This invention is concerned with apparatus for folding web sheet into a stack of sheets about pre-formed fold lines in the web. Such apparatus is useful, for example, for use in conjunction with a machine which prints continuous stationery (such as financial statements) onto the web.

If the web material is folded about the preformed fold lines and then allowed to build up in a stack, the folded edges of the stack tend to a adopt a greater height (due to the presence of air spaces in the folds) than the middle so that the stack adopts a concave top surface which ultimately limits the stable height of the stack. It is an object of this invention to alleviate this particular problem.

According to the present invention there is provided a web folding device comprising web feeding means for directing alternate folds in the web to one side or the other of a support table, and at each side of the table an arm on a gripping member for holding a folded web edge onto the table, and indexing means for moving said arm or a similar associated arm on the gripping member onto a subsequent fold in the web to hold that fold and the previous stack of folds down onto the side of the table, and spacing means for progressively increasing the distance between the table and the gripping members. By using such a device the folds in the web are com¬ pressed so that the stack tends to retain a generally flat top surface and a stack of substantial height can be built

up without problems of instability occurring.

The gripping member may take many forms but a preferre arrangement is provided by forming the arms as paddle-lik members on a rotating gripping member. Four such paddle are preferred but the number may be decreased or increase as desired.

Ideally the apparatus will incorporate a sensing devic for registering the approach of a fold to the grippin member, and for controlling operation of the indexin member. It is also preferred that a stop plate should be provided at each side of and above the support table to limit the extent of movement of the web to either side of the table.

Whilst the gripping members could conceivably be raised progressively it is preferred that the spacing means should comprise a device for lowering the table to the extent of measured increase in the stack of the folded sheets. Ideally, a mechanism will be provided for reversing the spacing means so as to give a momentary decrease in the spacing between the table and the gripping members to compress the folds into the web.

The invention may be performed in various ways and a preferred embodiment thereof will now be described with reference to the accompanying drawings in which:- Figure 1 is a diagrammatic side view of a web folding apparatus incorporating the features of this invention;

Figure 2 is a side view of the main web folding device of the apparatus of Figure 1; and

Figure 3 is an enlargement of a part of the device shown in Figure 2.

The folding machine illustrated generally in Figure 1 takes a continuous web 1 of printed material from a laser printer (not shown) and folds this into piles of material up to 3,000 or more sheets high or alternatively separates the material into jobs as indicated by end-of-job marks printed on the web. At the infeed side of the machine is a multi¬ pass accumulator 2 which provides web storage during the pack ejection cycle of the machine and also permits cooling of the hot web exiting from the printer f ser section.

The web is pulled down into the folder section 3 through a pair of rubber covered nip rolls 4 (see also Figure 2), through a pair of burster rolls 5 for web separation, and down through a set of folder belts 6 where the material is zig-zagged onto a variable-height delivery table 7. As the pack of material is built up, the delivery table 7 is automatically lowered and, at package ejection, the table will fall to a lower position and discharge the finished pack onto a fixed conveyor (not shown) for subsequent discharge onto a further conveyor system or for unloading by hand. The machine will be preset for form depth and the number of sheets in a stack and/or job separation. When the folder stops for pack ejection, material will fill the accumulator 2, allowing a moving carriage to fall. In the event of the folder not re-starting the carriage will automatically stop the printer as it reaches the bottom of

its stroke. Under normal circumstances the accumulator will reach a position halfway down its stroke when the folder re¬ starts and will cause the folding section to run at high speed, which rapidly empties the accumulator, and raises the carriage back to its normal running position. In the event of a printer stop the accumulator carriage will rise above its normal running position and this automatically stops the folder. As the printer re-starts the carriage will fall again and re-start the folder. A safety device is fitted tc the accumulator carriage to prevent the carriage falling in the event of a web break and causing damage to the bottom carriage stops.

Mark reading equipment is fitted between the exit of the accumulator and the nip rolls 4 and 5 is adjustable across the machine to coincide with marks printed on the web. A first reader detects the end of job mark and slows the machine, with a second reader actuating the burster section 5 and pack ejection or table 'off setting' device. The folder section 3 is illustrated in more detail in Figures 2 and 3. The web 1 is fed into the machine by the two rubber nip rolls 4 which are connected to a variable speed motor whose speed is controlled by the accumulator as described above. Below the nip rolls are the pair of burster rolls 5 which, in the normal operating mode, are running faster than web speed but make no contact with the web until a burst is required when they are closed by two actuators and burst the web. On completion of the burst the web is indexed forward until the incoming form interrupts a

sensor, for example a photo-electric switch 8, and this is the datum point in the machine.

