Preloaded Force Sensor Linearity via Spring Biasing
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Solution Overview
Problem
Force sensors often exhibit non-linear responses at low force measurements, leading to inaccuracies and requiring complex calibration processes, which limits their precision and dynamic range, especially in medical applications where precise dosing and fluid pressure measurement are critical.
Innovation Solution
A preloaded force sensor design that applies a predetermined preload force, ensuring a substantially linear electrical signal response for externally-applied forces above a threshold, using mechanisms like springs or gel transfer members to improve measurement accuracy and simplify calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If force sensors operate without preloading, then they can measure a wider range of forces including zero and negative forces, but they exhibit non-linear responses at low force measurements leading to inaccuracies
Solution Approach 1:
The patent applies preliminary action by preloading the force sensor with a spring mechanism before actual force measurement. The spring maintains a constant preloading force on the diaphragm, ensuring the sensor operates in its linear response region. This preliminary force application eliminates non-linearities at low forces while the sensor still measures the full range of external forces by detecting changes from this preloaded state
2Measurement precision
If force sensors operate without preloading, then they can detect low and zero forces directly, but they require complex calibration processes to achieve acceptable accuracy
Solution Approach 1:
The spring preloading mechanism performs preliminary action by establishing a known initial force state before measurement. This preloading creates a consistent operating point that simplifies calibration, as the sensor now operates in its linear region where the relationship between applied force and output signal is predictable and proportional, reducing calibration complexity
Solution Approach 2:
The patent changes the operating parameter of the force sensor by introducing a preloading force that shifts the operating point from the zero-force region to a higher-force linear region. This parameter change transforms the sensor's response characteristics from non-linear at low forces to linear across the measurement range, improving accuracy while simplifying calibration
3Measurement precision
If preloading force is applied to the force sensor, then measurement linearity and accuracy are improved for positive forces, but the sensor cannot measure forces below the preload threshold
Solution Approach 1:
The preloading spring applies a preliminary force to the diaphragm, establishing a baseline tension that ensures linear operation. The sensor measures external forces by detecting deviations from this preloaded state, allowing it to measure both forces that increase and decrease the preload, effectively maintaining linearity across the full measurement range
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 preloaded force sensor enhances measurement accuracy, repeatability, and precision, particularly at low force values, expanding its dynamic range and enabling precise fluid pressure measurement without compromising sterility, thus improving medical device performance and patient care.
Implementation Method 1
a spring having a predetermined spring coefficient may apply the predetermined preload force to the force-transfer member
Implementation Method 2
a piezo-resistive force sensor that generates an electrical signal in response to a force directed toward a bottom interface of the piezo-resistive force sensor
Data Source
AI summary
Apparatus and associated methods relate to a preloaded force sensor, the preloaded force being greater than a force threshold separating a non-linear response region of sensor operation from a substantially linear response region of sensor operation. In an illustrative embodiment, the total applied force includes the preloaded force and an externally-applied force, the preloaded force being predetermined such that electrical signal response is substantially linear for positive externally-applied forces which when added to the preload force do not exceed the maximum force. In some embodiments, the externally-applied force may be transferred to a force-sensing die via a force-transfer member. In an exemplary embodiment, a spring having a predetermined spring coefficient may apply the predetermined preload force to the force-transfer member. In an exemplary embodiment, externally-applied positive forces may be simply calibrated using gain and offset corrections.