A-B 1746-QS System Overview Synchronized Axes Control Module

What Is the 1746-QS Module?

The 1746-QS Synchronized Axes Module provides four axes of

closed-loop synchronized servo positioning control, and lets you

change motion parameters while the axis is moving. The module has

four optically isolated inputs for signals from linear displacement

transducers (LDTs) and four optically isolated ±10 volt outputs that

interface with proportional or servo valve amplifiers.

The module’s microprocessor provides closed-loop control. The

module reads the axis position and updates the drive output every

two milliseconds, for precise positioning even at high speeds.

What Is the

Hydraulic Configurator

The module is designed for use with the Hydraulic Configurator, a

software product that you can obtain from the Allen-Bradley website on

the Internet. The Hydraulic Configurator is an interactive executable

that lets you configure the module and tune its axes. With it, you can:

• configure axes and store configuration parameters

• tune each axis independent of the ladder program

• store multiple commands to initiate repetitive axis motion

• display a log of the last 64 motion commands sent to the module

• observe and/or store plots of each axis

• access help screens that explain and/or describe module features

Important: The Hydraulic Configurator saves considerable time when

tuning axes and troubleshooting faults. Thereafter, your ladder logic

sequences module operation with the machine.

What Is an

SLC-500 System?

The Allen-Bradley Small Logic Controller (SLC) system is a programmable

control system with an SLC processor, I/O chassis containing

analog, digital, and/or special-purpose modules, and a power supply.

The 1746-QS module occupies one slot of the I/O chassis and

communicates with the SLC processor over the backplane using 32

words in the SLC processor’s output image table and 32 words in the

input image table. The processor loads or reads the module’s

configuration parameters using M0 or M1 files, respectively. Your

ladder logic sequences synchronized axes movement with machine

operation. The system can be illustrated as follows:

Why Use This System?

Because you can interact quickly and easily with the module’s control of

axis motion via the Hydraulic Configurator, this control system has

these benefits:

• faster setup and tuning of axes – the Hydraulic Configurator lets you

quickly set up and tune each axis independent of your ladder program.

• reduced cycle time – you can increase axis speed for faster operation

• smoother operation for longer machine life – you can profile accelerations

and decelerations of the hydraulic actuator to limit pressure spikes

• faster change-over to new parts – you can store setups (configuration

parameters) for quick an accurate change-over between parts

How Does It Work?

Monitoring Axis Position

The module has four LDT inputs. You configure each axis for an LDT

with a Pulse Width Modulated output (DPM) or a Start/Stop output

(RPM) by changing axis configuration parameters.

Controlling Axis Output

The module is a targeting controller: every two milliseconds its microprocessor

updates TARGET POSITION and target SPEED values. For

point-to-point moves, TARGET POSITIONS are generated so that

resulting speed, accelerations, and decelerations follow either a

trapezoidal or s-curve profile.

The MODE, ACCELERATION, DECELERATION, SPEED, and

COMMAND VALUE (requested position) are used to generate the

profile. You send these command words to the module through the

processor’s output image table. You may change them “on-the-fly“

while the axis is moving.

The module compares ACTUAL POSITION with TARGET POSITION to

determine position error. Every update, it uses the position error to adjust

drive output. PID gains are adjustable and can be applied selectively.

The module also provides two different feedforward algorithms;

EXTEND/RETRACT FEEDFORWARD, and EXTEND/RETRACT

ACCELERATION FEEDFORWARD. These feedforward terms provide

additional drive output to help the axis follow the target, freeing the

PID loop to correct for system nonlinearity and changes in load.