Focal length measurement device and method

Abstract

The focal length measurement device is provided in a working device that performs a task on an object, and measures the focal length of a lens of the working device away from the object. The focal length measurement device includes an image acquisition unit that is disposed on a path of light incident from the object through the lens and acquires an image from the object; an image extraction unit that extracts a plurality of first divided images from the image acquired by the image acquisition unit and selects at least one second divided image from the plurality of first divided images, the definition of which is equal to or greater than a predetermined standard; and a focal length calculation unit that calculates the focal length of the object from each position of the at least one second divided image selected by the image extraction unit, and the image acquisition unit is disposed to have a predetermined angle with respect to a direction perpendicular to the path of light incident from the object through the lens.

Description

[Technical Field]

[0001] The present invention relates to a focal length measurement device and method, and more particularly to a focal length measurement device and method that can easily and accurately measure the focal length of a working device relative to an object using a simpler structure and control method. [Background technology]

[0002] Generally, laser processing devices such as laser marking devices and laser welding devices, as well as devices for performing various types of work (hereinafter referred to as work devices), are equipped with an optical system for irradiating a laser beam or the like onto an object.

[0003] In order for such a working device to perform work on an object more stably and efficiently, it is very important to accurately measure and adjust the focusing state of the optical system equipped in the working device with respect to the object. In particular, in order to improve the work quality of the object being worked on, the focal length, which is the distance from the lens equipped in the working device to the object, is a very important measurement factor.

[0004] For example, a laser marking device, which is one type of laser processing device, receives characters, figures, etc. from an external source and controls the operation of a laser oscillator and a laser scanner to mark the characters, figures, etc. on an object with a laser beam. However, since the size (spot size) of the laser beam irradiated by the laser scanner is on the order of several μm to several tens of μm, it is very important to maintain an accurate and constant focal length.

[0005] As described above, there are various methods for measuring and determining the focal length of a work tool relative to an object. However, most focal length measurement devices use various types of sensors to measure the focal length, or use a CCD camera to capture an image of a pattern formed on the object, and then determine the focusing state by image processing the image.

[0006] For example, Patent Document 1 (Lens focal length measuring device) (published on January 2, 2008) discloses a technology that adjusts the position of the lens to be tested, which is the object of focal length measurement, and adjusts the distance between the lens to be tested and the objective lens to find the point where the size of the image projected on the screen is smallest, and then calculates the focal length of the lens to be tested based on information about that point.

[0007] As another example, Patent Document 2 (Device and method for measuring focal length of optical system) (published on June 26, 1995) discloses the structure of a focal length measuring device that includes a collimator unit that emits light rays parallel to the optical axis, an aperture unit that can adjust the amount of parallel light rays from the collimator unit, an optical system that refracts the parallel light rays that have passed through the aperture unit, a CCD that detects the light adjusted by the optical system, conversion means connected to the CCD that converts the detected light into an electrical signal, and a screen on which the refracted light is imaged.

[0008] However, conventional focal length measurement devices require an imaging device such as a CCD camera, various types of sensors, and a driving means for moving the lens under test, which not only makes the device structure complicated and increases costs, but also requires a driving means to move the lens under test while comparing the size of the image projected on the screen, which takes a long time to measure.

[0009] Therefore, there is a need for a focal length measurement device and method that can easily and accurately measure the focal length of a working device relative to an object using a simpler structure and control method. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Republic of Korea Registered Patent Publication No. 10-0790706 [Patent Document 2] Republic of Korea Registered Patent Publication No. 10-0090801 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention has been invented to solve the above problems, and the problem to be solved by the present invention is to provide a focal length measurement device and method that can easily and accurately measure the focal length of a working device relative to an object with a simpler structure and control method by dividing an image of the object acquired by an image acquisition unit arranged at an angle to the path of light incident from the object through a lens into a plurality of first divided images, and then calculating the focal length of the object using the clarity of each of the plurality of first divided images.

