Multi-turn Encoder With Redundant Sensing For Fault Tolerance
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Solution Overview
Problem
Existing multi-turn absolute encoders face issues with indeterminate measurements when sensing devices fall into intermediate positions and are prone to failure if sensing elements malfunction, limiting their ability to accurately indicate angular positions over multiple turns.
Innovation Solution
A system comprising multiple rotatable members with unique ratios of revolution and corresponding sensing devices that can discard faulty readings, allowing for the determination of absolute positions using remaining members, ensuring continued functionality even if one or more components fail, and utilizing a lookup table to calculate positions based on relationships between members.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple rotatable members with unique ratios are used to determine absolute position over multiple turns, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The encoder is divided into multiple independent rotatable members (first, second, and third detection gears) with unique tooth counts (e.g., 20, 24, and 28 teeth). Each member is sensed by a separate sensing device, segmenting the measurement function across multiple components. This segmentation allows the system to determine absolute position over multiple turns by combining measurements from all members, achieving high precision while maintaining modular complexity
Solution Approach 2:
The rotatable members are arranged concentrically on the same shaft, with each member nested within the radial space of the others. The first, second, and third detection gears share the same rotational axis and are positioned at different radial distances, creating a compact nested structure. This nesting approach maximizes the use of available space while accommodating multiple sensing elements without proportionally increasing device complexity
2Reliability
If redundant sensing elements are added to provide fault tolerance, then reliability is improved, but device complexity increases
Solution Approach 1:
Each rotatable member has a unique local quality in terms of its tooth count and rotational characteristics (e.g., 20 teeth vs. 24 teeth vs. 28 teeth). This local differentiation ensures that each sensing device measures a distinct aspect of the shaft's rotational position. The unique characteristics of each member provide inherent redundancy, as the loss of one member's data can be compensated by the others, improving reliability without requiring duplicate sensing devices
Solution Approach 2:
The processor continuously monitors the measurements from all sensing devices and uses feedback algorithms to detect faults. When a sensing device or rotatable member fails, the system receives feedback about the anomaly and automatically adjusts by using only the remaining functional members to calculate the absolute position. This feedback mechanism enables the system to maintain reliability even when components fail, without requiring physical redundancy of all sensing elements
3Measurement precision
If the encoder uses intermediate position sensing to increase resolution, then measurement precision is improved, but the system becomes prone to indeterminate measurements when sensors fall between index positions
Solution Approach 1:
Multiple rotatable members with predetermined unique tooth counts are installed on the shaft before operation. These members are positioned such that their index positions (reference marks) are pre-aligned or have known angular relationships. By having the index positions predetermined and known, the system can reliably determine absolute position even when individual sensors are between index positions, as the combined measurements from multiple members provide sufficient information to resolve the ambiguity
Solution Approach 2:
The encoder uses a composite measurement approach, combining data from multiple rotatable members with different tooth counts and index position configurations. Just as composite materials combine different properties to achieve superior performance, this composite sensing approach combines multiple discrete measurements to achieve both high resolution and deterministic accuracy. The unique characteristics of each member (different tooth counts create different measurement patterns) work together to eliminate indeterminate states that would occur with a single sensing system
Data Source
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AI summary
Apparatus (100) adapted to provide an indication of an angular position of an input member (106) over multiple turns includes a set of rotatable members comprising at least two rotatable members (104A -104D) configured, in use, to rotate in accordance with rotation of an input member (106), and a set of sensing devices (114A) configured to measure and output an angular position of at least one of the rotatable members. The rotatable members are configured to rotate simultaneously but at different rates. The apparatus further includes a device (114) configured to use the angular position measurements from the set of sensing devices to produce an indication of an angular position of the input member over multiple turns. The set of sensing devices (114A) comprises more than one said sensing device (114A) which is provided for measuring the position of a single said rotatable member (104), such that if one of the sensing devices in the set develops a fault then another said sensing device in the set is used instead.