GB2078591A - A Platen Press - Google Patents

Abstract

A platen press having two flat platens (10, 11), one carrying a cutting or creasing forme (13), which are brought together to cut or crease a sheet (25) of material passed between them, wherein the platens move in orbital paths of opposite sense such that the forme engages and disengages a sheet whilst moving generally in the direction of sheet feed, there being drive means for the platens and the sheets and a spaced controller forming part of a means for matching the speeds of the platens and the sheets during the cutting operation. In one embodiment, the sheets move at a constant speed and the platen speed is varied between cuts, and in another embodiment, the platens move at a constant speed and the sheet speed is varied between cuts. In a third alternative, the speeds of both the platens and the sheets may be varied to ensure synchronism. <IMAGE>

Description

SPECIFICATION A Platen Press This invention relates to platen presses of the kind wherein two flat platens, one carrying a cutting or creasing forme, are brought together to cut or crease a sheet of material passed between the two.

It is known for such presses to consist of one stationary platen and another platen which is movable relative thereto in a linear reciprocatory manner so that the forme engages a sheet entirely perpendicularly thereto. The sheets are conveyed successively through the work station, usually by a plurality of carrier bars having spikes or grippers and spaced equally around a pair of driven endless chains, and the chains are driven intermittently such that the sheets are arrested for cutting or creasing. Thus, complex and expensive systems are needed for driving the chains and for accelerating the sheet out of the work station and the sheets are often too fragile to be accelerated rapidly since there is a tendency for them to break up under the forces imposed.Therefore, production rates are severely limited by the necessity to stop the sheets in the work station and to restrict the acceleration forces imposed thereon.

An object of the present invention is to provide a platen press which is able to meet the required production rates whilst the difficulties mentioned above are substantially overcome.

According to the present invention, there is provided a platen press comprising a pair of flat movable platens, at least one of which carries a forme for cutting or creasing sheets successively passed between the platens, at least one of the platens being movable in an orbital path such that the forme engages and disengages a sheet whilst moving generally in the direction of sheet feed, drive means for the platens and the sheets, and means for synchronising the drive means such that the forme and the sheet, whilst in engagement, move substantially at the same speed.

Preferably, a stop is fixed relative to one of said platens to provide a register position for said sheet prior to engagement with the forme, said stop having a ramp surface adapted to engage a carrier bar attached to the sheet and to match the speed of movement thereof with that of the platen as the forme enters the sheet.

Two embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic side elevation of a part of a platen press with a sheet to be cut positioned therein; Fig. 2 is an enlarged schematic drawing of a part of the arrangement of Fig. 1 illustrating the operational position of the parts just prior to engagement of the forme with the sheet; and Fig. 3 is a diagrammatic view of a drive system for the press.

The press comprises upper and lower platens 10 and 11 respectively, the upper platen 10 carrying a forme consisting of a wooden board 12 having fixed therein a matrix of knives 13. The cooperating surface of the lower platen 11 comprises a steel anvil plate 14. Each platen is mounted on a pair of crankshafts 1 5 each carrying a pinion 16. A pair of pinions 1 7 mounted on shafts 1 8 are driven preferably by a single variable speed electric motor 19, to drive the platens in a pair of co-operating orbital paths of opposite sense. A reduction gear box 20 is interposed to permit the motor 1 9 to be driven at high speed.

In the first embodiment, a rotating sensor 21 is attached to one or more of the crankshafts 1 5 and its rotation is detected by, for example a proximity switch 34 producing a signal which is transmitted to a speed controller 22 whose output is used to vary the speed of the motor 19 during each revolution of the sensor 21, as will be described.

Fig. 1 shows a plurality of carrier bars 23 spaced equally around a pair of driven chains 24, wrapping sprockets 32 driven by a constant speed electric motor 33. Each bar 23 carries a sheet of board 25 to be cut. The sheet 25 is impaled on a plurality of spikes 26 attached to the associated carrier bar 23.