[0012] The technical problems of the present invention are not limited to those mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0013] In order to achieve the above object, a focal length measurement device according to one embodiment of the present invention is provided in a work device that performs work on an object, and measures a focal length at which a lens provided in the work device is separated from the object. The focal length measurement device includes: an image acquisition unit that is disposed in a path of light incident from the object through the lens and acquires an image from the object; an image extraction unit that extracts a plurality of first divided images from the image acquired by the image acquisition unit and selects at least one second divided image from the plurality of first divided images, the definition of which is equal to or greater than a predetermined standard; and a focal length calculation unit that calculates the focal length of the object from the position of each of the at least one second divided image selected by the image extraction unit, wherein the image acquisition unit is disposed at a predetermined angle with respect to a direction perpendicular to the path of light incident from the object through the lens.

[0014] At this time, the image capturing unit includes a charge coupled device (CCD) type image sensor.

[0015] The image extracting unit may extract the plurality of first divided images by dividing the entire area of ​​the image into a first direction perpendicular to the path of light incident from the object through the lens, and a second direction perpendicular to the path of light incident from the object through the lens and the first direction.

[0016] The image extracting unit extracts a plurality of frequencies for each of the plurality of first divided images by performing a Fast Fourier Transform (FFT) operation, and then selects at least one second divided image having the highest frequency from among the plurality of first divided images.

[0017] The focal length measurement device further includes a position adjustment unit that adjusts at least one of an angle of the image acquisition unit, a position of the image acquisition unit, and a position of the object according to a calculation result of the focal length calculation unit.

[0018] Meanwhile, to achieve the above object, a focal length measurement method according to one embodiment of the present invention measures a focal length at which a lens provided in a working device performing a work on an object is spaced from the object, the method comprising the steps of: an image acquisition unit disposed in a path of light incident from the object through the lens acquiring an image from the object; an image extraction unit extracting a plurality of first divided images from the image acquired by the image acquisition unit; the image extraction unit selecting at least one second divided image from the plurality of first divided images, the definition of which is equal to or greater than a predetermined standard; and a focal length calculation unit calculating the focal length of the object from the position of each of the at least one second divided image selected by the image extraction unit; and the image acquisition unit being disposed to have a predetermined angle with a direction perpendicular to the path of light incident from the object through the lens.

[0019] In this case, the step of extracting the plurality of first divided images by the image extracting unit is characterized in that the image extracting unit extracts the plurality of first divided images by dividing the entire area of ​​the image into a first direction perpendicular to the movement path of light incident from the object through the lens, and a second direction perpendicular to the movement path of light incident from the object through the lens and the first direction.

[0020] The step of selecting at least one second divided image by the image extraction unit includes the steps of: the image extraction unit extracting a plurality of frequencies for each of the plurality of first divided images by performing a Fast Fourier Transform (FFT) operation; and the image extraction unit selecting at least one second divided image having the highest frequency from the plurality of first divided images.

[0021] The focal length measuring method may further include, after the focal length calculation unit calculates the focal length of the object, a step of a position adjustment unit connected to the image acquisition unit and the object adjusting at least one of an angle of the image acquisition unit, a position of the image acquisition unit, and a position of the object according to a calculation result of the focal length calculation unit.

[0022] Specific details of other embodiments are included in the detailed description and drawings. [Effects of the Invention]

[0023] According to a focal length measurement device according to an embodiment of the present invention, an image of an object captured by an image capture unit arranged at an angle to the path of light incident from the object through a lens is divided into a plurality of first divided images, and the focal length of the object is calculated using the sharpness of each of the plurality of first divided images, thereby making it possible to easily and accurately measure the focal length of a working device relative to the object with a simpler structure and control method.

