Probe Tip Force Calibration Using Load Cell and Accelerometer
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Solution Overview
Problem
Existing electrical impedance spectroscopy (EIS) techniques for predicting preterm birth face challenges in ensuring consistent pressure application on cervical tissue, leading to measurement errors and reduced accuracy.
Innovation Solution
An apparatus equipped with a load cell and tri-axial MEMS accelerometer measures and compensates for the force applied to the probe tip, using calibrated measurements to ensure consistent pressure, thereby improving measurement accuracy and repeatability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If manual pressure application is used during EIS measurement, then the measurement process is simple and quick, but the pressure consistency is poor leading to measurement errors
Solution Approach 1:
The patent replaces manual mechanical pressure application with an automated feedback control system. A load cell measures the actual contact force between the probe and tissue, this measurement is fed to processing means that compares it with a target force, and a display provides feedback to guide the operator. This substitutes the imprecise mechanical sense of manual pressure with an automated measurement and feedback system, resolving the contradiction between measurement precision and device complexity.
Solution Approach 2:
The patent implements a feedback mechanism where the load cell continuously measures the contact force during measurement, the processing means calculates the difference from the target force, and the display presents this information to the operator in real-time. This closed-loop feedback enables the operator to adjust pressure dynamically to achieve the target force, significantly improving pressure consistency and measurement accuracy without requiring complex automated actuation systems.
2Measurement precision
If constant force spring is used to maintain consistent pressure, then pressure consistency improves, but the device complexity and cost increase
Solution Approach 1:
The patent enables the operator to self-regulate the contact pressure using real-time feedback from the display showing the difference between actual and target force. This self-service approach allows the human operator to perform the pressure control function that would otherwise require complex mechanical constant force mechanisms, achieving pressure consistency while keeping the device relatively simple and cost-effective.
Solution Approach 2:
The real-time feedback system provides continuous information about the contact force status, enabling the operator to make immediate adjustments to maintain the target pressure. This feedback mechanism achieves pressure consistency comparable to constant force springs but avoids the complexity and cost of mechanical force maintenance systems by using electronic measurement and human-in-the-loop control.
3Measurement precision
If probe mass is not compensated for, then the measurement system is simpler, but the force measurement accuracy deteriorates due to gravity effects
Solution Approach 1:
The patent performs preliminary compensation for the probe mass effect by having the operator hold the probe against the tissue before measurement and displaying the required adjustment to reach target force. The processing means calculates and displays the difference between the force generated by probe mass and the target contact force, enabling the operator to apply the correct additional pressure before the actual measurement begins. This preliminary action eliminates the need for complex real-time compensation algorithms during measurement.
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 apparatus provides real-time feedback and calibrated force measurements, maintaining pressure within desired limits, enhancing the reliability of EIS measurements for predicting preterm birth.
Implementation Method 1
said load cell comprises four strain gauges in a bridge configuration
Implementation Method 2
said accelerometer is an analogue tri-axial MEMS accelerometer
Implementation Method 3
said load cell comprises four strain gauges in a bridge configuration
Data Source
Figure 1
AI summary
An apparatus capable of determining the force applied to the tip of an electrical impedance spectroscopy probe comprises: • an elongate probe comprising a probe tip attached to a handle, the probe tip having a substantially planar distal end for contacting human or animal tissue; • a load cell located in said handle and capable of measuring a force Fload cell applied axially along a longitudinal axis when said probe tip is in contact with said human or animal tissue; • an accelerometer located in the handle for measuring a gravity vector Aaxial; • processing means for compensating for the mass of the probe tip using said measured force and gravity vector to produce a calibrated measurement of force F applied to said probe tip.