METHOD AND APPARATUS IN UNWINDING

Abstract: In the method in unwinding, paper web (W) is discharged from a reel (R1) that is becoming empty and the paper web of a new full reel (R2) is spliced at the discharge speed to the paper web discharged from the reel that is becoming empty. The terminal end point (L) of the web of the reel (R1) that is becoming empty is stored as information indicating its position in the longitudinal direction of the web in a readable memory (M) corresponding to the reel. During the discharge the distance travelled by the web is determined and compared to the memory, and when there is a predetermined length of web to the terminal end point (L) remaining on the reel (R1) that is becoming empty, a splicing command is given, whereafter the leading end of the paper web of a new full reel (R2) is spliced to the paper web (W) being discharged.

Description: Method and apparatus in unwinding The invention relates to a method and apparatus in unwinding. The invention relates to the splicing phase of a continuous unwind, in which the web of a new machine reel brought to the unwind is attached at full speed to the web of the machine reel that is becoming empty by cutting the web and pressing the web of the machine reel that is becoming empty against the splice in the new machine reel. In off-machine coating machines for paper, a continuous unwind is used in which a new, full machine reel that is brought to the unwind is attached to the end of the paper web in the machine reel that is becoming empty. In present-day fast coating machines the splicing method is essentially the same, i.e. a splice is prepared in the leading end of the web of a new machine reel by means of a two-sided adhesive tape, the splice being attached on the surface of the reel by pieces of fastening tape. The surface speed of the new machine reel is accelerated to be equal to the running speed of the machine, i.e. the web speed of the paper web discharged from the reel, whereafter the web of the reel becoming empty is pressed against the aforementioned splice for example by means of a roll or a brush. The old web is cut with a blade above the splice. The splicing in an unwind has become problematic at current running speeds (1200 — 1600 m/min). Therefore, the running speed of the coating machine often has to be dropped for the duration of the splicing. A negative pressure is generated in the so-called splicing gap between the splicing roll and the machine reel, which are brought close to each other at high speed, which negative pressure can be pulsating if the new machine reel is out-of-round. The negative pressure tends to draw the old web partly against the splice already before the splicing, and causes fluttering of the old web. Furthermore, the negative pressure tends to detach the tape splice from the surface of the new machine reel, wherein the new machine reel opens before splicing. In order to make the web travel in a controlled manner, a bend is necessary at the splicing roll, which, in turn, requires stretching of the web, when the splicing roll is rapidly struck against the surface of the machine reel. The aim is to keep the tension peak caused by the stroke of the roll on a low level, by using a small splicing gap (8 to 12 mm), which causes a strong phenomenon of negative pressure. Even the currently used bending angle causes a problematic tension peak in the web. At higher running speeds, an even larger bending angle would be necessary. A solution to this problem is presented in the Finnish patent 100323, and in the related US patent 5709355. The splicing device comprises a splicing roll, by means of which the the web of the machine reel that is becoming empty is pressed against the splice in the new machine reel, and at least one auxiliary roll. The splicing roll and the auxiliary roll are attached to a lever device, which is journalled at an articulation point between the axes of the rolls in such a way that before the splicing and in the splicing the web travels in such a manner that the length of the web is substantially the same both in the splicing position and in the basic position of said rolls. The aforementioned solution has made it possible to eliminate the problems occurring in the vicinity of the splicing gap, and it enables a splicing with high running speeds of even over 1600 m/min. In the so- called flying splicing described above, the control of the cut tail of the old reel spool has become problematic at high running speeds and especially in connection with heavy paper grades. After the splicing, the aim is to rapidly stop the reel spool that has formed the core of the reel. The paper left on the reel spool must not be discharged therefrom to such an extent that it cannot be controlled by means of air blows. The discharged paper web as well as the pieces, so-called chaff, detached therefrom, tend to enter the nip between the splicing roll and the machine reel rotating in the primary station. This will almost always cause a break