Hydraulic Displacement Control

Hi guys, I have an idea for controlling the displacement of hydraulic jacks and I’m wondering if any of you can tell me if it would work, or if there’s a better way to do it. I’m looking to do it cheaply, but reliably.

So, my idea is to have an arduino uno with the jack that gets feedback from a displacement sensor and uses PID control to match the cylinder displacement to a reference input by controlling the current to the motor with PWM (pulse width modulation). The main questions I have here are a) will this even work? and b) how do I control the motor? What I’m currently thinking for the motor is to use parallel MOSFET’s connected to the PWM pin on the arduino. I couldn’t find very much info on the motor (it’s a Monarch 08111 motor built for hydraulic cylinders) and I haven’t found an explicit current draw number, but I’ve been using 300A as a max estimate based on some figures I found. 300A seems high to me, but I’m not sure, the power source for the motor is a 12V, 500CCA car battery. I have been thinking 5, 100A parallel MOSFET’s between positive on the battery and the motor would work, but circuits is definitely not in my wheelhouse, and any advice you guys could offer would be great.

Thanks for reading. I guess I should give a little background, this system is for lifting buildings. There are anywhere from 4 to 8 hydraulic jacks bolted to the side of a building (a steel building like you see at a power plant or substation) that all lift together. Currently, there’s just a master on/off switch for them all, which leads to jacks with a slightly heavier load falling behind. The goal of this is to decrease the amount of “eyeballing” needed to lift a building. Rather than lift a little, then adjust, then lift a little more, then adjust again etc… we want to be able to just go up, and go down without worrying.

Hi, There are systems around that use proportional valve control to adjust the ram extension. This method allows the hydraulic pump to operate at its most efficient speed and pressure.

If you start trying to control pump speed you will need to keep the pump cool as its efficiency will suffer and the motor and pump reliability will suffer.

Tom.... :)

Thanks for the reply Tom!

This makes a lot of sense. The hangup is that the hydraulics of the jack are already designed, and the goal is to still be able to use the existing jacks. Currently it is just a simple extend/retract system with a counterbalance on the extend line, would adding a proportioning valve be an easy fix or would the whole system have to be re-done? Also, would you be able to control the valve electronically?

I did some more research and found the motor to be rated for cycles of 150 seconds on and 450 seconds off at 100A, or 9.5 minutes continuously at 100A. Hope that helps clarify a little bit.

-Ben

Hi, Google Parker Hydraulics or Rexroth

It would be worth talking to the hydraulic equipment guys.

Tom.... :)

I think you're right. I looked into it a little more, and this will definietly work better. I agree that it would be best to talk to some hydraulic people.

Thanks for your help!

i suggest you to use a valve on system. If your system may not need too many direction changes or start and stops, and also if you do not want to vary the speed and ramping, you can use cheap on-off valves. However It depends on hydraulic setup, speeds and precision tolerance at positioning. Controlling motor at hydraulics is not a good idea when you use pid. Because sofware may need to start and stop the motor with little time intervals. Also there are many options of reducing oil flow without reducing motor rpm.You may think of them before controlling motor. Let motor keeps running and restrict flow simply.

Adding valve is very simple, only needs some wrench and some fabric to clean oil spill.

If you have questions or i miss sth, please let me know.

Regards.