Optical Mouse Edge Detection Offset Adjustment

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Solution Overview

Problem

Optical pointing devices using coherent laser illumination suffer from high spatial frequency content leading to spatial aliasing, which results in loss of resolution and 'reverse' motion effects, and smaller pixels exacerbate this issue by reducing mouse-speed/acceleration capability and sensitivity.

Innovation Solution

Introducing an adjustable offset into the comparators of a photodetector array, aligned into quadrants, to selectively prefer one type of edge over the other, and adjusting the offset based on the Gaussian roll-off and central point of the illumination to control inflexion density and handle non-uniform illumination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If smaller pixels are used to handle higher spatial frequency content from laser illumination, then spatial resolution is improved, but mouse-speed/acceleration capability and light sensitivity deteriorate

Engineering Contradiction:

Improvespatial resolutionVSAvoidmouse-speed/acceleration capability

Core Design Contradiction:

Measurement precisionVSSpeed

Solution Approach 1:

The patent applies parameter changes by adjusting the offset threshold parameter in the edge detection algorithm. This allows the system to adapt to different spatial frequency conditions without changing the physical pixel size, thereby maintaining both resolution and speed performance. The offset parameter is modified based on the detected spatial frequency content to optimize edge detection under varying illumination conditions.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If laser illumination is used to expand surface compatibility, then the variety of working surfaces is improved, but spatial aliasing and resolution loss worsen due to high spatial frequency content

Engineering Contradiction:

Improvesurface compatibilityVSAvoidspatial resolution

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent converts the harmful effect of high spatial frequency content (which causes aliasing) into a beneficial feature by using it to enhance edge detection. The high frequency content from laser illumination is deliberately exploited to provide more pronounced edge information, which is then selectively processed through the offset-based edge detection algorithm to extract meaningful motion data while filtering out aliasing artifacts.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

3Quantity of substance

If a threshold is applied to reduce excessive optical features, then the number of inflexions is reduced, but the complexity of processing increases due to per-pixel threshold adjustment

Engineering Contradiction:

Improvenumber of optical featuresVSAvoidprocessing complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The patent applies local quality by introducing an offset parameter that is specifically applied at the pixel level during edge detection. This offset is added to the intensity difference calculation for each pixel, allowing localized adjustment of edge detection sensitivity without requiring complex per-pixel threshold analysis. The local offset approach simplifies processing while maintaining the ability to control feature density.

Inventive Principle:

Principle #3Local quality

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 method effectively reduces inflexion count, preventing aliasing and improving motion detection reliability by maintaining a stable edge detection logic and avoiding confusion from Gaussian roll-off, thus enhancing resolution and sensitivity.

Implementation Method 1

a photodetector array for measuring the varying intensity pattern of a portion of a surface which is illuminated with radiation of a laser illuminated source

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Implementation Method 2

illuminating under a determined gradient by means of a coherent light source the surface portion

Methodology Applied

Scientific EffectLaser Coherent Light: Coherent Light

Implementation Method 3

a coherent light source, the radiation from which underlies a determined gradient

Methodology Applied

Scientific EffectLaser: Laser

Data Source

PatentEP1868066B1Optimization of statistical movement measurement for optical mouse, with particular application to laser-illuminated surfaces

Publication Date: 2015.08.12 EM MICROELECTRONIC-MARIN

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Figure 2~2a
Figure 2b~3

AI summary

A method for measuring relative motion between an illuminated portion of a surface and an optical sensing device comprising a coherent light source and a photodetector device comprising an array of pixels and comparators for extracting motion features, said method comprising the steps of: a) illuminating by means of said coherent light source said surface portion at a determined flash rate; b) detecting by means of said array of pixels a speckled light intensity pattern of said illuminated portion of the surface for each flash; c) extracting edge direction data of two different types from said detected speckled light intensity patterns by comparing light intensity between pixels; d) determining a measurement of the relative motion between said optical sensing device and said illuminated portion of the surface based on extracted edge direction data; wherein the extracting edge direction data step comprises a preliminary step consisting of introducing a selecting factor which promotes detection of one type of edge direction data rather than the other type.