JPH05196562A - Hardness measurement method - Google Patents

Abstract

PURPOSE:To well execute automatic focusing in which pushed dent image is focused on the light receiving surface of a two dimensional imaging element in the measurement method for automatic hardness measurement of a measured sample. CONSTITUTION:In a full-automatic hardness measurement method, a pushed dent is formed on a measured sample 0 put on a moving stage 10 with a pusher 23 and an object lens 22 is selected. A magnified image IA of the pushed dent is focused with the object lens 22 on the light receiving surface 1 of an imaging element to read the pushed dent image and the hardness of the measured sample O is calculated. After selecting the object lens 22, autofocusing is performed by setting slightly wider area than the pushed dent image IA including the focused position of the pushed dent image IA as DAF of AF and thus, the pushed dent image IA is focused on the light receiving surface 1 of the imaging element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hardness measuring method.

[0002]

2. Description of the Related Art Conventionally, a method of marking a square quadrilateral indentation on a measurement sample with a predetermined pressure and measuring the diagonal length of the indentation to specify the hardness of the measurement sample has been conventionally related to a Vickers hardness tester. A device disclosed in Japanese Examined Patent Publication No. 3-34819 is known as a device for performing such a measuring method. In this conventional apparatus, since the indentation is read by using a one-dimensional image pickup device, it takes a long time to focus the objective lens on the measurement sample on which the indentation is formed, and it takes a long time to measure the hardness. There is a problem.

In order to solve such a problem, the present inventors have stated that "they are movable in the X, Y and Z directions which are orthogonal to each other, and Z
A revolver in which a movable stage rotatable about a rotation axis parallel to the direction and a two-dimensional image pickup device are opposed to each other in the Z direction, and an objective lens and an indenter are equidistant from the rotation axis. After the movable stage and the image sensor are arranged so as to be rotatable about the rotation axis parallel to the Z direction and movable in the Z direction, an indentation is formed by an indenter on the measurement sample installed on the movable stage. , The revolver is rotated to select the objective lens, the magnified image of the indentation is formed on the light receiving surface of the image sensor by the objective lens, the indentation image is read, and the hardness of the measurement sample is calculated. Is intended for practical use.

In this measuring method, the process of setting the measurement sample on the moving stage and then calculating the hardness is automatically performed. When the objective lens is selected, autofocus is performed to form an image of the indentation on the light receiving surface of the image pickup device.

At this time, assuming that the entire light receiving surface of the image pickup device is an AF area (autofocus area: an area for fetching a signal for performing autofocus processing), a small "scratch" on the surface of the measurement sample or the same adheres to the surface. There is a problem that "dust" or the like affects the autofocus and causes an error in the autofocus. Further, if autofocusing is performed based on the information of the entire light receiving surface, there is a problem that the autofocusing takes a long time because a large amount of information is handled.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and the autofocus is not easily affected by scratches or dust on the surface of the measurement sample, and the autofocus can be shortened in time. The object is to provide a new hardness measuring method.

[0007]

According to the hardness measuring method of the present invention, there is provided a moving stage which is movable in X, Y and Z directions orthogonal to each other and is rotatable about a rotating shaft parallel to the Z direction.
A three-dimensional image pickup device facing each other in the Z direction, and a revolver provided with an objective lens and an indenter at positions equidistant from the rotation shaft is provided between the moving stage and the image pickup device in the above-mentioned rotation axis parallel to the Z direction. It is arranged so as to be rotatable around and movable in the Z direction, and after the indenter is formed on the measurement sample installed on the moving stage by the indenter, the revolver is rotated to select the objective lens, and the indentation is removed by the objective lens. The magnified image is formed on the light-receiving surface of the image sensor to read the indentation image, and the hardness of the measurement sample is calculated. The "rotation axis" of the moving stage and the "rotation axis" of the revolver may be aligned or may be offset from each other.

According to the method of claim 1, "after selecting the objective lens, an area including the image forming position of the indentation image and slightly wider than the indentation image is set as an AF area for autofocusing to pick up the indentation image. Form an image on the light receiving surface of the device. "
It is characterized by

Since the objective lens and the indenter are arranged at positions equidistant from the "rotation axis" of the revolver, the indenter was formed when the indentation was formed by forming the indentation on the measurement sample and then rotating the revolver. If the objective lens occupies the position, the image formation position of the indentation image is uniquely determined except for a mechanical error. Therefore, the AF area may be fixedly set in advance in the control program. In the above description, “selecting the objective lens” means “rotating the revolver so that the objective lens occupies the position occupied by the indenter when the indentation was formed”.

