Harmonic drive

A harmonic gear assembly, comprising:

• an input shaft having an input shaft axis, coupled to the motor;
• and
• a removable epicyclic carrier unit, removably mounted around, and coaxial with the input shaft, the epicyclic carrier unit comprising, in a single unit for removable mounting around the input shaft, and configured for being rotationally fixed to the input shaft when mounted to the input shaft, the removable epicyclic carrier unit including:
• a carrier having an interior circumference designed to match an outer circumference of the shaft;
• a plurality of roller assemblies mounted to the carrier, each including one of a plurality of rollers, including:
• a first roller assembly mounted at a first axial location along the input shaft and at a first circumferential location around the circumference of the carrier unit and comprising a first roller shaft extending substantially parallel to the input shaft axis and a first roller rotatably mounted around the first roller shaft;
• and
• a second roller assembly mounted at the first axial location along the input shaft and at a second circumferential location around the circumference of the carrier unit and comprising a second roller shaft extending substantially parallel to the input shaft axis and a second roller rotatably mounted around the second roller shaft;
• a third roller assembly mounted at a second axial location along the input shaft that is adjacent to the first axial location, and at the first circumferential location around the circumference of the carrier unit, so that a third roller is circumferentially aligned with the first roller and rotates about the first roller shaft;
• and
• a fourth roller assembly mounted at the second axial location along the input shaft and at the second circumferential location around the circumference of the carrier unit, so that the fourth roller is circumferentially aligned with the second roller and rotates about the second roller shaft;
• wherein the plurality of rollers extend radially outwards from the carrier such that a radially outer surface of each of the plurality of rollers is at a distance L from the input shaft axis A and a radially outer surface of the carrier at locations between the plurality of rollers is at a distance i from the input shaft axis, wherein i is less than L;
• wherein a combination of the carrier and the plurality of rollers, mounted on the input shaft, define an elliptical envelope with a major axis defined by the outer surfaces of the first and second rollers and a minor axis defined by the outer surface of the carrier;
• and
• wherein a wave generator is defined by the input shaft and the removable epicyclic carrier unit;
• a flex spline mounted around and compliant with the removable epicyclic carrier unit, wherein the flex spline rotates in an opposite direction of the wave generator;
• an outer ring mounted to the flex spline;
• a bracket fixed to the outer ring;
• and
• an output shaft fixed to the flex spline;
• and
• needle bearings between the rollers and the respective roller shafts.