Camera module back focus offset test method

Abstract

The invention discloses a camera module back focus offset test method, which comprises a collimator, a camera module and an image acquisition box for controlling the camera module, and is characterized in that data of the back focus offset of the camera module can be calculated through the method realized by the device; effective data support can be provided for improvement in the directions of camera assembly process, material, light path design and the like; therefore, the stability and the applicability of the camera module in the actual use process are improved, and the production and the design of high-quality cameras in China are facilitated.

Description

Technical Field

[0001] The invention relates to camera module packaging test, in particular to a camera module back focus offset testing method. Background Art

[0002] At present, the back focus offset of optical modules can only be measured for individual lenses. For the detection of packaged camera modules, since it is a sealed whole and the interior is not visible, there is no accurate back focus offset detection method, and only the final image quality is detected. However, the accuracy of the back focus position of the sensor (image sensor) in the camera module is often the main factor determining the camera imaging quality.

[0003] Simple imaging quality testing can only detect the imaging results of the camera module and intercept defective products; it is unable to analyze the key reasons, and thus cannot provide more powerful data basis for improvements in camera assembly technology, materials, lens optical path design, etc. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a method for testing back focus offset of a camera module.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] The camera module back focus offset test method includes a collimator, a camera module and an image acquisition box for controlling the camera module, and is characterized in that it includes the following test steps:

[0007] S1: Turn on the collimator and the image acquisition box, and preview the camera module screen to make the image of the target of the collimator symmetrical left and right and up and down in the camera module screen;

[0008] S2: Control the lens group in the collimator to move along the optical axis from the starting position of the negative distance of the simulated distance to the ending position of the positive distance, and move to m points P1, P2...Pm with equal spacing throughout the whole process;

[0009] S3: Capture pictures taken at m points through the camera module, and calculate the MTF value V1, V2...Vm of each picture;

[0010] S4: Analyze V1, V2...Vm to obtain the peak value Vk and the corresponding coordinate position Pk;

[0011] S5: Take the MTF values ​​of x points before and after Vk to obtain Vk-1, Vk-2...Vk-x and Vk+1, Vk+2...Vk+x, and find the coordinates Pk-1, Pk-2...Pk-x and Pk+1, Pk+2...Pk+x corresponding to the above MTF values;

[0012] S6: Control the lens group in the collimator to move from Pk-x to Pk+x with equal spacing to n points PP1, PP2...PPn;

[0013] S7: Capture images of n points and calculate the MTF value VV1, VV2...VVn of each image;

[0014] S8: Substitute VV1, VV2...VVn and the corresponding coordinates PP1, PP2...PPn into the quadratic polynomial fitting curve formula to obtain the peak coordinate PPf of the MTF value;

[0015] S9: Obtain the actual optimal object distance D1 corresponding to the coordinate PPf according to the collimator simulation distance comparison table, the theoretical optimal object distance of the camera module is D2, and then obtain the change D3=D1-D2 of the theoretical optimal object distance caused by the back focus offset;

[0016] S10: Substitute D1, D2, and D3 into the formula DisBlf=1000*(Efl*Efl*D3) / (Efl-D2)*(D1-Efl) to calculate the back focus offset value DisBlf, where Efl is the focal length of the camera module.

[0017] In the above S1:, the position of the camera module is adjusted to achieve left-right and top-bottom symmetry in the imaging of the target of the parallel light tube in the camera module screen.

[0018] The test frame comprises a column and a test platform, the column is provided with a connecting plate, the test platform is located below the connecting plate, the parallel light tube is fixed on the connecting plate, and the camera module and the image acquisition box are arranged on the test platform.

[0019] The camera module and the image acquisition box are moved by being driven by a spatial displacement mechanism.

[0020] The connecting plate is arranged on the column through a lifting and adjusting structure.

[0021] The lifting and adjusting structure comprises a frame plate fixed on a column, a sliding rod and an adjusting screw rotatably matched with the frame plate are arranged on the frame plate, and the connecting plate is slidably matched with the sliding rod and threadably matched with the adjusting screw.

[0022] The beneficial effects of the present invention are: the following effects can be achieved through this method:

[0023] 1. It helps to analyze whether the back focus position of the camera module is accurate.

[0024] 2. It helps to analyze the amount of shrinkage caused by the curing of glue at the connection of the camera module.

[0025] 3. It helps to analyze the back focus temperature drift of the camera module when it works continuously for different lengths of time.

[0026] 4. It helps to analyze the change in back focus caused by the camera module’s transportation vibration (or after a certain life span).

[0027] 5. It helps to analyze the material expansion and contraction of the camera module under different ambient temperatures.

[0028] 6. It helps to analyze the change of back focus of the camera module under different pressures.

[0029] In summary, the calculation of the back focus offset of the camera module can provide effective data support for improvements in camera assembly technology, materials, optical path design, etc.; thereby improving the stability and applicability of the camera module during actual use, and contributing to the production and design of high-quality cameras in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0031] Figure 1 It is a test structure diagram of the present invention. DETAILED DESCRIPTION

[0032] The advantages and features of the present disclosure and its implementation methods will be explained by the following embodiments described with reference to the accompanying drawings. However, the present disclosure can be embodied in different forms and should not be interpreted as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure will be comprehensive and complete, and will fully convey the scope of the present disclosure to those skilled in the art. In addition, the present disclosure is limited only by the scope of the claims.

