Hydraulic Motion Control

[Metstamper]

I am in the metal fabricating business and have been using a pneumatically assisted hydraulic cylinder for a stamping trimming operation. This cylinder has about 1/2 ton of pressure with a 4" stroke and can be set to a rapid advance and then slows for the final 1/4" of stroke. I would like to convert this system to a hydraulics. The existing cylinder often needs to be rebuilt as its oil sight glass is plastic and the oil deteriorates the seal resulting in leakage, the controls are difficult to set up for different jobs and the nnedle valve for speed control is very delicate and wears out rapidly. I am new to this sight and would appreciate some advice on how to begin this conversion process. Also, I would love to learn how to program and implement a plc controller for this purpose.
Many Thanks

 

[Peter Nachtwey]

The first thing is the specifications. How fast, how accurate and how much can it cost.
On the low end you can use bang-bang valves. This wouldn't be that much better than what you already have. On the high end you can use a servo quality valve with MDT feed back and a hydraulic motion controller. Then you can program the motion control to handle many different parts.

For a servo system:
The cylinder rod would need to be gun drilled so that a Temposonic or Balluff SSI transducer can be used for feedback. An accumulator should be added to keep the supply pressure constant. The servo quality valves should be mounted on the cylinder with NO hose between the valve and the cylinder.
The big thing is getting the hydraulic design right, then the tuning and programming will be easy.

One place where production can be gained is that the stamping machine can be lifted just high enough to clear the parts so the cycle time is reduces or the required speed is reduced. The closed loop control and programming will allow for quick and consistent transitions between parts.

PLCs are not fast enough to control hydraulic cylinders directly. You should get a hydraulic motion controller that can close the loop internally and has the motion profiles programmed in. In many cases a PLC isn't even required because the hydraulic motion controller is faster, easier to program and has better diagnostics than the PLC.

 

[shooter]

why a sight glass?
try to keep any side forces away from piston.
if using a parralleogram construction the speed is different.
hydraulic is expensive.

 

[baldone]

Depending on the app and force requirements you might be able to use a servo controlled high force linear actuator and get rid of both the hydraulics and pneumatics.

Exlar has several models that go over 10k lbs of force and you can get whatever servo motor/drive package you want.

I usually use Yaskawa motors/drives/motion controllers and have had good luck with this combo.

http://exlar.com/product/gsx-series/

 

[shooter]

yeah 500 kg can be done with a flywheel and a small motor.