Page 701 - Mechatronics with Experiments

ELECTRIC ACTUATORS: MOTOR AND DRIVE TECHNOLOGY 687

Voltage DC motor model
amplifier

V t e i m (t)
+ _ T
a a a T

e

FIGURE 8.62: Block diagram of transfer functions for a DC servo motor driven by a voltage
amplifier.

The transfer function from the terminal voltage and load torque to the motor speed
in terms of time constants and dc gains are shown in block diagram form in Figure 8.61.

8.8.1 Voltage Amplifier Driven DC Motor
If a voltage amplifier is used to drive the motor, the transfer function between voltage
amplifier input and motor speed is given by (Figure 8.62)
̇
̇
(s) (s) V (s)
t
= = G amp (s) G motor (s)
V (s) V (s) V (s)
in
t
in
where the voltage amplifier is represented by a first-order filter model,
V (s) A
t v
= G amp (s) = (8.306)
V (s) ( s + 1)
in
a
8.8.2 Current Amplifier Driven DC Motor
In the majority of cases, the DC motor terminal voltage is controlled by an amplifier which
regulates armature current (Figure 8.63). Directly regulating current is essentially directly
regulating the torque generated by the motor, since generated torque is proportional to the
current. The transfer function of the current amplifier plus DC motor combination from the

Amplifier DC motor model
with current F.B.

t e i m (t)
+ _ + _ T
a a T

e

FIGURE 8.63: Block diagram of DC motor and amplifier using current feedback.