JPH11325851A - Work surface measurement device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the need of measuring a distance from a work beforehand, to provide images sufficient for measurement without using an expensive automatic focusing device, and to perform highly accurate measurement by fetching plural images while continuously changing the distance between a camera and the work, selecting the image of maximum contrast in them, and performing an image processing. SOLUTION: A Z stage to which a CCD camera is fixed is moved to an initial position, photographing is started from the position and movement is started in an upper direction. Image picked-up video data are successively stored inside an image memory. When the prescribed number of sheets are stored, the image data of the maximum contrast in them are searched. Then a work surface is measured by using only the searched image of the maximum contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for measuring a work surface, and more particularly to an apparatus and a method for observing a work surface obtained by an image sensor.

[0002]

2. Description of the Related Art Generally, when measuring the position and dimensions of a semiconductor chip or the like with high precision using an image processing apparatus, a high-power lens having a small depth of field is required. For this reason, conventionally, it has been necessary to measure the height of the surface of the semiconductor chip with a displacement sensor, drive the stage based on the measured value, focus the camera, or attach an expensive autofocus mechanism. FIG. 3 shows a configuration example of such a system.

[0003]

However, in the method of measuring the height with the displacement sensor, the cost of the displacement sensor for measuring the height increases, and the field of view of the camera does not interfere with the displacement sensor. In addition, it is necessary to perform measurement at another place, the apparatus becomes large, and it is necessary to accurately adjust the height of the work positioning table between the height measurement and the image measurement.

[0004] When the autofocus mechanism is attached, the structure becomes complicated and the cost increases as described above.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and provides an in-focus image with a simple configuration without using an expensive auto-focus mechanism and a sensor for detecting the height of a work. It is an object of the present invention to provide a measuring method and a measuring device.

[0006]

In order to solve this problem, for example, a work surface measuring method of the present invention includes the following steps. That is, an imaging unit for observing the work surface and a stage for changing a relative distance between the work, an imaging control unit for imaging the imaging unit a plurality of times while moving the stage, and the imaging control unit. The image having the maximum contrast among the obtained plurality of images is determined, and the work surface is measured with only the determined image.

[0007]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

In the embodiment, as a method for observing the surface of a work, the present invention is applied to an apparatus for inspecting whether a heater board in a recording head for discharging ink droplets by thermal energy is attached to a proper position with respect to a base plate. I will explain.

FIG. 1 is a schematic configuration diagram of the present inspection apparatus.

The work positioning table can be moved by a shifter. The work (the heater plate mounted on the base plate) placed on the work positioning table is positioned at the reference position by the butting cylinder. The CCD capable of observing the pattern on the surface of the heater board is mounted on the Z stage, and can continuously change the distance to the work.
The image signal output from the CCD camera can store a plurality of images in a memory via an A / D converter in the image processing apparatus.

The controller can control the Z stage,
It controls various actuators such as shifters and butting cylinders, and exchanges signals with peripheral devices.

Next, the operation of the present inspection apparatus will be described with reference to the time chart of FIG.

First, the work supplied on the work positioning table is moved to below the CCD camera by the shifter.
The work is positioned at the reference position by the butting cylinder on the positioning table.

Next, the Z stage is raised from a position slightly below the position where the focus is considered to be in focus. The moving speed of the stage at this time is, for example, 50 μm / 33 msec = 1500 μm / sec if the depth of field of the optical system is 50 μm and the image capturing period is 33 msec.
The degree is appropriate.

At the same time as the stage is lifted, the capture of an image is started. In FIG. 2A, data is captured five times. After the image capturing is completed, the positioning cylinder of the work is released, and the Z stage is returned to the original position.

At the same time, the image processing apparatus selects a screen having the maximum contrast from the stored image data of five screens,
Then perform image processing based on the selected image,
Measure the position of the heater board.

As a result, an in-focus image can be obtained within the same time as in the conventional case of FIG.

The method of calculating the position of a predetermined pattern from an image having a suitable contrast can be easily realized by using functions such as image correlation. However, since this processing is not directly related to the present invention, it is omitted here.

Now, the principle for selecting the image having the highest contrast from a plurality of images will be described. An example of this principle will be described below.

Generally, when the subject is out of focus, the contrast (difference between the maximum luminance and the minimum luminance) is low (small), and when the subject is in focus, the contrast is high (large). In other words, it is sufficient to use the fact that the brightness (or density) change becomes gentle for an image that is out of focus, and the brightness change becomes large if the image is in focus.

