Patent Publication Number: US-2002008173-A1

Title: Roll changer with motor brake

Description:
FIELD OF THE INVENTION  
       [0001] The present invention pertains to a drive for a roll changer, as is used especially in rotary printing presses in newspaper, offset or job printing.  
       BACKGROUND OF THE INVENTION  
       [0002] Roll changers are used to unwind web-shaped material, which is wound up on rolls, and are used mainly in conjunction with rotary printing presses, e.g., in newspaper offset printing or the intaglio printing of newspapers, in order to feed to the printing presses paper webs which are then printed on in the printing presses. However, the drive according to the present invention can also be used in roll changers in which a material web consisting of a material other than paper shall be unwound. However, the present invention will be described below as an example on the basis of a roll changer for a printing press. The designation “roll changer” being used here covers any driven device for unwinding a material web, but without a change of the material web specifically having to take place during the operation or without such a changing device having to be provided at all.  
       [0003] A paper web shall be fed possibly continuously to a printing press during the running printing operation, preferably at a preset paper speed and web tension. This requires paper webs to be unwound from the respective paper rolls in a controlled manner and as uniformly as possible, and it is desirable that a paper roll that has been unwound completely, i.e., an empty paper roll, be able to be replaced, i.e., changed with a full roll automatically during full run. The paper web of the unwound roll is usually spliced to the paper web of the full roll during the running printing operation, and an adhesive strip extending at right angles to the direction of conveying shall preferably be applied.  
       [0004] DE 44 37 147 C1 discloses a winding roll changer of a rotary printing press, in which a drive, as well as a disk brake acting as a separate braking means are provided, which transmit a torque via a coupling. This coupling compensates an axial offset.  
       SUMMARY AND OBJECTS OF THE INVENTION  
       [0005] The primary object of the present invention is to provide a drive for a roll changer as well as a process for driving a roll changer, which make possible the economic operation of a roll changer.  
       [0006] According to the invention, a drive for a roll changer has at least one motor for driving the roll changer, especially the central axis or core of the paper roll to be unwound, where a driving electronic unit is provided for this motor, so that the motor can be driven, on the one hand, as it is necessary, e.g., during the acceleration or synchronous run or the uniform unwinding of the paper roll. On the other hand, the motor can be driven by means of the driving electronic unit such that this motor is operated as a generator, i.e., it delivers energy, as a result of which a braking effect can be produced. The electric energy generated from the rotation energy in this process can, e.g., be fed back into an electric network.  
       [0007] Furthermore, it is also possible to drive the motor such, e.g., by a suitable phase shift of the voltages fed in, that the electric motor generates a braking force which exceeds the braking force in the simple generator mode. An electric motor can thus be operated actively as a brake by supplying energy, and the intensity of the breaking force can be set, e.g., by selecting the angle of the phase shift. The term phase shift is defined as the angle between the voltage signal or voltage signals that must be applied in a three-phase or a.c. motor to drive the electric motor synchronously at the instantaneous circumferential velocity and the drive or actuating signals applied, which shall generate the desired braking effect. Expressed in simpler terms, an electric motor connected to a rotating axis shall be driven such that it will generate a braking force directed in the direction opposite the direction of rotation of the axis. However, the voltages applied to the electric motor shall not be limited to sinusoidal oscillations, but they may also have other suitable signal shapes, e.g., cut-off partial segments of a full sinusoidal oscillation, as is known, e.g., in the case of a phase control.  
       [0008] Such a driving electronic unit for a motor can consequently bring about a regulated acceleration and unwinding as well as simple braking and also a rapid stopping of the roll using a simple motor, and the motor is operated, depending on the desired mode of operation, as a simple electric motor for acceleration and driving, as a generator or as an active brake. It is thus possible to brake a roll changer exclusively by means of one or more motors, which do not have to be provided with any additional auxiliary brakes, even if the roll changer must be stopped rapidly with full paper roll. Since a rather intense increase in the temperature of the motor may occur depending on the mode of operation of the motor, it is desirable to provide active cooling or passive cooling elements, e.g., cooling fins or similar means on the motor.  
