control of pneumatic actuators

Our team has little experience with pneumatics, and we want to get some during the off season. We would like to use a pneumatic actuator in situations where electric motors are too slow, not strong enough.

But is it possible to move an arm, for instance, to intermediate positions like you can with an electric motor? Or does it have to be all the way up, all the way down.

If intermediate positions are possible, can there be a continuous range? What type of control systems do you need?

Any advice about this would be much appreciated. Any links that would be helpful?

For nearly all intents and purposes, pneumatic cylinders are a binary mechanism. They are either fully extended or fully retracted.

Take a look through the Bimba catalog. There are lots of different kinds of actuators. I rarely see FRC robots use the cool stuff Bimba has.

Rotary style actuators use pneumatics to give high torque applications in a simple to use small package. You can select the degree of travel and number of positions. Way simpler that a motor, transmission, speed controller, limit switches and a sensor and code to operate.

Rod less style cylinders give travel with half the length of a typical cylinder. There are also position feedback cylinders that use magnetics to sense position. If you had a design I’m sure one of the Bimba controls engineers would talk with you.

Do a search in CD-Media on keyword “pneumatics”, and you will find a couple of papers on continuously variable positioning for pneumatics.

Thanks all for your help.
I have downloaded the two papers and will look at them shortly. And I’ll check with Bimba.
As usual, FIRST teams have the answer.l

Be aware that FIRST limits the types of valves you are allowed to use in your pneumatic system, which in effect limits the flow rate. You are also limited to 60 PSI working pressure. The intent seems to be to limit the speed and force of some types of cylinders for safety reasons. Real industrial pneumatic systems are capable of very fast operation, but do not expect to get similar speeds from a FIRST legal system.

Pneumatic cylinders are not practical to use intermediate positions but you can gang two or more together and on the same element to get one or more intermediate positions. I believe there may be two position cylinders in the Bimba line up but in either case you need two control valves to have two positions. The advantage of pneumatics is they are very fast, have lots of power and very reliable.

You CAN hold intermediate positions with pneumatics. You just need the right kind of valve.

You need a “5 port, 3 position Center Closed” valve. This type of valve can shut off both ports and holds the current position indefinitely using NO POWER - something motors can’t do …

The types of valves we normally use in FRC are 5 port 2 position valves - they don’t have the 3rd closed position so yes, they are “binary.”

In conjunction with the center-closed valves, limit switches can be used to detect how far the cylinder has extended. Bimba makes a strap-on reed switch for their magnetic plunger series of cylinders. If you haven’t got your KoP cylinders from them yet, just specify those styles for your testing.

A thorough exploration of either Bimba’s or Festo’s catalogs is indeed an off-season exercise. You think AP Calc is hard? navigation of some of the suppliers’ offerings rivals it.