How to adjust focus

Abstract

A method for adjusting the focus of a camera module (20) comprising: an adjustment step for adjusting the position and angle of a camera substrate (50) with respect to an optical system (30); an assembling step, after the adjustment by the adjustment step, for fixing the camera substrate to the optical system by thermally curing an adhesive in a state where the optical system is attached to the camera substrate by the adhesive; and a prediction step for predicting a contraction deviation amount (E100) caused by the approach of the optical system and the camera substrate after the adjustment by the adjustment step and before the fixing of the camera substrate in the assembling step is completed. The prediction step is performed before the adjustment step, and in the adjustment step, the camera substrate is moved away from the optical system by the shrinkage deviation amount, as compared with the in-focus state, so as to cancel the shrinkage deviation amount predicted by the prediction step.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2021-207023 filed on December 21, 2021, the contents of which are incorporated herein by reference. [Technical field]

[0002] The present disclosure relates to a camera focus adjustment method. [Background technology]

[0003] Traditionally, vehicles have come to be equipped with multiple camera modules, which has led to an increase in the demand for camera modules. Camera modules mainly use CCD sensors or CMOS sensors. For such camera modules, it is necessary to perform proper focus adjustment, which adjusts the mounting position of the image sensor relative to the lens.

[0004] Although there are cases where focus adjustment is performed manually by visual inspection, there are variations in accuracy and the work is time-consuming and laborious, so in recent years, focus adjustment is often performed automatically (for example, Patent Documents 1 to 3). According to Patent Documents 1 to 3, it has become possible to reduce the work time without reducing the accuracy of focus adjustment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-267923 A [Patent Document 2] JP 2009-3152 A [Patent Document 3] JP 2008-171866 A Summary of the Invention

[0006] Incidentally, when a lens module is fixed to a camera board on which an image sensor is mounted, a thermosetting adhesive is generally used, and the adhesive is heated and hardened. During this process, the components constituting the camera module expand and contract due to heat, and the adhesive shrinks due to thermal hardening. Therefore, when the adhesive is thermally hardened after adjusting the position of the image sensor relative to the lens, a deviation occurs in the positional relationship between the lens and the image sensor. As a result, it has been difficult to assemble with high accuracy.

[0007] The present disclosure has been made in consideration of the above circumstances, and has an object to provide a focus adjustment method that enables assembly of an image sensor with high accuracy.

[0008] A focus adjustment method for solving the above problem is a focus adjustment method for a camera module including an optical system, an image sensor, and a camera board on which the image sensor is mounted, the focus adjustment method including: an adjustment step of adjusting a position and angle of the camera board relative to the optical system by a position adjustment device; an assembly step of assembling the optical system and the camera board with an adhesive based on the adjusted position and angle after the adjustment by the adjustment step; and a prediction step of predicting an amount of shrinkage misalignment that will occur when the optical system and the camera board get closer to each other after adjustment by the adjustment step and before the adhesive is thermally cured to fix the optical system and the camera board in the assembly step, wherein the prediction step is performed before the adjustment step, and in the adjustment step, the position and angle of the camera board relative to the optical system are adjusted so as to offset the amount of shrinkage misalignment predicted by the prediction step.

[0009] In this way, after adjusting the position and angle of the image sensor, the amount of shrinkage deviation that occurs when the optical system and the camera board get closer to each other before the thermal curing is completed is predicted, and the position and angle are adjusted so that the camera board is moved away from the optical system by a distance equivalent to the amount of shrinkage deviation. This makes it possible to offset the amount of shrinkage deviation and assemble the image sensor with high accuracy. [Brief description of the drawings]

[0010] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 is an exploded perspective view of a camera; [Diagram 2] FIG. 2 is a conceptual diagram of a camera module; [Diagram 3] FIG. 3 is a block diagram showing a configuration of a focus adjustment system; [Figure 4] FIG. 4 is a conceptual diagram showing a mode of transport of a camera board; [Diagram 5] FIG. 5 is a conceptual diagram showing an adjustment mode of the camera board; [Figure 6] FIG. 6 is a conceptual diagram showing how an image sensor captures an image of a cross light source. [Figure 7] FIG. 7A is a conceptual diagram of a cross light source in an imaging region, and FIG. 7B is a conceptual diagram of a cross light source in a scanning region. [Figure 8] FIG. 8 is a diagram showing an example of an MTF curve; [Figure 9] FIG. 9 is a conceptual diagram showing the depth of focus; [Figure 10] FIG. 10 is a diagram showing an example of an MTF curve in a focused state; [Figure 11] FIG. 11 is a conceptual diagram showing a laser light irradiation mode; [Figure 12] FIG. 12 is a flowchart of the focus adjustment process. [Figure 13] FIG. 13 is a conceptual diagram showing the process of thermal expansion and associated contraction during temporary curing. [Figure 14] FIG. 14 is a flowchart of a prediction process; [Figure 15] FIG. 15 is a conceptual diagram for explaining the separation distance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, multiple embodiments of the "focus adjustment method" according to the present disclosure will be described with reference to the drawings. In the present embodiment, the direction parallel to the optical axis is defined as the Z direction, the vertical direction (up and down direction) perpendicular to the Z direction is defined as the X direction, and the horizontal direction (left and right direction) is defined as the Y direction.