       [0009] Depending on the desired performance capacity, it may happen that the drive or motor of the roll changer must be designed for a higher torque or output than in the case of a roll changer with additional braking elements, which is due especially to the motor load during the braking of full paper rolls during a rapid stop. However, since auxiliary brakes can be omitted due to the design of the motor, the roll changer will have, on the whole, a more inexpensive design. It is particularly advantageous that the control and regulation functions of a roll changer are simplified by the above-described arrangement because the coordination of driving and braking modes is clearly transparent. For example, it is no longer necessary to make sure that the drive of a motor is definitely switched off when a brake is actuated because the driving and braking take place via the same motor. Furthermore, it is an important advantage for the running operating costs that braking operations can be carried out without wear, which is not true, e.g., in the case of the use of mechanical auxiliary brakes.  
       [0010] The motor is advantageously provided as a central drive of the paper roll, so that the torque or the driving force of the motor acts on the core of a paper roll, e.g., via truing-in trunnions. Compared with a circumferential drive, in which a paper roll is driven via belts on its circumference, such a central drive offers the advantage that an adhesive strip to be applied in the transverse direction of a paper web for connecting two paper webs can be applied in a relatively simple manner due to the beltless drive. The amount of work needed to prepare the bonding site and the bonding of the paper rolls can thus be reduced by a central drive, so that the bonding of the paper web of a new roll with the paper web of an old roll can be carried out in a simple manner during a roll change due to the free access to the entire paper web, which is not obstructed by the drive system. It is advantageous, in general, to drive a roll changer by means of such a central drive, and it is not absolutely necessary to provide a motor with the above-described functionality. In the case of a central drive, it is consequently possible to provide a motor which makes do without additional auxiliary brakes, because this motor generates a sufficient braking force. However, it is also possible to provide a prior-art motor with additional auxiliary brakes for the drive. Such a central drive can be used for a roll changer with or without every individual element of the drive being described here or with or without a combination of a plurality of elements of the drive being described here, without inevitably using the specially described motor functionality. However, the present invention shall not be limited to a central drive, but it also covers other types of drive, e.g., the circumferential drive described.  
       [0011] It is especially advantageous to provide at least two motors for driving and braking the roll changer, and it is also conceivable to use three, four or more motors, depending on the possibility of application. The motors are preferably connected to the roll core on both sides of the roll via truing-in trunnions, so that the roll can be driven from both sides. Thus, only half the torque acts on each side of the roll core in such an arrangement compared with a one-sided central drive, as a result of which the mechanical load of the roll core in acceleration or braking modes is markedly reduced. It is advantageous to use motors of identical design.  
       [0012] If a plurality of motors are used, the driving may take place such, depending on the desired mode of operation of the roll changer, that all motors are operated as generators, e.g., during a simple braking mode. To generate a stronger braking effect, one or more motors may be braked actively, i.e., electric signals are sent to these motors, so that these generate a braking force acting opposite the direction of rotation. It is also possible in this case to continue to operate at least one motor in the generator mode, so that the energy obtained from this motor is fed into the motor or motors being braked actively via a frequency converter. To generate an even stronger braking effect, it will then be possible to actively brake all motors provided by sending suitable electric signals. It is conceivable, e.g., to provide two motors on each side, operating one motor as a generator during a deceleration mode, which generates the energy needed for the active braking of the other motor.  
       [0013] The motor or motors used is/are advantageously three-phase asynchronous motors, but it is also possible, in general, to use other types of motors, e.g., general three-phase or a.c. motors, universal motors or d.c. motors.  
