Abstract:
An apparatus in a multicolor rotary printing machine for determining register deviations, including a scanning device disposed behind a print gap of a last printing unit of the printing machine; at least one register mark line disposed on printing material movably disposed relative to the scanning device, wherein the scanning device is directed to the register mark line; a control circuit connected with the scanning device for processing signals from the scanning device, and a measuring, steering and regulating device receiving inputs from the control circuit in operative engagement with registers of the printing machine, and a plurality of section reference marks on the printing material, in alignment with the register mark line within scanning range of the scanning device for correcting the register deviations.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 08/389,980, filed Feb. 14, 1995, now abandoned which was a file-wrapper continuation of Ser. No. 08/073,122, filed Jun. 7, 1993, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a multicolor rotary printing machine for printing sheets or webs, having on-line register adjustment, or register measuring devices. The invention serves for determining register deviations between different ink colors, especially deviations in regard to circumferential, side and diagonal register, which are to be minimized with register adjusting devices connected with a steering and control device. 
     The known art includes a stationary installed photo-electric scanning device for register marks, which is connected with a switching device for measuring register mark positions (DE 32 26 078 A1, DE 26 43 481 A1, DE 27 31 914 A1, DE 26 58 659 A1, DE 40 14 706 A1, and DE 40 14 708 A1). 
     The times between the register signals are evaluated between each other or in response to a reference signal, wherein the time/path relations of position deviations of the register marks can be evaluated. In the known devices, the scanning arrangement is connected with start/stop inputs of a counter circuit, whose counting state is proportional with the timed appearance of reference signals and register mark signals (DE 32 26 078 A1). As reference signal, it is possible to use, for example, a fixed edge on a cylinder transporting the printed material, which is detected by means of a scanning device. The known art has the drawbacks that the velocity of the printing material must be constant, which in practice cannot be assured. The peripheral velocity of a printing cylinder swings back and forth even at a constant printing speed as much as several tenths of a percent, which leads to an impermissibly high error in the measurement of the register marks when the register marks are sensed by the scanning device on the surface of the printing cylinder. The uneven velocity is a result of variations in the load on the printing machine drive since the load during printing is subject to strong variations both in regard to time and in regard location in the machine. 
     Furthermore, there are known devices by means of which the angular position and velocity of a cylinder transporting printing material can be measured with incremental or absolute angle transmitter (DE 26 58 659 A1, DE 27 31 914 A1). 
     In that manner, the appearance of the register marks are evaluated in relation to the angular position of the cylinder, and from which the actual deviation of a register mark can be determined on the basis of the sheet length in the form of a nominal value. In that case incremental angle transmitters are used, for generating a specially generated reference or zero pulse, which is used as a reference for the angular position at which the register mark signal appears. 
     Such angle transmitters for determining register deviation require additional investment, especially since the angle transmitter requires a certain mounting space and must, for the purpose of measurement, be mounted very precisely. Furthermore, the transmission of the measuring signals from the angle transmitter require additional electronic investments in order to assure high validity of the signals in the presence of noise. The measurement of the position of the register mark with angle transmitter is subject to error, since during the printing, especially due to forces caused by the gripper and forces appearing during and after the print slot in the printed material (i.e. the point of contact between superimposed rollers or cylinders or printing cylinders and forms), and at least in subregions a relative movement relating to the surface of the transporting cylinders, which can cause errors in the register signals relating to the angle transmitter signals. 
     In the European Patent application EP 04 44 583 A2, there is described marks printed on a printing material for determining registration, which include crossing lines visually printed for each print color, and which include a linear and a curved section which are machine-readable. The visual sensing of the register deviations is performed in economical off-line manner by means of an optical register cross reader. The machine sensing is performed by means of a video camera, by means of which scanning signals serve to control register adjusting devices. 
     The aforesaid method has the drawback that for on-line precise register adjustment the data for machine evaluation must be present in predetermined mutually separate positions on the printed material, which requires a relatively wide section of the printed material for the register marks, and require a photo-electric sensor matched to the register marks, and has a scanning width adjusted to the width of the register marks. Furthermore, this approach does not provide information as to which reference the measurements of the register deviations are related. 
     SUMMARY OF THE INVENTION 
     It is accordingly an object of the invention to provide an arrangement for determining register deviations in a multicolor rotary printing machine, which provides a high degree of accuracy, combined with low investment for determining positions of register marks printed on printing material. 
     The invention includes an arrangement for determining register deviations in a multicolor rotary printing machine, wherein at least one scanning device, positioned behind the last printing unit, and behind the printing slot, which scans at least one register mark line on the moving printing material in direction of additional section reference marks on the printing material. The section reference marks are designated in this manner, since the reference marks are formed as short line sections. 