[0012] As shown in Fig. 1, a camera 10 is equipped with a lens-equipped CMOS camera module (hereinafter, simply referred to as camera module 20). As shown in Fig. 2, the camera module 20 includes a lens module 30 as an optical system, an image sensor 40, and a camera board 50 on which the image sensor 40 is mounted. The image sensor 40 is an imaging element such as CMOS. The camera module 20 is configured by fixing the lens module 30 to the camera board 50. The lens module 30 is fixed to the camera board 50 via an adhesive (thermosetting adhesive) 70.

[0013] Next, a description will be given of the focus adjustment system 100. As shown in Fig. 3, the focus adjustment system 100 includes a six-axis stage 110 as a position adjustment device, a conveyance device 120, a distance measurement sensor 130, a calculation device 140, and a laser 150 capable of emitting laser light.

[0014] The six-axis stage 110 includes a mechanism for changing the position and inclination of the camera board 50 on which the image sensor 40 is mounted. In this embodiment, the six-axis stage 110 can adjust the position in the X, Y, and Z directions, and adjust the roll, yaw, and pitch angles (six axes in total).

[0015] The transport device 120 transports the six-axis stage 110 on which the camera board 50 is installed. As shown in Fig. 4, the transport device 120 transports the six-axis stage 110 together with the camera board 50 until the image sensor 40 of the camera board 50 reaches a position facing the lens of the lens module 30.

[0016] The distance measuring sensor 130 measures the installation distance and installation angle of the image sensor 40 on the camera board 50 being transported by the transport device 120. That is, the image sensor 40 is fixed to the camera board 50 by adhesive, soldering, or the like, but some error may occur depending on the assembly accuracy. Therefore, the state (installation distance and installation angle) in which the image sensor 40 is fixed on the camera board 50 is measured. The distance measuring sensor 130 measures the installation distance and installation angle of the image sensor 40 based on a predetermined reference point. Specifically, the distance measuring sensor 130 measures the position in the X direction, Y direction, and Z direction, as well as the roll angle, yaw angle, and pitch angle. The reference point is, for example, a point that is predetermined on the camera board 50.

[0017] The arithmetic device 140 includes a CPU, RAM, ROM, etc., and executes programs stored in the ROM to realize various functions. Also, the arithmetic device 140 includes various input / output devices, and is configured to be able to input various instructions and output results. As shown in Fig. 3, the arithmetic device 140 is connected to the six-axis stage 110, the conveying device 120, the distance measuring sensor 130, and the laser 150, and is configured to be able to input and output various signals. The various signals include, for example, an instruction signal that notifies an instruction and a measurement signal that notifies a measurement result.

[0018] The arithmetic device 140 has various functions, for example, a function as a transport unit 141, a function as a measurement unit 142, a function as an adjustment unit 143, a function as a focal point identification unit 144, and a function as an assembly unit 145. Note that it is not necessary for one arithmetic device 140 to have all the functions, and the functions may be shared among multiple arithmetic devices.

[0019] The arithmetic device 140 as the transport unit 141 controls the transport device 120 so that the camera board 50 and the six-axis stage 110 are transported until the image sensor 40 reaches a position facing the lens of the lens module 30 .

[0020] The arithmetic device 140 as the measurement unit 142 controls the distance measurement sensor 130 to measure the installation position and installation angle of the image sensor 40 on the camera board 50 during transportation.

[0021] The arithmetic device 140 as the adjustment unit 143 controls the six-axis stage 110 to adjust the position and angle of the camera substrate 50 relative to the lens module 30. Specifically, as shown in Fig. 5, after the six-axis stage 110 is transported by the transport device 120, the adjustment unit 143 adjusts the position and angle of the image sensor 40 relative to the lens module 30 to an optimal position and optimal angle, taking into account the installation position and installation angle of the image sensor 40 measured by the measurement unit 142. The optimal position and optimal angle respectively correspond to the setting position and setting angle predetermined by the lens module 30.

[0022] The optimum position and angle are determined in advance by the lens module 30 so that the image sensor 40 will be substantially in focus when the image sensor 40 is installed at the optimum position and angle. The optimum position and angle are measured in advance by the manufacturer of the lens module 30, as shown by the dashed line in FIG. 4. The adjustment unit 143 adjusts the position and angle of the image sensor 40 relative to the lens module 30 to the optimum position and angle. As described above, there may be a deviation in the installation position and installation angle of the image sensor 40 installed on the camera board 50, and the position and angle of the camera board 50 are adjusted taking this error into consideration.

[0023] The optimum position and the optimum angle are generally determined by selecting and measuring several of the completed lens modules 30, and using the average value. Alternatively, the optimum position and the optimum angle may be calculated by calculation from a design drawing or the like. For this reason, some manufacturing error may occur depending on the lens module 30. In other words, even if the position and angle of the image sensor 40 are adjusted to be the optimum position and the optimum angle, the image sensor 40 may not be in focus.

[0024] Therefore, the arithmetic device 140, which functions as the in-focus point specifying unit 144, causes the image sensor 40 to capture an image of a chart placed at a predetermined position via the lens module 30, and analyzes the captured image data to specify the assembly state of the image sensor 40 that results in the in-focus point. This will be described in detail below.

