EP0775656A2 - Sheet feeder and method of separating sheets - Google Patents

Abstract

At least the top part of the stack of sheets (2) is partially curved by a base plate (1). At least two friction wheels (7) positioned apart from each other on the top of the stacked sheets press partly and/or intermittently on the top of the stack. At least one friction wheel is driven so that the adhesive surfaces pressing onto the top of the stack are moved towards or away from each other. A gap (14) is formed between the two topmost sheets in the stack. The base plate (1) consists of one or more movable pick-up pieces picking up the topmost sheet and drawing it off the stack.

Description

The feeder of a sheet-fed printing press has the task of separating the sheets which have been precisely pre-stacked on a sheet support plate and then feeding them to the printing press in succession. Today there are mainly two feed systems for sheetfed offset printing presses, namely single sheet feeders with a suction rod and scale feeders with a suction head.

In the case of a single sheet feeder, the top sheet of the stack is lifted pneumatically by several suction cups attached to a rod in the front edge and then taken over by feed grippers or transport rollers. These guide the sheet individually to the press. By adjusting the suction power, by changing the tilting of the suction rod and by blowing air against the front edge of the stack, the single sheet feeder can be adapted to different paper thicknesses and paper qualities. As soon as the separated sheet has run into the machine, a new sheet can be separated. Therefore, with a single sheet feeder, the separating process must take place very quickly in order to achieve the desired machine speed.

For higher machine speeds, scale feeders are used, in which the sheets are separated by a suction head on the rear edge of the stack. A shed feeder has various pneumatic separating and drag suction devices that remove the top sheet and then feed it continuously to the feed table. In addition, there are several in the rear edge of the feeder Blowers, scraper brushes, scraper plates and sheet hold-down are attached, which have the task of ensuring a trouble-free separation and ensure a smooth, straight transport of the sheets that are overlapped on a system table. During a short stop at the system, each sheet is aligned precisely. Both the blowing and suction air as well as the other aids mentioned must be set exactly by the printer to the respective substrate.

In the known feeder systems, suction or blowing air is therefore required, and the higher the working speed, the more and the more powerful suction and blowing devices are required, with a correspondingly high air consumption. The suction and blowing devices cause considerable noise, and the periodic switching on and off of the air flows and the movement of the suction heads in the machine cycle lead to vibrations that are difficult to control.

The invention has for its object to provide a sheet feeder and a method for sheet separation, which have a high working speed and reduced effort for suction and blowing devices and reduced air consumption.

This object is achieved according to the invention by a device with the features of claim 1 and by a method with the features of claim 10. Advantageous embodiments of the invention result from the features of the subclaims.

The sheet stack resting on a sheet support plate is bulged, preferably by the sheet support plate not being made flat. A concave shape of the stack of sheets, at least in the upper region, can alternatively be used e.g. B. also achieve that attack on the sides of a sheet stack lying flat drivers, which raise it partially. It is sufficient if the curvature is created on the machine side or on the side of the sheet stack facing away from the machine. If a convex curvature is desired, the curvature which a stack of sheets often has on its own can be used under certain circumstances.

A plurality of adhesive elements press on the uppermost sheet, which are preferably arranged in the vicinity of the lateral sheet edges and have the adhesive surfaces which touch the sheet. In the case of a convex curvature, the adhesive elements or their adhesive surfaces are then moved towards one another. As a result, the uppermost sheet is partially raised from the sheet stack, so that a space is created between the uppermost sheet and the rest of the sheet stack.

If a concave stack of sheets is used, the adhesive surfaces are moved away from each other so that the top sheet is stretched. Stretching the sheet has the advantage that even thin papers can be separated safely. In addition, the dimensions of the resulting space are particularly well defined. This is advantageous if the resulting space is used to completely detach the sheet from the sheet stack and feed it to the printing press. Some examples of this are described below.

