Re: CIM Motor Reversing
 

Thats what i meant, but also tried to suggest that it to stays activated while resting on the hard stop. I have seen fast moving arms fly past the limit switch, the motor pauses, and then restarts when it clears the switch. It then powers into the hard stop as if the switch wasn't there.

I think Ether, MrForbes and myself are saying the same thing. Limit switches should be mounted next to the moving arm such that the arm sweeps past the switch; NOT directly in the arm's path such that the arm smacks the switch and uses it as the hard stop.

Re: CIM Motor Reversing
 

Yes, or an encoder and PID if you feel like doing extra work.

Re: CIM Motor Reversing
 

I've seen this referred to as a whisker or cat's whisker.

Re: CIM Motor Reversing
 

I encourage this as well. We've found hall effect sensors to be much easier to work with than limit switches.

Re: CIM Motor Reversing
 

In what ways are they easier to work with?

Re: CIM Motor Reversing
 

They are non-contacting sensors, so less susceptible to mechanical damage. They can be easier to coordinate with hard stop protection also. However, they do require repeatable clearance from sensor to target at the desired switch point, so their function will change if the arm or frame is distorted.

Generally, a stronger target magnet makes the Hall sensor less susceptible to switch point shifting when clearances change slightly. Sensor manufacturers usually provide details (sensitivity curves, operate/release magnetic field levels, etc.) in their data sheets and application notes.

Re: CIM Motor Reversing
 

Or the limit switch contact closes. Milliseconds later, the arm crushes the limit switch. Another few milliseconds later, the switch contacts open again, never to close again, and the mechanism with over 400 ft.-lb. of torque procedes to destroy itself...