Compact Rotary Actuator Radial Position Sensing
Solution Overview
Problem
Existing rotary actuators for robot joints, particularly finger units, face challenges due to their axial length and unsuitability for compact designs, especially when equipped with optical rotary encoders for position sensing, which further increase the axial length, making them inappropriate for small-sized applications.
Innovation Solution
A compact rotary actuator design featuring a cylindrical housing with a motor and reducer concentrically disposed within, a rotary arm rotating on the circular outer face, a scale for position detection, and a position sensor integrated into the arm, eliminating the need for additional axial or radial space for the sensing mechanism.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an optical rotary encoder is attached to the motor shaft or joint shaft for position sensing, then the rotational position can be detected, but the axial length of the actuator increases significantly
Solution Approach 1:
The patent moves the sensing mechanism from the axial dimension to the radial dimension. The scale is formed on the circular outer face of the cylindrical housing, and the position sensor is mounted on the rotary arm that rotates along this circular face. This dimensional shift allows position detection without extending the axial length, as the sensing occurs in the radial plane rather than along the axis.
Solution Approach 2:
The circular outer face of the cylindrical housing serves multiple functions: it provides the external surface of the actuator housing and simultaneously serves as the mounting surface for the scale. The rotary arm's rotation along this circular face integrates the sensing function into the existing structural element, eliminating the need for separate axial space for the encoder.
2Volume of moving object
If the actuator is designed for compact size with short axial length, then it is suitable for finger joints, but conventional sensing mechanisms cannot be integrated without increasing size
Solution Approach 1:
The sensing mechanism is nested within the existing actuator structure. The scale is formed on the outer face of the cylindrical housing, and the position sensor is mounted on the rotary arm that is already part of the actuator's mechanical structure. This nesting approach integrates the sensing function into the existing components without requiring additional axial or radial space.
3Measurement precision
If a reflective plate and external reflecting photosensor are used for position detection, then the rotational position can be sensed, but the axial length increases due to the external sensor mounting
Solution Approach 1:
The patent merges the scale (reflective element) and the position sensor into a single integrated sensing system mounted on the rotary arm. The scale is formed on the circular outer face of the housing, and the position sensor reads this scale as the arm rotates, combining the detection function with the existing mechanical structure rather than adding external sensors that would extend the axial length.
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 configuration results in a small-sized, compact rotary actuator with a short axial length, enabling effective position sensing without increasing the actuator's size, suitable for use in finger joints of robot hands.
Implementation Method 1
a scale formed along the circular outer direction on the circular outer face in order to detect the rotational position of the rotary arm; a position sensor mounted on the facing section of the rotary arm in order to read the scale
Data Source
AI summary
A rotary actuator equipped with a sensing mechanism includes a motor and a reducer concentrically disposed inside a cylindrical housing; a scale for detecting the rotational position of a rotary arm, the scale being disposed on the circular outer face of the cylindrical housing; and a position sensor mounted in the facing section of the rotary arm that rotates along the circular outer face, the facing section being in a facing arrangement with the circular outer face. A detection mechanism includes the scale and the position sensor detects the rotational position of the rotary arm capable of rotating within a finite angular range along the circular outer face of the cylindrical housing. The components are concentrically disposed. The actuator is suitable for use as a digital joint unit.