[0024] The technical object of the present invention is not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a diagram illustrating a schematic structure of a laser processing device to which a focal length measurement device according to an embodiment of the present invention is applied; [Figure 2] 1 is a diagram illustrating a focal length measurement device according to an embodiment of the present invention; [Figure 3] 1 is a flowchart illustrating a focal length measurement method using a focal length measurement device according to an embodiment of the present invention. [Figure 4] 3 is a diagram illustrating an image capturing unit of a focal length measurement device according to an embodiment of the present invention capturing an image from an object; [Figure 5] 10 is a diagram illustrating an image extracting unit included in a focal length measurement device according to an embodiment of the present invention extracting a plurality of first divided images from an image. [Figure 6] 10 is a diagram illustrating an image extracting unit included in a focal length measurement device according to an embodiment of the present invention, selecting at least one second divided image from a plurality of first divided images. [Figure 7] 10 is a diagram showing how a focal length calculation unit constituting a focal length measurement device according to an embodiment of the present invention calculates the focal length of an object from at least one second divided image. FIG. [Figure 8] FIG. 10 is a diagram schematically illustrating a modified example of a focal length measurement device according to an embodiment of the present invention. [Figure 9] 10 is a flowchart showing a focal length measurement method using a modified example of the focal length measurement device according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings to such an extent that those skilled in the art can easily carry out the present invention.

[0027] In describing the embodiments, technical details that are well known in the technical field to which the present invention pertains and that are not directly related to the present invention will be omitted in order to more clearly convey the gist of the present invention without obscuring it.

[0028] For the same reason, in the accompanying drawings, some components are exaggerated, omitted, or illustrated schematically, and the size of each component does not entirely reflect the actual size. The same or corresponding components in each drawing are denoted by the same reference numerals.

[0029] Furthermore, the expressions and terms used herein regarding terms such as the orientation of devices or elements (e.g., "front," "back," "up," "down," "top," "bottom," "left," "right," "lateral") are used to simplify the description of the present invention and do not indicate or imply that the associated devices or elements should simply have a particular orientation.

[0030] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to the drawings for explaining a focal length measurement device according to an embodiment of the present invention.

[0031] FIG. 1 is a diagram schematically showing the structure of a laser processing apparatus to which a focal length measurement device according to one embodiment of the present invention is applied, and FIG. 2 is a diagram schematically showing a focal length measurement device according to one embodiment of the present invention.

[0032] 1 and 2, a focal length measurement device 100 according to an embodiment of the present invention is provided in a working device 20 that performs a task on a workpiece 10, and may include an image acquisition unit 110, an image extraction unit 120, and a focal length calculation unit 130. The focal length measurement device 100 is provided inside the working device 20 and can measure the focal length of a lens 21 provided in the working device 20 that is spaced from the workpiece 10 to perform a specific task.

[0033] In the present invention, a laser processing device such as a laser marking device or a laser welding device is given as an example of the working device 20, but this is not limited to this, and the focal length measurement device 100 according to one embodiment of the present invention can be applied to various types of working devices that include optical systems such as a lens 21 to perform work on the object 10.

[0034] The image acquisition unit 110 is disposed in the path of light incident from the object 10 through the lens 21, and can acquire an image from the object 10 whose focal length is to be measured. For convenience of explanation, FIG. 2 shows an example in which the object 10 has a thin plate-like shape and the working surface 10a of the object 10 is a flat surface, but this is not limiting, and the working surface 10a of the object 10 may be a curved surface.

[0035] Preferably, the image capture unit 110 is a sensor that converts light into an electrical signal to obtain an image, and may include a charge coupled device (CCD) type image sensor.

[0036] 2, although not shown in detail, the object 10 is supported in a seated state on the object support unit 11, and can be moved in the X-, Y-, and Z-axis directions or rotated about the X-, Y-, and Z-axis by the object support unit 11 as needed. In addition, the image acquisition unit 110 can be moved in the X-, Y-, and Z-axis directions or rotated about the X-, Y-, and Z-axis by a separate driving device as needed.