at the splicing device. Moreover, pieces detached from the web often travel along with the air currents on top of the web (e.g. from the sides of the machine), which also causes a break. By means of air jets it is not possible to fully control the paper travelling at high speed and the pieces detached therefrom. The length of the paper discharged after cutting from the reel spool that is becoming empty is proportional to the gravity of the problem. In constructions currently in use, the aim is to minimize the length of the discharged paper with a shortest possible braking time. However, the braking time is increasing, because the speeds of the machines are growing, and as the sizes of the machine reels grow, the diameters of the reel spools grow as well. Even the present-day speeds and diameters of the reel spools set high demands on the braking devices, and the brakes have to be maintained and changed often, which increases the operating costs. It is an aim of the invention to eliminate the aforementioned drawbacks and to present a method and apparatus, by means of which the problems caused by the splicing and the paper discharged after cutting can be avoided. To achieve this purpose, the method is primarily characterized in what will be presented in the characterizing part of the appended claim 1. The invention is based on the idea that the end point of the discharge- able web on the reel is stored in a memory, which indicates the location of the end point in the longitudinal direction of the web, and when the web is discharged from the reel, the length of the discharged web is simultaneously monitored and compared to the memory. The comparison indicates the remaining amount of paper in linear measure units. When the end point of the web is approaching, it is possible to give a splicing command when a predetermined length is left on the reel. Thus, the rest of the length of the web on the reel that is becoming empty can be minimized, and this short web section which can still issue from the roll can be controlled more easily. In practice it is possible to proceed in such a manner that for example in a rereeler before the coating machine after the tail threading, an attachment point for the web is produced on the bottom of the machine reel, for example a two-sided tape, or glue is fed thereto. The end point of the web can be attached either on the surface of the reel spool or on the paper layers on the bottom after a few windings, wherein the adhesive substances do not enter in contact with the surface of the roll. Thereafter the person operating the machine performs the necessary steps by means of a storing device, for example a terminal. The attachment point is transferred to the memory as a position information indicating its location in the longitudinal direction of the machine. Each machine reel is allotted a memory of its own, which can be read later under the control of a program in connection with unwinding. It is possible to use for example a fault map known as such as the memory. Thanks to an identification system for the machine reel, the reel is automatically accompanied with the machine reel specific fault map when passed to the unwinding for the paper coating machine. The edge of the paper is provided with locating marks at regular intervals, as well as beginning and end marks of the reel, by means of which the fault map is synchronized in the unwinding. In this system, the point in which the unwinding of the reel is proceeding is known with the accuracy of 1 to 2 m. The invention is utilized to set the time of the splicing in the unwinding. The system gives advance information in the form of a signal when the end point of the web is approaching. On the basis of this information, the drive is capable of accelerating the full machine reel to the web speed at the correct time. Another signal gives a splicing command, whereafter the splicing sequence (striking the web onto the surface of the machine reel and cutting the web) is conducted when the full machine reel is in the correct position. The timing of the splicing command is set in such a way that the end point of the web, whereafter the web can no longer get loose from the reel, is brought as close to the surface as possible. In the following, the invention will be described in more detail with reference to the appended drawings, in which Fig. 1 shows a side-view of the apparatus according to the invention, Fig. 2 illustrates the timing of different commands in connection with the splicing process, Fig. 3 shows the apparatus of Fig. 1 in a situation where another method is applied, and Fig. 4 illustrates the provsion of a special attachment point in a reel that is becoming empty. Fig. 1 shows a side-view of an apparatus, which is of the type presented in the aforementioned Finnish patent 100323. In the apparatus, a web W is continuously discharged from machine reels brought thereto, the machine reels being produced at an earlier reeling stage, and the web is passed on to a finishing