Control.com - Nerds in Control

In a hydraulic system where a hydraulic cylinder is pushing a very big load and then its speed slows down and then stops at end point. My question is how can we decide ramp time while slowing down and stopping. Is there any calculation for it?

Sure, with hydraulics, motion is displacement. Controlling the flow is controlling the speed. With a proportional valve and controller, it's
simply ramping the control voltage.

Regards

cww

About the only danger I can see in ramping down too fast is that the cylinder will lose contact with the very big load and the load will continue moving due to inertia. If that is the problem, then the calculation or measurement you want is the dynamics of that very big load. What forces are resisting its motion? Gravity? Friction? The gravity factor would probably be the easiest to calculate (if the load is moving up a ramp, for example). The friction effect would probably have to be determined empirically rather than calculated.

Robert Scott
Real-Time Specialties
Embedded Systems Consulting

Thanx friends,

Yes as I told you, it's not gravity related work. In fact we are pushing and pulling the load. Now suppose the distance between the two limit switches, i.e for slowdown and end is half meter, then ramp time should be selected such that when slow limit comes ramp starts and should end before the final limit switch. Or in other words, if I increase the reference for slow down, I will have to change the ramp time also. So is it only decided with trial and error method only?

Yes. What are you trying to do exactly? Are you using closed loop control?

Ramping down too quickly when extending can cause cavitation on the cap side. Also, the actuator has a natural frequency, do you know that? The ramping up or down can't follow motion profiles that have frequency components greater than about 1/5 the natural frequency. Are you trying to follow a motion profile?

No, sorry I don't know about this frequency. Can you explain in detail?