Abstract:
A method of driving a machine related to printing technology, wherein movable elements forming a kinematic chain are coupled with one another via at least one gear mechanism, includes infeeding torque components by a respective motor of at least one group of two motors, respectively located at least at two elements associated with one another. The torque components are of equal amplitude but have opposite directions of rotation, for suppressing disruptive oscillations at least at the one group of two motors. The amplitude of the torque components is proportional to relative rotation of the two elements associated with one another. Rotary encoders are provided to obtain signals for reproducing rotational positions of the elements.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a method of driving a machine related to printing technology. 
     German Published, Non-prosecuted Patent Application DE 42 10 988 A1 describes a multi-motor drive for a printing press wherein a rotary encoder is assigned to each motor. The rotary encoders generate signals relating to the rotary position of a respective element to which a torque is fed in a gear mechanism or transmission of the printing press. The rotary encoder signals are fed to phase measuring devices, by which the phase difference between adjacent feed points are determined. Depending upon the phase difference, the motors are driven in such manner that elastic stresses in the gear train can be kept constant. Controlling the stress between two adjacent feed points ensures continuous tooth surface or flank contact in the gear train and therefore has a positive effect upon maintenance of register, but only a slight effect upon vibration characteristics of the printing press. 
     In a method disclosed in German Published, Non-prosecuted Patent Application DE 199 14 627 A1, corresponding to U.S. Pat. No. 6,401,620, for compensating for rotational oscillations of a printing press, opposing torques are infed at locations where rotational oscillations occur most intensely. The infeeding of opposing moments may be effected by driving a main drive motor or a separate motor, by which a variable-speed opposing torque component may be produced. The opposing torques to be infed are stored permanently in a control system and are changed only when the machine configuration is changed, so that the locations with the oscillations which occur most intensely occur with an offset. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide a method of driving a machine related to printing technology, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods of this general type and which permits a suppression of undesired oscillations over a wide rotational speed range. 
     With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of driving a machine related to printing technology, which comprises providing movable elements forming a kinematic chain being coupled with one another via at least one gear mechanism. Torque components are fed in by a respective motor of at least one group of two motors respectively located at least at two elements associated with one another. The torque components have equal amplitude but opposite directions of rotation, for suppressing disruptive oscillations at least at the one group of two motors. The amplitude of the torque components is proportional to relative rotation of the two elements associated with one another. Rotary encoders are provided to obtain signals for reproducing rotational positions of the elements. 
     In accordance with another mode, the method of the invention further includes placing the motors, in at least the one group thereof, at the start and the end of the kinematic chain. 
     In accordance with a further mode, the method of the invention further includes driving the one group of two motors independently of signal processing of further motors. 
     In accordance with an added mode, the method of the invention further includes driving the motors of the one group, for shifting the natural frequency of the kinematic chain into a non-disruptive range. 
     In accordance with an additional mode, the method of the invention further includes providing a printing press having a large number of printing units forming the kinematic chain. A main drive torque is fed in by a main drive motor and a natural frequency is shifted by auxiliary drive motors forming a group. 
     In accordance with yet another mode, the method of the invention further includes providing the auxiliary drive motors for acting at the start and the end of the kinematic chain. 
     In accordance with a concomitant mode, the method of the invention further includes driving the auxiliary drive motors independently of the control of the main drive motor. 
     Applying and controlling additional motors, in particular electric motors, and using previously provided motors at one or more elements, also in addition to a main drive motor, makes it is possible to operate motors pairwise so that a torque output by one motor corresponds to that from a mechanical spring which is connected between two pairwise coupled motors. In the case of a printing press of in-line construction, having a multiplicity of printing units, an increase in the critical natural frequency of the printing press of 50% can be achieved, for example with two auxiliary motors at the start and the end of the printing press, and coupling these two drives via a previously provided gear train. Accordingly, the number of prints at resonance can be increased, for example, from the usual 10,000 prints per hour to 15,000 prints per hour. The pairwise coupled motors form an electromechanical spring which changes the natural form of the machine that is related to printing technology. The natural form can be influenced by a suitable selection of the stiffness or rigidity of such an electromechanical spring, so that the relative excursions and, therewith, the dynamic sectional torques in a gear train that couples the driven elements can be improved in the range that is critical for backlash. It is possible to realize or implement electromechanical springs, by which the natural frequency of a printing machine can be increased even further, by using a main drive motor in conjunction with auxiliary drive motors. 