device of the paper web, for example to a coating machine. The apparatus is provided with a secondary drive 1 , which rotates a machine reel R1 that is becoming empty, and with a primary drive 2, which rotates a new, full machine reel R2 that has been brought to the apparatus. The main principle of a continuous unwinding is to bring reels successively to the apparatus in such a manner that the full reel is brought to be rotated by the primary drive 2, its paper web is attached to the web W issued from the reel that is becoming empty, which web W is then cut, whereafter the web is discharged from the full reel rotated by the primary drive 2. When there is a certain amount of web left on the reel rotated by the primary drive 2, it is transferred to be rotated by the secondary drive 1 , and a new, full reel is brought to the primary drive, whereafter the webs are attached to each other again in the above-described manner. The transfer of the full reel to the primary drive, the removal of the empty reel from the secondary drive and the change of the reel being unwound from the primary drive to the secondary drive can be performed by using known solutions, and since they are not part of the invention, they will not be described in more detail in this context. Fig. 1 describes a change situation, in which the web of the full machine reel R2 that has been brought to the primary drive in a primary station is joined to a web discharged from the machine reel R1 that is becoming empty at the secondary drive 1 in the secondary station. The circumference of the full machine reel R2 is bounded by a splicing station provided with a splicing roll 3 guiding the web W discharged from the reel R1 that is becoming empty in close proximity to the outer surface of the circumference in the full machine reel R2 rotated by the primary drive 2, in such a way that a splicing gap of a given width is formed between the web and the machine reel R2. In the situation of Fig. 1 , the splicing is performed by striking the splicing roll 3 rapidly towards the opposite surface of the reel, wherein the splicing gap is closed. The splicing stroke is synchronized by striking the web W against the surface of the full machine reel R2 when the attachment point on the surface of the reel, for example a splicing tape, enters the splicing station. This point is marked with the letter S. The tape assembly in question can be for example a tape assembly in the transverse direction of the web by means of a tape whose both sides are adhesive, the tape assembly being attached to the end of the web of a full machine reel R2 and having typically the shape of a saw blade or the like for the purpose of improving the grip. Furthermore, the cutting of the web to be discharged is conducted in a synchronized manner with the splicing stroke by utilizing a cutting device illustrated by arrow C, which cutting device performs the cutting stroke and is located before the splicing roll 3 in the travel direction of the web. The cutting device can be e.g. a striking blade cutter. The drawing also illustrates an auxiliary roll 4 cooperating with the actual splicing roll 3 and guiding the discharged web W after the splicing station (splicing gap). The auxiliary roll is attached together with the splicing roll 3 to a common lever 5 articulated at a point of articulation 5a located between the axes of the rolls 3 and 4. When the splicing roll 3 is struck on the surface of the full machine reel R2 by means of an actuator (not shown), the motion is transmitted to the auxiliary roll 4 by means of the lever, this motion of the auxiliary roll backwards along a path determined by the point of articulation compensating the stretch otherwise produced on the web. In Fig. 1 , full lines illustrate a situation where the web W is struck against tiie surface of the reel R2 by means of the splicing roll 3 to form a splicing nip, and the point of attachment S is entering the nip into contact with the web W travelling on the surface of the splicing roll 3. The initial situation where there is a splicing gap between the splicing roll 3 and the reel R2, is illustrated by means of broken lines. After the web discharged from the reel R1 becoming empty has been cut, part of the web still remains around the spool constituting the core of the reel, and it tends to continue its motion towards the splicing station, the shred, chaff etc. discharged therefrom causing problems. According to the invention, the amount of dischargeable web is minimized in such a way that the terminal end point of the web is attached for example by means of a glueing or a taping L provided on the bottom of the reel. This point is also entered in a readable memory M, which is connected to an electronic control unit D. When the web is discharged from the reel R1 , the distance travelled by the web is determined by means of a device for determining the distance by utilizing the locating marks on the edge of the web, which have been stored in the memory to synchronize