       [0014] A common driving electronic unit is advantageously provided when a plurality of motors are used, so that the particular motors can be driven in agreement at the same speed and the same torque in order to exert an accelerating or braking force on the paper roll arranged in the roll changer. It is advantageous, in particular, to provide a common drive controller and a common power stage for the individual motors, in which case the motors can be connected to the power stage in parallel or in series. As a result, it is also possible to ensure in a simple manner that the motors, which are preferably of identical design, will always act acceleratingly or deceleratingly on the paper roll in parallel and in the same manner, so that it is possible to prevent the motors from acting against one another via the roll core. If the drive is to be designed such that at least one motor is operated at the same time as a generator, where at least one other motor is operated by applying suitable voltage signals such that it generates an active braking effect, it is possible to provide, e.g., common drive controllers or power stages for the motors operating in the generator mode, on the one hand, and the actively braking motors, on the other hand, in the case of the use of a plurality of motors.  
       [0015] The driving electronic unit is preferably designed such that different drive characteristics of the motors being used, which may result, e.g., from manufacturing tolerances in the case of motors of identical design, are entered as parameters or are represented as motor models, so that the driving electronic unit can prevent torque differences, which may occur in the case of the use of identical signals for different motors, from occurring. For example, a correction algorithm may be provided for one or more of the motors or drives, which compensates differences in the outputs of the particular drives by driving signals, to which compensating actuating variables, e.g., a correction current or a correction voltage are applied or superimposed, being sent to at least one of the motors or drives.  
       [0016] Suitable sensors are preferably provided at the motors or the paper webs and control elements in the driving electronic unit, so that the output signals for driving the motor depend on individual set points and/or actual values of certain parameters or on a plurality of the set points and/or actual values of certain parameters, e.g., the paper web speed, measured, e.g., on the circumference of the paper roll, the web tension, the position of a dancing roller or the like.  
       [0017] The driving electronic unit advantageously drives the motors such that, depending on measured input signals, the speed at which the paper web is unwound is controlled on the circumference of the paper roll, i.e., it is maintained, e.g., at a value equal to the paper speed of the printing press. A dancing roller provided additionally is preferably maintained now in a certain position.  
       [0018] The driving electronic unit may advantageously implement a control, which comprises, e.g., an upstream control function for the position of the dancing roller and a downstream control function for the desired paper speed, where the difference between the set point and the actual value of the dancing roller position is determined for controlling the position of the dancing roller and a speed correction value is produced based on this difference. This speed correction value is subsequently added to the measured paper web speed of the printing press, and this sum forms the set point of the speed control function. This speed control function also takes into account the difference between the sum formed and the actual value of the speed at which the paper web is unwound on the circumference of the paper roll and generates a set point, which is used to drive the motors, i.e., drives the frequency converter of the driving electronic unit.  
       [0019] The driving electronic unit is preferably designed such that it has a drive controller and a power stage with a power supply unit and a frequency converter. The power stage advantageously contains a supply unit suitable for feedback, which can feed a braking energy generated by a motor during braking mode back into an electric network.  
       [0020] Depending on the desired field of use of the drive for the roll changer, it may be advantageous to connect the individual motors in parallel to the output of the driving electronic unit, e.g., to the frequency converter, in which case each of the motors can always be operated with the same voltage and if the motors are of the same design, each of the motors will take up an equal fraction of the total current of the frequency converter.  
       [0021] As an alternative, the motors may also be connected in series to the output of the driving electronic unit or of the frequency converter, so that the same current will always flow through the motors, and the voltage of the frequency converter will be present on the motors proportionately, so that one fourth of the voltage of the frequency converter will be present in an individual motor if, e.g., four motors of the same type are used.  
       [0022] It is, in general, advantageous to implement the control functions provided in the driving electronic unit as programs, which can be carried out cyclically, e.g., on digital controllers or computers. Other possibilities of implementation of the control functions are also possible, e.g., analogous circuits or the like.  
