Bi-Directional Anti-Back Drive Coupling for Prosthetic Grip Locking
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Solution Overview
Problem
Existing anti-back drive devices are unidirectional, failing to prevent back drive in both senses of rotation, which limits their effectiveness in applications like prosthetic hands where maintaining grip without energy dissipation is crucial.
Innovation Solution
A bi-directional anti-back drive device is designed with a rotary drive member and a ring featuring cam recesses with lock members, plungers, and protuberances that allow forward drive while inhibiting back drive in both directions, utilizing a free-play coupling mechanism for efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a unidirectional anti-back drive device is used, then back drive is prevented in one direction, but back drive cannot be prevented in both directions of rotation
Solution Approach 1:
The cam recesses are designed with asymmetric geometry where one end is deeper and the other end is shallower. This asymmetric shape allows the lock member to be retained at the deeper location during forward rotation while permitting movement toward the shallower location during backward rotation, enabling directional control without preventing bi-directional operation
Solution Approach 2:
The device incorporates at least two cam recesses spaced around the periphery of the driven member, with each recess handling a specific rotational direction. This segmentation allows independent control of locking actions for different rotation directions, enabling bi-directional anti-back drive functionality
2Ease of operation
If lock members are retained at deeper locations during forward drive, then forward motion is permitted, but rapid locking action during back drive is not achieved
Solution Approach 1:
Resilient parts are pre-installed to urge lock members toward the shallower locations of the cam recesses. This preliminary positioning ensures that when back drive occurs, the lock members are already predisposed to move rapidly into the shallower location, achieving quick locking action without requiring additional activation mechanisms
Solution Approach 2:
The lock members are designed to dynamically transition between different positions within the cam recesses based on rotation direction. During forward drive, they remain at deeper locations permitting motion; during back drive, they rapidly move to shallower locations to inhibit motion, providing adaptive response to operational conditions
3Reliability
If protuberances extend into cam recesses to retain lock members, then locking position is maintained, but frictional contact increases
Solution Approach 1:
Roller members are introduced as intermediary elements between the protuberances and the cam recesses. These rollers maintain the locking position by contacting the cam surfaces while reducing frictional contact through rolling motion, eliminating direct sliding contact between the protuberances and lock members
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device ensures rapid locking during back drive, reduces friction, and maintains grip effectively in both rotation senses, enhancing the functionality of prosthetic hands by preventing back drive in both directions.
Implementation Method 1
resilient parts to urge the lock members towards the shallower locations of the recesses
Implementation Method 2
Each lock member may comprise a roller member. This further increases a rapid locking action in the event of back drive of the driven member and decreases frictional contact between the ring and the lock members
Data Source
Figure 1
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AI summary
An anti-back drive device 10 comprising a rotary drive member 12 coupled to a rotary driven member 18 to enable the rotary drive member 12 to drive the rotary driven member 18. The device 10 further comprises a ring 40 which surrounds the rotary driven member 18. The rotary driven member 18 is provided with at least two cam recesses 24 on its periphery containing respective lock members 30 between respective cam surfaces 26 of the cam recesses 24 and the said ring 40. Each recess 24 is sufficiently deep towards one of its ends to accommodate its associated lock member 30 but not at locations towards its other end where the recess 24 is shallower relative to the ring 40. As a result drive of the driven member 18 by the drive member 12 will be permitted by each lock member 30 in a given sense of rotation of the driven member 18 relative to the ring 40 but each lock member 30 will inhibit back drive rotation of the driven member 18 in the opposite sense of rotation relative to the ring 40. The said at least two cam recesses 24 extend from their deeper to their shallower locations in opposite directions around the driven member 18. The coupling between the drive member 12 and the driven member 18 is a free-play coupling whereby a reversal in the sense of rotation of drive results in the disengagement of the coupling between those two members 12 and 18, a predetermined relative rotation between those two members 12 and 18 in which they are disengaged from one another, and then re-engagement between them. Respective protuberances 16 extend from the drive member 12 into the said at least two cam recesses 24 to retain one of the lock members 30 associated with one of those recesses 24 at the deeper location thereof whilst permitting movement of the other lock member 30 towards the shallower location of its associated recess 24. Upon reversal of the sense of rotation of the driven member 18 by the drive member 12, the protuberances 16 retain the said other of the said lock members 30 at the deeper location of its associated recess 24 whilst permitting movement of the said one of the lock members 30 towards the shallower location of its associated recess 24, so that the device 10 is a bi-directional anti-back drive device. Also, a prosthesis having such an anti-back drive device.