Touchpad Force Sensing With Differential PCB Electrode Compensation
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Solution Overview
Problem
Existing force sensing touchpads in computing devices face errors in force estimation due to component bending, aging, and environmental factors, which affect the accuracy of capacitance-based force calculations.
Innovation Solution
A touchpad configuration with a printed circuit board (PCB) and springs featuring four PCB electrodes and four spring electrodes in a cross pattern, utilizing differential capacitive sensing to calculate local gradients and correct for bending errors along both x- and y-axes, reducing errors in force estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitance measurements are used to estimate force applied to the touchpad, then force sensing capability is achieved, but measurement precision deteriorates due to component bending, aging, and environmental factors
Solution Approach 1:
The touchpad structure is segmented into multiple sensing zones with separate capacitance measurement circuits for each zone. This allows independent measurement and compensation of bending effects at different locations, improving overall force estimation accuracy while maintaining reliability of force sensing
Solution Approach 2:
The system continuously monitors capacitance changes and uses feedback algorithms to distinguish between force-induced capacitance changes and those caused by component bending or environmental factors. This feedback mechanism maintains measurement precision over time and across varying conditions
2Device complexity
If simple capacitance-based force calculation is used, then device complexity is reduced, but measurement precision deteriorates due to inability to compensate for bending errors
Solution Approach 1:
The system transitions from single-point capacitance measurement to multi-point spatial measurement across the touchpad surface. By measuring capacitance at multiple locations and analyzing the spatial distribution pattern, the system can distinguish between uniform bending effects and localized force application, improving precision without significantly increasing device 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
The solution provides more accurate force calculations by compensating for component bending, enhancing the precision of force sensing in touchpads.
Implementation Method 1
the touchpad utilizes capacitance measurements to estimate a force applied to the touchpad
Data Source
AI summary
Methods for estimating a force F exerted on a touchpad are disclosed. In one example, a force sensing touchpad comprises a printed circuit board (PCB) comprising four PCB electrodes and a spring spaced from the PCB and comprising four spring electrodes. Changes in capacitance at two of the PCB electrodes are determined and used to calculate a first local gradient between the two electrodes. Changes in capacitance at the other two PCB electrodes are determined and used to calculate a second local gradient between these two electrodes. The local gradients are used to calculate local forces at each PCB electrode, and the local forces are used to calculate the force F exerted on the touchpad.