Sensor for cyclically scanning the height of a pile

A feeler for cyclically sensing the pile height of a feed pile in a sheet-fed machine, in particular a printing machine, having a lever drive linkage with a sensing roller, which at least during paper travel is in constant touch contact by means of a spring with a cyclically drivable drive cam; having a four-bar guide linkage with two levers, disposed one above the other and each with one end pivotally supported on the frame, which levers are each pivotally supported by their other lever end, spaced apart from one another, on a coupler, wherein a feeler foot for sensing the pile height is secured to a downward-extending vertical extension of the coupler; having a carrier stop, which is secured to the drive linkage; having a stop face on the guide linkage, which face is embodied and disposed in a fashion corresponding to the carrier stop for cyclically establishing touch contact for raising the feeler foot; and having a spring, one spring support of which is secured in a manner fixed to the machine and whose other spring support is secured to the guide linkage, and whose spring force presses the stop face in the direction toward the carrier stop.

The invention relates to a sensor or feeler for cyclically scanning the 
height of a feeder pile of a paper sheet processing machine, such as a 
printing press, especially. German Published Non-Prosecuted Patent 
Application (DE-OS) 40 09 175 discloses a sensor which, via a four-bar 
linkage guide transmission which is rigidly connected with a four-bar 
linkage drive transmission which, in turn, is controlled by a cam drive, 
is lowered to a surface of a sheet pile for cyclically sensing or scanning 
the sheet pile and is again lifted for releasing the upper paper sheet 
after the pile height has been sensed, for acceptance or take-over of the 
paper sheet by downline suckers. With such a double four-bar linkage 
drive, all of the inertial forces of both four-bar linkages act when the 
governor foot is lowered. After the governor foot has been seated upon the 
upper paper sheet of the pile, this paper sheet, for one thing, because of 
the high inertial forces of both four-bar linkage drives and, for another 
thing, due also to the somewhat farther downwardly extending drive, is 
pressed with great, further driving forces against the upper paper sheet 
via the contact point of the governor foot with the upper paper sheet, 
which is required for a reliable measurement. The upper paper sheets can 
thereby be deformed with corrugations or ripples, due to which a reliable 
sheet acceptance and conveyance of the paper sheet after acceptance or 
pick-up by the lifting suckers, especially at high speeds, is endangered. 
The lifted paper sheets are usually accepted or picked up by pull suckers 
from the lifting suckers and conveyed over leading edge stops of the sheet 
pile. A rippled or corrugated formation in the paper sheet can result, for 
one thing, in stumbling or halting phenomena of the paper sheet during 
conveyance thereof, for example, over the leading edge stops and, for 
another thing, facilitates the non-uniform or irregular rippling or 
corrugations as well as an irregular underflow of the sheet, especially 
when using portable air blowers, due to which fluttering phenomena occur. 
Moreover, it is hardly possible to effect a reliable height measurement 
and height adjustment with the undefined indentation depth of the sensor 
into the pile in the case of such a sensing device. Deviations in the 
measured pile height depend upon the inertial forces and upon the 
conveying speed with regard to such a sensing device. Furthermore, the 
type of paper is an important factor. An imprecise height measurement 
results in an imprecise height adjustment and, accordingly, in problems 
with regard to effecting a reliable sheet acceptance and sheet conveyance. 
Furthermore, it is possible that the paper sheets may become damaged. 
Especially at high speeds, for which such a drive demands a drive 
transmission of massive proportions for attaining a reliable drive 
formation, these dangers are increased. With such a conventional sensing 
device, it is therefore only possible with great difficulty to assure 
reliable sheet separation or singling and sheet conveyance at high speeds 
in spite of the use of a four-bar linkage drive which is especially 
advantageous for the guidance. 
From U.S. Pat. No. 4,786,043, a sensor has become known wherein a governor 
foot is driven by a cam-controlled swivel lever and a four-bar linkage 
guide transmission. A guide bar around which a compression spring is wound 
is fastened to the four-bar linkage guide transmission. The guide bar is 
movably mounted in the swivel lever. The compression spring presses 
against the swivel lever. After the governor foot has been seated upon the 
pile surface, the high inertial forces of the solidly or massively formed 
swivel lever do no longer fully act upon the pile surface. However, the 
pivot lever which, after the moment of application, moves a short distance 
farther downwardly does compress the spring over the entire further 
downwardly driving drive region of the pivot lever and, as a result, the 
force exerted upon the pile by the spring via the feeler foot, after the 
feeler foot has been placed upon the pile surface, nevertheless rises 
further continuously over the downwardly driving drive cycle. The feeler 
foot, because of the sharply increasing spring force, is pressed 
undesirably strongly against the pile surface and, as a result, the top 
sheets can also be pressed inwardly in an undefined fashion. Reliable 
separation or singling and conveying of the sheets away therefrom, a 
reliable ascertainment of the pile height, and a reliable pile 
readjustment are also not assured with a sensor or feeler arrangement. 