In one embodiment, in which the curvature of the sheet stack is in the region of its front side, ie the side of the sheet stack which faces the printing press, z. B. grippers are provided which capture the leading edge of the sheet. The grippers pull the top sheet from the sheet stack, the remaining sheets being held back by a stop, and transfer it to the printing press. Because the adhesive elements only the top sheet partially lifted off the sheet stack, its position is precisely defined at the moment it is gripped. Therefore, the transfer can take place without a stopover, e.g. B. on transport rollers that convey the sheet in register in one go into the printing press. This smoothes the movement and the machine speed can be increased.

Even higher speeds are possible with an embodiment in which the sheet stack is arched not in the front but in its rear area. The adhesive elements lift the uppermost sheet from the stack in its rear area, and one or more touch fingers can be inserted into the resulting space to hold the remaining sheets. This can be done on the back of the sheet stack and / or in the back of its sides. For transporting the top sheet to the printing press, e.g. B. rotating friction wheels can be used. Before the sheet is completely removed from the stack, the finger or fingers can be released, the next sheet can be lifted with the aid of the adhesive elements and the finger or fingers can be brought back into position to feed the next sheet. The sheets can thus be fed to the printing press in close succession or even staggered. Nevertheless, there is enough time for the moving components to take up their various positions. Therefore, the sequence of movements can be designed so that only very slight accelerations of the components occur. As a result, the moving components and their drives can be dimensioned weaker and vibrations are reduced.

A particularly advantageous development of this embodiment consists in that such a touch finger, which holds the remaining sheets, simultaneously forms a counterpressure device for a friction wheel. The top one The sheet is clamped between a low-friction, for example polished surface of the touch finger and the friction wheel, and the friction wheel conveys the sheet to the printing press reliably and practically without slippage. Since the coefficient of friction between the friction wheel and the sheet is significantly greater than the coefficient of friction between the sheet and the finger, the trigger behavior remains constant for a long time.

In order to move the adhesive surfaces towards or away from each other, it is sufficient in itself if one of the adhesive elements is driven accordingly. In the case of a mirror-image drive of opposing, identically constructed adhesive elements, the risk is lower, however, that the uppermost sheet is shifted when lifting on the stack. Alternatively or additionally, fixed or movable stacking stops can be used to keep the sheets precisely aligned. The deduction of the sheets from the sheet stack z. B. carried out by means of friction wheels that pass the sheet to transport rollers, so the sheet of the printing press can be fed in register in a quiet, straight run, so that an alignment of the sheet before entering the printing units can be dispensed with.

The adhesive elements that stretch or contract the top sheet, z. B. be movable fingers that grip from the side over the sheet stack and carry adhesive surfaces at their ends. In the preferred embodiment, the adhesive elements are continuously or intermittently driven friction wheels, the surfaces of which form the adhesive surfaces and which press resiliently against the upper side of the sheet. Appropriate adjustment of the contact pressure of the friction wheels enables adaptation to different papers.

So that the friction wheels or other adhesive elements do not hinder the transport of the raised sheets to the printing press, they can be raised in the machine cycle and lowered back onto the sheet. If friction wheels are used, this effect can also be achieved by friction wheels which are mounted eccentrically and driven synchronously with the machine cycle.

While the above-described embodiments work entirely without air and are correspondingly inexpensive to operate and low-noise, embodiments with a limited use of air are also conceivable. For example, the uppermost sheet can also be pulled off the stack by a suction device instead of by friction rollers, the remaining sheets being reliably held on the stack. Instead of friction rollers, suction rollers can also be used, which have a porous jacket and in which a negative pressure prevails, so that the sheet adheres to it. The intervention in the space between the two uppermost arches can also be carried out by air or air-assisted, provided the flow dynamics allow it. For the initial separation of the sheets, for which a lot of air is required in the conventional feeder systems, no or very little air is required in all of these embodiments, and the number of suction or blowing devices required is smaller.

Further features and advantages of the invention will become apparent from the following description of several embodiments and from the drawing, to which reference is made.

