AUTOMATIC DIGITAL WELDING HELMET USING CAMERA Technical Field [1] The present invention relates, in general, to an automatic digital welding helmet using a camera and, more particularly, to an automatic digital welding helmet using a camera, which photographs welding or cutting surroundings, and allows a worker to perform welding work while viewing moving images received from the camera, thus safely protecting the worker's eye. Background Art [2] Conventionally, in order to adjust the shielding of harmful rays that are generated by welding or cutting torches, a welding helmet, with which an antiglare plate having variable light transmissivity is provided, has been used. [3] That is, in the conventional welding helmet, a light sensor is mounted, and the light transmissivity of the antiglare plate is adjusted according to the intensity of welding light, thus protecting a worker's eyes. [4] However, when the actual intensity of welding light is weak but the intensity of in¬ terference light is strong due to interference light that is generated in surroundings, not based on the welding light, the light transmissivity of the antiglare plate is lowered, so that a faulty operation in which an object to be welded may not be clearly observed occurs frequently. [5] Furthermore, inconvenience occurs in that the worker must personally adjust the degree of shade of the antiglare plate and the sensitivity of the light sensor to be ap¬ propriate to welding surroundings. [6] Furthermore, an inevitable problem occurs in that the harmful rays cannot be completely blocked and some of the harmful rays are incident on the worker's eyes even though the light transmissivity of the antiglare plate is appropriately adjusted to the welding surroundings. [7] Furthermore, in the case of welding in air tank, high-pressure gas and aerospace fields, welding errors occasionally result in large-scale accidents, such as explosions. In cases where welding is critical, a problem occurs in that the weld condition must be confirmed later but it consumes time and cost to personally travel to an actual work site and confirm the weld condition. Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an automatic digital welding helmet using a camera, which allows a worker to perform welding work while viewing the moving images of the welding work, which are received from the camera, using a Liquid Crystal Display (LCD) monitor, so that harmful rays are completely blocked and errors caused by interference light do not occur. [9] Another object of the present invention is to provide an automatic digital welding helmet using a camera, which stores the moving images of welding work in memory, and allows weld condition to be confirmed later using the memory in the case of critical welding work, thus determining whether weld condition is faulty. [10] A further object of the present invention is to provide an automatic digital welding helmet using a camera, which stores the identification number of the welding helmet along with the moving images of the welding work in memory, and allows the weld condition and the worker who performs corresponding welding work to be determined later. Technical Solution [11] In order to accomplish the above objects, the present invention provides an automatic digital welding helmet using a camera, including a monitoring unit for monitoring welding work using a camera selected from among a plurality of cameras; a control unit for selecting any one from among the plurality of cameras, and storing moving images, which are received from the selected camera, in memory; and a display unit for displaying the moving images received from the selected camera. [12] Furthermore, it is preferable that the monitoring unit include a first camera for pho¬ tographing a front scene, a second camera for photographing a left side scene, a third camera for photographing a right side scene, a fourth camera for photographing an upper scene, and a fifth camera for photographing a lower scene. [13] Furthermore, it is preferable that the first to fifth cameras each have a zoom function. [14] Furthermore, the monitoring unit may be mounted on the outer side of the welding helmet, and the display unit may be mounted on the inner side of the welding helmet. [15] Furthermore, the automatic digital welding helmet further may include an opening and closing unit mounted on the welding helmet to be openable, wherein the monitoring unit is mounted on the outer side of the opening and closing unit, and the display unit is mounted on the inner side of the opening and closing unit. [16] Furthermore, it is preferable that the displaying unit indicates which camera be selected from among the plurality of cameras. [17] Furthermore it is preferable that the display unit be a LCD monitor. [18] Furthermore, it is preferable that the control unit include a camera selection module for selecting any one from among the plurality of cameras through a camera selection button, and a moving image storage module for storing the moving images, which are received from the camera selected by the camera selection module, in the memory when a moving image storage switch is turned on. [19] Furthermore, it is preferable that the camera selection module be mounted on the outer side of the welding helmet. [20] Furthermore, it is preferable that the moving image storage module store an iden¬ tification number of the welding helmet along with the moving images in the memory. [21] Furthermore, it is preferable that the memory be detachably attached to the welding helmet. [22] Furthermore, it is preferable that the automatic digital welding helmet further include a light mounted on the outer side of the helmet. [23] Furthermore, it is preferable that the automatic digital welding helmet further include a light on and off switch mounted on the outer side of the helmet. [24] Furthermore, it is preferable that the control unit further comprise a wireless transmission and reception module for wirelessly transmitting the moving images received from the camera. Advantageous Effects [25] Since, the automatic digital welding helmet using a camera according to the present invention allows a worker to perform welding work while viewing the images of the welding work, which are received from the camera, using an LCD monitor, harmful rays are completely blocked and errors caused by interference light do not occur at all. [26] Furthermore, since the automatic digital welding helmet using a camera according to the present invention can store the images of the welding work in memory, weld condition can be confirmed later using the memory in the case of critical welding work, thus determining whether the weld condition is faulty. [27] Furthermore, since the automatic digital welding helmet using a camera according to the present invention can store the identification number of the welding helmet along with the images of the welding work in the memory, the weld condition and the worker who performed corresponding welding work can be determined. [28] Furthermore, since the automatic digital welding helmet using a camera according to the present invention allows the worker to select any one from among cameras for photographing front, left side, right side, upper, and