Page 119 - Adaptive Identification and Control of Uncertain Systems with Nonsmooth Dynamics

114 Adaptive Identification and Control of Uncertain Systems with Non-smooth Dynamics

Figure 7.3 Dead-zone in the upper-limb model.

Figure 7.4 Block diagram of USM.

spinal cessation. In [12], this approach has been applied to stimulation of
the upper limb, concentrating on elbow flexion/extension. Two dead-zone
models are employed to represent the biceps and triceps non-linear “gains”
appearing at the input of limb dynamics block in Fig. 7.3.Asimilarmodel
was employed in [13], [1], and [14] to adaptively control the knee joint of
paraplegics.

7.3.2 Ultrasonic Motor

Ultrasonic motor (USM) is a new type motor as shown in [15], which
is driven by the ultrasonic vibration force of piezoelectric elements. This
motor has a non-linear speed characteristics, which vary with driving con-
ditions. In position control systems, the motor shows a variable dead-zone
in the control input (phase difference of applied voltages) against load
torque. The block diagram of USM is shown in Fig. 7.4 [11]. This USM
is typical traveling-wave type USM and consists of a stator and rotor made
by elastic body, piezoelectric elements.