Rotary Encoder Plausibility Check for Gear Fault Detection
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Solution Overview
Problem
Existing multi-turn rotary encoders face reliability issues due to mechanical failures and errors in gear units, particularly at the shaft output and first gear stages, which can lead to incorrect rotation counting, failing to meet safety standards like SIL2 or SIL3 for functional safety.
Innovation Solution
A rotary encoder design with two independent gear units, each with a detection unit at specific stages, where the evaluation unit compares rotations for plausibility based on a known ratio greater than 2:1, allowing detection of inconsistencies and potential errors, and optionally omitting detection units to reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single multi-turn gear unit is used, then the device complexity is reduced, but the reliability is insufficient to meet safety standards like SIL2 or SIL3
Solution Approach 1:
The patent applies local quality by placing detection units at specific locations within the gear units - specifically at the first gear stage and at a downstream gear stage of the second gear unit. This selective positioning ensures that critical measurement points are monitored with high precision while avoiding unnecessary detection units elsewhere, thereby achieving functional safety without excessive complexity.
Solution Approach 2:
The evaluation unit performs preliminary plausibility checks by comparing rotation counts from different gear units before final evaluation. By anticipating potential errors and verifying consistency in advance, the system prevents incorrect rotation counting from propagating, thus ensuring functional safety through proactive error detection.
2Measurement precision
If detection units are added to all gear stages, then the measurement precision is improved, but the device complexity and cost increase
Solution Approach 1:
The patent implements local quality by strategically positioning detection units only at the first gear stage and at a downstream gear stage of the second gear unit, rather than uniformly across all gear stages. This targeted approach ensures measurement precision at critical points while minimizing the number of detection units, thereby reducing device complexity and cost.
3Reliability
If the ratio of rotation between gear stages is close to 1:1, then the gear unit design is simplified, but the ability to detect mechanical errors is reduced
Solution Approach 1:
The patent applies parameter changes by selecting a specific rotation ratio greater than 2:1 between the first gear stage and the downstream gear stage of the second gear unit. This parameter optimization ensures that mechanical errors produce detectable inconsistencies in rotation counting, thereby enhancing error detection capability while maintaining a manageable gear ratio configuration.
Data Source
AI summary
A rotary encoder (1) is provided, including a shaft (W) connected to and drivable by an external shaft, a first gear unit (G1) and a second gear unit (G2), each following rotations of the shaft (W). Both gear units (G1, G2) (G1 and G2) are drivable independently of one another by the shaft (W), a first gear stage (G1S1) of the first gear unit (G1) has a first detection unit (E1), and a gear stage (G2S2) downstream of a first gear stage (G2S1) of the second gear unit (G2) has a second detection unit (E2). An evaluation unit derives the angular position from signals of the detection units (E1, E2) and compares the rotations of the first gear stage (G1S1) and the downstream gear stage (G2S2) for plausibility, taking into account a known ratio of the rotation of the first gear stage (G1S1) to the rotation of the downstream gear stage (G2S2).