Damage to the sheets is also possible there. Especially at high speeds, 
the strong inward pressures and the imprecision of the undulation are 
disadvantageous for an exact conveyance. U.S. Pat. No. 4,786,043 indeed 
shows a four-bar linkage guide transmission wherein the feeler foot is 
lowered from above for placement on the surface of the pile and, after the 
pile height is ascertained, is swiveled out of the pile region again so 
that the lifting suction devices can more rapidly engage the sheet, but 
reliable progress through the pile at very high speeds is unattainable 
with this mechanism for the reasons given hereinabove. 
German Published Non-Prosecuted Patent Application DE-OS 32 18 565 
discloses a suction lock with a guide member which can be moved vertically 
up and down and which engages in an oblong slot in a tongue with a contact 
pressure tab. The tongue is secured to a frame via a spring. By raising 
the guide member, the contact pressure tab is lifted vertically. Upon 
lowering, it is lowered vertically by spring force until the contact 
pressure tab touches the surface of the pile and presses against it under 
spring force. Upon further lowering of the guide member, no increasing 
force is exerted on the pile of sheets by the contact pressure tab, 
nevertheless, the purely vertical motion of the drive tab makes a fast, 
reliable progress through the pile by suction devices virtually 
impossible. For a reliable takeover of a sheet, the contact pressure tab 
must first move into a position above the level or height to which the 
lifting suction devices raise the sheets. Only after the sheet has been 
transported out of the stroke or lifting range of the contact pressure 
tab, for example, by means of pull or forwarding suction devices, can the 
contact pressure tab be lowered again to measure the height. This 
chronologically purely sequential course of the various operations 
consumes an undesirably large amount of time. This is a hindrance to 
conveying at high speeds. Moreover, the contact pressure tab, which always 
remains located above the top sheet because of the vertical motion, 
cannot, once the sheet is raised, firmly hold the sheet located underneath 
the raised sheet, so that this underlying sheet, as the upper sheet is 
transported away, may be ripped out of its position and the top sheet may 
sag, because of the effects of friction or flow phenomena. This imperils 
both height sensing and the acceptance and conveyance of the sheets. 
Furthermore, at high speeds, reliable progression through the pile is not 
possible with this kind of sensor. 
It is accordingly an object of the invention to form a sensor for 
cyclically sensing the pile height of a feed pile of a sheet processing 
machine, particularly a printing machine, in such a way that reliable 
unpiling or unstacking is possible even at high speeds. 
According to the invention, this object is attained by providing a feeder 
for cyclically sensing the height of a feed pile in a sheet processing 
machine through which sheets periodically travel, which includes a 
cyclically drivable drive cam, a lever drive transmission having a sensing 
roller spring-biased into continuous contact engagement with the 
cyclically drivable drive cam during travel of the sheets, a four-bar 
linkage guide transmission having two levers disposed above one another 
and being articulatingly affixed, at one respective end thereof, to a 
support frame, a coupler having a downwardly directed vertical extension, 
the levers, at respective other ends thereof, being articulatingly 
supported at a spaced distance from one another on the coupler, a feeler 
foot for sensing the height of the feed pile being secured to the vertical 
extension of the coupler, an entrainer stop secured to the lever drive 
transmission, a stop face formed on the guide transmission and disposed in 
a manner corresponding to the entrainer stop so as to be cyclically 
engageable thereby for raising the feeler foot, and spring means affixed 
at one bearing location thereof to the support frame and at another 
bearing location thereof to the guide transmission and having a spring 
force for pressing the stop face in a direction towards the entrainer 
stop. The lever drive transmission permits a reliable drive of the sensor. 
