Optical Navigation Sensor Spatial Frequency Filter
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Solution Overview
Problem
Conventional optical navigation sensors with circular apertures suffer from tracking distortion and sensitivity to sensor height and angle alignments, particularly over dark surfaces, due to the transmission of higher spatial frequency harmonics and limited ability to optimize signal ratios.
Innovation Solution
The use of a spatial frequency filter with non-circular, non-convex apertures such as diamond-shaped or multi-aperture patterns that selectively pass pre-selected frequencies while attenuating undesired harmonics, optimizing the autocorrelation function to enhance signal transmission at desired spatial frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a circular aperture is used in the spatial frequency filter, then the device structure is simple and easy to manufacture, but tracking distortion occurs and the sensor is sensitive to height and angle alignment variations
Solution Approach 1:
The patent replaces the conventional circular aperture with a non-circular aperture (such as rectangular, triangular, or polygonal shapes). This asymmetric shape modification changes the spatial frequency transmission characteristics, allowing selective passage of desired frequencies while attenuating harmonics that cause tracking distortion. The non-circular geometry inherently provides different transmission properties along different axes, which helps in reducing sensitivity to alignment variations.
Solution Approach 2:
The patent introduces multiple apertures with different shapes, sizes, and orientations within the spatial frequency filter. Each aperture is strategically positioned and dimensioned to transmit specific spatial frequency components. This local differentiation allows the filter to selectively pass desired spatial frequencies while blocking unwanted harmonics, thereby improving tracking accuracy without requiring complex external filtering mechanisms.
2Device complexity
If a circular aperture is used, then the filter structure is simple, but higher spatial frequency harmonics are transmitted causing tracking distortion
Solution Approach 1:
By using non-circular aperture shapes, the patent modifies the spatial frequency transmission profile. The asymmetric geometry naturally attenuates certain spatial frequency harmonics while transmitting others, providing built-in frequency selectivity without adding complex filtering stages. This shape-based filtering reduces tracking distortion while maintaining relatively simple filter structure.
Solution Approach 2:
The patent divides the spatial frequency filtering function into multiple discrete apertures with different characteristics. Instead of using a single complex aperture, multiple simpler apertures are arranged to collectively achieve the desired frequency selection. Each aperture segment handles specific frequency components, and their combined effect provides the overall filtering performance needed to eliminate tracking distortion.
3Quantity of substance
If the aperture passes a broad range of spatial frequencies, then more signal content is transmitted, but noise and higher order harmonics are also transmitted degrading tracking performance
Solution Approach 1:
The patent employs multiple apertures with varying sizes, shapes, and orientations to selectively transmit different spatial frequency components. Larger apertures transmit lower spatial frequencies while smaller apertures transmit higher frequencies. By strategically designing the aperture characteristics, the system passes the desired signal content while filtering out noise and harmful harmonics, achieving frequency-selective transmission.
Solution Approach 2:
The non-circular aperture shapes provide inherent frequency selectivity. The asymmetric geometry creates specific transmission patterns that favor certain spatial frequencies while attenuating others. This shape-based discrimination allows the system to transmit useful signal content while naturally suppressing noise and harmonics without requiring additional filtering components.
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 tracking performance and speed over dark surfaces by minimizing the transmission of higher order harmonics, reducing noise, and maintaining robustness to sensor alignment variations.
Implementation Method 1
The spatial frequency filter includes a number of non-circular openings to pass radiation of at least one pre-selected frequency while attenuating other frequencies and harmonics of the pre-selected frequency
Implementation Method 2
light from a coherent source reflected or scattered off of an optically rough surface to generate a complex interference pattern of light known as speckle
Implementation Method 3
radiation scattered from the surface
Data Source
AI summary
An optical navigation sensor (ONS) is provided having a spatial frequency filter to transmit radiation at selected spatial frequencies while attenuating other, undesired frequencies and harmonics. The ONS includes a radiation source to transmit radiation toward a portion of a surface that diffusely reflects radiation incident thereon. The spatial frequency filter is disposed to receive radiation scattered from the surface, and, in one embodiment, includes a number of non-circular openings to pass radiation of at least one pre-selected frequency while attenuating other frequencies and harmonics of the pre-selected frequency.