servo stall shut off circuit

[wcarrothers1]

Anyone have any info on making a servo stall shut off circuit. MadVac talked about changing to servos and such here and about making up a circuit to do that. But no details..

http://www.cnczone.com/forums/showthread.php?t=11024

b.

[daedalus]

Some motor drives have current limiters in them, which will make the drive fault if you draw extra current (like in a stall condition).

how about a fuse rated above running current, but below stall current, inserted before each motor drive? Thats the easiest way to stop the drives at stall. You could also use tripswitches.

[wcarrothers1]

My geckos apear to already stall and fault pretty quick when stopped but I was more interested in what the circuit Mad was talking about actually looked like.

I would also like to figure a method of informing MACH 3 when the Gecko's decide to fault out and stop so it also stops rather then keep running the Gcode. probably an easy way to do this just have not looked it up..

b/

[mlaws1172]

Here is a board that will do that. It is a dfx file
mike

[NC Cams]

If you install a shunt in the power line to the servo motor (assuming it is a DC servo) you can readily sense current flow.

By feeding the voltage into an op amp or a comparator, you can program the amp or comparator to trip and shut down the drive circuit when current reaches or exceeds a preset limit.

The trick is to sense the current at the bottom of the H bridge drive circuit.

Go here and download the app note:

http://focus.ti.com/lit/an/slua137/slua137.pdf (U102 app note)

This is exactly what they're doing with the current sense feedback that is being fed to pins 12 and 13 of the UC3637 IC. In this case, the preprogrammed current is done internally to the IC

You could do it externally with an op amp to first AMPLIFY the signal coming off of the current sense shunt. You'd then compare it to a reference voltage via a second OP AMP or COMPARATOR which would trip the SHUTDOWN pin on your bridge driver circuit.

Got that???

[Madclicker]

Originally Posted by NC Cams If you install a shunt in the power line to the servo motor (assuming it is a DC servo) you can readily sense current flow. By feeding the voltage into an op amp or a comparator, you can program the amp or comparator to trip and shut down the drive circuit when current reaches or exceeds a preset limit. The trick is to sense the current at the bottom of the H bridge drive circuit. Go here and download the app note: http://focus.ti.com/lit/an/slua137/slua137.pdf (U102 app note) This is exactly what they're doing with the current sense feedback that is being fed to pins 12 and 13 of the UC3637 IC. In this case, the preprogrammed current is done internally to the IC You could do it externally with an op amp to first AMPLIFY the signal coming off of the current sense shunt. You'd then compare it to a reference voltage via a second OP AMP or COMPARATOR which would trip the SHUTDOWN pin on your bridge driver circuit. Got that???

Yep, that's it in a nutshell.