Load Cell Error Detection Circuit for Hospital Beds
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Solution Overview
Problem
Conventional load cell systems in person support apparatuses, such as hospital beds and stretchers, face challenges in accurately detecting error states, including electrical disconnection or malfunctioning of load cells, and require recalibration of replaced load cells.
Innovation Solution
The improved load cell system includes a detection circuit that monitors electrical current changes to identify malfunctioning or disconnected load cells and stores load cell-specific calibration data, allowing for automatic error detection and seamless integration of replacement load cells without recalibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional load cell systems are used to detect weight and exit status, then the basic functionality is provided, but the system cannot accurately detect error states such as electrical disconnection or malfunctioning of load cells
Solution Approach 1:
The detection circuit performs preliminary checks on load cell electrical connections and functionality before the main weight measurement function is activated. This allows error states to be detected proactively, preventing unreliable data from being processed while maintaining system simplicity through staged initialization.
Solution Approach 2:
A dedicated detection circuit is introduced as an intermediary component between the load cells and the main controller. This intermediary handles the complex task of error state detection through current monitoring and resistance measurement, isolating the complexity from the main control system while improving overall reliability.
2Ease of repair
If load cells are replaced in conventional systems, then the defective component is substituted, but recalibration is required which consumes time and resources
Solution Approach 1:
Calibration data is pre-stored in the controller's memory for multiple load cell configurations before any replacement occurs. When a load cell is replaced, the system automatically retrieves the appropriate pre-stored calibration data, eliminating the need for time-consuming recalibration procedures and simplifying the repair process.
Solution Approach 2:
The system creates and stores copies of calibration data for different load cell configurations in advance. These copied calibration parameters are readily available when load cells are replaced, allowing immediate restoration of accurate weight measurement functionality without requiring recalibration of the replacement components.
3Measurement precision
If the system monitors only weight measurements, then the primary function is performed, but error states such as electrical disconnection or malfunctioning remain undetected
Solution Approach 1:
The detection circuit merges multiple monitoring functions into a single integrated system that simultaneously checks electrical connections, measures resistance values, and validates load cell functionality. This unified approach detects error states without requiring separate complex monitoring subsystems, maintaining measurement precision while controlling overall system complexity.
Solution Approach 2:
The detection circuit is designed with multi-functionality, serving both as an error detection mechanism and as part of the normal weight measurement system. By using the same hardware infrastructure for both purposes, the system achieves comprehensive monitoring capability without proportionally increasing device complexity.
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 effectively detects error states in load cells and facilitates the integration of new load cells without recalibration, enhancing the reliability and efficiency of weight measurement and exit detection functions.
Implementation Method 1
a plurality of load cells supported by the frame... such that a weight of the occupant is detectable by the load cells when the occupant is positioned on the support surface
Implementation Method 2
The detection circuit detects changes in a total amount of electrical current supplied to all of the first sets of leads from the activation power source
Data Source
AI summary
A person support apparatus, such as a bed, stretcher, recliner, cot, or the like, includes a frame, a plurality of load cells, a support surface supported by the load cells, a detection circuit, and a controller. The controller determines if any of the load cells are in an error state based upon information from the detection circuit. If the load cells include memory having calibration data stored therein, the controller communicates with the memory and uses the calibration data to determine an amount of weight supported on the surface. The detection circuit may include one or more Wheatstone bridges wherein the controller monitors voltages between midpoints of the Wheatstone bridges. The load cells may include an activation lead that is monitored by the detection circuit and a sensor lead that is used by the controller to determine an amount of weight supported on the patient support apparatus.