Technical field The present invention relates to a punching machine for a flexible printed circuit board, and more particularly, to a punching machine for a flexible printed circuit board which punches a hole in the flexible printed circuit board based on a coordinate value of a mark on the flexible printed circuit board obtained by photographing the mark with a camera and processing image data of the mark using a computer.

Background Art A punching machine is a machine for punching holes in a workpiece by means of a punch and die. For example, a plurality of guide holes or locator holes, which function as reference points during the manufacture of a flexible printed circuit, are punched by the punching machine. A conductive pattern and marks indicating locations at which the holes will be punched are printed on the flexible printed circuit board, and it is important that the holes be punched such that the centers of the holes are exactly coincident with those of the marks. In the conventional punching machine, the punch is moved horizontally in X- axis and Y-axis directions by a Cartesian motion device and also moved vertically in a Z- axis direction by an up/down device to punch holes in the flexible printed circuit board which is set on the die of a working table. The horizontal motion of the punch is performed by numerically controlling the Cartesian motion device. However, since the punch of the punching machine is moved and set on locations, over which the holes will be punched, by numerically controlling the Cartesian motion device, an error in which the centers of holes to be actually punched are not coincident with those of the marks may occur. To avoid alignment error between the punch of the punching machine and the marks on the flexible printed circuit board, Korean Patent Laid-Open Publication No. 2003-15869 discloses a punching machine in which a coordinate value of a mark on a flexible workpiece is computed by photographing the mark with a camera and processing image data of the mark so obtained using a computer program, and a die is then moved in X-axis and Y-axis directions by means of a Cartesian motion device at a predetermined location corresponding to the computed coordinate value of the mark to punch the flexible workpiece. However, in the punching machine disclosed in Korean Patent Laid-Open Publication No. 2003-15869, since the optical axis of the camera is disposed parallel to the central axis of the punch to prevent interference between the punch and the camera, there is a considerable distance difference, i.e. an offset, between the optical axis of the camera and the central axis of the punch. Accordingly, the amount of the horizontal motion needed to move the punch to the location corresponding to the coordinate value of the mark obtained by the image data processing is increased. Thus, there is a problem in that the working speed of the punching machine is greatly reduced.

Disclosure øf Invention The present invention is conceived to solve the aforementioned problems in the prior art. Accordingly, an object of the present invention is to provide a punching machine for a flexible printed circuit board which can reduce an amount of horizontal motion of the punch with respect to a coordinate value of a mark on a flexible printed circuit board obtained by photographing the mark with a camera and processing image data of the photographed mark using a computer, thereby enabling a working speed of the punching machine to be remarkably enhanced. According to an aspect of the present invention for achieving the object, there is provided a punching machine for a flexible printed circuit board including a punch for punching a hole in the flexible printed circuit board at a location with a mark indicated thereon, an up/down device for moving the punch upward and downward with respect to the flexible printed circuit board, and a Cartesian motion device for horizontally moving the punch along the two axes perpendicular to each other. The punching machine of the present invention further comprises a camera which photographs the mark on the flexible printed circuit board to acquire image data of the mark, is installed to be movable together with the punch by the Cartesian motion device and has a first optical axis parallel to a central axis of the punch; a light guide which is installed at the front of the camera to allow light emitted from the camera to be as close as possible and parallel to the central axis of the punch; and a computer which processes the image date received from the camera to compute a coordinate value of the mark and controls an operation of the Cartesian motion device to enable the punch to be aligned with the mark based on the coordinate value of the mark.

Brief Description of Drawings Fig. 1 is a front view showing the configuration of a punching machine for a flexible printed circuit board according to the present invention. Fig. 2 is a front view illustrating the operation of the punching machine for the flexible printed circuit board according to the present invention. Fig. 3 is a perspective view showing a part of the flexible printed circuit board to be punched by the punching machine according to the present invention. Fig. 4 is a front view schematically showing the layout of a camera, a lighting device and a light guide used in the punching machine for the flexible printed circuit board according to the present invention.

