AB Quality ALLEN-BRADLEY 1771-QB User manual

Linear Positioning Module
User Manual
Cat. No. 1771-QB

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, the
Allen-Bradley Company, Inc. 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 which should be taken into
consideration when applying products such as those described in this
publication.
Reproduction of the contents of this copyrighted manual, in whole or in part,
without written permission of the Allen-Bradley Company Inc. is prohibited.
Throughout this manual we use notes to make you aware of safety
considerations:
ATTENTION: Identifies information about practices or
circumstances that can lead to personal injury or death, property
damage or economic loss.
Attentions help you:
identify a hazard
avoid the hazard
recognize the consequences
Important: Identifies information that is especially important for
successful application and understanding of the product.
PLC is a registered trademark of Allen-Bradley Company, Inc.
Important User Information

Preface P1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Organization of the Manual P1. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Audience P2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Related
Publications P2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Related Software P2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Frequently Used Terms P3
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introducing the Linear Positioning Module 11. . . . . . . . . . . .
What is the Linear Positioning Module? 11. . . . . . . . . . . . . . . . . . . .
Product
Compatibility 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transducers 12
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Servo and Proportional Valves 13
. . . . . . . . . . . . . . . . . . . . . . . .
System Overview 14
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Positioning Concepts 21. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Axis Motion 21. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ClosedLoop
Positioning 22. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Linear Displacement Transducer 22
. . . . . . . . . . . . . . . . . . . . . . .
A
Simple Positioning Loop 23. . . . . . . . . . . . . . . . . . . . . . . . . . .
Proportional
Gain 24. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Feedforwarding 25
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Integral Control (Reset Control) 25
. . . . . . . . . . . . . . . . . . . . . . . .
Derivative Control (Rate Control) 26
. . . . . . . . . . . . . . . . . . . . . . .
Deadband 27
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PID Band 27
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Positioning with the Linear Positioning Module 31. . . . . . . . .
How the Module Fits in a Positioning System 31. . . . . . . . . . . . . . . .
How the Module Interacts with a PLC 32
. . . . . . . . . . . . . . . . . . . . . .
Read Operations 32
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Write Operations 32
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Axis Movement 32
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Commanding
Motion 34. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setpoints 34
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Jogging 35
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motion Blocks 35
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Table of Contents

