Method for checking the correct manufacture of cross bottom valve sacks

For manufacturing cross bottom valve sacks, the ends of continuously transported tubular sections are opened out with the formation of so-called "bottom squares" with triangular corner folds lying opposite each other. A valve leaf or a valve tube is tacked onto one side of an opened-out bottom square in such a way that, after the side folds of the opened-out bottom have been folded-in with a mutual overlap, the leaf forms a valve tube leading into the inside of the sack, and with its outer end freely accessible at one side of the sack bottom. For checking the correct position of the valve leaves or of the valve tube, the valve leaf or the valve tube, or the zone of the corner fold, covered thereby when the leaf is tacked in its correct position, is provided with a mark that can be registered by a photocell device fixed to the frame. The photocell device is activated by a reference pulse when, in the manufacturing installation, the sack bottom has reached its predetermined position to be checked. Sacks with an incorrect position of their valve tubes or leaves are eliminated.

FIELD OF THE INVENTION 
The invention concerns a method for checking the correct manufacture of 
cross bottom valve sacks, wherein the ends of continuously conveyed 
tubular sections are opened out with the formation of so-called bottom 
squares having triangular side folds lying opposite each other, and a 
valve leaf is tacked 10 onto one side of an opened out bottom square in 
such a way that after the side folds of the opened out bottom square have 
been folded in with a mutual overlap, the leaf forms a valve tube leading 
into the inside of the sack whose outer end is freely accessible at one 
side of the bottom. 
PRIOR ART 
Usually, the valve leaves are tacked in their correct positions onto the 
opened out sack bottom by spots of adhesive, or adhesive deposits in a 
desired formatted form. During the subsequent folding-in of the corner 
folds, when the fold edges are defined by straps or folding plates or 
folding knives, the valve leaves may become distorted, in particular when 
residues of the adhesive stick to the means for folding-in the side folds. 
If, during manufacture, the valve leaf or valve tube becomes distorted 
during the folding of the side folds, or during the conveying to a 
processing station down the line, inaccurately glued-in valve leaves will 
be obtained so that during the subsequent filling of the sacks these 
cannot be fitted on the filling nozzle of a sack-filling apparatus, or at 
least not fitted in their correct position, which may result in the fill 
drapping onto the floor or into the filling machine. 
OBJECT OF THE INVENTION 
It is, therefore, the object of the invention to create a method of the 
kind indicated at the outset which ensures that only sacks with correctly 
glued filler valves leave the sack manufacturing machine. 
SUMMARY OF THE INVENTION 
In accordance with the invention this problem is solved, in a method as set 
out above in the Field of the Invention, in that the valve leaf or valve 
tube, or the zone of the corner fold covered by the valve leaf or valve 
tube if it is correctly tacked in position, is provided with a mark that 
can be registered by a photocell device fixed to the frame, in that the 
photocell device is activated by a reference pulse when the sack bottom in 
the manufacturing installation has reached its predetermined position 
which is to be checked, and in that sacks with an incorrect position of 
their valve tubes or valve leaves are eliminated. 
In the method in accordance with the invention, the photocell device 
registers the position of the valve leaf or valve tube at the time of its 
activation by the reference pulse which at this time, when the sack bottom 
or sack workpiece is situated in its position to be checked, must 
correspond to a predetermined position when the valve leaf or valve tube 
has been arranged in its correct position and has not subsequently been 
displaced. 
The photocell device registering the valve tubes or valve leaves can of 
course be adjusted relative to the frame to match different sack or sack 
bottom formats. The photocell device serving for the check is then only 
fixedly arranged in the frame with respect to the particular format to be 
checked on each occasion. 
The reference pulse can be generated by the control unit of the machine 
itself. For example rotating machine components, such as cog wheels or 
guide wheels or drive wheels of the conveyor belts, may generate pulses in 
predetermined angular positions by means of attached cams or marks, which 
pulses correspond to the respective positions to be checked on the basis 
of the geometry of the machine. 
The reference pulse can also be generated by a mechanical feeler which 
responds to parts or edges of the passing sack bottom or sack workpiece. 
