ROLL BRAKE

Abstract: The invention relates to a roll brake which can be particularly used for braking a film and/or a film roller when pulling a film out of a film roller. The roll brake comprises an eddy-current brake built inside a brake roll and including a rotatable, steel roll jacket (1) which contains a non-rotatable multipolar stator (2). A magnetization current delivered to the stator is used to produce a magnetic field which induces eddy currents in roll jacket (1) during the rotation thereof. The braking force can be made in a desired manner dependent on the speed of rotation.

Description: Roll brake The present invention relates to a roll brake particular¬ ly for braking a film and/or a film roller when pulling a film out of a film roller. The currently available roll brakes include a brake and a rotation sensor mounted outside the braking roll. A drawback in such prior known brake systems is that a brake mounted outside a roll and its associated transmis¬ sion require space outside the brake roll. In addition, being small in size relative to their braking power, they overheat in continuous operation, change in their braking characteristics and have short service lives. The installation of a separate rotation sensor is also often troublesome and, furthermore, such devices do not indicate the uncoupling of a brake. An object of the invention is to provide a roll brake capable of eliminating the above drawbacks. A particular further object of the invention is to pro¬ vide a roll brake, wherein the braking power is in a desired manner dependent on the speed of rotation. This is important especially when using the roll brake in film wrapping machines as a roll decelerating the pull¬ ing of a film. If the film being pulled begins to stretch and, as a result of this, the speed of rotation slows down, the braking power must diminish in order to avoid the breaking of a film. These objects of the invention are accomplished on the basis of the characterizing features of the invention set out in the annexed claims. One embodiment and a few of its practical applications of the invention will now be described in more detail with reference made to the accompanying drawings, in which fig. 1 shows a roll brake of the invention in a cross- section and fig. 2 shows the same in a longitudinal section. Fig. 3 shows a practical embodiment of the invention ' when pulling a film out of a film roller having its axis of rotation in a horizontal position. Fig. 4 shows a practical embodiment of the invention when pulling a film out of a film roller having " its axis of rotation in a vertical position and fig. 5 shows a further embodiment when pulling a film out of a film roller having its axis of rotation in a vertical position while rotating the film roller and its associated brake roll around one axis of rotation. Fig. 6 is a schema ical plan view of a film wrapping machine for wrapping a .film 12 around a roller of stock 17 by means of an assembly shown in fig. 4 or fig. 5. Fig. 7 shows in association with fig. 6 the next film wrapping stage for wrapping a film 12 around a roller of stock 17 by rotating the roller of stock around its axis. This makes it possible to employ the assembly of fig. 3. A decelerating roll or a roll brake shown in figs. 1 and 2 comprises a steel roll, -jacket 1, rotatably jounalled gn a shaft 8 with bearings 9. Inside the roll jacket 1, said shaft 8 carries a non-rotatable multipolar stator 2. The stator poles are provided with excitation windings 4 into which a magnetization current is delivered by means of conductors 6. The magnetization current source can be a 0 - 240 V alternating current source or also a 0 - 230 V. If necessary, the excitation volt¬ age can be adjustable. The dimensioning of a stator 2 is dependent on the length, diameter, necessary braking power of a required brake roll and on the desired variation of braking force as a function of the speed of rotation. The thickness of steel roll jacket 1 is 2 mm or more according to a particular application. During the rotation of roll jacket 1, the stator produces a magnetic field for creating eddy cur¬ rents in jacket 1 , said eddy currents heating a jacket 1 and the power spent therefor producing, a braking force which resists the rotation of roll 1. The magnitude of a braking force is dependent on the strength of a magnet¬ ization current and the design and dimensions of stator 2. The more poles included in a stator, the lower a speed of rotation required for producing a given braking force. The smaller an air gap between poles 3 and jacket 1 , the stronger a braking force at a given speed of ro¬ tation. Selection of the axial length of stator poles 3 relative to the length of roll jacket 1 has an effect on how the " braking force depends on the speed of rotation. When the length of roll jacket 1 suitably exceeds that of poles 3, there will be a free zone left at the ends of a roll jacket for allowing the passage of eddy currents. When the roll ends are provided with a sufficient vacant zone for eddy currents, there will be produced a braking force which increases as the speed of rotation increases. This offers_a major advantage e.g. when using the brake in a film wrapping machine, wherein the film is deceler- ' ated to a certain tension. Due to manufacturing, however, the film will contain spots of reduced thickness, which means that the film can be broken by a braking force weak¬ er than that used for wrapping. As the film begins to stretch between a brake and a parcel being wrapped, the speed of rotation of a roll brake decelerates thus di-. minishing the braking force and preventing the breakage of a film for this reason. The longer said poles 3 are designed relative to the length of roll jacket 1 , the lesser the effect that any speed of rotation has on the braking force. Hence, a braking force substantially in¬ dependent of a speed of rotation can be obtained this way. This is due to the fact that, with the above di¬ mensioning, the short-circuit current rapidly reaches its maximum value which it cannot exceed, and a conse¬ quence of this is that the braking force cannot exceed a certain level. It should further be appreciated that the dissipation heat generated in a roll brake transfers effectively from a brake roll to a material to be decelerated. When using a roll brake in film wrapping " machine, the heating of a film improves its wrapping qualities. Adjacent to the end of roll jacket 1 is mounted a rota¬ tion sensor coil 5 which is provided with a low alternat¬ ing voltage produced by a magnetic field induced by eddy currents travelling within the end zone of said roll jacket. When the rotation of roll jacket 1 is stopped or the magnetization current is cut-off, the voltage re- ceived from sensor coil 5 is also cut off in wires 7. The alternating voltage received from wires 7 can be carried in a rectified state to a transistor amplifier that can be used for controlling the relay action. This rotation sensing signal can also be used for controlling- an excitation voltage regulating means. The transistor amplifier along with its relay can be mounted in con¬ nection with the excitation voltage regulating means which, when built in the relay housing, provides a read¬ ily replaceable unit. In the 'Currently available film wrapping machines, the decelerating roll does not bear against a roller of film, which means that a brake is also required for a roller of film. Its braking action is troublesome as the roller radius changes continuously, whereby the braking force must also diminish as the roller diminish¬ es in size. The control device will be complicated. Figs. 3-5 illustrate the application of a roll brake of the invention in a manner that the roll brake also ef¬ fects the deceleration of a film roller 11. The braking force diminishes as as the speed of unfolding becomes slower. At the end of a wrapping operation, the force for stopping the roller is produced by passing to the roll brake for a few seconds a sufficient excitation voltage for producing a braking force sufficient for stopping. In the case of fig. 3, a film 12 is pulled out of a film roller 11 around a roll brake 10 while said roll brake - 10 bears against the film roller 11 with its dead weight. This arrangement provides a sufficient friction both be¬ tween roll ' brake 10 and film 12 and between roll brake 10 and film roller 11. No separate brake is needed on the shaft of roller 11. In the case of fig. 4, a roll brake 10 is pivotably jour- nalled at the end of a lever arm 13 whereby the tension- al force of a film 12 urges said roll brake 10 against a film roller 11. Of course, it is also possible to employ a spring but its use involves other problems. In the case of fig. 5, a roll brake 10 is so positioned relative to a roller 11 at the end of a lever arm 16 pivotable around an axle 15 that, as the entire system is rotated around an axis 14, a centrifugal force urges said-roll brake 10 against film roller 11. In the case of fig. 6, a film 12 is wrapped around a roller of stock 17, the wrapping taking place in a hori¬ zontal plane while rotating said roller of stock 17 slowly around its horizontal axis. A roll brake 10 is arranged in connection with a film roller 11 as shown in either fig. 4 or in fig. 5. In the case of fig. 7, a film 12 is wrapped around a roller of stock 17 in the peripheral direction whereby a brake roll 10 is arranged in connection with a film roller 11 as shown in fig. 3. The wrapping operation shown in figs. 6 and 7 is carried out in successive wrapping machines included in a wrapping apparatus. When using a roll brake of the invention, the start and finish of film pulling can take place with the brake coupled on since the braking force at a low rate of pulling is small with respect to the actual rate of wrapping. During a wrapping operation, the unfolding rate of film is appr. 50 - 150 m/min depending on a wrapping machine. In a roll brake shown in figs. 1 and 2, the length of roll jacket 1 exceeds that of pole 3 at each end roughly by a distance that matches the peripheral width of pole 3. Thus, the increase of braking force is roughly direct¬ ly proportional to the increase of the speed of rotation. However, this correlation is also affected by several other dimensional factors included in a roll brake, as already pointed out above. If there is only needed a small braking force relative to the diameter and length of a roll jacket, a stator . can be designed to be very short and positioned e.g. at just one end of a roll jacket. A roll brake of the invention can naturally be used also as a separate brake, the same way as currently available brakes. Neither is the invention limited to the above- described applications but the roll brake can also be used in certain conveyor designs.

