Harmonic Drive Torque Sensing to Exclude Ripple Error
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Solution Overview
Problem
Current methods for measuring output torque in harmonic drives, such as using elastic elements or strain gauges, are not conducive to miniaturization and suffer from measurement accuracy issues due to torque ripple and inconsistent strain values.
Innovation Solution
A harmonic drive system with multiple sets of torque sensors, each set comprising strain gauges arranged alternately to measure torque transmitted during rotation, and a processor that calculates the true torque by excluding torque ripple from the signals, using equations that account for the angle of the wave generator relative to the flexible spline.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If strain gauges are arranged discretely inside the harmonic drive to measure output torque, then the measurement can be performed internally, but the strain values from each strain gauge are inconsistent and torque ripple causes measurement fluctuation, reducing measurement accuracy
Solution Approach 1:
The torque measurement function is divided into multiple independent measurement channels, each with its own strain gauge set. By segmenting the measurement system into multiple parallel channels and combining their outputs, the patent achieves more reliable torque measurement that overcomes the limitations of single discrete strain gauge arrangements.
Solution Approach 2:
The patent implements a feedback mechanism where the outputs from multiple strain gauge sets are continuously monitored and processed. The control system uses this feedback information to calculate and compensate for torque ripple effects, thereby improving measurement accuracy and reliability through active correction.
2Measurement precision
If elastic elements are used to measure output torque by arranging torque sensors on them, then torque measurement is achieved, but the number of parts increases, making miniaturization and cost reduction difficult
Solution Approach 1:
The patent merges the torque measurement function with the existing harmonic drive structure by integrating strain gauges directly onto the harmonic drive components. This consolidation eliminates the need for separate elastic elements and external torque sensors, thereby reducing part count while maintaining measurement capability.
Solution Approach 2:
The harmonic drive structure is designed to serve multiple functions: it provides both the speed reduction mechanism and the torque measurement function. By making the harmonic drive structure multi-functional, the patent eliminates the need for additional dedicated torque measurement components, reducing overall system complexity.
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
This approach effectively eliminates torque ripple, enhancing measurement accuracy and sensitivity, thereby providing a precise measurement of real torque in harmonic drives.
Implementation Method 1
each set of torque sensors includes a plurality of strain gauges, each set of torque sensors is respectively configured to measure torque transmitted by the harmonic drive during rotation of the flexible spline
Data Source
AI summary
A harmonic drive includes: a wave generator; a circular spline provided with internal teeth; a flexible spline provided between the wave generator and the circular spline and configured to be engaged with the internal teeth of the circular spline; and a plurality sets of torque sensors. Each set of torque sensors includes a plurality of strain gauges, each set of torque sensors is respectively configured to measure torque transmitted by the harmonic drive during rotation of the flexible spline. Signals measured by each of the plurality sets of torque sensors include a torque ripple, and the plurality sets of torque sensors are alternatively arranged. The harmonic drive further includes a processor configured to calculate a true torque transmitted by the harmonic drive based on signals measured by the plurality sets of torque sensors. The torque ripple is excluded from the true torque.