Accumulated pulses?

[MattTheNoob]

Long time lurker, first time poster. I checked the FAQ's and didn't find what I was looking for, but I'm sure its been covered somewhere.

Does the 320 'accumulate' pulses if the pulses are coming faster than the motor is moving?

The reason I ask, I have just picked up a CNC mill with a vintage 1980's control system which I want to retrofit. BTW Bostomatic has the most detailed documentation I've ever seen. They discuss pulses being 'added' to an error counter while encoder pulses 'subtract' from the error counter. The voltage to the DC servo motor is proportional to the number in the error counter.

I'm sure many, many more questions to come.

MattTheNoob

[ger21]

No. The G320 tries to move the motor as the steps are received. The motor can lag behind the commanded position by up to 128 encoder counts, but if the motor is out of position by more than 128 counts, the drive will fault.

However, after rereading your post a few times, I guess you could say that it does??

The drive will always try to move the motor to the commanded position, but if the motor can't keep up, it's allowed to lag behind by up to 128 counts, but it'll always be trying to catch up if it can. I can't tell you how the drive does this internally, but they would appear to operate similarly.

[Andre' B]

Page 5 of the PDF has a block diagram of the drive.
http://www.geckodrive.com/upload/G320-REV-7-Manual.pdf

The step/dir go the clock and up down inputs of an 8 bit up down counter and the phase signals from the encoder go to the clock and up down inputs of a second counter. the outputs of the two counters go to an adder where a summing operation happens (the encoder count subtracted from the step/dir count) to get a digital error signal. If the step/dir count is larger then the encoder count you get a positive error and need to speed up the motor, if the step/dir count is smaller the error is negative and the power to the motor needs to be reduced or even made negative to drive the motor in the opposite direction.
These 8 bit counters and the adder are why the following error is limited to 128 counts, the max value of a signed 8 bit word.

The error signal is converted to analog and then feed to the PID amplifiers and the resulting command signals are summed and feed to the PWM to drive the power amp to drive the motor.

[MattTheNoob]

Excellent! Thanks guys.

It sounds like the servo systems of the Bostomatic work like the geckos, only rather than in a neat, palm-sized package, it's a refridgerator-sized electrical panel.