Therefore, in the embodiment, for each of a plurality of captured and stored images, the difference in luminance between adjacent pixels is calculated, and the maximum value is obtained. However, since the luminance difference includes positive and negative signs, in the embodiment, the absolute value of the luminance difference between adjacent pixels is calculated, and the maximum value is calculated.

Further, since the CCD element usually has an imaging capability of at least hundreds of thousands of pixels, in order to reduce the above calculation amount, for example, it is performed on several lines near the center in a captured image.

The above operation is performed on all of the photographed image data, and it is determined that the position of the Z stage at the time of photographing the image having the maximum calculation result is in focus. Thereafter, the subsequent steps are performed.

FIG. 4 is a block diagram of a system (mainly the image processing apparatus of FIG. 1) in the embodiment. In the figure, reference numeral 1 denotes a CPU that controls the entire apparatus, and 2 denotes a ROM that stores a program corresponding to a flowchart of FIG. 5 described later. Reference numeral 3 denotes an R which can be used as a work area of the CPU 1 and can store a plurality of captured images.
AM. Reference numeral 4 denotes an A / D converter for converting video data from the camera into, for example, 8-bit digital data for each pixel. Reference numeral 5 denotes a control device (see FIG. 1) for controlling a Z stage and a shifter.

The operation of the above configuration will be described below with reference to the flowchart of FIG.

First, in step S1, the Z stage is moved to an initial position. This initial position is a position that is a predetermined distance below a position (average position) where the focus (focus) is considered to be in focus on the heater board.

Next, proceeding to step S2, the Z stage is started to move upward at a predetermined speed, and an image is taken by a camera in step S3. The photographed video (image) data is stored in a RAM together with the Z stage position information at the time of the photographing.
3 is stored in the image memory 3a. Then, step S5
In this case, this operation is performed a predetermined number of times N (5 in the above embodiment).
Repeat) until it is determined that the number of times has been reached.

When the imaging and storing process has been completed N times while the Z stage is being raised, the process proceeds to step S6, and the Z stage is stopped.

In step S7, the image memory 3a
Is searched for the image having the maximum contrast from the image data stored in. In this process, as described above, the maximum of the absolute value of the difference between adjacent pixels is obtained for each image, and the image having the maximum calculation result is searched.

Then, proceeding to step S8, the position of the heater board is measured using only the searched image, and this processing ends.

According to the present embodiment as described above,
While continuously changing the distance between the CCD camera and the work, multiple images were captured, and the image with the highest contrast was selected for image processing, so it was necessary to measure the distance to the work in advance. Even without using an expensive autofocus device, an image sufficient for measurement can be obtained, and high-precision measurement can be performed.

Although the above description has been made on the assumption that an image is taken by the camera while the Z stage is being moved, the Z stage may be stopped until the imaging is started and completed (exposure time). . However, from an operator's point of view, it is instantaneous and looks as if it is moving continuously. This is the same in the following second embodiment.

<Second Embodiment> In the above embodiment, Z
While the stage was being lifted, N images were taken and stored in the image memory 3a. However, in order to improve the accuracy, the moving speed of the Z stage was reduced or the shooting interval was shortened. What is necessary is just to increase the number of captured images. However,
This requires more image memory.

Thus, in the second embodiment, an example will be described in which more images are captured with a small memory capacity and higher-precision measurement is possible.

The principle of the second embodiment is as follows.

After the first image is photographed and stored in the image memory 3a together with the position information of the Z stage at that time, two adjacent pixels having the maximum luminance difference in the image data in the image memory 3a are obtained. Detect the position. Then, the position of a pixel group in an appropriate spread range including the two adjacent pixel positions (for example, a range including the left and right pixels of the two adjacent pixels with respect to the horizontal scanning line) and the data of the pixel group are stored in another area (tentatively, RAM3). The image data already stored in the image memory 3a is opened so that the image taken at the next timing can be overwritten. For the sake of simplicity, the number of the pixel groups to be extracted is 10 pixels, that is, pixels represented by four pixels on the left and right of two pixels considered to have the maximum luminance difference are stored in another area of the RAM 3 at that time. It is stored together with the position of the Z stage.

When the above processing is completed, the upward movement of the Z stage is started, and the second and subsequent imaging starts.
The process for the first captured image requires a lot of time since it processes one image data, so the movement of the Z stage was started when the second and subsequent imaging was performed.

The result of the second image pickup is stored in the RAM 3
Is temporarily stored in the image area 3a, and the image data of the pixel group at the previously determined position is stored in the area 3b together with the Z stage position information at that time. This processing may be simply data transfer, and since the data to be transferred is at most several pixels, it can be realized at a speed sufficient for the shortest imaging cycle by the CCD camera. Then, the image memory 3a is opened for storing the next imaging result.