In order to perform autofocus more accurately in consideration of the mechanical error and the like, as in the method of claim 2, "after selecting the objective lens, the entire light-receiving surface of the image pickup device is roughly defined as an AF area. Perform autofocus, binarize the image sensor output in a roughly focused state, select the raster with the longest black area in the scanning direction, and set the center of the black area in this raster as the center of the indentation,
Based on this center portion, the AF area for indentation is set according to the size of the indentation to perform finer autofocusing. "

Depending on the measurement conditions, a plurality of indentations may be formed on the measurement sample, and the hardness may be calculated for each indentation formed. In such a case, "After forming indentations at predetermined multiple positions on the measurement sample installed on the moving stage, select the objective lens, and then move the moving stage to bring the indentations to the optical axis position of the objective lens. The process of performing hardness measurement is repeated for all indentations ”(claim 3). In this way, when "a plurality of indentations are formed on the surface of the measurement sample", "When performing hardness measurement on each indentation after selecting the objective lens, bring the indentation group to the image formation area by the objective lens and then take an image. The entire light-receiving surface of the device is used as the AF area for rough autofocusing, and the light-receiving content of all light-receiving surfaces is binarized in a roughly focused state, and the black area is the expected area of the indentation ± 50%.
Area is selected, the square root of the area of the selected area and the ratio of the perimeter are used as parameters for identification, a pattern close to a square is specified as an indentation, and the center coordinates of the specified indentation are calculated. The AF area can be set around the coordinates "(claim 4).

[0012]

First, the outline of the hardness measurement, which is the premise of the present invention, will be described with reference to a concrete apparatus example.

FIG. 5 (a) schematically shows only an essential part of an example of a hardness measuring apparatus for carrying out the present invention. In the figure, reference numeral 10 is a moving stage, reference numeral 20 is a revolver, and reference numeral 3
0 is an illumination system, 40 is a CC as a two-dimensional image sensor
Reference numeral 50 denotes a D camera, and an image processing unit. Also, reference numeral 6
Reference numeral 0 represents a display, reference numeral 70 represents a revolver / indenter driving device, reference numeral 80 represents a stage controller, and reference numeral 90 represents a computer. The whole of them is appropriately supported by a supporting means (not shown).

The moving stage 10 is an X-direction stage 10X which is displaced in the X direction corresponding to the direction orthogonal to the drawing of FIG. 5A, and a Y which is displaced in the Y direction corresponding to the left-right direction in the figure.
Direction stage 10Y and Z corresponding to the vertical direction in FIG.
It is configured by combining Z-direction stages 10Z that are displaced in the direction, and the whole is rotatable about a predetermined Z axis (rotation axis) parallel to the Z direction. The step motor MX is operated to move the X-direction stage 10X in the X-direction, and the step motors MY and MZ are operated to displace the Y- and Z-direction stages 10Y and 10Z, respectively. Further, in order to rotate the entire moving stage 10 around the Z axis, the step motor Mθ is operated. The measurement sample 0 is the X-direction stage 10X of the moving stage 10.
Placed on top.

In FIG. 5 (a), the chain line indicated by symbol S indicates the "reference axis" in the hardness measuring device. The reference axis S is fixedly set in the measuring device space in parallel to the Z direction, which is the moving direction of the Z direction stage 10Z that can be placed on the moving stage 10, and in this device example, Z is the "rotational axis" of the stage described above. Aligns with the axis.

The revolver 20 includes a main body 21 having a "rotation axis" 25 parallel to the reference axis S, an indenter 23 and an objective lens 2.
2 are fixedly provided, can rotate around the rotation shaft 25, and can also move in the direction of the rotation shaft 25 (direction parallel to the reference axis S). The rotary shaft 25 is set apart from the reference shaft S (the rotary shaft of the moving stage 10) by a predetermined distance H.

The revolver 20 is rotated and moved by a revolver / indenter drive unit 70. The revolver / indenter driving device 70 drives the stepper motor for rotating the revolver 20 around the rotary shaft 25, the motor for displacing the revolver 20 in the direction of the rotary shaft 25, and the indenter 23 when the indentation is formed. Indenter drive device 23A
Has means for operating.

