Two-Stage Force Measuring System for Presses
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Solution Overview
Problem
Load cells used in presses face a trade-off between high force measurement accuracy and low force resolution, with higher force ratings resulting in lower resolution and increased electrical noise, leading to precision loss in lower force ranges.
Innovation Solution
A 2-stage force measuring system employing two load cells, one with a high force range and another with a low force range, automatically transitioning between them to improve sensitivity and reduce noise, ensuring accurate measurement across a wide force range without user intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a high force range load cell is used to maintain high force capacity, then maximum force measurement capability is improved, but low force resolution and accuracy deteriorate
Solution Approach 1:
The force measurement system is segmented into two distinct load cells: a high force range load cell (e.g., 10,000 lb capacity) and a low force range load cell (e.g., 1,000 lb capacity). Each load cell is optimized for its specific force range, allowing the system to achieve high maximum force capacity while maintaining excellent low force resolution. The system automatically selects or transitions between load cells based on the applied force magnitude.
2Force
If a high force range load cell is used, then maximum force capacity is improved, but electrical noise increases leading to precision loss
Solution Approach 1:
By segmenting the measurement system into two load cells with different force ranges, the system isolates the high force capacity function (handled by the high range load cell) from the low force precision function (handled by the low range load cell). The low range load cell operates in a lower noise environment and provides cleaner signals for small force measurements, while the high range load cell handles only the heavy lifting without compromising overall system precision.
3Device complexity
If a single load cell covers the full force range, then device complexity is reduced, but measurement precision across the full range deteriorates
Solution Approach 1:
The system accepts the increased complexity of using two load cells with separate A/D converters as a necessary trade-off to achieve high measurement precision across the full force range. The automated transition logic between load cells manages this complexity transparently, providing accurate measurements from zero force up to the maximum capacity without requiring manual intervention or complex calibration procedures.
4Force
If the load cell force rating is increased, then maximum force capacity is improved, but force resolution becomes coarser
Solution Approach 1:
The system segments the force measurement task into two precision-optimized zones: the low force range load cell provides fine resolution for small forces (e.g., 0-1,000 lb), while the high force range load cell provides adequate resolution for large forces (e.g., 1,000-10,000 lb). This segmentation allows each load cell to be manufactured and calibrated for its specific range, achieving the highest possible precision for each segment rather than compromising with a single mid-range cell.
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 achieves significantly improved low force accuracy and repeatability while maintaining high force capacity, reducing noise by a factor of 10 and providing seamless transitions between force ranges, enhancing precision without sacrificing maximum force capacity.
Implementation Method 1
Feedback from a force transducer (e.g. a strain gage based load cell)
Data Source
AI summary
A 2-stage force measuring system particularly useful for a high capacity press. A first stage load cell provides a high force range for measurements over 1,000 lbs. A second stage load cell is for measurements below 1,000 lbs. The assembly improves sensitivity and reduces noise by a factor of 16 (16,000 pounds/1,000 pounds) when pressing less than 1,000 pounds. If a press cycle exceeds 1,000 pounds, the force monitor will automatically and seamlessly transition from the low range load cell to the high range load cell. If the force required is less than 1,000 pounds, only the low range load cell will detect the load, providing a dramatic improvement in force resolution and accuracy.