proportional hyd valve

can any give me a sample on how to write a program so the my temposonic readout in my cylinder tells my valve to stop the cyl. there and keep it there until the next imput. we tried using math (less than or = to) even though we slowed it down it justs blows right past the number we are looking for

Yep, that less than or equal too stuff doesn't work. You need a PID and then a way of ramping the target position/set point from where the actuator is to where you want it to be. There is a lot of math involved.

Back in the dark ages we used ramping tables. The error was used to index into a table and that value was used to generate an output. If you are already doing that and the actuator still over shoot you have a slow PLC or your ramps are too steep.

What is the application?

Why don't you get a hydraulic motion controller?

What Peter said would be the easiest and most accurate. We have many applications using Hydraulic servos with Delta RMC75 with Horner Mini OCS.

It is posible to do this with a PLC but to do it well is not a trivial task and the PLC will never match the performance/response of a dedicated motion controller.

To do it very crudely you could make it proprtional only:
By varying the gain and the clamps you alter the proportional band and the maximum velocity. This is a very crude method and will never reach the actual setpoint position. This may be all you require for your application.

If you require anything more sophisticated then I suggest that you speak to Delta Motion. If you still want to do it in a PLC then here are few things to think about:

Make a virtual master to generate a position setpoint; this must ramp up and down producing a position setpoint and a velocity demand.

The servo valve will need to be profiled in the software (non-linear) so that the velocity demand can be used to generate a valve command that generates approximately the correct velocity of the axis.

Make a PID function based on the demand position from the virtual master and the actual position from your cylinder then sum the PID output with the predicted valve command to correct the position error.

I should also add that you will need a fast PLC and fast I/O with response times < 5mS to make a decent job of it.

Good luck,

Nick

just by a servo valve with input -10/+10 Volt
or if that is to costly use two valves one with full flow and another when you are close to target.

manglemender said:

Make a virtual master to generate a position setpoint; this must ramp up and down producing a position setpoint and a velocity demand.

Click to expand...

Depending on what you want to do, this can be quite complicated. If you know what you are doing the clamp idea is good enough for point to point moves.

manglemender said:

Make a virtual master to generate a position setpoint; this must ramp up and down producing a position setpoint and a velocity demand.

Click to expand...

Servo quality proportional valves and servo valves should be pretty linear already by definition but some are more linear than others. What you want to avoid are valves that have terms like closed center, dead band, dual gain or curvi-linear.

shooter said:

just by a servo valve with input -10/+10 Volt
or if that is to costly use two valves one with full flow and another when you are close to target.

Click to expand...

Buying a servo valve will do no good with out a good hydraulic design, mechanical design and good controls. Buying a hydraulic motion controller does little good if the other components are good. It is a matter of the system running as well as the weakest link. We see a botched system about once a week. You know those engineers you guys like to complain about? I complain about them too.

Before we put too much time into this we need to know what the application is and what the specifications are. I wish people would start with this so we would have the context of the problem.

Welcome to the forum Jamie.

What you are asking about is done all the time. Is not as simple as people sometimes expect, but once you understand some things its a task that is do-able for most programmers.

A good place to start might be to get the design guide here: http://www.deltamotion.com/other/designguide/register.php