US-12625340-B2 - Lens alignment

US12625340B2US 12625340 B2US12625340 B2US 12625340B2US-12625340-B2

Abstract

The present disclosure relates to lens alignment methods, lens alignment software, lens alignment apparatuses, and vehicle cameras. In an aspect, a lens alignment method includes performing a scan at a plurality of regions of interest of the lens to determine optical characteristics for each region of interest as the position of the lens relative to the imager is adjusted. Focus windows for each region of interest are determined based on the optical characteristics and the position of the lens relative to the imager is adjusted based on predetermined positions of the focus windows relative to one another.

Inventors

Maciej Krzanowski
Jakub Szela

Assignees

Aptiv Technologies AG

Dates

Publication Date: 20260512
Application Date: 20230717
Priority Date: 20220718

Claims (14)

1 . A lens alignment method comprising: scanning a plurality of regions of interest of a lens to determine optical characteristics for each region of interest as a position of the lens relative to an imager is adjusted; determining a focus window for each region of interest based on the optical characteristics, wherein determining the focus windows for each region of interest comprises determining positions where the optical characteristics are above a predetermined threshold; and adjusting the relative position of the lens to the imager based on the determined positions of the focus windows relative to one another, wherein adjusting the relative position of the lens to the imager comprises determining a center depth of focus for each focus window and adjusting the position of the lens in relation to the determined center depth of focus.
2 . The method according to claim 1 , wherein scanning the plurality of regions of interest of the lens to determine the optical characteristics for each region of interest as a position of the lens relative to the imager is adjusted further comprises: determining Modulation Transfer Function characteristics as a distance between the lens and the imager is varied.
3 . The method according to claim 1 , wherein adjusting the position of the lens comprises: adjusting the position for aligning the focus windows to within a predetermined range.
4 . The method according to claim 1 , wherein adjusting the position of the lens comprises: adjusting at least one of a pitch, yaw, roll, position in a transverse plane, or position in a camera axis.
5 . The method according claim 1 , wherein adjusting the position of the lens comprises: applying a material compensation factor for compensating for material tolerances.
6 . The method according to claim 5 , wherein the material tolerances include at least one of material shrinkage or predicted aging movement characteristics.
7 . The method according to claim 1 , further comprising: providing the lens on a mount relative to the imager, wherein a curable adhesive is provided between the mount and the lens for fixing the lens in position when cured.
8 . The method according to claim 1 , further comprising: fixing the position of the lens once its position is adjusted.
9 . The method according to claim 1 , wherein scanning the plurality of regions of interest of the lens to determine the optical characteristics for each region of interest as a position of the lens relative to the imager is adjusted further comprises: determining Modulation Transfer Function characteristics as a distance between the lens and the imager is varied.
10 . The method according to claim 1 , further comprising: providing the lens on a mount relative to the imager, wherein a curable adhesive is provided between the mount and the lens for fixing the lens in position when cured.
11 . The method according to claim 1 , wherein scanning the plurality of regions of interest of the lens to determine the optical characteristics for each region of interest as a position of the lens relative to the imager is adjusted further comprises determining Modulation Transfer Function characteristics as a distance between the lens and the imager is varied, and the method further comprises: providing the lens on a mount relative to the imager, wherein a curable adhesive is provided between the mount and the lens for fixing the lens in position when cured.
12 . The method according to claim 1 , wherein scanning the plurality of regions of interest of the lens to determine the optical characteristics for each region of interest as a position of the lens relative to the imager is adjusted further comprises determining Modulation Transfer Function characteristics as a distance between the lens and the imager is varied, and the method further comprises: fixing the position of the lens once its position is adjusted.
13 . A lens alignment apparatus comprising: a jig for holding a lens and an imager and adjusting their positions relative to one another; an optical scanner for scanning a plurality of regions of interest of the lens to determine optical characteristics of the lens at each region of interest as the position of the lens relative to the imager is adjusted; and a controller configured to determine a focus window for each region of interest based on the optical characteristics, wherein determining the focus windows for each region of interest comprises determining positions where the optical characteristics are above a predetermined threshold, and adjust the relative positions of the lens to the imager based on the predetermined positions of the focus windows relative to one another, wherein adjusting the relative position of the lens to the imager comprises determining a center depth of focus for each focus window and adjusting the position of the lens in relation to the determined center depth of focuses.
14 . A camera comprising: an imager; and a lens fixed relative to the imager for focusing an image thereon, wherein the fixed position of the lens relative to the imager is aligned by: an optical scanner configured to scan a plurality of regions of interest of a lens to determine optical characteristics for each region of interest as a position of the lens relative to an imager is adjusted and determine a focus window for each region of interest based on the optical characteristics, wherein determining the focus windows for each region of interest comprises determining positions where the optical characteristics are above a predetermined threshold, and a controller configured to adjust the relative position of the lens to the imager based on the determined positions of the focus windows relative to one another, wherein adjusting the relative position of the lens to the imager comprises determining a center depth of focus for each focus window and adjusting the position of the lens in relation to the determined center depth of focuses.

