VSD-A Spindle control in MACH3?

[mkuivamaki]

Hi.
How VSD-A should be configured in Mach when it's used at spindle control? It's probably controlled with step/dir(?) but I haven't got this working yet

[nicad]

I too would like to know... I assume one just drives the spindle with S/D just like a big, fast rotary axis.. but setup as the spindle in Mach.

I also have a question regarding using a large Fanuc AC servo +VSD-A for the spindle drive on a 5C collet size lathe (to allow A-axis positioning). Fanuc is a 10s/3000 rated 145V, 15A (stall) 12nm torque (stall). Will trying to drive it like a "ridged" axis make it error out all the time when taking cuts? I assume I would make the fault range (step +/- range) about as large as possible, to allow the spindle/drive time to correct before faulting when taking cuts??

[Xerxes]

One may use position mode for spindle but there is also a velocity mode which works also thru step/dir. Velocity mode is much like position mode with following differences:

• Following error fault limit is defined as velocity error, not position error
• Velocity mode allows position "slipping" if motor is overloaded. It doesn't wind-up to catch the position. That's actually what velocity mode means, it just tries to keep velocity controlled, not position.

[nicad]

Xerxes-
Thank you for the distinction between s/d and velocity modes.
My next two questions are:
1) I assume velocity mode is the desired mode for a lathe spindle control, but what about cutting threads? There will be a 500-1000 count encoder on the spindle motor, but if velocity mode allows slipping, and the software is out of the control loop, how is thread accuracy held?
2) When I want to use the spindle as a rotary axis, I assume I need to use s/d mode again for position accuracy, correct? Can the VSD-A change between velocity and s/d modes on the fly?

Thanks for the information. The spindle control is still the hazy part of the project for me, especially since I am needing C-axis positioning on the spindle. I am open to any comments and suggestions.

mkuivamaki- have you made any progress on setting up Mach for your spindle?

[Xerxes]

Sounds like you would need to use the position mode to get guaranteed spindle orientation. Mode can be changed on fly but only via SPI bus, so with Mach you need to use single mode.

[mkuivamaki]

Yes I got it working. I configured spindle to position mode. Spindle is controlled with step/dir. I have still one problem, with another computer (I made vsd-a configuration with this computer) command M5 in Mach stops spindle rotation smoothly as it should be. But when I tested spindle with my cnc control PC spindle stops immediately (in rough way). With high rpm's vsd-a goes over current error when spindle stops. All parameters should be same in both Machs. Spindle acceleration/deceleration curves aren't sharp. Acceleration works as it should be.

[Xerxes]

Overcurrent fault is symptom from incorrect tuning, that should never happen if tuning is good. Overcurrent fault means that measured motor current got higher than commanded (above the overcurrent fault leven you set in GDtool). Adjusting overcurrent limit and/or torque controller PI gains will fix this.

To Mach problem I don't know an answer. Perhaps there is acceleration/deceleration setting somewhere?

[mkuivamaki]

The error is this: "Other fault, get details via SPI bus.
Possibly over current fault." So it might be something else than over current? Acceleration and deceleration time are set to 2sec. There is still that problem when servo stops on high speeds.

[Xerxes]

Are you sure it's not fault #10 which has quite similar LED pattern? That would be overvoltage (regenerative) which is typical problem in deceleration. Try measuring HV bus voltage after fault.