JP6327123B2 - Camera focus adjustment device - Google Patents

Description

  The present invention relates to a camera focus adjustment device that adjusts the focus of a camera.

  Conventionally, in Patent Document 1, when fixing an imaging lens used in a camera unit and a solid-state imaging device, focus adjustment is performed by adjusting a relative position between the imaging lens and the solid-state imaging device in the optical axis direction. An adjustment device is described.

  In this prior art, the MTF value is measured while changing the relative position of the imaging lens and the solid-state imaging device in the optical axis direction by a predetermined pitch. When the measured MTF value exceeds a preset MTF set value, the imaging lens and the solid-state imaging device are fixed at that position.

JP-A-8-251348

  However, according to the above prior art, it is necessary to change the relative position of the imaging lens and the solid-state imaging device in the optical axis direction until the measured MTF value exceeds the MTF set value, so that the number of MTF values to be measured increases. And adjustment time becomes long. Therefore, there is a problem that it is difficult to improve the productivity of the camera unit.

  The present invention has been made in view of the above points, and an object thereof is to shorten the time for adjusting the relative position between a lens and an image sensor.

In order to achieve the above object, in the invention described in claim 1,
A lens (1a) for imaging light;
An image sensor (1b) that converts light that has passed through the lens (1a) into a digital signal;
A collimator (14) for projecting an inspection chart (C1, C2, C3, C4, C5) for focus adjustment onto the lens (1a) and the image sensor (1b);
Relative position changing means (13) for changing the relative position of the lens (1a) and the image pickup device (1b) in the optical axis direction (Z);
Image processing means (15) for imaging the digital signal converted by the image sensor (1b),
The image processing means (15) calculates the MTF value of the inspection chart (C1, C2, C3, C4, C5) at a plurality of relative positions, and based on the calculated MTF value, determines the relative position at which the MTF value is maximum. estimated,
The relative position changing means (13) changes the relative position at a first pitch and changes at a second pitch smaller than the first pitch,
The image processing means (15) determines the relative position at which the MTF value is maximum when the relative position changing means (13) changes the relative position at the first pitch and when the relative position is changed at the second pitch. Estimated separately,
The estimated relative position values (Pf1, Pf2) at which the MTF values are maximized are compared with each other .

  According to this, since the relative position where the MTF value becomes maximum can be obtained by estimation without actually measuring, the number of times of changing the relative position and the number of times of calculating the MTF value can be reduced. Therefore, the time for adjusting the relative position in the optical axis direction (Z) between the lens (1a) and the image sensor (1b) can be shortened.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

It is a perspective view of the lens unit and lens holder in one embodiment. It is a perspective view of the camera module in one embodiment. 1 is an overall configuration diagram of a camera focus adjustment device according to an embodiment. It is a figure which shows the test | inspection chart for focus adjustment in one Embodiment. It is a flowchart which shows the control processing which the control apparatus of the camera focus adjustment apparatus in one Embodiment performs. It is a graph explaining the maximum value and the minimum value of the contrast value of the inspection chart in one embodiment. It is a graph which shows the starting point of the MTF characteristic curve in one Embodiment. It is a graph which shows the 1st candidate value of the falling point of a MTF characteristic curve and lens fixed position in one embodiment. It is a graph which shows the 1st candidate value and final search position of a lens fixed position of an inspection chart in one embodiment. It is a graph which shows the MTF curve prepared in advance in one Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. The camera focus adjustment device 10 adjusts the relative position of the lens unit 1a and the lens holder 1b shown in FIG. 1 in the optical axis direction Z to an appropriate focus position, and at the adjusted relative position, the lens unit 1a and the lens holder 1b Is a device for assembling the camera module 1 shown in FIG. The camera module 1 is used as, for example, an in-vehicle camera of a vehicle driving support system.

  The lens unit 1a has a plurality of lenses and a case for housing them. A plurality of lenses image light. The lens holder 1b has an image sensor. The imaging device converts light that has passed through the lens of the lens unit 1a into a digital signal.

