Dual Strain and Pressure Sensor for Wide Force Touch
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Solution Overview
Problem
Existing electronic devices with touch-sensitive displays face challenges in accurately detecting a wide range of input forces due to the close placement of components, which can lead to unreliable strain sensor readings when the input surface deflects and contacts internal components, limiting the detection range and increasing the risk of sensor failure.
Innovation Solution
The use of a dual force-sensing system comprising a strain sensor and a pressure sensor, with processing circuitry that determines which sensor to use based on the deflection state, allowing for extended force detection range by switching between partial strain-sensing and partial pressure-sensing modes, and employing various configurations such as separate layers or a common substrate for the sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the input surface or its structural layers are allowed to deflect more to detect greater forces, then the detection range is improved, but the input surface may contact internal components and become unable to deflect further, causing sensor failure
Solution Approach 1:
The patent divides the sensing function into two separate sensors: a strain sensor for detecting forces when the input surface can deflect, and a pressure sensor for detecting forces when deflection is limited. This segmentation allows each sensor to operate in its optimal range without interference from the deflection limitation problem.
Solution Approach 2:
The patent introduces a compressible layer between the input surface and internal components as an intermediary element. This layer allows controlled deflection and force transmission to the sensors while preventing direct contact between the input surface and rigid internal components, thereby maintaining sensor reliability across a broader force range.
2Weight of stationary object
If internal components are placed close together to decrease device weight and thickness, then device compactness is improved, but the input surface may contact internal components during deflection, limiting force detection capability
Solution Approach 1:
The compressible layer serves as a mediator between the input surface and closely-placed internal components, enabling safe deflection even when components are positioned close together. This allows the device to maintain compact dimensions while preserving force detection capability across a wider range.
Solution Approach 2:
By segmenting the sensing system into two sensors with different operational ranges, the patent enables accurate force detection even when the input surface is constrained by closely-placed internal components. The pressure sensor specifically captures forces in the regime where deflection is limited.
3Device complexity
If a single sensor type is used to detect all force levels, then device complexity is reduced, but the detection range and reliability are limited
Solution Approach 1:
The patent implements a multi-functional sensing system where two different sensor types (strain and pressure sensors) work together to cover the entire force detection range. Each sensor type contributes its strengths, creating a universal solution that handles both low-force and high-force scenarios reliably.
Solution Approach 2:
The system dynamically switches between strain sensor and pressure sensor based on the current force level and deflection state. This dynamic operation allows the system to maintain optimal measurement accuracy across varying force conditions without requiring a overly complex fixed-architecture sensor system.
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 accurate detection of a broader range of input forces by ensuring reliable sensor data even when the input surface deflects sufficiently to contact internal components, maintaining the small form factor and reducing the risk of sensor failure.
Implementation Method 1
a strain sensor that can be used to estimate the applied force by measuring a displacement in a material caused by the applied force
Implementation Method 2
The pressure sensor may work by detecting either changes in a capacitance or a resistance caused by the applied force
Implementation Method 3
The pressure sensor may work by detecting either changes in a capacitance or a resistance caused by the applied force
Data Source
AI summary
Structures and methods are disclosed for an electronic device having an input surface that uses dual sensors to measure forces applied to the input surface. The forces can be estimated over a greater range of values than would be possible with either sensor alone. A second sensor can be used after a first sensor has reached a limit. A first sensor can be a strain sensor and a second sensor a pressure sensor. Both sensors may be resistance based, with signals from both sensors can be combined and measured by processing circuitry. Each sensor type may be part of planar arrays disposed beneath the input surface.