Trackpad Force Sensor Calibration via Spatial Parameter Mapping
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Solution Overview
Problem
Existing trackpads face challenges with unit-to-unit variations, spatial non-uniformity, and non-linearity in force input detection, leading to inconsistent user experiences and potential false triggers or missed inputs.
Innovation Solution
A method involving multiple physical objects of different masses placed at various locations on the trackpad to register force sensor readings, selecting sensitivity parameters through linear least squares and polynomial fitting, and updating zero offset vectors based on resting conditions to calibrate the trackpad's force sensing circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If force sensors are used to detect user input on trackpad, then force detection capability is provided, but unit-to-unit variations and spatial non-uniformity occur leading to inconsistent measurements
Solution Approach 1:
The patent applies local quality by determining separate sensitivity parameters for different regions of the trackpad. Each region is calibrated using test weights placed at specific locations, allowing the system to account for spatial non-uniformity in force sensor response. This ensures consistent force detection across the entire trackpad surface by adjusting parameters locally for each region rather than using a uniform calibration approach.
Solution Approach 2:
The patent changes parameters by determining sensitivity parameters and zero offset values that are specific to each region and test weight combination. The system adjusts these parameters based on the mass of test weights used during calibration, allowing the force sensing circuitry to compensate for unit-to-unit variations and non-linearity through parameter modification rather than hardware changes.
2Measurement precision
If multiple test weights are used for calibration, then non-linearity is reduced, but calibration complexity increases
Solution Approach 1:
The patent applies preliminary action by performing calibration before the trackpad is put into service. Test weights are placed at predetermined locations and sensitivity parameters are determined in advance during manufacturing or initial setup. This preliminary calibration stores the necessary parameter data in non-volatile memory, allowing the trackpad to operate without requiring complex real-time calibration procedures during normal use.
Solution Approach 2:
The patent uses copying by creating a digital model of the trackpad's force sensor response characteristics through calibration measurements. The sensitivity parameters and zero offset values derived from testing with multiple weights create a computational replica of the physical trackpad's behavior, allowing accurate force detection without physically adjusting or redesigning the hardware.
3Measurement precision
If sensitivity parameters are determined through linear least squares, then measurement accuracy is improved, but computational requirements increase
Solution Approach 1:
The patent applies preliminary action by performing the computationally intensive linear least squares calculations during the calibration phase rather than during normal operation. The sensitivity parameters are pre-computed and stored in non-volatile memory, so that during actual use, the trackpad simply needs to retrieve and apply these pre-determined parameters, significantly reducing real-time computational requirements while maintaining high measurement accuracy.
Data Source
AI summary
A method includes: placing a first physical object at each of a first plurality of locations on a trackpad; while the first object is at each of the first plurality of locations, registering respective first readings from each of a second plurality of force sensors of the trackpad, the first plurality greater than the second plurality; selecting a first plurality of sensitivity parameters for the trackpad based at least in part on the first readings; and providing the first plurality of sensitivity parameters to force sensing circuitry of the trackpad, the force sensing circuitry coupled to the second plurality of force sensors.