Laser Optical Mouse Motion Detection Speckle Filtering
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Solution Overview
Problem
Optical pointing devices using laser illumination suffer from interference patterns known as speckle, which hinder motion detection due to high spatial frequency content, leading to poor performance, especially on surfaces like wood or glass, and incorrect detection of 'loss of tracking' conditions during high acceleration.
Innovation Solution
A method involving a coherent light source and photodetector array that illuminates a surface with a determined gradient, detects speckled light intensity patterns, extracts specific motion features, and adjusts the gradient to determine relative motion, using filtering means such as offsets or intensity thresholds to enhance tracking performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If laser illumination is used to improve surface coverage, then tracking performance on wood or glass surfaces is improved, but speckle patterns with high spatial frequency content are generated that prevent motion detection algorithms from working efficiently
Solution Approach 1:
The patent changes the illumination parameters by using a coherent light source (laser) with specific temporal characteristics (flash rate) and spatial characteristics (gradient) to illuminate the surface, transforming the illumination approach to achieve both broad surface coverage and reliable motion detection despite speckle patterns
Solution Approach 2:
The patent dynamically adjusts the flash rate of the laser illumination source based on detected motion conditions, allowing the system to adapt the illumination timing to match the motion characteristics being measured, thereby maintaining reliable motion detection across varying surface types and motion speeds
2Measurement precision
If laser illumination with high spatial frequency speckle patterns is used, then more motion features are detected, but the detection of 'loss of tracking' conditions becomes incorrect especially during high acceleration
Solution Approach 1:
The patent applies partial action by using a determined gradient of the coherent light source that illuminates only a portion of the surface with optimized characteristics, rather than uniform full-surface illumination, thereby obtaining sufficient motion features while avoiding the excessive speckle noise that causes false loss of tracking detection
Solution Approach 2:
The patent implements feedback by continuously monitoring the detected speckled light intensity patterns and using this information to dynamically adjust the flash rate and gradient of the laser illumination, ensuring that motion features are detected accurately without triggering false loss of tracking conditions during high acceleration
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 approach improves motion detection reliability by filtering out unnecessary motion features, accurately detecting 'loss of tracking' conditions and maintaining performance during high acceleration, thereby enhancing the tracking capabilities of optical pointing devices.
Implementation Method 1
the image that results from laser illumination is dominated by interference patterns commonly referred to as speckle
Implementation Method 2
a photodetector array for measuring the varying intensity pattern of a portion of a surface that is illuminated with radiation
Data Source
AI summary
A method for measuring relative motion between an illuminated surface and an optical sensing device comprising a coherent light source and a photodetector array is described. The method includes illuminating under a determined gradient, using the coherent light source, a surface portion at a determined flash rate; detecting, using the photodetector array, speckled light intensity pattern of the illuminated surface portion for a first flash; detecting a second speckled light intensity pattern of the illuminated surface portion for a second flash; extracting motion features of two different types from the detected first and second speckled light intensity patterns; determining a measurement of relative motion between the optical sensing device and the illuminated surface portion based on comparison of motion features extracted; wherein the method further comprises a filtering step in order to adjust, and preferably decrease, the number of motion features used in the step of determining a measurement of relative motion.