Description

INCORPORATION BY REFERENCE This application claims priority to European Patent Application No. EP22185519.0, filed Jul. 18, 2022, the disclosure of which is incorporated by reference in its entirety. BACKGROUND Automotive cameras are required to provide a high optical performance over a long operating life. In order to maximise optical performance, the manufacturing process includes a multi-axis lens alignment step to achieve optimized alignment between the lens and the imager. During this step, in order to optimise the depth of focus, the position of the lens is adjusted relative to the imager so that one or more regions of interest (ROI) are in focus. In this respect, FIG. 1 shows a typical Modulation Transfer Function (MTF) response chart used for this alignment step when assembling an automotive camera. Each region of interest has an associated MTF curve 2 characteristic of the optical performance for that region, and the position of the lens is adjusted so that the measured MTF peaks 1 are as close together as possible. Consequently, the MTF peak 1 for each respective MTF curve 2 indicates the maximum focus for the associated tested region of interest. Accordingly, by adjusting the position of the lens, the MTF peaks 1 may be aligned so that the optical performance is optimised for the particular regions of interest. This alignment process may also include compensation for adhesive shrinkage and desired focussing distance. Once aligned, the lens is then initially fixed in that position using a UV curable adhesive, and later thermally cured to secure the fixing. The adhesive shrinkage compensation may compensate for both the UV and thermal curing stages. In use, however, the optical performance of a camera will typically degrade over time, as the lens shifts out of alignment relative to the imager. For example, built-in stresses within components in the assembly will relax over time, particularly as automotive cameras are subjected to mechanical and thermal stress cycles. This leads to the shifting of the position of the lens through the operating lifespan of the camera. A consequence of the above shifting is that the MTF curves 2 associated with some regions of interest will move over time, with some regions being affected more than others. For instance, a camera may have a minimum MTF performance threshold, such as MTF 0.4, and the camera's depth of focus 3 is therefore defined by the positions where all the MTF curves 2 are above that threshold. At the same time, lenses typically exhibit corner defocus where a narrower depth of focus is achieved at peripheral regions of interest. Consequently, where the MTF curves associated with these ROIs shift, the camera's depth of focus 3 may be reduced, because these ROIs may no longer be adequately resolved. For example, in FIG. 1, the depth of focus 3 is defined by MTF4 curve at the near Z position and MTF3 curve at the far Z position. Therefore, if the MTF4 curve shifts to a higher Z position or the MTF3 curve shifts to a lower Z position, the depth of focus 3 is reduced. As a consequence, the camera may begin to drop below its required specifications. Accordingly, there remains a need for an automotive camera with a longer operating lifespan. SUMMARY According to a first aspect, there is provided a lens alignment method including: scanning a plurality of regions of interest of the lens to determine optical characteristics for each region of interest as the position of the lens relative to the imager is adjusted; determining a focus window for each region of interest based on the optical characteristics; and adjusting the relative position of the lens to the imager based on predetermined positions of the focus windows relative to one another. In this way, the alignment process may maximise the depth of focus across all the applicable regions of interest. Consequently, a camera with a high long-life performance may be achieved because, even as the lens shifts position over time, the regions of interest will be above the minimum optical performance requirements for longer. Therefore, better compensation of defocus related to ageing may be achieved. In embodiments, the step of determining the focus windows comprises determining positions where the optical characteristics are above a predetermined threshold. In this way, the threshold may be used as a minimum optical performance requirement, and the position where those optical performance requirements are met for each region of interest can be determined based on the optical characteristics, such as MTF characteristics. In embodiments, the scan includes determining MTF characteristics as the distance between the lens and the imager is varied. In embodiments, the step of adjusting the position of the lens includes determining a centre depth of focus for each focus window and adjusting the position of the lens in relation to the determined centre depth of focuses. In this way, the focus provided by each region of