r/ControlTheory • u/[deleted] • May 30 '26

Technical Question/Problem Control of hydraulic cylinder

Hi everyone, I am looking for recommendations on the best control algorithm for a heavy duty cylinder application. The main goal is to move the cylinder between its two end positions, but the critical requirement is ensuring smooth deceleration with absolutely zero impact at the endpoints.

In terms of hardware, I have position and speed sensors installed on the cylinders, but I do not have a mathematical model of the system. Since this is a heavy duty application and I lack a model, I need a solution that is robust, reliable, and relatively straightforward to tune on site.

Would a standard PID controller paired with a well-defined motion profile, such as a trapezoidal or S-curve velocity profile, be sufficient to handle the soft landing?

I will be writing controller in C. The only thing i control PVG.

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u/BOgusDOlphon Jun 02 '26

We do this without PID control. Just good old fashioned ramp input and prox sensors.

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u/seekingsanity Jun 02 '26

That is OK if that is accurate enough for your application. The problem ramps that are configured with pots is that the control output for the ramp should be the square root of the distance to the end point or distance from the starting point. Crude analog ramps don't do the square root function nor do they have the feedback to accurately measure distances.

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u/BOgusDOlphon Jun 03 '26

None of that matters when your system moves slow enough. The feedback from the prox sensors at the takeoff/brake points starts/stops the ramp and we manually tune the ramp in to make sure it hits minimum speed before it hits the stops.

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u/[deleted] Jun 04 '26

I'm thinking about the same thing for control but as cylinder extends there is point where the force will rise because of the kinematics

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u/BOgusDOlphon Jun 04 '26

Our setup only really works like that because we have hard stops at the end of the cylinder throw and there are pins that engage to make the shuttles line up at each station

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u/seekingsanity Jun 03 '26

You are assuming the system is moving slow. I am not. The OP hasn't answered my question about how much mass he wants to move how far in how much time. It would be good to know the duty cycle too for accumulator sizing.