By repeating the above operation a predetermined number of times, the area 3b stores only image data in a range centered on the position where the first captured image is considered to have the highest contrast. Moreover, there is no need to store a plurality of image data, and the capacity of the memory 3 can be significantly reduced.

With respect to the image data (here, 10 pixels) stored in the area 3b as described above,
Calculate the maximum value of the absolute value of the difference between adjacent pixels,
The Z stage position where the largest data is taken is determined as having taken the image with the maximum contrast,
The Z stage may be moved to that position.

As described above, according to the second embodiment, compared with the first embodiment, the required memory capacity is drastically reduced, and the position of the focused Z stage can be determined with higher accuracy. Become.

The present invention may be applied to a system constituted by a plurality of devices or to an apparatus constituted by a single device.

Another object of the present invention is to provide a storage medium storing a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to provide a computer (or CPU) of the system or apparatus.
And MPU) read and execute the program code stored in the storage medium.

In this case, the program code itself read from the storage medium realizes the function of the above-described embodiment, and the storage medium storing the program code constitutes the present invention.

As a storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD
-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used.

When the computer executes the readout program code, not only the functions of the above-described embodiment are realized, but also the OS (Operating System) running on the computer based on the instruction of the program code. ) May perform some or all of the actual processing, and the processing may realize the functions of the above-described embodiments.

Further, after the program code read from the storage medium is written into a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, based on the instructions of the program code, It goes without saying that the CPU included in the function expansion board or the function expansion unit performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0048]

As described above, according to the present invention, a plurality of images are fetched while continuously changing the distance between the camera and the work, and the image having the largest contrast is selected from among the images. Therefore, it was not necessary to measure the distance to the workpiece in advance, and an image sufficient for the measurement was obtained without using an expensive autofocus device, and high-precision measurement became possible.

[0049]

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a system according to an embodiment.

FIG. 2 is a timing chart for comparing operation processing according to the embodiment with that of the related art.

FIG. 3 is a configuration diagram of a conventional system.

FIG. 4 is a block diagram of an image processing apparatus according to the embodiment.

FIG. 5 is a flowchart illustrating an operation processing procedure in the embodiment.

Claims (6)

[Claims] An imaging unit for observing the surface of the work, a stage for changing a relative distance between the work and the imaging unit; an imaging control unit for imaging the imaging unit a plurality of times while moving the stage; A work surface measuring device comprising: a control unit that determines a video having the maximum contrast among a plurality of images obtained by the control unit and determines a work position using only the determined video. 2. The image processing apparatus according to claim 1, wherein the control unit includes a calculating unit configured to calculate a maximum value of a difference between adjacent pixels in a plurality of captured image data, and using only an image having a maximum value calculated by the calculating unit. The work surface measuring apparatus according to claim 1, wherein the work position is determined by using the work position. 3. The control means detects a position having a maximum luminance difference between adjacent pixels in video data obtained by first capturing an image, and stores a pixel group in a predetermined range in the vicinity including the position. A second storage unit that stores only a pixel group in the range that is stored in the first storage unit with respect to video data obtained by imaging the second and subsequent times; With respect to the pixel data stored in the first and second storage means, the stage position is determined when the video data in which the sum of the luminance differences between adjacent pixels in the pixel group obtained at each of the imaging timings is the largest is captured. The work surface measuring apparatus according to claim 1, wherein the measuring is performed. 4. An imaging means for observing a work surface, and a work surface measuring method capable of changing a relative distance to the work by a stage, wherein the imaging means is imaged a plurality of times while moving the stage. A work comprising: an imaging control step; and a control step of determining an image having a maximum contrast among a plurality of images obtained by the imaging control step, and determining a work position using only the determined image. Surface measurement method. 5. The controlling step includes a calculating step of calculating a maximum value of a difference between adjacent pixels in a plurality of captured video data, and using only the video having a maximum value calculated in the calculating step. The method for measuring a work surface according to claim 4, wherein the work position is determined by using the method. 6. The control step detects a position having a maximum luminance difference between adjacent pixels in video data obtained by first capturing an image, and determines a pixel group in a predetermined range in the vicinity including the position. A first storage step of storing the number of pixels in the storage means, and for the video data obtained by imaging the second and subsequent times, only the pixel groups in the range stored in the first storage step are stored in the storage means. A second storage step of storing, and an image in which the sum of the luminance differences between adjacent pixels in the pixel group obtained at each of the imaging timings is maximum with respect to the pixel data stored in the first and second storage steps 5. The work surface measuring method according to claim 4, wherein a stage position when data is imaged is determined.