Abnormal-paper sensing apparatus in a printing machine

An abnormal-paper sensing apparatus in a printing machine which senses the presence of a front folded corner of a sheet of printing paper. The sheet of paper hits against front lays provided at a front end of an insertion guide plate and stops. The insertion guide plate has a pair of recesses provided in a front end portion thereof so as to extend thereacross at positions where the recesses can face the front corners of the sheet of paper which passes over the recesses. The recess have a triangular cross section with a longer side positioned on the side of the front end of the insertion guide plate and with a shorter side positioned on the side of the rear end of the insertion guide plate. When the sheet of paper hits against front lays provided at the front end of the insertion guide plate and stops, and if the sheet of paper has a folded angle at its front end, the corresponding recess is exposed and reflects the projected light diffusively, so that the sensors do not receive a quantity of reflected light enough to continue paper feeding.

BACKGROUND OF THE INVENTION 
This invention relates to printing machines and more particularly to an 
abnormal-paper sensing apparatus in the printing machine which senses a 
folded corner of a sheet of printing paper which hits against front stays 
provided at a front end of an insertion guide plate and stops thereat in 
response to the disappearance of reflected light from the folded corner of 
the sheet of paper. 
In a sheet-fed printing machine, sheets of printing paper stacked on a 
stacker of a paper feeder are drawn and fed one by one by a sucker, 
starting with the top sheet, to a feeder board and then delivered onto an 
insertion guide plate with the aid of a carrier tape and feed rolls. The 
sheet of paper then hits against front stays provided at a front end of 
the insertion guide plate and stops thereat with it being adjusted with 
reference to the vertical by the front stays and also with respect to 
right and left by a transverse needle device. The sheet of paper which has 
hit against and stopped is then captured and carried by a pawl of a swing 
device and then is printed while it is being carried with it being 
captured by a thicker pawl. 
Sheets of paper are required to be fed one by one to the printing machine 
without being bent or folded. Therefore, when undesirable feeding such as 
feeding of a sheet of paper having a folded corner of double-sheet feeding 
has occurred, this is sensed and capture by the pawls and paper-feeding 
onto the insertion guide plate are stopped. An abnormal sheet of paper of 
this type is folded at its front right and/or left corner into a triangle. 
In order to sense this corner folding, reflection type sensors are 
conventionally provided several millimeters before the front stays above 
the sheet of paper to sense the presence of reflected light from the sheet 
of paper which hits against the front stays and stops to thereby determine 
that there is corner folding in the sheet due to the fact that no 
reflected light is received. When a sheet of paper having a different size 
is used, the sensor is moved correspondingly. 
In such corner folding sensor, however, the insertion guide plate itself 
will reflect light which is projected to its exposed portions. Therefore, 
the sensor is likely to erroneously determine that there is no corner 
folding although there is actually corner folding, and thereby continue 
paper feeding. In order to avoid this, through holes are provided in the 
insertion guide plate so as to cause the projected light to pass through 
the hole without reflecting the projected light when there is 
corresponding corner folding. However, in order to cope with a different 
paper size or alter the sensing position, the holes must be elongated in 
the form of slots, so that a sheet of paper sliding on the insertion guide 
plate may be hooked at its corner into the elongated slot and bent to 
thereby operate the sensor, thus stopping feeding of the sheet of paper. 
Provision of such an elongated hole would weaken the strength of the end 
portion of the insertion guide plate. 
SUMMARY OF THE INVENTION 
Therefore, it is the object of the present invention to provide an improved 
abnormal-paper sensing apparatus in a printing machine. 
In order to solve these problems, according to this invention, for example, 
the insertion guide plate has a pair of recesses provided in a front end 
portion thereof so as to extend there-across at positions where the 
recesses can face front corners of the sheet of paper which passes over 
the recesses, the recess having a triangular cross section with a longer 
side positioned on the side of the front end of the insertion guide plate 
and with a shorter side positioned on the side of the rear end of the 
insertion guide plate. 
When a sheet of paper fed onto the insertion guide plate normally hits 
against the front stays and stops thereat, the sensor receives light 
emitted by the sensor itself and reflected by the sheet of paper, so that 
normal paper feeding continues. When corner folding occurs and the sheet 
of paper is stopped by the front stays, the light projected by the sensor 
reaches the exposed slant bottom of the recess and reflected diffusively 
because the exposed bottom is slanting. Thus the sensor does not receive 
the reflected light. As a result, a signal is generated to stop the paper 
feeding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIGS. 1 to 4, an abnormal-paper sensing apparatus according this 
invention includes an elongated strip-like insertion guide plate or 
feedboard 1 which extends across the feeding direction of the printing 
machine. It is also supported slightly slanting between a paper feeder 
(not shown) and a printing unit (not shown), as shown in FIG. 4. A 
plurality of leaf springs 2 are disposed parallel to each other across the 
machine and supported by supports 4 above the front end of the feedboard 1 
by means of brackets 3. The front ends of the leaf springs 2 abut slidably 
on an upper surface of the front end of the feedboard 1. A plurality of 
front stays 5 are supported in parallel with each other across the 
printing machine by a shaft 6 supported above the front end of the 
feedboard 1. The front stays 5 are received in corresponding grooves 1a 
provided at the front end of the feedboard 1 whereby a reciprocating 
rotation of the shaft 6 through a predetermined angle at a predetermined 
timing causes the front stays to descend and rise vertically relative to 
the feedboard 1 so that they are withdrawn therefrom, as shown. The sheet 
of paper 7 fed onto the feedboard 1 through a feeder board (not shown) 
from a paper feeder (not shown) is decelerated by the leaf springs 2 and 
stops by engagement with the front stays 5. 