In this example, the body 21 of the revolver 20 is provided with one indenter 23 and one objective lens 22. The objective lens 22 and the indenter 23 are shown in FIG.
As shown in (a), it is provided in axial symmetry with respect to the rotating shaft 25, and the distance between the tip of the indenter 23 and the optical axis of the objective lens 22 from the rotating shaft 25 is set to a distance H. The arrangement of the indenter and the objective lens in the revolver is not limited to this example, and as shown in FIG. 6B, a plurality of objective lenses 22A, 22B, 22C may be provided in addition to the indenter 23. If necessary, the revolver body may be provided with two or more types of indenters. The tip of the indenter 23 has a vertical angle of 90.
It forms a regular quadrangular pyramid-shaped point.

Returning to FIG. 5A, CC is on the reference axis S.
D camera 40 is provided, and revolver 20 and CC
An illumination system 30 is provided between the D camera 40 and the D camera 40.
The illumination system 30 includes a casing 31, a light source lamp 32, a collimator lens 33, and a semi-transparent mirror 34. The semi-transparent mirror 34 is located on the reference axis S and is inclined by 45 degrees with respect to the reference axis S. The casing portion of the portion through which the reference axis S passes is formed in the window. When the objective lens 22 is selected as shown in the figure and the light source lamp 32 is caused to emit light at the reference axis S position, the light is collimated by the collimator lens 33, reflected by the semitransparent mirror 34, and passed through the objective lens 22. Illuminate the measurement sample 0. The reflected light from the measurement sample 0 enters the light receiving surface of the CCD camera 40 via the objective lens 22 and the semitransparent mirror 34. Depending on the objective lens provided in the revolver, the illumination light flux from the illumination system may not be a parallel light flux.

For hardness measurement, as shown in FIG. 5B, after "sample setting", "indentation formation" is performed, and then the objective lens is selected by "revolver rotation", and "imaging / calculation" is performed.
The hardness is calculated by the procedure.

The indentation is formed by the revolver / indenter driving device 7
0 is operated to move the indenter 23 toward the measurement sample 0, and the tip of the indenter 23 is pushed into the surface of the measurement sample 0 at a predetermined pressure. A square quadrilateral indentation AK is formed as shown in a). FIG. 7B shows the cross-sectional shape of the indentation AK. Depending on the tip shape of the indenter, the angle γ in the figure is generally 90 degrees.

Since the pressure at which the tip of the indenter 23 is pushed is constant at a "predetermined pressure", the larger the hardness of the measurement sample 0, the smaller the indentation AK formed. Therefore, the indentation A
If the magnitude of K is measured by the diagonal lines L1 and L2, the magnitude of the diagonal lines L1 and L2 and the hardness of the measurement sample have a correspondence relationship, and the hardness can be calculated according to this correspondence relationship. The pressure applied to the indenter and the pressing time are set appropriately in advance according to the measurement sample. That is, in general, it is possible to know in advance how hard the hardness of the measurement sample is. Therefore, an appropriate indenter pressure and pressing time are set accordingly.

When the indentation is formed, the indenter 23 is returned to the revolver 20 side, and then the objective lens 22 is selected by rotating the revolver 20. With this choice,
The optical axis of the objective lens 22 is matched with the reference axis S.

Next, the illumination system 30 illuminates the measurement sample 0,
After autofocusing, the objective lens 22 is the CCD camera 4
The indentation image formed on the light receiving surface of 0 is read by the CCD camera 40, the diagonal length of the indentation is calculated from the output of the CCD camera 40, and the hardness of the measurement sample 10 is calculated based on the diagonal length. A conventionally known calculation program can be appropriately used for the calculation calculation for calculating the hardness from the diagonal length. The hardness thus calculated is output as the hardness of the measurement sample.

A feature of the present invention resides in autofocus, which is a part of the image pickup / calculation process in the above-described measurement process. As described above, an AF area slightly larger than the indentation image is set in the image formation portion of the indentation. The autofocus is performed "based only on the information in the AF area".

[0026]

FIG. 1 shows an embodiment of the method of claim 1. This embodiment is carried out by the procedure shown in FIG. The measurement process is executed by the apparatus example described with reference to FIG.

