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Dear Friends I am reading emails about the PID. I too have few question about position control. 1. What is the position error actually mean? Why i am asking this question is as everybody knows that in control loop we give the setpoint and feedback is compared and correction is made depending upon the error. Lets take an example of velocity loop.We set some speed and we get the set speed after some time and it is maitained constant until we change the setpoint. But in case of the position control if we give some set point position but motor takes time if the move is long enough( Set point is in pulses and feedback is also inpulses)to reach the required positiion. Initially error is equal to the set point position since motor just started to move and feedback pulses are zero. Then at this point how PID acts. My confusion is that for long moves PID will saturate. But once the position is achioved PID will maintain the same position if we try to move the axis by hand PID will bring back to it setpoint position. But does PID acts when moves are long? 2.Why position feedforword is required if there is integrator term in the PID loop to take care of the steady state error? Thanks. Vikas ************************************************************************** Vikas W. Meshram Scientific Officer, Laser Instrumentation, Center For Advanced Technology, Indore- 452 013, MP,INDIA. Email:[email protected]