I am working on a motor control system, and I'd like to be able to know when the motor has reached its max output and has locked up (shaft no longer able to rotate, due to mechanical force pushing back). The motor will be used with a ball ramp mechanism to create a linear motion. I need to know when the motor stops spinning so that I can move on to the next task in the system. What would be the best/most efficient way to do this?
Change in the voltage/current when motor is locked up? How to one sense this
controlmotorsystem
Related Solutions
Use a Hall Effect switch like this - Honeywell Hall effect Vane Sensors catalog
I believe that the performance that you describe requires a servo motor with a high resolution shaft position feedback to a high quality controller. In order to select a torque rating, you need to quantify "force so that a human can not hold the shaft" and also define the maximum speed for shaft rotation under motor power. A servo motor system can hold a shaft at a fixed position quite well, but not as solidly locked as a friction brake.
Best Answer
You should be able to measure the current during normal load operation (from experimentation) and then measure the current during an overload (stall) condition, and then use a shunt resistor (like, a 1% 0.1 ohm resistor) and an op-amp based comparator circuit to indicate when it has reached it's end-point/cannot move any further.
Measure the resistance across the motor terminals (this is assuming a simple 2 terminal DC brushed motor) with an ohm-meter. Then you can estimate the stall current by Ohms law, V = IR, meaning I_stall = V_applied / R_motor.
As the motor begins to move and starts generating back EMF, it will reduce the input current to something more reasonable.
When the motor meets something which stops the output shaft from moving, the resistance reduces again back to the motor's armature resistance (R_motor i mentioned earlier).