Spindle Step/Dir servo ramp down before stop on M stop command.

Well, That works very nicely!
I did change :

to:You had said in an earlier post to delete net c-enable => pid.c.enable since it is in the M100 script

Then, the P gain was way too high - was 1000 in that file, and I went down to P=4 and it is completely stable. P=10 is to high, large overshoot and then returns to position. P=1 works fine, but takes long to get to position ( seconds). I increased D to 10 - made no difference, so left it ( this on a change of G01 C0 F1000 to G01 C1 F1000, ie, one rotation).
Then I played with FF1 ( is 1 in the file) - increasing to 5, unstable, to 0.5, stable but slow to approach final angle.
P=1, D=0, FF1=1 is stable, but overshoots a little, and then returns to correct angle - this happens slowly
P=4, D=0, FF1=0.8 is good, very slight slight overshoot and return to position.

In operation, from startup -
I home all axes, C included. Then M100. Then if I jog ( on AXIS, set jog increment to 0.5, ie 0.5 X 360deg = 180deg) , the very FIRST jog will rotate to the 180deg position, 'almost' come to a halt, then run on past , fast, 360deg, and reach the 180deg position and stop smoothly. Thereafter a jog to any position goes where intended without moves past the point.

In MDI mode, G01 Cxx Fxx commands move the axis to the angular position OK, but also the very FIRST C axis move command ( WITHOUT having done the jog movement above first) also rotates to commanded position, then runs past 360deg to get to the position again. And G01 Cxx commands thereafter move to the correct position directly.

Almost as though some counter is not cleared on the very first move/jog?

Having done a few MDI C axis moves, if I then do M101, and do a MDI spindle on for a few seconds, then spindle OFF again, then do a M100, the spindle moves to the last C_Axis position it was at before the M101 command. Very Nice!

Andy, this looks very promising indeed. Scaling the C axis next I guess..
I only wish I had a tenth of your abilities with HAL!

Thanks Andy - very nice to watch the lathe do its thing like this!
Joe

I think I did not follow correctly what you intended - Probably made the changes incorrectly - HAL attached in full, but excerpts below:

The spindle starts spinning fast right away with M100 - seems to be reducing RPM very slowly.

Then in AXIS C Joint 2:

Getting Somewhere..
First, I think the scaling is inverted - to my mind it should be :

That seems to get the spindle to the correct angles.
However, its very unstable with odd behaviour.
Pgain is set to 0.1 - anything above 0.5 or so oscillates. Pgain of 0.05 is painfully slow, and does not change the behaviour below.

I set MAX Velocity to 10 and MAX Accel to 50 ( I tried 5 and 5, and 40 and 200 - the latter makes the response worse).
After homing, using MDI -
G01 C90 F1000 moves slowly to 90 deg, past, continues way past, then return to 90 suddenly..
G01 C0 F1000, ditto, the other direction.
Halmeters show: ( For PID.C.Command and PID.C.Feedback)

Feedback starts at big value, and decreases rapidly to 0, and continues -Ve, while Command changes value much more slowly, and when it reaches final value, Feedback has a large -Ve value, which unwinds quickly to converge to the same value as command.
Likewise, the spindle moves from old position, say 0deg, to new, say 90deg, slowly, continues past 90deg, and when command reaches terminal value, feedback and spindle unwind rapidly to the 90deg position.

I played with Pgain, added some Igain, etc made things slower or unstable.

What makes PID.C.Command change so slowly? The C_Axis DRO changes value in tune to the change in the command - the spindle overshoot while feedback grows in the other direction is not reflected in the C_Axis DRO.

What fun...
Thanks Andy!
Joe

andypugh wrote:

NoJo wrote:

What makes PID.C.Command change so slowly?

F1000

1000 degrees / minute is about 3 minutes for a full revolution.

Now you are playing with me...
1000degrees/minute is about 1/3 minute for full revolution - (360deg in 21sec..)
Problems here with 3/1 and 1/3 and 1/360 and 360/1....!

I will try tomorrow - I know though when I set Max Vel to 40 and Max Accel to 200, the thing went unstable, with Pgain - 0.5.

The Max Vel and Max Accel exists in two places under the C axis in the ini file, once for C_Axis and again for JOINT_2


Could you explain how this works please? And which ones do I change to your suggested test values?

Apart from a few issue discussed further below, I believe we have a working solution!
I believe I have the PID control working well, but still need to test with varying inertial mass ( workpiece) in the spindle.
Max Vel and Accel are set to 360 and 3000 resp.

Initially any setting of Pgain between 3 and 0.001 was still unstable, with P>1 being very bad. Small changes in angle <5deg were 'reasonbly' quick and almost stable, so this had to be related to the magnitude of the position change.
Looking at how the PID controller output is structured, the Feedforward term (FF1) would appear to be the culprit since it is multiplied by the command derivative - this forms part of the PID output, and since the change in command is large and instantaneous ( say from 0deg to 360deg), the contribution could be excessive.

I set FF1 = 0 to verify, and it works...the angular changes are rapid, stable, with no discernable overshoot at all.
There was a slight wobble around setpoint, but Deadband was set to 0.0 - since I have a 4096 ppr encoder = 0.088deg/encoder line, I set Deadband to 0.05 and now it is dead still around setpoint.

I will have to optimise the PID later as I am due to replace the integral 5C spindle with a new spindle with a 4" 5C chuck fitted - a long story, but basically a problem with the current spindle design resulting in oil leaks that I cannot resolve, and that the tool plate in the ATC will have to be excessively large in diameter for boring bars/drills to clear the headstock..
Anyway, the 5C chuck will add inertial mass to the spindle so PID may need some work then.

The issues I have..
The behaviour is thus:
Home all Axes, in MDI M100 - all is stable and still.
Then G0 C360 > rotates to 360deg, stops momentarily, then does a fast 360deg rotation and stops at 360deg position and is stable
After that, any C_axis move is stable and correct.
Then do M101, M03 S500 > spindle powers up and is at 500rpm.
Then M05 > spindle stops.
Then M100, and spindle rotates back to the last angular position it was at before the last M101, BUT-
it does this rotate very fast and oscillates heavily - past the point, stops, back again, past the other way, etc - takes a few seconds to stabilise, and thereafter all C_axis moves are fine again. This is repeatable, ie, do M101>M03 S100>M05>M100 and it repeats.

It is as though there are some PID parameters not being used in that initial move to setpoint angle?
For testing ease, is there a way I can setup the INI/HAL so that I only have to home the C axis before doing these tests? Homing X and Z and then C many many times while tuning is boring..

And again, Thanks for all your assistance. Much Appreciated. I do think this topic should somehow be starred as 'important' on the forum as when I started I searched the forum for many hours on the C_axis issue - I found many posts, many attempts, lots of frustration, and seemingly not many solid results - all the variants, using the orient component, and many other ways...Your solution is elegant , simple ( if you know how..) and brilliant!

Thanks
Joe