CN114813051A

CN114813051A - Lens assembly method, device and system based on inverse projection MTF detection

Info

Publication number: CN114813051A
Application number: CN202210426122.1A
Authority: CN
Inventors: 李长明; 李亮; 郭崇波; 李旦
Original assignee: Jiangxi Lianyi Optics Co Ltd
Current assignee: Jiangxi Lianyi Optics Co Ltd
Priority date: 2022-04-21
Filing date: 2022-04-21
Publication date: 2022-07-29

Abstract

The invention provides a lens assembly method, device and system based on inverse projection MTF detection. The lens assembly method includes: placing the first lens group and the second lens group which are subjected to the preliminary alignment of the optical axes at a preset position in the inverse projection MTF detection device; detecting by a back projection MTF detection device to obtain a modulation transfer function curve group of the first lens group and the second lens group at a preset position, wherein the modulation transfer function curve group comprises an off-axis modulation transfer function curve and an on-axis modulation transfer function curve; directionally adjusting the postures of the first lens group and/or the second lens group according to the modulation transfer function curve group; and adjusting the relative position of the first lens group relative to the second lens group in a plane perpendicular to the optical axis so as to improve the coincidence ratio of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve. The lens assembling method has the advantages that: the optimal relative pose among the mirror groups can be quickly and accurately found, and the product assembly yield can be effectively improved.

Description

Lens assembly method, device and system based on inverse projection MTF detection

Technical Field

The present invention relates to the field of lens assembly technologies, and in particular, to a lens assembly method, device and system based on inverse projection MTF detection.

Background

When an optical lens with a plurality of lenses is assembled, the higher the coincidence degree of the optical axes of the lenses is, the higher the imaging quality of the finished lens is.

In order to ensure the imaging quality of finished lenses and improve the assembly yield of lenses, there is a lens assembly method that continuously adjusts the relative pose between two lens groups during the assembly process of the two lens groups, detects the imaging quality of the two lens groups in various relative poses by using a Modulation Transfer Function (MTF) detection device, selects the best relative pose with the best imaging quality from the relative poses, and fixes the two lens groups after adjusting to the best relative pose. The lens assembling method needs to seek the optimal relative pose from a plurality of relative poses, and basically belongs to blind adjustment and blind measurement; in addition, because the relative poses between the two lens groups are various, in the process of seeking the optimal relative pose, a large amount of time is consumed for adjusting the relative poses of the two lens groups and carrying out data recording and comparison, and the assembly efficiency is low.

The statements in the background section are merely prior art as they are known to the inventors and do not, of course, represent prior art in the field.

Disclosure of Invention

The invention provides a lens assembly method, a device and a system based on inverse projection MTF detection, and aims to solve the problem of low assembly efficiency in the existing lens assembly method.

In order to solve the technical problems, the invention adopts the following technical scheme: a lens assembly method based on inverse projection MTF detection, the lens comprising a first lens group and a second lens group, the lens assembly method comprising:

placing the first lens group and the second lens group which are subjected to the preliminary alignment of the optical axes at a preset position in the inverse projection MTF detection device;

detecting by a reverse projection MTF detection device to obtain a modulation transfer function curve group of the first mirror group and the second mirror group at a preset position, wherein the modulation transfer function curve group comprises an off-axis modulation transfer function curve and an on-axis modulation transfer function curve;

directionally adjusting the postures of the first lens group and/or the second lens group according to the modulation transfer function curve group; and

and adjusting the relative position of the first lens group relative to the second lens group in a plane perpendicular to the optical axis so as to improve the coincidence ratio of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve.

According to an aspect of the invention, wherein the set of modulation transfer function curves comprises a set of off-axis modulation transfer function curves measured at least three locations under the same off-axis field of view and an on-axis modulation transfer function curve measured under a central field of view, respectively.

According to an aspect of the invention, wherein the at least three positions under the same off-axis field of view are at least three equally spaced positions under the same off-axis field of view.

According to one aspect of the invention, the back-projection MTF detection device comprises a reticle mask arranged at an image surface position and an image sensor arranged at an object surface position, wherein the image sensors are arranged in one and adjustable in position or in multiple;

the step of detecting the modulation transfer function curve group comprises the following steps:

controlling the reticle mask to gradually move towards the direction close to or away from the lens by a preset step pitch; after the reticle mask moves by one step distance every time, measuring on-axis MTF values through the image sensor, and measuring off-axis MTF values at the at least three positions;

generating an on-axis modulation transfer function curve according to the distance between the reticle mask and the lens and the on-axis MTF value;

and generating at least three off-axis modulation transfer function curves according to the distance between the reticle mask and the lens and the off-axis MTF value at each position.

According to an aspect of the present invention, wherein said step of directionally adjusting the pose of said first set of lenses and/or said second set of lenses comprises:

determining the inclination angle of the first lens group relative to the second lens group according to the off-axis modulation transfer function curve group;

and quantitatively inclining and leveling the first lens group and/or the second lens group in the opposite direction according to the inclination angle.

