Load Cell Mounting Channels for Zero-Free Weight Detection
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Solution Overview
Problem
Person support apparatuses, such as beds and recliners, often require zeroing sensors before arming the exit detection system or taking weight readings, which is inconvenient and may introduce calibration errors due to manufacturing tolerances and misalignments.
Innovation Solution
The design incorporates load cells supported by channels that constrain movement in specific directions, eliminating the need for zeroing by using spring washers and load cell brackets that accommodate manufacturing variations, allowing the controller to determine occupancy and weight without person-specific calibration data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If load cells are used for exit detection and weight measurement, then the system can detect occupancy and measure weight, but the sensors require zeroing before use which introduces calibration errors and reduces operational efficiency
Solution Approach 1:
The patent applies preliminary action by pre-calibrating the load cells during manufacturing with reference weight values stored in memory. The system performs automatic tare function upon startup without requiring manual zeroing by the user. This preliminary calibration eliminates the need for repeated zeroing operations and ensures consistent measurement accuracy throughout the product lifecycle.
Solution Approach 2:
The system implements self-service through automatic tare functionality that performs calibration autonomously upon startup. The controller automatically references stored weight values to establish baseline measurements, eliminating the need for user intervention in the zeroing process. This self-calibrating mechanism maintains measurement precision while maximizing operational convenience.
2Stability of the object's composition
If load cells are rigidly mounted to the frame and support surface, then the structure is stable, but manufacturing tolerances and misalignments cause calibration errors
Solution Approach 1:
The patent segments the mounting structure into separate components: load cells are mounted independently to either the frame or support surface through dedicated mounting brackets. This segmentation allows each component to be manufactured and calibrated separately with higher precision, then assembled together. The modular approach isolates manufacturing tolerances to individual components rather than requiring perfect alignment across the entire assembly.
Solution Approach 2:
The system compensates for manufacturing variations by changing the reference parameter from absolute position to relative weight measurement. During manufacturing, reference weight values are stored in memory that account for specific load cell characteristics and mounting conditions. The controller uses these stored parameters to calculate accurate weight readings regardless of minor manufacturing tolerances, effectively decoupling structural stability from calibration accuracy.
3Reliability
If manual zeroing is required before each use, then calibration can be adjusted, but this process is time-consuming and may introduce user error
Solution Approach 1:
The patent performs calibration in advance during manufacturing by measuring known reference weights and storing the corresponding values in memory. This preliminary calibration creates a reliable baseline that eliminates the need for repeated manual zeroing. The system maintains calibration reliability through this pre-established reference data while reducing setup time to minimal automated operations.
Solution Approach 2:
The system implements automatic tare functionality that performs calibration autonomously upon startup without requiring user intervention. The controller automatically references stored weight values and adjusts measurements accordingly, eliminating manual zeroing operations. This self-calibrating mechanism maintains reliable calibration while reducing setup time to essentially zero user action required.
4Measurement precision
If individual calibration data is stored for each person support apparatus, then measurement accuracy is maintained, but manufacturing complexity and data storage requirements increase
Solution Approach 1:
The patent implements a universal calibration approach where a single set of reference weight values is stored in memory and used by all load cells across multiple person support apparatus units. Instead of requiring individual calibration data for each device, the same reference parameters serve multiple functions: calibrating different load cells, accommodating manufacturing variations, and maintaining accuracy across production batches. This universal reference system reduces data storage requirements and simplifies the calibration infrastructure while maintaining measurement precision through the automatic tare function that applies these universal references to individual measurements.
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
This solution enables the exit detection system to function without requiring sensor zeroing and provides accurate weight readings without individual calibration, enhancing operational efficiency and reducing manufacturing complexities.
Implementation Method 1
The load cells each have a nose and a body and are coupled to the frame and the support surface such that a weight applied to the support surface is detected by the load cells
Data Source
AI summary
A person support apparatus, such as a bed, cot, recliner, chair, stretcher, or the like, includes a frame, a support surface, a plurality of load cells, and first and second channels dimensioned to receive noses of at least one of the load cells. The first channel constrains a first one of the load cells in a first direction but not a second direction that is perpendicular to the first direction. The second channel constrains the second load cell in the second direction but not the first direction. The person support apparatus may also include a plurality of load cell brackets that are each adapted to support an end of one of the load cells. When included, the load cell brackets are constructed such that no forces from the support surface, other than weight forces, are applied to the load cells after the support surface is coupled to the frame.