Two sets of folder belts 6 are incorporated into the machine to pull the material down and cause it to fold by throwing the web 1 against two sets of adjustable end-stops

9. The folding belt system runs at a higher speed than web speed to allow separation of the burst and to provide a window for the photo-electric datum switch 8 to operate. In the start-to-fold position the elevating table 7 would be at the top of its stroke and will form a triangle with the folder belts 6 to collapse the cross-perforations of the web at the end-stop position. At the start of fold the new end of the web 1 is fed down through the folder belts 6 and an air blast from pipe 10 blows the tail towards one set of end-stops 9 with further assistance from the elevating table conveyor belts 11 which run for a short period of time.

As the folding web approaches the stop 9 it will cover a sensor 12, which will in turn cause a shaft 13 to be rotated through 90° so that a further one of four paddles 14 of a member carried by the shaft 13 presses down onto the web fold. This fold is then held between the paddle 14 and the top of the table 7. These paddles 14 therefore ensure that the fold in the web is sharply defined and also hold the fold firmly down onto the table 7. This ensures that the pack 15 of folded sheets is kept in a relatively flat state, thus avoiding the usual concave bow-ing of the top of the stack which occurs if the folds are not held in a compressed state.

If the paddle member stalled this would be indicative of the fact that the stack is compressed to too great an extent and sensing of such stalling would result in a suitable lowering of the table 7. In addition table movement can be controlled by a sensor 17 looking across the top of the pack. This would detect the formation of a convex surface at the top of the pack, which would fill the triangle between the top of the pack and the folder belts, and obstruct the flow of material into the folding area. Across the width of the web 1 there will be a series of belts 6 interleaved with paddle members 14 and the stop plates 9.

As the folded sheets start to build on the table 7 the latter is automatically indexed down to maintain correct folding geometry between the folder belts 6 and the top of the pack 15. After two to three hundred sheets have been folded onto the table a considerable amount of air will be trapped in the pack and to expel this the table 7 may be raised, compressing the pack against the folding belt 6 and paddle members 14, to expel the air and to set the folds firmly. Once this has been completed the table 7 moves down and folding continues. Further pack-compression cycles take place until the stack is complete. Once a pile of forms has been completed the table 7 will stroke to its bottom position, and the table conveyor belts 11 start to discharge the pack onto the exit conveyor.

Built into the folder belt section are two detectors 16 whose primary purpose is to count sheets. When the machine

is operating correctly only one detector 16 will be covered by the incoming web. In the event of a mis-fold the material will form very short folds and fill the triangle between the folder belts and top of the pack. Both detectors 16 will now see the web and in this instance the machine will stop, burst the web and eject completed work. Little permanent damage will have taken place on the web and normally the pack can be tidied by hand outside the machine. Alternatively, in the event of a mis-fold, folds will not be seen by the detectors 12 in the correct sequence. This will indicate that a mis-fold has occurred and automatically eject the pack and/or stop the machine.

It will be appreciated that means other than the detectors 12 could be employed to operate the paddles, such as a Geneva crank linked to the rollers 4 (or tractors provided with pins which fit into holes on the edges of the paper web. The length of paper which is passed through the machine can then be determined by calculating the number of holes as a function of the extent of rotation of the roller or tractor belt.

Other modifications may be made to the general design of the equipment. For example, the folding belts 6 could be replaced by some other form of mechanism for directing the web down onto the table 7. More particularly, however, the member carrying the paddles 14 could be modified in various ways. The number of paddles could be increased to any practical number and could be decreased, even down to just one which will be indexed rapidly through 360° at the

required instants. Another possibility is for the paddles to be more in the form of thin flaps which are laid down, one on top of another, with the lowermost flap being with¬ drawn at each indexing operation. As illustrated in Figure 2, the positioning of the folder belts 6 and the end-stop 9 (and the paddle members 14) can be modified, as required, to the dashed line positions to accommodate folded sheets of varying lengths.