Strain Wave Gearing Hub Displacement Sensing for Thrust Control

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Solution Overview

Problem

There is no existing proposal for small detectors that can be built into strain wave gearings to detect thrust generated during reduced-speed and increased-speed operations, which limits the ability to perform operation control based on thrust information.

Innovation Solution

A strain wave gearing with a built-in detection mechanism that detects thrust by measuring the miniscule displacement of a hub linked to the wave generator, allowing for operation control based on detected thrust.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a detection mechanism is built into the strain wave gearing to detect thrust, then operation control based on thrust information becomes possible, but the device complexity increases

Engineering Contradiction:

Improveoperation control capabilityVSAvoidstructure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The detection mechanism is merged with the existing hub structure of the wave generator. The hub serves dual purposes: transmitting rotational motion and detecting thrust through displacement measurement. This integration adds detection functionality without requiring a completely separate detection system, thereby reducing the increase in device complexity.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The hub is designed to perform multiple functions: it transmits rotation from the wave generator and simultaneously acts as a displacement sensor for thrust detection. By making the hub multi-functional, the patent avoids adding separate components for detection, thus improving adaptability while minimizing complexity increase.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Measurement precision

If a detection mechanism is added to detect hub displacement, then thrust detection becomes possible, but the axial length of the gearing increases

Engineering Contradiction:

Improvethrust detection capabilityVSAvoidaxial length

Core Design Contradiction:

Measurement precisionVSLength of moving object

Solution Approach 1:

Instead of adding the detection mechanism in the axial direction (which would increase axial length), the patent utilizes the radial dimension. The detection mechanism measures radial displacement of the hub, which corresponds to axial thrust through the mechanical relationship in the strain wave gearing. This dimensional transformation allows thrust detection without increasing axial length.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The detection mechanism is nested within the existing radial space of the hub structure. The detector is positioned radially outward from the hub center, utilizing the existing radial clearance and structure. This nesting approach allows the detection mechanism to be accommodated within the current axial boundaries without extending the axial length.

Inventive Principle:

Principle #7Nested doll (Nesting)

3Measurement precision

If the hub is made movable in the axial direction to detect thrust, then thrust detection becomes possible, but the retention torque required to retain the wave generator increases

Engineering Contradiction:

Improvethrust measurement capabilityVSAvoidretention torque

Core Design Contradiction:

Measurement precisionVSForce

Solution Approach 1:

The patent replaces direct axial movement detection with radial displacement detection. Instead of allowing the hub to move axially and measuring that movement (which would require overcoming retention forces), the system measures radial displacement of the hub that occurs naturally under thrust load. This substitution of measurement approach eliminates the need to overcome retention torque for detection purposes.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The detection mechanism acts as an intermediary that measures radial displacement rather than directly measuring axial thrust forces. This indirect measurement approach through radial displacement avoids the need to directly counteract or measure against the retention torque, thereby maintaining low retention torque requirements while still enabling thrust detection.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

Enables operation control corresponding to detected thrust, improving the management of thrust during strain wave gearing operations without increasing the axial length of the gearing.

Implementation Method 1

detects displacement produced in the wave generator in the direction of an axis by the thrust

Methodology Applied

Scientific EffectDisplacement: Displacement

Data Source

PatentUS12234903B2Strain wave gearing and actuator

Publication Date: 2025.02.25 HARMONIC DRIVE SYST IND CO LTD

AI summary

In the interior of a device housing of a strain wave gearing, a detection mechanism is incorporated at a site on the outer peripheral side of a hub of a wave generator. The hub of the wave generator is linked to a motor shaft so that axial force does not act thereon. The detection mechanism detects minute displacements in the axial direction that occur in the hub of the wave generator due to thrust acting on the wave generator. Thrust acting on the wave generator is obtained on the basis of the detected minute displacements. With this strain wave gearing in which the detection mechanism is incorporated, operation control that is responsive to sensed thrust is possible through the use of thrust information during operation.