Rockwell Automation 1771-QB Linear Pos. - Manual (Page 26)

Positioning with the Linear Positioning
Module
Chapter 3
3Ć2
The module is a dual-loop position controller, occupying a single slot in the
Allen-Bradley 1771 universal I/O chassis. The module communicates with the
PLC through the 1771 backplane. There are two kinds of transfers–read
operations and write operations. By programming the PLC you can transfer
parameter, setpoint, motion and command blocks to the module to control the
two axes. You can also use the PLC to monitor the status of the module’s two
loops through block read operations. For more details on block transfers, see
Chapters 6 and 7.
Read Operations
Read operations enable the programmable logic controller to monitor the status
of both axes through the status block. The status block includes detailed
information on the two axes: fault conditions, current axis position, positioning
error, and diagnostic information.
Write Operations
The following four types of write operations enable the programmable
controller to control axis movement:
Parameter Block - defines the module’s operating parameters for each axis.
These parameters include calibration constants, software travel limits,
zero-position offset, in-position and PID bands, PID gains, maximum
velocities, jog rates, maximum accelerations and decelerations and more.
Setpoint Block - defines up to 12 setpoints for each axis with optional
acceleration, deceleration and velocity parameters for each setpoint move.
The programmable controller selects from among the 12 setpoints using the
command block.
Motion Block - permits complex profiles to be executed by the module. This
advanced feature can be used to blend or chain multiple motion segments in a
single, continuous motion.
Command Block - you use the command block to select the next setpoint or
motion segment to which the axis will move; to set a delayed start, software
stop or reset; to set jog bits; to select jog rate (low or high); to set
auto/manual, to enable/disable integral control and to define a 13th setpoint.
When the module receives a setpoint command, motion segment command, jog
command, or a discrete jog input, it automatically calculates the velocity curve
for the requested axis movement using parameters that you define for the move.
(See Figure 3.2.)
How the Module Interacts with
a PLC
Axis Movement