Current Limiting a motor

[brywisco]

I am designing a a device that will use a 24VDC motor driven linear actuator to apply force to an object. I need to stop the actuation when the desired force is reached. This force will correspond with some current drawn by the motor. This will effectively be a limit switch activated by motor current instead of actuator position.
I would appreciate any advice on how to accomplish this!

 

[Skogsgurra]

A simple current limit. Is that too simple?

Drive systems with an inner current (or torque) loop have settable limits for positive and negative torque. It is especially simple if you are using a 24 V DC system. No need for fancy isolation amplifiers or anything.

You may need to think about torque variations along the way. But if you are positive that the end torque is significantly higher than any torque seen along the way, it is a sure way of doing it.

Let the activated torque limit set an output to get an indication that you have reached end of travel. One output for each end position is possible.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[DanDel]

If you know the current at which the motor is to be limited, you may be able to use a DC circuit breaker or overcurrent relay.

 

[brywisco]

Thanks for the input. I should explain that the electric actuator is activated via momentary pushbuttons. One PB extends and one retracts the actuator. The actuator extends against a load that it has no hope of lifting, only need to provide some downforce for drivewheel traction. The actuator is rated at 169lbs and I would like to provide around 100-120lbs then switch the actuator off allowing the operator to only retract the actuator. There is a retract limit switch, so no worries there.