  As shown in FIG. 3, the camera focus adjustment device 10 includes a gantry 11, a setting jig 12, a barrel chuck mechanism 13, a collimator 14, a control device 15, and the like.

  Devices such as a setting jig 12, a barrel chuck mechanism 13, a collimator 14, and a control device 15 are fixed to the gantry 11.

  The setting jig 12 holds the lens holder 1b. The barrel chuck mechanism 13 holds the lens unit 1a. The barrel chuck mechanism 13 has an actuator that adjusts the distance in the optical axis direction Z of the lens unit 1a with respect to the lens holder 1b. The barrel chuck mechanism 13 is a relative position changing unit that changes the relative position in the optical axis direction Z between the lens of the lens holder 1b and the imaging device of the lens holder 1b to a plurality of positions.

  The collimator 14 projects an inspection chart for focus adjustment onto the imaging elements of the lens unit 1a and the lens holder 1b. As shown in FIG. 4, the collimator 14 projects five inspection charts C1, C2, C3, C4, and C5 with black and white stripes at the center and the four corners.

  The control device 15 is an image processing unit that images and processes the digital signal converted by the imaging device, and also a control unit that controls the operation of the actuator of the barrel chuck mechanism 13.

  The control device 15 is a personal computer composed of a central processing unit (CPU) and its peripheral circuits, and operates according to a program read into the central processing unit. A display monitor that displays various information is connected to the control device 15.

  Furthermore, the camera focus adjustment device 10 includes a hot air device (not shown). The hot air device is a device that blows out hot air to bond the lens unit 1a and the lens holder 1b at a high temperature. The operation of the hot air device is controlled by the control device 15.

  The control device 15 executes the control process shown in the flowchart of FIG. This control process is executed in a state in which the lens unit 1a is separated from an appropriate focus position with respect to the lens holder 1b.

  First, in step S100, the MTF value is searched by bringing the lens unit 1a close to the lens holder 1b in rough steps.

  Specifically, the actuator of the barrel chuck mechanism 13 moves the lens unit 1a closer to the lens holder 1b at a relatively large pitch (for example, 15 μm). The control device 15 acquires images of the five inspection charts C1 to C5 projected by the collimator 14 from the imaging device, and calculates MTF values for each of the five inspection charts C1 to C5. The MTF value is calculated using the following mathematical formula.

MTF value = (Cmax−Cmin) / (Cmax + Cmin) × 100
As shown in FIG. 6, Cmax is the maximum contrast value in one inspection chart (black and white stripes), and Cmin is the minimum contrast value in one inspection chart (monochrome stripes). The larger the MTF value, the stronger the contrast of the inspection chart. In FIG. 6, a part of the inspection chart (black and white stripes) and the corresponding contrast value (sinusoidal curve) are superimposed.

  In subsequent step S110, it is determined whether or not the MTF values of the five inspection charts C1 to C5 are all equal to or greater than the threshold value.

  If any of the MTF values of the five inspection charts C1 to C5 does not exceed the threshold value, the process returns to step S100. When the MTF values of the five inspection charts C1 to C5 all exceed the threshold value, the process proceeds to step S120, and the position of the lens unit 1a at that time is determined as the rising point Pm1 (FIG. 7).

  In subsequent S130, the falling point Pm2 is estimated. As shown in FIG. 8, the falling point Pm2 is at least one of the MTF values of the five inspection charts C1 to C5 when the lens unit 1a is brought closer to the lens holder 1b side than the rising point Pm1. This is a position where two MTF values are below the threshold.

  Specifically, for each of the five inspection charts C1 to C5, a plurality of (for example, three or more) MTF values calculated up to the rising point Pm1 are minimum 2 on the MTF curve Lm (FIG. 9) prepared in advance. The falling point Pm2 is estimated by approximating by multiplication.