[0037] The image extraction unit 120 extracts a plurality of first divided images (A(1,1) to A(5,5) in the example of FIG. 5(a)) from the image acquired by the image acquisition unit 110, and then selects at least one second divided image (C(3,1) to C(3,5) in the example of FIG. 6(b)) from the plurality of first divided images whose clarity is equal to or exceeds a predetermined standard.

[0038] Preferably, the image extraction unit 120 can extract a plurality of first divided images by dividing the entire area of ​​the image into a first direction (X direction in the example of FIG. 1) perpendicular to the travel path of light incident from the object 10 through the lens 21, and a second direction (Y direction in the example of FIG. 1) perpendicular to the travel path of light incident from the object 10 through the lens 21 and the first direction.

[0039] In addition, preferably, the image extraction unit 120 can perform a Fast Fourier Transform (FFT) operation to extract multiple frequencies for each of the multiple first divided images, and then select at least one second divided image having the highest frequency from the multiple first divided images.

[0040] A method in which the image extracting unit 120 extracts a plurality of first divided images from an image and a method in which the image extracting unit 120 selects at least one second divided image from the plurality of first divided images will be described in detail below with reference to FIGS.

[0041] The focal length calculation unit 130 can calculate the focal length (F in the example of FIG. 7) of the object 10 from each position of at least one second divided image selected by the image extraction unit 120. A method for the focal length calculation unit 130 to calculate the focal length of the object 10 from each position of at least one second divided image will be described in detail below with reference to FIGS. 3 and 7.

[0042] Preferably, as shown in FIG. 2, the image acquisition unit 110 constituting the focal length measurement device 100 according to an embodiment of the present invention may be positioned to have a predetermined angle (θ) with a direction perpendicular to the travel path of light incident from the object 10 through the lens 21.

[0043] That is, the image acquisition unit 110 is not arranged perpendicular to the path of light passing through the lens 21 and receives the light reflected from the work surface 10a of the object 10 equally throughout, but is arranged at an angle at a predetermined angle to the direction perpendicular to the path of light passing through the lens 21, so it is inevitable that the amount of light absorbed will differ depending on the surface position.

[0044] Therefore, the focal length measurement device 100 according to one embodiment of the present invention can accurately measure the focal length of the working device 20 relative to the object 10 and the height deviation on the working surface 10a of the object 10 without moving the object 10 or with minimal movement by using the image acquisition unit 110 arranged at an angle to the path of light incident from the object 10 through the lens 21.

[0045] Hereinafter, a method for measuring the focal length of the lens 21 provided in the working device 20 using the focal length measurement device 100 according to an embodiment of the present invention will be described with reference to FIGS.

[0046] FIG. 3 is a flowchart showing a focal length measurement method using a focal length measurement device according to an embodiment of the present invention.

[0047] First, the image acquiring unit 110 may acquire an image from the object 10 whose focal length is to be measured (S110). As described above, the image acquiring unit 110 may include a charge coupled device (CCD) type image sensor.

[0048] FIG. 4 is a diagram showing how an image capture unit constituting a focal length measurement device according to an embodiment of the present invention captures an image from an object.

[0049] 4, the image capturing unit 110 may be disposed at an angle (θ) perpendicular to the path of light incident from the object 10 through the lens 21. Therefore, since the amount of light absorbed by the image capturing unit 110 varies depending on the surface position, it is inevitable that the image 111 captured from the object 10 will have different clarity depending on the corresponding position on the image capturing unit 110.

[0050] Also, referring to FIG. 3, after the image acquiring unit 110 acquires the image 111 from the object 10 (S110), the image extracting unit 120 can extract a plurality of first divided images from the image 111 acquired by the image acquiring unit 110 (S120).

[0051] FIG. 5 is a diagram illustrating how an image extracting unit included in a focal length measurement device according to an embodiment of the present invention extracts a plurality of first divided images from an image.

