The present invention generally relates to paper converting machines and, more precisely, it relates to a transversal cutting machine of logs of paper and the like, for the production of rolls of toilet paper, general purpose towels, industrial rolls, stacks of napkins and the like.
In particular, the invention relates to a device for clamping the log during the cut off step of a saw.
Transversal cutting machines are known, for making small rolls or stacks of paper, for example rolls of toilet paper, general purpose towels, stacks of napkins and the like, that are supplied with logs of paper rolled upstream.
In said machines one or more logs are normally loaded on a stepped pushing bench. Then, the end of the logs being cut is in turn held by means of clamps and a rocking saw is driven in succession into the paper thus cutting off the logs into rolls or stacks. More precisely, before that the saw is driven onto the logs, the latter are pushed forward axially for distances equal to the height of each roll or stack. Then, the logs are blocked only at the moment of the cut by means of a clamping device that allows, instead, their sliding during a pushing step.
The clamping device has normally an encircling shape so that the log does not collapse but at the same time the log cannot slide at the moment of the cut.
A transversal cutting machine should be adjustable to cut into portion logs of different diameter, according to the production needs. Each clamping device, therefore, must be equipped with means for clamping the log with interchangeable or adjustable clamping surfaces, for adapting itself in turn to a range of different diameters.
A first type of known clamping device provides the replacement of the elements for clamping the log, further to a stop of the machine. This type of machine, however, requires long stops, since the elements of the clamping device must first be disassembled after removal of their driving apparatus, then must be replaced with other elements of different size, and finally assembled again along with their driving apparatus for starting again the machine.
A second type of cut off machines provides a holding device with flexible surfaces, which however are of composite and expensive structure.
Concerning the systems for driving the saw, the cut off step is carried out by means of a quickly rotating belt saw or circular saw, whose support has an oscillating movement which can be reciprocating, rotating along a circle or along a more complex orbit.
Means are provided for synchronising the stepped movement of the log and the moment in which the saw is at the top dead center between two consecutive cuts. In particular, most of machines are equipped with means for pushing the logs and means for rocking the saw support with independent motors, synchronised by programmable means.
US 3049954 relates to a cutoff machine for logs of paper having a saw and two sections of clamp elements upstream and downstream the saw. A top clamp element of the upstream section rotates about a longitudinal pivot and an adjustable stop is provided. A top clamp element of the downstream section rotates about a transversal pivot and a spring is provided. The shells of the clamps are not replaceable and the positioning of adjustable stop is manual. No change-over of the clamp elements or adjustment of the height of the top clamps for change of log diameter is provided.
It is an object of the present invention to provide a transversal cutting machine in which the log cutting off step carried out by the saw is assisted by a clamping device which is flexible for different ranges of diameters of the log and requires only short stops for the change over.
This and other objects are achieved by the transversal cutting machine according to the present invention of the type comprising a clamping device in two sections crossed by a rocking saw.
According to the invention, the clamping device comprises a support base for the log and a top clamp element capable of pushing from the above the log against the base, and has the characteristic that means for quick adaptation to the change of diameter of said log (2)are provided comprising:
The shells engage with the supports preferably by means of quickly releasable lock pins .
Preferably, the top clamp element and the base are divided into two sections upstream and downstream of the saw, the means for automatically adjusting the height each section of the top clamp elements comprising said transversal support means, mounted on uprights having adjustable height.
The top clamp element and the base of the downstream section are advantageously linked to the transversal bar supported by first and second upright whereas the top clamp element and the base of the upstream section are linked to transversal bar supported by third and fourth upright, each upright being raised or lowered, for carrying out the height adjustment of the transversal bars.
The uprights are preferably raised or lowered by means of screwed shafts, means being provided, for driving in synchronism the rotation of the shafts.
The second and fourth upright, are preferably linked by a fork which is raised or lowered for the height adjustment of the transversal bars whereas the first and third upright, are directly raised or lowered by means of screwed shafts.
Advantageously, the transversal bar of the top clamp element of the downstream section comprises an actuator that moves vertically the top clamp element with respect to the transversal bar.
Preferably, the transversal bar of the top clamp element of the upstream section is pivotally supported by the third upright and is supported by the fourth upright which comprises an actuator that adjusts the pressure of the top clamp element against the log by pivoting the transversal bar about the third upright.