Fig. 1

einen Anleger für eine Bogendruckmaschine von hinten;

Fig. 2 bis 5

den Anleger von Fig. 1 im Längsschnitt von der linken Seite aus gesehen in verschiedenen Phasen eines Vereinzelungszyklus;

Fig. 6

eine Ansicht von oben auf den Anleger von Fig. 1 bis 5;
und

Fig. 7

eine weitere Ausführungsform eines Anlegers für eine Bogendruckmaschine im Längsschnitt.

In it show:

Fig. 1

a feeder for a sheet-fed printing machine from behind;

2 to 5

the feeder of Figure 1 seen in longitudinal section from the left side in different phases of a separation cycle.

Fig. 6

a top view of the feeder of Fig. 1 to 5;
and

Fig. 7

a further embodiment of a feeder for a sheet-fed printing machine in longitudinal section.

The feeder shown in FIGS. 1 to 6 contains a sheet support plate 1 which can be moved in height and a sheet stack 2 resting on the sheet support plate 1.

A printing machine connects to a front of the feeder, of which only transport rollers 3 are shown, which are rotatably mounted parallel to the front edge of the sheet stack 2. In each case two transport rollers 3, which are adjacent to one another along their circumference along a line, form a pair of rollers for transferring sheets to the printing press. Movable front stacking stops 4 and stationary side stacking stops 5 (FIGS. 2 to 6) are also arranged at the front of the feeder.

The sheet support plate 1 is flat in its front and middle area. In the area of the two rear corners of the sheet support plate 1, that is, facing away from the printing press, the top of the sheet support plate 1 is designed such that it extends from the flat area towards the corners increases. The sheet support plate 1 thus has an at least partially concave upper side. The sheet stack 2 resting on the sheet support plate 1 assumes essentially the same shape, so that the two rear, upper corners of the sheet stack 2 lie higher than its remaining surface.

Above the uppermost sheet 6 of the sheet stack 2, a friction wheel 7 is arranged in the area of the two rear corners, which has an axis 8 which extends parallel to the side edges of the sheet 6. The friction wheels 7 are resiliently biased towards the top of the uppermost sheet 6 by means not shown, whereby they can deflect resiliently upwards. The position of the friction wheels 7 and thus the top edge of the stack can be detected by sensors, not shown, in order to keep the top of the sheet stack 2 at the same height by moving the sheet support plate 1 during operation. The friction wheels 7 then press on the rear corners of the uppermost sheet 6 with a defined force. The axes 8 of the friction wheels 7 are connected to drive devices (not shown) for rotating the friction wheels 7.

At the rear edge of the sheet stack 2 there is a feeler foot 9 which has an elongated touch finger 10 which runs approximately parallel to the top of the sheet stack 2. The feeler foot 9 is movable in the direction of the sheet stack 2 and away from it by being pivotable about a pivot point 11 in the sheet plane of FIG. 2. Alternatively, the feeler 9 can be linearly movable or pivotable about a pivot point that lies in the plane of the top of the sheet stack 2. Drive means, not shown, are provided for moving the feeler foot 9.

Between the two friction wheels 7, a friction wheel 12 is arranged, which has an axis 13 which is parallel to the The rear edge of the sheet stack 2 extends. The friction wheel 12 is located exactly above the touch finger 10 of the touch foot 9 when the touch foot 9 has been pivoted in the direction of the sheet stack 2. The friction wheel 12 and its axis 13 can be moved from above in the direction of the sheet stack 2 or the touch finger 10 and away therefrom. Drive means, not shown, are provided for this movement and for a rotation of the friction wheel 12.

During operation of the feeder, the friction wheels 7 are first rotated in opposite directions, as indicated by arrows in FIG. 1, so that the top sheet 6 is pulled apart and stretched between the friction wheels 7. In this way, an intermediate space 14 is formed between the two uppermost sheets of the sheet stack 2. In order to ensure that only a single sheet is securely separated from the sheet stack 2, even with critical papers, such as very thin sheets, 9 wiper springs or wiping brushes can be provided on the side next to the feeler foot, which press against the rear edge of the sheet stack 2 (not shown in the drawings) ).

