Cover-Mounted Force and Capacitance Sensing for False Touch Rejection
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Solution Overview
Problem
Capacitance sensing systems face challenges in accurately detecting user input, particularly in rejecting false signals and providing refined information such as force of touch, due to limitations in distinguishing between water droplets and finger presence.
Innovation Solution
A user-input system incorporating a force-measuring device with a strain-sensing element or piezoelectric micromechanical force-measuring element (PMFE) mounted on an elastic circuit board substrate, which transmits mechanical deformations to detect user input through voltage signals, while also measuring capacitance between sensor electrodes and their environment or adjacent electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitance sensing is used to detect user input, then the system can detect finger presence, but it cannot reliably distinguish between water droplets and finger presence causing false signals
Solution Approach 1:
The patent combines capacitance sensing with force sensing in a hybrid sensing system. The capacitance sensor detects changes in electrical capacity caused by proximity objects, while the force sensor (strain gauge or piezoelectric element) simultaneously measures mechanical force applied to the cover. By merging these two sensing modalities, the system can distinguish between water droplets (which cause capacitance changes but minimal force) and actual finger presses (which cause both capacitance changes and significant force), thereby resolving the false signal problem.
2Loss of information
If only capacitance sensing is used, then the system structure remains simple, but it cannot provide refined information such as force of touch
Solution Approach 1:
The cover structure serves multiple functions: it acts as both the user interface surface and as a force transmission element. The force sensor is integrated into the cover assembly, allowing the same structural element to both protect internal components and transmit touch forces for measurement. This multi-functional design adds force sensing capability without proportionally increasing overall system complexity.
3Measurement precision
If a force-measuring device with strain-sensing element is added to the capacitance sensing system, then force of touch can be detected, but the device complexity increases
Solution Approach 1:
The patent introduces an elastic circuit board as an intermediary element between the cover and the force sensor. This elastic board mechanically couples the cover to the force sensor, transmitting touch forces while providing electrical connectivity for the sensor elements. The intermediary structure allows force measurement integration without requiring direct complex mounting arrangements, thereby adding capability while controlling complexity.
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
Enhances the accuracy of user input detection by differentiating between water droplets and finger presence, improving the rejection of false signals and providing more refined force feedback, thereby enhancing the overall performance of user-input systems.
Implementation Method 1
The strain-sensing element is configured to output voltage signals in accordance with a time-varying strain at the strain-sensing element resulting from the secondary mechanical deformation
Implementation Method 2
The force-measuring device includes a piezoelectric micromechanical force-measuring element (PMFE). The PMFE is configured to output voltage signals (PMFE voltage signals) in accordance with a time-varying strain at the PMFE resulting from the secondary mechanical deformation
Implementation Method 3
measure a capacitance between the respective sensor electrode and its surrounding environment (self-capacitance data) and/or measure a capacitance between the respective sensor electrode and an adjacent one of the sensor electrodes (mutual capacitance data)
Data Source
AI summary
A user-input system includes a force-measuring device, a cover member, and an elastic circuit board substrate interposed between the force-measuring device and the cover member and mechanically coupled to the cover member and to the force-measuring device. The force-measuring device includes a strain-sensing element. The force-measuring device is mounted to and electrically connected to the elastic circuit board substrate. The cover member undergoes a primary mechanical deformation in response to forces imparted at the cover member. The elastic circuit board substrate transmits a portion of the primary mechanical deformation to the force-measuring device resulting in a concurrent secondary mechanical deformation of the force-measuring device. The strain-sensing element is configured to output voltage signals in accordance with a time-varying strain at the strain-sensing element resulting from the secondary mechanical deformation.