The four-bar linkage guide transmission with the levers disposed above one 
another and with the feeler foot secured to the coupler makes it possible 
to swivel the feeler foot inwardly and outwardly over a curved path, so 
that the feeler foot can be placed on the surface of the pile 
substantially vertically and can be swiveled back again reliably out of 
range of the pile for faster acceptance of sheets. As a result, the next 
sheet can be picked up or accepted faster by post-connected or down-line 
conveying means, such as lifting suction devices, due to which the length 
of a conveyance or feed cycle can be reduced. Placing the feeler foot 
vertically permits a shift-free, reliable placement of the feeler foot for 
the sheet located therebeneath, which is advantageous especially at high 
speeds. The coupling between the drive transmission and the four-bar 
linkage guide transmission, by means of an entrainer stop and a stop 
surface for lifting the feeler foot permits a reliable, fast lifting of 
the feeler foot in accordance with the drive control. At the instant the 
feeler foot is set in place, only the masses of the feeler foot and the 
guide transmission, and the spring force are operative. The decoupling of 
the drive transmission and the guide transmission permits a simple, easy 
construction of the guide linkage, so that the force exerted by the guide 
transmission and the feeler foot when the feeler foot is put in place can 
be minimized. The spring mounted fixed to the machine presses the feeler 
foot against the pile surface with a defined spring force when the feeler 
foot is seated in place. This spring force can be selected, by 
dimensioning the spring, so that, at the moment of placement, it is just 
strong enough that reliable sheet height measurement is yet possible. 
Although the mass or inertial forces and drive forces of the drive 
transmission, after the instant at which the feeler foot is put in place, 
further move the drive transmission onward in the same direction beyond 
the instant of the placement, the feeler foot stays on the pile surface 
with only the force exerted upon the feeler foot by the spring at the 
instant the feeler foot is put in place. Because, accordingly, after the 
instant it is put in place, the feeler foot rests on the upper sheet of 
the pile merely with a constant, minimized force, it is possible to avoid 
an undesirably strong inward pressure on the upper sheets of the pile. The 
sheet conveyance, height measurement and height readjustment thereby 
become more reliable, independently of speed. It is thus possible with 
such a sensor or feeler, even at high speeds, to assure reliable unpiling 
or unstacking of a feed pile. Moreover, after a sheet pile is lifted, the 
feeler foot can already be swiveled inwardly beneath the lifted sheet and 
placed on the pile located beneath the raised sheet. Once the raised sheet 
has been removed, the top sheet on the pile is reliably held in its 
position by the feeler foot, and its position cannot be varied by the 
sheet which has been conveyed away. 
In accordance with another feature of the invention, the entrainer stop is 
pivotable about a pivot point of one of the two levers of the guide 
transmission, the pivot point being fixed to the support frame. In such a 
construction, the stop surface can be made especially small and simple, 
because the entrainer stop, in any position of the contact engagement with 
the stop surface, assumes the same position relative to the stop surface. 
Inaccuracies as a result of manufacturing and motion tolerances between 
the stop surface and the entrainer stop, which have a negative effect upon 
the feeler or sensor motion, are thereby reducible. 
An especially simple and reliable drive is made possible by the 
construction in accordance with a further feature of the invention, 
wherein the lever drive transmission is a four-bar linkage drive 
transmission having two levers, respectively, pivotally supported, at one 
end of a respective lever arm thereof, on a pivot point fixed to the 
support frame; and a coupler to which the two levers are pivotally 
connected in common, at a spaced distance from one another at the other 
respective end thereof; the fixed pivot point of a first one of the two 
levers being a fixed pivot point of a first one of the two levers of the 
guide transmission, the entrainer stop being disposed on the first lever 
of the drive transmission, and the corresponding stop face being disposed 
on the first lever of the guide transmission. The number of articulating 
locations can be minimized while maintaining the advantages of the 
four-bar linkage drive for guidance, drive and mass distribution purposes. 
In accordance with an added feature of the invention, the guide 
transmission is formed with a sensing surface having a position which is 
variable as a function of the height of the feeler foot, and a sensor 
arrangement is fixed to the support frame for ascertaining the position of 
the sensing surface, the sensor arrangement being in communication with an 
evaluation and control device for readjusting the pile height. In a 
preferred embodiment, the feeler foot is secured to the extension of the 
coupler so that it is adjustable in height. This enables a simple, exact 
setting and readjustment of the feeler foot. Reliable unpiling or 
unstacking can thus be assured in a simple manner. 
In accordance with a preferred embodiment of the invention, the spring 
support secured to the guide transmission is disposed on the other one of 
the two levers of the guide transmission. 
In accordance with another preferred embodiment of the invention, the 
sensing roller is rotatably supported on the second one of the two levers 
of the four-bar drive linkage. 