[0033] The shapes, sizes, ratios, angles and numbers disclosed in the drawings for describing the embodiments of the present disclosure are only examples, and therefore the present disclosure is not limited to the details shown. Throughout this specification, the same reference numerals refer to the same elements. In the following description, when the detailed description of the relevant known functions or configurations is determined to be unnecessary to blur the focus of the present disclosure, the detailed description will be omitted. In the case of using "including", "having" and "comprising" described in this specification, other parts may be added unless "only" is used. Unless otherwise indicated, the terms in the singular may include plural forms.

[0034] When explaining an element, although not explicitly described, the element is understood to include a range of error.

[0035] When describing a positional relationship, for example, when the positional relationship is described as "on," "above," "below," and "adjacent to," unless "immediately" or "directly" is used, one or more parts may be arranged between two other parts.

[0036] When describing a time relationship, for example, when a time sequence is described as “after,” “subsequently,” “next,” and “before,” discontinuous cases may be included unless “just” or “directly” is used.

[0037] It should be understood that although the terms "first", "second", etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from other elements. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element without departing from the scope of the present disclosure.

[0038] As those skilled in the art can fully understand, the features of the different embodiments of the present disclosure can be coupled or combined with each other in part or in whole, and can cooperate with each other in various ways and be driven technically. The embodiments of the present disclosure can be performed independently of each other, or can be performed together in a mutually dependent relationship.

[0039] Reference Figure 1 The present invention discloses a method for testing the back focus offset of a camera module, comprising a collimator 1, a camera module 2 and an image acquisition box 3 for controlling the camera module 2. The test structure of the present application is as follows: comprising a test frame 4, the test frame 4 comprising a column 5 and a test bench 6, the column 5 is made of aluminum, a connecting plate 7 is arranged on the column 5, the test bench 6 is located below the connecting plate 7, the collimator 1 is fixed on the connecting plate 7, the camera module 2 and the image acquisition box 3 are arranged on the test bench 6, and the collimator 1 is directed toward the camera module 2 through the above structure. Of course, because it is difficult for the camera module 2 to be aligned with the collimator 1 when it is placed on the test bench 6, the camera module 2 and the image acquisition box 3 are driven and moved by a spatial displacement mechanism 8, and the alignment of the camera module 2 and the collimator 1 is achieved through plane movement. Of course, the spatial displacement mechanism 8 is mainly composed of a plurality of servo motors in conjunction with a plurality of sets of lead screw assemblies and guide rail assemblies. The above are all realized by the prior art, so the specific structure and connection are not described in detail.

[0040] Because it is necessary to test different styles of camera modules 2, the connecting plate 7 is arranged on the column 5 through a lifting and adjusting structure. The specific structure is: the lifting and adjusting structure includes a frame plate 9 fixed on the column 5, the frame plate 9 is provided with a slide bar 10 and an adjusting screw 11 that rotates with the frame plate 9, the connecting plate 7 is slidably matched with the slide bar 10 and threadedly matched with the adjusting screw 11, and the lifting and lowering of the connecting plate 7 can be realized by rotating the adjusting screw 11, thereby driving the lifting and lowering of the collimator 1.

[0041] The specific test includes the following test steps:

[0042] S1: Turn on the collimator 1 and the image acquisition box 3, and preview the camera module 2 screen in real time, so that the image of the target of the collimator 1 in the camera module 2 screen is symmetrical left and right and up and down; if the image is asymmetrical, it means that the light of the target has not completely entered the camera module 2, so the MTF value measured is inaccurate, because the camera module 2 is a component, so it needs to be powered and control instructions are sent to it through the image acquisition box 3 during the test. The image acquisition box 3 is an existing device, and it will also be used in the previous camera module 2 test, so the specific structure and connection method are not described in detail.

[0043] The above-mentioned adjustment of the position of the camera module 2 realizes that the imaging of the target of the collimator 1 in the camera module 2 is symmetrical left and right and up and down, and the position of the camera module 2 is achieved by adjusting the plane of the test bench 6.

[0044] S2: Control the lens group in the collimator 1 to move along the optical axis from the starting position of the negative distance of the simulated distance to the ending position of the positive distance, and move to m points P1, P2...Pm with equal spacing throughout the whole process; preferably m is 70,

[0045] S3: The images of the target imaged in the camera module 2 screen taken when the camera module 2 captures m points are taken, and the MTF values ​​V1, V2...Vm of each image are calculated, and there are 70 corresponding MTF values;

[0046] S4: Analyze V1, V2...Vm to obtain the peak value Vk of the MTF value and the corresponding coordinate position Pk;

[0047] S5: Take the MTF values ​​of x points before and after Vk to obtain Vk-1, Vk-2...Vk-x and Vk+1, Vk+2...Vk+x, and find the coordinates Pk-1, Pk-2...Pk-x and Pk+1, Pk+2...Pk+x corresponding to the above MTF values; x is preferably 3, so that the number of points taken in this step is 7 in total, and the corresponding coordinate points are also 7,

[0048] S6: Control the lens group in the collimator 1 to move from Pk-x to Pk+x at equal intervals to n points PP1, PP2...PPn; the value of n is to be greater than the number of points taken in step S5. If the number of points taken is 7 in total, n must be greater than 7. In this application, n is preferably 35.

