JPH01262511A - Automatic focusing mechanism for image pickup device - Google Patents

Abstract

PURPOSE:To obtain the title mechanism whose structure is simple and inexpensive by calculating a difference value of an output in a scan of each time and obtaining that which is maximum in an absolute value, and also, extracting the maximum one of them as a focusing information value. CONSTITUTION:The title mechanism is provided with a signal processing means 13 for calculating a difference value of an output in a scan of each time, obtaining that which is maximum in an absolute value, and also, extracting the maximum one of them as a focusing information value. That is, when that which is maximum in its absolute value by which a difference value of each electrical image signal obtained by a scan of each time is calculated by the signal processing means 13 is obtained, it can be obtained as information for showing the best focusing degree on a screen in each scan. Subsequently, the maximum one in the maximum difference value in a scan of each time is extracted as a focusing information value by the signal processing means 13, and a focusing position at the time when a scan which has obtained it has been executed becomes a focused position. In such a way, a special optical system and a controller are not required.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an automatic focusing mechanism for an imaging device.
For example, it is used for automatic focus adjustment for pattern recognition by an imaging device.

2. Description of the Related Art As this type of automatic focusing mechanism, the one shown in FIG. 7 is conventionally known. This one is image controller a
In this device, a pattern on a workpiece d is recognized and processed by an image pickup device controlled by an image pickup device and an objective lens C placed on the imaging optical path. A first ranging optical path is formed which branches from the imaging optical path r by the half mirror e and reaches the line sensor g, which forms a light receiving surface equivalent to the imaging surface of the imaging device. The first distance measuring optical path is further branched by a half mirror 1 provided in the middle, and a second distance measuring optical path k is formed by a reflecting mirror j to reach a position different from the first distance measuring optical path of the line sensor g. is forming.

The first distance measurement optical path creates an imaging state equivalent to the imaging plane on the line sensor g, whereas the second distance measurement optical path is longer than the first distance measurement optical path. Rather than in the case of , the image formation state of the front focus is created, and the combination of the states of the outputs m, , mz when the re-imaging state is viewed at the electrical level is used to focus, front focus,
It is designed to judge back pins.

Problems to be Solved by the Invention However, in the conventional method as described above, an optical system for distance measurement and a controller for automatic focusing that processes signals obtained by this optical system are specially required. Therefore, the structure is complicated and expensive, and the device becomes large. There is also the inconvenience that automatic focusing can only be performed on one point on the imaging screen.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an automatic focusing mechanism for an imaging device that can solve the above-mentioned problems by skillfully employing an imaging device that can scan a desired portion on an imaging screen. .

Means for Solving the Problems In order to achieve the above-mentioned objects, the present invention provides an imaging means capable of repeatedly scanning a desired portion of an imaging surface, a focus adjustment means in the most image means, and a focus adjustment means that an operation control means that operates within a range and causes the imaging means to scan a specific portion at each predetermined focus adjustment position, and calculates the difference value of the output in each scan of the desired portion and obtains the maximum absolute value. and a signal processing means that extracts the largest one of the deflections as a focus information value and sets the focus adjustment position at the time when the scan obtained is performed as the focus position. This is a characteristic feature.

Preferably, the imaging means is a MOS camera, and the focusing means uses a piezo actuator as a drive source.

In the above-mentioned feature, the focus adjustment means of the imaging means is operated within a predetermined range by the operation control means, and the imaging means adjusts the desired portion of the image capture screen at each predetermined focus adjustment position in this operation. is scanned. The electrical image signal obtained by each scan corresponds to each focus adjustment position, and includes information on the degree of focus at each focus adjustment position as a difference in contrast depending on the degree of focus. By setting the predetermined range of the focal point tJ4 to always include the in-focus position with respect to the test surface, it is possible to include focus information in the image signal.

Therefore, the signal processing means calculates the difference value of each electrical image signal obtained in each scan, and when the maximum absolute value is obtained, it is used as information indicating the best degree of focus on the screen in each scan. Obtainable. Next, the signal processing means extracts the maximum of the maximum difference values in each scan as a focus information value, and the focus adjustment position at which the scan obtained from this value is performed is determined as the focus position. , corresponding to the fact that the focus position is within the predetermined range of focus adjustment, it is possible to obtain a result that matches the actual focus position.

The operation control means and the signal processing means can be replaced by the functions of the electronic control means possessed by the imaging means.

If a MOS type camera is used as the imaging means, the scanning and signal processing can be performed at high speed, and if the focus adjustment means uses a piezo actuator as the driving source, the focus adjustment operation can be performed in minute strokes at high speed and without vibration, and at a predetermined position. Can be stabilized in position. Therefore, when a MOS type camera and a piezo actuator are used in combination, a high-speed and accurate autofocus function can be achieved.

