Off-Center Magnet Rotary Position Sensor
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Solution Overview
Problem
Non-contacting position sensors face challenges with precision and accuracy due to magnetic irregularities and mechanical vibrations, which can cause misalignment and require temperature compensation electronics.
Innovation Solution
A sensor assembly with a magnet coupled to a shaft in an off-center relationship, using a Hall effect device to sense the magnetic flux direction and generate an electrical signal indicative of the shaft's position, incorporating a semi-circular magnet for uniform flux field and a compact design with temperature-independent Hall Effect sensor to eliminate the need for temperature compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-contacting position sensors use magnets to generate magnetic fields for position measurement, then durability is improved by reducing physical wear, but measurement precision deteriorates due to magnetic irregularities and misalignment from mechanical vibrations
Solution Approach 1:
The sensor assembly is divided into separate functional components: a rotor portion containing the magnet and a sensor portion containing the Hall effect device. This segmentation allows independent optimization of each component and facilitates temperature compensation through separate thermal management of the electronics
Solution Approach 2:
A magnet housing is introduced as an intermediary component between the magnet and the environment. This housing provides mechanical support, maintains precise alignment, and isolates the magnet from thermal and mechanical disturbances, thereby preserving measurement precision while maintaining the non-contacting durability advantage
2Measurement precision
If temperature compensation electronics are added to maintain accuracy across temperature ranges, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The temperature compensation functionality is merged with the main signal processing circuitry in the sensor portion. The Hall effect device output is processed through compensation circuits that are already present in the sensor assembly, eliminating the need for separate temperature compensation electronics and reducing overall device complexity
Solution Approach 2:
The system compensates for temperature effects by detecting and correcting changes in magnetic field parameters. The sensor measures actual magnetic field strength and polarity, then applies parameter-based compensation algorithms to maintain accuracy across varying temperatures without requiring complex hardware modifications
3Volume of moving object
If the magnet is positioned off-center relative to the shaft, then compact design is improved, but manufacturing precision requirements increase
Solution Approach 1:
The magnet is pre-positioned in a precisely machined recess in the rotor portion during manufacturing. This preliminary positioning action ensures accurate off-center placement without requiring high-precision assembly operations later, as the magnet location is established in the initial manufacturing stage
Solution Approach 2:
A template or jig is used during magnet installation to replicate the precise off-center position. This copying method ensures consistent magnet placement across multiple units, reducing the need for complex individual positioning and lowering overall manufacturing precision requirements
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 solution enhances durability and accuracy by reducing physical wear and drag, maintaining precision and linearity across varying temperatures and mechanical conditions, while allowing for compact and sealed electronic components.
Implementation Method 1
A sensor is retained in the housing in proximity to the magnet. The magnet and the sensor are movable relative to each other and the sensor is adapted to sense the direction of the flux field and generate an electrical signal that is indicative of the direction of the flux field, the position of the shaft, and the position of the movable object coupled to the shaft
Data Source
AI summary
A sensor assembly for sensing a movable object which, in one embodiment, includes a housing defining an interior cavity. A rotor is retained in the cavity. The rotor defines a central bore and a magnet is mounted in an off-center pocket defined by the rotor. The rotor is coupled to the shaft of the movable object whose position is to be measured. A sensor is also retained in the cavity in a relationship at least partially overlying the magnet and adapted to sense at least the direction of the magnetic field generated by the magnet to generate an electrical signal indicative of the position of the movable object. In another embodiment, the rotor and sensor are mounted in separate interior housing cavities separated by an interior housing wall.