Page 535 - Mechatronics with Experiments

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JWST499-c07
JWST499-Cetinkunt
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 521
External
disturbances
Command
signal Servo Servo Output
Actuator Load
amplifier valve

Sensor

FIGURE 7.89: Block diagram of a closed loop controlled one-axis electrohydraulic motion
system.

The following simplifying assumptions are made for the linear dynamics model of
the hydraulic system.

1. The valve dynamics and its nonlinear flow rate–current–pressure relationship is
approximated with a linearized flow rate–current relationship (K ). Notice that this
q
assumption is accurate only to the extent that the orifice area versus spool displace-
ment geometry of the valve is linear and that the pressure drop across the valve is
constant.
2. The pump pressure is assumed to provide a constant pressure drop across the valve,
to justify the above approximation ((p − p ) is constant).
l
s

P T
Position
i sensor
X cmd Amp
Valve

K S K a
Load
M
F d
Actuator

F d
K
pq
A c
i
X cmd V X
K sa K q 1/A c 1/S
Amp Valve Actuator

K fx
Position sensor
FIGURE 7.90: (a) Components, and (b) linear block diagram model of a postion servo
controlled one axis electro-hydraulic motion system.