Rockwell Automation 1746-BLM Installation Instructions
Blow-molding Module
ATTENTION
!
WARNING
!
(catalog number 1746-BLM )
Before you begin
Installation Instructions
Use this document as a guide to installing and powering-up your Blow-molding
Module. W e assume tha t you are already familiar with the SLC 500
Logic Controllers and associated I/O modules.
™
family of Small
Tools that you need
• 1/8” slotted screwdriver
Handling the Module
Take these precautions to guard against ESD damage:
Electrostatic discharge can damage the module. Follow these
guidelines:
• touch a grounded object to discharge potential static
• wear an approved grounding wriststrap
• do not touch circuit components inside the module
• if available, use a static-safe work station
• when not in use, store the module in its anti-static bag.
Do not insert or remove this module while backplane power is
on. An electrical arc may occur that can cause an explosion in
a hazardous environment and/or cause damage to the module
or degrade its performance.
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2 Blow-molding Module
ATTENTION
!
IMPORTANT
Important User Information
Because of the variety of uses for the products described in this publication, those
responsible for the application and use of this control equipment must satisfy
themselves that all necessary steps have been taken to assure that each application
and use meets all performance and safety requirements, including any applicable
laws, regulations, codes and standards.
The illustrations, charts, sample programs and layout examples shown in this guide
are intended solely for purposes of example. Since there are many variables and
requirements associated with any particular installation, Allen-Bradley does not
assume responsibility or liability (to include intellectual property liability) for actual
use based upon the examples shown in this publication.
Allen-Bradley publication SGI-1.1, Safety Guidelines for the Application, Installation
and Maintenance of Solid-State Control (available from your local Allen-Bradley
office), describes some important differences between solid-state equipment and
electromechanical devices that should be taken into consideration when applying
products such as those described in this publication.
Reproduction of the contents of this copyrighted publication, in whole or part,
without written permission of Rockwell Automation, is prohibited.
Throughout this manual we use notes to make you aware of safety considerations:
Attention statements help you to:
• identify a hazard
• avoid a hazard
• recognize the consequences
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Identifies information about practices or circumstances that can
lead to personal injury or death, property damage or economic
loss
Identifies information that is critical for successful application
and understanding of the product.
Blow-molding Module 3
Recommendation for using associated software
To program the SLC processor to interface the module with molding machine
operation, your PC should be equipped with programming software RSLogix 500™
from Rockwell Software. For instructions on using the software, refer to the
documentation that accompanied it.
What you need to do to set up and operate the module?
This document covers a description of the module and its operation, wiring and
configuring the module, writing ladder logic and using associated data files,
calibrating, tuning, troubleshooting, and specifications.
Step Description Page
1 Module description 4
2 Machine applications of the module 9
3 Module operation with an accumulator machine 14
4 Module operation with a continuous extrusion machine 16
5 Determining an axis setpoint 18
6 Wiring the module 19
7 Configuring the SLC processor (including I/O, M0/M1, and G file) 25
8 Axis Control Structures in M0/M1 Files 30
9 Using output and input image tables 31
10 Writing Ladder Logic 35
11 Calibrating the module 37
12 Tuning a PID Loop 38
13 Troubleshooting 39
Specifications 41
Descriptions of module parameters 43
European Communities (EC) Directive Compliance 44
Rockwell Automation Support 45
Hazardous Location Approval 46
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Step: 1 Module description
We cover these aspects of module description:
• features
• overview
• communication with SLC processor
• internal microprocessor
• internal PID control algorithm
• analog I/O
• digital I/O
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
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Blow-molding Module 5
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 si gnals, respectively. An e xcitation
voltage is provided for use with linear potentiometers.
Digital
PLC Interface
Shared Memory
Module µP
Local Memory
I/O
Analog
I/O
Excitation
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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.
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Blow-molding Module 7
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.
Handshake with control and status bits
To ease the task of synchronizin g module op erations with y our ladder program, all
control bits in the Output File have a corresponding status bit in the Input File.
Upon detecting a change in a control bit from zero to one, the module performs
any associated processing and then acknowledges completion by setting the
corresponding status bit to one. The status bit w ill r emain se t as long as the control
bit remains set. When the control bit is cleared, the status bit will be cleared
immediately in acknowledgment.
Exceptions to this protocol are the profile enable control/status bits and the
control/status bits for the digital inputs and digital outputs. See step 9 for complete
descriptions of these and other bits.
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Module’s microprocessor
The module processor is a 16-bit fixed-point digital signal processor (DSP). It
communicates with the analog I/O channels over a high speed (2MHz) full-duplex
synchronous serial link. Serial connection between the processor and analog I/O
hardware facilitates electrical isolation. Digital I/O is performed in a similar fashion.
