Page 371 - The Mechatronics Handbook

18.12 Saturation

All real actuators have some maximum output capability, regardless of the input. This violates the linearity
assumption, since at some point the input command can be increased without significantly changing the
output; see Fig. 18.9. This type of nonlinearity must be considered in mechatronic control system design,
since maximum velocity and force or torque limitations affect system performance. Control systems mod-
eled with linear system theory must be carefully tested or analyzed to determine the impact of saturation
on system performance.

18.13 Deadband

Another nonlinear characteristic of some actuators and sensors is known as deadband. The deadband is
typically a region of input close to zero at which the output remains zero. Once the input travels outside
the deadband, then the output varies with input, as shown in Fig. 18.10. Analog joystick inputs frequently
use a small amount of deadband to reduce the effect of noise from human inputs. A very small movement
of the joystick produces no output, but the joystick acts normally with larger inputs.
Deadband is also commonly found in household thermostats and other process type controllers, as
shown in Fig. 18.11. When a room warms and the temperature reaches the setpoint (or desired value)

FIGURE 18.9 Saturation.

FIGURE 18.10 Deadband.

FIGURE 18.11 Thermostat deadband.

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