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Can Pneumatics Play a Bigger Role in Mechatronics Designs?

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warren@fourward.com
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Re: Pneumatics
warren@fourward.com   7/18/2012 12:19:57 PM
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A lot of us would like to learn what you have learned.  Is there a way to break into the pneumatics gig?  I would like to be able to counsel your engineers in the ways of the wind.

ttemple
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Re: Pneumatics
ttemple   7/18/2012 1:46:44 PM
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Unfortunately, for me it was baptism by fire, the school of bumps and hard knocks, etc.  My normal role was the controls programmer, trying to get things to work, which forced me to learn.

If there are vendors in your area that sell pneumatic components, I would contact them.  They usually have demo equipment, and might put on training sessions.  I think you really have to get your hands on the hardware to get a feel for things.  It is especially interesting to create situations where the actuators are undersized for the load.  You can really see the effect of air as a compressible fluid.

Jon Titus
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No Pneumatics for Positioning Systems
Jon Titus   7/18/2012 2:17:08 PM
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I wouldn't use pneumatic devices for precise positioning, but for devices such as actuators and grabbers they seem to work well.  If you have a positioner that moves from one limit to another, pneumatics might do the job quite well. 

akili
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Re: Pneumatics
akili   7/18/2012 4:31:03 PM
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An advantage of air being compressible is that provided you use sensible size actuators that give enough force to work but are not over-sized, accidental collisions or foul-ups need not cause serious damage.  I'm not recommending frequent foul-ups but they'll happen sooner or later if an operator loads something incorrectly or a work-piece falls out of a gripper.  Foul-ups with hydraulics usually end in tears before bed-time.  I have also seen buckled lead-screws from even quite modest servo positioners where torque limits haven't been set correctly.

Charles Murray
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Re: Pneumatics
Charles Murray   7/18/2012 6:18:43 PM
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Al, what's the best positioning resolution a servopneumatics system can get these days? You mention that servopneumatics isn't being used in high-precision applications. Is that because they can't get the resolution or is it because the resolution is too costly?

apresher
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Pneumatics
apresher   7/19/2012 8:59:44 AM
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Chuck, During the interviews for an article I did on servopneumatics last year, the parameters they used to describe the applications for the technology is where high precision and positioning accuracy (<0.2 mm) is NOT required.  Not sure how they would answer the resolution question. They also identified a good application fit for servopneumatic axes when there is a need to move large loads continuously (24/7 or high duty cycle operation), positioning systems operating on a low voltage, or solutions with space constraints requiring high feed forces and high dynamics. Hope that helps.

apresher
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Pneumatics
apresher   7/19/2012 9:01:55 AM
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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.

mrdon
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Re: Pneumatics
mrdon   7/22/2012 6:18:40 PM
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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.

ttemple
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Re: Pneumatics
ttemple   7/23/2012 9:05:04 AM
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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.

Charles Murray
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Re: Pneumatics
Charles Murray   7/23/2012 9:21:13 PM
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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.

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