[0025] In this embodiment, as shown in FIG. 6, a sheet (e.g., black paper) with a cross slit is placed over the light source 61, and light is irradiated from the light source 61 to the camera module 20, thereby generating a cross light source 60 as a chart image, as shown in FIG. 7. That is, the cross light source (cross slit light) 60 generated by passing through the cross slit of the sheet becomes the chart image. The cross light sources 60 are generated at a plurality of locations, each of which is disposed at a predetermined position. For example, as shown in FIG. 7, the cross light sources 60 are disposed at five locations, namely, the center, upper right, lower right, upper left, and lower left, of an imaging area 63 in which the camera module 20 can capture an image.

[0026] The arithmetic device 140, functioning as the in-focus point identification unit 144, causes the image sensor 40 to capture an image of each cross light source 60 via the lens module 30, and analyzes the captured image data to calculate the MTF curve of each cross light source 60. The MTF (Modulation Transfer Function) curve is one of the indices for evaluating lens performance, and represents the degree to which the contrast of the subject (chart image) can be faithfully reproduced as a spatial frequency characteristic in order to know the imaging performance of the lens.

[0027] Specifically, the calculation device 140 captures images of each cross light source 60 at multiple positions in the Z axis direction (Z axis positions), analyzes the captured image data of each cross light source 60, and calculates an MTF value (%) that corresponds to contrast. Note that when calculating the MTF value, the calculation distinguishes between the vertical (X direction) slits and the horizontal (Y direction) slits in each cross light source 60. For this reason, in this embodiment, a total of 10 MTF values ​​are calculated at each Z axis position.

[0028] Then, after moving and scanning the camera board 50 within a predetermined scanning range, the calculation device 140 plots the calculated MTF values ​​on a coordinate system with the vertical axis representing the MTF value and the horizontal axis representing the Z-axis position, and calculates an MTF curve by connecting the calculated MTF values. In this embodiment, a total of 10 MTF values ​​are calculated at each Z-axis position, so that a total of 10 MTF curves are calculated, as shown in FIG.

[0029] After obtaining the ten MTF curves, as shown in FIG. 9, the arithmetic device 140 calculates values ​​for correcting the position and inclination of the image sensor 40 so that the focal depth is maximized when the MTF value is a value (e.g., 35%) that is predetermined in the product standard. Specifically, the apexes of the MTF curves are moved closer to each other so that the distance corresponding to the focal depth shown in FIG. 9 is maximized. Then, as shown in FIG. 10, when the focal depth is maximized, the movement amount in the Z-axis direction of each MTF curve is calculated, and from each movement amount, the correction values ​​of each position in the X-axis direction, the Y-axis direction, and the X-axis direction, and the correction values ​​of each angle of the roll angle, the yaw angle, and the pitch angle are calculated. Then, the arithmetic device 140 specifies the assembly state of the image sensor 40 that is the focal point based on the calculated position and angle correction values. After that, as shown in FIG. 6, the arithmetic device 140 adjusts the position and angle of the camera board 50 based on each correction value, and controls the six-axis stage 110 so that the image sensor 40 is in the specified assembly state.

[0030] After the image sensor 40 reaches the specified assembled state, the computing device 140 as the assembly unit 145 controls the laser 150 to irradiate the adhesive 70 applied to the camera board 50 with laser light, as shown in Fig. 11. That is, in a state in which the lens module 30 and the camera board 50 are bonded together via the adhesive 70, the adhesive 70 is irradiated with laser light to heat it. This temporarily hardens the adhesive 70, and the camera board 50 is assembled to the lens module 30.

[0031] Incidentally, as described above, in order to calculate the MTF curve, it is necessary to capture images of the cross light source 60 at a number of different Z-axis positions, and it is necessary to move the camera board 50 in the Z-axis direction. However, when the camera board 50 is stopped after being moved, vibration occurs when the board is stopped. If a chart image is captured in a state where vibration occurs, this will cause an error, so it is necessary to provide a waiting time until the vibration subsides each time the board is stopped. This lengthens the work time. Therefore, in this embodiment, the following measures are taken to shorten the work time.

[0032] As a first innovation, the arithmetic device 140 controls the six-axis stage 110 so as to move the position in the Z-axis direction within a predetermined scanning range set based on the optimal position and optimal angle. The scanning range is, for example, within a predetermined range in the Z-axis direction centered on the optimal position.

[0033] As a second innovation, the arithmetic device 140 captures images while continuously moving the camera board 50 within a predetermined scanning range without stopping, acquires a plurality of pieces of imaging data, and analyzes the plurality of pieces of imaging data. In this embodiment, the arithmetic device 140 captures images while moving the camera board 50 at a constant speed within the scanning range.

[0034] As a third innovation, the exposure time is shortened to the extent that the chart image can be identified. In this embodiment, since the cross light source 60 is used as the chart image, the exposure time can be shortened compared to the case of capturing an image of a chart image printed on paper. In this embodiment, the exposure time is shorter than the general exposure times of 33.3 ms and 16.7 ms, and specifically, the exposure time is set to 0.7 ms.

[0035] As a fourth innovation, the scanning area 62 is set by restricting the imaging area 63 that can be imaged by the image sensor 40. Specifically, since the area where the cross light source 60 exists is determined in advance, the area where the cross light source 60 does not exist is not imaged. For example, as shown in FIG. 7(a), a partial area 65 at the upper end and a partial area 64 at the lower end where the cross light source 60 does not exist are omitted from the original imaging area 63 to form the scanning area 62. In this embodiment, when the vertical width of the original imaging area 63 is 1876 (pix) in the vertical direction (X-axis direction), the vertical width of the scanning area 62 is set to 1369 (pix). It is desirable to set the scanning area 62 to a degree that allows the cross light source 60 to be sufficiently imaged, taking into account an error.

