On 07/23/2020 02:00 AM, John Dammeyer wrote:
Hi Tomp,
I understand the process and the step response. One thing in the mix that we
haven't discussed, and I really was hoping Jon Elson would chime in again, is
exactly how much impact the servo drive has on all this.
Well, both the motor and the drive have current limits.
Often the drive has a lower limit than the motor, so it is
the dominant one. Current in the motor equals torque, and
torque is proportional to linear force on the axis. So, the
drive (or motor) current limit absolutely sets the
acceleration that can be achieved.
You can crank up the MAX_ACCELERATION parameter in the .ini
file and watch the error with Halscope (on machines equipped
with encoders) and see when the servo drive "runs out of
juice". Then, back off on the accel parameter by 10 - 15 %
to account for cutting forces, and you should be at the optimum.
The application of DC voltage to a motor and then measuring up to speed brings
up the question as to how you know the motor is up to speed. But anyway.
Could do it with the scope monitoring step pulses and using evenly spaced
pulses as the up to speed indication.
Well, actually, it isn't voltage, but current, that should
be applied to the motor. Using a small resistance in series
would approximate a constant current source, and give
constant acceleration.
Jon
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