WO2000073029A1

WO2000073029A1 - Device with thermal system for controlling the interference between two members moving relative to each other

Info

Publication number: WO2000073029A1
Application number: PCT/IT2000/000206
Authority: WO
Inventors: Guglielmo Biagiotti
Original assignee: Fabio Perini S.P.A.
Priority date: 1999-05-28
Filing date: 2000-05-22
Publication date: 2000-12-07
Also published as: ITFI990127A0; AU5100900A; IT1308281B1; ITFI990127A1

Abstract

The device comprises a first mechanical member (3) and a second mechanical member (1) which are movable relative to each other. The members are arranged at a close distance so as to cooperate with each other. A heating element (41) is provided in order to heat at least one of said first and second members, so as to maintain the dimensional stability thereof.

Description

DEVICE WITH THERMAL SYSTEM FOR CONTROLLING THE INTERFERENCE BETWEEN TWO MEMBERS MOVING RELATIVE TO EACH OTHER

Description Technical field

The present invention relates generally to a device comprising at least a first and a second mechanical member performing a relative movement with respect to each other, with means for controlling the distance between them and any mutual interference during movement. Generally the two members may be, for example, two embossing cylinders, two calendering cylinders or the like.

More particularly, and in accordance with one of its specific aspects, the invention relates to a perforating device for producing perforated lines on web material, for example a web of paper for the production of rolls of toilet paper, all-purpose drying paper or the like. More particularly the present invention relates to a perforating device of the type comprising a rotating member equipped with one or more rotatabie blades cooperating with at least one fixed blade.

The invention also relates to a method for controlling the interference between the fixed blades and rotatabie blades in a perforating device and more generally between two mechanical members moving relative to each other. Background art

In many technological sectors there exists the need to produce perforated lines on web material fed in a substantially continuous manner toward a perforating assembly. This requirement arises in particular in the field of paper converting for the production of rolls or small rolls of toilet paper, all- purpose drying paper and other similar products, for the production of continuous stationery for computer printers, etc. The wound material (typically so-called tissue paper) is perforated at regular intervals so as to form tearing lines along which the end user is able to tear off portions of web material with the desired length for use. Examples of perforating devices of this type are described in US patents Nos. 5125302 and 5284304.

In order to produce perforations along lines which are spaced at intervals which may also vary greatly, a perforating device has been provided, in which device the rotating member, generally referred to below also as a rotating cylinder, has a central core and a series of replaceable external components which have seats for the blades. A perforating device of this type is described in Italian patent No. 1 ,259,660. The replaceable external components are formed such that the seats for the blades have different angular intervals for the various components. The central core and the external components are normally made of metallic materials which are different from each other. In particular, the central core is made of steel, while the external components are made of aluminum so as to reduce the weight.

The use of materials with different thermal expansion coefficients results in certain difficulties. In particular, since the material used for the external components of the rotating cylinder has a thermal expansion coefficient different from that of the remaining structure, heating of the device during operation causes a variation in the interference between the rotatabie blades and the fixed blade such that the thermal expansion of the aluminum parts of the rotating cylinder is not compensated by a corresponding expansion of the support structure.

Moreover, the friction produced between the rotatabie blades and the fixed blade generates heat and therefore causes localized thermal expansion of the blades which is not compensated by a corresponding expansion of the supporting structure. The thermal expansion causes an undesirable increase in the interference and therefore the friction with a consequent increase in heat and therefore a worsening of the situation during operation.

The temperature of the device may vary considerably during operation between initial start-up and the running speed after a considerable number of hours of operation. The interference between the rotatabie blades and the fixed blade must be adjusted with extreme precision: insufficient interference results in the risk of a perforating action which is imperfect, incomplete or even fails to produce a perforation at all; excessive interference results in rapid wear or even breakage of the blades.

Problems of a similar kind, although less serious in nature, may also occur in devices where the rotating cylinder is made entirely of a single material.

Fluctuations in the temperature of the environment may also give rise to difficulties in maintaining the correct interference between the blades.

In other devices with moving members similar problems may arise, with the need to control the degree of relative interference or the relative distance between the members. For example, in embossing assemblies for embossing sheet materials, there may be the need to compensate, to a certain degree, the thermal expansion of the embossing rolls in order to control the interference between them at the point of contact. Objects of the invention

The object of the present invention is to eliminate the abovementioned drawbacks.

More particularly, one object of an embodiment of the present invention is to provide a perforating device with a fixed blade and a rotating member having one or more rotatabie blades, in which the correct interference between fixed blade and rotatabie blades may be maintained more easily during operation.

