Photoelectric Sensor Pulse Patterns Against Light Interference
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Solution Overview
Problem
Photoelectric sensors face malfunctions due to both disturbance light from inverter or LED lighting and mutual interference between multiple sensors, with existing solutions only addressing one type of interference.
Innovation Solution
A photoelectric sensor design featuring a light projecting unit that emits pulse light following two distinct patterns, one with increased and one with reduced light projecting periods, along with a light receiving controller using hysteresis in the comparator to distinguish signal light from disturbance light and prevent mutual interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a light projector and light receiver are installed to face each other for basic photoelectric detection, then detection function is achieved, but the system becomes vulnerable to disturbance light from inverter or LED lighting that operates in fixed cycles
Solution Approach 1:
The light projector emits pulse light at irregular pulse intervals instead of fixed periodic intervals. This irregular periodic action prevents synchronization with disturbance light from inverter or LED lighting, allowing the receiver to distinguish signal light from disturbance light based on timing patterns
Solution Approach 2:
The light projecting unit switches between multiple projected light patterns (first pattern with increasing periods, second pattern with decreasing periods) dynamically. This dynamic adjustment of pulse intervals prevents fixed-cycle disturbance light from consistently interfering with detection
2Object-affected harmful factors
If existing solutions use irregular pulse intervals to prevent disturbance light interference, then resistance to disturbance light is improved, but no protection exists against mutual interference between multiple photoelectric sensors
Solution Approach 1:
The light projecting unit is divided into multiple independent light projecting units, each capable of emitting light with different projected light patterns. This segmentation allows each unit to have unique timing characteristics, preventing mutual interference between sensors while maintaining resistance to disturbance light
Solution Approach 2:
Multiple photoelectric sensors are configured with asymmetric projected light patterns where each sensor has unique increasing and decreasing period sequences. This asymmetry ensures that even if multiple sensors operate in the same environment, their interference patterns differ, allowing the receiving unit to distinguish between signal and interference
3Area of stationary object
If multiple photoelectric sensors operate in the same environment, then coverage area is increased, but mutual interference between sensors causes malfunctions
Solution Approach 1:
The system segments the detection environment by assigning different projected light patterns to multiple light projecting units. Each unit operates independently with unique timing characteristics, allowing expanded coverage area while preventing mutual interference through pattern differentiation
Solution Approach 2:
Each light projecting unit serves multiple functions: it provides detection coverage for its specific area while simultaneously contributing to the overall anti-interference network. The receiving unit can process signals from multiple sources using the same irregular interval detection mechanism, achieving both expanded coverage and interference prevention
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
Effectively prevents malfunctions caused by both disturbance light and mutual interference, ensuring accurate light detection and operation stability by differentiating signal light from disturbance light and mitigating interference between multiple sensors.
Implementation Method 1
a light receiving element configured to receive the signal light from the light projecting unit
Data Source
AI summary
A photoelectric sensor capable of preventing a malfunction caused by mutual interference is provided. The photoelectric sensor includes: a light projecting unit that repetitively emits a set of pulse light, which follows a projected light pattern in which a light projecting period is made different by a fixed time, as signal light; a light receiving element that receives the signal light; and a light receiving controller that distinguishes a light incident state and a light blocked state based on a received light signal from the light receiving element. The light projecting unit has a first pattern having the light projecting period increased by a fixed time and a second pattern having the light projecting period reduced by a fixed time as the projected light pattern, and in the first and second patterns, a pulse indicating a shortest period is included in the light projecting period other than the shortest period.