  For each of the five inspection charts C1 to C5, MTF values are calculated at a plurality of (for example, three or more) positions closer to the lens holder 1b than the rising point Pm1, and the calculated plurality of MTF values are prepared in advance. The falling point Pm2 may be estimated by approximating the MTF curve Lm by the method of least squares.

  In the example of FIG. 9, the MTF curve Lm prepared in advance is a single continuous curve. The MTF curve Lm prepared in advance may be composed of a plurality of curves divided according to the position of the lens unit 1a. For example, the MTF curve Lm may be configured by three curves divided into a region near the rising point Pm1, a region near the position where the MTF value is maximum, and a region near the falling point Pm2.

  In the subsequent step S140, a first candidate value Pf1 for the lens fixing position is calculated. The lens fixing position is a position for fixing the lens unit 1a to the lens holder 1b. At the lens fixing position, the MTF value needs to be good for all of the five inspection charts C1 to C5.

  The first candidate value Pf1 is calculated based on the rising point Pm1 and the falling point Pm2. For example, as shown in FIG. 10, a position near the middle between the rising point Pm1 and the falling point Pm2 is set as the first candidate value Pf1.

  In subsequent step S150, the MTF value is searched by bringing the lens unit 1a closer to the lens holder 1b from the rising point Pm1 in small increments.

  Specifically, the actuator of the barrel chuck mechanism 13 brings the lens unit 1a closer to the lens holder 1b at a smaller pitch (eg, 4 μm) than in step S100. The control device 15 acquires images of the five inspection charts C1 to C5 projected by the collimator 14 from the imaging device, and calculates MTF values for each of the five inspection charts C1 to C5. The MTF value is calculated using the mathematical formula described in step S100.

  In subsequent step S160, a second candidate value Pf2 of the lens fixing position is calculated. Specifically, for each of the five inspection charts C1 to C5, a plurality of finely divided MTF values calculated by repeating step S150 a plurality of times are approximated to the MTF curve Lm prepared in advance by the method of least squares. Thus, the position of the lens unit 1a having the maximum MTF value is estimated, and the average value of the positions estimated for each of the five inspection charts C1 to C5 is set as the second candidate value Pf2.

  In the subsequent step S170, it is determined whether or not the difference between the first candidate value Pf1 and the second candidate value Pf2 is within an allowable range. When it is determined that the difference between the first candidate value Pf1 and the second candidate value Pf2 is within the allowable range, the process proceeds to step S180, and the lens fixing position is determined as the first candidate value Pf1. Thereby, the lens holder 1b is fixed to the lens unit 1a by high temperature adhesion at the position of the first candidate value Pf1.

  On the other hand, if it is determined in step S170 that the difference between the first candidate value Pf1 and the second candidate value Pf2 is not within the allowable range, the process proceeds to step S190, where the position (search position) of the lens holder 1b reaches the final search position Pe. Determine whether or not.

  The final search position Pe is a position set in the control device 15 in advance, and is set to a position before the position of the lens unit 1a where the MTF value is maximized (a position away from the lens unit 1a).

  If it is determined that the position of the lens holder 1b has not reached the final search position Pe, the process returns to step S150.

  On the other hand, when it is determined that the position of the lens holder 1b has reached the final search position Pe, the process proceeds to step S200, and the lens fixing position is determined as the second candidate value Pf2. Thereby, the lens holder 1b is fixed to the lens unit 1a by high temperature adhesion at the position of the second candidate value Pf2.

  Thus, in the present embodiment, the barrel chuck mechanism 13 changes the relative position in the optical axis direction Z between the lens of the lens unit 1a and the imaging device of the lens holder 1b. Then, the control device 15 calculates the MTF values of the inspection charts C1 to C5 at a plurality of relative positions, and estimates the relative position at which the MTF value is maximum based on the calculated MTF values.

