Kirk Wallace wrote: > On Sat, 2008-01-19 at 11:54 -0800, Peter C. Wallace wrote: > ... snip >> A simple Voltage to frequency converter would probably do, for example the >> AD654 in 8 pin DIP is probably quite a better than required. (500KHz max >> frequency, .03% linearity) >> >> I would count the frequency with one of the spare encoder counters (set up >> for >> up/down mode) and use count difference accumulated over some number of >> sample >> periods (to average out the sample period jitter) > ... snip > > On my Mitsubishi Freqrol U100 and Z200 VFD's there is a monitor output > called FM, which is an 8 Volt pulsed signal with a frequency of 1440Hz > at full scale. Both VFD's monitor output frequency (motor speed), or the > U100 can be programed to monitor output current. I suppose a > opto-coupler could be used to (almost) directly connect this signal to > an encoder input. > > I'm not sure how handy motor speed would be. The motor current would be > nice to have though. All my VFD's have a number or alarm outputs, which > should probably be incorporated into my configuration, but most likely I > won't get to it until something bad happens. >
Like taking a cut that is heavy enough that the VFD trips on overload, and the machine keeps driving the no-longer-spinning cutter through the workpiece. SNAP! My Van Norman mill had the feedmotor interlocked to the spindle motor to avoid exactly that issue (designed in about 1939). When I replaced the motor starters with VFDs I did the same, and I'm glad I did. That little machine is very rigid - enough so that it can take a 1-1/2HP cut that will trip the spindle drive with no audible sign of struggling. Last week I was doing a slot in cast iron with a 1/2" endmill. The cut started 0.3" deep, but due to a slipping collet it wound up 0.7" deep before the spindle tripped. There was no indication that the mill minded taking that cut. Regards, John Kasunich ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