     The method encompasses the possibility, depending upon the then occurring machine speed or upon other parameters, such as the machine configuration, of the connection or disconnection of the electromechanical springs or the use of various combinations. A linear damping characteristic between pairwise connected machine elements can also be realized or implemented by the motor control system, in addition to the spring characteristic, in order to increase the oscillation damping. For this reason, the method can advantageously be combined with electrical infeeding of compensation torques. 
     Other features which are considered as characteristic for the invention are set forth in the appended claims. 
     Although the invention is illustrated and described herein as embodied in a method of driving a machine related to printing technology, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
     The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic, side-elevational view of a printing press having one group of motors, and a block diagram of a drive for the printing press; 
     FIG. 2 is a view similar to that of FIG. 1 wherein the printing press has two groups of motors; 
     FIGS. 3A,  3 B and  3 C are plot diagrams or graphs respectively depicting variations of rotational angles, relative rotational angles and rotational torques for a pair of motors; and 
     FIG. 4 is a plot diagram or graph depicting a variation of rotational oscillations as a function of numbers of prints in a printing press. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a printing press of in-line construction having twelve printing units  1  to  12 . Sheets  14  are individually separated or singled from a sheet pile  15  and fed to the first printing unit  1  by using a feeder  13 . The last printing unit  12  is followed by a varnishing unit  16  and a chain delivery  17  for depositing the completely printed sheets  14  on a pile or stack  18 . Each respective printing unit  1  to  12  has a form cylinder  19 , a transfer cylinder  20  and an impression cylinder  21 . The printing units  1  to  12  are connected to one another by transfer drums  22  to  24 . In the printing units  1  to  12 , there are also rollers  25  for applying dampening solution and printing ink to the respective form cylinder  19 . All of the rotating elements of the printing press are coupled with one another by a gear train. A main drive motor  26 , which is provided in order to drive the printing press, is coupled with the transfer drum  28  via a gear mechanism or transmission  27 . A further motor  29  is coupled directly with a feed cylinder in the first printing unit  1 . The feed cylinder is in turn coupled with the aforementioned gear train. A further motor  30  is disposed on the chain delivery  17 , directly on a chain looping or return cylinder. The motor  30  is therefore likewise capable of feeding torques into the aforementioned gear train. All of the motors  26 ,  29  and  30  and the elements respectively driven thereby have rotary encoders  31  to  33  and control systems  34  to  36  respectively assigned thereto. Actuating outputs from the control systems  34  to  36  are connected to the motors  26 ,  29  and  30 . A signal output from the rotary encoder  32  is fed to a first input of a first comparator  37  and to a second input of a second comparator  38 . A signal output from the rotary encoder  33  is fed to a first input of the comparator  38  and to a second input of the comparator  37 . A signal output from the rotary encoder  31  is connected directly to the control system  34 . 
     Signals phi 1  and phi 2  at the outputs of the rotary encoders  32  and  33  highly accurately reproduce the rotational position of the feed cylinder driven by the motor  29 , and the chain looping cylinder driven by the motor  30 . The course of the rotational angle phi over time t is illustrated in FIG.  3 A. Due to the elasticity of the entire gear train of the printing press, angle curves phi 1  (t) and phi 2  (t) are not exactly linear. Output signals delta_phi 1  and delta_phi 2  from the comparators  37  and  38  are plotted in the plot diagram or graph shown in FIG.  3 B. The output signals delta_phi 1  and delta_phi 2  fluctuate with the same period and have a phase shift from one another. The control systems  35  and  36  of the respective motors  29  and  30  process the output signals delta_phi 1  and delta_phi 2  at high speed, and dynamically produce torque actuating variables m 1  and m 2  for the respective motors  29  and  30 . This occurs at least approximately independently of the control system  34  of the main drive motor  26 . The motors  29  and  30  have sufficiently high dynamics to be able to realize a prescribed behavior in the frequency range of interest. As can be ascertained from FIG. 3C, the torque curves m 1  (t) and m 2  (t) are likewise periodic and have a phase shift from one another, like the curves of the relative angles delta_phi 1  (t) and delta_phi 2  (t). The motors  29  and  30  act directly on the cylinder shafts, without layshafts or countershafts or the like, for the purpose of producing a high mechanical stiffness or rigidity. The torques m 1  (t) and m 2  (t) respectively infed by the motors  29  and  30  have an additional stationary component for avoiding flank or side changes in the gear train and for avoiding a two-quadrant operation. 
