Harmonic Drive Clutch for Back Drivability
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Solution Overview
Problem
Existing harmonic drives face challenges in improving back drivability due to high reduction gear ratios and increased friction and rotational inertia, which limit their ability to efficiently transfer torque in reverse directions without requiring higher motor power.
Innovation Solution
Incorporating a clutch mechanism with claws and a plunger that allows the circular spline to fix or rotate based on the transfer direction of rotational energy, enabling the harmonic drive to operate in both forward and reverse directions with improved back drivability without increasing motor power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the reduction gear ratio is lowered to improve back drivability, then back drivability is improved, but motor power must be increased to obtain the wanted output torque
Solution Approach 1:
The clutch mechanism dynamically changes the engagement state of the circular spline based on the direction of torque transfer. During forward driving, the circular spline is engaged to provide high reduction gear ratio. During reverse driving, the clutch disengages the circular spline, transforming the drive train into a direct drive configuration, allowing the motor to rotate in reverse without overcoming the high friction and inertia of the engaged harmonic drive components.
Solution Approach 2:
The system changes the effective reduction gear ratio parameter based on operating conditions. By switching the clutch state, the system transitions between a high reduction gear ratio state (forward driving) and a low or zero reduction gear ratio state (reverse driving), optimizing performance for each direction.
2Reliability
If the reduction gear ratio is lowered to improve back drivability, then back drivability is improved, but friction force between motor and drive and rotational inertia of input stage must be reduced
Solution Approach 1:
The clutch mechanism dynamically disengages the circular spline during reverse driving, removing the friction interfaces between the circular spline teeth and flex spline teeth. This dynamic disengagement eliminates the source of high friction forces that would otherwise oppose reverse motion, significantly improving back drivability without requiring changes to the fundamental harmonic drive structure.
Data Source
AI summary
A harmonic drive having improved back drivability includes a wave generator, a flex spline, and a circular spline. The wave generator, the flex spline, and the circular spline transfer rotational energy; and a clutch is configured to permit and fix a rotation of at least one of the wave generator, the flex spline, and the circular spline in accordance with a transfer direction of the rotational energy.