1. Field of the Invention
The present invention relates to a method for welding panel fixing springs to the four sides of an apertured grill of a color cathode ray tube (hereinafter abbreviated as CRT). Additionally, the present invention relates to a post-fixing spring welding apparatus for welding a spring to one remaining side of the apertured grill to which the springs are welded.
2. Description of the Related Art
A type of CRT having an apertured grill to be used in a television set or a computer or a monitor TV is constructed such that an apertured grill having a plurality of slits formed therein is fixed to an inner side of a panel having fluorescent coatings of three primary colors (R, G, B). Electron beams for the three primary colors injected from electron guns pass through the slits of the apertured grill and are radiated against the fluorescent coating locations corresponding to the respective colors at the inner surface of the panel.
The aforesaid apertured grill is supported by a frame which is substantially formed into a rectangular frame-like shape by the upper, lower, right and left members. A grill is tensioned and arranged on this frame and the aforesaid plurality of slits extend upward and downward and are formed at locations spaced apart laterally on the grill.
The above mentioned panel is comprised of a panel part of a size which is two times larger than that of the aforesaid grill. It has a substantially rectangular shape and a fluorescent coating on its inner surface. Upper, lower, right and left skirts extend from and are formed at the four sides of the panel. The aforesaid panel part is formed to be two times larger than that of the aforesaid grill.
Fixing of the aforesaid apertured grill to the panel is carried out in such a way that the panel fixing springs are welded to three or four members of the apertured grill so as to cause the pin holes of the springs to engage the pins fixed to the inner surfaces of three or four skirts of the panel.
In this way, if the spaces between the surface of the grill and the inner surface of the panel are different from each other depending on their locations when the apertured grill is fixed to the panel, the electron beams which passes through the slits in the grill does not accurately radiate against the corresponding fluorescent coated locations of the panel. This may result in some disadvantages such as color mismatching or the like in the CRT after its complete assembly.
Due to this fact, for a CRT which is used as a monitor in a computer system which requires a high precision display or for a CRT having a large screen size or the like, it is important that the spaces between the surface of the grill and the inner surface of the panel are always kept constant.
A position of the surface of the grill with respect to the inner surface of the panel is determined by a position of the inner surface of the panel as viewed from a plane which includes the three or four pins of the panel and a position of the surface of the grill as viewed from a plane which includes the three or four pin holes of the apertured grill. The position of the inner surface of the panel as viewed from the aforesaid plane is defined due to the fact that the pins are already fixed to the panel.
Due to this fact, the position of the grill surface with respect to the inner surface of the panel is determined, but the positions of the pin holes when the springs are welded to each of the members may substantially influence this. Accordingly, when the springs are welded to each of the members, it is necessary that the welding locations of the springs on the members be made in consideration of the position of each of the pins in the panel.
In recent years, as the size of the CRT screen as well as its weight have increased, a four-point supporting system is frequently employed. This structure has four pins on the panel and four springs on the apertured grill.
When the springs are welded to each of the members of the CRT in the four-point supporting system as described above, it is preferable that the four springs are welded simultaneously in such a way that the relative positions of the pin holes for each of the springs is not displaced.
In this case, since the arrangement and orientation for each of the four springs is different, each of the springs is welded by applying a respective welding machine one by one. This requires four welding machines arranged inside the frame in order to avoid interference with the position setting members or the like of the apertured grill.
However, for a CRT having a relative small screen size such as 16", for example, the size of the frame becomes small in comparison with that of the screen size, so that there was insufficient space for arranging the four welding machines inside the frame and so the simultaneous welding of the four springs was difficult for this structure.
In addition, the simultaneous welding of the four springs generated some disadvantages in that the displacement of the relative positions of the springs could not be maintained within an allowable range even if the displacement of the welded location of each of the springs was within an allowable range. When each of the springs was thus welded to a location slightly displaced from the desired welding location, all the springs were necessarily removed from each of the members and welded to them again.
In light of the foregoing, one solution to this problem is that the pin hole of one spring of the four apertured grill springs is formed to have a larger size than that of the panel pin. A coin having a pin hole with a size engageable with the panel pin is then welded to the spring afterward as in the system disclosed in the gazette of Jap. Pat. Laid-Open No. Hei 5-299017. The positional displacement of each of the springs from the welded locations can be accommodated and corrected through a fine adjustment of the welded location of the coin with respect to the spring even if the four springs are welded separately.
However, this proposed solution had its own flaws and actually, either one or both the coin and the spring were deformed by heat or the like generated when the coin was welded to the spring. Thus the position of the pin hole of the coin after welding to the spring could not be accurately aligned with the position of the corresponding pin of the panel.
In addition, in this type of system, the coin must be welded to the spring when the panel pin is engaged with the coin and the pin hole of the spring and only a slight space is formed between the panel and the coin. This is a disadvantage in that welding between the coin and the spring is very difficult.