Linear Servo to Operate Remote Lever

From the sparse critical information, I recommend using a true servo system with feedback from the hydraulic ram and a servo controller. I recognize that this does bring in the possibility of instability (oscillation) in the system but normally the slow response of hydraulics mitigates these concerns. I also suspect your existing lever control provides some analog control of the ram, too.

In fact the servo - as the input seems to be - controls the lever of the valve which controls the cylinder. In the mid-position the valve is closed and in the the other positions delivers the hydraulic fluid to the cylinder for extension or retraction. So that if this is true your suggestion is on the wrong side. The best solution if the local hand control is still required is to place in parallel to the manual valve a proportional valve with an electric control. The solution presents the drawback that leakage but avoids the risk of interference (you could not control manually after the servo is in place). If the manual local control is not anymore needed then you can replace the manual valve with the other type.

I HAVE LOOKED AT Solenoid operated valves CETOP 3 as a replacement and cost is high plus I loose any chance of manual operation, with the servo attached with a clevis I can always remove the pin and regain manual control.

This could be done with two 1.5" stroke pilot cylinders and two discrete on/off signals.

Forgive my ignorance but what is a pilot cylinder? pilot valves I know about a bit. Interested in this so any further details welcome.

A pilot cylinder is a small pneumatic or hydraulic cylinder that operates a valve to actuate a larger "main" cylinder (or other device).

Ok thanks. But I still can't see what sort of setup your proposing? I can see how I can place an electrically operated cylinder (linear servo) to push and pull the lever but I cant see how I can control a hydraulic cylinder with out going to a solenoid operated valve. Any examples or links to the device your thinking off? Maybe I am just not thinking straight.

Further to Tornado's reply, connect the two cylinders driving the lever in series. Both off = Back. Both on = Forward. One on. one off = Center. Much cheaper than a servo, but you may need a bit of logic to get your "one on - one off" condition.

What control signals do you have?

If something goes horribly wrong, is there a possibility for harm to anyone, this includes loss of limb or death? If you are going to automate this remote lever, did it have an operator that closed the safety loop by hand eye in this safety loop?

Does this system need to be fail safe, fail passive?

Just asking questions before you automate something that requires system thoughts about safety. If this is the case you may need monitoring that performs a safety cutout if unintended operation occurs.

Yep fully understand and agree. Have looked at all possible situations and any effect on safety. I work in railway signaling so am hammered by H&S and right side / wrong side failure :-)

You have not said how much force the lever must exert, so the size of system required is unknown. It seems to me that for a simple 3-position system, you are working too hard! A simple DC motor with pulleys and a belt, a leadscrew and nut, or perhaps a rack and pinion, would do the job. 3 limit switches would turn the motor off at the appropriate positions. One polarity would move in one direction, while the opposite polarity would move in the opposite direction. I'd have to think just a tiny bit to wire the switches correctly, but I'll do it if you wish...

Thanks for that. Someone else suggested using a solenoid (pull) each side of the lever firing the solenoids via a relay. This may be the way to go? I dont really need the porponital control of the servo, a bang-bang system would be fine. A rack and pinion may be another route.

Is you valve spring centered ? If yes then the 2 sol solution is OK. It has the advantage to allow when the sol are not active to allow the manual control. Use push solenoids and select them according to the force -travel function you need. Best way you pull or push the lever with a spring scale an measure as well the displacement with respect to the mid position as the force required to move versus travel. Look at the force - displacement curve of the solenoid and make sure that it offers all the travel along a force > the one needed by the lever.

It is more complicated if the spool is not spring centered.

Yes the spool is spring centered so I guess that makes it come together easily. One question if I may? Why push instead of pull? Maybe this is just me thinking along the lines of the old wood saw between the European push and it bends and the Japanese pull and it stays in tension therefore straight. Yep I need to measure the force and travel required. Will get a chance this weekend to test out the theory and the practical on the rig. Thanks.

If you push you do not need any mechanical connection between pluger of sol and lever. It is much more simple to implement. If the solenoids are with a zero spring return the lever is free as long as no solenoid is energized.

Ok I see wher your coming from. I can just let the ram from the sol contact against the lever and push it rather than having a clevis pin connection. Right? Just means mounting the sol closer to the lever. Thanks for you help and input.

In fact I am not coming from I just aim at a good solution!

Keep it as simple as possible.

I am looking at using a Arduino to control the PWM signals. So far I am guessing that the linear servo will have a band of input signals e.g 100 fully retracted 600 mid stroke 1100 fully extended so I can program the position into the Arduino and control its position. As I would only need three positions I can use simple inputs to the Arduino.