Optical Force Sensor with Compliant Layer for Temperature Compensation
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Solution Overview
Problem
Traditional touch sensors in electronic devices face challenges in accurately measuring force inputs due to temperature variability and the need for both sensing and optical performance in a compact form factor, especially when integrated with display screens.
Innovation Solution
An optically transparent force sensor is designed with two or more force-sensitive layers separated by a compliant layer, using anisotropic piezoelectric materials to compensate for temperature variations, and sensor circuitry to compute a temperature-compensated force estimate by comparing the relative electrical responses of these layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional touch sensors are used to detect touch location, then the device can identify where a user touches, but the sensor cannot measure the force of the touch and only provides binary output
Solution Approach 1:
The sensor is divided into multiple independent force-sensitive substrates (first substrate with first force-sensitive component, second substrate with second force-sensitive component) separated by a compliant layer. Each substrate can independently respond to applied force, enabling differential measurement of force magnitude while maintaining separate sensing regions.
Solution Approach 2:
The patent replaces traditional mechanical touch detection with electrical resistance-based detection. Force-sensitive components made of conductive material change their electrical resistance in response to applied force, allowing the sensor to measure force magnitude through electrical measurements rather than mechanical displacement.
2Measurement precision
If force-sensitive components are used to measure touch force, then non-binary touch input can be obtained, but temperature fluctuations introduce unacceptable variability in force measurements
Solution Approach 1:
A compliant layer is introduced as an intermediary between the first and second force-sensitive substrates. This compliant layer has different thermal expansion characteristics that compensate for temperature-induced resistance changes in the force-sensitive components, thereby reducing temperature variability impact on force measurements.
Solution Approach 2:
The patent utilizes the temperature coefficient of resistance as a compensating parameter. By designing the compliant layer with specific material properties, the system exploits the relationship between temperature and electrical resistance to cancel out temperature-induced measurement errors in the force-sensitive components.
3Adaptability or versatility
If the force sensor is incorporated with a display or transparent medium, then both sensing and optical performance can be achieved, but achieving both performance requirements in a compact form factor is challenging
Solution Approach 1:
The patent employs thin-film force-sensitive components and a compliant layer with low shear modulus to achieve the required functionality in a compact form factor. The force-sensitive components are deposited as thin films on transparent substrates, maintaining optical clarity while providing force sensing capability. The compliant layer is also designed as a thin film structure that does not significantly increase the overall device thickness.
4Reliability
If multiple force-sensitive layers are used to compensate for temperature variations, then temperature-compensated force measurement can be achieved, but the device structure becomes more complex
Solution Approach 1:
The patent combines temperature compensation functionality with the force sensing structure by integrating the compliant layer directly between the force-sensitive substrates. The same multi-layer structure that provides force sensing also provides temperature compensation, eliminating the need for separate compensation mechanisms and reducing overall device complexity.
Solution Approach 2:
The compliant layer serves multiple functions simultaneously: it acts as a mechanical separator between substrates, provides temperature compensation through its thermal expansion properties, and maintains optical transparency. This multi-functionality reduces the need for additional components and simplifies the overall device structure.
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 solution enables accurate force measurement while minimizing the impact of temperature fluctuations, maintaining optical performance, and integrating seamlessly with display screens in electronic devices.
Implementation Method 1
the first transparent substrate is configured to deflect in response to the force of a touch
Implementation Method 2
the first transparent substrate experiences a first amount of tension
Implementation Method 3
the second transparent substrate which experiences a reduced, second amount of tension
Implementation Method 4
anisotropic piezoelectric materials are used to compensate for variations in temperature
Implementation Method 5
the compliant layer conducts heat between the first force-sensitive layer and the second force-sensitive layer to achieve a substantially uniform temperature distribution
Implementation Method 6
sensor circuitry that is configured to compare a relative electrical response between the first force-sensitive layer and the second force-sensitive layer
Data Source
AI summary
An optical force sensor that may compensate for environmental effects, including, for example, variations in temperature of the device or the surroundings. In some examples, two force-sensitive layers are separated by a compliant layer. The relative electrical response of the two force-sensitive layers may be used to compute an estimate of the force of a touch that reduces the effect of variations in temperature. In some examples, piezoelectric films having anisotropic strain properties are used to reduce the effects of temperature.