the memory and the distance travelled by the web is compared with the memory M. In determining the distance i.e. the length travelled by the web, it is possible to utilize the measurement of a variable which is directly proportional to the length of the web such as time, i.e. the length is known when the running speed and the time elapsed is known. There are also other possible ways of determining the length, such as direct length measurement. The electronic control unit D, which has the date of the length of the web, gives a signal when there is a certain amount of web remaining on the reel that is becoming empty, and this signal can be given by means of the thickness measurement of the reel R1 known as such or the distance information of the memory M. Because of the signal, the primary drive 2 of the full reel R2 accelerates the reel into the web speed, i.e. its peripheral speed is increased to be equal to the speed of the web that is being discharged. The location (angular position) of the attachment point S on the surface of the full reel R2 is monitored for example by means of a sensor 6 located in the vicinity of the rotating reel, the sensor 6 transmitting the information to the control unit D. The location of the attachment point can be marked in a suitable manner in the reel by means of one more locating marks in such a way that the sensor 6 can give unambiguous information on the location of the point S at a given time. The splicing is conducted under the control of the control unit, when the following conditions are fulfilled successively: 1) Comparison with the memory M indicates that the distance to the terminal end point L equals a predetermined minimum length (splicing command), and 2) The attachment point S of the full machine reel R2 lies in such an angular position with respect to the splicing station that the splicing stroke can be conducted (splicing mark). To implement a reliable function, the splicing can be performed in such a manner that the splicing stroke is conducted only at the second splicing mark after the splicing command. The set minimum distance to the terminal end point L, when measured from the point where the web departs from the reel R1 that is becoming empty, can be twice the peripheral length of the full reel R2 with an added given safety distance corresponding to the error tolerance of the length measurement, which is, in any case, smaller than the peripheral length, and 3 m at the most. The error tolerance sufficient for the length measurement is advantageously only 2 m. Fig. 2 illustrates the progress of the splicing stage. On each revolution of the full reel R2, the splicing mark is obtained when the sensor 6 indi- cates that the attachment point S is in the correct position. The splicing command may be given at any time between two splicing marks, or simultaneously with a splicing mark. The splicing (splicing stroke and cutting of the web) is performed at the second splicing mark after the splicing command. The first splicing mark follows after the splicing command or occurs simultaneously with the same. Thus, if the minimum distance to the terminal end point L that triggers the splicing command, i.e. the minimum length of the web W remaining on the reel R1 , is twice the peripheral length of the full reel R2 plus the safety distance, it is possible to ensure that the web W on the reel does not run out before the splicing, because the reel R may rotate yet two revolutions at the most before the splicing. Thus, the length of the web left after the cutting around the reel spool is in its minimum, i.e. it is only the aforementioned back-up distance + length measurement error + distance from the discharge point to the cutting point determined by the cutting device C. When a safety distance of 2 m is used, the length of the web which tends to be discharged from the cutting point towards the splicing station is only the aforementioned 2 m, if the length measurement error = 0. Correspondingly, if the splicing command is given immediately before the splicing mark or simultaneously with the splicing mark, the full reel R2 rotates only one revolution, wherein the amount of web remaining on the reel R1 equals one peripheral length of the full reel R2 + safety distance. This maximum amount is considerably small when compared even to the optimal amount obtained with the present methods. For example with the peripheral length of the machine reel of 11 m and with a safety distance of 2 m (length measurement error = 0), the amount that tends to be discharged towards the splicing station is only 13 m, which is less than one third of the amount obtainable with the present methods (45 m). This length can be easily controlled by means of air jets or other auxiliary means, by means of which the travel of the web to the nip between the reel and the splicing roll is prevented. Fig. 3 presents an embodiment developed from the embodiment of Fig. 1. Here, the splicing principle and the measuring procedures are the same as