  According to this, since the relative position where the MTF value becomes maximum can be obtained by estimation without actually measuring, the number of times of changing the relative position and the number of times of calculating the MTF value can be reduced. Therefore, the time for adjusting the relative position in the optical axis direction Z between the lens of the lens unit 1a and the imaging device of the lens holder 1b can be shortened. As a result, the productivity of the camera module 1 can be improved.

  In the present embodiment, the barrel chuck mechanism 13 changes the relative position in the optical axis direction Z between the lens of the lens unit 1a and the imaging device of the lens holder 1b at a first pitch, and is smaller than the first pitch. Change at a pitch of 2.

  Then, the control device 15 separately estimates the relative position where the MTF value is maximum when the barrel chuck mechanism 13 changes the relative position at the first pitch and when the barrel chuck mechanism 13 changes the relative position at the second pitch. The estimated values Pf1 and Pf2 of the relative position where the MTF value is maximum are compared.

  According to this, since the relative position where the MTF value is maximized is estimated by two different methods and the two estimated values Pf1 and Pf2 are compared, the estimation accuracy of the relative position where the MTF value is maximized can be improved. it can.

  In the present embodiment, the collimator 14 projects a plurality of inspection charts C1 to C5 on different locations. Then, the relative position where the MTF value is maximized is estimated for each of the plurality of inspection charts C1 to C5.

  According to this, since the relative position where the MTF value is maximum is estimated for a plurality of locations, the accuracy of focus adjustment can be improved.

  In the present embodiment, the control device 15 estimates the relative position at which the MTF value is maximized based on the MTF values at a plurality of positions and a preset MTF curve Lm. The MTF curve Lm is composed of a plurality of curves divided according to the relative positions. Thereby, the estimation accuracy of the relative position where the MTF value becomes maximum can be increased.

(Other embodiments)
The above embodiment can be variously modified as follows, for example.

  (1) In the above embodiment, when estimating the position of the lens unit 1a where the MTF value is maximum, the calculated MTF value is approximated to the MTF curve Lm prepared in advance by the least square method, but the present invention is limited to this. Without limitation, various estimation methods can be used.

  (2) In steps S100 and S150 of the above embodiment, the pitch at which the lens unit 1a is brought closer to the lens holder 1b can be variously changed.

  (3) In the above embodiment, the camera focus adjustment device 10 assembles the camera module 1 used as an in-vehicle camera of the vehicle driving support system, but the camera focus adjustment device 10 can assemble camera modules for various uses. .

1a Lens unit (lens)
1b Lens holder (image sensor)
14 Collimator 13 Barrel chuck mechanism (relative position changing means)
15 Control device (image processing means)

Claims (2)

A lens (1a) for imaging light;
An image sensor (1b) that converts light that has passed through the lens (1a) into a digital signal;
A collimator (14) for projecting an inspection chart (C1, C2, C3, C4, C5) for focus adjustment onto the lens (1a) and the image sensor (1b);
Relative position changing means (13) for changing the relative position of the lens (1a) and the image sensor (1b) in the optical axis direction (Z);
Image processing means (15) for imaging the digital signal converted by the imaging device (1b),
The image processing means (15) calculates MTF values of the inspection charts (C1, C2, C3, C4, C5) at a plurality of the relative positions, and the MTF value is maximized based on the calculated MTF values. estimating the relative position at which,
The relative position changing means (13) changes the relative position at a first pitch and changes at a second pitch smaller than the first pitch,
The image processing means (15) has the MTF value when the relative position changing means (13) changes the relative position at the first pitch and when the relative position is changed at the second pitch. Separately estimate the relative position to be the maximum,
A camera focus adjustment device that compares estimated values (Pf1, Pf2) of the relative positions at which the MTF value is maximum . The collimator (14) projects a plurality of the inspection charts (C1, C2, C3, C4, C5) to different locations,
The camera focus adjustment apparatus according to claim 1 , wherein the relative position at which the MTF value is maximized is estimated for each of the plurality of inspection charts (C1, C2, C3, C4, C5). .

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