Semi-transparent mirror calibration for stereoscopic camera alignment

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Solution Overview

Problem

Existing devices for recording three-dimensional images with multiple cameras face challenges in aligning beam paths without interference, requiring complex and heavy positioning mechanisms, which can introduce vibrations and limit the wide angle of lenses, especially when cameras have different geometric properties and cannot be positioned closely due to physical constraints.

Innovation Solution

A device with a semi-transparent mirror firmly installed in a vibration-free mirror box, allowing horizontal or vertical translation, and adjustable at corners with ball joints or motorized drives, along with adjustable optical elements and sensors to compensate for calibration, enabling precise alignment without geometric distortions and allowing partial image reading to conserve bandwidth.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If cameras are positioned side by side to achieve stereoscopic recording, then two separate views can be obtained, but the camera bodies and lenses are too large to position them close enough, preventing the beam paths from overlapping

Engineering Contradiction:
Improvedistance between camerasVSAvoidbeam path alignment mechanism
Core Design Contradiction:
Volume of moving objectVSDevice complexity

Solution Approach 1:

The patent introduces a semi-transparent mirror to redirect one camera's beam path through a different spatial dimension (vertical direction), allowing the two cameras to be positioned at different heights rather than side by side. This enables the beam paths to overlap while keeping the cameras physically separated to avoid housing interference.

Inventive Principle:
Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

A semi-transparent mirror is introduced as an intermediary element between the two cameras. This mirror allows one camera to capture the scene directly while the other camera captures the scene through the mirror, enabling beam path overlap without direct physical proximity between cameras.

Inventive Principle:
Principle #24Intermediary (Mediator)

2Adaptability or versatility

If different types of cameras and lenses are used to suit specific tasks, then recording flexibility is improved, but the geometric properties (e.g., optical axes) never match exactly, requiring alignment adjustment

Engineering Contradiction:
Improvecamera selection flexibilityVSAvoidoptical axis alignment
Core Design Contradiction:
Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent implements adjustable mounting mechanisms for both cameras and the semi-transparent mirror, allowing dynamic adjustment of their positions and orientations. This enables precise alignment of optical axes and beam paths after the cameras are installed, accommodating different camera types while achieving accurate stereoscopic calibration.

Inventive Principle:
Principle #15Dynamics

3Manufacturing precision

If a positioning device is used to adjust the camera itself for alignment, then beam path alignment is achieved, but a very expensive, robust, precise and complex positioning mechanism is required, increasing overall weight

Engineering Contradiction:
Improvecamera positioning precisionVSAvoidpositioning mechanism weight
Core Design Contradiction:
Manufacturing precisionVSWeight of moving object

Solution Approach 1:

Instead of positioning the heavy camera itself, the patent uses a semi-transparent mirror as an intermediary that can be adjusted more easily. The mirror's adjustment mechanism is lighter and less complex than a camera positioning device, achieving the same beam path alignment goal with reduced weight and complexity.

Inventive Principle:
Principle #24Intermediary (Mediator)

Solution Approach 2:

The alignment function is segmented into separate adjustable components: the camera mounting and the mirror mounting. This allows the lighter mirror adjustment mechanism to handle the precision alignment task, while the camera remains relatively fixed, reducing the need for heavy positioning mechanisms on the camera itself.

Inventive Principle:
Principle #1Segmentation

4Manufacturing precision

If the mirror is rotated about a fixed axis in a mirror box, then beam path alignment is possible, but a very robust, precise, heavy and complicated mechanism is required to install the mirror in a vibration-free manner

Engineering Contradiction:
Improvemirror alignment precisionVSAvoidmirror rotation mechanism
Core Design Contradiction:
Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent transitions from a fixed-axis rotation mechanism to a multi-degree-of-freedom adjustable mounting system. The mirror can be adjusted in multiple directions (horizontal, vertical, and angular) using simpler mechanisms, eliminating the need for a complex fixed-axis rotation system while achieving the same alignment precision.

Inventive Principle:
Principle #15Dynamics

5Manufacturing precision

If a fixed-axis mirror rotation mechanism is used, then alignment is possible, but a lot of valuable space on the sides of the mirror box is wasted, severely limiting the wide angle of the lens

Engineering Contradiction:
Improvebeam path alignmentVSAvoidmirror box space
Core Design Contradiction:
Manufacturing precisionVSArea of stationary object

Solution Approach 1:

The patent repositions the mirror vertically above the cameras rather than horizontally in a mirror box. This vertical arrangement eliminates the need for lateral space in the mirror box, allowing lenses to have wider angles without being constrained by the mirror box's side space requirements.

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 solution simplifies the calibration process, reduces the need for complex mechanisms, minimizes vibrations, and allows for wider lens angles by enabling precise alignment and adjustment of camera positions and optical elements, resulting in improved three-dimensional image quality and reduced weight and cost.

Implementation Method 1

brings together the beam paths of at least two cameras via a semi-transparent mirror

Methodology Applied
Scientific EffectReflection: Reflection

Implementation Method 2

semi-transparent mirror in such a way that the beam paths of both cameras can overlap

Methodology Applied
Scientific EffectLight transmission: Light

Data Source

PatentEP2476260B1Apparaturs for positioning and calibration of at least two cameras with a semi transparent mirror for stereoscopic image pickup
Publication Date: 2018.02.14 MAIER FLORIAN
  • EP2476260B1 patent drawingFigure 1~2

AI summary

The invention relates to a device for positioning and calibrating at least two cameras, said device comprising a semi-transparent mirror for three-dimensional image recording, and wherein calibration is achieved by a displaceable mirror box, by a movably mounted mirror or by an image converter, the data from which can be read in image parts.