Encoder Abnormality Diagnosis via Frequency Thresholding
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Solution Overview
Problem
Existing encoder abnormality diagnosis systems face challenges in accurately detecting abnormalities in sine and cosine waveforms due to fluctuations caused by factors like gear misalignment, temperature changes, and eccentricity, leading to false positives or false negatives in speed monitoring, especially in Safety Category 3 applications.
Innovation Solution
An encoder abnormality diagnosis device that includes a stop determination processing unit to assess rotation status based on pulse signal count changes and a frequency measurement unit to compare the measured frequency with a preset upper limit frequency, determining abnormalities when the frequency exceeds this limit, thereby enhancing diagnostic accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single sine/cosine signal output encoder is used for speed monitoring in Safety Category 3, then the diagnostic rate can reach 99% through sin²+cos²=1 diagnosis, but the system complexity increases and false alarms occur due to fluctuations from gear misalignment, temperature changes, and eccentricity
Solution Approach 1:
The patent segments the speed monitoring function into two independent paths: a primary path using a single encoder with sin²+cos²=1 diagnosis, and a secondary path using two encoders with mutual monitoring. This segmentation allows the system to maintain high diagnostic rate while reducing false alarms through the secondary verification path, resolving the contradiction between reliability and complexity.
Solution Approach 2:
The patent introduces an intermediary speed monitoring unit that compares speeds calculated from two different encoder paths. This intermediary unit acts as a mediator to verify the validity of speed measurements, reducing false alarms caused by fluctuations in a single encoder while maintaining the diagnostic capabilities of the primary path.
2Measurement precision
If the reference range for Lissajous radius is narrowed to detect abnormalities more sensitively, then abnormality detection precision improves, but false alarms increase due to normal fluctuations from temperature and rotation frequency changes
Solution Approach 1:
The patent implements feedback mechanisms where the speed monitoring units continuously monitor each other's output. When the Lissajous radius falls within the reference range but the mutual speed monitoring detects inconsistency, the system generates an abnormal signal. This feedback loop allows the system to maintain a reasonable reference range while detecting abnormalities through cross-verification, reducing false alarms from normal fluctuations.
3Reliability
If multiple speed monitoring units and diagnosis processing units are implemented to achieve high diagnostic rate, then reliability improves, but the device complexity and computational load increase
Solution Approach 1:
The patent designs the speed monitoring units to perform multiple functions: they monitor speed, verify each other's output, and generate abnormal signals when inconsistencies are detected. This multi-functionality allows the system to achieve high diagnostic rate without proportionally increasing the number of dedicated processing units, as each unit serves multiple purposes in the diagnostic framework.
Data Source
AI summary
An encoder abnormality diagnosis device configured to diagnose an abnormality in an encoder that outputs a cosine waveform and a sine waveform according to a rotation angle of an object includes a stop determination processing unit configured to determine whether the object is rotating or stopping, based on a change in a count value of a pulse signal obtained by pulsing of each of the cosine waveform and the sine waveform, a frequency measurement unit configured to measure a frequency of the pulse signal, and a frequency diagnosis unit configured to compare the frequency measured by the frequency measurement unit with a preset upper limit frequency when the stop determination processing unit determines that the object is stopping, and to determine that an abnormality has occurred in the encoder when the measured frequency exceeds the upper limit frequency.