[0036] Next, the flow of the focus adjustment method in this embodiment will be described with reference to Fig. 12. The focus adjustment process shown below is executed by the arithmetic unit 140.

[0037] First, after the camera board 50 is placed on the transport device 120, the arithmetic device 140 as the transport unit 141 starts to control the transport device 120 so that the camera board 50 and the six-axis stage 110 are transported until the image sensor 40 reaches a position facing the lens module 30 (step S101). This step S101 corresponds to a transport step. In step S101, the adhesive 70 for bonding the lens module 30 has already been applied to the camera board 50. However, if the adhesive 70 is to be applied in a later process (e.g., step S107, etc.), it does not have to be applied at this stage.

[0038] Moreover, the arithmetic device 140 as the measurement unit 142 controls the distance measurement sensor 130 to measure the installation position and installation angle of the image sensor 40 on the camera board 50 during transportation (step S102). This step S102 corresponds to the measurement step.

[0039] Then, after the image sensor 40 reaches the opposing position, the arithmetic device 140 as the adjustment unit 143 controls the six-axis stage 110 to adjust the position and angle of the camera substrate 50 (step S103). In this step S103, the arithmetic device 140 adjusts the position and angle of the camera substrate 50 so that the position and angle of the image sensor 40 become optimal, taking into account the installation position and installation angle of the image sensor 40 measured in step S102.

[0040] Thereafter, the calculation device 140 as the in-focus point identification unit 144 causes the image sensor 40 to capture each cross light source 60 as a chart image via the lens module 30, and analyzes the captured image data to calculate the MTF curve of each chart image (step S104). In step S104, the calculation device 140 captures an image while moving the camera board 50 at a constant speed within a scanning range set based on the optimal position. The scanning area 62 at this time is narrower than the imaging area 63 of the image sensor 40, and the exposure time is also shortened to reduce the frame rate. The timing of analyzing the captured image data to calculate the MTF curve of each chart image may be in parallel with the acquisition of the captured image data, or may be collectively analyzed after all the captured image data are acquired. In this embodiment, the captured image data is sequentially analyzed in parallel with the acquisition of the captured image data to calculate the MTF curve of each chart image.

[0041] After obtaining the MTF curve, the calculation device 140 calculates a correction value for correcting the position and inclination of the image sensor 40 so that the focal depth becomes maximum (step S105). These steps S103 and S104 correspond to a focal point specifying step.

[0042] Thereafter, the arithmetic device 140 readjusts the position and angle of the camera board 50 based on the correction value calculated in step S105, and controls the six-axis stage 110 so that the image sensor 40 is in a specific assembly state where the image sensor 40 is in focus (step S106). These steps S106 and S103 correspond to the adjustment step. In other words, the adjustment step may be performed once or multiple times as necessary.

[0043] Then, the computing device 140 controls the laser 150 to irradiate the adhesive 70 applied between the lens module 30 and the camera board 50 with laser light to harden (temporarily harden) the adhesive 70 (step S107). That is, in a state in which the adhesive surface of the lens module 30 and the adhesive surface of the camera board 50 are attached to each other via the adhesive 70, the adhesive 70 is heated and hardened by irradiating it with laser light. Step S107 corresponds to an assembly step. Thereafter, the camera board 50 and the lens module 30 are stored in a thermostatic chamber to harden the adhesive 70 completely, and the lens module 30 is reliably fixed to the camera board 50. This completes the camera module 20.

[0044] After adjusting the position and angle of the image sensor 40, in step S107, the adhesive 70 is temporarily cured by irradiating it with laser light. However, it has been found that the position tends to shift after the adjustment before the temporary curing is completed.

[0045] More specifically, when laser light is applied as shown in FIG. 13(a), the adhesive 70, the lens module 30, and the camera board 50 are heated and thermally expanded temporarily as shown in FIG. 13(b). Thereafter, as shown in FIG. 13(c), the adhesive 70 is temporarily cured, and the lens module 30 and the camera board 50 are bonded to each other at their respective bonding surfaces with the adhesive 70. At this time, as shown in the enlarged view in FIG. 13(c), the adhesive 70 bonds to the lens module 30 and the camera board 50 at their respective bonding surfaces, and the adhesive 70 itself cures and shrinks. Therefore, as the adhesive 70 cures and shrinks, the lens module 30 and the camera board 50 are pulled by their respective bonding surfaces and move closer to each other as shown by the arrows.

[0046] After that, when the heat is released, the lens module 30, the camera board 50, and the adhesive 70 each contract by the amount that they expanded, as shown in the enlarged view of FIG. 13(d). At this time, the lens module 30 and the camera board 50 are pulled by their respective adhesive surfaces, and come closer to each other by the amount that they contracted. As a result, after the adjustment, the distance between the lens module 30 and the camera board 50 comes closer until the provisional curing is completed, causing a misalignment. In addition to this, it was also found that the camera board 50 warps and becomes misaligned due to heat from the laser light.

