Page 286 - Modern Control Systems

260 Chapter 4 Feedback Control System Characteristics

assistance that the anesthetist can obtain automatically will increase the safety
margins by freeing the anesthetist to attend to other functions not easily auto-
mated. This is an example of human computer interaction for the overall control
of a process. Clearly, patient safety is the ultimate objective. Our control goal
then is to develop an automated system to regulate the depth of anesthesia. This
function is amenable to automatic control and in fact is in routine use in clinical
applications [24,25].
We consider how to measure the depth of anesthesia. Many anesthetists regard
mean arterial pressure (MAP) as the most reliable measure of the depth of anesthe-
sia [26]. The level of the MAP serves as a guide for the delivery of inhaled anesthesia.
Based on clinical experience and the procedures followed by the anesthetist, we
determine that the variable to be controlled is the mean arterial pressure.
The elements of the control system design process emphasized in this example
are illustrated in Figure 4.23. From the control system design perspective, the con-
trol goal can be stated in more concrete terms:

• Topics emphasized in this example

Regulate the mean arterial
Establish the control goals < pressure to any given set point.
1
Identify the variables to be controlled Mean arterial pressure.
Five specifications:
1 DS1: settling time
DS2: percent overshoot
Write the specifications
DS3: tracking error
1 DS4: disturbance rejection
DS5: system sensitivity
Establish the system configuration See Figure 4.24.
Controller, pump, patient,
1 and sensor.
Obtain a model of the process, the
actuator, and the sensor See Equations: (4.69H4.7I).
i

Describe a controller and select key Three PID controllers given.
parameters to be adjusted See Equation (4.72) and Table 4.2.
1
Optimize the parameters and This chapter deals
analyze the performance with analysis only.
I
If the performance does not meet the If the performance meets the specifications,
specifications, then iterate the configuration. then finalize the design.

FIGURE 4.23 Elements of the control system design process emphasized in the blood pressure
control example.