Optical Pointing Device Tracking on Low-Diffusive Surfaces
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Solution Overview
Problem
Optical pointing devices fail to effectively track movement on extremely smooth surfaces like marble or glass due to weak diffusively scattered light, which results in insufficient usable signals for motion tracking.
Innovation Solution
A computer input device with a light source assembly producing an incident light beam at a large angle and a light sensing assembly equipped with a band-pass filter, positioned with a barrier to prevent direct light from reaching the sensor, enhances diffusive scattering by minimizing specular reflection and transmission, allowing for effective tracking on weak-diffusive surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a typical light source and sensor configuration is used, then the device works effectively on rough surfaces, but it fails to generate usable signals on extremely smooth surfaces like glass or marble
Solution Approach 1:
The patent changes the incident angle parameter from typical angles to large angles (greater than 45 degrees from the normal). This parameter change causes the light to interact differently with smooth surfaces, generating sufficient diffusive scattering patterns even on glass or marble surfaces, thereby enabling reliable tracking across diverse surface types
Solution Approach 2:
The patent introduces a barrier as an intermediary element positioned between the light source and sensor. This barrier blocks direct specular reflections and transmitted light from reaching the sensor, allowing only diffusively scattered light to be detected, which enables the system to work on smooth surfaces that would otherwise be invisible to the sensor
2Illumination intensity
If light strikes a smooth surface at typical angles, then specular reflection is strong, but diffusive scattering is too weak to generate usable signals
Solution Approach 1:
By changing the incident angle to large angles (greater than 45 degrees), the patent reduces the strength of specular reflection while increasing the proportion of light that undergoes diffusive scattering. This parameter change shifts the balance between reflection types, generating sufficient diffusive patterns for tracking while minimizing specular interference
Solution Approach 2:
The patent converts the typically harmful specular reflection into a beneficial blocking mechanism. By positioning the barrier to block specular reflections, the system transforms what would be interfering light into a useful exclusion criterion, allowing only the desired diffusive scattering patterns to reach the sensor
3Device complexity
If no barrier is used, then the device structure is simpler, but direct light from the light source reaches the sensor creating interference
Solution Approach 1:
The patent introduces a barrier as a simple intermediary element that blocks direct light paths from the light source to the sensor. This straightforward addition eliminates interfering direct light signals without requiring complex optical filtering or shielding mechanisms, maintaining structural simplicity while significantly improving signal accuracy
Solution Approach 2:
The patent extracts or removes direct light paths from the optical system using the barrier. By blocking these direct paths, the system isolates the sensor from interfering light sources, ensuring that only diffusively scattered light from the surface reaches the sensor for accurate tracking
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 high incidence angle and band-pass filter configuration increase the proportion of scattered light detected, enabling reliable x-y motion tracking on smooth surfaces by capturing usable speckle patterns, even on glass, by filtering out interfering light and focusing on diffusively scattered signals.
Implementation Method 1
Diffusive scattering is caused by roughness or debris on the surface. Diffusive scattering can scatter the light in many different directions.
Implementation Method 2
A barrier is located directly above the area where the light beam is incident on the top surface to prevent any light from traveling directly from the light source assembly to the light sensing assembly.
Implementation Method 3
A light sensing assembly in the input device is positioned to detect the corresponding signal and includes a band-pass filter.
Implementation Method 4
an array of light sensors such as a Complementary Metal-Oxide-Semiconductor (CMOS) sensor
Data Source
AI summary
A computer input device includes a light source assembly forming an incident light beam that strikes an area on a surface beneath the input device with large incident angle. A light sensing assembly in the input device is positioned to receive scattered light and includes a band-pass filter. A barrier is located directly above the area where the light beam is incident on the top surface to prevent light from traveling directly from the light source assembly to the light sensing assembly.