[0047] Therefore, these deviations are predicted, and when readjustment is performed in step S106, the predicted deviations are offset to minimize deviations at the completion of provisional curing. Here, the distance by which the lens module 30 and the camera board 50 approach each other in the Z-axis direction from after readjustment in step S106 until the completion of provisional curing (the distance they shrink, the amount of shrinkage deviation) is simply referred to as shrinkage distance E100. First, the prediction of this shrinkage distance E100 will be described.

[0048] After the process of step S105 and before the process of step S106, the calculation device 140 performs the prediction process shown in Fig. 14. The calculation device 140 first acquires a first distance L1 (see Fig. 15) from the surface of the image sensor 40 (the surface on the lens module 30 side) to the surface of the camera board 50 (the surface on the lens module 30 side) in the Z axis direction (step S201). In step S102, the calculation device 140 calculates and acquires the first distance L1 from the measured installation position and installation angle of the image sensor 40 on the camera board 50.

[0049] Since the rectangular image sensor 40 may be fixed at an angle relative to the camera substrate 50, the first distance L1 may differ depending on which position on the camera substrate 50 is used as a reference. However, taking into consideration that the difference is slight, an arbitrary position is used as a reference to determine the first distance L1. In this embodiment, the distance from the surface position of the image sensor 40 at the center of the image sensor 40 to the surface position of the camera substrate 50 is determined as the first distance L1.

[0050] Next, the arithmetic device 140 acquires a second distance L2 (see FIG. 15) from the surface of the image sensor 40 to the bonding surface of the lens module 30 in the Z-axis direction (step S202). The lens module 30 is bonded to the camera board 50 at four sides so as to surround the rectangular image sensor 40. In addition, the camera board 50 may be assembled at an angle relative to the lens module 30 for focus adjustment, so the second distance L2 may differ depending on which position is used as the reference.

[0051] However, taking into consideration that the difference is slight, the adhesive surface of the lens module 30 at any position among the four sides is used as the reference. In this embodiment, the distance in the Z-axis direction between the adhesive surface at any corner among the four corners of the lens module 30 and the center of the image sensor 40 is specified as the second distance L2. Since the image sensor 40 is disposed at an optimal position and optimal angle, the second distance L2 can be specified from the optimal position and optimal angle of the image sensor 40 and the shape (design dimensions) of the lens module 30. The second distance L2 may be actually measured by a sensor or the like.

[0052] Then, the calculation device 140 calculates the difference between the first distance L1 and the second distance L2, and acquires the difference as the separation distance L3 (see FIG. 15) in the Z-axis direction from the lens module 30 to the camera board 50 (step S203).

[0053] The arithmetic device 140 calculates the amount of misalignment E10 due to the cure shrinkage of the adhesive 70 by multiplying the separation distance L3 by a coefficient C10 based on the physical properties of the adhesive 70 (step S204). That is, it has been found through experiments that the distance at which the camera board 50 and the lens module 30 approach each other due to the cure shrinkage of the adhesive 70 increases in proportion to the separation distance L3. It has also been found through experiments that the proportionality coefficient (coefficient C10) differs depending on the physical properties of the adhesive 70. Therefore, in this embodiment, the amount of misalignment E10 due to the cure shrinkage of the adhesive 70 is calculated by multiplying the separation distance L3 by the coefficient C10 based on the physical properties of the adhesive 70. The coefficient C10 based on the physical properties of the adhesive 70 is identified through experiments or the like.

[0054] Next, the arithmetic device 140 acquires the amount of deviation E11 due to the thermal expansion of the adhesive 70 and the associated contraction during heat dissipation (step S205). Hereinafter, the amount of deviation E11 due to the thermal expansion of the adhesive 70 and the associated contraction during heat dissipation may be simply referred to as the amount of deviation E11 due to the thermal expansion of the adhesive 70. It has been found through experiments that the amount of deviation E11 due to the thermal expansion of the adhesive 70 increases in proportion to the temperature rise of the adhesive 70 caused by the laser beam. It has also been found through experiments that the proportionality coefficient (coefficient C11) varies depending on the shape of the adhesive 70 (the thickness of the adhesive portion and the amount of the adhesive 70) and the physical properties of the adhesive 70. Therefore, the arithmetic device 140 calculates and acquires the amount of deviation E11 due to the thermal expansion of the adhesive 70 by multiplying the temperature rise of the adhesive 70 caused by the laser beam by the coefficient C11 based on the shape and physical properties of the adhesive 70.

[0055] The temperature rise value of the adhesive 70 due to the laser light is approximately constant, and therefore can be specified by experiments. Similarly, the shape and physical properties of the adhesive 70 are also approximately the same, and therefore the coefficient C11 can be specified by experiments. Therefore, the calculation device 140 may store them in advance, and in step S205, read them from the storage unit to calculate the deviation amount E11 due to the thermal expansion of the adhesive 70. Similarly, the deviation amount E11 due to the thermal expansion of the adhesive 70 is approximately constant, and therefore can be specified by experiments. Therefore, the calculation device 140 may store the deviation amount E11 due to the thermal expansion of the adhesive 70 in advance, and in step S205, read and acquire it from the storage unit. In this embodiment, the deviation amount E11 is stored in advance.

