Injector and control method for an ultrasonic motor

An injector which injects a liquid, the injector including:

• an ultrasonic motor unit including an ultrasonic motor;
• a drive mechanism to be driven by the ultrasonic motor unit so as to feed the liquid when the ultrasonic motor rotates forwardly;
• and
• a control device controlling the ultrasonic motor of the ultrasonic motor unit,
• the ultrasonic motor including a stator and a rotor;
• and
• the control device controlling the ultrasonic motor to alternately repeat forward rotation and reverse rotation multiple times within a preset time period to release adhesion between the stator and the rotor, and controlling the ultrasonic motor to stop for a predetermined time period between the forward rotation and the reverse rotation, and the control device controlling the ultrasonic motor so that, when the forward rotation and the reverse rotation are repeated multiple times, a predetermined stopping time period is provided after a preceding operation including forward rotation and reverse rotation, and before a succeeding operation including forward rotation and reverse rotation and performed subsequently to the preceding operation.