Solution repository

Hello Everyone
I have recently been given a relatively simple control problem to deal with. It could be summed up as a problem where a rotary hydraulic
motor was moving something into position and I had feedback from a rotary encoder as to that position. The motor and encoder I/O was fed from and into a Wago PLC. I ended up using an open loop type solution, where the speed of the motor depended on the distance I was from the position setpoint and then eventually stopped the motor at a specified distance away from the setpoint. I have called this OL because I am not reading back the motor speed, I just change the speed and wait for the system to reach the next position for a speed change. This method has worked every time I have run it. I would be grateful for comments on this solution, but this is not really the purpose of this post.
While trying to solve this, I started thinking "I can't be the first person to do this". So I searched for an online repository of standard solutions to simple problems. Or simple control methods based around kinds of equipment used. Does anything like this exist or would it be impossible?
Thanks, looking forward to some interesting discussion
Lee Russell
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Lee Russell wrote:

No, this is common in many industries like the lumber industry. You would need to add an increment encoder, resolver or SSI absolute encoder for position feedback.

Yes, hydraulic motor controllers exist and you can buy them off the shelf. For well behaved simple systems just about any motion controller will do.

Not only can you control position, velocity and acceleration now, you can even control the torque by using pressure sensors on each port of the hydraulic motor and controlling or limiting the differential pressure across the hydraulic motor.
In short, you can do just about anything with a hydraulic motor that you can do with an electric servo motor.
The new bay bridge spans are being lifted into place using hydraulic motor to control winches. Three winche motors must be synchronized so the span is lifted without tilting the roadway sections. http://www.newbaybridge.com/constructionlog/cl_040728_firstsections.htm
Our controller is being used to control and synchronize the winch motors.
Peter Nachtwey
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Only three motors?? That's simple stuff..
Several years ago I looked at a Ship Lift in Malaysia that uses 110 winch motors (55 on each side) and is capable of lifting cargo ships up to 70,000 DWT out of the water for cleaning and inspection. It was a small one. The motors all had to be precisely synchronised and fail-safe - dropping or twisting the ship even a tiny amount would be extremely embarrasing for all concerned ;-)
Cameron:-)
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You should be able to achieve a closed loop position controller if you only have a position sensor. Think in terms of a scaled step input, a unity feedback loop, and the position output reaching the desired location according to the dominant system time constant. I'm not certain that a PLC would be useful here. You would have to know some basic characteristics of the hyddraulic actuator. However, your overall performance would improve.You should be able to achieve zero position error, in much less time.

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