The module processor manages all communications between the module and the
SLC processor. It performs such functions as interpolation between profile
setpoints, loop tuning, and calculation of calibration coefficients in addition to
executing the control algorithm.
Module’s PID control algorithm
For servo control, the module uses a Proportional + Integral + Derivative a lgorithm
with anti-windup, high-frequency derivative gain limiting and setpoint weighting.
Anti-windup is achieved by modeling the actuator (normally a valve amplifier) as a
nonlinear device that operates linearly over a limited range, beyond which it
saturates.
An additional error signal is formed by taking the difference of raw controller
output, v(n), and control output, u(n), which is clamped at the actuator saturation
limits. This signal is multiplied by gain 1/Tt, where Tt is called the integrator
tracking time and summed into the integral term. High-frequency derivative gain
limiting lets you compensate for derivative term susceptibility to high frequency
noise. Setpoint weighting provides a mechanism for independent tuning of setpoint
and load response.
Digital I/O
There are four fully isolated digital inputs on the module. They are of the
current-sinking type. Their primary use is for start-of-parison-drop synchronization
on continuous extrusion machines. The digital inputs may be used as general
purpose inputs if the start of drop synchronization feature is not needed.
There are four isolated digital outputs on the module. They are of the
open-collector (current-sinking) type and share a common 24VDC (nominal)
external power supply. Their primary use is as profile step-synchronization
indicators. The digital outputs may be used as general purpose outputs if the step
synchronization feature is not needed. See page 41 for complete specifications.
Analog I/O
There are four analog I/O channels on the module. Each channel consists of a
14-bit analog-to-digital converter and a 14-bit digital to analog converter. As a
group, the four I/O channels and excitation output are optically isolated from the
remainder of the module. The high common mode input range of the input
amplifiers and the isolated nature of LVDTs and linear potentiometers make it
unnecessary to isolate the channels from one another. See page 41 for complete
specifications.
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Blow-molding Module 9
Step: 2 Machine applications of the module
Each module can control up to four axes of closed-loop position control on most
types of blow-molding machines. Configurations include:
• accumulator push-out control and three parison axes
• two accumulator push-outs and two parison axes
You can use multiple modules on machines with more than four heads.
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Control of Accumulator Head Machines
The module controls parison wall thickness on accumulator machines by following
a setpoint profile of wall thickness vs. accumulator ram position. In this
configuration, the module is capable of controlling up to three blow molding
heads. One analog I/O channel is used for accumulator ram velocity control while
the others are used for mandrel position control.
Optionally the module may simply monitor ram position. Mandrel position and
accumulator ram velocity are normally both specified as a function of accumulator
ram position. Since the module supports a mixture of time- and position-based
modes, you may also specify accumulator position as a function of time.
Proportional
Valve and
Cylinder
Position
Transducer
ram
mandrel
Valve
Amp
accumulator
Proportional
Valve and
Cylinder
Position
Transducer
Valve
Amp
Analog
Outputs
Analog
Inputs
1746-BLM
Module
Analog
Outputs
Analog
Inputs
parison
Valve
Amp
Valve
Amp
accumulator
Proportional
Valve and
Cylinder
Position
Transducer
mandrel
Proportional
Valve and
Cylinder
Position
Transducer
ram
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Blow-molding Module 11
Control of Continuous Extrusion Machines
The module controls parison wall thickness on continuous extrusion machines by
following a setpoint profile of wall thickness vs. time. The module is capable of
controlling up to four blow molding heads in this mode. Each of the m odule’s four
analog I/O channels is used for mandrel position control. Mandrel position is a
function of the elapsed time since the last synchronization signal, indicating start of
parison drop.
Servo Valve and
Hydraulic
Cylinder
mandrel
Servo Valve and
Hydraulic
Cylinder
mandrel
LVDT
LVDT
Valve
Amp
Valv e
Amp
Analog
Outputs
Analog
Inputs
Digital
Sync Pulses
parison
1746-BLM
Module
Analog
Outputs
Analog
Inputs
Digital
Sync Pulses
parison
Valve
Amp
Valve
Amp
Servo Valve and
Hydraulic
Cylinder
LVDT
mandrel
Servo Valve and
Hydraulic
Cylinder
LVDT
mandrel
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Control of Reciprocating Screw Machines
Reciprocating screw machines have multiple heads and a single accumulator.
Control of accumulator position is performed by the SLC processor. The module
may be used to monitor the accumulator (screw) position in either of two ways on
this type of machine:
• with an analog input to the module: Each module configured in this
manner can control three heads. This method offers optimal performance.
However, hardware utilization may not be as high as the following method
depending on the number of extrusion heads.