[0056] The arithmetic device 140 also acquires the amount of deviation E12 due to the thermal expansion of the lens module 30 and the associated contraction during heat dissipation (step S206). Hereinafter, the amount of deviation E12 due to the thermal expansion of the lens module 30 and the associated contraction during heat dissipation may be simply referred to as the amount of deviation E12 due to the thermal expansion of the lens module 30. It has been found through experiments that the amount of deviation E12 due to the thermal expansion of the lens module 30 increases in proportion to the temperature rise value of the lens module 30 due to the laser light. It has also been found through experiments that the proportionality coefficient (coefficient C12) varies depending on the shape (size and shape) of the lens module 30 and the material of the lens module 30. Therefore, the arithmetic device 140 multiplies the temperature rise value of the lens module 30 due to the laser light by the coefficient C12 based on the shape and physical properties of the lens module 30 to calculate and acquire the amount of deviation E12 due to the thermal expansion of the lens module 30.

[0057] In addition, the temperature rise value of the lens module 30 due to the laser light is approximately constant, and therefore can be specified by experiments. Similarly, the shape of the lens module 30 is also approximately the same, and therefore the coefficient C12 can be specified by experiments. Therefore, the arithmetic device 140 may store them in advance, and in step S206, read them from the storage unit to calculate the deviation amount E12 due to the thermal expansion of the lens module 30. Similarly, the deviation amount E12 due to the thermal expansion of the lens module 30 is approximately constant, and therefore can be specified by experiments. Therefore, the arithmetic device 140 may store the deviation amount E12 due to the thermal expansion of the lens module 30 in advance, and in step S206, read and acquire it from the storage unit. In this embodiment, the deviation amount E12 is stored in advance.

[0058] The arithmetic device 140 also acquires the amount of deviation E13 due to the thermal expansion of the camera substrate 50 and the associated contraction during heat dissipation (step S207). Hereinafter, the amount of deviation E13 due to the thermal expansion of the camera substrate 50 and the associated contraction during heat dissipation may be simply referred to as the amount of deviation E13 due to the thermal expansion of the camera substrate 50. It has been found through experiments that the amount of deviation E13 due to the thermal expansion of the camera substrate 50 increases in proportion to the temperature rise value of the camera substrate 50 due to the laser light. It has also been found through experiments that the proportionality coefficient (coefficient C13) varies depending on the shape (size and shape) of the camera substrate 50 and the material of the camera substrate 50. Therefore, the arithmetic device 140 multiplies the temperature rise value of the camera substrate 50 due to the laser light by the coefficient C13 based on the shape and physical properties of the camera substrate 50 to calculate and acquire the amount of deviation E13 due to the thermal expansion of the camera substrate 50.

[0059] In addition, the temperature rise value of the camera substrate 50 due to the laser light is approximately constant, and therefore can be specified by an experiment or the like. Similarly, the shape of the camera substrate 50 is also approximately the same, and therefore the coefficient C13 can be specified by an experiment or the like. Therefore, the arithmetic device 140 may store them in advance, and in step S207, read them from the storage unit and calculate the deviation amount E13 due to the thermal expansion of the camera substrate 50. Similarly, the deviation amount E13 due to the thermal expansion of the camera substrate 50 is approximately constant, and therefore can be specified by an experiment or the like. Therefore, the arithmetic device 140 may store the deviation amount E13 due to the thermal expansion of the camera substrate 50 in advance, and in step S207, read and acquire it from the storage unit. In this embodiment, the deviation amount E13 is stored in advance.

[0060] Then, the arithmetic device 140 calculates the amount of deviation E14 due to thermal warping of the camera board 50 caused by the temperature rise due to the laser light (step S208). The amount of deviation E14 due to thermal warping of the camera board 50 caused by the temperature rise due to the laser light is almost constant if the shape and material of the camera board 50 are the same, so it is identified by an experiment or the like and stored in the storage unit. Step S208 is obtained by reading it.

[0061] Then, the calculation device 140 sums up the various deviation amounts E10 to E14 acquired in steps S204 to S208 to predict the contraction distance E100 (step S209). Then, the prediction process ends. Note that steps S201 to S209 correspond to the prediction step.

[0062] The computing device 140 adjusts the position of the camera board 50 after the readjustment in step S106 so as to increase the distance between the lens module 30 and the camera board 50 in advance by the contraction distance E100 thus predicted. That is, in step S106, the computing device 140 moves the camera board 50 away from the lens module 30 by the contraction distance E100 compared to a specific assembly state that results in a focal point so as to cancel (offset) the predicted contraction distance E100. Note that the contraction distance E100 may be reflected in the correction value calculated in step S105, thereby offsetting the contraction distance E100 during the readjustment in step S106.

[0063] The effect of the focus adjustment method in this embodiment will be described.

[0064] In step S102, the arithmetic device 140 measures the installation position and installation angle of the image sensor 40 on the camera board 50. Then, in step S103, the position and angle of the camera board 50 are adjusted so that the position and angle of the image sensor 40 relative to the lens module 30 are optimal, taking into account the measured installation position and installation angle. That is, the state of how the image sensor 40 is installed on the camera board 50 is measured in advance, and the camera board 50 can be accurately adjusted so that the image sensor 40 is at a predetermined optimal position and optimal angle, taking into account the measured installation position and installation angle. Therefore, when the camera board 50 is assembled to the lens module 30, it is possible to reduce the effort required to adjust the image sensor 40 so that it is in focus. In addition, since the measurement is performed during transportation, there is no need to take the time to measure, and the time required for adjustment can be reduced.

