US-12627886-B2 - Focal length measuring device and method

US12627886B2US 12627886 B2US12627886 B2US 12627886B2US-12627886-B2

Abstract

A focal length measuring device, which is provided in a work device that performs work on a workpiece, and measures a focal length at which a lens provided in the work device is separated from the workpiece, includes: an image acquisition unit disposed in a movement path of light incident from the workpiece through the lens and configured to acquire an image from the workpiece; an image extraction unit configured to extract a plurality of first divided images from the image acquired by the image acquisition unit and select at least one second divided image having a sharpness greater than or equal to a preset reference from among the plurality of first divided images; and a focal length calculation unit configured to calculate a focal length of the workpiece from a position of each of the at least one second divided image selected by the image extraction unit, wherein the image acquisition unit is disposed to have a preset angle with respect to a direction perpendicular to the movement path of the light incident from the workpiece through the lens.

Inventors

Goo Cheol KWON

Assignees

K-LAB CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20230223
Priority Date: 20220421

Claims (9)

1 . A focal length measuring device, which is provided in a work device that performs work on a workpiece, and measures a focal length at which a lens provided in the work device is separated from the workpiece, the focal length measuring device comprising: an image acquisition unit disposed in a movement path of light incident from the workpiece through the lens and configured to acquire an image from the workpiece; an image extraction unit configured to extract a plurality of first divided images from the image acquired by the image acquisition unit and select at least one second divided image having a sharpness greater than or equal to a preset reference from among the plurality of first divided images; and a focal length calculation unit configured to calculate a focal length of the workpiece from a position of each of the at least one second divided image selected by the image extraction unit, wherein the image acquisition unit is disposed to have a preset angle with respect to a direction perpendicular to the movement path of the light incident from the workpiece through the lens.
2 . The focal length measuring device of claim 1 , wherein the image acquisition unit comprises a charge coupled device (CCD) image sensor.
3 . The focal length measuring device of claim 1 , wherein the image extraction unit is configured to extract the plurality of first divided images by dividing an entire area of the image into a first direction perpendicular to the movement path of the light incident from the workpiece through the lens and a second direction perpendicular to the first direction and the movement path of the light incident from the workpiece through the lens.
4 . The focal length measuring device of claim 1 , wherein the image extraction unit is configured to perform a fast Fourier transform (FFT) operation to extract a plurality of frequencies for the plurality of first divided images, and select at least one second divided image having a highest frequency from among the plurality of first divided images.
5 . The focal length measuring device of claim 1 , wherein the focal length measuring device further comprises a position adjustment unit configured to adjust at least one of an angle of the image acquisition unit, a position of the image acquisition unit, and a position of the workpiece according to a calculation result of the focal length calculation unit.
6 . A focal length measuring method for measuring a focal length at which a lens provided in a work device that performs work on a workpiece is separated from the workpiece, the focal length measuring method comprising: a step in which an image acquisition unit disposed in a movement path of light incident from the workpiece through the lens acquires an image from the workpiece; a step in which an image extraction unit extracts a plurality of first divided images from the image acquired by the image acquisition unit; a step in which the image extraction unit selects at least one second divided image having a sharpness greater than or equal to a preset reference from among the plurality of first divided images; and a step in which a focal length calculation unit calculates a focal length of the workpiece from a position of each of the at least one second divided image selected by the image extraction unit, wherein the image acquisition unit is disposed to have a preset angle with respect to a direction perpendicular to the movement path of the light incident from the workpiece through the lens.
7 . The focal length measuring method of claim 6 , wherein the step in which the image extraction unit extracts the plurality of first divided images comprises a step in which the image extraction unit extracts the plurality of first divided images by dividing an entire area of the image into a first direction perpendicular to the movement path of the light incident from the workpiece through the lens and a second direction perpendicular to the first direction and the movement path of the light incident from the workpiece through the lens.
8 . The focal length measuring method of claim 6 , wherein the step in which the image extraction unit selects the at least one second divided image comprises: a step in which the image extraction unit performs a fast Fourier transform (FFT) operation to extract a plurality of frequencies for the plurality of first divided images; and a step in which the image extraction unit selects at least one second divided image having a highest frequency from among the plurality of first divided images.
9 . The focal length measuring method of claim 6 , further comprising, after the step in which the focal length calculation unit calculates the focal length of the workpiece, a step in which a position adjustment unit connected to the image acquisition unit and the workpiece adjusts at least one of an angle of the image acquisition unit, a position of the image acquisition unit, and a position of the workpiece according to a calculation result of the focal length calculation unit.

