WO2008096037A1

WO2008096037A1 - Method of utilizing a drive capacity reserve in winding of a fiber web

Info

Publication number: WO2008096037A1
Application number: PCT/FI2008/050031
Authority: WO
Inventors: Asko Heikola; Pertti Vainio
Original assignee: Metso Paper, Inc.
Priority date: 2007-02-06
Filing date: 2008-01-31
Publication date: 2008-08-14
Also published as: FI20070108A; EP2117981A1; FI20070108A0; FI119806B

Abstract

The present invention relates to a method of utilizing a drive capacity reserve in winding of a fiber web. The method described in the present the invention may particularly advantageously be applied in connection with web winding machines in which one or several fiber web rolls and /or sets are formed from one reel. It is characteristic of the method of the invention that the changing acceleration and/or deceleration capacity of the electric drive is utilized during the treatment of the web reel to be unwound in the web reeling machine.

Description

METHOD OF UTILIZING A DRIVE CAPACITY RESERVE IN WINDING OF A FIBER WEB

(001) The present invention relates to a method of utilizing a drive capacity reserve in the winding of a fiber web. The method described in the present invention may particularly advantageously be applied in connection with web winding machines in which one or several fiber web rolls and /or sets are formed from one fiber web reel.

(002) In many varying applications of the web winding in the paper industry, a roll must be accelerated to the normal drive velocity or decelerated from it to a full stop or close to a stop. In the finishing, a fiber web reel is unwound for a coating unit, for super calendering, soft calendering, intermediate winding, rewinding or for a slitter winder. In all these applications the fiber web reel must be accelerated to the speed of the finishing treatment device as quickly as possible in order to maintain the maximum production capacity. Naturally, the finishing produces one or more rolls which in turn must be accelerated to full speed and then decelerated to a stop before they can be transferred either to another finishing treatment stage or to packing.

(003) It is known from prior art to limit the acceleration and deceleration values in the unwinding while the diameter of the reel is the largest. This is done in view of the torque transfer capacity of the existing reeling drum mandrel, the mechanical drive or the core chuck, or in order to optimize the size of the electric drive. These techniques have conventionally employed the simple limit value approach method, according to which higher acceleration and deceleration speeds can be introduced when the diameter of the web reel has fallen below a predetermined fixed limit value. An essential feature in these techniques is the absence of online optimization or dynamic calculation, and/or the limitation merely to the dependency on the diameter.

(004) Then it is typical that the dimensioning of the electric drives is designed based on the "worst case" scenario, in other words they are dimensioned for the greatest possible inertia, for the highest possible web tension, for the highest possible web speed and at the slitter for the least advantageous torque difference possible of the winding rolls and the maximum acceleration conceivable. Further, the size or efficiency classification of the drives sometimes results in unavoidable over- dimensioning. Thus, as the electric drive is dimensioned supposing that at a drive situation the maximum values of all the winding parameters are needed simultaneously, the capacity of the electric drive is underutilized most of the time.

(005) It is also known from prior art to use for each paper grade accelerating and deceleration values which depend mainly on the strength properties of the grade. Also the accelerating and decelerating of the freely rotating rolls may impose limitations to the usable acceleration and deceleration values, depending on the paper grade.

(006) A method in accordance with WO publication no. 2004/044665 of controlling the winding is still worth mentioning as prior art. Although the method discussed in the publication is quite advanced, the described method of vibration dampening limiting the drive velocity has the drawback that some of the capacity is lost when the method is employed.

(007) Thus, no prior art technique of controlling the winding allows taking full advantage of the electric drive capacity for each paper grade. If the acceleration and deceleration values of the rolls could be optimized according to the properties of each paper grade it would be possible to use lower operational speeds and still achieve the same production capacity as before. At the same time the process risks would decrease. These process risks are for example: web cuts, roll dislocations caused by them, and the machine damages caused by the dislocations standstills caused by the web cuts the durations of which have been found to increase as a function of the operating speed as both the number of web cuts and the volume of paper waste generated by them increase as a function of the operating speed; - production disturbances caused by the operators; and production disturbances caused by the machinery. (008) An object of the present invention is to reduce the number of web cuts and the downtime caused by them.

(009) Another object of the present invention is to utilize the capacity of the winder drives to the maximum extent.

(0010) In order to solve at least some of the problems described above and in order to achieve at least some of the above objectives, it is suggested as a direct solution to use as strong accelerations and decelerations as possible and lower operating speeds in the winding than according to the prior art.

