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PI vs PD for position, speed, force, current control

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mawad

mawad

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Dec 8, 2010
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Dear all,
I have a question regarding using PI or PD control based on the control variable. Is there a relation? As I found a lot of people use PI controller for speed or current control for servo systems. However, PD is used a lot for position or force control. I am wondering if there are reasons for that or recommendations for the type of the control based on the control variable and the application.
 
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If there is a double integration in the plant under control -- for instance, from a torque/force command thru velocity to position -- you need derivative action to get the damping required for stability. Proportional gain here is just a spring (no shock absorber -- the car suspension analogy is a good one here).

If there is only a single integration in the plant under control -- for instance torque/force to velocity, or voltage command to current thru an inductive load -- you do not need derivative action. The system is much more inherently stable.

Curt Wilson
Omron Delta Tau
 
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Many thanks Curt. You provided me with very useful information. where can I read more about these about these recommendations for PT, PID and PD.
Regards,
 
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I have Ogata, but I can't find these information

If there is a double integration in the plant under control -- for instance, from a torque/force command thru velocity to position -- you need derivative action to get the damping required for stability. Proportional gain here is just a spring (no shock absorber -- the car suspension analogy is a good one here).

If there is only a single integration in the plant under control -- for instance torque/force to velocity, or voltage command to current thru an inductive load -- you do not need derivative action. The system is much more inherently stable.


I am wondering about guidance for when each type is used
 
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Many textbooks talk about the "type" of the physical system. A "Type N" system has N integrations (poles of the system at the origin of the S-plane).
 
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