Kirk Wallace wrote: > I wanted to have a real motor/encoder system for my office EMC instead > of using a simulated configuration. So, ruined a surplus printer to get > the motor/encoder assembly, which I connected to an L298 and a +12 Volt > motor supply. When I got to testing it, I had a hard time with tuning. > On occasion, the motor would not move. I connected a voltmeter to the > motor leads and found around a Volt going to the motor. Then I increased > P until I got about 2.5 Volts and still no movement, so I helped it > rotate, at which, it jumped to the commanded position and started > oscillating. So, my thinking is, the the commutator configuration does > not allow for a constant torque vs. voltage at every angle and the > system friction is high enough to cause a stall at reasonable P values > at certain start points. This seems like it might be a common problem > for small systems where a torque/friction ratio might be fairly low. Or, > is this more of a problem with inexpensive DC motors. This motor was > designed to position paper to within a few thousandths of an inch plus > traverse the length of the paper in about a second, so from my > experience, the printer designers must have spent a fair amount of time > with tuning. Do Etch-Servo setups have the same problem? >
If these motors were designed in a constant speed/position following servo application like a printer, they could run acceptably even with dead spots and significant torque ripple that would be totally unacceptable in a low-speed positioning servo application like CNC. Or, the motor could just be "bad". You do not see this on "good" motors. You can check for this with either a variac- or electronically-controlled power supply that you can turn down to a fraction of a volt. Set the supply so the motor just rotates, at maybe 10 RPM. If it just stops somewhere, that motor either needs the commutator to be cleaned, or it has an open connection to the commutator. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
