Strain Wave Gear Positioning With Flexspline Strain Compensation
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Solution Overview
Problem
Existing drive units with stress wave gears face challenges in precisely controlling the angular position of the output shaft due to torsional stretching of the flexible ring during acceleration, leading to imprecise positioning and overshoot, especially when using rotary encoders for fine positioning.
Innovation Solution
Incorporating a third sensor to detect strain in the flexible ring, combined with a calibration procedure to account for the non-linear relationship between the angular positions of the drive and output shafts, allows for precise control by using the second sensor as an actual value transmitter only after accounting for the strain, and adjusting the output shaft position accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a second sensor is used for fine positioning of the output shaft, then positioning precision is improved, but the flexible ring stretching during acceleration causes measurement inaccuracy and overshoot
Solution Approach 1:
A third sensor is introduced as an intermediary device to detect the strain state of the flexible ring. This mediator provides information about the ring's deformation, which is then used to compensate for the measurement errors in the second sensor during acceleration phases, resolving the contradiction between measurement precision and reliability.
Solution Approach 2:
The system implements feedback control by continuously monitoring the flexible ring strain through the third sensor and using this information to correct the position measurements from the second sensor. The control unit adjusts the positioning commands based on the strain feedback, ensuring accurate positioning even during acceleration when the flexible ring is stretching.
2Power
If the flexible ring is used to transmit torque from drive shaft to output shaft, then gear ratio and torque multiplication are improved, but torsional stretching during acceleration causes position control inaccuracy
Solution Approach 1:
The third sensor acts as an intermediary that monitors the torsional stretching of the flexible ring. By detecting the strain state, it provides correction data that compensates for the position inaccuracies caused by the ring's elastic deformation during torque transmission and acceleration, maintaining measurement precision while preserving the power transmission function.
Solution Approach 2:
The system dynamically adjusts position control parameters based on the strain state of the flexible ring. During acceleration phases when the ring stretches, the control unit modifies the positioning commands using strain compensation calculations, thereby maintaining angular position transmission accuracy despite the changing physical state of the flexible ring.
3Measurement precision
If a third sensor is added to detect strain in the flexible ring, then positioning accuracy is improved, but device complexity increases
Solution Approach 1:
The third sensor serving strain detection purposes is integrated into the existing monitoring system, where it simultaneously provides data for both structural health monitoring and position compensation. This multi-functionality approach justifies the added complexity by delivering multiple benefits from a single sensor addition.
Solution Approach 2:
The third sensor is positioned as an intermediary element that leverages existing system infrastructure (power supply, data processing, control unit). Rather than creating a completely separate monitoring system, it integrates with the current architecture, minimizing the actual complexity increase while maximizing the measurement precision improvement.
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 precise control of the output shaft to any desired angular position by compensating for the strain-induced inaccuracies, ensuring accurate positioning even during acceleration.
Implementation Method 1
the flexible ring on the output shaft is stretched by torsion, particularly during acceleration
Implementation Method 2
the flexible ring, also called a flexspline, which is deformed around its circumference
Implementation Method 3
a third sensor for detecting strain in the flexible ring
Data Source
Figure 1
Figure 2~3
Figure 4~7
AI summary
The invention relates to a drive unit (1) for a robot (15), having an input shaft (3), a drive motor (4) for driving the input shaft (3) and a strain wave gear mechanism (5) for transmission from the input shaft (3) to an output shaft (11), wherein the strain wave gear mechanism (5) has a wave generator (5a) which is operatively connected to the input shaft (3), a flexible ring (5c) and a toothed ring (5d) which can be connected to the output shaft (11), comprising a first sensor (6a) for detecting an angular position (Θi) of the input shaft (3) and a second sensor (6b) for detecting the angular position (Θο) of the output shaft (11). In order to make it possible in such a drive unit (1) to precisely adjust the angular position of the output shaft (11) to each setpoint angular position, it is proposed that the drive unit (1) has a third sensor (6c) for detecting an expansion (ω) of the flexible ring (5c). The invention also relates to a robot (15) having such a drive unit (1) and to a method for precisely adjusting the angular position (Θο) of the output shaft (11) during positioning.