Page 161 - Servo Motors and Industrial Control Theory -

156 9 The Choice and Comparison of Servo Motors

Fig. 9.11 Dynamic settling 1.0
time of servo motors with
no load inertia, when accel-
eration feedback is used as .8
compensation
tr1[sec] .6

.4

.2

0
0 2 4 6 8 10
Power (kw)

Fig. 9.12 Dynamic settling 10
time of servo motors for
a unit load inertia when
acceleration feedback is 8
used as compensation 6
tr1 [sec/kg-m 2 ] 4

2

0
0 2 4 6 8 10
Power (kw)

Stepping motors are not readily available in large sizes. Hydraulic motors are
not available in a wide range of sizes. AC and DC motors are available in almost all
power ranges. The availability of rare earth magnet and brushless DC motors is as
yet limited to small ranges of power.

9.4 An Example on Choosing a Servo Motor

Suppose that a designer requires to move a load inertia of 0.1 kg m from 0 speed
2
to 1,000 rpm at maximum of 500 ms. At this rotating speed a torque of 10 N m is
applied to the motor which could, for example, be an equivalent of a cutting force in
a machine tool. Following the procedure set out in the previous section;