Further characteristics and/or advantages of the transversal cutting machine and of the clamping device according to the present invention will be made clearer with the following, but not limitative, exemplifying description of several exemplifying embodiments thereof, with reference to the attached drawings wherein:
With reference to figure 1, a transversal cutting machine according to the present invention comprises a bench 1, capable of slidingly supporting a log of paper 2, for example toilet paper, to cut off into rolls by means of a rocking and rotating saw 3, supported and driven by a mechanical transmission 3a fixed to a frame 3b. The saw 3 is shown in the position of top dead center of its orbit and, with dotted line, it is shown in the position of bottom dead center in which the saw has been completely driven into log 2.
With reference also to figure 2, according to the present invention, the log 2 is held, in the cutting zone, by a clamping device 4, divided in two sections 5 and 6 respectively upstream and downstream of the slot 7 through which saw 3 passes. Each section respectively consists in a base, 5a and 6a, and a top clamp element 5b, 6b, that pushes the log 2 from the above against base 5a, 6a for holding it in synchronism with the lowering of the saw 3 that passes through slot 7.
In the preferred embodiment, only section 5, the downstream one, completely opens itself with respect to log 2, for releasing the cut roll 2a, whereas section 6, the upstream one, continues to hold loosely log 2, so that it slightly brakes the log when pushed forward. Section 6 has a funnel shaped opening for making easier the inlet of the log 2 to cut off into rolls.
As shown in figures 3 and 4, bases 5a and 6a consist in symmetrical bottom shells, that are fixed by means of quickly releasable lock pins 8 to symmetrical bottom supports 8a integral to bench 1. The two symmetrical bottom shells 5a, 6a allow the passage between them of a pusher 9, that pushes forward log 2 and is dragged by a loop chain 9a through bench 1 and protruding from it.
The top clamp elements 5b and 6b comprises, instead, top shells, releasably fixed to transversal bars horizontal 10 and 11 by means of quick releasable lock pins 12a, 12b.
More precisely, in case of the front section 5, shown in figure 3, the top clamp element 5b is releasably locked by means of pins 12a to transversal bar 10 not directly, but by means of a cylinder 13. Transversal bar 10 (fig. 2 and 3) is supported by uprights 14 and 15, to the first of which is also pivotally connected.
Similarly, transversal bar 11 (fig. 2 and 4) is supported by uprights 16 and 17 to the first of which is also pivotally connected. Upright 17 is discontinued by a cylinder 20 that adjusts the pressure of shell 6b onto log 2, thus having a damping function. The top clamp element 6b is releasably locked by means of pins 12b directly to transversal bar 11.
Uprights 14-17 are linked to a height-adjusting device comprising a drive unit 19 that operates vertical screwed shafts 22a, 22b and 22c. In this way, it is possible to move transversal bars 10 and 11 translating them vertically parallel to themselves. More precisely, by operating the drive unit it is possible to lower or raise uprights 15 and 17 integral to one another by a fork 18 linked to one of the vertical screwed shafts 22a. Screwed shafts 22b and 22c of uprights 14,16 are operated, in synchronism to shafts 22a of uprights 15 and 17, by a chain 21 extending through bench 1.
The clamping device according to the invention is flexible according to different ranges of diameters of the log to cut off into rolls. In fact, for small differences of diameter within a certain range, for example differences of several centimetres, the surrounding shape of both shells 5b and 6b and bases 5a and 6a is enough to assure a pressure on the log 2 without that this it escapes during the cut, which is carried out at high frequency. When the logs to cut belong to much more different classes of diameters, it is sufficient to stop the machine for several minutes for releasing shells 5b, 6b from transversal bars 10 and 11 and replacing them with a set of other shells of different shape, suitable for a diameter larger or shorter than the previous, as well as replacing bases 5a, 6a with a set of bases suitable for a larger or shorter diameter than the previous. At the same time, by means of the drive unit, the height of the transversal bars 10 and 11 is changed by displacing them vertically for adjusting the position of the top clamp element 5b, 6b to the new range of diameters. This step can be carried out manually or automatically.
The peculiarity of the clamping device according to the invention is therefore that of assuring a sufficient flexibility to different ranges of diameters with easy replacement of the shells and quick adjustment of the position of the top clamp element. This, in particular, is possible with the presence of the interchangeable shells and the motorised positioning of the height of transversal bars 10 and 11.
The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.