Best Mode for Carrying out the Invention Hereinafter, a preferred embodiment of a punching machine for a flexible printed circuit board according to the present invention will be described in detail with reference to accompanying drawings. Referring first to Figs. 1 and 2, a punching machine 10 of the present invention includes a punch 12 that is chucked into a punch holder 11 to punch a hole 2 in a flexible printed circuit board 1. The punch holder 11 is provided at a side of a head 13. The punch holder 11 is moved in a Z-axis direction, i.e. moved upward and downward, by operation of an up/down actuator 20 which is provided at a side of the head 13. The up/down actuator 20 can be composed of a solenoid 21, an air cylinder and a linear motion actuator, and the like. The head 13 is moved horizontally in X-axis and Y- axis directions by operation of the Cartesian motion device 30. Since the configuration and operation of the Cartesian motion device 30 are well known, a detailed description thereof will be omitted herein. The Cartesian motion device can be replaced with a general three-axes robot that can move the head 13 of the punching machine 30 in the X- axis, Y-axis and Z-axis directions. In this case, the head 13 is moved in a stroke longer than the stroke of the up/down actuator 20 by the Z-axis motion of the three-axes robot, and then, the punch 12 can be further operated in the short stroke of the up/down actuator 20. The punching machine 10 of the present invention includes a working table 14 installed below the punch 12. The table 14 can be moved horizontally in the X-axis and Y-axis directions by a conventional Cartesian motion device or can be rotated by a conventional rotating device. A jig 15 or fixture for fixing the flexible printed circuit board 1 thereto is installed on an upper surface of the table 14, and a die 16 is mounted to the jig 15 that cooperates with the punch 12 to punch a hole in the flexible printed circuit board 1. As shown in Fig. 3, the flexible printed circuit board 1 includes a hole 2, a mark 3 indicating the location at which the hole 2 is punched, and a pattern 4. The mark 3 may be indicated in the form of a circle or cross, and a portion with a mark indicated thereon is formed into a hole 2 by the punching operation of the punching machine 10. Referring to Figs. 1 and 3, the punching machine 10 of the present invention comprises a camera 40 for photographing the mark 3 and acquiring image data of the mark. A lighting device 50 of the camera 40 illuminates the mark 3 along the same line as a first optical axis O1 of the camera 40 such that the camera 40 can photograph the mark 3 to capture an image of the mark 3. In the present invention, the camera 40 is constructed as a CCD (charge coupled device) camera, and the camera 40 is disposed in such a manner that the first optical axis O1 of the camera 40 is parallel to a central axis L of the punch 12. As shown in Fig. 4, the lighting device 50 comprises a light emitting diode 51 which is disposed perpendicular to the first optical axis O1 of the camera 40, a collimator 52 which converts the light emitted from the light emitting diode 51 into collimated light beam, and a beam splitter 53 which projects the collimated light beam from the collimator 52 onto the mark 3 through an objective lens 41 of the camera 40 and projects scattered light of the mark 3 from the objective lens 41 of the camera 40 onto a CCD image sensor 42 of the camera 40. Referring to Figs. 1, 2 and 4, the punching machine 10 of the present invention includes a light guide 60 which allows the final optical path from the camera 40 to be as close as possible and parallel to the central axis L of the punch 12. The light guide 60 includes a first reflector 61 which is installed at the front of the objective lens 41 of the camera 40 to cause the light traveling along the first optical axis O1 of the camera 40 to be reflected toward the central axis L of the punch 12 along a second optical axis O2 of the camera, and a second reflector 62 which causes the light traveling along the second optical axis O2 to be again reflected toward the mark 3 along a third optical axis O3 of the camera parallel to the first optical axis O1. The first and second reflectors 61 and 62 are placed in a housing 63 mounted at the front of the objective lens 41 of the camera 40, and may be constructed as a reflective prism or mirror. Meanwhile, the punching machine 10 of the present invention includes a computer 70 for processing the image data of the mark 3 obtained by photographing the mark 3 with the camera 40 to compute a coordinate value of the mark 3. The computer 70 numerically controls the operation of the Cartesian motion device 30 and the up/down actuator 20 based on the computed coordinate value of the mark 3. Hereinafter, the operation of the punching machine for the flexible printed circuit board according to the present invention so configured is described. Referring to Figs. 1 and 3, an operator fixes the flexible printed circuit board 