[0065] In step S104, when calculating the MTF curve, the calculation device 140 captures images while changing the Z-axis position within the scanning range. The scanning range in step S104 is set based on the optimal position and optimal angle. This allows the scanning range to be narrowed. In other words, when the image sensor 40 is placed at an arbitrary position facing the lens module 30, there is a possibility that the focus is not correct, and therefore the position of the MTF curve (the apex position or the peak position) may be significantly shifted. For this reason, when the image sensor 40 is placed at an arbitrary position facing the lens module 30, it is necessary to enlarge the scanning range assuming a large shift.

[0066] However, in this embodiment, the position and angle of the image sensor 40 are adjusted to be the optimal position and optimal angle. Therefore, there is a high possibility that the focus is correct and the positional deviation of the MTF curve is small. Furthermore, in this embodiment, in step S102, the installation position and installation angle of the image sensor 40 on the camera board 50 are measured, and the position and angle of the camera board 50 are adjusted taking these into consideration, so there is a high possibility that the positional deviation of the MTF curve is even smaller. Therefore, the scanning range can be narrowed compared to the case where the image sensor 40 is disposed at an arbitrary position facing the lens module 30.

[0067] Therefore, in this embodiment, in step S103, the focal position is searched for from a state in which the focus is already achieved to a certain extent, so that the scanning range can be narrowed, and as a result, the time required to identify the focal point can be shortened.

[0068] Furthermore, in step S104, when calculating the MTF curve, the arithmetic device 140 captures images while continuously moving the camera board 50 without stopping it using the six-axis stage 110. This eliminates the need to provide a waiting time until the vibrations converge, as compared to the case where the camera board 50 is stopped before capturing images, and the time required for adjustment can be shortened.

[0069] Furthermore, in step S104, the cross light source 60 is used as the chart image, and the exposure time is shortened to the extent that the cross light source 60 can be identified, so that the frame rate can be shortened. In other words, the speed at which the camera board 50 is moved can be increased, and the time required for adjustment can be shortened.

[0070] In step S104, a partial area 65 at the upper end and a partial area 64 at the lower end, which are areas of the imaging area 63 where no chart image exists, are omitted to form the scanning area 62. This makes it possible to reduce the frame rate. That is, the speed at which the camera board 50 is moved can be increased, and the time required for adjustment can be reduced.

[0071] A contraction distance E100 that occurs from after the adjustment until the completion of the provisional curing is predicted, and the camera board 50 is moved away from the lens module 30 by the contraction distance E100 compared to a specific assembly state that results in a focal point so that the contraction distance E100 is offset. This allows the image sensor 40 to be assembled so as to accurately achieve a focal point even if the distance between the lens module 30 and the camera board 50 becomes closer until the provisional curing of the adhesive 70 is completed.

[0072] The shrinkage distance E100 includes the displacement amount E10 due to the hardening shrinkage of the adhesive 70. This makes it possible to more accurately offset the position of the camera board 50. In addition, the displacement amount E10 due to the hardening shrinkage of the adhesive 70 is calculated taking into account the separation distance L3 and a coefficient C10 based on the physical properties of the adhesive 70, making it possible to accurately predict the displacement.

[0073] The amount of deviation due to the thermal expansion of the camera module 20 and the associated contraction during heat dissipation is predicted and included in the contraction distance E100. The amount of deviation due to the thermal expansion of the camera module 20 and the associated contraction during heat dissipation is predicted based on the temperature rise value during the thermal expansion of the camera module 20 and coefficients according to the shape and material of the camera module 20.

[0074] More specifically, the contraction distance E100 includes the amount of deviation E11 due to thermal expansion of the adhesive 70. This makes it possible to more accurately offset the position of the camera board 50. Also, the amount of deviation E11 due to thermal expansion of the adhesive 70 is calculated by taking into account the temperature rise value of the adhesive 70 due to the laser light and a coefficient C11 based on the shape and physical properties of the adhesive 70, making it possible to accurately predict the deviation.

[0075] Moreover, the contraction distance E100 includes the displacement amount E12 due to thermal expansion of the lens module 30. This makes it possible to more accurately offset the position of the camera board 50. Moreover, the displacement amount E12 due to thermal expansion of the lens module 30 is calculated by taking into consideration the temperature rise value of the lens module 30 due to the laser light and a coefficient C12 based on the shape and material of the lens module 30, so that the displacement can be accurately predicted.

[0076] Moreover, the contraction distance E100 includes the amount of deviation E13 due to thermal expansion of the camera board 50. This makes it possible to more accurately offset the position of the camera board 50. Moreover, the amount of deviation E13 due to thermal expansion of the camera board 50 is calculated by taking into consideration a coefficient C13 based on the shape and material of the camera board 50 to the temperature rise value of the camera board 50 due to the laser light, and therefore it is possible to accurately predict the deviation.

[0077] The contraction distance E100 includes the displacement amount E14 due to thermal warping of the camera board 50. This makes it possible to offset the position of the camera board 50 more accurately.

[0078] (Modification) The focus adjustment method in the above embodiment may be partially modified. Modifications will be described below.

[0079] In the above embodiment, the imaging data of the chart image is analyzed to identify the installation state of the image sensor 40 that is the in-focus point, and the position of the camera board 50, etc. are readjusted (steps S104 to S106). However, if the required accuracy is satisfied, these steps may be omitted.

