Infrared Reflectivity Sensor for Door Position Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing door proximity sensors in security systems are vulnerable to intentional or inadvertent interference, such as using metal strips, additional magnets, or sunlight, which can compromise their accuracy.
Innovation Solution
An infrared (IR) sensor system with a processor and memory is used, where the IR sensor has an active and idle period, transmitting control data packets and comparing the packet IR reflectivity to stored door IR reflectivity to determine the door position, and includes a method to filter background noise and detect tampering attempts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an IR sensor constantly transmits IR to detect door position, then the detection capability is improved, but the system becomes vulnerable to interference from external light sources such as flashlights and sunlight
Solution Approach 1:
The IR transmitter operates in periodic cycles with active periods for transmitting control data packets and idle periods for receiving reflected packets. This periodic operation allows the system to distinguish between transmitted IR signals and external light interference, as external lights do not follow the same periodic transmission pattern. The receiver only processes signals during expected reflection windows, effectively filtering out continuous external light sources.
Solution Approach 2:
The system uses reflected data packets as feedback to determine door position. By comparing the received reflected IR signals against expected reflection patterns stored in memory, the system can verify whether the signal originates from the intended door surface or from external interference sources. The feedback mechanism includes validating that the reflected signal timing and intensity match predetermined criteria for legitimate door reflections.
2Device complexity
If simple IR transmission is used, then the device complexity is reduced, but the system becomes vulnerable to defeat by external objects such as metal strips, magnets, or light sources
Solution Approach 1:
The system performs preliminary calibration by storing door-specific IR reflectivity data in memory before actual door position monitoring begins. This predetermined reference data includes the unique reflection characteristics of each door surface, allowing the system to later compare received signals against these known patterns. The preliminary action of storing reference data enables the simple sensor to distinguish between legitimate door reflections and tampering attempts without adding complex hardware.
Solution Approach 2:
The system detects changes in IR reflectivity characteristics, analogous to color changes, to identify tampering attempts. Different materials (metal strips, magnets, painted surfaces) have distinct IR reflection properties compared to the original door surface. By monitoring deviations in reflected IR signal patterns from the stored baseline, the system can detect when foreign objects are attached to or placed against the door, maintaining security with simple sensor hardware.
3Measurement precision
If the IR sensor compares reflected IR to transmitted IR, then the door position detection is achieved, but the system remains vulnerable to defeat by shining light at the sensor
Solution Approach 1:
The system transmits IR in periodic bursts rather than continuously, creating distinct transmission windows followed by reception windows. External light sources cannot synchronize with this periodic transmission pattern, so their interference appears as random noise during the reception windows rather than coherent signals. The receiver is configured to only process signals arriving during expected reflection time windows, effectively rejecting unsynchronized external light.
Solution Approach 2:
The system uses the door surface itself as an intermediary to verify signal authenticity. By storing the unique reflectivity characteristics of each door in memory and comparing received signals against these patterns, the system creates an intermediary verification layer. Legitimate door reflections match the stored patterns, while external light interference does not, allowing the system to distinguish between valid door position indicators and tampering attempts.
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
The IR sensor system effectively reduces interference and tampering by accurately determining door positions and detecting foreign objects, enhancing the reliability of security systems.
Implementation Method 1
The IR transmitter has an active period and an idle period. The IR transmitter transmits control data packets which are provided by the processor during the active period. The IR receiver has an active period for detecting IR data and reflected data packets.
Implementation Method 2
The reflected data packets reflect off a surface and have a packet IR reflectivity. The processor compares a door IR reflectivity associated with the a door surface to the packet IR reflectivity to determine a door position of the door.
Data Source
AI summary
The IR sensor is configured to be mounted proximate to a door to be monitored. The IR sensor has an IR transmitter and an IR receiver. The IR transmitter has an active period and an idle period. The IR transmitter transmits control data packets which are provided by the processor during the active period. The IR receiver has an active period for detecting IR data and reflected data packets. Each of the reflected data packets has a packet IR reflectivity. The memory stores a door IR reflectivity associated with a door surface of the door, and the processor compares the packet IR reflectivity to the door IR reflectivity to determine at least a door position of the door.