GB2309409A

GB2309409A - A device for cutting individual pieces from a string of plastic material

Info

Publication number: GB2309409A
Application number: GB9701316A
Authority: GB
Inventors: Albrecht Roehrdanz; Guenter Foerster; Gerd-Reiner Israel
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1996-01-24
Filing date: 1997-01-22
Publication date: 1997-07-30
Anticipated expiration: 2017-01-22
Also published as: CH692081A5; DE19602411C1; ITMI970027A1; IT1289166B1; GB2309409B; JPH09201792A; GB9701316D0; JP4008521B2

Description

23019409 1 A device for cutting individual pieces State of the art The

invention proceeds from a device for cutting individual pieces. A device is known from DE 33 15 925 C2, which comprises two cutting blades arranged respectively above and below a line of material conveyed at constant velocity. The two cutting blades are coupled to one another via a gearing arrangement. The gearing arrangement causes each cutting blade tip to define a circular path of movement, which extends in each case at least over half the thickness of the line of material. The separation of the individual piece from the line of material is effected when the two cutting blade tips have each penetrated the line of material through half the line of material thickness. As a result of the two cutting blades, the known device has a complex structure. In addition, there is a danger of the two blades contacting one another and therefore becoming damaged, since the cutting gap between the two blades has to be relatively small in order to obtain a straight cutting edge. Furthermore, when two cutting blades are used, the line of material tends to produce splinters which contaminate the device, so that relatively high maintenance is necessary. However, even the use of a single cutting blade which is guided along a circular path having a correspondingly larger diameter would not result in the desired success. This type of design would have the disadvantage that the arc section required to this end would deviate considerably from a path section which is as straight as possible and necessary for producing a straight cutting surface.

2 Advantages of the invention In contrast, the device according to the invention for cutting individual pieces according to claim 1 offers the advantage that the cutting surface quality is high in spite of the use of a single cutting blade on account of the special path of movement of the cutting blade. As a result of the fact that the device comprises only one cutting blade, the device has a relatively simple structure and operates without being prone to disturbance. At the same time, the production of splinters is prevented, so that the device requires only relatively low maintenance.

Further advantages and advantageous developments of the device according to the invention for cutting individual pieces will be clear from the subclaims and the description. The quality of the cutting surface can be further improved by providing a special position of the path of movement of the cutting blade relative to the line of material. By using two planetary gearings, the path of movement of the cutting blade can be simply produced and if necessary can be easily adapted to different parameters, such as the line of material thickness or the feed velocity of the line of material. By using only a single scraping drum and a single cutting blade, it is possible to use a drum having a relatively small diameter as an additional guide. In particularly, this reduces the structural size of the device.

Drawings An embodiment of the invention is illustrated in the drawings and described in further detail in the following description. Figure 1 is a simplified longitudinal section through a device for cutting individual pieces and Figure 2 is similarly a simplified longitudinal section through part of the device during operation.

3 Description of the embodiment

The device 10 for cutting individual pieces 11 from a line of sweet material 12 comprises a continuously operating conveying device for the line of sweet material 12, of which only a guide duct 13 is shown in Figure 1. The outlet end 14 of the guide duct 13 opens centrally into the region between two drums 15, 16 of the device 10, the cylindrical surfaces of the drums 15, 16 guiding the line of sweet material 12 and the individual pieces 11. The distance between the cylindrical surfaces of the drums 15, 16 corresponds to the thickness D of the line of sweet material 12.

The first drum, referred to in the following as the scraping drum 15, is mounted on an axle 17 and comprises a larger diameter than the other drum, which is mounted on an axle 18 and is referred to as the counter drum 16. The scraping drum 15 and the counter drum 16 are forcibly coupled and driven, for example by means of a gearing, not shown, so that the circumferential velocities of their cylindrical surfaces are identical and correspond to at least the feed velocity VBx of the line of sweet material 12. Furthermore, the arrangement of the scraping drum 15 and the counter drum 16 is such that a straight line 19 connecting the axles 17, 18 extends perpendicular to the feed direction X of the line of sweet material 12.

