Strain Wave Robot Drive Positioning Under Flexible Ring Torsion
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Solution Overview
Problem
Existing drive units with strain wave gear mechanisms suffer from imprecise angular positioning of the output shaft due to torsional expansion of the flexible ring during acceleration, which is not accurately detected by existing sensors, leading to overshooting and inaccurate positioning.
Innovation Solution
Incorporating a third sensor to detect the expansion of the flexible ring, combined with a calibration method that accounts for non-linear relationships between the drive shaft and output shaft positions during acceleration, allowing for precise adjustment of the output shaft position using the second sensor as the actual value generator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the flexible ring is used to transmit motion during acceleration, then high transmission ratio and compact structure are achieved, but torsional expansion occurs causing measurement inaccuracy and positioning error
Solution Approach 1:
A collar is introduced as an intermediary component that connects to the flexible ring but remains outside the strain wave gear mechanism. The collar rotates with the flexible ring during acceleration, allowing the second sensor to detect the expansion torsion indirectly. This mediator enables measurement of the torsional effect without being subjected to the high forces and vibrations inside the strain wave gear mechanism.
Solution Approach 2:
The collar creates a copy of the rotational motion and expansion torsion of the flexible ring. By placing the second sensor on the collar rather than directly on the output shaft, the system captures a replicated version of the motion that is free from the harmful vibrations and forces present in the original transmission path, enabling accurate measurement of the torsional expansion.
2Measurement precision
If the second sensor is placed on the output shaft to detect angular position, then fine positioning capability is provided, but vibrations and force input during acceleration cause measurement errors and overshooting
Solution Approach 1:
The collar serves as an intermediary between the flexible ring and the second sensor. It transfers the rotational position information to the sensor while isolating the sensor from the high-force vibration environment of the strain wave gear mechanism during acceleration, ensuring reliable measurements even under load.
Solution Approach 2:
The second sensor and its mounting collar are extracted from the high-stress environment inside the strain wave gear mechanism and placed in a lower-stress environment outside the mechanism. This extraction removes the sensor from the harmful vibrations and forces while maintaining its ability to detect the angular position through the collar's rotation.
3Speed
If the first sensor is used for coarse positioning, then sufficient range and speed are achieved, but insufficient precision is provided for fine positioning tasks
Solution Approach 1:
The positioning function is segmented into two distinct stages using two different sensors: the first sensor (rotary encoder) handles coarse positioning during normal operation with high speed and adequate precision, while the second sensor (on the collar) handles fine positioning during acceleration by detecting the expansion torsion with high precision. Each sensor operates in its optimal performance range.
Solution Approach 2:
The system dynamically switches between using the first sensor and the second sensor based on the operational state. During acceleration, the second sensor on the collar provides high-precision feedback for fine positioning. During normal operation, the first sensor provides sufficient precision at higher speeds. This dynamic adaptation allows the system to optimize performance for each operational phase.
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 angular positioning of the output shaft by compensating for torsional expansion, ensuring accurate adjustment even during acceleration, thereby improving the precision and stability of the drive unit.
Implementation Method 1
when the output shaft is moved, the flexible ring is expanded in the form of a torsion, particularly during acceleration
Implementation Method 2
the flexible ring is deformed all the way around
Data Source
AI summary
A drive unit for a robot, having an input shaft, an input shaft drive motor and a strain wave gear mechanism for transmission to an output shaft. The strain wave gear mechanism has a wave generator which is operatively connected to the input shaft, a flexible ring and a toothed ring are connectable to the output shaft, a first sensor for detecting an angular position of the input shaft and a second sensor for detecting the angular position of the output shaft. In order to allow the drive unit to precisely adjust the angular position of the output shaft to each setpoint angular position, the drive unit has a third sensor for detecting an expansion of the flexible ring. A robot having such a drive unit and a method for precisely adjusting the angular position of the output shaft are also provided.