A-B 1746-BLM Blow-molding Module

Features

This 4-axis position-control module has these features:

• Open-loop or closed-loop control

• Independent and coordinated axis control

• Position- and time-based control

• Accumulator push-out control

• Zero-scale/full-scale (offset & span) calibration for position inputs

• PID with anti-windup, bumpless parameter changes, setpoint weighting, and 

limited high-frequency derivative gain.

• Profile interpolation (linear or cubic spline) between setpoints

• Converging/diverging tooling (direct/reverse acting control)

• Three hold values per axis: manual position, purge, or die gap

• Independent profile scale and offset adjustments 

• Automatic parison weight adjustment

• Setpoint marking

Overview

The module performs its servo control task independently, but is dependent on the 

SLC processor for all of its configuration and run-time information. The processor 

may be also be used to supply process data or timing information over the 

backplane in certain situations (e.g. parison drop synchronization on continuous 

extrusion machines, or accumulator position in reciprocating screw machines).

The module uses a digital signal processor running a 

Proportional-Integral-Derivative (PID) algorithm to control four axes of motion. 

Four analog inputs and four analog outputs are used for process variables and 

signals, while four digital inputs and four digital outputs are used for start-of-drop 

synchronization and profile step synchronization signals, respectively. An excitation 

voltage is provided for use with linear potentiometers.

Communication with the SLC Processor

• shared memory

• control bit/status bit handshake

• micro processor

• PID control algorithm

• digital I/O

• analog I/O

Shared memory

From the ladder programmer’s perspective, communication with the module is via 

five data files located in shared memory on the module:

Config(G) File

contains information regarding the operational mode and feature 

settings of the module. You specify the contents of this file with 

the ladder logic programming utility (RSLogix500). Entries in the 

file are static and read-only from the module’s perspective (e.g. 

time vs. position based operation). This file is automatically 

downloaded to the module when you switch the SLC processor to Run mode. 

Output File

contains 32 16-bit entries used by ladder program to command 

module operation. The Output File may also be used to supply 

process data to the module in certain situations. Entries in this 

file are updated automatically, at the end of each scan, by the 

SLC processor from the user data file but may be written at any 

time by immediate I/O instructions in the ladder program.

Input File

contains 32 16-bit entries used by ladder program to extract 

status information from the module. The Input File contains 

acknowledge bits corresponding to control bits in the Output 

File, as well as information pertaining to the profile executing on 

each analog I/O channel (step number, setpoint, analog input, 

process variable, control output, etc.) and a parameter error flag. 

The entries in this file are read automatically, once per scan, by 

the SLC processor into the user data file, but may be read at any 

time by immediate I/O instructions in ladder program.

M0 File

contains four axis control structures and five setpoint profiles. 

Each axis has a variety of PID and profiling options, controlled 

by its axis control structure. Each axis also has a unique 

256-point setpoint profile. A single master setpoint profile is used 

with an “interpolate” command to ease the task of generating setpoint profiles. 

Entries in the M0 File are written by move or copy instructions in 

ladder program. Unlike changes made to the Output File, which 

are automatically detected by the module, the module must be 

explicitly instructed to download axis-control structures and 

setpoint profiles from shared memory (done by setting bits in the Output File).

M1 File 

contains four axis-status structures, four process-variable profiles, 

and a single interpolated profile. Axis-status structures are copies 

of respective axis-control structures, except that status 

information has been inserted by the module. Each 

process-variable profile provides a record of the actual position 

response to a setpoint profile. The interpolated profile is the 

result of either a linear or natural cubic-spline interpolation 

performed between the setpoints specified in the master setpoint profile. 

Unlike the Input File, which is automatically updated, the 

module must be explicitly instructed to upload axis-status 

structures, process variable profiles, and the interpolated profile 

to shared memory (done by setting bits in the Output File). 

Entries in this file are then read by move or copy instructions in ladder program.