ROLL DRIVE FOR MOVING ROLLS

Abstract: A roll drive for moving rolls, the drive comprising a roll (1) connected to a moving structure (3), and a motor (2) arranged to rotate the roll and comprising a stator and a rotor. The motor of the roll drive is an axial flux motor (2) whose rotor shaft (5) is directly connected to a shaft (4) of the roll (1) so that the shaft of the roll supports the motor (2), and that the motor (2) is supported at the stator by means of a supporting arm (6) on said moving structure (3). The roll drive further comprises a frequency converter arranged to control the axial flux motor (2) fixed to the shaft (4) of the roll (1).

Description: ROLL DRIVE FOR MOVING ROLLS BACKGROUND OF THE INVENTION [0001] The present invention relates to a roll drive for moving rolls, the drive comprising a roll connected to a moving structure, and a motor ar- ranged to rotate the roll and comprising a stator and a rotor. [0002] Some rolls and operating positions of paper machines and other similar machines as well as of paper post-processing machines are movable. The movement can be from a few centimetres even to a couple of metres. Such rolls include, for instance, size press, calender and centre reeler rolls. In such objects, the torque produced by a motor rotating the roll has to be transferred to the moving roll. [0003] Previous known solutions are based on either a stationary motor and a complex mechanics connected thereto or a conventional motor fixed to a moving part of a machine. [0004] A stationary motor can be connected to a moving roll, for instance, by means of a long cardan, the joints of which allow the movement of the roll. It is also possible to use a belt transmission when a motor or other primary wheel of the belt transmission is mounted at the axis of movement. The complex mechanics then allows the roll movement and transmits the torque of the motor to the roll in spite of its movement. As a solution, the stationary motor with a transmission allowing the roll movement is expensive and takes up a lot of space. Because of the system's low natural vibration frequency in the direction of rotation, long cardans and belt drives cause control problems for the electric drive. Also the angular velocity variation caused by cardan joints reduces the accuracy of the control. The belt transmission requires maintenance and causes noise. [0005] In a solution model, a conventional motor can be fixed at its frame to a moving part of the machine and a motor shaft by means of a coupling to a roll to be used. Thus, despite the roll movement, the torque of the motor is transmitted via the coupling to the roll to be used. This kind of solution, however, increases the mass of the moving mechanics and the need for space considerably, because the motor requires a mounting base and the shaft needs a coupling in order for it to be fixed to the roll shaft. When a conventional squirrel-cage induction motor is used, also a reduction gear must often be used in order to achieve the required torque. The reduction gear fur- ther increases the mass of the moving mechanics. The publication US 3997952 discloses such a roll drive to which a motor is connected, and a reduction gear transmitting the torque from the motor to the roll. [0006] The publication DE 4422097 A1 discloses a drive arranged to rotate a cylinder of a printing machine and comprising a radial type of motor as a motor. In the solution of the publication, the rotor of the motor is arranged directly at the shaft of the cylinder and the stator is secured to the wall to prevent the stator from rotating. The motor disclosed in the publication is very difficult to replace if there is a failure, because the rotor is directly arranged at the shaft of the roll, whereby in case of failure, the entire combination must be replaced. Therefore, the solution according to the publication is not suitable for objects where the sizes of cylinders and motors rotating them are large and where the defective motor has to be replaced quickly. BRIEF DESCRIPTION OF THE INVENTION [0007] An object of the present invention is to provide a roll drive which avoids the above mentioned drawbacks and enables a moving roll to be controlled in a more reliable way than before and by utilising simpler equipment. The object is achieved by a roll drive according to the invention, which is characterized in that the motor of the roll drive is an axial flux motor whose rotor shaft is directly connected to a shaft of the roll so that the shaft of the roll supports the motor, and that the motor is supported at the stator by means of a supporting arm on said moving structure, and that the roll drive further comprises a frequency converter arranged to control the axial flux motor fixed to the shaft of the roll. [0008] The invention is based on the idea that an axial flux motor can be directly connected to the shaft of a movable roll, whereby no gears nor couplings are required between the motor and the roll when the rotor shaft of the motor is directly fixed to the shaft of the roll. Implemented in this way, the mass to