Photoelectric Sensor Threshold Setting Using Light Variation Rate

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Solution Overview

Problem

Existing photoelectric sensors face challenges in accurately detecting objects due to gentle changes in light reception amounts near the threshold, leading to variations in detection timing and reduced accuracy in machine control and image sensor triggers.

Innovation Solution

A sensor system that includes a sampling unit, calculator, and setting unit to set a threshold based on the variation in light reception amount per unit time, excluding extreme variations potentially influenced by noise, and updating the threshold during detection to enhance accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the threshold is set as an intermediate value between maximum and minimum light reception amounts, then the sensor has extension in the decision range for object detection, but the detection timing varies and control accuracy deteriorates

Engineering Contradiction:

Improveextension in decision rangeVSAvoiddetection timing accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent changes the threshold setting parameter from a static intermediate value to a dynamic value based on the rate of change of light reception amount. By using the derivative dR/dt (rate of change of light reception amount with respect to time) to determine the threshold, the system adapts the threshold to the actual detection conditions, thereby improving detection timing accuracy while maintaining appropriate decision range extension.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If the threshold is set considering variation in light reception amount per unit time, then the detection accuracy is improved, but the device complexity increases

Engineering Contradiction:

Improveobject detection accuracyVSAvoidthreshold setting complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces complex mechanical or manual threshold adjustment mechanisms with an electronic calculation system. The controller automatically computes the rate of change dR/dt and determines the threshold based on this calculation, eliminating the need for manual intervention or complex mechanical adjustment devices while achieving high detection accuracy.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The system performs self-adjustment of the threshold by automatically calculating the rate of change of light reception amount and setting the threshold accordingly. The controller continuously monitors the light reception amount R, computes its derivative dR/dt, and autonomously determines the appropriate threshold without requiring external intervention, thereby simplifying the overall system architecture.

Inventive Principle:

Principle #25Self-service

3Ease of manufacture

If sampling is performed with constant period, then the calculation of variation per unit time is simplified, but noise influence may increase

Engineering Contradiction:

Improvecalculation simplicityVSAvoidnoise influence

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent implements a feedback mechanism where the calculated rate of change dR/dt is continuously monitored and used to adjust the threshold setting. By feeding back the variation information to the threshold determination process, the system can distinguish between genuine signal changes and noise, as noise typically exhibits different statistical characteristics in the derivative domain compared to actual object detection signals.

Inventive Principle:

Principle #23Feedback

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 improves the accuracy of object detection by narrowing the range of light reception amounts equal to the threshold, minimizing detection signal jitter and maintaining high precision in object detection.

Implementation Method 1

a sensor for detecting an object by reception of light from a light projecting unit (103) in a light receiving unit (104)

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS10429510B2Sensor and method for setting threshold of sensor

Publication Date: 2019.10.01 OMRON CORP

AI summary

A photoelectric sensor is configured to detect an object by reception of light from a light projecting unit in a light receiving unit. The photoelectric sensor differentiates a sampled light reception amount with respect to time to calculate a variation in the light reception amount per unit time, and sets as a threshold a light reception amount corresponding to an extreme value of the variation in the light reception amount. In this manner, the threshold is set with the variation in the light reception amount per unit time taken into account, thereby enhancing the accuracy in detection of the object by comparison between the light reception amount and the threshold, to allow minimization of jitter of a detection signal from the photoelectric sensor to a programmable logic controller.