PID-filter routine (2nd try).

[RodSTAR]

hi Henrik;
i see you are a motor control specialist..
first of all thank you for sharing your work on your PID routine. About it i have some questions to understand.
_________
question1:
i don't understand theese variables:
pid_I_Clamp = 100 'Clamp I-term to max ±100
pid_Out_Clamp = 511 'Clamp the final output to ±511

_________
question2:
I see it controls position. ¿Does it control speed?

_________
question3:
from my pc i get two parameters: position and speed. i want to preset a 1 second of gradual speed increasing (you know, for not damaging mechanism & stuff..) and speed decreasing for before getting to the given position. Do any of your PID inc file variables handle this parameter/s or i need to do it by myself?

to let you breathe, it's all for now thank you.

regards, Rodrigo

[HenrikOlsson]

Hi Rodrigo,
No, no motorcontrol specialist at all actually, just a guy who tinkers with a lot of stuff, trying to pick up on what ever interests me at the moment ;-)

question1:
i don't understand theese variables:
pid_I_Clamp = 100 'Clamp I-term to max ±100
pid_Out_Clamp = 511 'Clamp the final output to ±511

The pid_I_clamp helps preventing what is called integrator wind-up. Let's say you are controlling the position of a motor. You command a new position but the mechanics that the motor is moving is blocked so it can't move. The I-term will now start to add "effort" to the total output of the filter to get the motor moving (decrease the error) but since the mechanics is blocked the error won't change so the I-term gets larger and larger and larger. When the mechancis finally "loosens up" you can imagine what happens. So with pid_I_clamp you can set the max amount of "effort" that the I-term will apply to the total output, no matter how big or how long the error persists.

(Another thing is that the I-term output is not protected from overflowing internally so we have to clamp it to something)

pid_Out_Clamp works the same way. Let's say you are running a 12V motor with a 24V powersupply. Applying full power (24V) to the motor may damage it so you can use the pid_Out_Clamp to prevent the final output of the PID-filter to ever go above a certain value, for example.

question2:
I see it controls position. ¿Does it control speed?

"It" controls anything you like. You provide it with an "error" and gives back a "drive-value" based on the gains etc that you've specified. It doesn't know or care what it is you are controling. With that being said it may lack features that is better suited for controling one thing or another, like feedforward etc but more or less, it doesn't care.

question3:
from my pc i get two parameters: position and speed. i want to preset a 1 second of gradual speed increasing (you know, for not damaging mechanism & stuff..) and speed decreasing for before getting to the given position. Do any of your PID inc file variables handle this parameter/s or i need to do it by myself?

No, there's no trajectory planner built in. If you want acceleration and deceleration ramps you need to "slowly" increase the "setpoint" to bring it up to speed and so on.

Hope that answers your questions.

/Henrik.

[RodSTAR]

Thank you so much Henrik, now I got it!
I'll test it as soon as I can. Then i'll bother you again

I have another question in a new thread, not related to PID, but related to counting position. Thread title: "Pulse count matching"

[infinitrix]

can i use the code to control speed and position of motor using same pic?

[RodSTAR]

can i use the code to control speed and position of motor using same pic?

First step (get), you Get variables from hardware (via pot, encoder, ...)
Second step (control), you correct those variables (PID between desired and got variables)) to reach your desired speed, direction & position by PWM and polarity (depending on the type of motor DC, BLDC or what ever). That is control.

And yes, both steps you can perform them in a single MCU. Motor control oriented MCU's works great for this, such as a dsPIC30F3011; or for this compiler, a PIC18F2431 (or any of the family PIC18Fxx31) which have QEI peripheral, where QEI stands for Quadrature Encoder Interface, which decodes signal from a rotary Quadrature Encoder, ideal for gathering motor rotation activity.

Rodrigo M.-

[infinitrix]

i'm using 1 channel incremental encoder and PIC16F877A.i use timer 1 to count pulse on background.to get the speed i use "count" instruction but it take a 0.5 second.is there any faster solution to calculate speed?

i decide to use incPID program to control speed,but how can i tune to find Kp,Ki, and Kd value..

[infinitrix]

anyone know how to tune PID coefficient? help me..