A drive unit includes a guide, a stage which is movable relative to the guide, an ultrasonic actuator for moving the movable body and a control unit for controlling the ultrasonic actuator. The ultrasonic actuator includes a driver element in contact with the stage and is fixed to the guide. A surface of the stage in contact with the driver element is an undulating surface. The control unit detects the position of the stage based on a change in contact pressure on the driver element due to the undulating surface.
1. A drive unit comprising: a stationary body; a movable body which is movable relative to the stationary body; a vibration actuator using a piezoelectric element for moving the movable body; and a control section for controlling the vibration actuator by feeding the piezoelectric element, wherein
the vibration actuator includes two driver elements spaced apart at an interval in a moving direction of the movable body and in contact with one of the movable body and the stationary body and is fixed to the other one of the movable body and the stationary body,
a surface of the one of the movable body and the stationary body in contact with the driver element is an undulating surface,
the control section detects the position of the movable body based on a change in contact pressure on the driver element due to the undulating surface, and
the undulating surface includes at least one of a concavity and a convexity having a width larger than the interval between the driver elements.
2. A drive unit comprising: a stationary body; a movable body which is movable relative to the stationary body; a vibration actuator using a piezoelectric element for moving the movable body; and a control section for controlling the vibration actuator by feeding the piezoelectric element, wherein
the vibration actuator includes a driver element in contact with one of the movable body and the stationary body and is fixed to the other one of the movable body and the stationary body,
a surface of the one of the movable body and the stationary body in contact with the driver element is an undulating surface,
the undulating surface includes at least one of a concavity and a convexity,
an arrangement or a shape of the at least one of the concavity and the convexity in the undulating surface changes as a function of position along the undulating surface, and
the control section detects the position of the movable body based on a change in contact pressure on the driver element due to the undulating surface.
3. A drive unit comprising: a stationary body; a movable body which is movable relative to the stationary body; a vibration actuator using a piezoelectric element for moving the movable body; and a control section for controlling the vibration actuator by feeding the piezoelectric element, wherein
the vibration actuator includes two driver elements spaced apart at an interval in a moving direction of the movable body and in contact with one of the movable body and the stationary body and is fixed to the other one of the movable body and the stationary body,
a surface of the one of the movable body and the stationary body in contact with the driver element is an undulating surface,
the control section detects the position of the movable body based on a change in contact pressure on the driver element due to the undulating surface, and
the undulating surface includes at least one of a concavity and a convexity having a width smaller than the interval between the driver elements.
4. A drive unit comprising: a stationary body; a movable body which is movable relative to the stationary body; a vibration actuator using a piezoelectric element for moving the movable body; and a control section for controlling the vibration actuator by feeding the piezoelectric element, wherein
the vibration actuator includes two driver elements spaced apart at an interval in a moving direction of the movable body and in contact with one of the movable body and the stationary body and is fixed to the other one of the movable body and the stationary body,
a surface of the one of the movable body and the stationary body in contact with the driver element is an undulating surface,
the control section detects the position of the movable body based on a change in contact pressure on the driver element due to the undulating surface,
the piezoelectric element has at least one piezoelectric body and at least two pairs of first and second electrodes provided to sandwich the at least one piezoelectric body,
the first electrodes are arranged nearer to one of the two driver elements than the other,
the second electrodes are arranged nearer to the other driver element than the one driver element, and
the control section detects a difference between a contact pressure on one of the driver elements and a contact pressure on the other of the driver elements based on a current flowing through the first and second electrodes.