US Patent 7140994 Gearbox torsional load sensor

A planetary gearbox with transmitted torque sensor comprises a gear housing, first and second coupling members, sensing assembly, and planetary gears. The coupling members have axial faces disposed in a spaced apart, opposing relationship. Formed therein are a plurality of conical seats arranged in opposing pairs, each pair receiving a ball therebetween. The sensing assembly is positioned between the housing and at least one of the coupling members, urging the members toward one another and detecting relative axial movement. The planetary gears transmit torque from the second coupling member to a second gearbox shaft. The balls roll partway up the conical seats when transmitting torque between the coupling members, thereby causing the members to move axially away from one another a distance proportional to the torque transmitted. The distance is detected by the sensing assembly to indicate the torque transmitted by the unit.