Document gap detecting device for use in facsimile

A document gap detecting device for facsimile is disclosed in which the bottom plate is formed in a stepped shape, and the linear speeds of an ADF roller and a carrying roller are designed to be same, thereby making it possible to produce a gap between the continuously fed document sheets without requiring a difference between the linear speeds of the ADF roller and the carrying roller. There are further provided with transmitting and receiving optical sensors. According to the present invention, there will occur no undesirable phenomenon such that the sheet at the receiving end is outputted in an extended length.

FIELD OF THE INVENTION 
The present invention relates to a facsimile document conveying device, and 
particularly to a facsimile document conveying device which is capable of 
producing gaps between the document sheets in the case of feeding a 
plurality of document sheets. 
BACKGROUND OF THE INVENTION 
As shown in the perspective view of FIG. 1, the prior art document 
conveying method at the transmitting end is carried out using a device 
constituted such that an ADF (automatic document feeding) roller 1, a 
carrying roller 2 and a document detecting device 5 are installed on a 
document guiding bottom plate 10 having a flat face, the automatically fed 
document sheets being thus conveyed along the flat face of the bottom 
plate 10. 
To generate gaps between the continuously fed document sheets, the prior 
art device of FIG. 1 is designed such that the linear speed of the ADF 
roller 1 should be slower than the linear speed the carrying roller 2. 
That is, the linear velocity V.sub.A of the ADF roller 1 as against the 
linear velocity V.sub.F of feeding roller 2 is set to have the following 
relationship; V.sub.F &gt;V.sub.A. 
Therefore, during the time when a document sheet 8 and a document sheet 9 
which are continuously fed are being conveyed along the bottom plate 10, 
if the leading edge and the trailing edge of the two document sheets 
arrive at the position of the document gap detecting device 5, there is 
produced a gap between the two document sheets, owing to the difference 
between the linear velocities of the two document sheets. 
Here, the two document sheets are discriminated by the function of the 
document gap detecting devices 5. That is, in order to discriminate the 
two document sheets which are continuously fed without gap, the document 
gap detecting device and the two rollers having different linear 
velocities are used, while the document gap discriminating device operates 
only when there is a gap between the two document sheets, the gap being 
obtained by providing a difference in the linear velocities of the two 
rollers. According to the standard, the document scanning speed 
corresponds with the linear velocity of the carrying roller. 
However, during the feeding of the document sheet, the document sheet is 
carried by the ADF roller 1 until the leading edge of the document sheet 
arrives at the carrying roller. 
Meanwhile, although the linear velocity of the ADF roller 1 is designed to 
be slower than the linear velocity of the carrying roller in order to 
generate gaps between the document sheets, the scanning speed of the lamp 
4 is designed to be same as the linear velocity of the feeding roller 2, 
and therefore, the scanning speed becomes slower as much as the difference 
between the linear velocities of the two rollers during the time when the 
document sheet moves between the scanning starting point and the carrying 
roller 2. Therefore, of the whole surface of the transmitting document 
sheet, the portion a which is scanned at a speed the same as the linear 
velocity of the ADF roller is received to the receiving end with an 
extended length b as shown in FIG. 1B, and therefore, the received sheet 
is out off in a changed length c. 
SUMMARY OF THE INVENTION 
The present invention is intended to overcome the above described 
disadvantaged of the conventional device. 
Therefore, it is the object of the present invention to provide a facsimile 
document feeding device in which a document guide having a step shaped 
coutour is installed at the transmitting end of the facsimile, so that, 
when a plurality of document sheets are fed automatically and 
continuously, the linear velocities of the ADF roller and the carrying 
roller should be same as each other, and at the same time, a gap should be 
produced between two continuously fed document sheets.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 2 is a perspective view showing the document gap detecting device of 
the present invention, while FIGS. 3A and 3B are sectional views showing 
the internal mechanism of the device of the present invention. If a 
plurality of document sheets are fed in the usual manner, the contents of 
the information of the document are scanned by a lamp, and the scanned 
contents of the information are transmitted by the facsimile to the 
receiving end. 
In such a facsimile, contrary to the conventional flat plane structure of 
the conventional bottom plate 10, the bottom plate 10, of the present 
invention is constituted in a stepped form. The vertical portion 11 of the 
step shaped bottom plate 10 is let to have a hole, and an RP sensor 5 is 
installed in the hole in such a manner that the RP sensor 5 should be 
exposed to the outside in the same way as that of an ADF sensor 6. 
The higher portion of the bottom plate 10 positioned to the right of the 
vertical portion 11 of the bottom plate 10 is provided with an ADF roller 
1, and ADF rubber 7 and an ADF sensor 6, while the lower portion of the 
bottom plate 10 positioned to the left of the vetical portion 11 of the 
bottom plate 10 is provided with a lamp 4, a carrying roller 2, and a 
punch roller 3. Here, it is required that the linear velocity of the ADF 
roller 1 and that of the carrying roller 2 are made to be the same as each 
other, that is, they are let to revolve at a speed producing that effect. 
Further, the device of the present invention is provided with optical 
sensor 13, 13', and the transmitting section of the sensor is attached to 
the main body of the facsimile, while the receiving section of the sensor 
is installed on a cover 12, so that the direction of the sensor units 
should correspond each other. 
Meanwhile, in order to make the document gaps sufficiently detected, the 
angle .theta. between the optical direction and the direction of the 
vertical portion of the bottom plate 10 is let to be formed as shown in 
FIG. 3B. The device of the present invention constituted as above will now 
be described as to its operations. 
As shown in FIG. 3A, during the time when the document sheet 8 moves toward 
the carrying roller 2 after passing the ADF roller 1 and the ADF rubber 7, 
the sheet 8 is carried by the ADF roller 1. Under this condition, the 
linear speed of the ADF roller 1 is same as that of the carrying roller 2, 
which is the standard speed. Therefore, the document sheet 8 moves in a 
state without producing any gap between the trailing edge of the document 
sheet 8 and the leading edge of the document sheet 9. 
However, when the trailing edge of the document sheet 8 and the leading 
edge of the document sheet 9 arrive at the vertical portion 11 of the 
bottom plate 10, the trailing edge of the sheet 8 drops to the lower face 
of the bottom plate 10, while the leading edge of the sheet 9 remains on 
the higher face of the bottom plate 10, with the result that there is 
naturally produced a gap between the sheets 8,9. 
Accordingly, the device of the present invention assured that a gap is 
produced between two continuously fed document sheets, without giving any 
difference between the linear velocities of the ADF roller 1 and the 
carrying roller 2. Further, the vertical portion 11 of the bottom plate 10 
can be formed in a sloped form as shown in FIG. 4. 
According to the present invention, the carrying speeds of the ADF roller 
and the carrying roller are same each other, and therefore, the scanning 
speed is also same, with the result that there will occur no phenomenon 
such that the sheet is received at the receiving end in an extended 
length.