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General Mach Discussion / Re: Racking Detection with Encoders
« on: April 21, 2009, 04:10:25 PM »How about feeding back the slaved servo encoder signal to a missing pulse detector or a phase locked loop. When the slave servo motor stopped or slowed down and the pulses no longer were in phase, the circuit would E-stop the master signal from Mach 3 to the driver servo motor. That would be exclusive of Mach 3 but would ultimately control the estop. That shouldn't be too tough to come up with on a small circuit board or pref board pin to pin. Possibly use the master encoder signal to sync the driver and the PLL, and the slaved encoder signal to initiate an estop through the PLL as the detected sync frequency. The LM 566 is a dedicated phase locked loop chip that can be configured for various pulse frequency spans with discreet components and outputs a fault signal when the phases are out of sync.
Or as Hood is saying - a macropump. There are a couple of guys here that know that stuff!
Bill C.
I thought of designing a simple counter circuit for each encoder that could be reset at the start of a run and then have a digital comparator generate an e-stop if the counts differ by a given amount. I have not started using Mach yet as I am stilll in the process of building the machine. I do not know what signal would be used to signify the "start of a run", but I assume there is something available. Worst case would be to reset on power up. However, I'd really prefer to do this in Mach and not have to add another circuit to the mix.