Capacitive Force Sensor Charge Integration for Small Deflections
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Solution Overview
Problem
Existing capacitive multi-way force sensor modules face challenges in accurately determining the deflection of actuating members with small displacements, particularly in applications requiring precise force measurements for triggering switching signals, due to symmetry in capacitance characteristics and limited sensitivity in detecting both positive and negative deflections.
Innovation Solution
The method involves keeping one stationary capacitor plate at ground potential and alternating the voltage potential between the central capacitor plate and the other stationary capacitor plate in successive cycles, transferring charge to an integration capacitor, and measuring the voltage using an A/D converter to generate redundant sensor values representing actuator deflection, thereby enhancing sensitivity and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitive sensors are arranged in pairs opposite each other to measure force in one or two axes, then the sensor module can detect actuator deflection in multiple directions, but the symmetry in capacitance characteristics reduces measurement precision for small displacements
Solution Approach 1:
The patent applies asymmetry by using an integration capacitor with a known capacitance value that is electrically connected to one of the capacitor plates in an unbalanced configuration. This asymmetric arrangement breaks the symmetry of the capacitance characteristics, allowing the integration capacitor to accumulate charge differences that correspond to small actuator deflections. The integration capacitor converts the symmetric capacitance changes into an asymmetric voltage signal that can be precisely measured, thereby resolving the contradiction between multi-directional measurement capability and measurement precision for small displacements
2Measurement precision
If the capacitance values are inversely proportional to the distance between capacitor plates, then the sensor can measure force based on deflection, but the symmetric characteristic curves make it difficult to distinguish between positive and negative deflections
Solution Approach 1:
The integration capacitor serves as an intermediary element that accumulates charge from the capacitor plates during successive measurement cycles. By integrating the capacitance changes over time and converting them into a voltage signal, the integration capacitor provides directional information that was previously lost in the symmetric capacitance measurements. The voltage output from the integration capacitor reflects the cumulative charge difference, which encodes both magnitude and direction of deflection, thereby resolving the information loss problem while maintaining measurement precision
3Measurement precision
If a continuously applied integration method is used in several successive cycles to transfer charge to an integration capacitor, then sensitivity for small deflections is improved, but the device complexity increases
Solution Approach 1:
The patent merges the measurement function with the signal processing function by using the integration capacitor to simultaneously perform charge accumulation and signal conditioning. The integration capacitor combines multiple small capacitance changes from successive measurement cycles into a single amplified voltage signal, thereby improving sensitivity for small deflections without requiring separate amplification stages. This merging approach enhances measurement precision while minimizing the increase in device complexity by using a single capacitive element for multiple functions
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 approach provides a cost-effective and reliable method for determining actuator deflection, especially in applications with small displacements, by generating accurate and redundant sensor values that effectively capture both positive and negative deflections, improving the sensitivity and reliability of the force sensor module.
Implementation Method 1
an amount of charge stored on the central capacitor plate is transferred to an integration capacitor with a known capacitance value
Data Source
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AI summary
A method for determining the deflection of the actuator of a capacitive multipath force sensor module having an actuator which can be adjusted from the neutral position thereof in at least two actuation directions and is moved back into the neutral position thereof again if an actuation force ceases, and to which a central capacitor plate is connected, which capacitor plate is at a distance from at least a first and a second stationary capacitor plate in the rest position of the actuator, and at least one first stationary capacitor plate is moved to and from at least one second path by adjusting the actuator, and wherein at least one measuring capacitor formed by the central capacitor plate with at least one first stationary capacitor plate is used to generate a sensor value representing the deflection of the actuator, is characterized according to the invention in that the first stationary capacitor plate (3) is held at an earth potential, in that, in a continuously applied integration method in a plurality of successive cycles in each case: - the central capacitor plate and at least the second stationary capacitor plate are connected to a voltage potential that differs from the earth potential and are then disconnected from said voltage potential again, - an amount of charge stored on the central capacitor plate is transferred to an integration capacitor having a known capacitance value, and in that, after a predefined number of cycles, the voltage then applied to the integration capacitor is measured by means of an A/D converter and is processed to form the first sensor value.