What is the significant value by using a higher resolution encoder over a lower resolution in a motor (specifically in a stepper motor)?

I will be interested to learn on the above topic. And also how the setting in motor controller influence the performance of the motor with these high and low resolution encoder.

Many thanks... do advise me where i can get some information on this topic...

 

Higher resolution is necessary for better motion control, unless the pulse rate exceeds the capability of the instrument with which you are measuring them.

--
Steve Myres, PE
Automation Solutions
(480) 813-1145

 

The choice of feedback resolution in a motion control
is pretty simple - if higher resolution is available
it will probably help performance. This is of course
subject to the ability of your controller to handle
the higher resolutions. I work regularly with
encoders having resolutions of 4,000,000 cts/rev or
more these days. The two issues that can decide if
your controller can provide increased performance with
increased resolution:

1) What is the maximum frequency input that the
controller can handle. We handle 20 MHz in a standard
quadrature encoder, and 5.34 GHz for an interpolated
sin encoder. This means that in a standard encoder we
can handle up to 20,000,000 cts/sec in velocity. The
max frequency defines the maximum velocity for your
motor. If you need to go faster than the max input
frequency of your controller either get a lower
resolution encoder or get a better controller.

2) Can your controller respond quickly enough to
pertubations in the system to make the increased
resolution effective? If you have 1+ ms updates in
servo control then it may be that increasing
resolution of the feedback will not yield any effecive
change in control, particularly if the system has
large high frequency pertubations.

As Ali Pak, our algorithm guru here, says, you can
never have too much 1) love, 2) money, or 3) resolution.

A caveat to the above - if you are using steppers,
then encoder resolution much above the resolution of
the step (microstep) is not terribly effective, except
to show you more accurately how far off you are - so
you will still be at the same position you would be
with a lower res encoder, but will have more accurate
reporting of that position.

Davis Gentry
Applications Engineer
Delta Tau Data Systems
[email protected]

 

Obviously, the resolution of the encoder must be better than the least increment of accuracy that is required. A major impetus for encoder resolution beyond that, however, is due to the position encoder replacing the tachometer as the velocity feedback device. This is done by calculating
the change in position in a time period divided by that time period to obtain the velocity. As the time period gets smaller (say 1 millisecond,)the number of counts per period decreases and the velocity feedback number becomes erratic. This became more evident at low speeds where cogging was seen. By increasing the resolution of the encoder, the calculated velocity was more stable and the servo ran smoother. Steppers do not usually run with a velocity servo loop, so it is not usually appicable there.

Tom

Thomas B. Bullock, President
Industrial Controls Consulting Div.
Bull's Eye Marketing, Inc.
104 S. Main St., Suite 320
Fond du Lac, WI 54935
Ph: 920: 929-6544
Fax: 920: 929-9344
E-mail: [email protected]

 

Wow!!! There sure is a lot of "feedback" on this one. For the purposes of closing the position loop of a stepper system, any encoder resolution that exceeds your commanded resolution is a waste of money.

Example: If your stepper & mechanical system allows you to command a position in increments of 0.001", then a resolution 0.0005" (or greater) is completely useless. If you're off by 0.0005", you can't correct for it... you can only correct in increments of 0.001". The only reason to exceed the commanded resolution is to compensate for lower quality encoders (poor accuracy & repeatibility).

Like others have said, make sure you check the maximum frequency input & minimum pulse width of your controller.

Guy H. Looney
Principal

A.C.E. Systems, LLC
176 Thompson Lane, Suite G-2 · Nashville, TN 37211
Phone (615) 833-2193 · Fax (615) 833-5413
www.acesystemsllc.com