Multispectral Filter Wheel Angular Segmentation

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Solution Overview

Problem

Existing multispectral image capture devices face challenges in increasing the number of filters without enlarging the wheel, achieving faster filter wheel rotation without increasing drive system power, capturing multispectral images quickly, and reducing color artifacts from moving objects, while also dealing with the cost and manufacturing difficulties of large, high-quality filters.

Innovation Solution

The solution involves using narrow angular sector filters that cover less than the entire optical field, allowing multiple filters to overlap and share the optical field, reducing the size and cost of individual filters, and enabling faster wheel rotation with a smaller, lighter design. This configuration allows for simultaneous capture of image portions through different filters, facilitating quicker image acquisition and reducing vibrations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the number of filters is increased without enlarging the wheel, then the spectral coverage is improved, but the angular extension of each filter must be reduced

Engineering Contradiction:

Improvenumber of filtersVSAvoidangular extension of filter

Core Design Contradiction:

Quantity of substanceVSArea of moving object

Solution Approach 1:

The optical field is segmented into multiple angular zones, with different filters covering different angular extensions. Each filter is optimized for its specific angular sector rather than covering the entire field, allowing more filters to be accommodated on the wheel while maintaining spectral coverage through angular distribution.

Inventive Principle:

Principle #1Segmentation

2Productivity

If the filter wheel rotation speed is increased, then the image capture time is reduced, but the drive system power must be increased

Engineering Contradiction:

Improveimage capture speedVSAvoiddrive system power

Core Design Contradiction:

ProductivityVSPower

Solution Approach 1:

The patent extracts only the necessary angular sector of the optical field for each exposure, rather than requiring the entire field to be covered by a single filter. This allows the filter wheel to rotate faster with lower power consumption, as each filter only needs to cover a portion of the angular field during its brief active period.

Inventive Principle:

Principle #2Taking out (Extraction)

3Manufacturing precision

If large-diameter filters are used to cover the entire optical field, then the image quality is improved, but the manufacturing cost and difficulty increase

Engineering Contradiction:

Improvefilter qualityVSAvoidfilter manufacturing difficulty

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

Each filter is designed with local quality optimization, covering only the specific angular sector it needs to serve rather than the entire optical field. This reduces the diameter and surface area of each individual filter, making them easier and less costly to manufacture while maintaining high optical quality within their designated angular zones.

Inventive Principle:

Principle #3Local quality

4Object-generated harmful factors

If the filter wheel size is reduced, then the vibrations are reduced, but the number of filters that can be accommodated is limited

Engineering Contradiction:

ImprovevibrationsVSAvoidnumber of filters

Core Design Contradiction:

Object-generated harmful factorsVSQuantity of substance

Solution Approach 1:

The patent transitions from a two-dimensional arrangement where filters cover the entire circular field to a dimensional approach where filters are distributed across angular sectors. This allows a smaller wheel to accommodate more filters by utilizing angular segmentation, reducing the wheel size and associated vibrations while maintaining the capability to capture multiple spectral bands.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 enables a higher number of filters on a smaller wheel, allowing for faster image capture, reduced vibrations, and shorter acquisition times, thereby improving the efficiency and quality of multispectral imaging, particularly in space imaging applications.

Implementation Method 1

a filter wheel, which comprises a plurality of spectral filters without overlaps between two neighboring filters; and a drive system, which is arranged to rotate the wheel around an axis of rotation, so as to bring each of the filters into the light beam

Methodology Applied

Scientific EffectOptical filtering: Filter (optical)

Data Source

PatentEP3105924B1Multispectral image capture device comprising a filter wheel and method

Publication Date: 2021.08.04 AIRBUS DEFENCE & SPACE SAS

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Figure 2~3a
Figure 3b~3c

AI summary

The invention relates to a multispectral image capture device comprising a filter wheel (4) and an image sensor. The filters (41-46) are located close to a focusing plane of a light beam used to form the images, and at least one of the filters is more angularly narrow than the optical field of the image sensor. The production of the filter is thereby facilitated. Advantageously, the filters are closer to one another in the wheel such that multiple filters are in the optical field of the sensor simultaneously. Each multispectral image can be captured more quickly than when each filter covers the entire optical field of the sensor.