       [0023] The present invention also pertains to a process for driving a roll changer, where at least one motor of the roll changer is driven such that it can be operated as a drive motor, as a generator for slightly braking or as an active brake, depending on the desired mode of operation, where suitable voltage signals, which can generate a relatively strong active opposing force against an instantaneous rotary movement, are sent in the latter mode of operation. As was mentioned above, e.g., suitably phase-shifted a.c. signals maybe used for this purpose. The motor is advantageously driven such that the driving signals applied to accelerate the motor, during which a stronger force is needed, are different from the driving signals applied during the synchronous run of the motor in continuous printing operation. For example, the amplitude of the voltages applied may be increased during the phase of acceleration, and it is gradually decreased to a lower value during start-up.  
       [0024] The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0025] In the drawings:  
     [0026]FIG. 1 is a schematic top view of a roll changer according to the invention;  
     [0027]FIG. 2 is a side view of another roll changer according to the invention;  
     [0028]FIG. 3 is a block diagram of the driving electronic unit of a roll changer with two motors connected thereto according to the invention; and  
     [0029]FIG. 4 is a block diagram of a control of an electric motor according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0030] Referring to the drawings in particular, FIG. 1 shows a top view of a roll changer with truing-in trunnions  2  provided on both sides of the core of the paper roll. The truing-in trunnions  2  are driven by the electric motors  1   a  and  1   b  provided on each side as a central drive in order to thus transmit a torque to the paper roll  3  for driving or deceleration. The paper roll  3  is unwound as a continuous paper web  4  during the printing operation. To regulate or control the desired web tension, a dancing roller  19  is provided, whose function will be described in greater detail on the basis of FIG. 2.  
     [0031]FIG. 2 shows a roll changer, which is driven by a motor offset laterally in relation to the paper roll  3  rather than directly by electric motors acting axially on the core  18  of the paper roll  3  as is shown in FIG. 1. The paper web  4  being unwound continuously from the paper roll  3  is led via a first, stationarily mounted roller  20   a  to the dancing roller  9  and from this over a second, stationarily mounted roller  20   b . As is indicated by the upwardly and downwardly pointing arrows at the dancing roller  19 , the dancing roller  19  can be moved actively up and down in order to influence the tension or the speed of the paper web  4  being led as a function of a certain preset control algorithm. It is also possible for the dancing roller  19  to act on the paper web  4  only under its own weight or via a spring mechanism in order to ensure a certain web tension or web speed.  
     [0032]FIG. 3 shows a block diagram of a driving electronic unit  9 , which has a drive controller  5 , into which certain signals of various actual values, which signals are picked up by sensors, are entered, e.g., the actual values of the paper speed, of the web tension or of the dancing roller position. Furthermore, a regulating or control algorithm is provided in the drive controller  5 , so that the drive controller  5  drives the power stage based on the regulating or control algorithms and input signals fed into it such that the electric motors  1   a  and  1   b  connected to the power stage  8  are driven in the desired mode of operation, e.g., for accelerating or decelerating a paper roll. The power stage  8  is composed of a power supply unit  7 , to which energy is supplied, e.g., from an electric network. A frequency converter  6  converts the primary energy supplied from, e.g., the electric network into suitable actuating or driving signals for the connected electric motors  1   a  and  1   b . The frequency converter  6  is connected to the power supply unit  7 . If the motors  1   a ,  1   b  are operated in the generator mode, the power supply unit  7  can feed the energy generated back into the network.  
     [0033]FIG. 4 shows a control which generates a manipulated variable  17  for the frequency converter  6  shown in FIG. 3. The difference between the set point  10  and the actual value  11  of the dancing roller position is formed as the input signal. The dancing roller controller  12  generates a speed correction value  13  as the output signal, to which the set point of the paper speed of a printing press is added. The actual value  14  of the paper speed of the paper web fed in, which is preferably measured on the circumference of the paper roll  3 , is subtracted from the sum of the signals  13  and  15 . The difference thus formed is sent as an input signal to the speed controller  16 , and the desired manipulated variable  17  is generated for the frequency converter using an algorithm.  
     [0034] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.