Claims: Claims 1. A roll brake particularly for braking a film and/or a film roller when pulling a film out of a film roller, c h a r a c t e r i z e d in that the roll brake comprises an eddy-current brake built inside a brake roll. 2. A roll brake as set forth in claim 1, c h a r a c ¬ t e r i z e d in that a rotatable, steel roll jacket (1) contains a multipolar stator (2) whose poles (3) are pro¬ vided with excitation windings (4) , a magnetic field generated by said stator inducing eddy currents in roll jacket (1) during the rotation thereof. 3. A roll brake as set forth in claim 1, c h a r a c ¬ t e r i z e d in that the poles (3) of stator (2) extend in the axial direction of roll jacket (1) to within a distance from the ends of a roll jacket leaving at the end of roll (1) a sufficient vacant zone for the passage of eddy currents. 4. A roll brake as set forth in claim 3, c h a r a c ¬ t e r i z e d in that the length of the poles (3) of stator (2) in the axial direction of roll jacket (1) is shorter than the length of a roll jacket by distance which is approximately twice the peripheral width of pole (3) . 5. A roll brake as set forth in any of claims 1-4, c h a r a c t e r i z e d in that adjacent to the end of roll jacket (1) is mounted a rotation sensor coil (5) which is provided with a voltage produced by a mag¬ netic field induced by eddy currents travelling within the end zone of roll jacket (1) . 6. A roll brake as set forth in any of claims 1-5, c h a r a c t e r i z e d in that the roll brake, which is surrounded over at least 120 by a film being pulled, is adapted to bear against a film roller (11) . 7. A roll brake as set forth in claim 6, c h a r a c ¬ t e r i z e d in that the roll brake bearing pressure against film roller (11) is adapted to be produced by means of a gravity, a centrifugal force or a film tensile force exerted on said-roll brake (10) . 8. The use of a roll brake as set forth in any of claims 1-7, c h a r a c t e r i z e d in that the roll brake is employed for wrapping a film (12) around a material, such as a roller of stock (17) to be wrapped. 9. A roll brake as set forth in claim 5, c h a r a c ¬ t e r i z e d in that the magnetization current of stator winding (4) is adapted to be controlled on the basis of control data received from a rotation sensor coil (5) .

Inventors: HAUTIO HEINO, HAUTIO, HEINO
Applicants: HAUTIO HEINO, HAUTIO, HEINO
Application year: 1989
Main classification: B65H23
IPC codes: B65H23, G03B1, G03B17, G03B21