Constructed in the scraping drum 15 is a plurality, for example five apertures 21 arranged at uniform angular distances apart, and one aperture 22 is for example provided in the counter drum 16. One aperture 21 of the scraping drum 15 and the aperture 22 of the counter drum 16 overlap in each case in the region of the straight line 19 during the rotational movement of the scraping drum 15 and of the counter drum 16.

4 Arranged inside the scraping drum 15 is a cutting device 24 with a movable blade 25. The movement of the blade 25 is coordinated with the rotary movement of the scraping drum 15 and the counter drum 16 in such a manner that, along its path of movement, the blade 25 penetrates an aperture 21 in the scraping drum 15, the line of sweet material 12 and the aperture 22 in the counter drum 16 each time. The size of the apertures 21, 22 is defined by the duration of cutting of the line of sweet material 12 or by the movement of the blade 25.

In order to produce the blade movement, the blade 25 i rigidly connected to a connecting rod 26 at a given distance therefrom and parallel thereto. The connecting rod 26 is in turn connected to a gearing arrangement 27, which is arranged on the opposite side of the counter drum 16 to the line of material 12. The gearing arrangement 27 comprises two planetary gearings 28, 29, which are arranged above one another in the embodiment and each comprises fixed, identical gears with inner toothings 31 and, inside the fixed gears, identical gears which are mounted eccentrically on cranks 32, 33 and have outer toothings 34. The gears with the outer toothings 34 each have half the number of teeth of the gears with the inner toothings 31. The crank 32 of the planetary gearing 28 driven by means, not shown, is connected to the connecting rod 26 via a first cam 35 and a rod 36 secured rigidly at right angles to the connecting rod 26. In contrast, the other crank 33 of the planetary gearing 29 is connected to a second cam 38, which is articulatedly connected to the connecting rod 26 via an intermediate member 37.

As a result of the above-described construction of the planetary gearings 28, 29 and the connecting rod 26, the blade 25 is always guided at right angles to the feed direction X of the line of sweet material 12.

The length of the cranks 32, 33, of the cams 35, 36 and of the rod 26 and intermediate member 37 are identical in each case. In order to obtain good mass balancing, the centre of gravity of the connecting rod 26 is advantageously located at the point of articulation of the cam 35 and the rod 36. This is achieved by means of balancing weights, not shown, which are connected to the connecting rod 26. Similarly, balancing weights, also not shown, are fitted for mass balancing on the two cranks 32, 33 and the cams 35, 37.

The above-described device 10 operates as follows: When the crank 32 of the planetary gearing 28 is driven in an anti-clockwise direction, then each point of the connecting rod 26, and therefore also the tip 39 of the blade 25 rigidly connected to the connecting rod 26 moves along an identical, elliptical path of movement. In Figure 1, the path of movement of the blade tip 39 is shown by the reference 40, the direction of rotation of the path of movement 40 also being anti-clockwise. During its movement, the tip 39 of the blade 25 penetrates one of the apertures 21 of the scraping drum 15, contacts the line of sweet material 12 and cuts off an individual piece 11, and then penetrates a short distance into the aperture 22 of the counter drum 16. The tip 39 of the blade 25 then returns in the reverse sequence into the interior of the scraping drum 15 and the procedures are repeated.

once the individual piece 11 has been separated from the line of sweet material 12, depending on the circumferential velocity of the scraping drum 15 and the counter drum 16, the individual piece 11 is either conveyed a further certain distance by the drums themselves, or by the pushing end face of the blade 25. The individual piece 11 is then transferred by a transfer device known per se to a wrapping station, for example.

6 The arrangement and construction of the gearing arrangement 27 is selected in such a manner that the large half axis 41 of the path of movement 40 lies on the straight line 29 between the scraping drum 15 and the counter drum 16. Furthermore, the small half axis 42 of the path of movement 40 arranged perpendicular to the large half axis 41 lies within the scraping drum 15. The length of the half axes 41, 42 is dependent upon the diameter of the gears with the inner toothings 31 and the gears with the outer toothings 34 and upon the lengths of the cranks 32, 33 and the cams 35, 38.