A further object of the invention is to provide a device which is able to eliminate or reduce substantially the effect of the temperature - including the temperature of the environment - on correct operation of the device.

An object of the invention, in particular, is to eliminate the negative effects arising from variations in temperature during operation of a perforating device especially when the rotating member is made of materials which have different thermal expansion coefficients.

An object of the present invention is also to provide a method for reliably controlling, during operation, the interference between two movable members and, in particular, between a fixed blade and one or more rotatabie blades in a perforating device for producing perforated lines in web material. Summary of the invention

These and further objects and advantages, which will be clear to those skilled in the art from reading the text below, are obtained by means of a device characterized by a heating element for heating at least one of the two movable members.

In the particular and specific case where the device is a perforating device, the invention envisages heating the rotating member carrying the rotatabie blades or, alternatively, only the rotatabie blades or, also alternatively, the fixed blade. It is also possible to combine heating of the rotating parts and heating of the fixed parts, although particular advantages are obtained by heating the rotating member or cylinder carrying the rotatabie blades. Generally, of the two members, it is preferable to heat and keep at a controlled temperature the member which is most sensitive to differences in temperature, for example the member which is made of several materials with different thermal expansion coefficients. In this particular application the underlying idea of the invention provides results which are particularly significant and unexpected with regard to control of the perforation quality and reduction in wear.

According to a particular advantageous embodiment of the invention, a temperature sensor which detects the temperature of the rotating member and a control unit are provided. The control unit, the heating element and the sensor form a temperature-regulated system which keeps the temperature of the rotating member at a controlled value by means of heating via the heating element. Basically, the value of the temperature is kept within a relatively limited temperature range with a minimum and maximum value.

With this arrangement, the rotating member is brought, from the very start of its operation, to a temperature (within the abovementioned range) substantially corresponding to the maximum temperature which can be reached at running speed or to a temperature higher than said temperature. The interference between the rotatabie blades and the fixed blade is adjusted so as to be correct when this temperature has been reached.

Within the context of the present invention frequent reference will be made to a rotating cylinder supporting the rotatabie blades since usually this term is used to indicate the member carrying the rotatabie blades. However, this term is not to be regarded as limiting, since the rotatabie blades may also be supported on a member of a different kind.

The heating element may in practice consist of a system for circulating a thermal carrier fluid, such as a diathermic oil, heated water, steam or the like, also by means of the introduction of hot air. However, for the sake of simplicity and also considering the relatively low level of power used for this purpose, it is preferable to use a heating system of the electrical type with an electrical resistance as the heating element.

Using an electrical resistance it is possible to provide a particularly simple heating system. According to a particularly advantageous embodiment of the invention, the rotating member has an axial cavity which is open at both ends. The electrical resistance of the heating element is arranged inside this axial cavity and extends inside the rotating member. The electrical resistance may thus be suspended from a system which is fixed, i.e. does not take part in the rotational movement of the member and projects from the open ends of the cavity. This avoids any problems with regard to supplying of the power to the resistance, since the need for a rotating distributor is eliminated. The entire heating system is static and therefore may be easily mounted on a support means integral with the fixed side walls which support the rotating member. The resistance preferably extends only along the portion of the rotating member which supports the blades and does not project from the cavity inside it.

The support means may be formed by means of a tensioned cable which passes through the cavity passing inside the rotating member and which is secured at its ends to two points which are fixed with respect to the structure.

Heating of the rotating member occurs by means of irradiation via the resistance located inside the axial cavity. With a device of this type it is possible to provide a method for controlling the interference between a fixed blade and a rotatabie blade mounted on a rotating cylinder, characterized by the fact of heating the rotating member and/or the rotatabie blades and/or the fixed blade to a given temperature, within a temperature range, and keeping the heated element or elements in this temperature range during operation of the device.

More generally, the device may be used for implementing a method for controlling the dimensional stability of two moving mechanical members, the interference or distance between which is to be controlled. Further advantageous features of the device and the method according to the invention are indicated in the accompanying claims.