(0011) The present method provides for example the following advantages: the method can be employed both in new deliveries and in improving the capacity of existing machinery; - the duration of the standstills caused by web cuts grows shorter as a function of the deceleration as a faster stopping decreases the volume of wasted paper; and the machine can be stopped and restarted faster in connection with a production disturbance.

(0012) It is a characterizing feature of the method of the invention for utilizing the drive capacity reserve in the winding of a fiber web to utilize the changing acceleration and/or deceleration capacity of the electric drive during the treatment of the unwinding web reel in the web reeling machine.

(0013) It is a characterizing feature of the method according to another preferred embodiment of the invention that the acceleration and/or deceleration capacity of the electric drive is calculated or modeled dynamically during a production cycle.

(0014) It is a characterizing feature of the method according to a third preferred embodiment of the invention that the changing of the acceleration and/or deceleration capacity of the electric drive has been predetermined. (0015) It is a characterizing feature of the method according to a fourth preferred embodiment of the invention that the inertia of the accelerating or decelerating web reel in the unwinding is taken into account in the calculation.

(0016) The rest of the characterizing features of the method of the invention are disclosed in the appended patent claims.

(0017) An exemplary application of the invention is a slitter winder in which paper or board from a machine reel is unwound, slit in the longitudinal direction into several partial webs and rewound to smaller rolls. Generally, but not necessarily, two control systems are used in web winding applications. One of them controls the web winding machine itself and the other one its electric drives. A web winding application can also be practiced with one control system, only, which guides both the web winding machine and the electric drives.

(0018) In the following, the method of the invention for utilizing the drive capacity reserve in the winding of a fiber web is described more in detail as illustrated by a preferred example.

(0019) In a method according to a preferred embodiment of the invention the initial situation is that the control system of the web winding machine has been told what kind of a web is treated and what kind of end products, that is web rolls, are needed. Then the control system of the web winding machine sends to the controls system of the electric drive the required data such as for example the initial velocity of the web, the initial web tension, the target velocity of the web, the target tension and at the slitter the torque difference of the winding rolls, the target torque difference and the specific gravity of the web and the dimension data of the web rolls. In some situations also other additional data may be needed and, on the other hand, sometimes all the above date is not needed. Based on the information received the control system of the electric drive determines what the electric drive is capable of performing. In other words, the maximum available/obtainable values of the acceleration of the unwinding and the rewinding in case of a starting web winding, or correspondingly, the maximum available/obtainable values of the deceleration of the unwinding and the rewinding in case of an ending web winding. To be more precise, the control system calculates the maximum acceleration and deceleration that each single electric drive can provide for the roll or cylinder it drives. Based on, for example, the diameter and web specific gravity data the control system of the electric drive can calculate for example the inertia of the web reel, whereby the maximum acceleration the drive can provide for a full web reel can be calculated, when the drive properties of the web reel to be unwound are known. Quite in a corresponding way the control system can calculate the inertia of a web roll to be rewound for example at the beginning of the deceleration whereby the maximum deceleration the drive can provide for the roll, can be calculated. The control system of the electric drive transmits the data in question to the control system of the web winding machine, which compares it with the values allowed for the web to be treated. In other words, if either a maximum value of acceleration or deceleration of a roll given by the control system of the electric drive exceeds the value allowed for the web to be treated the control system of the web winding machine transmits the value allowed for the web to the control system of the electric drive for use as the design value based on which the control system of the electric drive guides the drive of each roll. On the other hand, if the maximum values of the electric drive are lower than the ones allowed for the web the control system of the web winding machine accepts the values and informs them to the control system of the electric drive for use as design values. In this embodiment, the control system has been designed so that only one value is determined for each acceleration and deceleration phase and that is used during the entire acceleration or deceleration. If only one control system guides the web winding machine the procedure described above is performed entirely by that control system.

(0020) In connection with the above embodiment, a special case is worth mentioning in which web is conveyed expressly from a machine reel to several successive web rolls. Then, according to the embodiment described above, at the beginning of each slitting cycle, or a so-called set, which thus means the slitting of one web roll, the maximum acceleration and deceleration readings are determined in the drive control system for both the machine reel and the web roll in the way described above. The control system of the slitter- winder compares these values with the values allowed for the web and instructs the drive control system to use the smaller one of the values of the comparison as the constant for both the acceleration and the deceleration values. The end result of this method is that the machine reel is driven with as many different acceleration and deceleration values as there are successive web rolls obtained from the machine reel, and that each web roll has acceleration and deceleration values of its own which differ from those of the previous and the following web roll, presupposing naturally that the maximum acceleration and deceleration values of the drives are determining and not the limit values specific to the web material. Thus, by calculating the acceleration and deceleration values specific to each set, the varying acceleration and/or deceleration capacity obtained from the electric drive during each running cycle can be utilized.

