cogoman wrote: > That price seems overkill to me too. I have been thinking about > trying to develop a product for just this kind of situation. The > solution seems simple, and inexpensive. Take an AVR microcontroller and > have it monitor the Q-encoder signals. The program would start out > counting the time between changes of the signals. When the RPMs get > high enough it could switch to counting encoder events for a certain > small amount of time. The RPM that is found would be converted to a DC > voltage by a PWM signal from one of the counters. The PWM would always > be clocked at a few MHz, so the RC filter would have a high corner > frequency, and the DC voltage would be able to change faster than most > (if not all) servo systems. For older servo motors that top out at > about 2500 RPM this should be overkill. > PWM is unlikely to be able to generate voltages that are stable enough for a servo drive. To increase smoothness of the PWM, you need to either use a faster PWM base frequency or use a larger RC filter. Using a fast PWM makes the resolution lower (for a given processor/crystal), and using a large RC filter makes the response slower. You'll have to find a good balance of PWM resolution and filter frequency.
Incidentally, you could make something that does a more direct conversion to analog, but it's still iffy as to whether it would work well. Just use a simple circuit to do quadrature edge detection, and have that trigger a short duration one-shot. The one-shot goes into an averaging filter and an amplifier that can invert the output depending on direction (the quadrature circuit would need to have a DIR output pin as well). The faster the pulses come in, the higher the output voltage. It more or less uses the quadrature data as the PWM. - Steve ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
