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So I have played with closed loop spindle . On my machine Where I have an older gearbox. I get alot of hunt and gear slap . I think that if I had my motor directly connected to the spindle this would be great. Also my encoder is not directly connected to the spindle it is connected to what used to be the lead screw gears. This is where it was connectd for the Anilam and AhHa conversion. I am going to move it to the spindle and try closed loop again. I need the machine to run smooth so I can make the parts for the spindle encoder. So off to another configuration with just spindle speed control. It dosen't get any better then this....


Jim

jbunch wrote:You possibly have the PID rather too active.

A spindle speed control probably works best based around mainly FF0 supplemented by I. Pgain isn't really right for this application, as you don't want zero-output when up to speed.

Andy,

I decided to play with closed loop a bit more. What I ended up with was stable performance with tese settings.

setp pid.2.Pgain 0.000
setp pid.2.Igain 0.0
setp pid.2.Dgain 0.000
setp pid.2.bias 0.0
setp pid.2.FF0 0.00000199
setp pid.2.FF1 0.0
setp pid.2.FF2 0.0
setp pid.2.deadband 0.1
setp pid.2.maxoutput 10.00

The motor runs up to speed based on this output and that is it. If I add and "I" even in realy small amounts I get overrun and hunting. So based on what I see FF0 is just scaling my RPM to output voltage.


Jim

jbunch wrote:I would expect Igain to be at most 1/1000th of FF0. And maybe 100x smaller than that.
I am assuming you have a very high-speed spindle?

Andy,

It looks like you are correct. The "I" works when it is way smaller then FF0. Also top speed on the lathe is 1800 on the plate.

So what does closed loop buy me? I would think that it would be added torque at low RPM's. Other then that I am not sure.

Can you gain enough torque to to run the spindle at 90 RPM and motor at 180 RPM and still make large cuts?

would that require a larger motor say 7hp instead of the 5 I have?

If so then the next project is to direct connet the motor to the spindle and bypass the gearbox.


Jim

jbunch wrote:Something seems a little odd, then.
Assuming S1800 your FF0 term comes out at .0036. Which is presumably full-scale on the PID input.
That "36" looks suspiciously like a 3600. I wonder if there are a couple of inverted 60x scalings in the system?
(Some things are in rpm and some in rps in HAL)
Not that it matters, the computer just sees numbers and treats them all the same.It means you have the cutter surface speed you asked for regardless of non-linearities in the system.
With a DC motor or a servo it will also give you much higher available torque at the set speed. You get some of the same effect with an induction motor, but not to the same extent.
This has set me wondering about setting up closed-loop spindle on my lathe, though, as it might help with parting. (The Mill already has it)