Jan de Kruyf wrote: > > This is very good off course. The lowest figure I have heard in the CNC > world is 500Usec. But that I would consider nonsense for the market LCNC is > operating in. 5 millisecs servo looptime is ample in almost all cases. > I have run my parallel-port attached hardware up to 4 KHz, but that burns a lot of CPU time, mostly waiting for the slow parallel port to work. I believe the Mesa people have run 10 KHz with their PCI boards.
5 ms servo loops actually perform pretty badly unless you have timestamped encoder velocity estimation. The problem is the encoder position is necessarily quantized in position. Then, to compound the noise, it is sampled in time. This leads to large variations in apparent velocity. Assume you are sampling at 1 KHz, and the machine is moving at a rate where 1500 encoder counts are coming in per second. So, every sample, you get 1, then 2, then 1, then 2 counts. So, it appears you have an instantaneous 2:1 fluctuation in velocity at a 500 Hz rate. Lowering the sample rate helps a bit as you get more samples per period, but it moves the fluctuation frequency lower. At a 5 ms sampling rate, the "buzz" would move down to 100 Hz, which is well withing the motor/drive bandwidth. Jon ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
