force limit a motor

[scottwnj]

I want to have a motorized mechanism controlled by an arduino. If the mechanism hits an obstruction, I want the arduino to know. I need to be able to adjust the threshold level in the arduino so I am hoping to be able to use the analog input for this. A similar example would be an automatic door opener/closer that stops if it hits a person. Or a robot moving something heavy and strong versus something light and fragile.

Can this be done electronically by monitoring the voltage and or current used by the motor or some other characteristics of a motor? I know I can add force sensors to the mechanical parts but I was wondering if there was a way to do this electronically.

Would using a certain type of motor make this possible? I am not sure yet if I want to use a stepper or dc with brushes or brushless (I have a couple different projects I am thinking about).

If I don't use a stepper, I may have some sort of encoder somewhere in the system.

I tried doing searches on the internet for obstruction detection and all that came up was ir and ultrasonic sensors.

If anyone can point me in the direction of some information, I would be grateful.
Thanks,
scott

[Hero999]

It's fairly straightforward with a DC motor or AC motor. The motor's impedance reduces (therefore drawing more current) as the mechanical load increases. A current limit could be used to restrict the torque or detect the shaft being jammed.

I don't know about a stepper motor. I think using a DC or AC motor with an encoder, forming a servo system, is the best route to take. It's also possible to measure the back EMF from a DC motor or synchronous AC motor to monitor the speed so an encoder won't be necessary for speed regulation, unless you need to know the exact position of the shaft.