Abstract:
A reel wire type of welding device for spot welding includes a first guiding portion rotatably mounted in a front end of the welding device such that the wire is supported and guided in a working area in which the wire contacts a target object. At least one second guiding portion is mounted in a rear of the roller such that the wire is supportedly guided in a zigzag manner as the wire is pressed in both upward and downward directions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to Korean Application No. 10-2003-0048298. Filed on Jul. 15, 2003, the disclosure of which is incorporated herein by reference. 
   TECHNICAL FIELD OF THE INVENTION 
   Generally, the present invention relates to a reel wire type of welding device for spot welding. More particularly, the reel wire type of welding device guides wire more securely and automatically senses abrasion and replacement timing of the wire. 
   BACKGROUND OF THE INVENTION 
   Typically, a reel wire type of welding device for spot welding of a vehicle has been proposed and published as Korean patent No. 337502. Such a welding device is re-formed from one according to the prior art that has an electrode fixedly inserted as a tip at a shank portion of a welding device. 
   In more detail, such a welding device includes a working unit, a wire, a first reel, and a second reel. The working unit includes a main body and a support portion. The wire is typically a Cr—Cu series alloy that is frequently used for spot welding. The first reel unrolls the wire and guides the wire to the working unit while the second reel rolls the wire received from the working unit. According to such a spot welding scheme, mutually contacting parts are welded by localized heating. According to such a scheme, a high current flows to overlapping plates to be welded by two overlapping welding devices through the wire. 
   A drawback of such a welding device occurs if tension between the two reels is lost, as the wire will become loose and unrolled. Therefore, the wire may lose direct contact with the plate such that no current flows between the wire and the plate. Welding is therefore not properly completed, and trouble may be caused by a nonconductive support portion coming into contact with the plate. 
   SUMMARY OF THE INVENTION 
   The present invention provides a reel wire type of welding device for spot welding. The present invention improves stableness in guiding a wire and the ability to sense an abrasion and replacement timing of the wire. 
   An exemplary reel wire type of welding device for spot welding includes a first guiding portion rotatably mounted in a front end of a welding device such that a wire is supported and guided thereby in a working area. Therefore, the wire contacts a target object. At least one second guiding portion mounted in a rear of the roller such that the wire is supportedly guided in a zigzag manner while being pressed in both upward and downward directions. 
   In a further embodiment, a plurality of optical sensors are employed for sensing a condition of the wire. In another further embodiment, a position detecting sensor for sensing wire abrasion is further included. Such a position detecting sensor includes an elastic spring and a variable resistor element such that wire abrasion is measured by a change of resistivity of the variable resistor element caused by a lengthwise deformation of the elastic spring. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and, read together with the detailed description, serve to explain the principles of the invention, wherein: 
       FIG. 1  is a perspective view of a welding device according to an embodiment of the present invention; 
       FIG. 2  is an enlarged lateral view of a roller portion of a welding device according to an embodiment of the present invention; 
       FIG. 3  is an enlarged perspective view of a position detecting sensor of a welding device according to an embodiment of the present invention; and 
       FIG. 4  is a cross-sectional view of the position detecting sensor and its circumstances with respect to a welding device according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   According to  FIG. 1 , the welding device  10  includes a main body  20 , an adapter  22 , and a support portion  24 . The main body  20  extends from a main portion. The adapter  22  extends cylindrically from a front of the main body  20 , while the support portion  24  extends from a front of the adapter  22 . The wire  200  is supplied in a direction shown by arrows and wound by a reel. During use, the roller  26  is guided toward a target object  500  to be spot welded, such as for example, overlapping pieces of material of a vehicle. 
   A wire guiding device according to an embodiment of the present invention includes a roller  26 , two guiding portions  30 , and two guiding portions  30 ′. The roller  26  is formed toward a front end of the support portion  24  and functions as a guiding portion. The two guiding portions  30  (hereinafter called front guiding portions) are disposed in front sides of the main body  20 . The two guiding portions  30 ′ (hereinafter called rear guiding portions) are disposed toward a rear of the sides of the main body  20 . 
   The roller  26  is rotatably connected at the front end of the support portion  24  by the rotating pin  26 ′. As shown in  FIG. 2 , the roller  26  is hollowed out at a central part thereof, to form a guiding groove  28 . The guiding groove  28  supports and guides the wire  200 . 
   The front guiding portions  30  are formed with a low height, and the rear guiding portions  30 ′ are formed with a height higher than the front guide portions. Such an arrangement produces merits such that the wire may be maintained at a high and constant tension, since the wire is guided in a zigzag manner being pressed in both upward and downward directions. In addition, a formation of rollers  300  and  300 ′ formed in the guiding portions  30  and  30 ′ is the same as that of the roller  26 . The front guiding portions  30  are respectively provided with two confronting plates  32 , a rolling pin  34 , and a roller  300 . The rolling pin  34  is tightly fitted into an upper part of the confronting plates  32 , and the roller  300  is rotatably mounted on the rolling pin  34 . 
