Method of driving joint device
Provided is a method of driving a joint device suitably used for a robot joint with improved back drivability. A first motor and a second motor are fixedly connected to a first link. An output shaft of the first motor is coupled to an internal gear of a differential speed reducer. An output shaft of the second motor is coupled to an external gear of the differential speed reducer. A second link is coupled to the internal gear of the differential speed reducer. When the first link and the second link are relatively stopped to keep a joint angle fixed, both of the first motor and the second motor are rotated with a rotational speed larger than zero, and the rotational speed of the first motor and that of the second motor are differentiated to stop the second link.
1. A method of driving a joint device comprising a drive unit and a differential speed reducer provided between a first link and a second link, the joint device controlling drive of the first link and the second link as joints, wherein
the differential speed reducer comprises an internal gear, an intermediate gear, and an external gear, and
the drive unit comprises a first motor and a second motor, the method comprising:
fixedly connecting the first motor and the second motor to the first link;
coupling an output shaft of the first motor to one of the internal gear, the intermediate gear, and the external gear of the differential speed reducer;
coupling an output shaft of the second motor to one of the internal gear, the intermediate gear, and the external gear of the differential speed reducer which is different from the gear coupled to the output shaft of the first motor; and
coupling to the second link one of gears of the internal gear, the intermediate gear, and the external gear of the differential speed reducer which is different from the gear coupled to the output shaft of the first motor and the gear coupled to the output shaft of the second motor; and
rotating both of the first motor and the second motor at a rotational speed larger than zero, and stopping the second link by differentiating the rotational speed of the first motor and that of the second motor when the first link and the second link are relatively stopped to keep a joint angle fixed.
2. The method of driving the joint device according to claim 1 , wherein the differential speed reducer is a harmonic drive gear mechanism or a planetary gear mechanism.
3. The method of driving the joint device according to claim 1 , comprising:
specifying a relation between a friction force and a relative speed difference among the internal gear, the intermediate gear, and the external gear as a friction model in the differential speed reducer, and
determining a rotational speed in each of the first motor and the second motor so as to approach a speed difference to minimize the friction with a rotational speed ratio which can achieve joint stop.