be moved does not increase considerably, because the torque ob- tained from the axial flux motor is considerably bigger than that of a common squirrel-cage induction motor with the corresponding frame sizes of the motor. In addition, the solution implemented with the idea according to the invention avoids the use of a coupling and gear, whereby the control becomes more accurate and the use of wearing mechanical parts can be avoided. BRIEF DESCRIPTION OF THE FIGURES [0009] In the following, the invention will be described in greater detail in connection with preferred embodiments, with reference to the attached drawings, in which Figure 1 schematically shows a side view of a roll drive according to the invention, and Figure 2 shows a perspective view of Figure 1. DETAILED DESCRIPTION OF THE INVENTION [0010] Figure 1 shows a roll drive of the invention for moving rolls, wherein a roll 1 is pivotally fixed to a moving structure 3. A motor 2 comprising a stator and a rotor is arranged to rotate the roll. Moving rolls are needed in many different objects, for instance paper machines and paper postprocessing apparatuses. Moving rolls are used, for instance, for controlling the opening of nips between the rolls. Such an application can be a calender wherein clear openings are formed between the rolls for the duration of the paper web feeding, whereas in the actual calendering stage the rolls are pressed firmly against each other in order to polish the paper in a desired way. Another application is in connection with centre reelers, whereupon as the amount of material to be rolled increases, the diameter of the roll increases. As the diameter increases, in certain applications the roll is moved a distance corresponding to the increase of the diameter. [0011] The motor of the roll drive according to the invention is an axial flux motor 2 whose rotor shaft 5 is directly connected to a shaft 4 of the roll so that the shaft 4 of the roll supports the motor 2. An axial flux motor is a motor whose rotor and stator are made of disc-like plates the surfaces of which are provided with elements producing an electromotive force. The stator is typically provided with windings magnetisable with electric current, which are magnetised in a desired manner by using a frequency converter, for example. [0012] The rotor of the axial flux motor 2 is permanently magnetised according to a preferred embodiment of the invention, whereby the surface of the disc-like rotor is provided with objects of a permanent magnet material in an appropriate manner. A permanent magnet rotor provides the advantages of reducing the need for cooling and providing the motor drive with a great torque. In addition, the axial flux motor thus operates as a synchronous ma- chine which can be controlled very accurately by utilising current frequency converters. As the figures show, the structure of the axial flux motor 2 is generally disc-like and the rotor plate is between two stator plates, whereby the main flux of the motor is in the direction of the motor shaft. The axial flux motor is very suitable for the drive of the invention, because the permanent magnets of the rotor are typically placed on the outer circumference of the rotor. The distance from the permanent magnets to the axis of rotation of the rotor directly affects the magnitude of the torque obtained from the motor. The rotor of the axial flux motor need not necessarily be permanently magnetised, but the motor may also comprise a reluctance rotor or a squirrel-cage rotor. [0013] The axial flux motor of the roll drive according to a preferred embodiment of the invention comprises a hollow rotor shaft 5. The hollowness of the rotor shaft and particularly the large inner diameter of the hollow rotor shaft are possible because of the disc-like structure of the motor. Due to the positioning of the permanent magnets, the central part of the disc-like motor will not be used for producing torque, which allows that lead-throughs can be made through the rotor shaft without reducing the efficiency of the machine or making the machine bigger because of the hollowness of the shaft. [0014] The axial flux motor 2 is fixed at its hollow rotor to the shaft 4 of the roll 1 so that the roll shaft supports the motor. In other words, the motor does not rest on a fixed mounting base, nor is the moving structure provided with any additional supporting structures but is directly fixed to the roll 1. [0015] Due to the fixing manner, the motor can also be mounted on retrofit objects, which means that a reduction gear possibly used earlier and a conventional motor can be replaced by an axial flux motor. The motor can be fixed to the roll shaft similarly as current gears that are to be fixed to the roll shaft. The fixing can be carried out, for instance, so that the end of the roll shaft is provided with a cone-shaped section against which the hollow rotor shaft of the motor pushes in reliably. The cone-shaped section at the end of the shaft journal can be implemented, for example, by fixing, for instance by welding, a separate matching section