Optoelectronic Sensor Contamination Detection via Accumulated Threshold Transitions
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Solution Overview
Problem
Existing optoelectronic sensors with pre-failure alarm functions fail to reliably detect impending failures, especially when detecting high-contrast objects, leading to unreliable pre-failure alarm outputs due to variations in reception signal levels caused by object contrasts.
Innovation Solution
The sensor evaluates an excessively long duration or frequent entering into a contamination state as a contamination criterion, considering the dynamics of object contrasts for resetting the pre-failure alarm, by summing up discontinuous contamination periods and counting frequent transitions between switching and contamination thresholds, rather than assuming a faultless state with a brief sufficient reception signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pre-failure alarm output responds to brief contamination states with sufficient reception signal, then the alarm can be reset quickly, but the alarm becomes unreliable for high-contrast objects
Solution Approach 1:
The evaluation unit accumulates contamination periods and counts threshold transitions in advance before triggering the pre-failure alarm. This preliminary accumulation allows the system to distinguish between temporary signal variations and actual contamination, improving reliability without excessive delay.
Solution Approach 2:
The evaluation unit continuously monitors reception signal levels and accumulates contamination evidence over time, maintaining continuous assessment rather than intermittent checking. This ensures reliable detection of high-contrast objects while providing timely alarm responses.
2Measurement precision
If the contamination threshold is set to detect all contamination cases, then detection sensitivity increases, but false alarms increase due to normal signal variations
Solution Approach 1:
The evaluation unit uses feedback from continuous monitoring of threshold transitions and contamination period accumulation to dynamically assess contamination states. This feedback mechanism distinguishes between normal signal variations and actual contamination, improving both detection sensitivity and alarm accuracy.
Solution Approach 2:
The system changes the evaluation parameters by counting the number of threshold transitions and accumulating contamination periods rather than using a single fixed threshold. This parameter transformation allows sensitive detection while filtering out false alarms from normal signal variations.
3Reliability
If the sensor requires long contamination duration for alarm output, then false alarms decrease, but detection of actual contamination is delayed
Solution Approach 1:
The evaluation unit performs preliminary accumulation of contamination periods and threshold transition counts before triggering the alarm. This advance preparation allows the system to maintain high reliability thresholds while responding timely to actual contamination events.
Solution Approach 2:
The system dynamically evaluates contamination based on accumulated evidence from multiple threshold transitions and contamination periods rather than using a static time threshold. This dynamic approach balances reliability with timely detection of actual contamination.
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 approach ensures a reliable and timely pre-failure alarm output for objects with high-contrast variations, such as printed paper or black-white boxes, even when a smaller fraction of target objects have poor remission, providing an early warning of sensor contamination.
Implementation Method 1
Light sensors of the scanning type thus transmit their transmission light into the open space, and it is reflected and registered if it impinges on an object
Implementation Method 2
a light transmitter and a light receiver face each other and the receiver registers the lack of the light signal upon interruption by an object
Data Source
AI summary
An optoelectronic sensor (10) is provided with a light transmitter (12) for transmitting a light signal (16) into a monitoring area (18), a light receiver (26) for receiving and converting the light signal (22) remitted or reflected from an object (20) in the monitoring area (18) into a reception signal, a switching output (30) for the output of a switching signal when the reception signal meets a switching criterion (E), a pre-failure alarm output (32) for the output of a pre-failure alarm signal, and an evaluation unit (28) configured to detect a contamination state that is present when the reception signal meets a contamination criterion (C) but not the switching criterion (E) and to output a pre-failure alarm signal when a contamination period during which the contamination state extends for more than a tolerated period (TPFA,ON) and/or when a contamination state occurrence number that is incremented upon each entry of the contamination state is larger than a tolerated number. The evaluation unit (28) is further configured to add up the contamination period also across several discontinuous periods of the contamination state or to count the contamination state occurrence number also across periods during which neither the switching criterion (E) nor the contamination criterion (C) are met, respectively.