Page 133 - Servo Motors and Industrial Control Theory -

128 7 Electrohydraulic Servo Motors

1.5 POSITION PER UNIT STEP INPUT

1.35
1.2
1.05 1
.9
2
.75 3
.6
.45
.3
.15 TIME ( SEC)
0
0 .1 .2 .3 .4 .5
Fig. 7.9 Position response of the system for a unit step input. 1 No load inertia. 2 Load inertia of
0.0024 kg m . 3 Load inertia of 0.0084 kg m 2
2

POSITION VARIATION ( Dog/N-M )
3
0 .1 .2 .3 .4 .5
0
1 TIME (SEC)
–3 2
3
–6

–9

–12

–15
Fig. 7.10 Position behavior for a unit step input of external torque. 1 No load inertia. 2 Load
2
inertia of 0.0024 kg m . 3 Load inertia of 0.008 kg m 2

extreme positions, first when there is no external torque and the motor operates at
very low velocity. In this case, the spool valve operates in the vicinity of closed
position. Secondly, when the motor runs at maximum speed maximum torque is ap-
plied to the motor. The second case represents the case when the spool valve is fully
opened. This is shown in Fig. 7.11. It shows that the linearized model can be used
for complete range of operation. It is usually a good idea to study the performance
over whole range of operation.