[0052] As shown in FIG. 5, the image extraction unit 120 can extract a plurality of first divided images by dividing the entire area of ​​the image 111 into a first direction (X direction in the example of FIG. 1) perpendicular to the travel path of the light incident from the object 10 through the lens 21, and a second direction (Y direction in the example of FIG. 1) perpendicular to the travel path of the light incident from the object 10 through the lens 21 and the first direction.

[0053] That is, the image extraction unit 120 can extract a plurality of first divided images by dividing the entire area of ​​the image 111 acquired by the image acquisition unit 110 into a plurality of divided areas (M×N) corresponding to predetermined sizes along the vertical and horizontal directions of the image acquisition unit 110.

[0054] 5A shows an example in which the image extraction unit 120 extracts 25 first divided images A(1,1) to A(5,5) by dividing the entire area of ​​the image 111 into five in the first direction (X direction) and five in the second direction (Y direction). Preferably, to increase the accuracy when the image extraction unit 120 extracts the sharpness (frequency in the example described below) of each of the plurality of first divided images, a pair of adjacent first divided images (e.g., A(2,2) and A(3,2)) among the plurality of first divided images may be extracted such that their boundaries overlap each other by a predetermined area.

[0055] Figure 5(a) shows an example in which the entire area of ​​image 111 is divided into equal intervals and equal numbers in the first and second directions, but this is not limited to this, and the intervals and numbers in the first and second directions can be set in various ways depending on the conditions.

[0056] As another example, (b) of Figure 5 shows an example in which the image extraction unit 120 divides the entire area of ​​the image 111 into five parts only in the first direction (X direction) in which the image acquisition unit 110 is tilted, and extracts a total of five first divided images B(1) to B(5).

[0057] That is, when the work surface 10a of the object 10 is a flat plane, the image acquiring unit 110 is spaced substantially the same distance from the object 10 regardless of its position in the second direction (Y direction) perpendicular to the first direction in which the image acquiring unit 110 is tilted, so division in the second direction (Y direction) does not need to be considered. Therefore, in the example of Fig. 5(b), the image acquiring unit 110 divides the entire area of ​​the image 111 only in the first direction (X direction), thereby simplifying the subsequent process of selecting the second divided image.

[0058] Similarly, a pair of adjacent first divided images (for example, B(2) and B(3)) among the plurality of first divided images may be extracted so that their boundary portions overlap each other by a predetermined area.

[0059] Also, referring to FIG. 3, after the image extraction unit 120 extracts a plurality of first divided images from the image 111 (S120), the image extraction unit 120 can select at least one second divided image from the plurality of first divided images, the second divided image having a clarity level equal to or higher than a preset standard (S130).

[0060] FIG. 6 is a diagram illustrating how an image extracting unit included in a focal length measurement device according to an embodiment of the present invention selects at least one second divided image from a plurality of first divided images.

[0061] Preferably, as shown in FIG. 6, the image extraction unit 120 may perform a Fast Fourier Transform (FFT) operation to extract a plurality of frequencies for each of a plurality of first divided images, and then select at least one second divided image having the highest frequency from among the plurality of first divided images.

[0062] That is, as shown in (a) of FIG. 6, the image extraction unit 120 can perform a Fast Fourier Transform (FFT) operation on the 25 first divided images A(1,1) to A(5,5) shown in (a) of FIG. 5 to extract multiple frequencies f(1,1) to f(5,5) for each of the first divided images A(1,1) to A(5,5).

[0063] Then, as shown in (b) of Figure 6, the image extraction unit 120 can select at least one second divided image with the highest frequency from the 25 first divided images A(1,1) to A(5,5), for example, five second divided images C(3,1) to C(3,5).

[0064] Meanwhile, in the present invention, an example is shown in which the image extraction unit 120 performs a Fast Fourier Transform (FFT) operation to select at least one second divided image having the highest frequency from among a plurality of first divided images, but this is not limited to this.