First, in the "measurement sample setting step", the measurement sample 0
Is installed on the moving stage. A position where the measurement sample 0 is set is marked on the moving stage, and when the measurement sample is set in accordance with this mark, the computer 90 as a control unit controls the moving stage 10 by the stage controller 80 to set the measurement sample 0. Move to the position of the reference axis S.

Subsequently, in the "indentation forming step", the indentation is formed by the indenter 23. As described above, the hardness of the sample to be measured is roughly known, and the pressure applied to the indenter and the indenter pressing time are stored in the computer 90 so that the size of the indentation formed is appropriate. Is set. Since the indentation is formed in this way, the size of the indentation formed can be expected to some extent. Subsequently, in the "objective lens selection step", the revolver is rotated and the objective lens 2 is rotated.
The two optical axes are aligned with the reference axis S. The "appropriate size of the indentation" means that the CC is magnified by the objective lens.
The size of the indentation image formed on the light receiving surface of the D camera is about 1/100 to 1/15 of the light receiving surface in terms of area ratio.

Following this, autofocus is executed, but prior to that, the "AF area setting step" is executed. An area indicated by reference numeral 1 in FIG. 1B is a CCD.
The entire light receiving surface of the camera is shown, and this figure shows a state in which the vicinity of the indentation forming portion of the measurement sample 0 is imaged on the light receiving surface 1. In the image-forming state, in the light receiving surface area 1, the image IA of the indentation formed on the measurement sample 0 and the scratch K on the surface are formed.
1, K2, K3, etc., dust Ho, etc. will be imaged. These scratches K1, K2, K3 and the like, dust Ho and the like generate noise signals for autofocus, which causes an error in autofocus, and in some cases, autofocus failure.

Therefore, in this embodiment, an AF area DAF which is slightly wider than the indentation image IA is set around the indentation image IA, and in the "AF step", autofocusing is performed only on signals from within the AF area DAF. The AF area is set by controlling the image processing unit 50 by the computer shown in FIG.

When the objective lens 22 is selected, the imaging magnification is 1
Computer 90 (Figure 5 (a))
First, the revolver / indenter driving device 70 moves the revolver 20 along the rotation axis 25, and the revolver 20 is arranged at a position (which is determined by a relative positional relationship with the CCD camera 40) according to the imaging magnification. Computer 90
Based on the control of 1., the Z direction stage 10Z of the moving stage 90 is driven by the stage controller 80, and the moving stage 10 including the measurement sample 0 is moved in the Z direction in predetermined steps. At each step, the output from the CCD camera 40 is taken into the image processing unit 50, and the AF area DA
The autofocus program is executed only for signals from inside F.

Since the size of the indentation is also set to an appropriate size as described above, the size of the AF area to be set may be uniquely determined, but in this example, the size of the indentation (predictably The size is adjusted accordingly.

Various methods are known for autofocus, and a known method may be used as a specific method. For example, the maximum and minimum of all pixel outputs in the AF area DAF of the CCD camera 40 are obtained, and the Z-direction stage 10Z
According to the method, the maximum and minimum difference is calculated each time the measurement sample 0 moves in the Z direction by one step, and the Z direction stage 10Z may be controlled so as to find the position where the calculation result is maximum.

In this way, when the autofocus operation is completed, an enlarged image IA of the indentation marked on the measurement sample 0 is formed on the light receiving surface of the CCD camera 40. continue,
In the "hardness measuring step", the diagonal length of the indentation is calculated from the output of the CCD camera 40, and the hardness of the measurement sample 10 is calculated based on the diagonal length. A conventionally known calculation is used as the calculation calculation for calculating the hardness from the diagonal length. The hardness thus calculated is output as the hardness of the measurement sample.

In the above embodiments, the setting position of the AF area is also set to be unique on the assumption that the positional relationship between the selected objective lens and the indentation is uniquely set in the X and Y directions.
However, in reality, the measurement sample may slightly move from its initial position on the moving stage due to some mechanical error or some reason. In consideration of such a point, the size of the AF area set in the case of the above-described embodiment is “a deviation from the theoretical position of the actual indentation image position” due to the error or movement.
It is necessary to set it with a margin. Then, the probability that scratches, dust, or the like causing an autofocus error will enter the inside of the AF area set according to the indentation also increases. Therefore, it is desirable to set the AF area as small as possible according to the impression image.