According to an aspect of the present invention, wherein the step of determining the tilt angle of the first lens group with respect to the second lens group comprises:

taking the coordinates of the projections of the at least three positions in a plane perpendicular to the optical axis as coordinate values of an X axis and a Y axis in a space coordinate system, taking an abscissa corresponding to the peak value of the off-axis modulation transfer function curve at each position as a Z axis coordinate value in the space coordinate system, and obtaining at least three space points corresponding to the at least three positions;

fitting an initial plane according to the at least three space points;

and taking an included angle between the initial plane and a plane perpendicular to the optical axis as an inclination angle of the first lens group relative to the second lens group.

quantitatively inclining and leveling the first lens group and/or the second lens group step by step according to the opposite direction of the inclination direction;

after the first lens group and/or the second lens group are leveled once quantitatively, an off-axis modulation transfer function curve and an on-axis modulation transfer function curve of the first lens group and the second lens group are measured through the inverse projection MTF detection device, if the coincidence degree of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve is high, quantitative inclination leveling in the same direction is continued, and if the coincidence degree is low, the direction of inclination leveling is changed until the coincidence degree meets a first preset condition.

According to an aspect of the present invention, the step of adjusting the relative position of the first lens group with respect to the second lens group comprises:

the method comprises the steps that a first lens group and/or a second lens group are/is translated step by step in a plane perpendicular to an optical axis, after the first lens group and/or the second lens group are translated once, off-axis modulation transfer function curves and on-axis modulation transfer function curves of the first lens group and the second lens group are detected, if the coincidence degree of the off-axis modulation transfer function curves and the on-axis modulation transfer function curves is high, the off-axis modulation transfer function curves and the on-axis modulation transfer function curves continue to move in the same direction, and if the coincidence degree is low, the off-axis modulation transfer function curves and the on-axis modulation transfer function curves move in the opposite direction until the coincidence degree meets a second preset condition; and the second preset condition is superior to the index of the first preset condition.

According to an aspect of the present invention, the lens assembling method further includes fixing the first lens group and the second lens group;

the step of fixing the first lens group and the second lens group comprises:

synchronously moving the first lens group and the second lens group to a dispensing device;

dispensing the mounting surfaces of the first lens group and the second lens group through the dispensing device;

and curing the glue through a curing device.

According to an aspect of the present invention, the lens assembling method further includes: and moving the fixed first mirror group and the second mirror group to a preset position in the inverse projection MTF detection device, and detecting the coincidence ratio of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve of the fixed first mirror group and the second mirror group through the inverse projection MTF detection device so as to determine whether the imaging quality of the fixed first mirror group and the second mirror group is qualified.

According to an aspect of the present invention, the step of placing the first and second mirror groups after the preliminary alignment of the optical axes at predetermined positions in the inverse projection MTF detecting apparatus comprises:

clamping the first lens group and the second lens group by using two clamping devices respectively, wherein at least one clamping device is a six-axis clamping device;

performing primary optical axis alignment on the first lens group and the second lens group by adjusting the six-axis clamping device;

and moving the two clamping devices, and synchronously moving the first lens group and the second lens group which are subjected to the preliminary alignment of the optical axes to a preset position in the inverse projection MTF detection device.

According to an aspect of the invention, two of the clamping devices are a six-axis clamping device and a clamping device disposed on the reference plane, respectively.

According to an aspect of the present invention, there is also provided a lens assembly apparatus based on inverse projection MTF detection, the lens assembly apparatus including:

at least one processor; and

a memory coupled to the at least one processor;

wherein the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the steps of the lens assembly method described above.

According to an aspect of the present invention, there is also provided a lens assembling system based on inverse projection MTF detection, including:

the first clamping device is used for clamping a first lens group of the lens;

the second clamping device is used for clamping a second lens group of the lens;

the object to be imaged is positioned on the image side of the lens;

the image acquisition unit is positioned on the object side of the lens and can acquire an image formed by the object to be imaged through the lens; and

a controller in communication with the image acquisition unit and configured to determine an off-axis modulation transfer function curve and an on-axis modulation transfer function curve based on the image acquired by the image acquisition unit; the controller is configured to perform the lens assembling method according to any one of claims 1 to 12.

According to an aspect of the present invention, one of the first and second clamping devices is a six-axis clamping device, and the other is a clamping device provided on a reference plane.

Compared with the prior art, the lens assembly method, the lens assembly device and the lens assembly system based on the inverse projection MTF detection have at least one of the following beneficial effects: the optimal relative pose among the mirror groups can be quickly and accurately found, and the product assembly yield can be effectively improved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 shows a flow diagram of a lens assembly method in accordance with one embodiment of the invention;

FIG. 2 shows a schematic view of a back-projected MTF detection apparatus and a holding apparatus in accordance with an embodiment of the invention;

FIG. 3 is a diagram illustrating a set of modulation transfer function curves of a first lens group and a second lens group at predetermined positions according to an embodiment of the present invention;

FIG. 4 is a schematic diagram illustrating respective view dividing planes of a lens according to an embodiment of the invention;

fig. 5 is a schematic diagram showing respective view dividing planes of a lens according to another embodiment of the present invention.