In accordance with a third preferred embodiment of the invention, the 
sensing face is formed on one of the two levers of the guide transmission. 
In accordance with a concomitant feature of the invention, the feeler foot 
is secured to the extension of the coupler so as to be adjustable in 
height.

FIG. 1 shows a feeder of a sheet-fed rotary offset printing machine, 
wherein in a known manner a topmost sheet of a feed pile 1 is raised by a 
lifting suction device 5 of a suction head 2 and is guided forwardly by 
following or down-line pull or forwarding suction devices 6 of the suction 
head 2, out of the range of the suction head, to non-illustrated conveyor 
means in the vicinity of the feeder table. Once the sheet has been taken 
over by the non-illustrated feed means, the sheet is transferred across 
the feeder table 3 to gripper bars of the pre-gripper drum 4 which, in a 
known manner, transfer it to a non-illustrated printing cylinder. The 
instant the topmost sheet has been lifted from the pile by the lifting 
suction device 2, a feeler foot 8 is swiveled underneath the raised sheet 
into the region above the feed pile 1 and lowered onto the feed pile 1 far 
enough so that the feeler foot enters into contact engagement with the top 
sheet of the feed pile 1. 
As shown in FIG. 2, the feeler foot 8 is secured in a vertically downwardly 
directed extension of a coupler 11. The coupler 11 is pivotally connected 
to a lever 14 by an upper articulation or joint 12 and to a lever 16 by a 
lower articulation or joint 13. The lever 14 is pivotally supported by its 
other end in a pivot bearing 15 fixedly attached to the machine. When the 
feeler foot 8 is lowered substantially parallel to the lever 14, the lever 
16 is aligned and is pivotally connected in a pivot bearing 17 fixedly 
attached to the machine. A lever 18 is connected in the pivot bearing 17 
concentrically with the pivot axis of the lever 16 so as to be pivotable 
about the pivot bearing 17. On its lower end, the lever 18 is pivotally 
connected by a joint 19 to a coupler 20, which in turn is pivotally 
connected at a joint 21 to a lever 22. The lever 22 is pivotally supported 
in a pivot bearing 23 fixed to the machine. A sensing roller 24 is 
rotatably supported on the lever 22 between the joint 21 and the pivot 
bearing 23. The lever 22 is engaged by a tension spring 27, which is 
supported, fixed to the machine, by its other spring bearing. The spring 
27 keeps the sensing roller 24 in permanent contact engagement with the 
outer contour of the radial cam 25. The radial cam 25 is secured to a 
control shaft 26 which extends transversely to the sheet conveying 
direction and is rotatably supported in a conventional non-illustrated 
manner in the suction head frame. The control shaft 26 is drive-connected 
with the machine drive in a known manner. 
A stop screw 30 is screwed into a lever arm 29 of the lever 18, below the 
lever 16. This stop screw 30 is formed with its upper face, which is 
directed towards the lever 16, as a stop face. Opposite thereto, the lever 
16 is provided with a corresponding stop face 31. A spiral spring 28 is 
wound around the pivot bearing 15 on the lever 14 and is supported by one 
spring support thereof on a stop 40 fixed to the machine and by its other 
spring support on the lever 14. The spiral spring 28 presses the lever arm 
14 downwardly. 
After the topmost sheet of paper has been taken from the feed pile 1 by the 
lifting suction device 5, the sensing roller 24 and thus the lever 22 are 
pivoted away, out of the position in FIG. 3a, about the pivot bearing 23 
as a result of the decreasing spacing between the sensing point of the 
contour of the face of the curve 25 and the feeler foot, due to the 
rotation of the control shaft 26 and hence of the control cam 25 because 
of the spring force of the spring 27. As a result, via the coupler 20, the 
lever 18 and hence the stop screw 30 are swiveled about the pivot bearing 
17, so that the stop screw 31 is swiveled downwardly. By the spring force 
of the spring 28, the lever 14, the coupler 11 and the lever 16 are moved 
downwardly with the swiveling of the lever 14 about the pivot bearing 15 
and of the lever 16 about the pivot bearing 17, the stop face 31 of the 
lever 16 being in permanent contact engagement with the stop screw 30. In 
this downward motion, the front or leading edge 42 of the feeler foot 8 
describes a curve 41; in other words, it is initially swiveled inwardly 
virtually horizontally from a region outside the feed pile into the range 
of the feed pile, beneath the non-illustrated sheet which has already been 
removed, and then changes to an essentially vertical range of motion, in 
which the feeler foot is lowered onto the surface of the pile. This 
downward motion continues until such time as the feeler foot, as shown in 
FIG. 3b, rests on the surface of the feed pile 1. After the placement of 
the feeler foot 8 on the surface of the feed pile 1, the control shaft 26 
is rotated onwardly in the same direction, due to which, the drive 
transmission comprising the levers 22, 20 and 18, further following the 
contour of the cam 25, is moved onward as described above, so that the 
stop screw 30 is lowered even farther, and the feeler foot 8 remains on 
the surface of the feed pile solely due to the spring force of the spring 
28. The feeler foot 8, the coupler 11, and the levers 14 and 31 are 
accordingly not further moved. The stop screw 30 as a result moves 
downwardly away from the stop face 31 of the lever 16, as shown in FIG. 
