Motion Detector Masking Detection Using Time-of-Flight
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Solution Overview
Problem
Existing motion detectors face challenges in accurately detecting masking, particularly with materials that absorb infrared light, leading to false detections and difficulties in identifying masking using black objects, especially when they are spaced away from the detector.
Innovation Solution
Incorporating an optical time-of-flight sensor as an ancillary sensing system, which uses ultraviolet or infrared light to determine the distance of objects within the monitored environment, reducing false masking detections by focusing on time-of-flight rather than intensity-based methods, and employing a dual-emitter and detector configuration to assess masking and window obscuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If intensity-based masking detection is used, then masking by absorbing materials can be detected, but false detections occur with highly reflective materials
Solution Approach 1:
The patent replaces intensity-based optical detection with time-of-flight measurement. Instead of measuring the intensity of reflected infrared light, the system measures the time it takes for light to travel to and from objects. This substitution of measurement principle eliminates the fundamental problem where reflective materials confuse intensity-based sensors, as time-of-flight measurement is independent of material reflectivity properties.
Solution Approach 2:
The patent changes the measurement parameter from optical intensity to time-of-flight. By measuring the temporal characteristic (time) rather than the amplitude characteristic (intensity) of reflected light, the system achieves masking detection capability that is independent of the optical properties (absorptive or reflective) of the masking material.
2Measurement precision
If sensitivity is increased to detect black masking materials, then masking detection improves, but false detections increase with reflective objects
Solution Approach 1:
The patent replaces intensity-based detection with time-of-flight measurement to avoid the sensitivity-reliability trade-off. Time-of-flight sensors naturally provide distance information without being influenced by the optical absorption or reflection properties of materials, thereby achieving high sensitivity for detecting black masking materials without increasing false detections from reflective objects.
3Reliability
If time-of-flight sensing is used, then false masking detections are reduced, but device complexity increases
Solution Approach 1:
The patent achieves masking detection functionality using the same time-of-flight sensor that is already employed for primary motion detection. The ancillary sensing system reuses the emitter and detector components, allowing the system to perform both motion detection and masking detection with a single sensor subsystem, thereby minimizing the increase in device complexity.
Solution Approach 2:
The time-of-flight sensor serves dual purposes: detecting motion in the monitored environment and detecting masking of the sensing system. By making the sensor universal for both functions, the patent avoids adding separate dedicated masking detection hardware, thus limiting the complexity increase to primarily software/algorithms processing.
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 solution effectively reduces false masking detections and improves the ability to identify masking, including black objects at a distance, by utilizing time-of-flight measurements to determine object proximity and window obscuration, enhancing the reliability of motion detection systems.
Implementation Method 1
an ancillary sensing system configured to detect masking of the primary sensing system, the ancillary sensing system comprising an optical time-of-flight sensor
Implementation Method 2
receiving a reflection of the optical signal at the motion detector, the reflected optical signal having been reflected by an object within the monitored environment
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A motion detector (1) for a security system comprises a primary sensing system including a PIR sensor (5) configured to detect movement of a person within a monitored environment (2), and an ancillary sensing system including a first emitter (7), a second emitter (8) and a receiver (9) configured to detect masking of the primary sensing system. Masking by an object (10) in the monitored environment (2) is determined using the first emitter (7) and the receiver (9) based on a time-of-flight of an optical signal emitted into the monitored environment (2) and reflected by the object (10). Masking by obscuring of a window (4) of the motion detector (1) is determined using the second emitter (8) and the receiver (9) based on the intensity of light transmission from the second emitter (8) through the window (4) to the receiver (9).