In this state, shown from the side in FIG. 2, the feeler foot 9 swivels without contact from the rear into the resulting space 14. By means of this swivel movement, it reaches the position shown in FIG. 3, in which the feeler finger 10 extends over the vertical center line of the friction wheel 12 has penetrated into the intermediate space 14. Then the feeler 9 lowers below the uppermost sheet 6 onto the sheet stack 2 in order to hold the remaining sheets on the sheet stack 2. This lowering process can be carried out separately, as indicated by an arrow in FIG. 4, or, if the pivot point 11 is suitably arranged, can result from the pivoting movement of the feeler foot 9.

Simultaneously with the lowering of the feeler foot 9 on the sheet stack 2 or subsequently, the friction wheel 12 lowers, as indicated by a further arrow in FIG. 4, the uppermost sheet 6 being clamped between the friction wheel 12 and the touch finger 10. 5, the movable stack stops 4 are then pivoted away from the sheet stack 2 and the friction wheel 12 is rotated in the direction of the arrow shown.

The top of the finger 10 is z. B. a polished metal surface, which has a low coefficient of friction compared to the sheet 6 compared to the friction wheel 12. As a result, the uppermost sheet 6 is pushed forward in the direction of the transport rollers 3. In order to facilitate this, the friction rollers 7 can be lifted off the sheet 6 in the meantime by means not shown. But it is also conceivable that the bias of the friction rollers 7 is so low that the sheet transport is not hindered.

The length of the touch finger 10 or the distance of the transport rollers 3 from the sheet stack 2 are chosen so that the top sheet 6 is gripped in time by the transport rollers 3 when it exits between the friction wheel 12 and the touch finger 10.

As soon as the uppermost sheet 6 has emerged between the friction wheel 12 and the touch finger 10 of the touch foot, the friction wheel 12, the touch foot 9 and possibly the friction wheels 7 are brought back into the positions shown in FIG. 2. Thereafter, the next singling cycle can be started immediately while the sheet 6 is still being pulled off the sheet stack 2, whereby it z. B. is in the position shown in dashed lines in Fig. 6. During the removal from the sheet stack 2, the sheet 6 is guided through the side stack stops 5.

Tensioning the uppermost sheet and reaching into the resulting space can not only be carried out on the trailing edge of the sheet, but alternatively or additionally on the side edges. Furthermore, it can be carried out on the leading edge of the sheet, as will be described below with reference to FIG. 7.

In the embodiment of FIG. 7, a sheet stack 15 is concavely curved in its front region by using a correspondingly curved sheet support plate 16. Two friction wheels 17 correspond in structure and function to the friction wheels 7 of the previous embodiment, but are arranged above the front corners of the sheet stack 15. One or more grippers 18 are attached to a rotatable gripper bar 19, which is arranged in front of the sheet stack 15.

After the friction wheels 17 have tensioned the uppermost sheet 20 of the sheet stack 15 according to the principle shown in FIG. 1, the grippers 18 pivot to the front edge 21 of the uppermost sheet 20, grasp the sheet 20 at the front edge 21 and pull it off the sheet stack 15, to feed it to a printing press. The remaining sheets are retained by a front stacking stop 22, over which the top sheet 20 is raised when the space 23 between the top two sheets is formed. In addition, 22 stripping springs or stripping brushes can be provided on the side next to the front stacking stop.

The embodiment of FIG. 7 does not allow quite as high working speeds as the previous embodiment, since the sheets cannot be pulled overlapping from the sheet stack. On the other hand, in the embodiment of FIG. 7, very few moving parts are required, the masses of which can moreover be kept small, so that the working speeds are more conventional Single sheet feeders can be easily reached or surpassed without excessive acceleration and the associated vibrations. In addition, the sheet separation is carried out by tensioning the top sheet much more reliably, with significantly less effort and with much less noise than with a conventional single sheet feeder working with air.