3c. Via a sensing face 33 of a lever arm 32 on the lever 31, the distance 
between the sensor and the measuring face 33 is ascertained by a 
contactless sensor 34. The sensor 34 communicates via an electrical 
connection 35 with a measurement and evaluation apparatus, such as a 
computer. From the distance between the sensor 34 and the measuring face 
33, the computer ascertains the instantaneous height of the feed pile in a 
known manner. The non-illustrated sheet of paper previously raised by the 
lifting suction device 5 is transferred by pull or forwarding suction 
devices 6 to non-illustrated conveyor means of the feeding table. The 
spring 28 is dimensioned so that the feeler foot rests with just enough 
force on the feeder pile that height measurement is yet possible. The 
feeler foot prevents the topmost sheet 10 present at that instant of time 
in the feed pile 1, whereon the feeler foot is resting, from being carried 
along by the sheet which has already been lifted and is being carried away 
by the pull or forwarding suction devices. 
To improve this separation, a blower nozzle 36 is mounted on the feeler 
foot 8 and, via a blown air delivery line 9, is connected to blowing air 
under cyclical control. As a result, air is blown beneath the raised 
sheet. This affords a better prevention of contact engagement with the 
pile. 
The instant the sensing roller 24 has reached the point on the contour of 
the cam 25 which is spaced the least distance from the control shaft 26, 
the contact screw 30 is then no longer lowered any further. As the control 
cam continues to rotate, the distance between the contour of the cam 25 
and the control shaft 26 increases again, so that the sensing roller 24 
and thus the lever 22 are again pivoted away from the control shaft 26. As 
a result, the lever 18 is swiveled around the pivot shaft 17 in such a 
manner that the stop screw 30 moves upwardly. The instant the stop face of 
the stop screw 30 comes into contact engagement with the stop face 31 of 
the lever 16, the stop screw 30, via its stop face and the stop face 31 of 
the lever 16, carries the lever 16 upwardly along with it, swiveling about 
the pivot axis 17. As a result, the coupler 11 and the lever 14 are 
likewise lifted, so that the lever 14 is pivoted upwardly about the pivot 
bearing 15, counter to the spring force of the spring 28. In the process, 
the feeler foot 8 lifts substantially vertically away from the surface of 
the pile and is pivoted out of the region above the pile back into a 
position in a region outside the pile. Such a position is shown in FIG. 
3a, for example. The lifting suction device 5 is cyclically lowered again 
in a known manner in order to take the next sheet from the pile. The 
lifting suction device 5 and the pull or forwarding suction device 6 are 
supplied with suction in a known, controlled manner via the suction head, 
with the aid of a suction supply line 7. 
Instead of the spiral spring 28 as shown in FIG. 2, a spiral spring may 
also be wound about the pivot axis 15. One arm of the spring is braced 
against a pin 38 secured in the suction-head housing, and the other arm of 
the spring is braced against a pin 39 secured in the lever arm. 
It is also conceivable for the feeler foot 8 to be displaceably secured in 
the coupler 11, as shown in FIG. 3. With known adjusting and locking 
means, not shown, the feeler foot may thus be precisely adjusted in its 
height. The pile height ascertained by the computer is used in a known 
manner to cyclically readjust the pile height. For example, the computer 
can simultaneously produce a control signal, which corresponds to the 
measured value, for the drive means of the lifting drive. Separating the 
drive transmission from the guide transmission makes a simple, lightweight 
construction for the guide linkage and the feeler foot possible. To a 
maximal extent, the parts may be made of plastic and/or aluminum.