To do this, for example, the process shown in FIG. 2 may be performed. That is, after the indentation is formed, first, the entire area of the light receiving surface of the CCD camera, that is, the "entire screen" is set as the AF area and rough autofocus is performed (in this rough autofocus process, one step of movement in the Z direction is appropriate. To make it bigger). Then, the position of the indentation is roughly measured in a roughly focused state. In a roughly focused state, the “concave portion” on the surface of the measurement sample becomes a high density portion. Therefore, if the output of each pixel is binarized in this state, the above concave portion becomes a “black” region. Further, in this state, the largest concave portion on the surface of the measurement sample is an indentation. Therefore, CC which is a two-dimensional image sensor
When the raster having the longest "black" area is selected in the scanning direction of the D camera, this raster is considered to pass approximately through the center of the indentation. Therefore, the center of the largest "black" area in this raster approximately gives the center of the indentation. Also, the length of the "black" region will give an approximate size of the indentation.

In this way, since the position and size of the indentation can be specified with considerable accuracy, the AF area is set based on the indentation position and size specified in this way. At this time, since the surface of the measurement sample is in a rough focused state, the size of the indentation image does not change significantly even if fine autofocus is performed thereafter. Therefore, based on the approximate size of the indentation determined as described above, it is possible to set an appropriate AF area according to the size of the indentation.

In each of the embodiments described above, it was premised that the number of indentations formed on the surface of the measurement sample was 1.
As described above, depending on the measurement conditions, a plurality of indentations may be formed on the same measurement sample, and the hardness may be calculated for each indentation. The procedure of one embodiment in such a case is shown in FIG.

In this embodiment, when a measurement sample is set, first, a predetermined number of indentations are formed. The number of indentations formed and the formation positions are entered in advance in the computer,
By moving the moving stage, the measurement sample is moved relative to the indenter to sequentially form indentations.

After forming a predetermined number of indentations, the objective lens is selected. Then, the process from setting the AF area to calculating the hardness is repeated for each indentation. If the number of indentations formed on the surface of the measurement sample is relatively small (2 to 3) and the images of the indentations all fit within the light receiving surface of the CCD camera at one time, move the moving stage after selecting the objective lens. Do not operate, A for each indentation on the light receiving surface of the CCD camera
It is sufficient to set the F area. At this time, after setting the AF area for one indentation image, autofocus is performed on this indentation image, and the diagonal line of the indentation is measured to calculate the hardness. The same process is then repeated for another impression image.

The AF area for each indentation can be uniquely set according to the data (the position where the indentation is formed and the expected size of the indentation) at the time of forming the indentation. It is desirable to set an AF area with a size that is slightly larger than the size of the indentation, and doing so increases the probability that scratches and dust will enter the set area. Therefore, even when a plurality of indentations are formed on the surface of the measurement sample, the AF area should be set as small as possible according to each indentation. One embodiment for implementing this method will be described with reference to FIG.

For the sake of concreteness of description, three indentations are formed on the surface of the measurement sample, and when the objective lens is selected, as shown in FIG. 4B, the images IK1, IK2 of the three indentations are formed.
It is assumed that the IK3 can form an image on the light receiving surface 1 of the CCD camera.

In this case, first, the entire light receiving surface 1 is used as an AF area to roughly perform autofocus. As a result, a state close to that shown in FIG. 4B is realized. A over the entire light-receiving surface
Since auto-focusing is performed as the F area, in a roughly focused state, there is a possibility that an image such as a scratch on the surface of the measurement sample or dust adhering to the surface is formed in the light receiving surface. In this state, the output of each pixel of the CCD camera is “binarized” (FIG. 4A), and a “noise removal” step is performed to erase an image having an area smaller than the expected area of the impression image.

Next, the noise-removed image information is used to sequentially number the patterns in the "black" area. The labeled pattern may include "things other than the impression image". Therefore, with respect to each of the labeled patterns, a region whose area is the expected area of the impression image ± 50% is selected.

With respect to the pattern of each selected region, the ratio of the square root of the area to the perimeter is used as an identification parameter, and one having this parameter close to 1/4 is selected.
As shown in FIG. 7A, the shape of the indentation is close to a square.
When the length of one side of the square is a, the square root of the area is a and the perimeter is 4a. Therefore, in the square, the identification parameter: a / 4a is 1/4. Therefore, calculate the above parameters for each pattern selected as above,
An image whose value is close to 1/4 is specified as an indentation image. Then, for each specified indentation image, its center coordinates are calculated. The selection of information required for these processes is shown in FIG.
The calculation is performed in the image processing unit (a), and necessary calculation is performed by fetching the information from the image processing unit 50 into the computer 90.

