A piezoelectric drive device includes a piezoelectric drive portion which includes a contact portion capable of coming into contact with a driven body and a piezoelectric material, and a drive circuit which drives the piezoelectric drive portion. The drive circuit sets an allowable maximum output torque Tlim or less to an allowable output torque range, sets output torque Td of the piezoelectric drive portion so as to be within the allowable output torque range, and operates the piezoelectric drive portion. The allowable maximum output torque Tlim is expressed by the following Expression (1).
Tlim=r1×μk×Ns×fs  (1)
In the expression, r1 is a distance between a rotation center of the driven body and a contact position of the contact portion, μk is a dynamic friction coefficient between the driven body and the contact portion, Ns is a pressing force by which the contact portion presses the driven body when an operation of the piezoelectric drive portion stops, and fs is a coefficient of 1 or less.

A motor control apparatus of the present invention is a motor control apparatus for compensating elastic deformation between a servo motor and a driven part, driven by the servo motor, which includes a position command generator for generating a position command of the motor, a compensation filter for compensating the position command generated by the position command generator and a servo control unit for controlling the movement of the motor based on a position command after compensation, i.e., the compensated position command by the compensation filter, and is constructed such that the compensation filter includes a filter F(s) having an inertia J.sub.L of the driven part, a stiffness coefficient K of an elastically deformable part and a damping coefficient C of the elastically deformable part as the elements of filter coefficients.

A driving device includes a driving unit disposed on a fixed member, a supporting member, an output member, an elastic member configured to couple the supporting member and the output member, a first scale, a first sensor configured to detect the rotation angle of the output shaft of the driving unit with the first scale, a second scale, and a second sensor configured to detect the relative displacement between the supporting member and the output member with the second scale. One of the first scale and the first sensor is disposed on the fixed member. The other of the first scale and the first sensor and one of the second scale and the second sensor are disposed on the supporting member. The other of the second scale and the second sensor is disposed on the output member.

A work piece processing device includes a tool device, a work piece holder and a servo-elastic actuator system having simultaneous precision force and position control that moves one of the tool device and the work piece holder to the other of the tool device and work piece holder. The servo-actuator system including a servo-actuator, a compliance elastic member and a weight compensation elastic member disposed in a force transmission path with the compliance elastic member and the weight compensation elastic member disposed with respect to each other so that a spring force exerted by the weight compensation elastic member is opposed to a spring force exerted by the compliance elastic member.

A driving device includes a driving unit disposed on a fixed member, a supporting member, an output member, an elastic member configured to couple the supporting member and the output member, a first scale, a first sensor configured to detect the rotation angle of the output shaft of the driving unit with the first scale, a second scale, and a second sensor configured to detect the relative displacement between the supporting member and the output member with the second scale. One of the first scale and the first sensor is disposed on the fixed member. The other of the first scale and the first sensor and one of the second scale and the second sensor are disposed on the supporting member. The other of the second scale and the second sensor is disposed on the output member.

A work piece processing device includes a tool device, a work piece holder and a servo-elastic actuator system having simultaneous precision force and position control that moves one of the tool device and the work piece holder to the other of the tool device and work piece holder. The servo-actuator system including a servo-actuator, a compliance elastic member and a weight compensation elastic member disposed in a force transmission path with the compliance elastic member and the weight compensation elastic member disposed with respect to each other so that a spring force exerted by the weight compensation elastic member is opposed to a spring force exerted by the compliance elastic member.

A control device includes: a command generating unit that generates a command for a motor; a correction-amount calculating unit that performs correction-amount calculation processing for calculating a correction amount for the command on the basis of elastic parameters of elastic elements; and a stage detecting unit that detects the fact that a transition has been made from a first stage in which a driving force generated by the motor acts on the first elastic element to a second stage in which the driving force acts on the second elastic element via the first elastic element. When the transition from the first stage to the second stage is detected, the correction-amount calculating unit switches from first correction-amount calculation processing based on the first elastic parameter of the first elastic element to second correction-amount calculation processing based on the second elastic parameter of the second elastic element and the first elastic parameter.