Table of Contentsii
Hardware Description 41. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Indicators 41. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wiring Arm Terminals 42
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transducer Interface 43
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Determining
the Optimum Number of Circulations 43. . . . . . . . . . . . .
Discrete
Inputs 45. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Auto/Manual
Input 46. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hardware
Start Input 46. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hardware
Stop Input 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Jog Forward Input 47
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Jog Reverse Input 47
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General Purpose Inputs 47
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analog
Output Interface 47. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Discrete
Outputs 48. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OUTPUT 1 49
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OUTPUT 2 49
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supplies 49
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Installing the Linear Positioning Module 51. . . . . . . . . . . . . .
Before You Begin 51. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Avoiding Backplane Power Supply Overload 51
. . . . . . . . . . . . . . .
Planning Module Location 51
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electrostatic Discharge 52
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setting
Analog Output Switches 52. . . . . . . . . . . . . . . . . . . . . . . . . .
Keying 55
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Inserting the Module 55
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wiring
Guidelines 56. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using Shielded Cables 56
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using Twisted Wire Pairs 58
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connecting AC Power 58
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supplies 510
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connecting the Transducer Interface 510
. . . . . . . . . . . . . . . . . . . . . .
Power Supply 511
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transducer Interface 512
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connecting the Discrete Inputs 512
. . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply 514
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Auto/Manual
Input 514. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hardware
Start Input 514. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hardware
Stop Input 514. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Jog Forward Input 515
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Jog Reverse Input 516
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
General Purpose Inputs 516
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connecting
Multiple Modules 516. . . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contents iii
Connecting the Analog Outputs 518. . . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply 519
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analog
Output 519. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connecting the Discrete Outputs 520
. . . . . . . . . . . . . . . . . . . . . . . . .
Power Supply 521
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OUTPUT 1 521
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
OUTPUT 2 521
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Interpreting ModuletoPLC Data (READS) 61. . . . . . . . . . . . .
PLC Communication Overview 61. . . . . . . . . . . . . . . . . . . . . . . . . .
Status Block 61
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Word Assignment 62
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Module Configuration Word (word 1) 62
. . . . . . . . . . . . . . . . . . . .
Status Word 1 (words 2 and 6) 63
. . . . . . . . . . . . . . . . . . . . . . . .
Status Word 2 (words 3 and 7) 67
. . . . . . . . . . . . . . . . . . . . . . . .
Position/Error/Diagnostic Words 69
. . . . . . . . . . . . . . . . . . . . . . .
Active Motion Segment/Setpoint (words 10 and 11) 613
. . . . . . . . . .
Measured Velocity (words 20 and 21) 614
. . . . . . . . . . . . . . . . . . .
Desired Velocity (words 22 and 23) 614
. . . . . . . . . . . . . . . . . . . . .
Desired Acceleration (words 24 and 25) 615
. . . . . . . . . . . . . . . . . .
Desired Deceleration (words 26 and 27) 615
. . . . . . . . . . . . . . . . . .
Percent Analog Output (words 28 and 29) 616
. . . . . . . . . . . . . . . .
Maximum Velocity (words 30, 31 and 32, 33) 617
. . . . . . . . . . . . . .
Formatting Module Data (WRITES) 71. . . . . . . . . . . . . . . . . . .
Data Blocks Used in Write Operations 71. . . . . . . . . . . . . . . . . . . . .
Parameter Block (Required) 71
. . . . . . . . . . . . . . . . . . . . . . . . . .
Setpoint Block (Optional) 71
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Command Block (Required) 71
. . . . . . . . . . . . . . . . . . . . . . . . . .
Parameter Block 71
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parameter Control Word (word 1) 73
. . . . . . . . . . . . . . . . . . . . . .
Analog Range (words 2 and 31) 75
. . . . . . . . . . . . . . . . . . . . . . .
Analog Calibration Constants (words 3, 4 and 32, 33) 76
. . . . . . . .
Transducer Calibration Constant (words 5, 6 and 34, 35) 77
. . . . . .
ZeroPosition
Of fset (words 7, 8 and 36, 37) 78. . . . . . . . . . . . . . .
Software Travel Limits (words 9, 10 and 38, 39) 79
. . . . . . . . . . . .
ZeroPosition and Software T
ravel Limit Examples 710. . . . . . . . . .
InPosition Band (words 11 and 40) 713
. . . . . . . . . . . . . . . . . . . . .
PID Band (words 12 and 41) 714
. . . . . . . . . . . . . . . . . . . . . . . . . .
Deadband (words 13 and 42) 715
. . . . . . . . . . . . . . . . . . . . . . . . .
Excess Following Error (words 14 and 43) 716
. . . . . . . . . . . . . . . .
Maximum PID Error (words 15 and 44) 716
. . . . . . . . . . . . . . . . . .
Integral Term Limit (words 16 and 45) 717
. . . . . . . . . . . . . . . . . . .
Proportional Gain (words 17 and 46) 718
. . . . . . . . . . . . . . . . . . . .
Gain Break Speed (words 18 and 47) 719
. . . . . . . . . . . . . . . . . . .

