Capacitive Shift-Force Sensor With Differential Gaps
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Solution Overview
Problem
Existing capacitive force sensors face challenges in accurately measuring forces, particularly in tribology applications, due to limitations in sensitivity and range of linearity, as well as interference from extraneous stray capacitances.
Innovation Solution
A capacitive shift-force sensor is designed with two parallel rigid plates interconnected by deformable members, allowing plane-parallel displacement and resulting in unequal capacitor gaps when a force is applied, which are measured as changes in electric current and recalculated into force values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single capacitor structure is used, then the device complexity is low, but the measurement precision and sensitivity are insufficient
Solution Approach 1:
The sensor is divided into two separate capacitors (first capacitor and second capacitor) with independent plate configurations. Each capacitor measures force in a different direction, allowing the system to achieve comprehensive force measurement capability while maintaining relatively simple individual capacitor structures. The segmentation enables differential measurement that improves precision without requiring a single complex sensor design.
2Measurement precision
If the capacitor plates are fixed, then the manufacturing precision is high, but the sensitivity to applied force is reduced
Solution Approach 1:
The plate configurations are designed to be movable rather than fixed. The first plate can move relative to the first fixed plate, and the second plate can move relative to the second fixed plate in response to applied forces. This dynamic capability allows the capacitors to sense force-induced displacements and generate measurable capacitance changes, significantly improving force sensitivity while maintaining manufacturing precision through controlled movable plate designs.
3Measurement precision
If extraneous stray capacitances are present, then the device complexity is low, but the measurement precision deteriorates
Solution Approach 1:
The harmful extraneous stray capacitances are extracted and isolated from the measurement system by introducing shielded plate configurations. The shielded plates are electrically isolated and positioned to block external electromagnetic interference from reaching the sensing plates. This extraction of harmful capacitance effects improves measurement precision without requiring complex active compensation circuits.
Solution Approach 2:
Shielded plates are introduced as intermediary elements between the external environment and the sensing capacitors. These shielded plates act as mediators that block extraneous electromagnetic fields and stray capacitances from directly interfering with the measurement capacitors, thereby improving measurement precision while adding only moderate structural complexity.
4Adaptability or versatility
If the capacitor gaps are equal in stationary condition, then the manufacturing precision is high, but the range of linearity is limited
Solution Approach 1:
The sensor employs asymmetric capacitor gap designs where the first capacitor gap and second capacitor gap can be differently sized and configured. This asymmetry allows the sensor to accommodate a wider range of force magnitudes while maintaining linear response characteristics. The asymmetric design provides greater adaptability to different measurement requirements without sacrificing manufacturing precision, as each capacitor can be optimized for its specific gap dimension.
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 design enhances sensitivity and range of linearity by measuring force through differential changes in capacitive characteristics, effectively addressing the limitations of existing sensors and improving accuracy in force measurement applications.
Implementation Method 1
Each capacitor (24a, 24b) is formed by a pair of capacitor plates (24a1, 22a2 and 24b1, 22b2, respectively) with capacitor gaps (d1, d2) formed between the respective plates
Implementation Method 2
interconnected by a pair of deformable members (22c, 22d) that allow plane-parallel displacement of the rigid plates (22a, 22b) with respect to each other
Data Source
AI summary
The capacitive shift-force sensor is made in the form of a deformable casing defined by two parallel rigid plates spaced from each other and interconnected by two deformable members. The sensor is provided with two capacitors, wherein one capacitor plate of each capacitor is rigidly connected to one rigid plate and the other capacitor plate is rigidly connected to the other rigid plate. In an unloaded state of the sensor, capacitor gaps of both capacitors are equal and the capacitors have the same capacitive characteristics. However, when one of the rigid plates is maintained immobile and the other one is shifter under the effect of an applied shift force, the capacitor gaps of the capacitors, and hence, the capacitive characteristics of the capacitors, change differently, and with the use of a differential amplifier this difference is measured and recalculated into the value of the applied shift force.