Non-Elliptical Harmonic Drive Flexspline for Cogging Torque Suppression

Solution Overview

Problem

Harmonic drives experience unwanted cogging torques due to manufacturing deviations in the shape of flexible transmission elements, leading to negative effects on controllability in servo motor systems.

Innovation Solution

A harmonic drive design featuring a flexible, externally toothed transmission element with a non-elliptical shape in its unloaded state, having a more complex deviation from a circular shape than a rigid elliptical component, which reduces cogging torques by ensuring concentric alignment and minimizing preferential positions of the wave generator.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a flexible transmission element with a circular or elliptical shape is used, then the manufacturing process is simpler, but cogging torques and resonances occur due to manufacturing deviations

Engineering Contradiction:

Improvemanufacturing simplicityVSAvoidcogging torques

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent applies asymmetry by designing the flexible transmission element with a non-elliptical, asymmetric cross-sectional shape that has no inflection points. This asymmetric geometry is specifically engineered to compensate for manufacturing deviations and eliminate the formation of preferential positions, thereby suppressing cogging torques that would otherwise occur with symmetric circular or elliptical shapes.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent changes the geometric parameters of the flexible transmission element by defining a specific cross-sectional shape characterized by radius values at different angular positions. The shape is defined by specific radius ratios (e.g., r1/r0, r2/r0, r3/r0) and angular positions that create an asymmetric profile, transforming the traditional circular or elliptical geometry into a controlled non-elliptical form that eliminates cogging effects.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If a rigid elliptical component is used in the wave generator, then the transmission mechanism is simpler, but preferential positions are created leading to reduced controllability

Engineering Contradiction:

Improvetransmission mechanism simplicityVSAvoidcontrollability

Core Design Contradiction:

Device complexityVSEase of operation

Solution Approach 1:

The patent applies asymmetry by designing the flexible transmission element with a non-elliptical, asymmetric cross-sectional shape that has no inflection points. This asymmetric geometry is specifically engineered to compensate for manufacturing deviations and eliminate the formation of preferential positions, thereby suppressing cogging torques that would otherwise occur with symmetric circular or elliptical shapes.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent changes the geometric parameters of the flexible transmission element by defining a specific cross-sectional shape characterized by radius values at different angular positions. The shape is defined by specific radius ratios (e.g., r1/r0, r2/r0, r3/r0) and angular positions that create an asymmetric profile, transforming the traditional circular or elliptical geometry into a controlled non-elliptical form that eliminates cogging effects.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If manufacturing deviations occur in the flexible transmission element, then production costs are reduced, but shape inaccuracies lead to increased cogging torques

Engineering Contradiction:

Improveproduction efficiencyVSAvoidshape accuracy

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent converts the harmful effect of manufacturing deviations into a benefit by designing the flexible transmission element with an asymmetric shape that actively compensates for these deviations. The specific geometric configuration with controlled radius variations and no inflection points transforms unavoidable manufacturing tolerances into a mechanism that suppresses cogging torques rather than exacerbating them.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent applies asymmetry by designing the flexible transmission element with a non-elliptical, asymmetric cross-sectional shape that has no inflection points. This asymmetric geometry is specifically engineered to compensate for manufacturing deviations and eliminate the formation of preferential positions, thereby suppressing cogging torques that would otherwise occur with symmetric circular or elliptical shapes.

Inventive Principle:

Principle #4Asymmetry

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 suppresses cogging torques and resonances, enhancing the operational performance of the harmonic drive by maintaining concentric alignment and reducing shape-related operational issues.

Implementation Method 1

a flexible, externally toothed transmission element, which is deformed continuously by a wave generator during the operation of the harmonic drive

Methodology Applied

Scientific EffectElastic deformation: Elasticity

Data Source

PatentUS11098796B2Harmonic drive

Publication Date: 2021.08.24 SCHAEFFLER TECHNOLOGIES AG & CO KG

AI summary

A harmonic drive is provided that comprises a wave generator, a flexible, externally toothed gear element that can be deformed by said wave generator, and at least one internally toothed gear component which meshes with the flexible, externally toothed gear element. The externally toothed element has, with respect to its mechanically unloaded state, a non-circular shape that deviates from an elliptical shape.