those presented in Fig. 1 , and the same parts are marked with the same reference numerals as in Fig. 1. The essential idea of the method is that the rotation of the full reel R2 and the reel R1 that is becoming empty is synchronized in such a way that the splicing mark is obtained when there is less than one revolution of web W remaining on the reel R1 to the terminal end point. Fig. 3 illustrates an ideal situation where the terminal end point L is located at a point where the web departs from the reel R1 , i.e. there is no dischargeable web left. Thus, the web W is taut between the splicing station and the core of the reel R1 , and a separate cutting device is not necessarily required, but the web W is provided with a weakening P, at which point the web breaks as a result of the draw. This weakening is provided in the reel in con- nection with the formation of the reel at a distance from the terminal end point L, which is smaller than the distance between the core of the reel and the splicing nip in the unwind. Thus, the paper web W breaks in the point located before the splicing nip, when it is taut straight in a linear position between the core of the reel R1 and the splicing nip. The transverse weakened point is obtained in the paper web by press- ing the web against a surface with a transverse member, for example a perforating blade, in the rereeler preceding the unwind. In practice, the synchronization of the rotation of the reels is implemented in such a way that the web is discharged at the running speed from the reel R1 that is becoming empty, and the on the basis of the length determination data obtainer on the traveling web, information in the memory M and the position information given by the sensor 6, the rotation of the full reel R2 is synchronized in such a manner that the attachment point on its surface is in the correct position in view of the splicing at that stage when there is a predetermined minimum amount of web remaining on the reel R1. The reel R1 that is becoming empty can also be provided with locating mark/marks to facilitate this synchronization, wherein the secondary station also comprises a measuring device indicating the position of these marks. Fig. 3 shows a sensor 6 connected to the control unit D, by means of which sensor the position of the locating mark/marks is monitored. The locating mark/marks can be fixed e.g. to the end of the reel spool. It is possible that in the alternative shown in Fig. 3, a longer "tail" of the old web remains parallel with the new web discharged from the full reel R, because the distance to the weakening WP from the splicing point determined by the attachment point S can be longer than that shown in the situation of Fig. 3, if there is still web left on the reel R1. Fig. 4 illustrates the possibility of making such a tail neat by producing a trans- verse adherent area WA in the point located before the weakening WP in the discharge direction of the web, the surface of the adherente area being capable of adhering to the surface of the web discharged from the reel R2 after the splicing point. As can be seen in Fig. 4, the area can be formed of a transverse strip whose surface is provided with a substance capable of adhering to the paper web. For example, the strip can be made of two-sided adhesive tape, which is positioned parallelly to the weakened point. To prevent the area WA from adhering to the bottom of the reel R1 , the reel can be provided with a release area WB opposite the adherent area. The surface of the release area is of suitable material, such as silicone, used for example in release papers. Such a release material can also be attached as a strip on the bottom of the reel by means of glue. As can be seen in the drawings, in the bottom of each reel to be reeled in the unwind, there is a terminal end point L entered in the memory such as a fault map, possibly a weakened point WP and an adherent area WA and on the surface of the reel an attachment point S for splicing. The invention is not restricted to the embodiments described above, but it can be modified within the scope of the inventive idea presented by the claims. As a readable memory it is possible to use a fault map describing the quality of the formed reel at different points, the fault map being supplemented with the location of the terminal end point L. In the longitudinal direction of the paper web W there are pacing marks, marked for example on the edge of the paper web, which pacing marks can be detected by the device from the web that is being discharged for determining the distance travelled. The invention is not, however, restricted solely to the use of pacing marks in the determination of length. In its simplest form the memory can be merely a numerical value, which indicates the distance from an easily recognizable point in the web on the reel to the terminal end point L, wherein the distance travelled by the web after this point is measured and compared to the aforementioned stored numerical value.

