Biomedical Engineering Reference
In-Depth Information
FIGURE 4-40
Proportional
controller of motor
speed.
FIGURE 4-41
Simulink model of a
proportional speed
controller for a
motor driving a load.
It is important to remember that the output of the controller will be limited to the
maximum allowable voltage for the motor, so the complete Simulink model is shown in
Figure 4-41.
The step response to a commanded speed of 600 rad/s in Figure 4-42 shows a residual
speed error of 15 rad/s because the commanded speed is beyond the capability of the
motor given the allowable voltage and the load torque. However, if the commanded speed
is reduced to 500 rad/s, the controller performs perfectly.
In many biomechatronic applications, it is not the motor speed but the angle that needs
to be controlled. This requires that an additional block be incorporated into the output of
the system to integrate the angular rate and to give angular position.
1
s
(
s
)
θ(
s
)
=
(4.90)
Therefore, the closed-loop position controller is as shown in Figure 4-43 and the Simulink
model in Figure 4-44.
In this case, the proportional controller is highly underdamped, as can be seen in
Figure 4-45. Increasing the gain doesn't improve the response time at all, but it does
increase the natural frequency of the system with the result that the oscillation frequency
increases.
