Door Ligature Detection Using Angle-Based Load Thresholds
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Solution Overview
Problem
Existing ligature detection systems for doors are limited in their sensing ability, unable to detect ligatures at points other than where a switch is directly located, and are prone to false negatives when the door is in motion, as recalibration during movement can miss ligature applications.
Innovation Solution
A system using a controller that integrates an angle sensor and load sensor to determine a threshold load value based on door angle, direction, and speed, enabling accurate ligature detection even when the door is in motion by using baseline load data and dynamically adjusting thresholds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a binary switch is used for ligature detection at a fixed location, then the system is simple and easy to implement, but it can only detect ligatures at specific locations and fails to detect ligatures at other points around the door
Solution Approach 1:
The door perimeter is divided into multiple discrete sensing zones, each monitored by its own load sensor. This segmentation allows the system to detect ligatures at multiple locations around the door rather than relying on a single fixed switch, thereby improving detection coverage without significantly increasing system complexity
Solution Approach 2:
The load sensors serve multiple functions: they monitor for ligatures, detect door movement, and provide baseline load data for calibration. This multi-functionality allows the system to achieve comprehensive detection capability while maintaining relatively simple hardware components
2Ease of operation
If the door is frequently open for access, then ease of operation is improved, but ligature detection reliability deteriorates because the door is in motion and baseline load cannot be accurately determined
Solution Approach 1:
The system performs preliminary calibration of baseline load data when the door is stationary and closed, establishing accurate reference values before normal operation begins. This preliminary action ensures that reliable baseline data is available even though the door will be frequently opened during operation
Solution Approach 2:
The system dynamically adjusts its detection threshold based on real-time door position and motion state. When the door is moving, the system uses adaptive thresholds that account for the dynamic load changes, allowing reliable ligature detection regardless of whether the door is open or closed, thus maintaining both ease of operation and detection reliability
3Device complexity
If the detection threshold is set to a fixed value, then the system is simple to implement, but it cannot accurately detect ligatures when the door is in motion due to varying load readings
Solution Approach 1:
The detection threshold is made dynamic rather than fixed, automatically adjusting based on real-time door position, motion state, and calibrated baseline load data. This dynamic thresholding allows the system to maintain high measurement precision for ligature detection across varying operational conditions without requiring complex manual threshold configuration
Solution Approach 2:
The system continuously monitors door position and load readings, using this feedback to update the detection threshold in real-time. This feedback mechanism ensures that the threshold remains accurate and appropriate for current operational conditions, improving measurement precision while keeping the system relatively simple to manage
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 system provides reliable ligature detection across various door angles and positions, reducing false negatives and false positives by dynamically adjusting thresholds based on door conditions, ensuring timely alerts to healthcare providers.
Implementation Method 1
a load sensor configured to determine a load applied by the door to the mounting means
Implementation Method 2
an angle sensor configured to detect an angle of the door with respect to the door frame
Data Source
AI summary
There is provided a controller, a system, computer software and a method for detecting a ligature on a door mounted within a door frame on mounting means. A load applied by the door to the mounting means is detected by a load sensor. An angle of the door relative to the door frame is detected by an angle sensor. Baseline load data is obtained, the baseline load data being indicative of an expected load applied by the door to the mounting means as a function of the angle of the door. The method comprises determining a threshold load value indicative of a ligature on the door for the measured angle in dependence on the baseline load data and the detected angle of the door; determining whether the detected load exceeds the threshold load value for the detected angle; and outputting an indication of a detected ligature event if the detected load exceeds the threshold load value.