Table of Contentsiv
Gain Factor (words 19 and 48) 720. . . . . . . . . . . . . . . . . . . . . . . .
Integral Gain (words 20 and 49) 721
. . . . . . . . . . . . . . . . . . . . . . .
Derivative Gain (words 21 and 50) 722
. . . . . . . . . . . . . . . . . . . . . .
Feedforward Gain (words 22 and 51) 722
. . . . . . . . . . . . . . . . . . . .
Global Velocity (words 23 and 52) 723
. . . . . . . . . . . . . . . . . . . . . .
Global Acceleration/Deceleration (words 24, 25 and 53, 54) 724
. . . .
Velocity Smoothing (Jerk) Constant (words 26 and 55) 724
. . . . . . .
Jog Rate (Low and High) (words 27, 28 and 56, 57) 726
. . . . . . . . .
Reserved (words 29, 30 and 58, 59) 727
. . . . . . . . . . . . . . . . . . . .
Setpoint Block 727
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setpoint Block Control Word (word 1) 729
. . . . . . . . . . . . . . . . . . . .
Incremental/Absolute Word (word 2) 729
. . . . . . . . . . . . . . . . . . . .
Setpoint
Position 730. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Local Velocity 731
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Local Acceleration/Deceleration 732
. . . . . . . . . . . . . . . . . . . . . . .
Command Block 732
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Axis Control Word 1 (words 1 and 8) 733
. . . . . . . . . . . . . . . . . . . .
Axis Control Word 2 (words 2 and 9) 738
. . . . . . . . . . . . . . . . . . . .
Setpoint 13 Words (words 3 to 7 and 10 to 14) 739
. . . . . . . . . . . . .
Initializing and Tuning the Axes 81. . . . . . . . . . . . . . . . . . . . .
Before You Begin 81. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Adjusting the Servo V
alve Nulls 82. . . . . . . . . . . . . . . . . . . . . . . . . .
Initializing the Parameter Block 82
. . . . . . . . . . . . . . . . . . . . . . . . . .
Verifying
Analog Output Polarity 87. . . . . . . . . . . . . . . . . . . . . . . . .
Verifying Transducer Calibration Constants 87
. . . . . . . . . . . . . . . . .
Axis Tuning 810
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analog Calibration Constants 810
. . . . . . . . . . . . . . . . . . . . . . . . .
Feedforward
Gain 811. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PID Loop Gains 812
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Update the Application Program 813
. . . . . . . . . . . . . . . . . . . . . . .
Advanced Features 91. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motion Block 91. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motion Block Control Word 94
. . . . . . . . . . . . . . . . . . . . . . . . . . .
Programmable
Input and Output 95. . . . . . . . . . . . . . . . . . . . . . . . .
Programmable
I/O Control W ord 95. . . . . . . . . . . . . . . . . . . . . . .
Default
I/O Configuration 98. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motion Segments 98
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motion Segment Control Words 98
. . . . . . . . . . . . . . . . . . . . . . . .
Desired
Position, Local V elocity, Local Acceleration
and Local Deceleration Words 911
. . . . . . . . . . . . . . . . . . . . . .
Trigger V
elocity/Position W ords 911. . . . . . . . . . . . . . . . . . . . . . . .
The Command Block and the Motion Block 911
. . . . . . . . . . . . . . . . . .
The Status Block and the Motion Block 911
. . . . . . . . . . . . . . . . . . . .

Table of Contents v
Using the Motion Block 912. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sample Application Programs 101. . . . . . . . . . . . . . . . . . . . . .
Programming Objectives 101. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Block Transfer Sequencing 102
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PLC5 Block Transfer Instructions 103
. . . . . . . . . . . . . . . . . . . . . . . .
Application Program #1 103
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Planning the Data Blocks for Application Program #1 105
. . . . . . . . .
Program Rungs for Application Program #1 108
. . . . . . . . . . . . . . .
Application Program #2 1011
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Planning the Data Blocks for Application Program #2 1012
. . . . . . . . .
Program Rungs for Application Program #2 1016
. . . . . . . . . . . . . . .
Troubleshooting 111. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fault Indicators 111. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Module
Fault Indicator 112. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Loop Active Indicators 112
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Indicator Troubleshooting Guide 112
. . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting Feedback Faults 113
. . . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting Flowchart 114
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Flowchart Notes 117
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Glossary of Terms & Abbreviations A1. . . . . . . . . . . . . . . . . .
Status Block B1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parameter Block C1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setpoint Block D1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Command Block E1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Motion Block F1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Hexadecimal Data Table Forms G1. . . . . . . . . . . . . . . . . . . . .

Table of Contentsvi
Data Formats H1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
BCD H1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2's Complement Binary H1
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Bit Inversion Method H2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Subtraction Method H2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Implied
Decimal H2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Position Format H3
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Double Word Position Format H4
. . . . . . . . . . . . . . . . . . . . . . . . . . .
Product Specifications I1. . . . . . . . . . . . . . . . . . . . . . . . . . .

