current mode, velocity mode and position mode in servo control system
current mode, velocity mode and position mode in servo control system
(OP)
For a servo amplifier, there are current mode, velocity mode and position mode. What is the difference between them. In some control system design, current mode is used even when velocity of the motor need to be controlled. I am really confused at this point.
Any artical or book could be helpful here?
Thanks.
Any artical or book could be helpful here?
Thanks.





RE: current mode, velocity mode and position mode in servo control system
http://www.micromo.com/library/docs/notes&tutorials/MCT.pdf
RE: current mode, velocity mode and position mode in servo control system
The current loop power stage can then be driven from a velocity control loop. The servo amplifier compares a velocity command to a velocity feedback (either to a tachometer in older systems or an optical encoder. An optical encoder gives position feedback but velocity is simply the rate of change of position) and drives the input to the current loop to maintain commanded velocity.
Velocity mode servo amplifiers are then often driven from a position controller. This arrangement is call "Cascade Control." It tends to allow a simpler position controller in that the velocity loop tends to take care of the disturbance rejection. This is often refered to as velocity mode control
If the servo amplifier is digital, the position loop and trajectory generation can be incorporated in the amplifier. This is usefull to implement (usually) simple canned moves (go to position 1, go to position 2, etc.).
A position controller can also drive a current mode servo amplifier directly to control position. This is often refered to as Current Mode Control.
RE: current mode, velocity mode and position mode in servo control system
There were several advances in hardware and software since the 70's when velocity mode was the best there was. Current/torque mode out performs velocity/position mode in any application as far as I know.
Barry1961
RE: current mode, velocity mode and position mode in servo control system
See Reference, e.g.:
Ned Mohan, Tore M. Undeland, William P. Robbins "Power Electronics Converters, Applications and Design," Third Edition, John Wiley & Sons, Inc., 2003, Section 13-6-4 Control of Servo Drives