Piezoelectric stepper motors are actuators that convert vibrations in a piezoelectric element (e.g., PZT) generated by an ac voltage (reverse piezoelectric effect) into rotary motion. Step angles on the order of 0.001° can be obtained by this method. In one design, as the piezoelectric PZT rings vibrate due to an applied ac voltage, radial bending vibrations are produced in a conical aluminum disk. These vibrations impart twisting (torsional) vibrations onto a beam element. The twisting motion is subsequently converted into a rotary motion of a frictional disk, which is frictionally coupled with the top surface of the beam. Essentially, because of the twisting motion, the two top edges of the beam push the frictional disk tangentially in a stepwise manner. This forms the output member of the piezoelectric stepper motor. List several advantages and disadvantages of this motor. Describe an application in which a miniature stepper motor of this type could be used.