Description

TECHNICAL FIELD The present disclosure relates to a focal length measuring device and method, and more particularly, to a focal length measuring device and method capable of easily and accurately measuring a focal length of a work device with respect to a workpiece with a simpler structure and control method. BACKGROUND ART In general, laser processing devices, such as laser marking devices and laser welding devices, and devices that perform various types of work (hereinafter referred to as work devices) are provided with an optical system for irradiating a laser beam or the like onto a workpiece. In order for such work devices to perform work on the workpiece more stably and efficiently, it is very important to accurately measure and control the focusing state of the optical system provided in the work device with respect to the workpiece. In particular, in order to improve work quality of a workpiece on which work is performed, a focal length, which is a distance from a lens provided in a work device to a workpiece, is a very important measurement factor. For example, the laser marking device, which is one of the laser processing devices, is a device that receives characters, figures, or the like from the outside and controls the operations of a laser generator and a laser scanner to mark the characters, figures, or the like on a workpiece with a laser beam. Since the size (spot size) of the laser beam irradiated by the laser scanner is several μm to several tens of μm, it is very important to maintain the focal length accurately and consistently. As such, there are various methods for measuring and determining a focal length of a work device with respect to a workpiece, but most focal length measuring devices use various types of sensors to measure a focal length, or use a charge coupled device (CCD) camera or the like to capture a pattern formed on a workpiece and then determine a focusing state through image processing. For example, Korean Patent Registration No. 10-0790706 (Lens Focal Length Measuring Device) (published on Jan. 2, 2008) discloses a technology for adjusting a distance between an inspection lens and an objective lens by adjusting the position of the inspection lens, which is an object for which a focal length is to be measured, finding a point at which a size of an image formed on a screen is minimum, and calculating the focal length of the inspection lens based on information about the point. As another example, Korean Patent Registration No. 10-0090801 (Focal Length Measuring Device and Method of Optical System) (published on Jun. 26, 1995) discloses a structure of a focal length measuring device including a collimator unit that emits light parallel to an optical axis, an aperture unit that may adjust the amount of parallel light from the collimator unit, an optical system in which the parallel light having passed through the aperture unit is refracted, a CCD that detects light adjusted in the optical system, a conversion means connected to the CCD to convert the detected light into an electric signal, and a screen on which the refracted light is imaged. However, conventional focal length measuring devices have the problem in that the structure of the device becomes complex and the cost increases because an imaging device such as a CCD camera, various types of sensors, and a driving means for moving an inspection lens are required. In addition, conventional focal length measuring devices have the problem in that the measurement time increases because the sizes of the images formed on the screen have to be compared while moving the inspection lens using the driving means. Therefore, there is a need for a focal length measuring device and method capable of easily and accurately measuring a focal length of a work device with respect to a workpiece with a simpler structure and control method. DISCLOSURE Technical Problem The present disclosure has been made to improve the problems described above, and the problem to be solved by the present disclosure is to provide a focal length measuring device and method, in which an image of a workpiece acquired by an image acquisition unit disposed obliquely in a movement path of light incident from the workpiece through a lens is divided into a plurality of first divided images and then the focal length of the workpiece is calculated by using the sharpness of each of the plurality of first divided images, thereby easily and accurately measuring a focal length of a work device with respect to the workpiece with a simpler structure and control method. The technical problems of the present disclosure are not limited to those described above, and other technical problems that are not mentioned herein will be clearly understood from the following description by those of ordinary skill in the art. Technical Solution To achieve the objects described above, a focal length measuring device, which is provided in a work device that performs work on a workpiece