Patient Exit Detection Using Obstruction-Aware Force Sensing

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Solution Overview

Problem

Existing hospital beds and stretchers face reliability issues with exit detection systems due to obstructions exerting forces on force sensors, leading to incorrect exit alerts or failures to issue alerts when a patient is about to exit.

Innovation Solution

An exit detection system that includes obstruction sensors to detect obstructions, allowing the system to disarm or compensate for sensor errors, adjust sensitivity levels, and recalibrate exit detection zones to accurately determine patient movement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the exit detection system uses force sensors to detect patient movement, then it can issue exit alerts when the patient moves toward exiting, but obstructions exerting forces on the sensors cause false alerts or failure to detect actual exits

Engineering Contradiction:
Improveexit detection reliabilityVSAvoidobstruction forces on sensors
Core Design Contradiction:
ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an obstruction sensor as an intermediary device that detects obstructions before they interfere with force sensor readings. This intermediary sensor allows the system to identify when an obstruction is present and take corrective actions (such as disarming the exit detection system or compensating for the obstruction's effect), thereby resolving the contradiction between maintaining reliable exit detection and dealing with obstruction forces.

Inventive Principle:
Principle #24Intermediary (Mediator)

Solution Approach 2:

The system implements feedback by continuously monitoring force sensor outputs and comparing them against expected ranges. When obstruction forces are detected (through abnormal force patterns or dedicated obstruction sensors), the system provides feedback to the controller, which then adjusts the exit detection state (arming/disarming) or applies compensation algorithms to maintain reliable patient exit detection despite the presence of obstructions.

Inventive Principle:
Principle #23Feedback

2Reliability

If the system disarms the exit detection upon obstruction detection, then false exit alerts are avoided, but the system cannot detect actual patient exits during the disarmed state

Engineering Contradiction:
Improveexit alert accuracyVSAvoidpatient exit detection capability
Core Design Contradiction:
ReliabilityVSLoss of information

Solution Approach 1:

The system dynamically adjusts the operational state of the exit detection system based on real-time obstruction detection. Rather than a static approach, the controller can switch between armed, disarmed, and compensated states depending on the nature and persistence of the obstruction. This dynamic behavior allows the system to maintain patient exit detection capability while avoiding false alerts caused by temporary obstructions.

Inventive Principle:
Principle #15Dynamics

Solution Approach 2:

The system takes preliminary action by detecting obstructions before they cause false exit alerts. Through continuous monitoring and predictive algorithms, the system can identify obstruction patterns that precede false alerts and preemptively adjust the detection sensitivity or state, thereby maintaining both alert accuracy and patient exit detection capability without complete disarming.

Inventive Principle:
Principle #10Preliminary action

Data Source

PatentEP4221587B1Exit detection system with obstruction reaction
Publication Date: 2026.01.07 STRYKER CORP
  • EP4221587B1 patent drawingFigure 1
  • EP4221587B1 patent drawingFigure 2~3
  • EP4221587B1 patent drawingFigure 4

AI summary

A person support apparatus, such as a bed, stretcher, cot, recliner, or the like, includes an exit detection system having a plurality of force sensors that support the weight of an occupant positioned on a support surface and obstruction detection system having one or more obstruction sensors. The force sensors are part of an exit detection system that issues an alarm when the occupant exits, or is about to exit, the person support apparatus. The bed exit system can react to detection of an obstacle. The distribution of weight applied to the force sensors is used to determine if the occupant is about to exit the person support apparatus. Compensation is made to the exit detection system for changes in the weight distribution that are not caused by movement of the occupant. Such changes may be due to not only movement of the person support apparatus or components thereof, but obstacles encountered by the person support apparatus or components thereof.