In the figure: 100. a back projection MTF detection device; 110. scribing a photomask; 120. a dome; 130. a support; 141. an on-axis image sensor; 142. an off-axis image sensor; 210. a first lens group; 220. a second lens group; 310. a first holding device; 320. a second holding device; 330. a reference plane.

Detailed Description

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the description of the present invention, it should be noted that unless otherwise explicitly stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection, either mechanically, electrically, or in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature "on," "above" and "over" the second feature may include the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly above and obliquely above the second feature, or simply meaning that the first feature is at a lesser level than the second feature.

The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

Fig. 1 shows a flow diagram of a lens assembly method 10 based on backprojection MTF detection according to an embodiment of the present invention. FIG. 2 shows a schematic diagram of a back-projected MTF detection apparatus and a clamping apparatus according to one embodiment of the invention.

As shown in fig. 2, the lens barrel includes a first lens group 210 and a second lens group 220. The first lens group 210 and the second lens group 220 may be a single lens, or may be an incomplete lens formed by assembling a plurality of lenses, which is not limited in the embodiment. In a specific embodiment, the first lens group 210 and the second lens group 220 can be a glass lens group, a plastic lens group, or a glass-plastic mixed lens group.

As shown in fig. 1, the lens assembling method 10 includes the following steps, which are described in detail below, respectively.

At step S11: the first mirror group 210 and the second mirror group 220 after the preliminary alignment of the optical axes are placed at the predetermined positions in the inverse projection MTF detection apparatus 100.

In the assembling process, the first lens group 210 and the second lens group 220 can be placed in different postures and relative positions, for example, the plane of the lens can be in the horizontal direction, and the two lens groups are placed one above the other; or the plane of the lens is vertical, and the lens is placed in a left-right mode; alternatively, the lens assembly unit may be disposed in an inclined manner, and in a specific embodiment, the lens assembly unit may be disposed according to a setting requirement of a lens assembly station on a production line, which is not limited in this embodiment. For convenience of description, the first lens group 210 is illustrated above and the second lens group 220 is illustrated below.

In order to improve the assembly efficiency, the first lens group 210 and the second lens group 220 may be initially aligned with respect to the optical axis, and then placed at a predetermined position in the inverse projection MTF detection apparatus 100 with the relative pose of the initial alignment of the optical axis.

The preliminary alignment of the optical axes may be performed by temporarily defining the center of the lens group as the optical center of the lens group, placing the first lens group 210 on the top side, placing the second lens group 220 on the bottom side, wherein a connection line between the center of the first lens group 210 and the center of the second lens group 220 is perpendicular to the mounting reference planes of the first lens group 210 and the second lens group 220, and a distance set by the lens during design is maintained between the center of the first lens group 210 and the center of the second lens group 220. In the embodiment of fig. 2, the lens assembly is illustrated as including two lens groups, and those skilled in the art will readily understand that the lens assembly may include more lens groups, and the present invention is also applicable.

Specifically, as shown in fig. 2, the first lens group 210 is clamped by a first clamping device 310, and the second lens group 220 is clamped by a second clamping device 320, in a specific embodiment, the first and second clamping devices can be automatically adjusted to achieve the preliminary alignment of the optical axes of the first lens group 210 and the second lens group 220, or the two clamping devices can be manually operated to achieve the preliminary alignment of the optical axes, which is not limited in this embodiment. In a specific embodiment, the first lens group 210 and the second lens group 220 after the primary alignment of the optical axes can be synchronously placed at a predetermined position in the inverse projection MTF detection apparatus 100 by automatically adjusting the position of the holding apparatus.

It should be noted that at least one of the first clamping device 310 and the second clamping device 320 is a six-axis clamping device. The six-axis clamping device is a clamping device which can adjust the pose of a clamped object in the space by adjusting parameters of six degrees of freedom, and can be realized by adopting a conventional six-axis clamping device, and the six-axis clamping device is not limited in the embodiment; the six degrees of freedom are respectively a moving degree of freedom parameter along the direction of X, Y, Z three orthogonal coordinate axes (an X coordinate axis and a Z coordinate axis are shown in fig. 2, and the direction of a Y coordinate axis is vertical to the drawing surface) and a rotating degree of freedom parameter around the three coordinate axes, and the posture of the clamped object in the space can be changed by adjusting any one parameter of the six-axis clamping devices.

