Bi-material Sensor Mount for Automotive Camera Thermal Drift
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Solution Overview
Problem
Automotive camera modules face challenges in maintaining image focus over varying temperatures due to thermal expansion, leading to image sensor displacement out of the image plane, which affects image sharpness, especially in fixed-focus systems without autofocusing mechanisms.
Innovation Solution
A bi-material element is used to hold the image sensor, designed to bend with temperature changes, ensuring the image sensor remains close to the image plane by utilizing materials with different coefficients of thermal expansion, elastic moduli, and geometries, such as metal layers or sandwiched structures, to compensate for thermal expansion and maintain focus precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a fixed-focus lens system is used to reduce cost, then manufacturing cost is reduced, but image sharpness deteriorates at extreme temperatures due to thermal expansion
Solution Approach 1:
The patent applies thermal expansion by designing a bi-material element with two different materials having different coefficients of thermal expansion. When temperature changes, these materials expand at different rates, causing the bi-material element to bend and move the image sensor to compensate for thermal drift, thereby maintaining image sharpness across temperature ranges while keeping the system fixed-focus and cost-effective
Solution Approach 2:
The patent uses composite materials by creating a bi-material element composed of two distinct materials bonded together. This composite structure exploits the differential thermal expansion properties of the materials to generate controlled bending motion, enabling passive thermal compensation without additional mechanical components or active control systems
2Reliability
If additional mechanical elements (athermalizers) are introduced to control image plane drift, then image sharpness is maintained, but device complexity increases
Solution Approach 1:
The patent merges the thermal compensation function directly into the existing image sensor mounting structure by using a bi-material element. This eliminates the need for separate athermalizer components, reducing mechanical complexity while maintaining image sharpness through integrated thermal compensation
3Measurement precision
If pixel size is reduced to improve resolution, then imaging precision is improved, but tolerance for image plane drift decreases
Solution Approach 1:
The patent changes physical parameters by selecting materials with specific coefficients of thermal expansion and designing the bi-material element with optimized geometry and layer thicknesses. These parameter adjustments enable precise control of the bending motion to match the reduced tolerance requirements for smaller pixel sizes, maintaining image plane accuracy despite higher sensitivity
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 bi-material element effectively keeps the image sensor in a predetermined positional relation to the image plane across the entire temperature range, maintaining image sharpness and focus without the need for additional mechanical components, thus enhancing the camera module's imaging performance.
Implementation Method 1
designed to bend with changing temperature. The bending action causes the image sensor to move... a thermal displacement of the bi-material element is able to compensate a thermal expansion of the lens holder
Data Source
AI summary
A camera module (12) for a motor vehicle having a lens assembly (20), a housing (22) with a back plate (32) and a lens holder (53). The back plate (32) carries an image sensor (24) within the housing (22). The lens holder (53) is mounted to the back plate (32) and holds the lens objective (20) such that the image sensor (24) is arranged in or close to an image plane (A) of the lens objective (20). The back plate (32) is formed of at least one bi-material element (31) holding the image sensor (24). The bi-material element (31) having at least two layers (33, 34) of materials having significantly different thermal properties and being joined together such that the bi-material element (31) is adapted to bend with changing temperature.