[0065] As an example, the image extraction unit 120 may calculate the pixel value of each of a plurality of first divided images extracted from the image 111, and then select at least one second divided image from the plurality of first divided images, the second divided image having a larger deviation in pixel value compared to adjacent first divided images.

[0066] Also, referring to FIG. 3, after the image extraction unit 120 selects at least one second divided image (S130), the focal length calculation unit 130 can calculate the focal length of the object 10 from each position of the at least one second divided image selected by the image extraction unit 120 (S140).

[0067] FIG. 7 is a diagram showing how a focal length calculation unit included in a focal length measurement device according to an embodiment of the present invention calculates the focal length of an object from at least one second divided image.

[0068] As shown in FIG. 7, the focal length calculation unit 130 can calculate the focal length F of the object 10 from the distance D between the portion 110a corresponding to each position C of at least one second divided image of the image acquisition unit 110 and the work surface 10a of the object 10.

[0069] For example, in the example of Figure 7, the focal length F of the object 10 corresponds to 1 / 2 of the distance D between the part 110a of the image acquisition unit 110 corresponding to the position C of the five second divided images C(3,1) to C(3,5) and the working surface 10a of the object 10.

[0070] Meanwhile, the focal length measurement device 100 according to an embodiment of the present invention may further include a position adjusting unit 140 for adjusting the positions of the image acquiring unit 110 and the object 10 .

[0071] FIG. 8 is a diagram illustrating a modified example of a focal length measurement device according to an embodiment of the present invention, and FIG. 9 is a flowchart illustrating a focal length measurement method using the modified example of the focal length measurement device according to an embodiment of the present invention.

[0072] As shown in FIG. 8, the position adjusting unit 140 can adjust at least one of the angle of the image acquiring unit 110, the position of the image acquiring unit 110, and the position of the target object 10 according to the calculation result of the focal length calculating unit 130.

[0073] That is, as shown in FIG. 9, a focal length measurement method using a modified example of the focal length measurement device 100 according to an embodiment of the present invention may further include a step (S150) in which a position adjustment unit 140 connected to the image acquisition unit 110 and the object 10 adjusts at least one of the angle of the image acquisition unit 110, the position of the image acquisition unit 110, and the position of the object 10 according to the calculation result of the focal length calculation unit 130, after the step (S140) in which the focal length calculation unit 130 of FIG. 3 calculates the focal length of the object 10.

[0074] That is, as shown in FIG. 9, if the focal length of the object 10 is not calculated as a result of the focal length calculation unit 130 calculating the focal length of the object 10, the working device 20 is in a state where it cannot perform work on the object 10, and therefore the position of the object 10 or the position of the working device 20 needs to be adjusted again.

[0075] Therefore, if the focal length of the object 10 is not calculated as a result of the focal length calculation unit 130 calculating the focal length of the object 10, the position adjustment unit 140 can adjust the angle and position of the image acquisition unit 110 in the Z-axis direction, or adjust the position of the object 10 in the Z-axis direction.

[0076] As described above, the focal length measurement device 100 according to one embodiment of the present invention divides the image of the object 10 acquired by the image acquisition unit 110 arranged at an angle to the path of light incident from the object 10 through the lens 21 into a plurality of first divided images, and then calculates the focal length of the object 10 using the clarity of each of the plurality of first divided images, thereby enabling the focal length of the working device 20 relative to the object 10 to be easily and accurately measured with a simpler structure and control method.

[0077] Meanwhile, in the present invention, a laser processing device is described as an example of the working device 20, but the present invention is not limited to this, and can be applied to various types of systems, such as laser processing devices such as laser marking devices and laser welding devices, as well as processing devices using robots.

