1. Field of the Invention
The present invention relates to a sheet guiding device for use in a facsimile or copying machine, for example, as a sheet guiding device of an original document feeding device for a facsimile or copying machine. More particularly, it relates to a sheet guiding device which guides sheets in a state where the conveyance reference thereof is located at the center of the sheet guiding device.
2. Description of the Related Art
FIGS. 17 to 19 illustrate a conventional sheet guiding device which is utilized as part of an original document feeding device for a facsimile machine.
In FIG. 17, reference character 1 denotes an original platen formed on the upper surface of a facsimile machine body. Original documents are placed on this original platen 1. Reference numerals 52 and 53 denote sheet guides which are position restricting members disposed in contact with or adjacent to side edge portions of an original document P (see FIG. 18) (hereinafter also referred to as a "sheet") placed on the original platen 1 to restrict the position of the sheet side edge portions. The sheet guides 52 and 53 are movable in a direction perpendicular to the sheet feeding direction, indicated by arrow A in FIG. 18, so that they can restrict the position of the side edge portions of sheets having various sizes, such as A row and B row, as shown in FIG. 18.
When one of the side guides 52 and 53 is moved, that movement is linked to movement of the other one, whereby the other one is also moved, so that the center of the sheet to be guided is located at a fixed position.
The structure of the sheet guides 52 and 53 will be described below with reference to FIGS. 20 and 21.
As shown in FIGS. 20 and 21, a portion of each of the sheet guides 52 and 53 is fitted into a groove 54 formed in the original platen 1 as a guide member. Rack members 57 and 58 are mounted on those portions of the sheet guides 52 and 53 by means of screws 59. Rack members 57 and 58 are arranged in mesh with a pinion 56 provided at the central portion of the original platen 1. When sheet guide 53 is moved in a direction indicated by an arrow `a`, pinion 56 is rotated in a direction indicated by an arrow `c`, whereby sheet guide 52 is moved in an outward direction indicated by an arrow `b`. When sheet guide 53 is moved in a direction opposite to the direction indicated by the arrow `a`, sheet guide 52 is moved in an inward direction reverse to the direction indicated by the arrow `b`. The width between the sheet guides 52 and 53 is thus adjusted by opening or closing the sheet guides according to the width of the original document. The sheet guides 52 and 53 may be fixed to a preselected position by means of a click (temporary fixing means).
However, in the aforementioned conventional sheet guiding device, since the sheet guides move in a direction perpendicular to the sheet feeding direction, by a distance corresponding to the width of the various types of sheets, and then guide the forward portion of the sheets with respect to the sheet feeding direction, indicated by the arrow A in FIG. 18, when large sheets having, for example, an A3 size, are fed, they may be fed slantingly because only the forward portions thereof are guided. When the guiding position is set for sheets having a large size (A3), sheets having a small size (A5) may be fed slantingly or may not be set correctly because only the trailing edge portions thereof are guided. Furthermore, since the sheet guides move in a direction perpendicular to the sheet feeding direction, if the click is weak, sheet guides 52 and 53 may be moved away from each other by the sheets. Consequently, correct guiding of the sheets may be prevented, and the sheets may be fed obliquely.
A sheet feeding device having sheet guides 52 and 53, as shown in FIG. 19, is also known. The sheet guides 52 and 53 have proximal end portions 52a and 53a formed parallel to the original platen 1. Pins 52c and 53c, projecting from the proximal end portions 52a and 53a in a downward direction, are fitted into grooves 52b and 53b formed in the original platen 1 in such a manner as to be slidable therealong, whereby sheet guides 52 and 53 are made movable in a direction perpendicular to the sheet feeding direction. In this structure, the space W1 between the pins 52c and between the pins 53c cannot be increased. Thus, sheet guides 52 and 53 have a backlash in a sub-direction thereof, as shown by arrows `d` in FIG. 19, and may thus make the sheets feed obliquely.
There is not a great difference in width between the sheet sizes A4 and LTR, and those sizes may be indistinguishable from each other by a size detecting device of the type which employs, for example, a microswitch. The size displayed on the original platen by means of a silk-screen process may not be visible at all or may not be clearly visible.
Furthermore, when large sheets are to be fed, an auxiliary member 51 provided at the rear end of the original platen 1 is rotated about a shaft 51a, as shown in FIG. 17, to receive the trailing edge portion of the large sheets (B4, A3). The trailing edge support plate has support portions 51a at the right and left thereof. A pin provided on each of the support portions 51a is in engagement with a hole opened in the original platen. The trailing edge support plate is mounted on the original platen by inserting the pins into the right and left holes utilizing the elasticity of the material which forms the trailing edge support plate. Therefore, the trailing edge support plate, which remains open in a state indicated by a dot-dashed line in FIG. 17, may become an obstacle. When a user bumps the opened trailing edge support plate, the plate may come off or the pins provided at the two ends thereof may break. Also, a large number of originals placed on the trailing edge support plate may bend the trailing edge support plate. Finally, it is difficult to open the trailing edge support plate after the originals are placed thereon.