Closed-Loop stepper control

[mmjpotter]

A question which surfaces from time to time on the Zone relates to whether stepper motor control systems provide a full closed-loop facility.

I must confess to having a preference for Servo systems and have spent a considerable amount of time developing a closed-loop servo motor controller. The system works well with a variaty of controllers for brushed /brushless DC motors, but could a stepper motor be hooked-up to replicate the response of the DC motor ???

The fundamental theory behind closed-loop control, is the generation of an outout signal which is proportional to the difference between the actual & required positions. In many controls this signal is an analoque command voltage of +/- 10volts and is used to vary the speed of the DC motor, whilst driving it to the 'requested posiotion'.

IF---- the +/- 10volt command signal is processed by a voltage to frequency converter (LM331 or AD625) a PULSE TRAIN whose frequency is proportional to the input voltage is produced.
Would the stepper motor speed respond to this change in pulse frequency and perform similarly to a DC motor?

My experience with stepper motors is very limited (well a bit less than that !! ) so I look forward to reading some of your comments on this theory.

[Al_The_Man]

Originally Posted by mmjpotter A question which surfaces from time to time on the Zone relates to whether stepper motor control systems provide a full closed-loop facility.

Steppers do not usually provide a closed loop, they are often used because of economics, the loop is assumed but not verified.

I also prefer servo's just because my experiences have been less than successful, but also alot of people use them, again, because of the economics.
They are probably closer to BLDC motors than DC brushed.

Originally Posted by mmjpotter could a stepper motor be hooked-up to replicate the response of the DC motor ???

I guess that begs the question, Why would you try? IMO if you are going to the effort of using encoder for feedback confirmation, then use a servo motor, which should offer smaller output increments, than the steppers 1.8°.
My 2¢.
Al.

[bunalmis]

We know the comman advantages of closed loop control but biggest advantage is "We can use advanced antiresonance methods in the controller".

But positions sensors increased the total system cost.