Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS - Manual (Page 22)

Positioning Concepts
Chapter 3
3Ć9
The following equation shows how these factors determine feedback
resolution:
leadscrew pitch
feedback resolution = (encoder lines) (feedback multiplier)
You must select the leadscrew pitch, encoder lines, and feedback
multiplier to provide desired feedback resolution and meet other
requirements of your application.
The programming resolution of the servo positioning system is 0.0001
inch or 0.001 millimeter. If you select a feedback resolution coarser than
that, round off your position commands so that the effective programming
resolution is no finer than the feedback resolution you chose.
If you select a feedback resolution finer than the programming resolution,
positioning can be smoother. However, the maximum axis speed is
directly proportional to the feedback resolution. There is always a
trade-off between feedback resolution and maximum axis speed. The
maximum encoder input frequency for the servo positioning assembly is
250kHz. Therefore, to avoid a programming error, you must limit the axis
speed to conform to this formula:
programmed 1.5 x 10 7
axis speed < 1.28 x feedback res x feedback mult
The 1.28 factor allows for a 127% feedrate override value.
Each encoder line represents a fraction of a revolution of the leadscrew.
For example, consider a 250 line encoder. Each line represents 1/250 of a
revolution of the leadscrew.
Also, consider a 4-pitch (per inch) leadscrew for this example. The slide
moves 1/4 inch for each revolution. With an x1 multiplier, each feedback
increment represents 1/250 of 1/4 inch or 0.001 inch slide movement.
This is the feedback resolution.
0.25 in/rev
feedback resolution = 250 lines/rev x 1 increment/line
= 0.001 in/increment