1 with the mark 3 indicated thereon to the table 14 via the jig. 15. The computer 70 operates the Cartesian motion device 30 using a numerical control program stored therein and horizontally moves the head 13 in the X-axis and Y-axis directions, such that the third optical axis O3 can be aligned with the mark 3. As shown in Fig. 4, the light emitted from the light emitting diode 51 of the lighting device 50 is projected onto the mark 3 on the flexible printed circuit board 1 via the collimator 52, the beam splitter 53, the objective lens 41 of the camera 40, and the first and second reflectors 61 and 62 of the light guide 60. The light scattered from the mark 3 on the flexible printed circuit board 1 passes through the second and first reflectors 62 and 61, the objective lens 41 of the camera 40 and the beam splitter 53, and then captured by the CCD image sensor 42 such that the image of the mark can be photographed. The image data of the mark 3 obtained by the camera 40 is input to the computer 70. Meanwhile, the light traveling along the first optical axis O1 of the camera 40 is reflected on the first reflector 61 of the light guide 60 and then travels along the second optical axis O2, which is perpendicular to the first optical axis O1, toward the central axis L of the punch 12. Further, the light traveling along the second optical axis O2 is again reflected on the second reflector 62 and then travels along the third optical axis O3 which is parallel to the central axis L of the punch 12. Accordingly, the offset D between the third optical axis O3 of the camera 40 and the central axis L of the punch 12 can be minimized without interference between the camera 40 and the punch 12. Upon receiving image data of the mark 3 from the camera 40, the computer 70 converts the gray level image of the mark 3 into a binary image by application of a threshold, detects the contours from the binary image of the mark 3, and then filters out noise using the least square error method to compute an edge line. Further, the computer 70 places the edge line on an image array coordinate system and then computes a coordinate value of the mark 3. Since the coordinate value of the mark 3 comes closet to the coordinate value of the central axis L of the standby punch 12, an amount of a horizontal motion of the punch 12 with respect to the coordinate value of the mark 3 is minimized. Next, the computer 70 operates the Cartesian motion device 30 according to the coordinate value of the mark 3 such that the coordinate value of the central axis L of the punch 12 is coincident with the coordinate value of the mark 3. As described above, the amount of the horizontal motion of the punch 12 can be minimized because the coordinate value of the mark 3 is maximally close to the coordinate value of the central axis L of the standby punch 12. Therefore, the working speed of the punching machine 10 can be greatly enhanced. As shown in Fig. 2, after the central axis L of the punch 12 has been aligned with the mark 3 by operating the Cartesian motion device 30, the up/down actuator 20 is operated to lower the punch 12. The descending punch 12 punches the hole 2 at a specific location on the flexible printed circuit board 1 on which the mark is indicated. After the hole 2 has been completely punched on the flexible printed circuit board 1, the computer 70 operates the up/down actuator 20 to return the punch 12 to its original position. In the same manner as described above, the computer 70 operates the Cartesian motion device 30 to horizontally move the head 13 based on the numerical control program stored therein such that the third optical axis O3 of the camera 40 can be aligned with another mark 3 indicated on the flexible printed circuit board 1.

Industrial Applicability According to the punching machine for the flexible printed circuit board according to the present invention so configured, there is an advantage in that, since the optical axis of the camera for acquiring the image date of the mark indicated on the flexible printed circuit board comes closest to the central axis of the punch without interference between the camera and the punch, the amount of the horizontal motion of the punch with respect to the coordinate value of the mark obtained by photographing the mark with the camera and processing the image data of the mark using the computer can be reduced, and thus, the working speed of the punching machine can be greatly enhanced. It is intended that the embodiment of the present invention described above should not be construed as limiting the technical spirit of the present invention. The scope of the present invention is not limited to the embodiment but should be defined only by the appended claims. It is apparent to those skilled in the art that various changes, modifications and substitutions can be made thereto without departing from its true spirit. Therefore, it should be understood that various changes, modifications and substitutions fall within the scope of the present invention.