(0021) Several different variations of the invention described above in an exemplary manner are possible. In a method according to another preferred embodiment of the invention the control system of the web winding machine sends continuously or intermittently information for example on the diameters of the unwinding web reel and the rewinding web roll based on which information the control system of the electric drive can calculate new values for the inertias of the reel and the rolls and using it thus further calculate new values for the acceleration and deceleration of the reel and rolls mentioned which the electric drive or the brake generator of each roll is capable of performing at that torque. When this data is transmitted to the control system of the web winding machine it in turn performs the comparison described above and gives the design values to the drive control system. In other words, in this embodiment both the unwinding machine reel and the rewinding roll/rolls are monitored continuously or intermittently. The advantage provided by this embodiment is that, as far as the strength properties of the web allow, the maximum acceleration and deceleration values can be used all the time which in turn permits maximum production capacity. Thus, this embodiment allows best utilizing the acceleration and/or deceleration capacity of each roll changing during the drive cycle and obtained from the electric drive. (0022) Yet another embodiment of the invention is a method which uses for example the design values obtained when a corresponding product has been produced before. These values can in that case at first be entered into the control system of the web winding machine which further transmits them to the drive control system. In this embodiment it is of course possible to use either the control method based on the constant acceleration and deceleration, or acceleration and deceleration values obtained from constant or intermittent monitoring and changing constantly or intermittently. If only one control system guides the web winding machine the above procedure is performed entirely by that control system.

(0023) A third possibility provided by the invention is to create a calculatory model estimating the change of the inertia of the web reel/rolls as a function of as many reel/roll parameter as possible and to use that instead of real measurements.

(0024) The most advantageous applications of the above invention are web winding machines in which one or several smaller rolls/sets are formed from one reel. If only one control system guides the web winding machine the above procedure is performed entirely by that control system.

(0025) It should be noted from what has been disclosed above that the term electric drive has been used generally. In this context it means alternating current, direct current or servo drives used to rotate the cylinders, reeling mandrel, cutting blades and web reel/rolls. The electric drive comprises electric motors, frequency transformers and/or input devices including input groups and transformers. The above description does not, however, intend to specifically limit the term "electric drive". Further the terms machine reel and web roll have been used in the examples above. They must be understood to cover, in addition to winding between a machine reel and a web roll, also winding between two machine reels or two web rolls. Thus the winding can take place both from one machine reel to another, from a machine reel via a slitter to several partial web rolls and from one web roll to another web roll. The last- mentioned alternative comes into question for example in connection with rewinding or intermediate rewinding when the rewinding or intermediate winding is stopped for a patch-up of a hole, for making a connection or for a check-up.

Claims

We claim:

1. A method of utilizing a drive capacity reserve in winding of a fiber web, characterized in utilizing the changing acceleration and/or deceleration capacity of the electric drive during the treatment of the unwinding web reel.

2. A method according to claim 1, characterized in that the acceleration and/or deceleration capacity of the electric drive is calculated or modeled dynamically during a production cycle.

3. A method according to any of the preceding claims, characterized in that the change of the acceleration and/or deceleration capacity of the electric drive has been predetermined.

4. A method according to any of the preceding claims, characterized in that the inertia of the web reel /roll to be accelerated or decelerated during the unwinding is taken into account in the calculation.

5. A method according to any of the preceding claims, characterized in that the inertia of the web roll/rolls to be accelerated or decelerated during the rewinding is taken into account in the calculation.

6. A method according to any of the preceding claims, characterized in that the web tension used and the torque difference between the winding drums at the slitter is taken into account in the calculation.

7. A method according to any of the preceding claims, characterized in that during the acceleration and deceleration, fixed or intermittently changing acceleration and deceleration values are used, which have been determined prior to the beginning of the acceleration or deceleration.

8. A method according to any of the preceding claims, characterized in that the change of the inertia of the reels/rolls is estimated and the estimate is used in the calculation instead of real measurements.

9. A method according to any of the preceding claims, characterized in that the properties typical to the paper grade are taken into account when deciding on the acceleration and deceleration values for the winding.

10. A method according to any of the preceding claims, characterized in that, when determining the acceleration and deceleration values, the acceleration and deceleration values based on the running parameters determined based on the typical paper grade properties are compared with the values obtained from the control system of the electric drive, and the lower ones of these are chosen to serve as the design values for the electric drives.

11. A method according to any of the preceding claims, characterized in that the web roll is a machine reel.

12. A method according to any of the preceding claims, characterized in that the web roll is a web roll of a rewinding or intermediate winding.