Piezoelectric Touch Sensor for Simultaneous Position and Force Detection
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Solution Overview
Problem
Existing touch type input devices face challenges in simultaneously detecting touch position and pressing force with high sensitivity due to issues like polarization relaxation and detection accuracy limitations, particularly in systems that require switching between detection modes.
Innovation Solution
A touch sensor design utilizing a piezoelectric film sandwiched between first and second detection conductors, with the second conductor acting as a reference potential, allows for simultaneous detection of touch position and pressing force by separating signals into different frequency bands, including commercial power supply frequency and other frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If common electronics are used to sense both pressure and capacitance changes, then device size and cost are reduced, but detection sensitivity and accuracy deteriorate due to polarization relaxation of the piezoelectric film
Solution Approach 1:
The patent segments the detection functions into two separate detection circuits: a capacitance detection circuit for touch position detection and a piezoelectric detection circuit for pressure detection. This segmentation allows each circuit to be optimized for its specific function, maintaining high detection sensitivity while using a unified sensor structure with a piezoelectric film and detection electrodes
Solution Approach 2:
The patent implements dynamic switching between detection modes (capacitance detection and piezoelectric detection) based on operational requirements. The control unit selectively activates different detection circuits depending on whether touch position or pressure information is needed, enabling the system to adapt its detection mode to maintain optimal sensitivity for each measurement type
2Device complexity
If intermittent switching between pressing force detection and touch position detection is performed, then device complexity is reduced, but detection accuracy deteriorates due to the 100Hz switching interval
Solution Approach 1:
The patent implements dynamic switching between detection modes (capacitance detection and piezoelectric detection) based on operational requirements. The control unit selectively activates different detection circuits depending on whether touch position or pressure information is needed, enabling the system to adapt its detection mode to maintain optimal sensitivity for each measurement type
Solution Approach 2:
By maintaining both detection circuits simultaneously ready for operation and switching between them based on need, the system ensures continuous detection capability. The capacitance detection circuit remains active for touch position tracking while the piezoelectric circuit is available for pressure detection, eliminating detection gaps that would occur with single-mode intermittent operation
3Measurement precision
If separate electronics are used for sensing pressure and capacitance changes, then detection sensitivity is improved, but device size and cost increase
Solution Approach 1:
The patent merges the sensor structure by using a single piezoelectric film with detection electrodes that serve dual purposes: capacitance detection for touch position and piezoelectric detection for pressure measurement. This unified sensor structure reduces device size while maintaining separate detection circuits for optimal sensitivity in each measurement mode
Solution Approach 2:
The detection electrodes in the patent serve multiple functions: they act as both capacitance sensors for touch position detection and piezoelectric sensors for pressure detection. This multi-functionality allows a single electrode structure to support both detection modes, reducing the need for separate sensor components and thereby reducing device size
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
Enables high-sensitivity, simultaneous detection of touch position and pressing force without the need for intermittent switching, maintaining detection accuracy and reducing device complexity.
Implementation Method 1
a piezoelectric film; a first detection conductor facing the piezoelectric film
Implementation Method 2
when a position detection sensor of capacitance type is used as the position detection sensor, the touch position can be detected by a change in capacitance
Data Source
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AI summary
A technique for detecting a touch position and a pressing force substantially simultaneously with high sensitivity is disclosed. An input device according to an aspect of the present invention includes a touch sensor and a control unit, in which the touch sensor includes: a piezoelectric film; a first detection conductor facing the piezoelectric film, and made up of divided electrodes having a plurality of electrode portions electrically insulated from each other; and a second detection conductor facing the first detection conductor, and disposed on a side opposite to the first detection conductor with respect to the piezoelectric film, and the control unit is configured to: separate a signal detected from the first detection conductor with the second detection conductor used as a reference potential into a first signal in a commercial power supply frequency band and a second signal in a frequency band other than the commercial power supply frequency band; and detect a touch position using the first signal, and detect a pressing force using the second signal. In addition, an input device according to an aspect of the present invention includes a touch sensor and a control unit, in which the touch sensor includes: a piezoelectric film; a first detection conductor facing the piezoelectric film, and including a plurality of first electrodes linearly disposed along a first straight line and a plurality of second electrodes linearly disposed along a second straight line, the plurality of first electrodes and the plurality of second electrodes being electrically insulated from each other; and a second detection conductor facing the first detection conductor, and disposed on a side opposite to the first detection conductor with respect to the piezoelectric film, and the control unit is configured to: separate a signal detected from the first detection conductor with the second detection conductor used as a reference potential into a first signal in a commercial power supply frequency band and a second signal in a frequency band other than the commercial power supply frequency band; and detect a touch position using the first signal, and detect a pressing force using the second signal.