Hello Tom.

I am building lathe with Kflop+Kstep boards and I have some questions regarding spindle closed loop control setup.

Spindle motor is 220V DC motor. I have designed controller to drive this motor, and it works fine.

DC motor controller drives thyristor bridge, and voltage applied to motor varies depending triac phase firing angle. I have connected controller to Kflop step dir channel. Each 1/100 sec controller counts steps, calculates commanded velocity and transfer it to voltage applied to motor drive. Commanded velocity is proportional to output voltage. I had to use some math approximation cause of 8 bit controller, but velocity to voltage plot is almost linear with  2-3 % error and some S-curve behavior. 

Spindle sensor is 1000ppr optical encoder, max speed is 2000 rpm, so max velocity is 133 333 pps.

First of all if motor is not loaded I get max RPM at ~165 Vrms, also i have noticed that applied voltage is not directly proportional to RMP, actually not directly at all :) Also at low speeds spindle can be just stopped by hand (30 RPM).

I have to close the loop to operate at CCS and for threading.

So the questions is:

Can this setup operate in closed loop mode using KFLOP step dir chanel closed loop PID and filters? Or i should make come C program to drive my controller? Also is selected velocity control method is ok or I should change my controller software to be driven from PWM or something ?

Thx. in advance

B.R. Danchik

Hi BR,

I would think the simplest approach to try first would be to just operate as a Closed Loop Step/Dir Axis.  I would scale the encoder Input gain such that Jogging the at some Step Rate at about half speed, the encoder count rate is approximately the same rate (in open loop mode).

Allow infinite Max Output, large following error, and use some I gain.

 

Hello Tom.

I am building lathe with Kflop+Kstep boards and I have some questions regarding spindle closed loop control setup.

Spindle motor is 220V DC motor. I have designed controller to drive this motor, and it works fine.

DC motor controller drives thyristor bridge, and voltage applied to motor varies depending triac phase firing angle. I have connected controller to Kflop step dir channel. Each 1/100 sec controller counts steps, calculates commanded velocity and transfer it to voltage applied to motor drive. Commanded velocity is proportional to output voltage. I had to use some math approximation cause of 8 bit controller, but velocity to voltage plot is almost linear with  2-3 % error and some S-curve behavior. 

Spindle sensor is 1000ppr optical encoder, max speed is 2000 rpm, so max velocity is 133 333 pps.

First of all if motor is not loaded I get max RPM at ~165 Vrms, also i have noticed that applied voltage is not directly proportional to RMP, actually not directly at all :) Also at low speeds spindle can be just stopped by hand (30 RPM).

I have to close the loop to operate at CCS and for threading.

So the questions is:

Can this setup operate in closed loop mode using KFLOP step dir chanel closed loop PID and filters? Or i should make come C program to drive my controller? Also is selected velocity control method is ok or I should change my controller software to be driven from PWM or something ?

Thx. in advance

B.R. Danchik

Hi Danchik,

I don't understand the statement:

>>> I have scaled my system step rates. Contoller step

 

Hi Tom, thank you very much for help.

I have scaled my system step rates. Contoller step rate is twice bigger than an axis chanel, and in open loop mode I get spindle max speed at a half of the maximum controler step rate.

If I close the loop and add some smal I-gain commanded jog rate and actual encoder rate is almost equal, but there is some overshooting, and still no torque at small RPM rates. Actualy it seems that I gain is so slow, and I need different I-gains for different RPM's ;)))

So, should I add some D-gain to stop overhooting, or PID filters ?

How should I deal with very slow I gain on low RPM rates ?

Thx. Danchik

Hello Tom.

Sorry for my bad explanation.

In my controller I have to transfer step pulses to output voltage, maximum voltage 220 v equals to  266  600 pps step rate. It is twice bigger then spindle max velocity which equals to 133 300 pps. So in open loop mode when kflop commands 133 300 pps velocity controller outputs 110 Vrms and real measured spindle velocity is about 100  000 pps.

Hi Danchik,

I expected you to change the InputGain0 for the encoder so that the open loop step rate more closely matches the commanded step rate.

So for example with a gain of 2.0 then commanding 266600sps rate should then read the spindle at 266600sps rate.

However I see now that the open loop speed is so non-linear that this may not help much at other speeds.

I don't see why the commanded and actual rates wouldn't be exactly equal.  The response to changes might be terribly slow but eventually the speed should be correct.  Please post a plot with all your settings for a large move so we can see what is happening.

I think P Gain may help stabilize the response.

 

Hello Tom.

 

Sorry for my bad explanation.

In my controller I have to transfer step pulses to output voltage, maximum voltage 220 v equals to  266  600 pps step rate. It is twice bigger then spindle max velocity which equals to 133 300 pps. So in open loop mode when kflop commands 133 300 pps velocity controller outputs 110 Vrms and real measured spindle velocity is about 100  000 pps.

Danchik

 

On 2016-05-22 05:42, stuntready@... [DynoMotion] wrote:
> Hi Tom,
>
> I made a user program. Writing Servo Output from spindle encoder
> channel to step/dir Frequency Generator works fine. With only P gain
> spindle response on low speed is significantly better. I have some
> questions regarding tuning the loop:
>
> Should I use PD-control or only I-control in the servo loop in my
> case?
> How can I increase loop response in low speeds, will feed/forward
> control help ?
> Should I use any IIR filters in my setup ?
>
> Thx for help, Danchik.