In a specific embodiment, when the first holding device 310 and the second holding device 320 are both six-axis holding devices 310, the relative pose between the first lens group 210 and the second lens group 220 can be adjusted each time by adjusting at least one degree-of-freedom parameter of at least one of the six-axis holding devices. When only one of the first holding device 310 and the second holding device 320 is a six-axis holding device, the relative pose between the first lens group 210 and the second lens group 220 can be adjusted by adjusting at least one degree-of-freedom parameter of the six-axis holding device each time; if the other holding device also has the capability of adjusting the pose of the lens sets, the relative pose between the first lens set 210 and the second lens set 220 can be adjusted by the holding device. In this embodiment, in order to improve the adjustment efficiency, the first holding device 310 for the first lens group 210 adopts a six-axis holding device; the second holding means 320 for the second lens group 220 is arranged on a reference plane 330, which can adjust the position of the object held by the second holding means arranged on the reference plane in space by adjusting three freedom parameters, wherein the three freedom parameters are the freedom parameters of movement along the directions of the three orthogonal coordinate axes X, Y, Z respectively. In the present embodiment, the relative pose between the first lens group 210 and the second lens group 220 can be adjusted by adjusting at least one degree of freedom parameter of the first holding device 310 (six-axis holding device) alone; the relative pose between the first lens group 210 and the second lens group 220 can also be adjusted by adjusting at least one degree of freedom parameter of the reference plane 330 alone; the relative pose between the first lens group 210 and the second lens group 220 can also be adjusted by simultaneously adjusting at least one degree of freedom parameter of the first holding device 310 and at least one degree of freedom parameter of the reference plane 330.

As shown in fig. 2, the backprojection MTF detection apparatus 100 includes a reticle mask 110, a dome 120 having a hemispherical shape, a holder 130 slidably mounted on the dome 120, and an image sensor mounted on the holder 130. Wherein, the reticle mask 110 has a pattern, such as a cross; the image sensors may be CCD (Charge Coupled Device) or CMOS (Complementary Metal-Oxide-Semiconductor), the image sensors correspond to the brackets 130 one by one, and the positions and the number of the image sensors and the brackets 130 may be configured according to actual requirements. In fig. 2, an on-axis image sensor 141 corresponding to the central field of view of the lens is shown, the on-axis image sensor 141 being used to measure the MTF value of the measured lens central field of view; also shown in fig. 2 is an off-axis image sensor 142 corresponding to the off-axis field of view for measuring the MTF value of the measured lens off-axis field of view.

The working principle of the back projection MTF detection apparatus 100 is to reverse the positions of the object and the image of the lens imaging system, dispose the reticle mask 110 (or other objects to be imaged) on the image plane of the measured lens, dispose the image sensor on the object plane of the measured lens, so as to obtain the MTF values of the central image field and/or the peripheral image field of the measured lens in the normal direction (S) and/or the tangential direction (T). The surface of the object space with clear focus is called the object surface, and the surface of the image space corresponding to the object surface is the image surface. In fig. 2, the reticle mask 110 is located on the image plane of the lens, and the image sensor is located on the object plane.

Before the back-projection MTF detection apparatus 100 operates, the reference plane 330, the reticle mask 110, and the on-axis image sensor 141 need to be coaxially disposed, and the process of disposing the reference plane, the reticle mask 110, and the on-axis image sensor 141 is as follows: the reference plane 330 is first placed at a predetermined position, the reference plane 330 is calibrated by the level, the reticle mask 110 is then adjusted to be perpendicular to the reference plane 330 by the collimator, and the on-axis image sensor 141 is adjusted to be perpendicular to the reference plane 330 and located directly above the reticle mask 110. The reference plane 330 is calibrated by the level so that the second lens group 220 is kept horizontal after the second lens group 320 is placed on the reference plane 330 and fixed by the second holding means 320.

For example, when the back projection MTF detection apparatus 100 includes a plurality of image sensors, the preset position may be a light path convergence point of each image sensor, and the placing of the first lens group 210 and the second lens group 220 after the optical axis is initially aligned at the preset position may specifically be in a relative posture where the optical axis is initially aligned, so that the optical center of the integral lens formed by the first lens group 210 and the second lens group 220 coincides with the light path convergence point of each image sensor. When the dome 120 is a spherical surface, the optical center of the integrated lens composed of the first lens group 210 and the second lens group 220 may be located at the center of the spherical surface.

At step S12: the modulation transfer function curve sets of the first mirror group 210 and the second mirror group 220 at the predetermined positions are obtained by detecting with the inverse projection MTF detecting apparatus 100.

It should be noted that the vertical axis of the modulation transfer function curve is the MTF value, the horizontal axis may be the defocus offset, the distance between the reticle mask 110 and the lens (e.g. the second lens group 220), or the flange focal length, and in this embodiment, the horizontal axis of the modulation transfer function curve adopts the defocus offset.