In known manner, rubber strips 27 are placed around the knives 13 such that when the platens are separated after cutting, the sheet 25 is stripped by the resilience of the rubber, from the knives.

A register stop 28 is attached to the lower platen 11 and engages a carrier bar 23 when the lower platen is in its raised position. A curved ramp surface 30 is provided near the top of the stop 28 for a purpose which will become clear in the following description relating to operation of the press.

In operation, as a sheet 25 carried by its bar 23 approaches the work station, and the platens are converging in their orbital paths, as detected by the sensor 21, the speed of the motor 19 is increased by the controller 22 so that the knives 1 3 are brought up to the speed of travel of the sheet as determined by the motor 30. The knives 13 then enter and cut the sheet, and are subsequently removed as the platens begin to separate. After the knives have become disengaged from the sheet, which condition is again detected by the continuously monitoring sensor 21, the controller 22 reduces the speed of the motor 1 9 such that the remainder of the orbital paths are traversed in such time as it takes for the next sheet to arrive at the register position.

For this purpose the speed of the motor 33 is detected by the controller 22 to which it is connected.

As each sheet approaches the register position, the associated carrier bar 23 engages the rising ramp surface 30 of the stop 28 and rides onto the latter to the position shown in Fig. 1 so that while cutting takes place, the sheet and the platens are entirely synchronised. The curved ramp surface 30 ensures that this synchronism is attained and lost smoothly during those periods respectively when the knives are entering and leaving the sheet. For this purpose, a small amount of relative movement is permitted between the carrier bars and their associated chains and this movement acts against a spring to permit the register stop 28 momentarily to restrain the carrier bar to ensure perfect register.

As an alternative, the speed of movement of the platens can be constant, provided the extent of the orbital paths is arranged to coincide with the distance apart of the sheets entering and passing through the cutting station. However, this would necessitate large orbital paths which might present engineering difficulties in view of the considerable mass of the moving parts, In the second embodiment, therefore, the platens are moved in a moderate orbit and at a constant speed, so that the sheets, as they pass between them, must be decelerated to be synchronised with the speed of the platens, and the speed of the platens must be determined according to the maximum acceleration forces which can be endured by the sheets as they leave the platens.

Again, with reference to Figs. 1 to 3, the orbital paths of the platens 10 and 11 take them through the cutting station at a speed which will be referred to as the cutting speed experienced by the sheets, and at that speed, the platens always return to their cutting positions in synchronism with the positioning of the sheets.

In operation, as each sheet 25 carried by its carrier bar 23 approaches the cutting station and the platens are converging in their orbital paths, the speed controller 22 temporarily reduces the speed of rotation of the motor 33 thus to reduce the speed of the chains 24 and the sheet 25 to the cutting speed equivalent to the peripheral speed of the platens 10 and 1 1.As soon as the cutting or creasing forme attached to the platen 10 has released the sheet then the speed controller 22 accelerates rotation of the motor 33 to a transfer speed which ensures that the next sheet to be cut or creased is brought into the cutting station upon completion of one further orbit of the platens 10 and 11.

As each sheet approaches the register position between the platens the associated carrier bar engages the ramp surface of the stop 19 and rides onto the latter to the position shown in the drawing so that while cutting or creasing takes place the speeds of the sheet and the platens are entirely synchronised.

It will be appreciated that whilst the foregoing description is concerned with platens carrying knives for cutting through the sheet, these can be replaced by other kinds of forme such as those used for creasing the sheet for subsequent folding thereof. Although such formes do not entirely penetrate the sheet it is nevertheless important to ensure that they perform the work on the sheet in a similar manner to that performed by cutting formes.

