Torque-Limiter Using Rolling Elements for Actuator Overload Protection
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Solution Overview
Problem
Existing torque-limiting devices in actuation systems face challenges in accurately setting the activation torque to prevent overloads while minimizing nuisance activations, due to variations in efficiency and drag torques caused by ambient temperature and structural stiffness, leading to a wide difference between minimum and maximum torque-limiter engagement thresholds.
Innovation Solution
The introduction of rolling elements between the sliding collar and the input shaft reduces sliding friction, making the torque-limiter less sensitive to load/torque rate changes, allowing for a tighter threshold between minimum and maximum engagement, thereby reducing the actuator's overall dimensions and weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sliding friction is used between the sliding collar and input shaft, then the torque-limiter is sensitive to load/torque rate changes and temperature variations, but this leads to a wide difference between minimum and maximum engagement thresholds
Solution Approach 1:
The patent replaces sliding friction with rolling friction by introducing rolling elements (balls or rollers) between the sliding collar and input shaft. This substitution reduces the coefficient of friction and eliminates the sensitivity to load rate and temperature variations that characterizes sliding friction, thereby narrowing the threshold variation range while maintaining reliable torque-limiting function.
Solution Approach 2:
The patent changes the friction parameter from sliding friction to rolling friction by introducing rolling elements. This parameter change fundamentally alters the friction characteristics, reducing both the magnitude and variability of friction forces, which directly narrows the engagement threshold range and improves activation accuracy across different operating conditions.
2Reliability
If the torque-limiter threshold is set to protect against overloads, then excessive torque is prevented, but nuisance activations occur under normal operating conditions due to friction variations
Solution Approach 1:
By replacing sliding friction with rolling friction through the introduction of rolling elements, the patent eliminates the friction variations that cause nuisance activations. The consistent and predictable rolling friction characteristics allow for more accurate threshold setting, enabling reliable overload protection without false triggering during normal operation.
Solution Approach 2:
The patent changes the friction parameter from variable sliding friction to stable rolling friction. This parameter change reduces the variability in friction forces, allowing the torque-limiter threshold to be set more precisely to distinguish between normal operating torques and excessive overloads, thereby preventing nuisance activations while maintaining protection.
3Weight of moving object
If the difference between minimum and maximum torque-limiter engagement thresholds is reduced, then the actuator dimensions and weight can be reduced, but this requires insensitivity to load/torque rate variations
Solution Approach 1:
The patent substitutes sliding friction with rolling friction, which inherently provides insensitivity to load/torque rate variations. This substitution enables the design of a compact, lightweight actuator with narrow torque-limiter threshold range, as the rolling friction mechanism maintains consistent characteristics across varying operating conditions, eliminating the need for oversized components to accommodate threshold variations.
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 solution results in a torque-limiter that is insensitive to external load/torque rate variations, reducing the risk of nuisance trips and enabling more precise setting of the activation threshold, leading to weight reduction and improved performance across the full temperature range.
Implementation Method 1
one or more rolling elements arranged between the sliding collar and the input shaft to allow the sliding collar to move axially relative to the input shaft
Implementation Method 2
the sliding friction in contribution 2) is replaced with rolling friction by providing one or more rolling elements arranged between the input shaft and the sliding collar
Data Source
AI summary
An actuator comprises an input shaft, a sliding collar arranged around the input shaft, and an output shaft. The input shaft, output shaft and sliding collar are arranged such that a torque applied to the input shaft can be transmitted via the sliding collar to the output shaft. The actuator comprises a torque-limiting device for limiting the transmission of torque between the input shaft and the output shaft if the torque exceeds a certain threshold. The torque-limiting device comprises one or more rolling elements arranged between the sliding collar and the input shaft to allow the sliding collar to move axially relative to the input shaft and engage with or disengage from the output shaft.