Regarding the acquisition of the modulation transfer function curve, a plurality of image sensors may be configured in the back-projection MTF detection apparatus 100 for acquiring images of the reticle mask 110, and the back-projection MTF detection apparatus 100 may include an image processing apparatus (not shown) that communicates with the image sensors to acquire images acquired by the respective sensors, and calculates MTF values according to the acquired images and acquires a plurality of modulation transfer function curves, specifically, the reticle mask 110 may be controlled to move gradually toward or away from the lens according to a preset step pitch; after the reticle mask 110 moves by one step distance, images are collected at respective positions through a plurality of image sensors, and an MTF value is measured by an image processing device according to collected image information; the MTF values measured by the same image sensor are then fitted to a modulation transfer function curve. Of course, an image sensor with an adjustable position may be configured in the back-projection MTF detection apparatus 100 to measure a plurality of modulation transfer function curves, specifically, the reticle mask 110 may be controlled to move gradually toward or away from the lens according to a preset step; after the reticle mask 110 moves by one step distance, measuring MTF values at different positions through the position-adjustable image sensor; the MTF values measured at the same position by the position-adjustable image sensor are then fitted to a modulation transfer function curve. For the sake of easy distinction, the modulation transfer function curve measured by the on-axis image sensor 141 is referred to as an on-axis modulation transfer function curve, and the modulation transfer function curve measured by the off-axis image sensor 142 is referred to as an off-axis modulation transfer function curve.

As shown in fig. 3, the set of modulation transfer function curves includes an on-axis modulation transfer function curve measured at a central field of view and off-axis modulation transfer function curves measured at least three locations under the same off-axis field of view (the graph includes four off-axis modulation transfer function curves measured at four locations under the same off-axis field of view). Wherein the off-axis field of view may be a field of view of interest for production or assembly, such as 0.3 field of view, 0.5 field of view, 0.8 field of view, etc.; the number of the off-axis modulation transfer function curves can be selected according to actual needs, but at least three off-axis modulation transfer function curves are provided, and the more the number of the off-axis modulation transfer function curves in the modulation transfer function curve group is, the more the yield of lens assembly is improved; the at least three positions may be at least three equally spaced positions in the same off-axis field of view, or may be any three positions in the same off-axis field of view, and relatively speaking, setting the at least three positions to be at least three equally spaced positions in the same off-axis field of view is more convenient for subsequent calculation.

Specifically, as shown in fig. 4, in the present embodiment, the back-projection MTF detection apparatus 100 is configured to have one on-axis image sensor 141 and four off-axis image sensors 142 of the same field of view, wherein the four off-axis image sensors 142 are arranged at four equally spaced positions under 0.3 field of view; thus, the set of measured modulation transfer function curves comprises the off-axis modulation transfer function curves measured at four equally spaced locations under the 0.3 field of view. In other embodiments, the inverse projection MTF detection apparatus 100 can also be configured to have one on-axis image sensor 141 and a plurality of off-axis image sensors 142, and the plurality of off-axis image sensors 142 can be arranged at different positions under a plurality of off-axis fields of view to acquire the off-axis modulation transfer function curves of the lens at different positions under different off-axis fields of view. For example, in the embodiment shown in FIG. 5, the backprojection MTF detection apparatus 100 has one on-axis image sensor 141 and four off-axis image sensors 142 each located in a field of view of 0.3 and four off-axis image sensors 142 each located in a field of view of 0.5.

As shown in fig. 1, the lens assembling method further includes step S13: the pose of first mirror group 210 and/or second mirror group 220 is directionally adjusted according to the set of modulation transfer function curves.

The on-axis modulation transfer function curve can be used for evaluating the imaging quality of the imaging center of the tested lens, and the off-axis modulation transfer function can be used for evaluating the imaging quality of each point of the peripheral image field of the tested lens group. In an ideal state, when the optical axis of the first lens group 210 completely coincides with the optical axis of the second lens group 220, the peak values of the off-axis modulation transfer function curves of the first lens group 210 and the second lens group 220 are the same or close to each other, the abscissa values corresponding to the peak values of the off-axis modulation transfer function curves of the first lens group 210 and the second lens group 220 are the same or close to each other, at this time, the coincidence degree of the off-axis modulation transfer function curves of the first lens group 210 and the second lens group 220 with the on-axis modulation transfer function curves is also the highest, and the imaging effect and quality of the lens are also the best.

Two deviation components may occur between the optical axis of the first lens group 210 and the optical axis of the second lens group 220, where the first deviation component is a posture deviation therebetween, that is, the optical axis of the first lens group 210 and the optical axis of the second lens group 220 are not parallel to each other but form a certain angle; the second type of deviation component is the misalignment of the optical centers of the two, i.e., spaced from each other in a plane perpendicular to the optical axis. Both of the two deviation components cause a larger deviation (i.e., a lower coincidence degree) between the off-axis modulation transfer function curve and the on-axis modulation transfer function curve, thereby affecting the imaging effect of the lens.

In step S13, the postures of the first lens group 210 and/or the second lens group 220 may be directionally adjusted according to the modulation transfer function curve group obtained in step S12, so as to correct the posture deviation therebetween as much as possible. For example, the deflection direction of first lens group 210 relative to second lens group 220 can be roughly confirmed according to the modulation transfer function curve set, and then the postures of first lens group 210 and/or second lens group 220 can be reversely adjusted to reduce the posture deviation of first lens group 210 relative to second lens group 220.

