Hollow Rotary Actuator Encoder Layout for Tilt-Accurate Detection
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Solution Overview
Problem
Existing rotary actuators face issues with decreased detection accuracy due to tilting of the output member and the need to route encoder wires externally, which affects usability and increases shaft length.
Innovation Solution
A rotary actuator design featuring a cylindrical sleeve extending through the actuator, with an output-side detector near the output member and an input-side detector on the motor rear-end, allowing for accurate detection and integrated wiring without tilting effects, and a sealed configuration to protect internal components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the output-side encoder is disposed on the front end of the output member, then the detection accuracy is maintained, but the shaft length increases and usability is reduced
Solution Approach 1:
The patent relocates the output-side encoder from the axial dimension (front end of output member) to the radial dimension (side surface of output member). This dimensional change allows the encoder to be positioned close to the output member for accurate detection while not extending the axial shaft length, thereby resolving the contradiction between detection accuracy and shaft length.
2Length of moving object
If the output-side encoder is incorporated inside the strain wave gearing, then the shaft length is reduced, but the encoder is affected by lubricant and wiring becomes complex
Solution Approach 1:
The patent uses the side surface of the output member as an intermediary positioning surface for the output-side encoder. This intermediary location allows the encoder to be close to the output member (reducing shaft length) while remaining outside the strain wave gearing (avoiding lubricant contamination). The encoder is mounted on the side surface rather than inside the gearing, eliminating the need for complex internal wiring while maintaining compact dimensions.
3Volume of moving object
If the sleeve is long in the axial direction with the front end fixed to the output member, then the hollow portion is formed, but tilting of the output member reduces detection accuracy
Solution Approach 1:
The patent segments the encoder system into two separate detectors: an input-side encoder mounted on the motor shaft and an output-side encoder mounted on the output member. This segmentation allows each encoder to be positioned independently on stable reference surfaces (motor shaft and output member respectively), eliminating the tilting problem that would occur with a single long sleeve encoder. The hollow portion is maintained through the cylindrical sleeve structure while detection accuracy is preserved by using distributed sensing points.
Data Source
Figure 1
AI summary
A rotary actuator (1) has a hollow motor (2), a strain wave gearing (4), and an output member (6). An actuator hollow portion (70) is defined by a sleeve (7) extending through the actuator in an axial direction, an output-side detector (9) is disposed at a front side of the strain wave gearing (4), and an input-side detector (8) is disposed at a motor rear side. A rear end part (71) of the sleeve (7) is fixed to a side of the motor housing (21), which is a fixed-side member, and a front end part (72) of the sleeve extends into a center hole of the output member (6). An outer peripheral surface of the front end part (72) of the sleeve, which is positioned near a center of rotation of the output member (6), is used as a part for attaching a fixed-side detector component of the output-side detector (9); therefore, it is possible to reduce any decrease in detection accuracy due to, inter alia, tilting of the output member (6).