Rigid Tapping - depth is short and retract overshoots

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cwatson1982
Posts: 14
Joined: Tue Jun 02, 2020 11:14 pm

Re: Rigid Tapping - depth is short and retract overshoots

Post by cwatson1982 » Mon Jun 08, 2020 6:11 pm

The drives on this system (including the spindle drive) all run their own configurable velocity loop. The drives themselves have adjustments for velocity gain and velocity integral as well as their own filtering. So anything done to the inner velocity loop has a pretty big effect on the PID values in the position loop. They can be run in velocity, torque or positioning mode.

The original control has a P gain and a Kv nominal gain as well as a Kv % offset. It also allows setting the nominal voltage per RPM. As far as I can figure out it scales the Kv based on commanded speed.

The RPM can be figured out but the whole thing is overly complicated. The machine has a 12k RPM spindle motor but was limited to 6k RPM due to spindle bearings. The electronic gearing in the drive is scaled to actually hit 12k at 10 volts, wasting half the bandwidth (I think). There is no easy way to offset it in the drive.

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