to the shaft or, alternatively, by peeling the shaft end in order to have a desired conical shape. Figures 1 and 2 show that the roll is supported by a moving structure 3 comprising the bearings of the roll. [0016] Since the motor is fixed to the roll shaft without a separate mounting bed, the motor is supported according to the invention at its stator by means of a supporting arm 6 on the moving structure 3. The support is neces- sary because otherwise the stator of the motor would rotate in an undesired manner. The supporting is carried out at the stator of the motor by means of a stiff supporting arm by connecting the supporting arm 6 to the moving structure 3 with which the motor 2 is intended to move. The supporting arm must be so strong that in spite of great torque acting on it, the motor stays, with respect to the moving structure, securely in its place. However, the function of the supporting arm 6, as was already explained earlier, is not the supporting of the motor. One end of the supporting arm is fixed to the motor frame and the other end is fixed to the moving structure, such as the arm or the like supporting the roll and motor. [0017] According to a preferred embodiment of the invention, the axial flux motor comprises water cooling. Water cooling can be implemented for example so that the supporting plate of the stator is provided with a spiral water pipe where cooling liquid is circulated. Said disc-like supporting plate is in close proximity to stator grooves containing windings, whereupon the heat produced by the motor can be efficiently transferred away from the motor. The spirally placed cooling pipe is perpendicular to the stator grooves, whereupon the cooling is efficient enough for mounting the motor in difficult thermal conditions. In addition, due to the cooling, the size of the motor can be minimised, because it is not necessary to have an additional cooling surface in the dimensioning, and it can be placed in narrow places better than before. An application requiring a small motor size is, for instance, a calender use wherein several rolls with rather small diameters are placed one on top of the other or side by side in close proximity to each other. However, it is possible to place the motors in calenders alternately at opposite roll ends in the adjacent rolls. In this way, the diameter of the motor can be considerably larger than the diameter of the roll. [0018] A frequency converter or other similar device, by which the rotational speed of the motor 2 and the torque it produces can be controlled reliably and accurately, is arranged to control the roll drive. Such a frequency converter can be a frequency converter with a voltage intermediate circuit, for instance. Since, according to an embodiment, the shafts of the roll and rotor are hollow, it is desirable for the simplicity of the drive that the frequency converter controlling the drive can carry out desired instructions regarding the torque and rotational speed without a direct feedback from the rotational speed of the roll and motor. It is cumbersome to arrange a tachometer deter- mining the rotational speed at the hollow shafts. Therefore, good choices for frequency converters are, for instance, solutions based on a direct torque control, whereby the state of the motor to be controlled can be modelled accurately and reliably after a model made of the motor, and whereby it is thus possible to avoid the mounting of the tachometer on the hollow shaft. [0019] It is obvious to a person skilled in the art that as technology advances, the basic idea of the invention can be implemented in a variety of ways. The invention and the embodiments thereof are thus not restricted to the examples described above, but they may vary within the scope of the claims.

Claims: CLAIMS 1. A roll drive for moving rolls, the drive comprising a roll (1) connected to a moving structure (3), and a motor (2) arranged to rotate the roll and comprising a stator and a rotor, characterized in that the motor of the roll drive is an axial flux motor (2) whose rotor shaft (5) is directly connected to a shaft (4) of the roll (1) so that the shaft of the roll supports the motor (2), and that the motor (2) is supported at the stator by means of a supporting arm (6) on said moving structure (3), and that the roll drive further comprises a frequency converter arranged to control the axial flux motor (2) fixed to the shaft (4) of the roll (1 ). 2. A roll drive as claimed in claim 1, characterized in that the rotor of the axial flux motor (2) comprises permanent magnets. 3. A roll drive as claimed in claim 1 or 2, characterized in that the rotor of the axial flux motor (2) comprises a hollow rotor shaft (5). 4. A roll drive as claimed in claim 1,2 or 3, characterized in that the axial flux motor (2) comprises water cooling.

Inventors: FRIMAN CARL-JOHAN, KAJANDER VESA, FRIMAN, CARL-JOHAN, KAJANDER, VESA
Applicants: ABB RESEARCH LTD, FRIMAN CARL JOHAN, KAJANDER VESA, FRIMAN, CARL-JOHAN, KAJANDER, VESA
Application year: 2001
Main classification: H02K7
IPC codes: D21F7, D21G1, H02K7, H02K21