Hollow Rotor Motor Position Sensor Design
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Solution Overview
Problem
In geared motors, the installation of a motor encoder to detect rotational position often requires additional space, leading to increased shaft length and reduced moment rigidity, making it challenging to achieve a flat, small-sized motor design.
Innovation Solution
A motor rotational position detection apparatus is integrated within the motor rotor's hollow portion, featuring a rotating unit and detection unit positioned inside the rotor hollow portion, eliminating the need for extended shaft length and allowing for a compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the motor encoder is mounted on the rear portion of the motor unit, then the rotational position can be detected with high precision, but the shaft length increases and the motor cannot achieve a flat profile
Solution Approach 1:
The detection unit is nested inside the rotor hollow portion, with the rotating unit (magnet) attached to the rotor and the detection unit (sensors) mounted on the bracket within the hollow space. This nesting arrangement allows the detection system to be housed within the existing motor structure without extending the shaft length, resolving the contradiction between detection precision and compact shaft dimensions.
2Ease of manufacture
If the motor encoder is placed on the load side, then the installation space can be provided, but the output shaft must be lengthened which reduces the moment rigidity and other characteristics of the reduction mechanism
Solution Approach 1:
The detection apparatus is merged with the rotor structure by utilizing the existing rotor hollow portion. The rotating unit is attached to the rotor and the detection unit is mounted on a bracket fixed within the hollow portion, combining the detection function with the rotor assembly. This eliminates the need for separate encoder mounting on the load side and avoids lengthening the output shaft, thereby preserving the moment rigidity of the reduction mechanism.
3Shape
If the detection components are housed internally in the rotor hollow portion, then the motor can achieve a flat profile with short shaft, but the installation space for detection components becomes limited
Solution Approach 1:
The detection components are arranged in a radial configuration within the rotor hollow portion, utilizing the radial space from the center axis outward. The bracket extends radially into the hollow portion, positioning the detection unit in a radial plane rather than extending axially. This dimensional arrangement maximizes the use of available radial space while maintaining a compact axial profile, achieving both flat motor shape and adequate installation space.
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 enables the creation of a flat, small-sized motor with a short shaft without compromising the motor's mechanical characteristics, as the detection components are housed internally, maintaining the motor's structural integrity and precision.
Implementation Method 1
the rotating unit is a ring-shaped or discoid magnet having a circular outer periphery surface subjected to multipolar magnetization along a circumferential direction
Implementation Method 2
the detection unit is composed of a plurality of magnetic detection elements arranged at fixed intervals around the circular outer periphery surface of the magnet
Implementation Method 3
the detection unit is composed of a plurality of magnetic detection elements arranged at fixed intervals around the circular outer periphery surface of the magnet
Data Source
AI summary
A magnetic absolute sensor for a geared motor comprises a dipole magnet and hall elements. The dipole magnet is fixed to a hollow portion of a hollow rotor shaft. A bracket attached to an end plate of a motor housing is coaxially inserted from the rear end side of the hollow portion. The dipole magnet is inserted from the front side in a cylindrical portion of the bracket. The hall elements are arranged at an interval of 90 degree on the circular inner periphery surface of the cylindrical portion. The hall elements face the circular outer periphery surface of the dipole magnet with a fixed gap therebetween. It is not necessary to increase a motor shaft length in order to incorporate the magnetic absolute sensor. The flux of a motor driven magnet is blocked by the hollow rotor shaft and the hall elements are not adversely affected.