Embodiment FIG. 1 shows an embodiment in which the present invention is applied to an imaging device for pattern recognition.

As shown in the figure, this imaging device images the inspection surface 2a of the workpiece 2 on the base plate 1 with a camera 4, and detects 50 kinds of patterns as shown in FIG. I'm starting to recognize it.

For this recognition work, an objective lens 3 is installed in the imaging optical path 15 of the camera 4, and these constitute an imaging optical system 10 with high magnification and a shallow depth of focus. In such an optical system, a slight focus adjustment can greatly change the degree of focus. On the other hand, high speed is required for the autofocus function in order to improve workability.

In order to cope with these problems, the camera 4 is an MO5 type camera having a partial scanning mode that can repeatedly scan a desired part of the imaged screen at high speed. In addition, a piezo actuator 6 is connected to the holder 16 of the objective lens 3 as a focus adjustment means, and by driving the piezo actuator 6 with a piezo power source 7, focus adjustment can be performed accurately in minute strokes, at high speed, and without vibration. There is.

The driving unit W8 of the camera 4 and the piezo power source 7 are connected to an electronic control device 9 such as a microcomputer via a distributor 11, and the control device 9 controls the camera 4 and the piezo actuator 6 for pattern recognition and automatic focusing. It controls the operation and performs the necessary signal processing associated with it.

Since the pattern recognition operation by the control device 9 is already known, a description thereof will be omitted.

The automatic focusing operation by the control device 9 is performed as necessary before the pattern recognition operation. As a specific configuration for this purpose, the control device 9 is programmed with a function as an operation control means 12 that causes the camera 4 and the piezo actuator 6 to perform automatic focusing operations, and a function as a signal processing means 13 that performs necessary signal processing. It is given by.

Depending on the function of the operation control means 120, the piezo actuator 6 is operated in a predetermined focus adjustment range Z, and a desired specific portion of the imaging surface of the camera 4 is scanned for each predetermined focus adjustment position.

The predetermined focus adjustment range Z is set so as to include the in-focus position with respect to the test surface 2a of the workpiece 2 normally positioned on the base plate 1, and is required to be about 30 μm. Further, in order to determine the focus position with high precision, it is preferable to set the step width for focus adjustment to about 2 μm. Therefore, the piezo actuator 6 is driven in 16 steps of 2 μm each. As a result, the displacement pz of the piezo actuator 6 is from 0 Bra to 32 μm, and the focus adjustment position is set to 17 addresses including a state of no displacement. Each piezo voltage Pv8 required to drive the piezo actuator 6 to obtain each address can be set from the relationship between the piezo voltage PvN and the displacement amount PZN of the piezo actuator 6 shown in FIG.
It is made into a table and programmed into the control device 9 in advance. The displacement speed of the piezo actuator 6 is lμIII
/ff1s.

The partial scanning performed by the camera 4 may be performed at a suitable portion on the surface to be inspected 2a, for example, a portion advantageous for determining the focus state.
Alternatively, this is performed on an image portion corresponding to a target portion P as shown by the imaginary line in FIG. 2, which is a portion to be particularly focused on. For this reason, input for setting a partial scanning area on the imaging plane is appropriately made to the control device 9.

One partial scan is divided into, for example, five scanning lines.

In actual partial scanning mode, 5 lines out of all normal scan lines are set as valid lines, 21 lines are set as invalid lines, and the next 5 lines are set as effective lines. It is done through repetition. As shown in FIG. 4, the monitor image of the camera 4 obtained by this partial scanning includes an effective line portion (white) 21 and an invalid line portion (
(diagonal lines) 22 are arranged alternately.

In this screen, among the effective line portions 21, each scanning line portion 21 .corresponds to the 17 focus adjustment addresses. ~2117, and each line part 21
．． In synchronization with the partial scanning performed in steps 2117 to 2117, a focus adjustment operation is performed so that the objective lens 3 is positioned at the corresponding address.

Each effective line portion 21+~211? As shown in FIG. 5 with a portion omitted, the image corresponding to the image at the target portion P on the test surface 2a is sharp according to the degree of focus of each focal point tA node of the objective lens 3. Formed in degrees.

If the focus level is low, the image 5a of the pattern 5 will be blurred, and the image 5a will be blurred.
The contrast between the border and the part without a is small. Furthermore, when the degree of focus is high, the image 5a of pattern 5 becomes clear, and the image 5a
There is a great contrast with the parts without. This difference in contrast can be known as a difference in output potential in partial scanning for each effective line portion 2L to 211F.