REFERENCE SIGN LIST

1

Sheet support plate

2nd

Sheet stack

3rd

Transport roller

4th

Stack stop

5

Stack stop

6

top bow

7

Friction wheel

8th

axis

9

Feet

10th

Touch finger

11

pivot point

12th

Friction wheel

13

axis

14

Space

15

Sheet stack

16

Sheet support plate

17th

Friction wheel

18th

Gripper

19th

Gripper bar

20th

top bow

21

Front edge of the top sheet

22

Stack stop

Claims (12)

Feeder for a sheet printing machine,
marked by
a device (1; 16) for at least partially arching a sheet stack (2; 15) at least in its upper region and by means of at least two adhesive elements (7; 17) which are arranged at a distance from one another on the upper side of the sheet stack and have the adhesive surfaces, which at least partially and / or temporarily press on the top of the sheet stack, at least one of the adhesive elements being drivable in order to move adhesive surfaces which are just pressing on the top of the sheet stack toward or away from one another, so that between the two uppermost sheets of the A gap (14; 23) is formed in the stack of sheets. Investor according to claim 1,
marked by
a device (10; 18) which engages in the space (14; 23) between the two uppermost arches. Investor according to claim 2,
characterized by
that the device which engages in the intermediate space comprises one or more movable grippers (18) which grip the uppermost sheet (20) and pull it off the sheet stack (15). Investor according to claim 2,
characterized by
that the device which engages in the intermediate space contains one or more touch fingers (10) which can move into the intermediate space without contact and which can be lowered onto the sheet below the uppermost sheet (6). Investor according to claim 4,
characterized by
that at least one of the touch fingers (10) has a low-friction surface, which forms a counterpressure device for a friction wheel (12) arranged above the touch finger, which can be lowered onto the uppermost sheet (6) in order to move the uppermost sheet in the direction of a system (3 ) of the printing press. Investor according to claim 5,
characterized by
that the system of an associated printing press comprises one or more pairs of transport rollers (3) arranged close to the sheet stack (2). Investor according to one of the preceding claims,
characterized by
that the adhesive elements are friction wheels (7; 17) which are biased towards the top of the sheet stack (2; 15). Investor according to claim 7,
characterized by
that a friction wheel (7; 17) is arranged on each side of the sheet stack (2; 15) in the vicinity of the sheet leading edges or the sheet trailing edges, which is drivably mounted on an axis (8) which is transverse to the sheet leading edges or sheet trailing edges runs. Investor according to one of the preceding claims,
characterized by
that the device for arching the sheet stack (2; 15) is an at least partially convex or concave sheet support plate (1; 16). Method for separating sheets that are stacked on top of one another in a feeder of a sheet-fed printing press,
characterized by
that the sheet stack (2; 15) is arched at least partially and at least in its upper area and that in the arched area of the sheet stack the uppermost sheet (6; 20) is tensioned or pushed together by mechanical engagement on the upper side of the sheet, so that between the two a gap (14; 23) is created in the uppermost sheet of the arched sheet stack. A method according to claim 10,
characterized by
that the sheet stack (2; 15) is concavely curved, that on each side of the sheet stack at least one adhesive element (7; 17) is pressed against the top of the uppermost sheet (6; 20) and that the surfaces of the adhesive elements against the uppermost Press the bow, move it sideways to tension the top bow. A method according to claim 10 or claim 11,
characterized by
that the intermediate space (14) is created on a side of the sheet stack which is remote from a system (3) of the sheet-fed printing machine, that the intermediate space between the two uppermost sheets is gripped in order to hold the sheet underneath the uppermost sheet (6), that the top sheet by mechanical means (12) in Directed to the printing press and transferred to this and that this process is started again while the last separated sheet is withdrawn from the sheet stack (2).

Images