Jack Ensor wrote: > I noticed when jogging at my maximum rate of 90 ipm the 2 quadrature > signals coming at a rate of 1 Khz have approximately 50 micro seconds of > jitter. Is this excessive? How much would it contribute to tracking > error? My tracking error is insignifcant when homing but but huge when > running Axis.ngc. Would you please define this term "tracking error"? I do not know what it means. From context, I believe you mean to say the machine's position differs from the displayed position. Is that correct?
How are you seeing the quadrature signals? On a "box" oscilloscope, or somehow with halscope? Unless halscope AND the software or hardware encoder input facility is sampling at a fast enough rate, you would miss some of the edges. For instance, on my minimill, at 60 IPM, with 16 TPI leadscrews and 4:1 motor reduction, and with 500 CPR encoders producing 2000 counts/revolution, you get 128,000 counts per second. Therefore, counts are coming at a rate of one every 7.8 us. Obviously, my jitter must be less than yours. But, a scope would need to be sampling it at a rate of once a microsecond or better before you could even begin to discern jitter on the signal. If you are using an analog oscilloscope, then there is no sampling. But, without specifying the rate of encoder pulses when you see the 50 us jitter, it is hard to know what it means. If you had 50 us jitter when the count rate was one millisecond, it is not a big deal. If it was when the count rate was 50 us, it would be reducing the quadrature angle to zero, and would clearly cause errors. So, you have to compare the jitter to the count rate. Ideally, there should be 90 degrees between the 4 states of the encoder's A and B signals. They never are, due to tiny errors in the manufacturing of the encoder's optics. The greater the error, the narrower some of the count states become, until they become so small the encoder counter's logic misses them. Then, the position will be off by multiples of 4 counts. When you say homing is OK, but axis is bad, is that all due to speed? Jon ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
