Rockwell Automation 1771-QA Stepper Positioning Assembly User Manual - Manual (Page 23)

Chapter
3
Publication 1771-UM002A–EN–P – May 2000
Programming and Operation
The desired motion of the stepper motor can be accelerated,
decelerated or maintained at constant rate by controlling the pulse
rate from the pulse output expander module. Motion can be
rotational such as used to position an indexing table, or can be linear
such as obtained when a linear slide is driven forward or backward
by turning a threaded shaft. In either case, the position at any given
moment is defined by the number of pulses sent to the stepper motor.
It can result in some number of degrees of rotation or linear units of
travel.
The motion can be programmed by manipulating data table words
(control blocks) arranged in a convenient format. Blocks of data are
also used to indicate that commands were received and desired
motion was implemented (status block). Control and status blocks
are communicated bidirectionally between the PC processor and
stepper controller module by block transfer programming.
The task of programming requires that control and status block be
assigned in the data table and that control data be entered using the
industrial terminal. Control blocks sent to the stepper controller
module by write block transfers govern acceleration, deceleration,
final rate and final position. Control blocks also contain control
words. Bits in control words must be set according to the particular
application and desired motion.
The stepper controller module sends status blocks of data to the PC
processor using read block transfers. Status blocks contain current
position information and diagnostic bits set by the stepper
positioning assembly.
The format of the data blocks and the function of status and control
bits will be covered later in this chapter.
There are three stepper positioning concepts which should be
understood before learning how the stepper positioning assembly is
programmed. They are:
•
Move Definition
•
Moveset
•
Positioning Modes
General
Positioning Concepts