As shown in fig. 2, the second holding device 320 is disposed on the reference plane 330, which fixes the second lens group 220. The first holding device 310 is a six-axis holding device, and the second holding device 320 cannot adjust the rotational degree of freedom around the coordinate axis, so that the angle of the first lens group 210 can be adjusted by the first holding device 310, and the optical axes of the first lens group 210 and the second lens group 220 are parallel as much as possible, so as to improve the contact ratio between the off-axis modulation transfer function curve and the on-axis modulation transfer function curve. An adjustment method according to an embodiment of the present invention will be described below.

In step S14, the relative position of the first mirror group 210 with respect to the second mirror group 220 in the plane perpendicular to the optical axis is adjusted to improve the coincidence ratio between the off-axis modulation transfer function curve and the on-axis modulation transfer function curve.

According to an embodiment of the present invention, the relative position of the first lens group 210 with respect to the second lens group 220 in a plane perpendicular to the optical axis can be adjusted by the first holding device 310 and/or the second holding device 320, in the orientation shown in fig. 2, such that the optical axis of the first lens group 210 is aligned with the optical axis of the second lens group 220 as much as possible.

In this embodiment, the imaging quality of the lens is measured by measuring and calculating the contact ratio between the off-axis modulation transfer function curve and the on-axis modulation transfer function curve of the lens. The higher the coincidence ratio of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve of the first mirror group 210 and the second mirror group 220 in one relative pose indicates that the imaging quality of the first mirror group 210 and the second mirror group 220 in the relative pose is higher.

There are various ways to determine the coincidence degree of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve of the lens. For example: judging by the total distance of the difference between the abscissa value corresponding to the peak value of each off-axis modulation transfer function curve and the abscissa value corresponding to the peak value of the on-axis modulation transfer function curve in the same off-axis field, wherein the smaller the total distance of the difference, the higher the contact ratio; or the discreteness between the abscissa value corresponding to the peak value of the off-axis modulation transfer function curve and the abscissa value corresponding to the peak value of the on-axis modulation transfer function curve is calculated to determine, and the smaller the discreteness, the higher the contact ratio. The manner of determining the overlap ratio between the off-axis modulation transfer function curve and the on-axis modulation transfer function curve is shown only by way of example in this embodiment, and is not limited thereto.

The specific manner of performing step S13 according to a preferred embodiment of the present invention is described below. From the set of modulation transfer function curves, the tilt angle of the first mirror group 210 with respect to the second mirror group 220 can be determined. Specifically, the coordinates of the projections of the positions of the four off-axis image sensors 142 on the same off-axis field in the plane perpendicular to the optical axis are taken as the coordinate values of the X axis and the Y axis in the space coordinate system; the abscissa corresponding to the peak of the off-axis modulation transfer function curve measured by each off-axis image sensor 142 is taken as the Z-axis coordinate value in the space coordinate system, and four space points corresponding to the positions of the four off-axis image sensors 142 are obtained. An initial plane is fitted according to the four spatial points, and an included angle between the initial plane and a plane perpendicular to the optical axis is taken as an inclination angle of the first lens group 210 relative to the second lens group 220.

The first lens group 210 and/or the second lens group 220 are quantitatively tilted and leveled according to the tilt angle of the first lens group 210 relative to the second lens group 220, so as to improve the coincidence ratio of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve. Specifically, the tilt angle represents the tilt direction and tilt magnitude of the first lens group 210 relative to the second lens group 220, and the first lens group 210 and/or the second lens group 220 are quantitatively tilted and leveled step by step at a certain angle according to the opposite direction of the tilt direction of the first lens group 210 relative to the second lens group 220; in this embodiment, the attitude of the first lens group 210 is adjusted by gradually adjusting the rotational degree of freedom parameters of the six-axis clamping device 310, so as to achieve the purpose of gradually and quantitatively leveling the tilt.

In the gradual quantitative inclination leveling process, after the first lens group 210 is leveled once quantitatively, an off-axis modulation transfer function curve and an on-axis modulation transfer function curve of the first lens group 210 and the second lens group 220 at the relative pose are measured through an inverse projection detection device, the contact ratio of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve is judged, and if the contact ratio is high, the quantitative inclination leveling is continued in the same direction; if the coincidence degree becomes lower, the tilt leveling is performed in the direction opposite to the original leveling direction and the leveling angle is reduced each time until the coincidence degree meets the first preset condition, or if the coincidence degree becomes lower, the relative pose of the first lens group 210 and the second lens group 220 with the highest coincidence degree is restored.

In step S14, the relative position of the first mirror group 210 with respect to the second mirror group 220 in the plane perpendicular to the optical axis is adjusted to improve the coincidence ratio between the off-axis modulation transfer function curve and the on-axis modulation transfer function curve. In this embodiment, the relative position of the first lens group 210 with respect to the second lens group 220 in the plane perpendicular to the optical axis is adjusted by adjusting the two cartesian-axis-direction movement freedom parameters X, Y of the six-axis clamping device 310 to adjust the position of the first lens group 210 and/or adjusting the two cartesian-axis-direction movement parameters X, Y of the reference plane 330 to adjust the position of the second lens group 220.

