Inductive Proximity Sensing for Shaft Position at Low Speed
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Solution Overview
Problem
Existing systems for monitoring the position, speed, and direction of rotating shafts in vehicles, such as aircraft components and dynamoelectric machines, are cumbersome and costly, often requiring multiple sensors and complex algorithms, and struggle to accurately operate at low speeds or when the shaft is stationary.
Innovation Solution
A shaft monitoring system utilizing a proximity sensor coupled to a target element on the shaft, which measures inductance changes as the shaft rotates, generating a signal that allows for determination of position, speed, and direction without additional sensors or algorithms, using a signal processing system to convert inductance into positional, speed, and directional data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple sensors and complex algorithms are used to monitor shaft position, speed, and direction, then measurement precision is improved, but device complexity increases and cost increases
Solution Approach 1:
The patent combines multiple measurement functions (position, speed, and direction detection) into a single proximity sensor that reads a coded disc with multiple concentric rings. Each ring encodes different information, and the sensor simultaneously captures all rings to determine all three parameters, eliminating the need for multiple separate sensors and complex algorithms.
Solution Approach 2:
The coded disc structure serves multiple functions: it provides position encoding through radial patterns, speed measurement through rotation frequency detection, and direction determination through the sequence of pattern passage. A single proximity sensor performs all three measurement tasks, making the system multi-functional with minimal components.
2Reliability
If traditional monitoring systems are used, then shaft position and speed can be detected, but reliability deteriorates at low speeds or when shaft is stationary
Solution Approach 1:
The coded disc is pre-configured with multiple concentric rings containing different binary patterns that are always present regardless of shaft speed or position. These pre-encoded patterns ensure that valid measurement signals are available even when the shaft is stationary or rotating very slowly, eliminating the need for minimum speed thresholds.
Solution Approach 2:
The system continuously monitors the reflected light patterns from the coded disc rings and provides feedback signals that maintain accurate position and velocity measurement across all operating conditions. The multiple rings provide redundant feedback paths that ensure reliable detection even when some patterns are obscured or degraded at low speeds.
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 solution provides accurate and cost-effective monitoring of shaft position, speed, and direction, eliminating the need for multiple sensors and complex algorithms, and ensures reliable operation at low speeds and when stationary.
Implementation Method 1
The proximity sensor measures an inductance of the target element based on one or both of a volume of the target element and a distance between the target element and the proximity sensor
Data Source
AI summary
A shaft monitoring system includes a rotatable shaft having a target element coupled thereto that rotates along with the shaft. A proximity sensor is located adjacent to the target element. The proximity sensor measures an inductance of the target element based on one or both of a volume of the target element and a distance between the target element and the proximity sensor, and generates a proximity sensor output signal based on the measured inductance. A signal processing system determines at least one of a position of the shaft, a rotational speed of the shaft, and a rotational direction of the shaft based on the proximity sensor output signal.