Provision may be made for the reference pulse to be generated by a second 
photocell device which registers the tip or a side edge of the sack 
bottom, or which responds to (i) a different edge of the sack bottom, or 
to (ii) a mark arranged on the sack bottom, the sack workpiece or the 
corner fold. In this design the second photocell device, together with the 
first photocell device registering the correct position of the glued-in 
valve tube, forms a kind of template, in which arrangement the photocell 
devices are arranged in a pattern registering the correct position of the 
valve tube. The above mentioned marks arranged on the corner fold and/or 
the valve leaf or the valve tube can be colour fields, with a 
predetermined position and size, which have to be registered by the first 
photocell device. In this arrangement, an incorrect position of the valve 
tube, leading to an elimination of the respective sacks via conventional 
reject shunts, may be indicated by a response of the first photocell 
device or even by an absence of its response. 
Expediently, at least the first photocell device is a reflecting photocell 
device which, for example, need not respond at the time of the activation 
of the second photocell device if the zone of the corner fold covered by 
the valve tube is coloured dark or black, so that no reflected signal is 
received, and a defect message is given. Correspondingly it is, of course, 
also possible to provide the valve tube with coloured marks which are only 
registered, or not registered, in the correct position of the valve tube. 
Provision may be made for several of the first photocell devices to be 
provided for registering the or each mark indicating the correct position. 
These multiple photocell devices permit a more accurate acquisition of the 
correct position of the valve tube. 
The zone of the corner fold covered in the correct position by the valve 
tube can expediently be provided with a colour marking, for example a 
black field.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The sack bottom 1 shown in FIG. 1 and FIG. 2 has been formed in the usual 
manner by the opening-out of one end of a continuously conveyed sack blank 
in the form of a tubular section. In this opening-out action, as shown in 
FIG. 2 two corner folds 2, defined by diagonal fold lines at the bottom 
corners of the sack blank, are formed into the shape of isosceles 
triangles by this opening out. 
Laterally outside the subsequent fold lines 3, 4 around which the side 
flaps 5, 6 are folded with a mutual overlap, these corner folds 2 were 
provided with cuts which are parallel to the median line 7 of the sack 
blank and which extend from the blank end as far as the fold lines of the 
corner folds 2 so that, as shown in FIGS. 2 and 3, the inner edges 
(defined in part by these cuts) of the folded-in corner folds 2 have a 
trapezoidal shape. 
Valve leaves or valve tube sections 8 are tacked onto the corner folds 2 by 
deposits of adhesive while the bottom has not yet been closed. In FIGS. 2 
and 3, such valve tube sections 8 are shown in dashes, and in FIG. 1 in 
solid lines. If valve leaves are tacked onto the still open bottoms, the 
leaves are closed into a valve tube only when the side folds 5, 6 are 
folded in with a mutual overlap. 
FIG. 2 shows a sack bottom which is provided with a valve tube 8 glued-in 
in its correct position. 
To check that the valve tube has been correctly arranged in its right 
position in the sack bottom, the corner fold 2 is provided with a 
rectangular black or dark coloured field 12 which is shown hatched in FIG. 
2. As shown in FIG. 3, it is a sign that the valve tube 8 has not been 
glued-in in its correct position if the valve tube 8 does not entirely 
cover the field 12 which defines a mark. 
For registering the incorrect position of the glued-in valve tubes, there 
is a first reflecting photocell device 14 directed, as shown in the 
drawing, towards the front edge of the rectangular mark 12 arranged on the 
corner fold 2. In this arrangement, at the time when it is activated, the 
photocell device 14 registers the point 15 on the sack bottom 1. 
The photocell device 14 is activated by the second photocell device 16 
which, in the embodiment shown, registers the tip 17 of the sack bottom 
leading in the transport direction A. 
As soon as this second photocell device 16 has registered the tip 17 of the 
sack, it activates the first photocell device 14 which, if this latter 
registers the dark mark 12 as shown in FIG. 3, will then generate a defect 
signal on the basis of the predetermined interspacing of the two photocell 
devices. 
However, if as shown in FIG. 2, the beam of the first photocell device 14 
strikes the surface of the valve tube, no defect signal is generated.