Strain Wave Gearing Ratcheting for Overload Protection
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Solution Overview
Problem
Prior rotation transmission mechanisms face issues with increased mass and assembly errors due to the addition of torque limiters and other components to prevent overloading, which can lead to damage in powertrain components.
Innovation Solution
A rotation transmission mechanism utilizing a strain wave gearing as a speed reducer, where the strain wave gearing is designed to function as a mechanical fuse by adjusting the tooth depth, fastening force, or radial flexure to absorb overload, thereby preventing damage to other components without compromising its functionality as a speed reducer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a torque limiter is added to the power transmission path to prevent overloading, then damage to powertrain components is prevented, but the mass of the rotation transmission system increases
Solution Approach 1:
The patent combines the speed reducer and torque limiting functions into a single integrated strain wave gearing unit. The strain wave gearing inherently provides torque limiting through its flexible gear mechanism, eliminating the need for a separate torque limiter component while maintaining both speed reduction and overload protection functions.
Solution Approach 2:
The strain wave gearing serves multiple functions simultaneously: it acts as a speed reducer to reduce motor rotation and as a torque limiter to prevent overloading. This multi-functional design eliminates the need for separate components and reduces overall system mass.
2Reliability
If a torque limiter is added to the power transmission path to prevent overloading, then damage to powertrain components is prevented, but the dimensions of the rotation transmission system increase
Solution Approach 1:
The patent merges the torque limiter and speed reducer into a single compact strain wave gearing unit, eliminating the need for separate components and thereby reducing the overall dimensions of the transmission system.
3Reliability
If a torque limiter is added to the power transmission path to prevent overloading, then damage to powertrain components is prevented, but assembly errors increase
Solution Approach 1:
By integrating the torque limiting function into the strain wave gearing structure itself, the patent eliminates separate torque limiter components and their associated assembly procedures, thereby reducing assembly complexity and potential assembly errors.
4Reliability
If the strain wave gearing is designed with lower tooth depth or fastening force to function as a mechanical fuse, then protection against overloading is achieved, but the strength of the strain wave gearing decreases
Solution Approach 1:
The patent applies local quality by creating specific weak points in the strain wave gearing structure (through reduced tooth depth or fastening force in particular areas) that will fail first under overload conditions. This localized weakness is strategically designed to protect the overall system while maintaining sufficient strength for normal operation.
Solution Approach 2:
The patent converts the potential harm of gear failure into a beneficial protective mechanism. By designing the strain wave gearing to fail in a controlled manner (ratcheting) at predetermined weak points, the system transforms what would be a harmful failure mode into a useful torque limiting feature that protects the entire powertrain.
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 strain wave gearing effectively absorbs overload, preventing damage to other powertrain components by ratcheting and functioning as a mechanical fuse, thus maintaining the integrity of the transmission mechanism without the need for additional torque limiters or components.
Implementation Method 1
a flexible externally toothed gear (13) disposed on the inner side of the internally toothed gear (12), and an ellipsoidally contoured wave generator (14) fitted to the inner side of the externally toothed gear (13), wherein the externally toothed gear (13) is made to flex into an ellipsoidal shape by the wave generator (14)
Implementation Method 2
attention is focused on the fact that ratcheting (tooth skipping) during overloading occurs in one failure mode of the strain wave gearing, and the invention is configured so that the strain wave gearing is first caused to undergo ratcheting during overloading
Data Source
AI summary
In a rotation transmission mechanism that transmits the rotational driving force of a motor to a load-side member via a speed reducer, a strain wave gearing is used as the speed reducer, and the allowable load torque of members in the powertrain other than the strain wave gearing is greater than a predetermined upper-limit load torque. The allowable load torque of the strain wave gearing is dictated by the ratcheting torque, which is set so as not to exceed the upper-limit load torque. In an overload state, ratcheting is generated in the strain wave gearing, so that the strain wave gearing functions as a mechanical fuse. Other power transmission members can be protected from an overload state without adding a separate member such as a torque limiter.