Rotary Actuator with Phase-Offset Strain Wave Gears
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Solution Overview
Problem
Strain wave reduction gears in rotary actuators experience angle transmission errors due to processing errors, misalignment, and assembly errors, leading to secondary vibration components that cause resonance and positioning failures, especially in applications requiring high motion accuracy.
Innovation Solution
A rotary actuator design featuring two strain wave reduction gears with flexible externally toothed gears flexed into ellipsoidal shapes, offset by 90 degrees in phase, which cancel out secondary vibration components when synthesized at the output shaft, reducing angle transmission errors and enhancing torque and rigidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If one motor and one strain wave reduction gear are used, then the structure is simple, but angle transmission errors occur causing vibration and positioning failure
Solution Approach 1:
The patent divides the single strain wave reduction gear into two separate strain wave reduction gears (first and second SWRGs), each with its own wave generator, externally toothed gear, and internally toothed gear. This segmentation allows the vibration components from each gear to be independent and subsequently cancel each other out when synthesized at the output shaft, thereby reducing angle transmission errors and improving positioning accuracy while maintaining relatively simple structure.
2Ease of manufacture
If processing errors and misalignment are present in the strain wave reduction gear, then manufacturing is easier, but secondary vibration components are generated causing resonance
Solution Approach 1:
The patent converts the harmful vibration components generated by processing errors and misalignment into a beneficial cancellation effect. By using two strain wave reduction gears with ellipsoidal externally toothed gears offset by 90 degrees in phase, the secondary vibration components from each gear are opposite in phase and cancel each other out when synthesized at the output shaft. This transforms the harmful effect of manufacturing errors into a beneficial vibration cancellation mechanism.
3Measurement precision
If high motion accuracy is required, then positioning precision is improved, but the system becomes more complex
Solution Approach 1:
The patent merges two strain wave reduction gears into a single actuator system with a common output shaft. Both gears are driven by one motor and their outputs are combined at the output shaft, allowing vibration cancellation while achieving high motion accuracy. This merging approach provides high precision without requiring completely separate actuator systems.
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
The design effectively reduces angle transmission errors, achieves high moment capacity, and ensures high rigidity by canceling out secondary vibration components, thereby improving the accuracy and reliability of the rotary actuator's output rotation.
Implementation Method 1
a flexible externally toothed gear is flexed into an ellipsoidal shape by a wave generator
Implementation Method 2
the secondary vibration components included in the angle transmission errors are opposite in phase with each other, and therefore are synthesized and cancelled each other out when transmitted to the output shaft
Data Source
Figure 1(A)~1(B)
Figure 2
Figure 3
AI summary
A rotary actuator (1) has: one motor (2), two strain wave reduction gears (3, 4) disposed symmetrically on both sides of the motor, and one output shaft (5). The output rotation of the motor (2) is reduced in speed at the same reduction ratio by the two strain wave reduction gears (3, 4) and is outputted from the output shaft (5) to a load side. The first and second externally toothed gears (32, 42) of the first and second strain wave reduction gears (3, 4) are flexed into ellipsoidal shapes with 90 degrees shifted in phase, and are meshed with first and second internally toothed gears (33, 44). The angle transmission errors of the first and second strain wave reduction gears (3, 4) transmitted to the output shaft (5) are reduced by cancelling each other out in the output shaft (5). Reduced-speed output rotation that has the reduced angle transmission errors is outputted to the load side from the output shaft (5) .