With the device and the method according to the invention it is possible to avoid variations in temperature due to operation and also compensate for variations in the temperature of the environment, while keeping the device within a precise temperature range compatible with the degree of accuracy which is to be set for interference between the rotatabie blades and the fixed blade. Brief description of the drawings

The invention will be better understood with reference to the description and the accompanying drawing which shows a possible non- limiting embodiment of the invention and, more particularly, in which:

Fig. 1 shows a partially sectioned side view of a perforating device to which the invention may be applied;

Figs. 2A and 2B show a partially longitudinally sectioned view of the two end portions of the rotating cylinders; and

Fig. 3 shows a cross section along the line Ill-Ill according to Fig. 2A. Detailed description of the preferred embodiment of the invention

Fig. 1 shows schematically a partially sectioned side view of a perforating device to which the present invention may be applied. The perforating assembly comprises a member rotating about an axis A, referred to below as a rotating cylinder 3. A plurality of rotatabie blades 5 are mounted on the rotating cylinder 3, extending in a substantially rectilinear manner parallel to the axis A of the rotating cylinder 3. The cutting edges of the blades 5 lie on a circular cylindrical surface C and cooperate with a helically extending fixed blade or counter-blade 7 consisting of a plurality of adjacent segments mounted on a beam 9. The structure of the fixed blade 7 may be, for example, that described in US-A-5125302. The rotatabie blades 5 mounted on the rotating cylinder 3 are serrated so as to obtain a discontinuous cut and therefore a perforation in the web material N which passes between the rotatabie blades and the fixed blade. The beam 9 is hinged about an axis B and is moved toward the rotatabie blades 5 by a cylinder/piston actuator 11. Suitable stops, not shown, define the working position of the fixed blade 7 with respect to the rotatabie blades 5.

The configuration of the perforating device described above is illustrated by way of example, it being understood that the system for regulating and maintaining the temperature of the rotating cylinder may also be applied to perforating devices with different structures.

As shown in greater detail in the cross section according to Fig. 3, the rotating cylinder 3 consists of a tubular core 15 around which external components 17 - which are two in number in the example shown - are fixed, the rotatabie blades 5 being fixed onto said components. Each rotatabie blade 5 is secured to the respective external component 17 by means of a joining plate 19 and a series of screws 21. An axial cavity 23 is provided inside the tubular core 15. In practice, the tubular core 15 may be made of steel, while the segments forming the external components 17 may be made of aluminum. In a manner known per se (see Italian patent No. 1259660) the external components 17 may be replaced so as to modify the number of rotatabie blades 5 mounted on the rotating cylinder 3, thus modifying the distance between said blades. The cylinder 3 has two end portions 3A and 3B shown in Fig. 2A and in Fig. 2B, respectively. Each end portion is supported in a respective bearing 25A, 25B mounted in the corresponding side wall 27A, 27B. The end portion 3A has, associated with it, a toothed wheel 27 which meshes with a system (not shown) for transmitting the rotational movement to the rotating cylinder 3. The end portion 3B has a pulley 29 on which a toothed belt of an encoder, not shown, is driven. The end portions 3A and 3B have respective axial holes 31 and

33 which open out toward the outside and communicate with the internal cavity 23 of the rotating cylinder 3. An axial passage which passes through the entire cylinder 3 and the associated supports is thus defined.

The side walls 27A and 27B have, fixed to them, two brackets 35 and 37 to which the ends 39A and 39B of a cable 39 are attached, said cable being tensioned between the two ends and passing axially through the rotating cylinder 3 along the passages 31 , 33 and the axial cavity 23. In order to compensate for the thermal expansion of the cable and keep it always correctly tensioned, suitable cup springs (not shown) or other resilient members are provided at at least one of the two securing points.

An electrical resistance 41 is fixed to the cable 39 by means of terminals 45 distributed along the length of the cable 39. The resistance 41 is connected by means of a power supply line 43 to a power supply system 47 which is supplied by an electrical line denoted generally by 49. The rotating cylinder 3 has, mounted on it, a temperature sensor schematically indicated by 51 and is connected by means of a lead 53 to a rotating ring 55 cooperating with a sliding contact, schematically indicated by 57, for energizing the sensor 51 and for picking up the signal generated by the latter. Said signal is sent to a central unit 59 connected to the system 47 for supplying power to the electrical resistance 41.

The temperature sensor may also consist of an infrared sensor which does not require contact with the blades. In this case it may be mounted in a fixed position so as to dispense with the need for a rotating commutator for receiving the sensor signal. The device described hitherto operates in the manner illustrated below. Before commencing processing of the web material N, the electrical resistance 41 is heated by means of the power supply system 47 until the temperature of the rotating cylinder 3 - detected by the sensor 51 - reaches a desired value. Heating is obtained by means of irradiation. The temperature value to which the rotating cylinder 3 is heated is chosen so as to be equal to or slightly higher than the maximum temperature which the device may reach during operation at running speed, as a result of the friction produced between the blades and on the bearings.

