Rotation transmission mechanism provided with strain wave gearing

A rotation transmission mechanism that transmits rotational driving force outputted from a rotation drive source to a load-side member via a speed reducer, the rotation transmission mechanism comprising:

• a powertrain configured from a plurality of power-transmitting members including the speed reducer;
• the speed reducer being a strain wave gearing;
• an allowable load torque of the power-transmitting members other than the strain wave gearing being greater than a predetermined upper-limit load torque;
• an allowable load torque of the strain wave gearing being prescribed by a ratcheting torque set to a value equal to or lower than the upper-limit load torque;
• and
• the strain wave gearing functioning as a mechanical fuse;
• wherein a rigid internally toothed gear in the strain wave gearing is fixed and fastened to a fixed-side member of the strain wave gearing by means of a plurality of fastening bolts;
• the fastening bolts are respectively inserted into bolt holes formed at a constant pitch in a circumferential direction of the rigid internally toothed gear;
• and
• slits, which extend outward in the radial direction from the bolt holes to an external peripheral surface of the rigid internally toothed gear, are provided to a portion of the internally toothed gear fastened by some of the fastening bolts in the circumferential direction and rigidity in a radial direction is made less than in other portions, so that
• a fastening force by which the rigid internally toothed gear is fixed by being fastened to the fixed-side member is set to a lesser fastening force in one portion of the internally toothed gear in a circumferential direction than a case in which the allowable load torque of the strain wave gearing is greater than the upper-limit load torque, whereby the ratcheting torque is set to be equal to or lower than the upper-limit load torque.