Compact Gearless Torque Drive With Rubbery Bushing Torque Limiting
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Solution Overview
Problem
Disposable torque-limiting devices for medical power tools fail to reliably limit torque at higher rotational speeds and often fall out of specification after increased RPMs, leading to insufficient performance.
Innovation Solution
A disposable torque-limiting device with a reduced-component drive assembly and rubbery bushing force assembly, featuring a cylindrical body with a partially closed distal end, upper and lower shank components, and torque-limiting interfaces that engage and disengage when a predetermined torque limit is exceeded, using a rubbery bushing to apply compressive force and maintain torque control at high speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If disposable torque-limiting devices are used for medical power tools at higher rotational speeds, then productivity is improved, but reliability deteriorates as the devices fall out of specification
Solution Approach 1:
The torque-limiting interface incorporates elastomeric material that dynamically adapts to rotational speed variations. The elastomeric component deforms elastically under torque load, and this deformation characteristic changes with rotational speed, allowing the interface to maintain consistent torque limitation across a wide RPM range from 50 to 1300 RPM
Solution Approach 2:
The invention changes the physical state and properties of the torque-limiting interface by using elastomeric material with specific durometer ratings (40-80 Shore A). The material's elastic modulus and friction characteristics vary with temperature and deformation rate, enabling reliable torque limitation at high rotational speeds where traditional rigid interfaces fail
2Ease of manufacture
If traditional torque-limiting interfaces are used, then manufacturing is simpler, but device complexity increases when attempting to maintain performance at high speeds
Solution Approach 1:
The elastomeric material serves multiple functions simultaneously: it provides the torque-limiting friction surface, acts as a damping element, compensates for manufacturing tolerances, and accommodates thermal expansion. This merging of functions into a single material component simplifies the overall device structure while maintaining high-speed performance
Solution Approach 2:
The torque-limiting interface uses composite construction combining rigid substrate material with elastomeric coating or overlay. This composite structure provides the dimensional stability of rigid materials while incorporating the flexible, speed-compensating properties of elastomeric materials, achieving both manufacturability and high-speed reliability
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 effectively limits torque between 0.1 and 6 Newton-meters at rotational speeds from 50 to 1300 RPM over multiple actuations, maintaining performance within a specified operational range and extending the device's lifespan.
Implementation Method 1
a rubbery bushing placed above the lower shank on at least partially around the neck configured to apply compressive force (F) along the axis to compress the first torque-limiting interface against the second torque-limiting interface
Implementation Method 2
an upper torque-limiting interface formed on the inside of the partially closed distal end and a lower torque-limiting interface disposed on the proximal end of the lower shank component with the first torque-limiting interface in contact with the second torque-limiting interface
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
Disposable torque-limiting mechanisms with an upper shank component with a torque- limiting interface, a lower shank component with a torque-limiting interface, and a rubbery spring material biasing element. Torque-limiting interfaces having a plurality of undulations arranged around an axial bore or drive socket and separated by a plurality of transition regions, with each undulation having an upslope, a peak, and a downslope. The torque- limiting interfaces are configured to engage and disengage to provide torque transmission with predetermined torque limits at various rotational speed s and for amounts of actuations while remaining within a specified operational range.