On 2009-07-06, wrote:
On Jul 6, 8:05*am, "Buerste" wrote:
Imagine a simple fractional hp DC gearmotor with a torque limiter or torque
limiting clutch *that powers a small machine at 60 or so RPM. *Lets say the
machine jams and the torque limiting device kicks out. *How can I cheaply,
easily sense this condition and turn off the motor?

You could put a photo sensor on the gear motor and the part of the
machine that stops turning when the terque limiter kicks out. Use
these to set and reset a flipflop. Integrate the output of the
flipflop. When the torque limiter kicks out the reset would no longer
occur, and the voltage from the integrator will go to high. Use this
to turn off the motor.

Or -- set up a retriggerable one-shot which times out a bit
slower than the optical sensor pulses so it keeps getting reset as long
as things are running at normal speed. When the shaft slows down, the
one-shot finally reaches the end of its time and triggers the motor stop
circuit. And it could be done with magnetic pickups as well if dust is
a problem with a optical sensor. For that matter -- if there are steel
or iron gears involved, a magnetic pickup near the teeth of the gear
could be used to generate the pulses.

Enjoy,
DoN.

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