[0049] S7: capturing images of the target imaged in the camera module 2 screen when the camera module 2 captures n points, and calculating the MTF value VV1, VV2...VVn of each image;

[0050] S8: Substitute VV1, VV2...VVn and the corresponding coordinates PP1, PP2...PPn into the quadratic polynomial fitting curve formula to obtain the peak coordinate PPf of the MTF value;

[0051] S9: Obtain the actual optimal object distance D1 corresponding to the coordinate PPf according to the simulated distance comparison table of the collimator 1, the theoretical optimal object distance of the camera module 2 is D2, and then obtain the change D3=D1-D2 of the theoretical optimal object distance caused by the back focus offset;

[0052] S10: Substitute D1, D2, and D3 into the formula DisBlf=1000*(Efl*Efl*D3) / (Efl-D2)*(D1-Efl) to calculate the back focus offset value DisBlf, where Efl is the focal length of the camera module 2.

[0053] The present invention tests the actual optimal object distance D1 (unit: mm) of the camera module 2 by controlling the actual simulation distance of switching the electric collimator 1, and then subtracts the theoretical optimal object distance D2 (unit: mm) to obtain the optimal object distance change D3 caused by the back focus offset, and derives the calculation method of the back focus offset through the optimal object distance change; the collimator 1 with positive and negative object distances can be simulated at the same time; the left and right points are taken in a way that the MTF value peak drops by a specific value, and then a quadratic polynomial fitting is performed to obtain a method for obtaining a precise peak position of the resolution.

[0054] The above is a detailed introduction to a method for testing the back focus offset of a camera module 2 provided in an embodiment of the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A camera module back focus offset test method, comprising a collimator, a camera module and an image acquisition box for controlling the camera module, characterized in that: The test steps include: S1: Turn on the collimator and the image acquisition box, and preview the camera module screen to make the image of the target of the collimator symmetrical left and right and up and down in the camera module screen; S2: Control the lens group in the collimator to move along the optical axis from the starting position of the negative distance of the simulated distance to the ending position of the positive distance, and move to m points P1, P2...Pm with equal spacing throughout the whole process; S3: Capture pictures taken at m points through the camera module, and calculate the MTF value V1, V2...Vm of each picture; S4: Analyze V1, V2...Vm to obtain the peak value Vk and the corresponding coordinate position Pk; S5: Take the MTF values ​​of x points before and after Vk to obtain Vk-1, Vk-2...Vk-x and Vk+1, Vk+2...Vk+x, and find the coordinates Pk-1, Pk-2...Pk-x and Pk+1, Pk+2...Pk+x corresponding to the above MTF values; S6: Control the lens group in the collimator to move from Pk-x to Pk+x with equal spacing to n points PP1, PP2...PPn; S7: Capture images of n points and calculate the MTF value VV1, VV2...VVn of each image; S8: Substitute VV1, VV2...VVn and the corresponding coordinates PP1, PP2...PPn into the quadratic polynomial fitting curve formula to obtain the peak coordinate PPf of the MTF value; S9: Obtain the actual optimal object distance D1 corresponding to the coordinate PPf according to the collimator simulation distance comparison table, the theoretical optimal object distance of the camera module is D2, and then obtain the change D3=D1-D2 of the theoretical optimal object distance caused by the back focus offset; S10: Substitute D1, D2, and D3 into the formula DisBlf=1000*(Efl*Efl*D3) / (Efl-D2)*(D1-Efl) to calculate the back focus offset value DisBlf, where Efl is the focal length of the camera module.

2. The camera module back focus offset testing method according to claim 1, characterized in that: In the above S1:, the position of the camera module is adjusted to achieve left-right and top-bottom symmetry in the imaging of the target of the parallel light tube in the camera module screen.

3. The camera module back focus offset testing method according to claim 2, characterized in that: The test frame comprises a column and a test platform, the column is provided with a connecting plate, the test platform is located below the connecting plate, the parallel light tube is fixed on the connecting plate, and the camera module and the image acquisition box are arranged on the test platform.

4. The camera module back focus offset testing method according to claim 3, characterized in that: The camera module and the image acquisition box are moved by being driven by a spatial displacement mechanism.

5. The camera module back focus offset testing method according to claim 3, characterized in that: The connecting plate is arranged on the column through a lifting and adjusting structure.

6. The camera module back focus offset testing method according to claim 5, characterized in that: The lifting and adjusting structure comprises a frame plate fixed on a column, a sliding rod and an adjusting screw rotatably matched with the frame plate are arranged on the frame plate, and the connecting plate is slidably matched with the sliding rod and threadably matched with the adjusting screw.

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