Neil Whelchel wrote: > Hello, > It is too early to tell what the reasonable maximums are, I will have a > better idea when I build a few modules. However, I have plans to count 16 > bits worth of changes, so reading the register 10 times a second would be > able to count just about 65536/2*10=327680 per second. With an encoder > with 1024 counts per rev, this works out to be 327680/1024*60=19200 rpm! > The microcontroller will be able to handle up to about 4.5 MHZ worth of > input pulses. I see the major limiting factor here as the response time > from the encoder itself, there are very few encoders around that don't > start missing pulses at around 150 khz, Well, 150 KHz on the actual A and B encoder signals is 600,000 quadrature counts/second. At 1000 cycles/rev or 4000 quad. counts/rev, that is 150 revs/second or 9000 RPM. Will your motors be running that fast? ones with less counts per rev can > usually exceed this however, but look at the resulting RPM.. > Also, when very large RPM ranges are needed, a common trick is to use 2 > encoders, one with a high pulse count for fine positioning, and another > with a low pulse count for high speed rough position. When the RPM falls > below a certain point, a calculation is made to determine the offset to > the high res pulses, and the handoff is made. (This is sometimes done in > the same physical encoder using only the index pulse above a certain RPM.) > What could you possibly need 100,000 counts per second for? Well, with a 1000 cycle/rev encoder, that is 25 revs/sec or 1500 RPM. That is not very fast for a small servo motor. I have 1000 cycle/rev encoders on some of the motors I have used on my minimill. It has 4:1 belt reduction and 16 TPI screws. So, that is 4000 * 4 * 16 = 256000 counts/linear inch motion. At 60 IPM=1 Inch/Sec, that is 256000 quadrature counts/second. That is also 3840 RPM at the motor.
Jon ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