Therefore, by the function of the signal processing means 13, first, a difference value N is determined for the scanning output given in time series in each effective scanning portion 211 to 21.7. The difference value N is obtained by comparing outputs for each predetermined pixel unit in continuous scanning outputs, and its absolute value INI becomes contrast information between pixels.

Therefore, each effective line portion 21. ~21+? By determining which part of the throat has the maximum INI, it is possible to know the effective line part where the image with the highest degree of focus was obtained, and it can be determined that the in-focus position is included in the predetermined focus adjustment range. Correspondingly, this means that the image in the effective line portion whose INI is maximum was actually in focus, and the focus adjustment address of the objective lens 3 when that scan was performed is the focus position. It can be determined that

This determination is also executed by the function of the signal processing means 13.

Specifically, each effective scanning portion 21. Find the INI for each of ~2117 and apply it to each effective scanning portion 2.
1. ~211? The maximum INI among them is extracted as focus information NM, and this ? The focus adjustment address of the objective lens 3 when scanning the effective scanning portion where JM was obtained is determined to be the in-focus position.

When this determination is obtained, the function of the operation control means 12 causes
The objective lens 3 is moved to the address related to the determination. As a result, the optical system IO is automatically and accurately focused on the inspection surface 2a of the workpiece 2 set on the base plate 1, even if it has a high magnification and a shallow depth of focus, and the pattern 5 can be recognized accurately. It will be held in

In the above embodiment, the focus adjustment is performed by moving the objective lens 3, but the invention is not limited to this, and the base plate l
It can also be done by raising and lowering the workpiece 2 using the camera 4.
It can also be done in a number of ways.

Effects of the Invention According to the present invention, an automatic focusing function can be achieved using only an imaging means capable of repeatedly scanning a desired area, its focus adjustment means, operation control means, and signal processing means, and operation control,
Each signal processing means can be replaced by the control function of the control device used for pattern recognition etc. in the imaging means, and the focus adjustment means is also commonly used, so there is no need for a special optical system or a conventional one. The structure is simple and inexpensive since no controller is required. Furthermore, the device does not become larger. Further, the scanning for automatic focusing in the imaging means is partial, and although it is performed sequentially at each focus adjustment position within a predetermined focus adjustment range, it does not extend the time. Partial scanning can be performed on any part of the imaging screen,
The autofocus function can be freely operated on necessary parts such as parts of the surface to be examined that are advantageous for focus adjustment and parts to be particularly focused.

Furthermore, if a MOS type camera is used as the imaging means and a piezo actuator is used as the drive source for the focus adjustment means, the automatic focusing operation by partial scanning can be performed at high speed, accurately, and without vibration due to their properties.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an imaging device for pattern recognition showing an embodiment of the present invention, FIG. 2 is a plan view of the surface to be inspected of a workpiece, and FIG.
The figure is a graph showing the relationship between the piezo voltage pv, 4 and the displacement mpz of the piezo actuator.
5 is a diagram showing the state of an image obtained by repeating partial scans, and FIG. 6 is an absolute value distribution graph of the maximum difference value obtained in each partial scan. FIG. 7 is a schematic diagram of an imaging device showing a conventional example of an automatic focusing mechanism. 2・・・−・・−−−−・・−・−−−−−・・−・
・−・・−・・Work 2a・−・−−−−−・
・・−・−・・−・・−・・−・−・・Test surface 3・
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・−・Objective lens 4−・−・−・−・・・
・・・−・−・・・MOS type camera 6・・・−
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Piezo actuator 7・−・・・・−・・・・・・・・・−・
−・・・−・−・・・・・・・・・・・・Piezo ti! 9・
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......Control device 12...-...--
・・−・・−・−・・・・−・−・−Operation control means 13
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・－・・・・・・－Signal processing means. Acting A4 Patent Attorney Toshio Nakao Number 1 Figure 2 Figure 5 Figure 3 Piezo pressure PVN () ≦2

Claims (2)

[Claims] (1) An imaging means that can repeatedly scan a desired part of the imaging surface, a focus adjustment means in the imaging means, and a method for operating the focus adjustment means within a predetermined range and scanning a specific part by the imaging means at each predetermined focus adjustment position. Calculate the difference value between the outputs of each scan at the desired portion, obtain the maximum absolute value, and further extract the maximum deviation as the focus information value. and a signal processing means that sets the focus adjustment position at the time when scanning is performed to obtain the autofocus mechanism. (2) The automatic focusing mechanism of the imaging device according to claim (1), wherein the imaging means is a MOS type camera, and the focus adjustment means uses a piezo actuator as a driving source.