Specifically, the moving degree of freedom parameter in the X-axis direction of the six-axis holding device 310 is adjusted quantitatively to adjust the position of the first lens group 210, and/or the moving degree of freedom parameter in the X-axis direction of the reference plane 330 is adjusted quantitatively to adjust the position of the second lens group 220, after the first lens group 210 and/or the second lens group 220 are translated once, the off-axis modulation transfer function curve and the on-axis modulation transfer function curve of the first lens group 210 and the second lens group 220 in the relative pose are measured by the inverse projection detection device, the degree of coincidence of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve is determined, if the degree of coincidence is high, the first lens group 210 and/or the second lens group 220 are continuously moved in the same direction, and if the degree of coincidence is low, the lens group is moved in the opposite direction, and the highest degree of coincidence in the X-axis direction is sought.

The position of the first lens group 210 is adjusted by quantitatively adjusting the motion freedom parameter in the Y-axis direction of the six-axis holding device 310, and/or the position of the second lens group 220 is adjusted by quantitatively adjusting the motion freedom parameter in the Y-axis direction of the reference plane 330, after the first lens group 210 and/or the second lens group 220 is translated once, the off-axis modulation transfer function curve and the on-axis modulation transfer function curve of the first lens group 210 and the second lens group 220 in the relative pose are measured by the inverse projection detection device, the coincidence degree of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve is determined, if the coincidence degree is higher, the first lens group 210 and/or the second lens group 220 are continuously moved in the same direction, if the coincidence degree is lower, the lens group is moved in the opposite direction, and the highest coincidence degree in the Y-axis direction is searched.

In the process of searching for the highest contact ratio in the X-axis direction and the highest contact ratio in the Y-axis direction, if the contact ratio is higher than the second preset condition, the continuous search for the higher contact ratio may be stopped, and the optimal relative pose of the first lens group 210 and the second lens group 220 is considered to be obtained; of course, the best relative poses of the first lens group 210 and the second lens group 220 can be obtained after the highest coincidence degree is found in both the X-axis direction and the Y-axis direction. It should be noted that the second preset condition is better than the index of the first preset condition.

According to an embodiment of the present invention, as shown in fig. 1, the lens assembling method further includes S15: the first lens group 210 and the second lens group 220 are fixed.

In the present embodiment, the first lens group 210 and the second lens group 220 are fixed by photo-curing after dispensing. Specifically, a dispensing device and a curing device are provided, and after the optimal relative poses of the first lens group 210 and the second lens group 220 are obtained, the two clamping devices are synchronously moved, so that the first lens group 210 and the second lens group 220 are synchronously moved to the dispensing device; the mounting surfaces of the first lens group 210 and the second lens group 220 are dispensed by a dispensing device, and the glue is cured by a curing device. The positions of the two holding devices can be automatically moved to synchronously move the first lens group 210 and the second lens group 220 to the dispensing device. Glue is optical glue, through the effect of pasting of glue, can guarantee that first mirror group 210 and second mirror group 220 are firmly pasted, compares in other pasting mode, and optical glue has avoided making absorption or shelter from light through first mirror group 210 and second mirror group 220 at light. The curing device may include an ultraviolet lamp, the irradiation direction of the ultraviolet lamp faces the butt-joint surface of the first lens group 210 and the second lens group 220, the curing speed of the glue between the first lens group 210 and the second lens group 220 can be increased by the ultraviolet lamp, the assembly can be completed as soon as possible, and the assembly efficiency can be increased.

According to a preferred embodiment of the present invention, as shown in fig. 1, the lens assembling method further includes S16: and inspecting the fixed lens.

In consideration of the fact that the imaging quality of the lens is not expected due to the shift of the relative pose of the first lens group 210 and the second lens group 220 and the error of dispensing in the curing process, in this embodiment, after the first lens group 210 and the second lens group 220 are fixed, the fixed first lens group 210 and second lens group 220 are moved to the preset position in the inverse projection MTF detection device 100 by synchronously moving the two holding devices, and the inverse projection MTF detection device 100 detects the coincidence degree of the off-axis modulation transfer function curves and the on-axis modulation transfer function curves of the fixed first lens group 210 and second lens group 220 to determine whether the imaging quality of the fixed first lens group 210 and second lens group 220 is expected. For example, if the calculated contact ratio is smaller than the second preset condition, it is determined that the cured first lens group 210 and the cured second lens group 220 are not qualified, and rework or other processes may be performed; on the contrary, if the calculated contact ratio is higher than the second predetermined condition, the solidified first lens group 210 and the solidified second lens group 220 are determined to be qualified.

Compared with the lens assembly method which continuously changes the relative poses of the two lens groups and measures the imaging quality of the lens at each relative pose to obtain the optimal relative pose, the lens assembly method provided by the embodiment of the invention adjusts the relative position of the first lens group 210 relative to the second lens group 220 in a plane perpendicular to the optical axis by directionally and quantitatively adjusting the poses of the first lens group 210 and/or the second lens group 220, so as to improve the overlap ratio of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve of the lens, further quickly and accurately find the optimal relative pose among the lens groups, and effectively improve the product assembly yield.