[0080] In the above embodiment, the installation position and installation angle of the image sensor 40 on the camera board 50 are measured, and taking these into consideration, the position of the camera board 50, etc. are adjusted so that the position and angle of the image sensor 40 are optimal. However, these processes may be omitted if the processes of steps S104 to S106 are performed.

[0081] In step S104 of the above embodiment, the scanning area 62 is set by omitting a part of the imaging area 63, but it does not have to be omitted.

[0082] In step S104 of the above embodiment, the scanning area 62 may be set by omitting parts of both the left and right ends of the imaging area 63.

[0083] In step S104 of the above embodiment, the chart image does not have to be the cross light source 60, and may be any mark printed thereon. Also, the number, shape, and arrangement may be changed as desired.

[0084] In step S104 of the above embodiment, the exposure time may be changed arbitrarily.

[0085] In the prediction process of the above embodiment, when predicting the shrinkage distance E100, it is not necessary to take into account the displacement amount E10 due to temporary hardening of the adhesive 70. This eliminates the need to calculate the separation distance L3, and reduces the processing load.

[0086] In the prediction process of the above embodiment, the temperature rise value of the adhesive 70, the temperature rise value of the camera board 50, and the temperature rise value of the lens module 30 may be the same value. This can save the effort of measurement.

[0087] In the prediction process of the above embodiment, when predicting the shrinkage distance E100, it is not necessary to take into account the deviation amount E14 due to thermal warping of the camera board 50.

[0088] In the prediction process of the above embodiment, the contraction distances E100 at a plurality of positions may be predicted, and the distance to be moved away may be different for each position so that the contraction distances E100 are offset at the plurality of positions. For example, the camera board 50 may be tilted relative to the lens module 30 when assembled, so that the separation distance L3 between the lens module 30 and the camera board 50 may be different at both ends in the left-right direction (Y direction). The shift amount E11 due to the effective contraction of the adhesive 70 varies depending on the separation distance L3. Therefore, the contraction distance E100 may be different at both ends in the left-right direction. Therefore, the separation distance L3 may be calculated at any position (predicted position) at both ends in the left-right direction, and the contraction distance E100 may be predicted accordingly. Then, the distance to be moved away may be different for each predicted position so that the contraction distances E100 are offset at the predicted positions at both ends in the left-right direction.

[0089] Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

Claims

1. A method for adjusting focus of a camera module (20) including an optical system (30), an image sensor (40), and a camera board (50) on which the image sensor is mounted, comprising: an adjustment step of adjusting a position and an angle of the camera board relative to the optical system; an assembly step of, after the adjustment step, bonding the optical system to the camera board via an adhesive, and fixing the camera board to the optical system by thermally curing the adhesive in a state where the optical system is bonded to the camera board via the adhesive; a prediction step of predicting a contraction deviation amount (E100) that occurs when the optical system and the camera board approach each other during a period from the state adjusted by the adjustment step to the completion of fixing of the camera board in the assembly step, The prediction step is performed before the adjustment step, In the prediction step, a deviation amount due to thermal expansion of the camera module and contraction during heat dissipation is predicted and included in the contraction deviation amount; In the adjustment step, the camera substrate is moved away from the optical system by the contraction shift amount compared to a state where the image is in focus, so that the contraction shift amount predicted in the prediction step is cancelled out.

2. 2. The focus adjustment method according to claim 1, wherein the prediction step predicts an amount of deviation due to thermal expansion of the camera module and contraction during heat dissipation based on a temperature rise value during thermal expansion of the camera module and a coefficient corresponding to a shape and material of the camera module.

3. 3. The focus adjustment method according to claim 1 or 2, wherein the amount of deviation due to thermal expansion of the camera module and contraction during heat dissipation includes an amount of deviation (E11) due to thermal expansion of the adhesive and contraction during heat dissipation, an amount of deviation (E13) due to thermal expansion of the camera board and contraction during heat dissipation, and an amount of deviation (E12) due to thermal expansion of the optical system and contraction during heat dissipation.

4. 4. The focus adjustment method according to claim 1, wherein in the prediction step, a deviation amount (E14) due to thermal warping of the camera board is predicted and included in the shrinkage deviation amount.

5. In the prediction step, the shrinkage deviation amounts at a plurality of positions are predicted, 5. The focus adjustment method according to claim 1, wherein in the adjusting step, the distances moved away from the respective positions are made different so that the contraction deviation amounts at the respective positions are cancelled out.

6. A method for adjusting focus of a camera module (20) including an optical system (30), an image sensor (40), and a camera board (50) on which the image sensor is mounted, comprising: an adjustment step of adjusting a position and an angle of the camera board relative to the optical system; an assembly step of fixing the camera board to the optical system by thermally curing the adhesive in a state where the optical system is bonded to the camera board via the adhesive after the adjustment step; a prediction step of predicting a contraction deviation amount (E100) that occurs when the optical system and the camera board approach each other during a period from the state adjusted by the adjustment step to the completion of fixing of the camera board in the assembly step, The prediction step is performed before the adjustment step, In the prediction step, a deviation amount (E14) due to thermal warping of the camera board is predicted and included in the shrinkage deviation amount, In the adjustment step, the camera substrate is moved away from the optical system by the contraction shift amount compared to a state where the image is in focus, so that the contraction shift amount predicted in the prediction step is cancelled out.

Images