A pair of right and left transeversely-disposed recesses 8--8 are provided 
between right and left grooves 1a-1a several millimeters 6 rearwardly of 
the front end of the feedboard 1. Each recess 8 is in the form of a 
rectangle extending transeversely of the feedboard 1 and is of 
right-angled triangle cross section having a longer side 8a positioned on 
the side of the front end of the feedboard 1 and a shorter side 8b 
positioned on the side of the rear end of the feedboard 1. The inner 
surface of each recess 8 is coated with a black material. These recesses 8 
are positioned and sized such that the end edge of a sheet of printing 
paper having any width between the maximum and minimum ones may pass over 
those recesses. Reference numeral 9 denotes a notched line showing one of 
several standard sizes of paper. A pair of clamps 11 are split-tightened 
in correspondence to the recesses 8 onto stays 10 supported above the 
front end of the feedboard 1. Each clamp 11 has fixed thereto by means of 
a holder 13 a reflection-type sensor 12 opposite to the corresponding 
recess 8. The sensor 12 is of the type which emits light and receives the 
light reflected by an object. In this embodiment, when the sensor receives 
no reflected light, it generates a signal which is delivered via a lead 14 
to a controller (not shown) to thereby stop the paper feeding. Namely, 
when a sheet of paper 7 covers the recesses 8--8, there exists reflected 
light, so that no signal is generated. The arrangement is such that when a 
sheet of paper 7 is folded at one of its front corners, the corresponding 
recess 8 is exposed, so that the projected light is reflected diffusively 
by the bottom surface of the recess 8--8. Thus, the diffused light is not 
received by the sensor 12, so that the sensor 12 generates a signal. 
In operation, when the sheet of paper 7 fed from the feed device via the 
feeder board onto the feedboard 1 hits against the front stays 5 and stops 
thereat, the sheet of paper 7 normally shields the recesses 8--8, so that 
the light projected by the sensors 12 is reflected by the sheet of paper 
7. Thus, the reflected light arrives at the sensors 12, so that the 
sensors 12 generate no signal and paper feeding continues. Namely, when 
the sheet of paper 7 abuts the front stays and stops thereat, the shaft 6 
is rotated clockwise in FIG. 4, the front stays 5 move away from the 
feedboard 1 and at the same time a pawl of a swing device (not shown) 
swings diagonally upwardly, captures the sheet of paper 7 and moves it to 
the printing unit. 
When a sheet of paper having its corner folded is fed onto the feedboard 1, 
into engagement with the front stays 5 and stops thereat, the folded 
corner of the sheet of paper does not shield so that the corresponding 
recess 8 is exposed. In this case, each recess 8 has a slant inner surface 
asymmetrical around a transverse plane therein and coated with a black 
material, so that the light projected from the sensors 12 is reflected 
diffusively by the recess bottom surface. Therefore, the reflected light 
does not arrive at the sensors 12, so that the sensors 12 produce a signal 
to stop the paper feeding. Thus the abnormal-sheet of paper with the 
folded corner is removed and printing is then resumed. 
When a sheet of paper having a different size is used, the clamps 11 are 
loosened and the sensor 12 are moved so as to cope with the different 
paper size. 
As will be described from the aforementioned description, according to this 
invention, the insertion guide plate has a pair of recesses provided in a 
front end portion thereof so as to extend thereacross at positions where 
the recesses can face front corners of the sheet of paper which passes 
over the recesses, the recess having a triangular cross section with a 
longer side positioned on the side of the front end of the insertion guide 
plate and with a shorter side positioned on the side of the rear end of 
the insertion guide plate. When a sheet of paper with a folded corner hits 
against the front lays and stops thereat, the corresponding recess is 
exposed, the light projected from the sensor to the exposed recess is 
reflected diffusively by the asymmetrically slant notch-like bottom 
surface of the recess. In addition, even when a sheet of paper having a 
different size is used, which has a folded corner, it does not cover the 
corresponding recess, so that the reflected light does not reach the 
sensor. Therefore, corner folding is reliably sensed irrespective of the 
paper size so as to stop the paper feeding to thereby improve the sensing 
accuracy. The front-side portion of the recess bottom is gently inclined 
at a low angle, so that a corner of a normal sheet of paper is not 
trapped, thereby reducing a quantity of wasted paper. In addition, the 
recesses do not extend through the insertion guide plate, so that it has a 
strength greater than the conventional one. If the recess bottom is coated 
with a black material, sensing will further be improved.