Preface
P1
Preface
This manual explains how to install and configure the Linear Positioning
Module. It includes sample application programs to illustrate how to program a
PLCto work with the Linear Positioning Module.
This manual contains eleven chapters and nine appendices that address the
following topics:
Chapter Title Describes:
1 Introducing the Linear Positioning
Module
the functions and features of the Linear Positioning
Module
2 Positioning Concepts concepts and principles of closedloop servo
positioning
3 Positioning with the Linear
Positioning Module
using the Linear Positioning Module in a positioning
system
4 Hardware Description module hardware, module interfaces, and other
hardware items you need for a positioning system
5 Installing the Linear Positioning
Module
configuring the module's analog outputs and
installing the module in your system
6 Interpreting ModuletoPLC Data
(READS)
monitoring module operation from a logic controller
by reading and interpreting data that the module
transfers to the logic controller's data tables
7 Formatting Module Data
(WRITES)
formatting parameter, move description, and control
data for block transfers to the Linear Positioning
Module
8 Initializing and Tuning the Axes bringing the module online
9 Advanced Features using the motion block to perform blended moves;
using programmable input and output operations
10 Sample Application Programs two application programs, one using basic concepts
and the other using advanced features, to control
and monitor the module
11 Troubleshooting using the module's indicators and the status block
to diagnose and remedy module faults and errors
Appendix A Glossary common terms and abbreviations
Appendix B Status Block status block word assignments
Appendix C Parameter Block parameter block word assignments
Appendix D Setpoint Block setpoint block word assignments
Organization of the Manual

Preface
P2
Chapter Describes:Title
Appendix E Command Block command block word assignments
Appendix F Motion Block motion block word assignments
Appendix G Hexadecimal Data Table Form hexadecimal data worksheets
Appendix H Data Formats valid data formats
Appendix I Product Specifications 1771QB product specifications
Read this manual if you intend to install or use the Linear Positioning Module
(Cat. No. 1771-QB).
To use the module, you must be able to program and operate an Allen-Bradley
PLC. In particular you must be able to program block transfer instructions.
In this manual, we assume that you know how to do this. If you don’t, refer to
the User Manual for the PLC you’ll be programming.
Consult the Allen-Bradley Industrial Computer Division Publication Index
(SD 499) if you would like more information about your modules or PLCs. This
index lists all available publications for Allen-Bradley programmable controller
products.
The Hydraulics Configuration and Operation Option (Cat. No. 6190-HCO)
operates within the ControlView Core (Cat. No. 6190-CVC) environment to
provide full configuration and realtime monitoring for the Linear Positioning
Module. Both software packages are available from:
Allen-Bradley Company, Inc.
1201 South Second Street
Milwaukee, WI 53204
[phone]
Servo Analyzer is a software package that aids in tuning the axes by letting you
display an axis profile as you tune it. The resulting graphics may be plotted,
printed or saved to a file. The software is available from:
Computer Software Design
P.O. Box 962
Roseburg, OR 97470
[phone]
Audience
Related Publications
Related Software

Preface
P3
Appendix A contains a complete glossary of terms and abbreviations used in
this manual.
To make this manual easier for you to read and understand, product names are
avoided where possible. The Linear Positioning Module is also referred to as
the “module”.
Frequently Used Terms

Chapter 1
11
Introducing the Linear Positioning Module
The Linear Positioning Module (Cat. No. 1771-QB) is a dual-loop position
controller occupying a single slot in the Allen-Bradley 1771 Universal I/O
chassis. It can control servo or proportional hydraulic valves, or some electric
servos. Position is measured with a linear displacement transducer. You use the
module to control and monitor the linear position of a tool or workpiece along
one or two axes.
Figure 1.1
Linear
Positioning Module
50110
What is the Linear Positioning
Module?