Claims: Claims: 1. Method in unwinding, in which paper web (W) is discharged from a reel (R1) that is becoming empty and the paper web of a new full reel (R2) is spliced at the discharge speed to the paper web discharged from the reel that is becoming empty, characterized in that the terminal end point (L) of the web of the reel (R1) that is becoming empty is stored as information indicating its position in the longitudinal direction of the web in a readable memory (M) corresponding to the reel, the distance travelled by the web is determined during the discharge and compared to the memory, and when there is a predetermined length of web remaining to the terminal end point (L) on the reel (R1) that is becoming empty, a splicing command is given, whereafter the leading end of the paper web of a new full reel (R2) is spliced to the paper web (W) being discharged. 2. Method according to claim 1 , characterized in that the splicing command is given when the amount of web remaining on the reel (R1) that is becoming empty, calculated from the discharge point to the ter- minal end point (L) is less than three times the peripheral length of the new, full reel (R2). 3. Method according to claim 2, characterized in that the splicing command is given when the amount of web remaining on the reel (R1) that is becoming empty is twice the peripheral length of the new, full reel (R2) plus a safety distance of 3 m at the most, preferably 2 m at the most. 4. Method according to claim 2 or 3, characterized in that the location of an attachment point (S) situated on the surface of the full reel (R2) in a suitable position with respect to the splicing station is registered as a splicing mark within each revolution of the reel (R2), and a splicing mark obtained after the splicing command is utilized to conduct a splicing of the leading end of the paper web of the full reel (R2) to the paper web (W) that is being discharged. 5. Method according to claim 4, characterized in that the splicing is conducted at a splicing mark that is next after a splicing mark registered simultaneously with the splicing command or after it. 6. Method according to claim 1 , characterized in that by means of reading the memory (M), the rotation of the new, full reel (R2) is synchronized before the splicing in such a way that the attachment point (S) on the surface of the reel enters the splicing station, when there is a predetermined minimum length of web to the terminal end point (L) remaining on the reel (R1) that is becoming empty. 7. Method according to claim 6, characterized in that the minimum length is one revolution at the most around the reel (R1) that is becoming empty. 8. Method according to claim 6 or 7, characterized in that the web (W) is provided with a weakening (WP), which is located before the splicing station at the moment of splicing, wherein the web breaks at the location of the weakening. 9. Method according to claim 8, characterized in that the web (W) is provided with an adherent area (WA) located in the discharge direction before the weakening (WP), which adheres to the surface of the paper web of the new reel (R2) after the attachment point (S). 10. Method according to any of the foregoing claims, characterized in that the terminal end point (L) of the web of the reel (R1) that is becoming empty is determined at the reel formation stage that precedes the unwinding by attaching the web to the bottom of the reel and by storing said point as a position information in the longitudinal direction of the web in the readable memory (M) describing the reel. 11. Method according to any of the claims, characterized in that the readable memory (M) used is a fault map produced at the reel forma- tion stage that precedes the unwinding. 12. Apparatus in unwinding which contains means for rotating a reel (R1) that is becoming empty, and means for guiding a paper web (W) discharged therefrom via a splicing station, means for rotating a full reel (R2), wherein the full reel (R2) is positioned in such a manner that its outer circumference is bounded by the splicing station, and a splicing device, such as a splicing roll (3) which is arranged to splice the paper web on the full reel to the paper web (W) discharged from the reel (R1) that is becoming empty, characterized in that the apparatus comprises a memory (M) in which the terminal end point (L) of the web of the reel (R1) that is becoming empty is stored as information indicating the position of said point in the longitudinal direction of the web, a distance determination device for determining the distance travelled by the discharged web (W), and a control unit (D) which is connected to the distance determination device and to the memory and arranged to read the memory and to compare the distance to the memory (M), wherein the control unit (D) is arranged to give a splicing command, when a predetermined length of web to the terminal end point (L) remains on the reel (R1) that is becoming empty. 13. Apparatus according to claim 12, characterized in that it comprises a sensor (6) connected to the control unit (D), which is provided in a primary station of the full reel (R2) and arranged to indicate the position of one or more locating marks attached to the reel (R2). 14. Apparatus according to claim 13, characterized in that it comprises a second sensor (6') connected to the control unit (D), which is provided in a secondary station of the reel (R1) that is becoming empty and arranged to indicate the position of one or more locating marks attached to the reel (R1). 15. Apparatus according to any of the foregoing claims 12 to 14, characterized in that the distance determination device is arranged to detect the locating marks provided at different locations in the longitudinal direction of the web, and the memory (M) contains information on these locating marks.

Inventors: ESKOLA TIMO, RIIHELAE VESA, ESKOLA, TIMO, RIIHELAE, VESA
Applicants: ESKOLA TIMO, RIIHELAE VESA, VALMET CORP, ESKOLA, TIMO, RIIHELAE, VESA, VALMET CORPORATION
Application year: 1999
Main classification: B65H19
IPC codes: B65H19, B65H21, B65H23