Pneumatic Cylinders 2

[JasonCarter]

need some help with pneumatics cyliders, I've got a pneumatics cylinder with a stroke of 500mm and need to lower a piece of material in 10 stages, so this means first stage it needs to be lowered 50mm and then without going back to its original position lower it another 50mm and so forth till its lowered 500mm. Any help will be much appreciated. It doesn't have to be with pneumatics any other suggestions will help.

Thanks

 

[zdas04]

If the travel is VERY smooth (i.e., coefficient of static friction is near zero), then you could calculate the mass that would have to be added to hold the pressure constant for the increased volume using the ideal gas law. I don't think that it will be terribly precise (because the coefficient of static friction is not zero), but you could eet it up to be close.

David

 

[gerhardl]

The final solution will have to be selected according to needed accuracy and stability, weight and forces necessary.

Some air pneumatic cylinders can be eqipped with a magnetic material strip attaced to the piston ring. Normally you will use this to detect lower and upper end position with outside mounted and adjustable proximity limit switches. As for instance used for piston cylinders to operate knife-gate valves.

It is also common to use such solutions together with a PLS (programmable logic steering unit).

A suggested solution could be a combination consisting of your pneumatic cylinder, proximity switches for end positions and your steps (switches either directly on cylinder or mounted on strokeside to react on proximity of 'metal flag' mounted on load, piston end or holding device) PLS and a 5/3- way solenoid valve to open/close or hold according to signals from switches and program.

If you do not need an automated operation the 5/3 way solenoid valve should be/is of type with two solenoids: current to solenoid one to move cylinder one way, current to solenoid two opposite way, and mid position (no current) to lock all ports as is (lock to existing position)

You can then hand operate current to solenoid with limit switches arranged to give you visual signals, for instance LED lights.

Throttle valves will let you adjust air in and out and slow down the movement. Seek advice on this from solenoid supplier because some 5/3 valves needs a a certain minimum pressure difference to operate properly and may lock if unsuitable throtteled.

An pure electrical solution would be slower but much more precise. A multiturn actuator for valves with rising stem could probably be used without alterations, but limit switches must be arranged or intergrated. Watch out for limits on allowed operation/running time per time unit for electrical actuators!

 

[gerhardl]

Addition to above answer: with an electrical actuator you have the additional possibillity to program running on/off time and hence give the ten stages without limitswitches or other outside detection. (Only the normal to signals for fully extended and fully retracted needed)

 

[JavaMoose]

Take a look at the linear glass scales used on machining equipment for Digital Read Out systems. A scale, with a properly designed mount to the cylinder/shaft, could give you more precision than you could want (.0001" easily) and give you a signal that you could feed to your valve control system. This way the system would always know the position of the shaft.

As far as the valve, I would use a stepper/servo controlled needle valve.

That should get you started...