Introducing the Linear Positioning Module
Chapter 1
12
PLCs
You can use the module with any Allen-Bradley PLC that uses block transfer
programming in local 1771 I/O systems including:
PLC-2 family
PLC-3 family
PLC-5 family
- PLC-5/10 (Cat. No. 1785-LT4)
- PLC-5/11 (Cat. No. 1785-LT11)
- PLC-5/12 (Cat. No. 1785-LT3)
- PLC-5/15 (Cat. No. 1785-LT)
- PLC-5/20 (Cat. No. 1785-L20)
- PLC-5/25 (Cat. No. 1785-LT2)
- PLC-5/30 (Cat. No. 1785-L30)
- PLC-5/40 (Cat. No. 1785-L40)
- PLC-5/60 (Cat. No. 1785-L60)
Transducers
The Linear Positioning (QB) Module is compatible with linear displacement
transducers manufactured by:
MTS Systems Corporation
Sensors Divisions
Box 13218, Research Triangle Park
North Carolina 27709
(919) 677–0100
Balluff Inc.
P.O. Box 937
8125 Holton Drive
Florence, KY 41042
(606) 727–2200
Product Compatibility

Introducing the Linear Positioning Module
Chapter 1
13
Santest Co. Ltd.
c/o Ellis Power Systems
123 Drisler Avenue
White Plains, NY 10607
[phone]
Lucas Schaevitz Inc.
7905 N. Route 130
Pennsauken, NJ 08110-1489
[phone]
All four manufacturers provide versions of the transducer that connect directly
to the module’s wiring arm, without an external digital interface box. The
module may also be compatible with other linear displacement transducers.
Servo and Proportional Valves
The module provides current ranges of up to +100 mA for direct interface to
most servo valves, most proportional valves, and a +10 volt option for
compatibility with other devices, such as electric servo interfaces. The module
is compatible with valves supplied by the following manufacturers:
Moog, East Aurora NY servo/proportional
Parker Hannifin Corporation, Elyria OH servo/proportional
Robert Bosch Corporation proportional
Rexroth Corporation, Lehigh Valley PA servo/proportional
ATOS proportional
Atchley, Canaga Park CA servo
Pegasus servo
Vickers Inc., Grand Blanc, MI servo/proportional
The module may also be compatible with other valves.
Important: Some proportional valves with LVDT loop controllers may limit
the module’s output and thus prevent the module from providing optimal
control.

Introducing the Linear Positioning Module
Chapter 1
14
Figure 1.2 shows one of the module’s two control loops within a linear
positioning system for closed-loop axis control. The module communicates with
a programmable controller through the 1771 backplane.
The programmable logic controller sends commands and user-programmed data
from the data table to the module as directed by a block-transfer write
instruction.
Figure 1.2
System
Overview
50033
PLC
Processor
Linear
Positioning
Module
DStatus Block
DParameter Block
DSetpoint Block
DMotion Block
DCommand Block
DJog Forward
DJog Reverse
DHardware Start
DAuto/Manual
DHardware Stop
DInput 1
DInput 2
Linear Displacement
Transducer
DOutput 1
DOutput 2
Discrete Outputs
D
Discrete Inputs
Transducer
Analog Output Servo Valve
PistonType
Cylinder
NOTE: All inputs and outputs are
duplicated for the second axis.
Interface
Using PLC programming, you can:
send configuration and control parameters to the module via parameter,
setpoint, motion, and command blocks. With this data the module determines
axis parameters, calculates velocity curves, and commands axis
end-positions. (See Chapters 7 and 9.)
read status blocks to monitor axis position and status indicators in your
process control system. (See Chapter 6.)
The module’s analog outputs (one for each control loop) connect to servo or
proportional valves via wiring arm terminals. The module controls speed and
position by adjusting the voltage or current levels of the analog outputs 500
times each second.
System Overview

Introducing the Linear Positioning Module
Chapter 1
15
The module also connects to linear displacement transducers (one for each of
the two axes) via wiring arm terminals. The transducer senses the axis position
and feeds it back to the module, thereby closing the control loop.
The module’s built-in processor samples the linear displacement transducer
interfaces and determines positions along each of the two axes every two
milliseconds. The module then updates the analog outputs based on a
proprietary algorithm designed specifically to handle hydraulic actuators. This
rapid update rate provides repeatable positioning and superior control of
velocity without jerky movement.
Motion blocks provide for complex motions by allowing motion segments to be
blended or chained together. These motion segments may also be synchronized
using the hardware input triggers and outputs.
Cam emulation permits motion segments in one axis to start motion segments in
another axis. Articulated motions and axis sequencing may be easily
accomplished.

