Query regarding PID control using ARM CortexM3

[kbm10]

I have implemented PID control on precision dc motors. The position of servo motor is determined through linear optical encoders. The encoder values are read using a counter/timer/ TIM4 in the microcontroller. When I make very small moves, the servo moves and stops. Then according to my algorithm , I check if the movement has finished or not. In some cases, the servo does not move and in some cases, as I can see on the debugger window, the encoder value changes, an error is detected in position causing the PID controller to move the servo back and forth( the error in position changes between +ve and -ve).. Any idea how I can remove this?

Thanks

 

[egeorgiev]

What type of arithmetic is used? What about your PID tuning? Check your gain and differential coefficients.

 

[kbm10]

What type of arithmetic is used? What about your PID tuning? Check your gain and differential coefficients.

I have double checked. It works 60% of times.. I have used this document for coding ....

http://igor.chudov.com/manuals/Servo-Tuning/PID-without-a-PhD.pdf

I was wondering if there is any noise problem or something which gets amplified. .. I have also observed that my encoder counts changes suddenly sometimes..i dont know why ?