Undulated Torque-Limiting Shank Interface for High-RPM Reliability
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Solution Overview
Problem
Disposable torque-limiting systems for medical power tools fail to reliably limit torque at higher rotational speeds and often fall out of specification with increased RPMs, leading to insufficient performance.
Innovation Solution
A torque-limiting mechanism comprising an upper shank component, a lower shank component, and a biasing element, with undulated torque-limiting interfaces that engage and disengage when a predetermined torque limit is exceeded, using materials like glass-filled polyetherimide resin to ensure durability and resistance to sterilization, and incorporating a biasing element to apply compressive force for precise torque control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If disposable torque-limiting systems are used for medical power tools, then cost and ease of disposal are improved, but torque limiting reliability deteriorates at higher rotational speeds
Solution Approach 1:
The torque-limiting mechanism is divided into separate disposable components including a driver bit with torque-limiting interface and a shank with complementary interface. This segmentation allows each component to be optimized independently for high-speed performance while maintaining cost-effectiveness as a disposable system. The interfaces are designed to work together to provide reliable torque limiting through controlled slipping mechanisms.
Solution Approach 2:
The torque-limiting interface incorporates dynamic elements such as undulating surfaces and flexible components that adapt to high-speed rotation. The interface geometry includes curved and undulating features that maintain contact and torque control during rapid rotational movements, preventing the reliability deterioration that occurs with static designs at high RPMs.
2Ease of manufacture
If traditional torque-limiting interfaces are used, then manufacturing simplicity is improved, but torque control precision deteriorates
Solution Approach 1:
The torque-limiting interface incorporates undulating and curved surfaces instead of flat traditional interfaces. These curved features include undulations with specific radii that provide progressive engagement and controlled slipping. The curvature allows for more precise torque control through gradual contact area changes while remaining manufacturable through molding processes.
Solution Approach 2:
The interface design utilizes specific geometric parameters such as undulation amplitude, wavelength, and radius of curvature to control torque transmission. By optimizing these parameters, the interface achieves precise torque limiting through controlled elastic deformation and progressive slipping, transforming the torque control mechanism from simple friction-based to geometry-controlled precision slipping.
3Productivity
If high rotational speeds are used, then productivity is improved, but torque limiting performance deteriorates
Solution Approach 1:
The interface is designed with dynamic characteristics including undulating surfaces and flexible elements that respond to high-speed rotation. The geometry is optimized to maintain stable torque control during rapid actuation cycles, with features that prevent vibration and ensure consistent performance across a wide RPM range from slow to high-speed operations.
Solution Approach 2:
The torque-limiting interface combines multiple functional features into a single integrated structure, including undulating surfaces, elastic deformation zones, and controlled slipping mechanisms. This merging of functions allows the interface to simultaneously provide torque control, high-speed capability, and durability without requiring separate components for each function.
4Measurement precision
If reusable torque-limiting drivers are used, then torque precision is improved, but maintenance complexity and sterilization requirements worsen
Solution Approach 1:
The torque-limiting driver bit is designed as a disposable component that can be manufactured at low cost using molding processes. This eliminates the need for sterilization and recalibration while maintaining torque precision through consistent manufacturing of the torque-limiting interface geometry. The disposable nature removes all maintenance complexity associated with reusable drivers.
Solution Approach 2:
The torque precision is achieved through controlled geometric parameters of the interface rather than through calibration adjustments. The undulation geometry, material properties, and contact surface characteristics are designed to provide repeatable torque control directly from manufacturing, eliminating the need for post-manufacturing calibration that complicates reusable systems.
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 mechanism effectively limits torque up to 6 N-m across various rotational speeds, maintaining performance over a large number of actuations while withstanding sterilization and cleaning processes, ensuring consistent torque delivery and extended durability.
Implementation Method 1
a biasing element configured to apply a compressive force along the axis to compress the first torque-limiting interface against the second torque-limiting interface
Implementation Method 2
The upper shank component and the lower shank component are configured to engage to rotate together when torque is applied to the lower shank component via the drive socket. The upper shank component and the lower shank component are configured to disengage when a predetermined torque limit is exceeded.
Data Source
AI summary
Torque-limiting mechanisms comprising an upper shank component with a torque-limiting interface, a lower shank component with a torque-limiting interface, and a 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 speeds and for amounts of actuations while remaining within a specified operational range.