Chapter 2
21
Positioning Concepts
This chapter explains concepts and principles of axis positioning. If you are
thoroughly familiar with the concepts of closed-loop servo positioning, you can
go on to Chapter 3.
Figure 2.1 illustrates a typical method of converting the flow of fluid into a
linear displacement.
Figure 2.1
PistonType
Hydraulic Cylinder
50032
SERVO VALVE
Electric
Control
Hydraulic
Fluid
Hydraulic
Fluid
Hydraulic fluid Hydraulic fluid
Axis
Motion
The servo valve controls the flow of hydraulic fluid into or out of the hydraulic
cylinder. Adding fluid to the left side of the cylinder extends the rod; adding
fluid to the right side retracts it.
Axis Motion

Positioning Concepts
Chapter 2
22
Closed-loop positioning is a precise means of moving an object from one
position to another. In a typical application, a positioning device activates a
servo valve controlling the movement of fluid in a hydraulic system. The
movement of fluid translates into the linear motion of a hydraulic cylinder. A
transducer monitors this motion and feeds it back to the positioning device. The
positioning device, in turn, calculates a positioning correction and feeds it back
to the servo valve.
Important: Throughout this manual we refer to servo valves, but you can also
use the analog outputs to control proportional valves or an electric servo.
Linear Displacement Transducer
A linear displacement transducer (see Figure 2.2) is a device that senses the
position of an external magnet to measure displacements.
Figure 2.2
Linear
Displacement T ransducer
50034
Magnet Transducer
Head
Magnet mounted to
the piston of actuator
The transducer sends a signal through the transducer wave guide where a
permanent magnet generates the return pulse. You can use the time interval
between the transducer’s signal and the return pulse to measure axis
displacement.
Circulations
Some linear displacement transducers provide circulations or recirculation to
improve resolution. (See Figure 2.3.) This technique stretches the pulse by a
factor of two or more and results in finer resolution in the circuitry monitoring
the pulse width.
ClosedLoop Positioning

Positioning Concepts
Chapter 2
23
Figure 2.3
Circulations
50035
Gate
(received from transducer)
Gate
(received from transducer)
Duration
(1 circulation)
Duration
(2 circulations)
resolution = 0.002
resolution = 0.001
A Simple Positioning Loop
To move a specified distance along an axis, you can command the hydraulic
device to move at a specific velocity for a specific length of time. However, this
method can be imprecise. To control the position of the hydraulic device
accurately you need a loop to monitor actual position. Figure 2.4 shows a
simple positioning loop.
Figure 2.4
Positioning
Loop
50036
Linear
Displacement
Transducer
Servo Valve
Desired
Velocity
D/A
Axis
Kp
Velocity
Command
s
Following
Error
dt
Position
Command
s
dt
+
-
Actual
Position
Integrator

Positioning Concepts
Chapter 2
24
In Figure 2.4:
desired velocity is the desired speed of axis motion from one position to
another
position command equals the integration of velocity over time
actual position value (transducer feedback) is the actual position of the
axis as measured by the LDT
following error equals position command minus actual position
velocity command is generated by amplifying the following error and
converting the result into an analog output
D/A (Digital to Analog convertor) generates the analog output controlling the
servo valve
KP(proportional gain) is the component that causes an output signal to
change as a direct ratio of the error signal variation
Proportional Gain
The following error is a function of the velocity command divided by the
proportional gain (KP). To generate the velocity command, multiply the
following error by the proportional gain. Proportional gain can be expressed in
ips/mil (where 1 mil = 0.001 inches) or mmps/mil (where 1 mil = 0.001 mm).
For example, with a velocity of 12 ips and a gain of 1 ips/mil, the following
error is:
Following Error =Velocity/Gain
=12 ips/(1 ips/mil)
=12 mil
When you increase the gain, you decrease the following error and decrease the
cycle time of the system. However, the capabilities of the system limit the gain.
Too large a gain causes instability.