lower scenes, the worker's view can be secured by selecting an appropriate camera in the case in which an object to be welded is placed at a corner location to which the worker's head cannot turn. Brief Description of the Drawings [29] FIG. 1 is a block diagram showing the construction of an automatic digital welding helmet; [30] FlG. 2 is a view showing an automatic digital welding helmet using a camera according to a first embodiment of the present invention; [31] FlG. 3 is a view showing the display unit of the present invention; and [32] FlG. 4 is a view showing an automatic digital welding helmet using a camera according to a second embodiment of the present invention. Best Mode for Carrying Out the Invention [33] Embodiments of the present invention are described in detail with reference to the accompanying drawings below. [34] FlG. 1 is a block diagram showing the construction of an automatic digital welding helmet. [35] Referring to FlG. 1, the automatic digital welding helmet 100 according to the present invention includes a monitoring unit 110 for monitoring welding work using a camera selected from among a plurality of cameras 111 to 115, a control unit 120 for selecting any one camera from among the plurality of cameras, and storing moving images, which are received from the selected camera, in memory (not shown), and a display unit 130 for displaying the moving images received from the selected camera. [36] The monitoring unit 110 includes a first camera 111 for photographing a front scene, a second camera 112 for photographing a left side scene, a third camera 113 for photographing a right side scene, a fourth camera 114 for photographing an upper scene, and a fifth camera 115 for photographing a lower scene. [37] Furthermore, the first to fifth cameras 111 to 115 each have a zoom function, and may include a lens protection filter. [38] FlG. 2 is a view showing an automatic digital welding helmet using a camera according to a first embodiment of the present invention. [39] Referring to FlG. 2, the monitoring unit 110 is mounted on the outer side of the welding helmet 200. That is, the first to fifth cameras 111 to 115 are mounted on the outer side of the welding helmet 200. [40] Referring to FIGS. 1 and 2, the control unit 120 includes a camera selection module 121 for selecting any one from among the plurality of cameras 111 to 115 using a camera selection button 123, and a moving image storage module 122 for storing the moving images, which are received from the camera selected by the camera selection module 121, in the memory when a moving image storage switch 124 is turned on. [41] Furthermore, the camera selection module 123 is mounted on the outer side of the welding helmet 200, and allows the worker to easily select a camera located in the direction in which a worker desires see even while wearing the welding helmet 200. Furthermore, the camera selection button 123 includes upper, lower, left and right direction keys and a central button, as shown in the drawing, and facilitates the worker's manipulation. [42] When the moving image storage switch 124 is turned off, the moving image storage module 122 do not store the moving images in the memory. [43] Meanwhile, the moving image storage module 122is configured to store the iden¬ tification number of the welding helmet 200 along with the moving images in memory, and the memory is configured to be detachably attached to the welding helmet 200. [44] Accordingly, when the welding worker completes the welding work, detaches the memory from the helmet, and then submits the memory to a department in charge, the department can check the welding performance of the corresponding welding worker, the weld condition of an object to be welded, etc. using the memory because the moving images of the welding work and the identification number of the worker's welding helmet have been stored in the memory. [45] Furthermore, the control unit 120 further includes a wireless transmission module (not shown), so that the moving images stored in the memory may be transmitted to the server of the department in charge, and the moving images received from the camera may be transmitted to the server in real time. [46] Meanwhile, a light 140 and a light on/off switch 125 are mounted on the outer side of the welding helmet 200, so that the brightness of a work site can be adjusted by turning on or off the light 140. [47] Although, in FIG. 2, the camera selection button 123, the moving image storage switch 124 and the light on/off switch 125 are illustrated as being mounted on the lower end portion of the outer side of the welding helmet 200, all of them may be mounted on the left side of the outer side of the welding helmet 200. Furthermore, the camera selection button 123, the moving image storage switch 124 and the light on/off switch 125 are mounted on each of outer and inner sides of the welding helmet 200, that is, at two places, and is configured such that the worker can operate either the inner buttons or the outer buttons, thus increasing the worker's convenience. [48] FIG. 3 is a view showing the display unit 130 of the present invention. [49] Referring to FIG. 3, the display unit 130 is formed of an LCD monitor, the moving images received from the camera selected by the camera selection button 123 are displayed on a moving image display region 131, and the selected camera is indicated in a selected camera display region 132. For example, when the third camera 113 for photographing a right side scene is selected, a character "R" is displayed, and when the second camera 112 is selected, a character "L" is displayed. [50] Furthermore, characters "REC" are displayed in the case in which the moving images are being stored in a recording display region 133, and characters "STOP" or no characters are displayed in the case in which the operation of storing the moving images is stopped. [51] FlG. 4 is a view showing an automatic digital welding helmet using a camera according to a second embodiment of the present invention. [52] Referring to FlG. 4, the automatic digital welding helmet using a camera is configured such that an opening and closing unit 210 is mounted on the welding helmet 200 so that the opening and closing thereof is possible, and the monitor unit 110 is mounted on the outer side of the opening and closing unit 210. Components other than the components are the same as those in the first embodiment of the present invention. [53] Accordingly, in accordance with the second embodiment of the present invention, the worker can freely open and close the opening and closing unit 210 while wearing the welding helmet and performing the welding work, so that the present invention is advantageous in that the worker can confirm an object to be welded by opening only the opening and closing unit 210 without removing the welding helmet when desiring to personally confirm the object to be welded with the naked eyes without the cameras. [54] The present invention is not limited to the above-described preferred embodiments, and those skilled in the art can easily make various modifications without departing from the scope and spirit of the invention. Such modifications are all included in the scope of the accompanying claims.