Once this temperature - and therefore the corresponding dimensions of all the mechanical members subject to thermal expansion - has been reached, the device may commence operation. The adjustments in the position of the various members and in particular the rotating cylinder 3, the fixed blade 7 and the rotatabie blades 5 on the cylinder 3 are performed so that the interference between the rotatabie blades 5 and the fixed blade 7 is correct at the temperature to which the rotating cylinder 3 is heated by means of the electrical resistance 41. During operation, this temperature is kept substantially constant, namely within a relatively limited range, through the control obtained by means of the central unit 59. The latter receives a temperature signal from the sensor 51 and controls the system 47 supplying power to the resistance 41 so that the latter emits the heat necessary for maintaining the operating temperature of the rotating cylinder 3. The power supply system 47 is able to operate, activating or deactivating the resistance 41 or suitably modulating the power used by said resistance.

It is understood that the drawing shows only one possible embodiment of the invention, the forms and arrangements of which may vary without departing from the scope of the idea underlying the invention. The presence of any reference numbers in the accompanying claims does not limit their protective scope, but merely has the function of facilitating reading thereof with reference to the description and the accompanying drawings.

Claims

1. A device comprising a first mechanical member and a second mechanical member, at least one of said members being movable, said members being arranged at a close distance so as to cooperate with each other, characterized by a heating element for heating at least one of said first and second members so as to maintain the dimensional stability thereof.

2. Device according to Claim 1 , characterized in that said first mechanical member is a rotating member carrying one or more rotatabie blades and said second mechanical member comprises a fixed blade, said two mechanical members forming a perforating device for producing perforating lines on web material.

3. Device according to Claim 2, characterized in that said heating element heats said rotating member and/or said rotatabie blades.

4. Device according to Claim 1 , 2 or 3, characterized by a temperature sensor and by a control unit connected to said temperature sensor and to said heating element, said control unit keeping the temperature of the heated member at a value controlled by means of said heating element.

5. Device according to one or more of the preceding claims, characterized in that said heating element comprises an electrical resistance.

6. Device according to Claims 2 and 5, characterized in that said rotating member has an axial cavity and in that said electrical resistance of the heating element is arranged inside said axial cavity.

7. Device according to Claim 6, characterized in that said axial cavity extends over the whole length of the rotating member and is open at its end so as to allow the connection of said electrical resistance to an external power supply line.

8. Device according to Claim 7, characterized in that said axial cavity has two end openings.

9. Device according to Claim 8, characterized in that it comprises a support cable which is tensioned between two fixed points and extends along said axial cavity and projects from the two openings and which supports said resistance inside the axial cavity.

10. Device according to Claim 9, characterized in that said resistance does not rotate together with the rotating member and does not make contact therewith, heating occurring by means of irradiation.

11. Device according to at least Claims 2 and 4, characterized in that said temperature sensor is mounted in the vicinity of the rotatabie blade or blades supported on the rotating member.

12. Device according to at least Claim 4, characterized in that said sensor is an infrared sensor which detects the temperature without making contact with the heated member and is kept in a fixed position.

13. Device according to Claim 11 or 12, characterized in that said rotating member has a central body and an external shell, in that the external shell and the central body are made of materials which have a different thermal expansion coefficient and in that the temperature sensor is associated with the external shell which supports the rotatabie blades or blade.

14. A method for controlling the dimensional stability of at least a first mechanical member cooperating with a second mechanical member, characterized by heating at least one of said mechanical members to a controlled temperature value and keeping said controlled temperature value within a temperature range during operation of said first and second mechanical members.

15. Method according to Claim 14, characterized in that said first mechanical member is a rotating member supporting at least one rotatabie blade of a perforating device so as to produce perforated lines in web material and said second mechanical member is a fixed blade cooperating with said rotatabie blade.

16. Method according to Claim 15, characterized by heating said rotating member.

17. Method according to one or more of Claims 14 to 16, characterized by detecting the temperature of at least one point of the heated member and supplying energy to a heating element depending on the temperature detected so as to maintain said heated member at a temperature within a controlled range.

18. Method according to Claims 16 and 17, characterized in that said point at which the temperature is detected is close to said at least one rotatabie blade.

19. Method according to Claim 16, characterized in that said rotating member is heated by means of irradiation.

20. Method according to at least Claim 16, characterized in that said rotating member is heated by means of an electrical resistance.

21. Method according to at least Claim 16, characterized by providing an axial cavity inside said rotating member and arranging a heating element inside said axial cavity.

22. Method according to Claim 21 , characterized in that said heating element comprises an electrical resistance.

23. Method according to Claim 22, characterized by supporting said electrical resistance in a fixed position inside said axial cavity.

24. Method according to Claim 23, characterized by supporting said electrical resistance by means of a cable which is tensioned inside said axial cavity, emerges from the latter at the two ends of the rotating member and is attached at two external points to the rotating member so as not to rotate with said member.