Surgical Screwdriver Torque Limiter With Rolling-Element Uncoupling
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Solution Overview
Problem
Existing torque limiters for surgical screwdrivers face challenges in maintaining accurate and consistent torque transmission due to the variability of elastomer O-rings under thermal stress, particularly during sterilization.
Innovation Solution
A torque limiter design featuring an outer sleeve, a snap sleeve, a rolling element cage, and an inner sleeve with V-shaped notches and recesses, where rolling elements are used to uncouple the inner sleeve at maximum permissible torque, ensuring reproducible actuating torques and preventing uncoupling in the unscrewing direction, with a polyetheretherketone (PEEK) snap sleeve for enhanced accuracy and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an elastomer O-ring is used as the elastic element in the torque limiter, then the device can provide torque limiting functionality, but the elasticity varies significantly and changes over time due to thermal stress during sterilization
Solution Approach 1:
The patent removes the elastomer O-ring from the torque limiter design and replaces it with a metal spring element. This extraction of the problematic elastic element eliminates the source of variability while maintaining the torque limiting function through the mechanical spring mechanism
Solution Approach 2:
The patent changes the material parameter from elastomer to metal spring, fundamentally altering the physical properties of the elastic element. This parameter change ensures stable elasticity characteristics that do not vary with thermal stress or time, while still providing the necessary torque limiting capability
2Reliability
If rolling elements are allowed to exit the V-shaped notches in both directions, then torque limiting in both screwing and unscrewing directions would be achieved, but unlimited force transmission in the unscrewing direction would be prevented
Solution Approach 1:
The patent employs asymmetric design of the rolling element mechanism where the V-shaped notches and rolling element geometry are configured to allow exit only in the screwing direction. This asymmetric arrangement enables different force transmission behaviors for screwing versus unscrewing operations, achieving torque limiting in one direction while maintaining unlimited force transmission in the other
Solution Approach 2:
Instead of trying to prevent rolling element exit in both directions, the patent inverts the approach by designing the mechanism to naturally allow exit only when needed (screwing direction with torque overload) while preventing exit in the unscrewing direction through the specific geometry of the V-shaped notches and rolling element positioning
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
This design ensures consistent and reproducible torque transmission, minimizes thermal stress effects, and provides a long functional life with reduced friction and torque inaccuracies, maintaining accurate actuation even under varying conditions.
Implementation Method 1
The rolling element cage is provided with a plurality of rolling element receiving areas, each of which holds a rolling element. The rolling element cage is also provided with a number of noses. The noses engage into the recesses.
Data Source
AI summary
A torque limiter for a surgical screwdriver that includes an outer sleeve (1); a snap sleeve (3), which is arranged in and rotates with the outer sleeve; a rolling element cage (6), which is arranged in the snap sleeve; an inner sleeve (10), which is arranged in the rolling element cage; and a force-transmitting shaft (11), which is received in and rotates with the inner sleeve. The inner wall of the outer sleeve is provided with recesses (8) that extend parallel to a rotational axis of the force-transmitting shaft. The rolling element cage is provided with a plurality of rolling element receiving areas (5), each of which holds a rolling element (4), and with a number of noses (7), which engage into the recesses. The inner sleeve is provided with a plurality of notches (9), which extend in a V-shape parallel to the axis and which receive the rolling elements.