PID-filter routine (2nd try).

[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..

[amgen]

.5 sec is too long to get speed reading, you may be able to timer/counter 1 pulse duration to get speed ref faster .
PID itself is hard to tune. Isn't each correction just how-much and how fast ? and slowing-down and reducing each correction until there is no overshoot ? I made an alternator/regulator controller that self-tuned by jointly reducing correction amount and slowing corrections (longer pauses) until there were no more overshoots. The output was the PWM to MOSFET. You could also adjust up/down the gain/time with a pot input ref.
Are you interested in PID discussion ?
don
amgen

[infinitrix]

i'm interested in pid to control position and speed.. can u show me some program and schematic for self tune pid.. i use 3 pot to adjust kp,ki and kd.. i'm just not very clear about tuning the pid..

[amgen]

do you need to move something to a position and stop, or shift motor from 1 speed to another speed or hold speed constant while the load changes.
That dictates the type of feedback needed and how fast the control needs to actuate.
Explain your control operation a little.

don
amgen

[HenrikOlsson]

Hello,
Sorry for the slow response on my behalf, I've been on the road so I haven't been on the 'net that much.

As I've written en previous posts in this thread the incPID routine itself does not know or care if it controls position, speed, temperature, waterlevel, light, torque or whatever. It simply returns a value based on the "error" you send it and the tuning parameters you set.

You can only run one PID-loop with it though (without rewriting the include) so controling BOTH speed AND position with the incPID won't work. What you CAN do though is to set up your system to control position and then in your program you continously change the targetposition. Set up a 100Hz (or whatever) interrupt and add to or subtract from the target position, the more you add or subtract the faster it will go. I've done that myself and it works fairly well.

Tuning is an art and there's more than a few ways to do it, Google Ziegler Nichols to read up on one of them. I've simply done it by "feel" but you can for example send the errror value to the USART and then plot the value on the PC using EXCEL or whatever to "see" the response of the system.

I suppose doing an autotune routine would be possible but it's not something I'm going to try. If you're going to write an autotune routine I suggest you read up and get good at manually tuning first so you know and understand how to respond to different situations. (Undershoot, overshoot, oscillation etc).

Hope it helps!
/Henrik.

[hadiengg]

Dear sir,
I check INCPID routine it works fine as position control.
I want to control speed via PWM what should i change in the INCPID routine
and also how can i give pid_Kp pid_Ki pid_Kd using external potantiometer
which is reading through ADC CH which gives 0-1023 value and how i convert
this value to $0xxx figure.