     Another embodiment of the invention having two groups of motors  39  to  41  is illustrated in FIG.  2 . Elements illustrated in FIG. 2, which have equivalent functions to those illustrated in FIG. 1, are identified hereinbelow by like reference numerals. The motors  39  to  41  are respectively seated directly on the feed cylinder of the first printing unit  1 , on a transfer drum  22  of the seventh printing unit  7  and on the chain looping drum of the delivery  17 , and are coupled with respective rotary encoders  31  to  33 . The motors  39  and  41  form a first group thereof. The signals from the rotary encoder  32  are fed to a first input of a comparator  42  and to a second input of a comparator  43 . The signals from the rotary encoder  33  are fed to a first input of the comparator  43  and to a second input of the comparator  42 . Outputs from the comparators  42  and  43  are respectively connected to control systems  44  and  45  for the respective motors  39  and  41 . An output from the control system  45  is connected to an input of a superimposition element  46 . 
     The motors  40  and  41  form a second group thereof. The signals from the rotary encoder  31  are fed to a first input of a comparator  47  and to a second input of a further comparator  48 . The signals from the rotary encoder  33  are applied to the respective other inputs of the comparators  47  and  48 . The outputs from the comparators  47  and  48  are respectively connected to control systems  49  and  50  for the respective motors  40  and  41 . While the control system  49  is wired directly to the motor  40 , the output from the control system  50  leads to a second input of the superimposition element  46 . The output from the superimposition element  46  is connected to the motor  41 . 
     During the operation of the printing press, rotational oscillations arise in the gear train. Those oscillations are not constant over the length of the printing press. With the aid of the rotary encoders  31  to  33  and the comparators  42  and  43 ;  47  and  48 , the rotational angle differences, respectively, within the motor groups  39 ,  41  and  40 ,  41  are determined and processed in the control systems  44 ,  45 ,  49  and  50  to form actuating signals for the motors  39  to  41 . The actuating signal for the motor  41 , which belongs to both groups, is formed by a superimposition of the signals from the control systems  45  and  50 . 
     In all the different embodiments described hereinabove, the motor groups form an electromechanical spring, the spring characteristic of which is set so that a shift occurs in the natural frequency of the elements of the printing press, which are driven by the motors. The natural frequency is shifted upwardly in a range lying outside the operating rotational speed range of the printing press. 
     The mode of action of the electromechanical springs is represented in the graph or plot diagram of FIG.  4 . The graph of FIG. 4 includes a rotational oscillation curve s on a transfer drum  23  between the printing units  6  and  7  against the number of prints n per hour which are made in the printing press. A curve  51  shows the state according to the prior art. The amplitudes of the rotary oscillations are high. If the printing press is operated close to the maximum number of prints, n max , there is a considerable peak in the rotational oscillation amplitudes at the number of prints n E,0  because of the natural frequency of the printing press, and this necessarily leads to printing faults. The curve  52  shows the state wherein an electromechanical spring, which includes two motors  29  and  30  according to FIG. 1, is used. Driving the motors  29  and  30  has the effect of shifting the natural frequency from the original number of prints n E,0  to the number of prints n E,1 . The natural frequency n E,1  therefore lies on the other side of the maximum possible number of prints n max . If the machine is operated with a number of prints n 1  below the maximum number of prints n max , the rotational oscillations then decrease by an amount (s 2 −s 1 ) in comparison with the solutions offered in the prior art. If three groups of motors are operated as electromechanical springs, a rotational oscillation curve according to curve  53  can be attained. The natural frequency n E,3  is shifted even further upwardly. The printing press can be operated without detrimental effects within a range up to the number of prints n max,3 , i.e., the productivity of the printing press rises for a quality remaining constant.