It is envisaged that since the sheets are driven by an electric motor under the accurate discipline of an electronic control it may be possible to omit the register stop 1 9 since the positioning of the sheets relative to the platens can be accurately achieved. This presents a particular advantage when operating with formes which occupy qnly a small part of the surface area of the platen to which it is attached. Conventionally the carrier bars must be made to stop or reach the cutting position at one edge of the platens thus to contact the register stop. If the stop is omitted then the electronic control system can be used to place the sheets in the cutting position anywhere in relation to the leading or trailing edges of the platens.

Thus, for example, the sheets may be arranged to reach the cutting position mid-way between the ends of the platens. Thus, a small forme can be located centrally along its associated platen whereby the loads on the platens can be applied centrally thereof.

When a small forme is being used this usually indicates that the sheet size is similarly small, and the usual hopper of the feed mechanism supplying sheets to the cutting station is variable in dimensions to accommodate different sized sheets. Conveniently, adjustment of the hopper walls can be used to produce a signal which when supplied to the speed controller for the drive motor for the carrier chains can automatically ensure that the sheets are decelerated to the cutting speed at positions commensurate with the size of sheets being transported.

The register stop may be retained but be adjustable in position automatically in accordance with the signal used to adjust the aforesaid positions.

The precise construction and arrangement of certain parts of the apparatus can be other than those specifically described herein. For example, whilst it may be preferably to impart an orbital movement to each of the platens, the anvil platen may slide horizontally whilst the forme platen moves in an orbital path.

In a further alternative arrangement the speed of movement of the platens may be varied slightly during each complete orbit, thus somewhat relieving the necessity for sharply accelerating and decelerating the sheets. Clearly, an optimum degree of speed variation for the sheets and the platens can be achieved, though it is preferable to drive the platens at a constant speed in view of considerable mass thereof, and the inherent difficulty in imparting a speed variation thereto.

The crankshafts 18 of each platen can be; placed slightly out of phase with each other to produce a small degree of rocking action by'the platen during its orbit, thus to assist in cuttipg the sheets, and consequently permitting the force applied by the platen to be reduced.

Claims (11)

Claims

1. A platen press comprising a pair of flat movable platens, at least one of which carries a forme for cutting or creasing sheets successively passed between the platens, at least one of the platens being movable in an orbital path such that the forme engages and disengages a sheet whilst moving generally in the direction of sheet feed, drive means for the platens and for the sheets, and means for synchronising the drive means such that the forme and the sheet, whilst in engagement, move substantially at the same ;speed.

2. A platen press according to Claim 1, wherein the sheets are driven at a constant speed, and said synchronising means is arranged to match the movement of the platens with the passage of the sheets therebetween.

3. A platen press according to Claim 1 or Claim 2, including sensing means to detect the instantaneous position of at least one of said platens and to determine via a speed controller the speed at which the platens are driven.

4. A platen press according to Claim 1, wherein the platens are driven at a constant speed, and said synchronising means is adapted to match the passage of the sheets between the platens with the movement of the forme in said sheet feed direction.

5. A platen press according to Claim 4, including sensing means to detect the instantaneous position of at least one of said platens and adapted via a speed controller to determine the speed of travel of the sheets.

6. A platen press according to any one of the preceding claims, including a register stop attached to one of said platens and adapted to engage a gripper bar carrying a sheet to be cut thus to ensure perfect register between the forme and the sheet, said register stop including a ramp surface whereby synchronism of the forme and the sheet is attained and lost smoothly during those periods respectively when the forme is engaging and disengaging the sheet.

7. A platen press according to any one of the preceding claims, wherein the platens move in similar orbital paths of opposite sense.

8. A platen press according to any one of claims 1 to 6, wherein the platen not carrying the forme moves in a reciprocating path.

9. A platen press according to Claim 1, wherein the synchronising means is adapted to cause variation of the speed of the platens and the speed of the sheets prior to each cutting operation.

1 0. A platen press according to any one of the preceding claims, wherein the orbital movement of at least one of said platens includes a degree of rocking movement of the platen end-to-end thus to assist the cutting of the sheets.

11. A platen press substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.