Harmonic Drive Torque Measurement via Axial Load Extraction
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Solution Overview
Problem
Current harmonic drive systems require a torque cell to measure output torque, which increases volume, weight, and inertia, degrading system responsiveness as output torque increases.
Innovation Solution
A harmonic drive system that measures axial force from a wave generator using a load cell and processor to calculate output torque without a torque cell, reducing the number of parts and inertia, and allowing for increased design freedom.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a torque cell is used to measure output torque, then measurement capability is provided, but volume and weight increase
Solution Approach 1:
The patent extracts the measurement function from a traditional torque cell and relocates it to the wave generator. The wave generator's inherent structure is modified to include measurement means (such as strain gauges or sensors) that directly measure the axial force generated during operation, eliminating the need for a separate torque cell component.
Solution Approach 2:
The measurement function is merged with the wave generator structure. The wave generator serves dual purposes: transmitting mechanical motion and measuring axial force. This integration combines the drive mechanism and measurement device into a single component, reducing overall system volume and weight.
2Measurement precision
If a torque cell is used to measure output torque, then measurement capability is provided, but system responsiveness degrades due to increased inertia
Solution Approach 1:
The patent removes the torque cell from the output stage, eliminating the additional mass and inertia it introduces. By measuring axial force at the wave generator instead, the system maintains measurement capability while preserving the low-inertia characteristics necessary for rapid acceleration and deceleration.
Solution Approach 2:
The measurement is performed preliminarily at the wave generator, where the axial force is first generated, rather than measuring at the output stage after the load has been applied. This allows for earlier detection of torque changes, improving system responsiveness.
3Measurement precision
If a torque cell is used to measure output torque, then measurement capability is provided, but device complexity increases due to additional components
Solution Approach 1:
The patent extracts the measurement function from a separate torque cell and integrates it into the wave generator, reducing the number of discrete components in the system.
Solution Approach 2:
The wave generator is designed to perform both mechanical transmission and measurement functions simultaneously, merging two previously separate functions into a single component and thereby reducing overall device complexity.
4Measurement precision
If a torque cell is used to measure output torque, then measurement capability is provided, but design freedom is restricted due to additional components
Solution Approach 1:
By removing the torque cell from the system and integrating measurement capabilities into the wave generator, the patent eliminates constraints on component placement and system configuration, thereby increasing design freedom.
Solution Approach 2:
The wave generator is designed as a multi-functional component that serves both as a drive mechanism and a measurement device. This universality allows for greater flexibility in system design and configuration, as fewer specialized components are required.
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 measurement of output torque without a torque cell, reducing volume and weight, improving responsiveness, and allowing for measurement of load changes based on reduction/acceleration states.
Implementation Method 1
a load cell that is installed in any one of the drive housing, the input shaft, or the wave generator and measures the axial load that occurs and is translated from the wave generator to the input shaft or the drive housing via the input shaft
Data Source
AI summary
A harmonic drive includes: an input shaft connected to a first element that is one of a wave generator, a flex spline, or a circular spline; a drive housing connected to the input shaft via a bearing; a load cell that is installed in any one of the drive housing, the input shaft, or the wave generator and measures an axial load that occurs and is translated from the wave generator to the input shaft or the drive housing via the input shaft; and a processor that reversely calculates output torque, which is output from a second element that is one of the two elements other than the first element, from the axial load measured by the load cell.