Dave Keeton wrote: > I checked....This is a dual winding integrated 6000 rpm 100hp VAC motor on > our Okuma MCV bridge mill. (Big Big Iron!)The Hall effect sensor is mounted > on top of the motor with the encoder rotor mounted directly to the motor > shaft. I have replaced this encoder before. The motor shaft bearing failed > and let the encoder rotor smack the sensor. The Z pulse is used for > orientation of the spindle for automatic tool changer functions on this > machine. The signal from this encoder on the A and B signals are sinusoidal. > The drive manual says they are used as a speed reference. Okuma says it is a > Hall Effect Sensor. I confirmed with their service department. Maybe it is > not a true Hall Effect? At least that is what they tell me....The sensor is > adjusted by monitoring the signals before they are processed in the > amplifier to adjust amplitude. The closer the sensor is to the rotor the > higher the amplitude. Is this different in a brushless dc motor? Again, this > is probably the extreme limit of my experience with them. Most our motors > (even brushless dc) use high resolution optical encoders. Most of our > systems are AC or permanent magnet DC. Out of 50 machines this the only one > we have now that has a "Hall Effect" (or so they say). OK, this is NOT your typical brushless motor, and especially with dual windings it almost certainly changes the number of poles for high and low speed ranges. So, it is no surprise the hall sensors are not industry standard compatible. Also, with needing the Hall sensors aligned to the motor windings but the index aligned to the machine spindle, I can see why two separate sensor systems are used. Hall effect sensors are inherently analog, but almost all applications for them desire a digital output, so most of them produce that yes/no output.
Yes, the typical brushless motor has Hall sensors that are digital right out of the sensor. Others make the commutation signals form a siz-channel optical encoder, like the Renco RCM21D or RHS21D series. These produce A,B and Z standard encoder signals, and S1, S2 and S3 "Hall" signals all off the same encoder disc. The only limitation on these is the alignment between commutation signals and encoder index is fixed by the encoder disc. You have to order the disc with the right number of poles for your motor. Most older brushless motors used these commutation signals, commonly called "Hall signals", whether there were really Hall sensors in the motor, or the signals were derived from some other sensing technology. Newer motor/drive systems often use either some form of proprietary encoder, like the Yaskawa Servo Pak, where the signal on the 3rd encoder channel has a phase relationship relative to the A and B signals to indicate which motor phases to drive, or they use a form of "sensorless" drive to get the motor moving until the index pulse comes by. Then, they count encoder pulses to control commutation. But, the so-called Industry Standard brushless motor still has 3 commutation signals that tell the servo amp which motor phases to drive. 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
