Page 567 - Mechatronics with Experiments

October 9, 2014 8:41 254mm×178mm
Printer: Yet to Come
JWST499-c07
JWST499-Cetinkunt
ELECTROHYDRAULIC MOTION CONTROL SYSTEMS 553
Operator
interface
device
DC PS
Motion
controller Current signal
to valve
Amp
To pump
Control signal
to amp

Accumulator
Metal tubing or
flexible hydraulic hoses Valve
Manifold
Pressure Cylinder
sensor at pump
output Magnetostrictive
position
Relief sensor
valve
Electric motor/ Pump Pressure Pressure
engine sensor (may be Magnet component sensor
located at the of the position sensor (may be located
E/M at the manifold)
manifold)
Reservoir

FIGURE 7.103: Components of a single degree of freedom electrohydraulic motion control
system: magnetostrictive position sensor is integrated into the cylinder for closed loop position
control, two-pressure sensors can be used for closed loop force control.

pump pressure is below maximum pressure setting, the relief valve is closed, but as soon as
pump pressure is equal or exceeds the maximum pressure, the relief valve opens to dump
the excess flow rate (flow rate difference between pump flow rate and the flow rate through
servo valve) to the tank. One way to mathematically model the fluid compressibility and
instantaneously acting relief valve is to limit the pressure integration output to the maximum
pressure setting.
The dynamic model for pump, relief valve, and fluid compressibility effect in the
volume between pump and servo valve is modeled as
Q (t) = D (t) ⋅ w (t) (7.541)
p p shaft
If p (t) < p (7.542)
p max
Q (t) = 0.0 (7.543)
r
Else (7.544)
Q (t) = Q (t) − Q (t) (7.545)
r p v
Endif (7.546)
dp (t)
p
= (Q (t) − Q (t)) (7.547)
v
p
dt V hose,pv