Rockwell Automation 1771-QB Linear Pos. - Manual (Page 19)

Positioning Concepts
Chapter 2
2Ć3
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