Metal deforming – With cutting – By shearing tool-couple
Reexamination Certificate
1999-10-15
2001-05-01
Crane, Daniel C. (Department: 3725)
Metal deforming
With cutting
By shearing tool-couple
C072S334000, C029S893330, C029S893340, C347S004000
Reexamination Certificate
active
06223578
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for manufacturing metal parts and sheet pressing wheels, and a printer in which such sheet pressing wheels are used in a sheet feeding mechanism. The present invention particularly relates to a metalworking technique suitable for forming a very fine outline shape of a metal part.
BACKGROUND OF THE INVENTION
Some sheet feed mechanisms mounted on printers use gear-shaped sheet pressing wheels (hereinafter referred to as “star wheels”) in which tooth portions with comparatively sharp tips are arrayed in an outer circumferential portion of each star wheel. A plurality of such star wheels are attached rotatably around a shaft disposed perpendicularly to the sheet feed direction, and each star wheel is disposed in opposition to a paper discharge roller. The star wheels catch a sheet, which is fed in a predetermined feed course by drive rollers, by means of the comparatively sharp tips of the tooth portions in their circumferential portions while the sheet is held between the sheet discharge rollers and the star wheels, so as to prevent the sheet from slipping off to the side and control the sheet to run in a regular feed direction.
Conventionally, when such a star wheel is manufactured, a gear-like plane shape is first formed by a punching process, and tips of tooth portions are thereafter thinned by an etching process in order to form acuminated shapes in the tips of the tooth portions. This is because the curvature radius in the plane shape of the tip of each tooth portion of the star wheel has to be made extremely small as 0.04 mm, and the thickness of the tip of the tooth portion has to be also made extremely small as 0.06 mm.
If the area of the tip of the tooth portion becomes large in the star wheel, in the case where ink printed on a sheet adheres to the tip of the tooth portion, this ink is transferred to other portions of the sheet so that spotted marks large enough to be visible are left on the sheet. On the other hand, if the tip portion of the tooth portion of the star wheel is too sharp or has a burr, the tip portion may damage the surface of the sheet discharge roller, or cut into the sheet and damage it. Therefore, the shape of the tip of any tooth portion of the star wheel has a very fine shape as mentioned above, and manufacturing precision is demanded.
In the above-mentioned manufacturing method, however, process control and others take a great deal of labor in the etching process so as to increase the cost. In addition, the corners of the tip portions get pointed by the etching process, so that there is a problem that it is impossible to avoid the above-mentioned disadvantage.
In addition, in the case where the plane shape is formed by press-working as mentioned above, there is a problem that since the curvature radius of the tip of each tooth portion is so small that it is difficult to perform press-working on a thick metal sheet, it is difficult to ensure the rigidity of the star wheel. Further, since very fine shapes having a small curvature radius have to be formed, there is another problem that a load on a press die becomes so large as to shorten the life of the press die.
Further, since there is an etching process after press-working as mentioned above, it is necessary to carry very small and individually separated star wheels and set them for the etching process. Such working is extremely troublesome, and it is difficult to mechanize all the working. Therefore, there is a problem that increase of the manufacturing cost is caused and the manufacturing efficiency cannot be improved to be higher than the current one.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for manufacturing a metal part in which the part is formed only by plastic working such as press-working, even if it is a very small part, so as to achieve reduction of the manufacturing cost and make it possible to improve the manufacturing efficiency.
It is another object of the present invention to provide a method for manufacturing a star wheel as such a very small metal part.
It is a further object of the present invention to provide a printer in which such star wheels are incorporated as a sheet feed mechanism.
A method for manufacturing a metal part by plastic working of a metal plate according to the present invention comprises a first forming step of performing a punching operation for roughly forming at least a part of the outline shape of the metal part; a second forming step of performing a face pressing operation on at least an outline edge portion of the metal part to thereby thin the outline edge portion; and a third forming step for shaping the thinned outline edge portion again by a punching.
Moreover, in a method for manufacturing a star wheel according to the present invention, a hole for forming a bearing portion therein is punched out in a center portion of the metal part manufactured in the above-mentioned manner.
Moreover, in a printer according to the present invention, a sheet feed mechanism is mounted thereon, and such star wheels as mentioned above are incorporated in the sheet feed mechanism.
According to the present invention, at least a part of the outline shape is roughly formed in the first forming step, a face pressing work is given in the second forming step to the outline edge portion so as to thin the outline edge portion, and the thinned outline edge portion is shaped again in the third forming step. Thus, since the face pressing work is given after the outline shape is roughly formed in the first forming step, forming in the second forming step becomes easy. In addition, since the outline edge portion thinned in the second forming step is shaped again, a fine outline shape can be easily and precisely formed in the third forming step. It is therefore possible to prolong the life of press dies for the forming steps. Further, since the metal part can be formed only by punching work and pressing work, it is possible to reduce the manufacturing cost and improve the productivity.
Here, assume that the metal part which is a target of the present invention has a protrusive portion in its outline edge portion. Then, it is preferable that the first forming step and the third forming step are carried out to form a plane surface shape of the protrusive portion out of a metal plate, and the second forming step is carried out to form a sectional shape of the protrusive portion out of the metal sheet.
In this case, according to the present invention, the plane shape of the protrusive portion is roughly formed in the first forming step; the sectional shape of the protrusive portion is formed in the second forming step; and the plane shape of the protrusive portion is formed in the third forming step. It is therefore possible to form the protrusive portion easily and precisely even if the protrusive portion has a very fine outline shape.
In this case, it is also preferable that the metal part is a gear or gear-shaped part having an array of teeth as the protrusive portion. According to the present invention, it is possible to form the outline shape of an array of teeth of a gear or a gear-shaped part easily and precisely. As many of gears or gear-shaped parts have a very fine teeth shape, the present invention is extremely effective in forming such a very fine outline shape at a low price.
Further in this case, it is preferable that the metal part is a star wheel for controlling the sheet feed direction in a sheet feed mechanism. According to the present invention, it is possible to form the tip shapes of the tooth portions of the star wheel easily and precisely. Particularly in the star wheel, the tips of the tooth portions have a very fine and sharp shape, and the shape of the sharp tips of the tooth portions has to be formed precisely for the sake of ensuring the performance. It is therefore possible to provide a high-performance star wheel at a low cost.
In the above-mentioned respective steps of the present invention, it is preferable to perform the respective forming step
Crane Daniel C.
Ladas and Parry
Seiko Epson Corporation
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