Important for the design of the lengths of the half axes 41, 42 is that, at the point of contact of the blade tip 39 with the line of sweet material 12, the value of the velocity component Vmx of the velocity vector of the blade tip 39 in the conveying direction X of the line of sweet material 12 is equal to or slightly greater than the size of the velocity vector VBx of the conveying direction of the line of sweet material 12 (Figure 2). Furthermore, as a result of a corresponding design of the lengths of the half axes 41, 42, it is possible to approximate the path curve section 45 of the blade 25 in the line of sweet material 12 between the contact point 44 and the exit point 46 out of the line of sweet material 12 to a straight line. An approximation to a straight line of this type can be attained in that the length of the longer half axis 41 is selected to be as large as possible in relation to the shorter half axis 42. Of course, it is necessary to take into account in particular the cutting behaviour of the line of sweet material 12 and the conveying velocity VBX Of the line of sweet material 12.

In order to adapt the device 10 to different parameters, such as a different line of material thickness D or a different conveying velocity VBx of the line of sweet material 12, it is merely necessary to displace the blade 7 relative to the connecting rod 26 perpendicular to the line of sweet material 12.

In addition, it should be noted that the outlet end 14 of the guide duct 13 on the side facing the counter drum 16 is extended to such a degree that the guide duct 13 forms an abutment for the blade 25 at the contact point 44. The guide duct 13 is ideally extended in such a manner that it acts as an abutment for the blade 25 over the entire path curve section 45.

In addition, it should be noted that differently designed gearing arrangements can be used in place of the gearing arrangement 27 with the planetary gearings 28, 29 for producing an at least approximately elliptical path of movement of the blade 25. In addition, the gearings can also be arranged, for example, above the guide duct 13 or adjacent one another.

8

Claims

1. A device (10) for cutting individual pieces (11) from a plastically deformable line of material (12) conveyed at constant velocity, with a single drum (15) comprising a movable blade (25), in whose cylindrical surface at least one aperture (21) cooperating with the blade (25) is formed, and with a device (27) connected to the blade (25) by means of a connecting member (26) for producing at least approximately elliptical paths of movement of at least the tip (39) of the blade (25), the path of movement (40) of the tip (39) of the blade (25) comprising a focal point (43) arranged within the drum (15) and two axes (41, 42) of different lengths, of which a first axis (41) projects by a distance out of the drum (15) corresponding at least to the thickness (D) of the line of material (12), and furthermore a second axis (42) of the path of movement (40) being arranged entirely within the drum (15).

2. A device according to claim 1, characterised in that the first axis (41) of the path of movement (40) extends perpendicular to the conveying direction (X) of the line of material (12), and the second axis (42) of the path of movement (40) extends parallel to the feed direction (X) of the line of material (12).

3. A device according to claim 1 or 2, characterised in that the first axis (41) is longer than the second axis (42).

9 is

4. A device according to one of claims 1 to 3, characterised in that the path of movement (40) of the tip (39) of the blade (25) is constructed in such a manner that, at the contact point (44) of the blade (25) with the line of material (12), the component (Vmx) of its velocity vector pointing in the conveying direction (X) of the line of material (12) has a value which is equal to or slightly greater than the vector in the conveying direction (X) of the feed velocity (VBX) of the line of material (12).

5. A device according to one of claims 1 to 4, characterised in that the device (27) is formed by two planetary gearings (28, 29) connected to one another by means of a connecting rod (26).

6. A device according to claim 5, characterised in that the planetary gearings (28, 29) each comprise fixed gears with inner toothings (31) and, inside the fixed gears, gears with outer toothings (34) mounted eccentrically on cranks (32, 33), the number of teeth of the gears of the inner toothings (31) being double the number of teeth of the gears of the outer toothings (34).

7. A device according to claim 5 or 6, characterised in that a first planetary gearing (28) is constructed so as to be driven and comprises a cam (35) rigidly connected to the connecting rod (26).

8. A device according to one of claims 1 to 7, characterised in that cooperating with the drum (15) is a counter drum (16) with a smaller diameter, the line of material (12) being guided between the drum (15) and the counter drum (16).

9. A device according to claim 8, characterised in that at least one aperture (22) is constructed in the counter drum (16), and the distance between the drum (15) and the counter drum (16) corresponds to the thickness (D) of the line of material (12).

10. A device according to one of claims 1 to 9, characterised in that the point of contact of the drum (15) with the line of material (12) lies on the first axis (41) of the path of movement (40).

A cutting device substantially as herein described with reference to the accompanying drawings.