Jam-free gear–clutch mechanism for load-sensitive step transmission in robotic joint

This paper introduces a novel gear–clutch mechanism that takes advantage of the difference between the directions in the reaction forces that occur during meshing and jamming to ensure jam-free engagement of the gears. The proposed mechanism is a more compact advancement of the previously developed linear rack-tilting clutch used to provide a step change in the reduction ratio. Mathematical models of the jam-free and stable meshing condition of the proposed mechanism are developed and experimentally verified, along with a discussion and recommendations to be considered as design guidelines. Additionally, a singularly actuated robotic joint prototype is developed to examine the performance of the proposed clutch mechanism. The joint was driven by a small 2-W DC motor. The maximum output torque was 4 Nm with a maximum travel range of over 200 during the high-force phase, and the maximum speed was 252/s with an infinite travel range during the high-speed phase. The mechanism exhibits potential for applications that benefit from a step transmission and long force-exerting travel range such as vices, grippers, and industrial punching and shearing machines, as well as robotic arms and power assist exoskeletons.