Absolute Position Control Definition


Thread Starter

Sandeep Shah

What does mean by the "absolute position control" in the motion world?
Does it mean you have to have an absolute encoder or a resolver for the position feed back? Another word, Can you call a system which uses the
incremental encoder for the position feedback loop control an "absolute position control"? Please share your opinion. Thanks a lot for your
response in advance.
At least in directing machine tools (EIA RS274D standard), absolute position means commanding it to the actual position from some fixed reference point. Incremental positioning means commanding to move a distance from its previous position.
It is independent of the type of feedback used because one can use an incremental encoder to update an absolute position register which is the feedback to the control. Conversely, one can have absolute feedback, but command the control in incremental steps.
Thomas B. Bullock, President
Bull's Eye Marketing Incorporated
Industrial Controls Consulting Division
104 S. Main Street, Suite 320
Fond du Lac, WI 54935
PH: 920: 929-6544
FX: 920: 929-9344
E-mail: [email protected]

Cameron Anderson

You do not need an absolute encoder or resolver. You could be an open loop step motor and still do absolute positioning.

What we mean by "Absolute Positioning" in Motion Control is where you always moving to a specific position where your reference point is always zero. For example. If the motor is at 0 revs and you say move to absolute postion 2. The motor will turn 2 revs to 2. Your position register is at 2 revs and you now want go to 8 revs. The motor will turn 6 revs (2 revs + 6 revs = 8 revs Absolute) Now your position register is at 8 revs, if you wnat to go to position zero, you say move to absolute position 0 and your motor goes -8 revs (8 revs - 8 revs = 0 revs absolute).

Hope that made sense to you.

Cameron Anderson
Advanced Products Specialist