase in cycle rates.
I would compare moving a load with air to using a rubber bat to play baseball, or a rubber stick to play hockey. You could do it, but why would you? ("Because I can" is not a good reason.)
What are the selling points for such a system?
If the system is not exponentially less expensive to purchase and operate, I don't see the advantage. I doubt if the systems are much less expensive to purchase than a comparable electric solution, and I seriously doubt whether the operation cost is lower, when the cost of clean compressed air is factored in. Then have one incident where the dryer floods the air line with contamination and see what the cost of repair is.
For explosive environments I can concede that air is compelling. Otherwise, I don't get it, and I wouldn't design it in over an electric servo system.
For grippers, clamping cylinders, and a host of other short stroke, bang-bang actuators, I'm all for pneunatics. It is also great for certain counterbalancing systems. I just don't see it for positioning systems.
I/we mostly deal with hydraulics. Pneumatic servo control is a very small part of our business because there are usually better solution. However, we use pneumatics as a means of testing hydraulic algorithms. If one can control pneumatics the hydraulics and servo motors are even easier.
Here is an example of what can be done.
http://deltamotion.com/peter/Videos/PneuMove.mp4
You may need to download the mp4 file before viewing depenind on your browser.
We have controlled pneumatics in some low pressure testing applicaitons.
Besides the energy lost in compressing and decompressing air the second problem is that feedback devices are still needed and the controller can't be a simple cheap PID controller. It takes some complicated math to do the control shown and this isn't cheap. For small jobs little linear motors are tough to beat.
It sounds as if you've had a frustrating experience with a poorly designed pneumatic servo system.
Modern, well designed systems are able to rapidly position heavy vertical loads without overshoot, without high levels of valve control activity, and to high levels of repeatability. The 0.005" accuracy you mentioned is readily achievable in many systems.
Thanks, Al. One more question for you: Do you have any idea what percentage of oneumatics systems today are servo? I would imagine the percentage is very small.
The last pneumatic positioner I worked on was in a vertical orientation, which created additional challenges for the actuator. The systems I have worked on used "magnetostrictive" position feedback ("Temposonics" would be one trade name). This feedback system is based upon timing pulses transmitted down a rod that get reflected back by a magnetic ring, or something like that. The time is converted to an analog output of some resolution. The resolution doesn't change as the length of the transducer gets longer, so the system resolution is typically affected by the transducer length.
The controls on this system were essentially analog in nature, comparing setpoints to the transducer position, and throttling air valves to try to keep the actuator in the correct position, and move it to new positions, etc.
The end result was less than what I would have desired (Fortunately I didn't pick the equipment, I was just called on to get it to work.). There was a tendency to overshoot significantly (large fractions of inches at least), especially when moving down. I don't know what the final position tolerance was, but it was not comparable to an electric servo actuator. It is also relatively noisy, due to the air valves constantly fighting with each other to try to position the load. I couldn't help but think that there would soon be a mechanical failure in the valves because of the frequency of the switching, etc.
Having worked with literally hundreds of servo systems of many different flavors, and a small number of pneumatic positioners (less than 10 probably), I would favor an electric solution unless there is some overwhelming reason to not use electric (explosive environment?).
Under ideal circumstances pneumatic positioners talk about 0.005" positioning resolution. That might be achievable under some circumstances, but if I were designing the system, I would be thinking a quarter of an inch and designing in energy absorbers and positive stops at the desired stopping points.
As a general substitution for this type of actuator, I would favor the belt drive style slides offered by a number of vendors. They offer high speed capability in a similar form factor, and the precision of a completely digitally controlled electric servo system.
Pneumatics is becoming an important component in the field of Mechatronics for efficiency and motion control precision. Festo is a leader in pneumatic based robotics with their gripper and arm products. I remember taking a Pneumatics class at community college back in the early 80s. I didn't see the importance of this class because of my fascination with electronics. I which more emphasis on system integration was discussed in class as it relates to Mechatronics, maybe I would have considered working for engineering companies like Festo who makes great and cool pneumatics based robots instead of just electronic/semiconductor jobs.
Chuck, Forgot the second part of your question. I don't think pneumatics is too costly. The precision limits are a reflection of the underlying technology, especially when compared to electromechanical solutions which can achieve very high precision, resolution and repeatable accuracy.
The Machinist Calc Pro computes speeds and feed rates for milling, turning, and drilling: cutting speed, spindle speed, feed rate (inches/minute), cutting feed, etc.
During a recent meeting with engineering-school faculty and alumni, Contributing Technical Editor Jon Titus talked about whether colleges should educate generalists or specialists. What do you think?
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