The embodiment of the invention also provides a lens assembling device based on the inverse projection MTF detection. The lens assembling device includes at least one processor and a memory connected with the at least one processor. Wherein the memory stores instructions executable by the at least one processor; the instructions are executable by the at least one processor to enable the at least one processor to perform the steps of the lens assembly method described above.

An embodiment of the present invention further provides a lens assembly system based on inverse projection MTF detection, as shown in fig. 2, the lens assembly system includes a first holding device 310, a second holding device 320, a reference plane 330, an object to be imaged 110, image capturing units 140 and 142, and a controller. Wherein, the first holding device 310 is used for holding the first lens group 210, the second holding device 320 is used for holding the second lens group 220, and the first holding device 310 and the second holding device 320 can respectively select a six-axis holding device 310 or a holding device arranged on the reference plane 330 according to actual situations; the object to be imaged 110 is located on the image side of the lens, and a reticle mask 110 can be selected; the image acquisition unit is positioned on the object side of the lens and can be selected to be a plurality of image sensors or an image sensor with a movable position according to actual conditions; the controller is in communication with the image acquisition unit, the controller is configured to determine an off-axis modulation transfer function curve and an on-axis modulation transfer function curve based on the image acquired by the image acquisition unit, and the controller may perform the lens assembly method described above.

According to an aspect of the present invention, one of the first and second clamp devices is a six-axis clamp device, and the other is a clamp device disposed on a reference plane.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A lens assembly method based on inverse projection MTF detection, the lens comprising a first lens group and a second lens group, the lens assembly method comprising:

detecting and obtaining a modulation transfer function curve group of the first mirror group and the second mirror group at a preset position through a back projection MTF detection device, wherein the modulation transfer function curve group comprises an off-axis modulation transfer function curve and an on-axis modulation transfer function curve;

2. The lens assembly method of claim 1, wherein the set of modulation transfer function curves includes a set of off-axis modulation transfer function curves measured at least three locations under the same off-axis field of view and an on-axis modulation transfer function curve measured under one central field of view, respectively.

3. The lens assembly method of claim 2, wherein the at least three positions in the same off-axis field of view are at least three equally spaced positions in the same off-axis field of view.

4. The lens assembly method according to claim 2 or 3, wherein the back-projection MTF detection device comprises a reticle mask disposed at an image plane position and an image sensor disposed at an object plane position, the image sensors being disposed in one and adjustable in position or in plurality;

5. The lens assembly method according to claim 4, wherein the step of directionally adjusting the posture of the first lens group and/or the second lens group comprises:

6. The lens assembling method according to claim 5, wherein the step of determining the tilt angle of the first lens group with respect to the second lens group comprises:

fitting an initial plane according to the at least three space points;

7. The lens assembly method of claim 5, wherein the step of directionally adjusting the pose of the first lens group and/or the second lens group comprises:

and quantitatively inclining and leveling the first lens group and/or the second lens group step by step according to the opposite direction of the inclination direction until the contact ratio meets a first preset condition.

8. The lens assembling method according to claim 1, wherein the step of adjusting the relative position of the first lens group with respect to the second lens group comprises:

9. The lens assembling method according to claim 1, further comprising fixing the first lens group and the second lens group;

the step of fixing the first lens group and the second lens group comprises:

synchronously moving the first lens group and the second lens group to a glue dispensing device;

and curing the glue through a curing device.

10. The lens assembling method of claim 9, further comprising:

and moving the fixed first mirror group and the second mirror group to a preset position in the inverse projection MTF detection device, and detecting the coincidence ratio of the off-axis modulation transfer function curve and the on-axis modulation transfer function curve of the fixed first mirror group and the second mirror group through the inverse projection MTF detection device so as to determine whether the imaging quality of the fixed first mirror group and the second mirror group is qualified.

11. The lens assembly method of claim 1, wherein the step of placing the first and second mirror groups after the preliminary alignment of the optical axes at the predetermined positions in the inverse projection MTF detection apparatus comprises:

respectively clamping the first lens group and the second lens group by using two clamping devices, wherein at least one clamping device is a six-axis clamping device;

12. The lens assembling method according to claim 11, wherein the two holding devices are a six-axis holding device and a holding device provided on a reference plane, respectively.

13. A lens assembly apparatus based on inverse projection MTF detection, the lens assembly apparatus comprising:

at least one processor; and

a memory coupled to the at least one processor;

wherein the memory stores instructions executable by the at least one processor to enable the at least one processor to perform the steps of the lens assembly method of any one of claims 1 to 12.

14. A lens assembly system based on inverse projection MTF detection, comprising:

the first clamping device is used for clamping a first lens group of the lens;

the object to be imaged is positioned on the image side of the lens;

15. The lens assembling system according to claim 14, wherein one of the first and second holding devices is a six-axis holding device, and the other is a holding device provided on a reference plane.