• with a separate high speed analog module: The SLC processor must
read position information from an analog module and update the 1746-BLM.
A selectable timed interrupt (STI) instruction can be used with a 4ms period
and variability << 1ms (tested on a SLC5/04 CPU with no other interrupt
sources). This is adequate for 256- setpoint profiles with drop times > 1
second (~4ms/setpoint). Drop times of less than one second necessitate
monitoring accumulator position with the 1746-BLM. Avoid using other STI
instructions with higher priority.
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Blow-molding Module 13
Proportional Valve and
Cylinder
Position
Transd ucer
ram
Servo Valve and
Hydraulic
Cylinder
LVDT
mandrel mandrel
Servo Valve and
Hydraulic
Cylinder
LVDT
mandrel
Valv e
Amp
Valve
Amp
Single accumulator controlled by
separate analog module and SLC
ladder logic.
Valv e
Amp
Analog
Outputs
Analog
Inputs
Digital
Sync Pulses
parison
1746-BLM
Module
Analog
Outputs
Analog
Inputs
Digital
Sync Pulses
Valv e
Amp
Valv e
Amp
Servo Valve and
Hydraulic
Cylinder
LVDT
Servo Valve and
Hydraulic
Cylinder
LVDT
mandrel
parison
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14 Blow-molding Module
IMPORTANT
Step: 3 Module operation wi th an ac cumulator machine
Position-based Operation
In position-based mode, setpoint profiles are specified as a function of the position
of a second, independent axis position. Here the independent axis corresponds to
the accumulator ram position, while the dependent axis corresponds to mandrel
position (or ram velocity).
Conceptually, the shot size of the independent axis is divided into 256 segments.
When the accumulator ram position falls within the range of a particular segment,
the number of that segment is used as an index into the setpoint profile to
determine the current setpoint for the mandrel position (or ram velocity).
Although you may specify profile sizes less than 256 in the
config file, the module expands these to 256-point profiles
after downloading from shared memory. Internally to the
module, all profiles are 256 points in l ength. Similarly, process
variable profiles are compressed from the module’s 256-point
internal representation to your desired profile size prior to
uploading.
Controlling Mandrel Position
Static control: Mandrel position may be controlled statically by means of the three
axis-hold values and corresponding hold-value control bits accessible via the
module output file. The hold values are prioritized with hold value #0 being highest
priority and hold value #2 being lowest.
In absence of an active profile, the highest priority enabled hold value becomes the
position setpoint. By convention, the fully-closed mandrel p osition is the zero-sc ale
calibration point, while the fully-open mandrel position is the full-scale calibration
point.
Dynamic control: Mandrel position may be controlled dynamically by
downloading a setpoint profile to the module’s M0 file and setting the profile
enable bit. Then, upon detecting the independent axis position at shot size, the
module will automatically update the mandrel position once per millisecond
through the last profile setpoint.
The last setpoint is maintained until all of the following are complete:
• profile enable bit is cleared
• independent axis is again at shot size
• profile enable bit is set again, which starts the next profile
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Blow-molding Module 15
Monitoring Mandrel Position
Instantaneous mandrel position may be monitored by reading the current process
variable from the module’s input file. Several other values of interest are also
available for each axis (e.g. control output, profile step, etc.). Process variable
profiles may be read from the module’s M1 file.
Controlling R a m Velo c ity
Accumulator ram velocity is controlled in position-based mode by specifying ram
velocity as a function of ram position. As with mandrels, rams are calibrated for
zero-scale and full-scale positions. Velocity is then expressed as velocity = change
of position/millisecond. By convention, the fully-forward ram position is the
zero-scale calibration point, while the fully-retracted ram position is the full-scale
calibration point. This implies that negative velocities result in moving the ram
forward.
Velocity can be controlled in either open loop or closed loop. You select
closed-loop velocity control by setting the appropriate axis’ velocity-control bit in
the module output file. Since hydraulic valves generally provide a constant
hydraulic flow with a constant command input, setpoints in open-loop mode
inherently specify velocity. Once closed-loop velocity control is enabled, hold v alue
#2 is interpreted as shotsize, and the axis’ step synchronization output is enabled as
an at-shotsize indicator.
Operation by Controlling Ram Velocity
Normally, ram velocity is controlled in closed loop using a single module analog
I/O pair. A velocity profile (as opposed to a position profile) is necessary since the
independent axis is the ram position. The remaining three analog I/O pairs are
available for controlling machine heads.
Operation by Monitoring Ram Velocity
This mode of operation is identical to operation with ram velocity control, except
ram position is monitored only (a velocity profile for the ram is not used). You can
control up to three machine heads per 1746-BLM. The resulting unused analog
output is available for general (open-loop) use.
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