Strain Wave Gearbox Clutch Layout for Compact Over-Torque Protection

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Solution Overview

Problem

Conventional strain wave gearboxes lack over-torque protection, which can lead to damage to actuators in robotic and other mechanical systems, especially in small, torque-dense applications where traditional clutches are too large and impractical.

Innovation Solution

A strain wave gearbox design that incorporates a clutch assembly within the unused space of the flex spline, utilizing a preload subassembly and unique tooth geometry to distribute axial and torsional loads, providing over-torque protection without damaging the clutch plate.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional clutch is used for over-torque protection, then the actuator is protected from damage, but the clutch size becomes larger than the actuator itself

Engineering Contradiction:

Improveover-torque protectionVSAvoidclutch size

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The clutch assembly is nested within the chamber formed by the flex spline, placing the protection mechanism inside the existing actuator structure rather than adding it externally. This allows the clutch to be housed in the unused internal space of the flex spline chamber

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The invention transitions from external clutch mounting to internal clutch integration by utilizing the three-dimensional space within the flex spline chamber, effectively using the radial and axial dimensions already present in the strain wave gearbox structure

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of operation

If the clutch is placed outside the flex spline chamber, then it has more space to operate, but it increases the overall device volume

Engineering Contradiction:

Improveclutch operation spaceVSAvoiddevice volume

Core Design Contradiction:

Ease of operationVSVolume of stationary object

Solution Approach 1:

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The flex spline chamber serves dual purposes: it provides the necessary flexibility for strain wave gearing operation while simultaneously housing the clutch assembly for over-torque protection, eliminating the need for separate external spaces

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Device complexity

If axial load is concentrated on a small contact area, then the clutch structure is simpler, but the clutch plate becomes damaged

Engineering Contradiction:

Improveclutch structureVSAvoidclutch plate durability

Core Design Contradiction:

Device complexityVSStrength

Solution Approach 1:

The clutch plates are segmented with multiple teeth distributed around the contact surface, dividing the axial load into multiple contact points. This segmentation distributes the concentrated force across several teeth rather than a single contact area

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The teeth are designed with specific geometric properties (angle between 15-45 degrees, variable pitch) to optimize load distribution and stress characteristics at each contact point, creating locally optimized stress fields that prevent damage

Inventive Principle:

Principle #3Local quality

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 design effectively protects the actuator from over-torque conditions by distributing loads across a contact patch, preventing damage and allowing for compact, efficient operation within small form factors.

Implementation Method 1

The preload subassembly includes a spring element that applies a preload force upon the clutch

Methodology Applied

Scientific EffectSpring: Spring

Implementation Method 2

The preload subassembly may further include a thrust bearing disposed between the spring element and the clutch

Methodology Applied

Scientific EffectThrust bearing: Ball Bearing

Implementation Method 3

Each of the teeth has a pair of spaced apart sides angled downward from an intermediate ridge at an angle in the range of 20 to 60 degrees. During use of the strain wave gearbox, a contact patch or pressure area is provided between each mating pair of the teeth

Methodology Applied

Scientific EffectFriction: Friction

Implementation Method 4

The flex spline 130 is shaped like a shallow cup, with sides of that are very thin but with a bottom that is relatively rigid. This results in significant flexibility of the walls at the open end due to the thin wall

Methodology Applied

Scientific EffectElasticity: Elasticity

Data Source

PatentUS11499592B2Strain wave gearbox with over-torque protection

Publication Date: 2022.11.15 DISNEY ENTERPRISES INC

AI summary

A strain wave gearbox configured to provide over-torque protection. The strain wave gearbox is designed to include a clutch that is at least partially housed within or positioned inside the internal space (herein labeled a chamber or void space interchangeably with internal space) of a flex spline. In some cases, the internal space is utilized to generate the preload for the clutch, and it may be used to provide room for a clutch preload subassembly. The clutch is located outside the flex spline's internal space and is formed to use geometric friction surfaces in the form of mating rings of teeth on mating surfaces or sides of the first and second clutch plates that once preloaded by the clutch preload subassembly require a greater torque than the design torque to rotate to the next tooth.