Polylobed Anti-Backdrive Lock for Compact Bidirectional Torque Holding
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Solution Overview
Problem
Existing gear systems face inefficiencies and high costs due to the need for large, expensive mechanisms to prevent backdrive, which limits their ability to handle torque effectively and efficiently in both rotational directions.
Innovation Solution
An anti-backdrive device utilizing a polylobed locking mechanism that engages and disengages with a housing to differentiate compression and expansion forces, allowing bidirectional operation while preventing backdriving by using the geometry of polylobes to generate greater compression forces than expansion forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a self-locking gear set with low helix angle is used to prevent backdrive, then backdrive prevention is achieved, but system efficiency decreases to less than 35%
Solution Approach 1:
The locking mechanism is segmented into multiple poly lobes (typically 3-6 lobes) distributed around the circumference of the input shaft. Each lobe engages with corresponding features in the housing to provide distributed locking points, allowing the system to prevent backdrive while maintaining higher efficiency compared to single-point locking mechanisms.
Solution Approach 2:
The poly lobe geometry is specifically designed with asymmetric profiles where the compression side has a steeper angle than the expansion side. This asymmetry creates greater compression forces than expansion forces during operation, enabling the mechanism to lock during backdrive while allowing efficient forward motion with reduced frictional losses.
2Reliability
If conventional anti-backdrive mechanisms are used to handle large torque, then backdrive prevention is achieved, but device size and complexity increase substantially
Solution Approach 1:
The poly lobe locking mechanism is integrated directly into the input shaft and housing structure, merging the locking function with the existing drive train components. This eliminates the need for separate, complex braking or locking mechanisms, thereby preventing backdrive without substantially increasing device size or complexity.
Solution Approach 2:
The locking action is achieved through radial engagement of poly lobes with the housing, converting axial torque forces into radial locking forces. This dimensional transformation allows compact implementation of high-torque locking capability without requiring large axial clearance or complex mechanical linkages.
3Power
If pins in larger holes are used to transfer torque in conventional anti-backdrive devices, then torque transfer is achieved, but system size increases to handle the required torque
Solution Approach 1:
The poly lobe structure utilizes composite geometric forms combining cylindrical and lobed profiles, creating a structure that efficiently distributes torque across multiple engagement points. This composite geometry allows high torque transfer capacity in a compact form factor, avoiding the need for oversized pins and holes that would increase system volume.
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
Enables efficient and cost-effective transfer of torque in both directions, preventing backdriving and maintaining loads in a stationary position without the need for large, complex mechanisms, thus reducing energy requirements and system size.
Implementation Method 1
poly lobe, or shape engagement, is a way to couple shafts to transmit the maximum torque load for a given shaft size
Implementation Method 2
uses the geometry of the polylobes to do so. That is, the out-of-round configuration of the perimeter of the mechanism causes braking wherein the polylobes generate a greater compression force than the expansion force of a driven shaft
Implementation Method 3
fabricate a worm and gear set that has a low helix angle, (typically less than 6 degrees), which may be considered self-locking because the frictional forces are greater than the back-driving forces
Data Source
AI summary
A backdrive braking element is provided for preventing backdrive of a shaft. It includes a poly-lobed locking mechanism including an unlock shaft that has a polygon shaped inside profile and is coupled to a poly lock drive and brake assembly. The poly lock drive and brake assembly includes a plurality of poly lock drive and brake segments and is contained within the interior cavity of a housing.