[0078] While the present specification and drawings disclose preferred embodiments of the present invention and use specific terms, these terms are used in a general sense merely to explain the technical content of the present invention in an easy-to-understand manner and to aid in understanding the invention, and are not intended to limit the scope of the present invention. It is obvious to those skilled in the art to which the present invention pertains that other modifications based on the technical concept of the present invention can be implemented in addition to the embodiments disclosed herein. [Industrial Applicability]

[0079] The present invention relates to a focal length measurement device and method, and more particularly, to a focal length measurement device and method that can easily and accurately measure the focal length of a working device relative to an object using a simpler structure and control method.

Claims

1. A focal length measurement device is provided in a working device that performs work on an object, and measures a focal length of a lens provided in the working device that is spaced apart from the object, an image capture unit disposed on a path of light incident from the object through the lens, and configured to capture an image from the object; an image extracting unit that extracts a plurality of first divided images from the image acquired by the image acquiring unit, and then selects at least one second divided image from the plurality of first divided images, the second divided image having a clarity equal to or greater than a predetermined standard; and a focal length calculation unit that calculates a focal length of the object from each position of the at least one second divided image selected by the image extraction unit; The image acquisition unit The lens is disposed inclined at a predetermined angle with respect to a direction perpendicular to the path of light incident from the object through the lens. A focal length measuring device characterized by:

2. The image acquisition unit Includes charge coupled device (CCD) image sensors 2. The focal length measurement device according to claim 1.

3. The image extraction unit The entire area of ​​the image is divided into a first direction perpendicular to a travel path of the light incident from the object through the lens, and a second direction perpendicular to the travel path of the light incident from the object through the lens and the first direction, and the plurality of first divided images are extracted.

2. The focal length measurement device according to claim 1.

4. The image extraction unit A plurality of frequencies for each of the plurality of first divided images is extracted by performing a Fast Fourier Transform (FFT), and then at least one second divided image having the highest frequency is selected from the plurality of first divided images.

2. The focal length measurement device according to claim 1.

5. The focal length measurement device is The image capturing apparatus further includes a position adjusting unit that adjusts at least one of an angle of the image capturing unit, a position of the image capturing unit, and a position of the object according to a calculation result of the focal length calculating unit.

2. The focal length measurement device according to claim 1.

6. 1. A focal length measurement method for measuring a focal length of a lens provided in a working device for working on an object, the focal length being measured at a distance from the object, the method comprising: an image capturing unit disposed on a path of light incident from the object through the lens capturing an image from the object; an image extracting unit extracting a plurality of first divided images from the image acquired by the image acquiring unit; The image extracting unit selects at least one second divided image from the plurality of first divided images, the second divided image having a clarity equal to or greater than a predetermined standard; and a focal length calculation unit calculating a focal length of the object from the position of each of the at least one second divided image selected by the image extraction unit; The image acquisition unit The lens is disposed inclined at a predetermined angle with respect to a direction perpendicular to the path of light incident from the object through the lens. A focal length measurement method characterized by:

7. The step of extracting the plurality of first divided images by the image extracting unit includes: The image extracting unit extracts the plurality of first divided images by dividing the entire area of ​​the image into a first direction perpendicular to a path of light incident from the object through the lens and a second direction perpendicular to the path of light incident from the object through the lens and the first direction.

7. The focal length measuring method according to claim 6.

8. The step of the image extracting unit selecting the at least one second divided image includes: The image extractor performs a Fast Fourier Transform (FFT) operation to extract a plurality of frequencies for each of the plurality of first divided images; and The image extracting unit selects at least one second divided image having the highest frequency from among the plurality of first divided images.

7. The focal length measuring method according to claim 6.

9. The focal length measurement method includes: After the focal length calculation unit calculates the focal length of the object, The method further includes a step of adjusting at least one of an angle of the image acquiring unit, a position of the image acquiring unit, and a position of the object, the position adjusting unit being connected to the image acquiring unit and the object, according to a calculation result of the focal length calculating unit.

7. The focal length measuring method according to claim 6.

Images