The indentation image identified as described above (see FIG. 4)
(B) IK1, IK2, IK3), and when the position and size are obtained, first, the impression image IK1 is taken and A
The F area DAF1 is set to perform fine autofocusing, the indentation image IK1 is formed on the light receiving surface, and the diagonal length thereof is measured to calculate the hardness. In this process, the impression image I
Repeat for K2 and IK3.

In this way, accurate hardness measurement is realized.

[0048]

As described above, according to the present invention, a novel hardness measuring method can be provided. Since this method is configured as described above, in a hardness measurement method in which the hardness is calculated automatically after setting the measurement sample, the image of the indentation formed on the measurement sample is automatically received by the two-dimensional image sensor. The autofocus imaged on the surface is not easily affected by scratches and dust on the surface of the measurement sample, and accurate autofocus can be performed, so that accurate hardness measurement is possible. Further, if the autofocus is performed with relatively little data in the AF area (claim 1), the calculation time required for the autofocus can be shortened, and the measurement speed can be improved.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a hardness measuring method of the present invention.

FIG. 2 is a flow diagram illustrating the method of claim 2.

FIG. 3 is a flow diagram illustrating the method of claim 3;

FIG. 4 is a diagram illustrating the method of claim 4;

FIG. 5 is a diagram conceptually showing an example of a hardness measuring device for carrying out the present invention.

FIG. 6 is a diagram for explaining a revolver.

FIG. 7 is a diagram for explaining an indentation formed on the surface of a measurement sample.

[Explanation of symbols]

 1 Light receiving surface of two-dimensional image sensor IK Image of indentation formed on light receiving surface K1 Image of scratch on surface of measurement sample Ho Image of dust adhering to surface of measurement sample

Claims (4)

[Claims] 1. A movable stage, which is movable in X, Y, and Z directions orthogonal to each other, and is rotatable about a rotation axis parallel to the Z direction, and a two-dimensional image sensor are opposed to each other in the Z direction. At the very least, a revolver equipped with the objective lens and the indenter at positions equidistant from the rotation axis can be rotated and moved in the Z direction with the rotation axis parallel to the Z direction between the moving stage and the image sensor. After forming an indentation on the measurement sample installed on the moving stage by the indenter, the revolver is rotated to select the objective lens, and an enlarged image of the indentation is picked up by the objective lens to obtain the light receiving surface of the image sensor. In the fully automatic hardness measurement method in which the hardness of the measurement sample is calculated by reading the indentation image on top of the image, after selecting the above objective lens, a slightly wider area than the indentation image including the imaging position of the indentation image is set in the AF area. As A hardness measuring method characterized by setting and autofocusing to form an indentation image on the light receiving surface of the image pickup device. 2. The hardness measuring method according to claim 1, wherein after the objective lens is selected, the entire light-receiving surface of the image sensor is roughly used as an AF area for roughly auto-focusing, and the image sensor output is binarized in a roughly focused state. , Select the raster with the longest black area in the scanning direction, set the center of the black area in this raster as the center of the indentation, and based on this center, set the AF area for indentation according to the size of the indentation. The method for measuring hardness is characterized by performing fine autofocus. 3. The hardness measuring method according to claim 1, wherein an indentation is formed at each of a plurality of predetermined positions of a measurement sample installed on a moving stage, and then an objective lens is selected, and the indentation is formed by moving the moving stage. A hardness measuring method characterized in that the process of bringing hardness to the optical axis position and measuring hardness is repeated for all indentations. 4. The hardness measuring method according to claim 3, wherein when the hardness is measured for each indentation after selecting the objective lens, the indentation group is brought to an image forming region by the objective lens, and then all light received by the image pickup device is received. The surface is used as an AF area for rough autofocusing, and the light-receiving content of all the light-receiving surfaces is binarized in a roughly focused state, and the black area is selected to have an indentation expected area of ± 50%. The feature is that the square root of the area and the perimeter is used as a parameter for identification, a pattern close to a square is specified as an indentation, the center coordinates of the specified indentation are obtained, and the AF area is set around this center coordinate. Hardness measurement method.