   The formation of the rear guiding portions  30 ′ is almost the same as that of the front guiding portion  30 . However, confronting plates  32 ′ of the rear guiding portions  30 ′ are higher than the confronting plates  32  of the front guiding portions  30 . Additionally, a position detecting sensor  50  is located between the two confronting plates  32 ′, which is further described below. 
   According to such a scheme for guiding a wire, the wire changes direction at the roller  26 , and is supported by the guiding portions  30  and  30 ′ in both upward and downward directions. Therefore, the wire is prevented from escaping the guide route since the wire is guided by the rollers and problems of defective welding caused by derailment of the wire and mechanical trouble of the support portion are minimized. In addition, the roller  26  can minimize damage to the wire by friction and the roller  26  dissipates heat generated during welding. 
   According to an embodiment of the present invention, a wire-cut detecting device is further adopted. The wire-cut detecting device includes two optical sensors  40  mounted in the main body  20 . The wire-cut detecting device is mounted between the front guiding portions  30  and the rear guiding portions  30 ′. As shown in  FIG. 1 , one optical sensor  40  is mounted on one side of the main body  20  and another optical sensor  40  is preferably mounted on the other side of the main body  20 . Each of the optical sensors  40  includes a light emitting portion, a light receiving portion, and a transmitting portion. The optical sensors  40  are electrically connected to a pressure welding controller. 
   Since the light emitting portion and the light receiving portion of the optical sensors  40  face the wire  200 , the sensor  40  can transmit a light signal to and receive the same in return from the wire. Because such optical sensors  40  are already known to a person of ordinary skill in the art, details thereof are not described in further detail herein. 
   If the light emitted from the light emitting portion of the optical sensor  40  is not reflected by the wire  200 , the light receiving portion does not sense any light reflected therefrom. In this case, the controller preliminarily determines that the wire is cut. However, non-detection of light by the light receiving portion may accidentally occur by other factors such as reduction and diffusion of light emitted from the sensor  40 , and the like. In order to avoid such an erroneous reading it is preferable that signals from both sensors  40  disposed on both sides of the main body  20  are compared before the wire is determined to be cut in the case that a difference between light signals the sensors  40  is larger than a predetermined level or when a light signal is not received from either sensor  40 . 
   As shown in  FIG. 3 , a wire abrasion sensing device includes a position detecting sensor  50  mounted between the two plates  32 ′ of guiding portion  30 ′. Obviously, such a wire abrasion sensing device may be mounted in a plurality of positions. 
   An embodiment of a scheme of the position detecting sensor  50  will be hereinafter described in detail with reference to  FIG. 4 . The position detecting sensor  50  includes an elastic spring  58  and a variable resistor element  56  internally mounted in an upper case  52  of the position detecting sensor  50 . The elastic spring  58  supports a bottom of the upper case  52  of the position detecting sensor  50 . 
   An output value of the variable resistor element  56  in the position detecting sensor  50  is changed by the height of the position detecting sensor  50  above the main body  20 . Such a position detecting sensor  50  is known to a person of ordinary skill in the art, and is not described in further detail herein. 
   The upper case  52  is electrically connected to the pressure welding controller by a signal line. An upper side of a roller on the upper case  52  of the position detecting sensor  50  faces the roller  300 ′ of the rear guiding portion  30 ′, and a predetermined clearance d is formed between the upper case  52  of the position detecting sensor  52  and the roller  300 ′. The wire  200  is guided through the clearance d. As abrasion of the wire  200  increases, the clearance d becomes narrower and the elastic spring  58  gradually expands upwards. Therefore, the position detecting sensor  50  moves upwards and the resistivity of the variable resistor element  56  is varied in accordance with the change of the height of the position. 
   If an electric current value of the circuit which includes the resistor is lower than a predetermined value (e.g., 50% of the initial value), the controller determines that abrasion of the wire  200  has reached a limit value. Subsequently, it relays the result to workers through a display or alarm. 
   According to an embodiment, the position detecting sensor  50  supports a lower side of the wire  200 . Therefore, it also functions to support and supply tension to the wire  200 , in cooperation with the roller  300 ′. 
   As a variation of an embodiment of the invention, the variable resistor element  56  of the wire abrasion sensing device can be replaced with, for example, a piezoelectric element or the like. In addition, the electric sensor  50  can be replaced with a display device that can capture an image of the wire such that a thickness of the wire or abrasion of the wire may be determined therefrom. 
   According to yet another embodiment of the present invention, escaping or derailment of the wire  200  is minimized and spot welding for a vehicle becomes more effective. Additionally, a wire-cut and excessive abrasion of the wire may be automatically detected, and thus a worker may be apprised of causes of abnormal welding. Therefore, the welding process becomes more stable and efficient. 
   The scope of the present invention is not limited by the above-described details of positions, structure, the number of guiding portions and optical sensors, or the internal structure of the position detecting sensor. While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalents included within the spirit and scope of the appended claims.