Jan de Kruyf wrote: > Jon: > when I started working in the CNC field we had 20msec loops and they > worked(cutting steel) from pure fanciness we would upgrade to 10msec, and > with a well tuned servo drive you could feel the distinct steps of the DAC > while accelerating. Yes, with velocity servo amps with tachometers, all the computer has to deal with is keeping the position within bounds. But, if there is no velocity feedback (current/torque-mode amps or pure voltage amps) then the computer has to work a lot harder at it. > Afterwards I learned to tune a servo by holding the > table feeling for those steps. > Off course on a small high speed machine the picture changes considerably. > But at the same time I guess that the problem you are describing might be > caused in the digital speed servoloop, by the jitter of the CPU board, and > / or a poor setup of the positioning loop. > > In any case: from the grumbles in this thread we might perhaps deduct that > there is money in a good micro stepping board, that takes position or speed > input every msec or so; for the stepper people. > Well, I make one of those, there are several other makes available, too. My board, the Universal Stepper Controller, turns a stepper into a servo. With no encoders, the "encoder" counter counts the step pulses, if you add an encoder, it reads actual position. LinuxCNC samples position typically every ms and sends a new velocity command. You can go to over 300K steps/second on each axis and still have velocity granularity of 3%. That can't be done in software.
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