Method for controlling back clearance of a motion transmission apparatus

A method for controlling back clearance of a motion transmission apparatus, the motion transmission apparatus comprising:

• a first electric motor with a first toothed drive member, a second electric motor with a second toothed drive member, and a toothed member to be engaged with the first and second toothed drive members, the method comprising the following steps:
• controlling the first electric motor and the second electric motor to rotate in opposite directions to fix the toothed member;
• controlling the second electric motor to output a torque capable of driving the toothed member to move, when a back clearance appears between the toothed member and the second toothed drive member, or between the toothed member and the first toothed drive member, the torque of the second electric motor will change, and the torque change of the second electric motor at different positions with respect to the toothed member will be recorded;
• when the toothed member needs to be precisely positioned, the back clearance between the second toothed drive member of the second electric motor and the toothed member at different positions of the toothed member will be controlled according to the torque change, so as to consequently change a position offset of the second electric motor with respect to the first electric motor, when the toothed member doesn't need to be precisely positioned, the second electric motor shouldn't be controlled.