     The section reference marks can be attained with exactly one printing unit, advantageously in the color which is especially or most suitable for the photo-electric receiver in the scanning device. The signals which are generated by the scanning of the register marks, and their section reference marks, are processed together in a circuit arrangement, and wherein the resulting signals derived from the register marks, and the section reference marks are available for determining the register deviations. The invention requires no additional transmitter for transmitting the machine rotary angle, or sensors for scanning of fixed edges on a transport cylinder in order to obtain a reference signal. 
     It is especially advantageous, for determining the diagonal register deviations, to provide register mark lines on the edge regions of the printing material, which each cooperate with a respective photo-electric scanning device, and to provide respective section reference marks for each register mark line. 
     A variation of the invention provides that a line of section reference marks is placed next to the respective register mark lines, wherein the line of section reference marks is composed of periodical line section screens, i.e. like steps in a ladder, wherein the line sections are placed at right angles (perpendicular) to the direction of movement of the printing material, and wherein the section reference marks are scanned with an additional photo-electric receiver in the scanning device. 
     An improvement in image resolution can be attained if a line of section reference marks is placed next to the respective register mark lines, and wherein the section reference marks are arranged as an uninterrupted row of right angle triangles, each having a respective short side of the triangle positioned on an uninterrupted straight line next to each other, and wherein the other short side of the triangle is perpendicular to the moving direction of the printing material, and wherein further the long sides of the triangles are parallel, and the section reference marks are scanned by an additional receiver of the scanning device. 
     In regard to the investment, it is advantageous if the section reference marks are located within the range of the register mark lines of a group of register marks, either ahead of or behind the register marks. Register mark signals and section reference mark signals can then be scanned by the same receiver of the scanning device. For signal processing, it is then advantageous if the section reference marks and the register mark groups are arranged so that the register mark group of one register mark line are aligned in time with the respective section reference marks on the other side of the printing material, and can be scanned with a respective scanning device for the other side of the printing material. 
     A further variation of the invention, which is advantageous for the signal processing, provides that the section reference marks are positioned within the respective register mark line, and the section reference marks are provided as equidistant line sections having their sides perpendicular to the moving direction of the printing material, and wherein the register marks from respective printing units are printed between adjacent line sections. 
     A version of the invention with especially low investment and high speed of signal processing can be attained if the section reference marks are positioned within the respective register mark lines, wherein each individual register mark is precisely located in the other register mark line, wherein the individual register marks and the individual section reference marks are sensed at substantially the same times by the respective scanning device, and the section register mark is formed as a single line section which has two parallel sides (i.e. edges) which are perpendicular to the moving direction of the printing material, and wherein the distance between the edges is exactly equal to the scanning with of the individual register marks, and which can be determined by scanning the individual respective register marks in their nominal positions. 
     In accordance with the invention, there is provided an apparatus in a multicolor rotary printing machine for determining register deviations, which includes a scanning device disposed behind a print gap of a last printing unit of the printing machine; at least one register mark line disposed on printing material movable relative to the scanning device, wherein the scanning device is directed to the register mark line; a control circuit connected with the scanning device for processing signals from the scanning device, and a measuring, steering and regulating arrangement receiving inputs from the control circuit in operative engagement with registers of the printing machine, and a plurality of section reference marks on the printing material, in alignment with the register mark line within scanning range of the scanning device for correcting the register deviations. 
     In accordance with another feature the apparatus includes a plurality of register mark lines, each connected with a respective scanning device, and wherein the scanning device is a photo-electric scanning device. 
     According to still another feature the apparatus includes a plurality of section reference marks arranged equi-distantly along the register mark line, wherein the section reference marks are each formed as a line section disposed perpendicular to the direction of movement of the printing material, and including a photo-electric receiver in the photo-electric scanning device for sensing the section reference marks. 
     According to an additional feature the apparatus further includes a plurality of section reference marks disposed next to the register mark line, wherein the section reference marks are arranged in the form of an uninterrupted row of right angle triangles, each triangle having a first short side, disposed uninterrupted on a straight line behind each other, a second short side, disposed at right angles to the direction of movement of the printing material, the triangles having respective long sides, disposed in parallel with each other, and including a further photo-electric receiver in the scanning device for scanning the long sides. 
     The apparatus according to the invention may further include a register mark group of register marks wherein the section reference marks are disposed at the side of the register mark line facing the center of the sheet, ahead of or following a respective group of register marks. 
     The apparatus can additionally include a first register mark line, and a first register mark group in the first register mark line, a second register mark line, and a second register mark group in the second register mark line, wherein the first register mark group in the first register mark line is sensed by a first scanning device, and wherein the second register mark groups are sensed simultaneously with the first register mark groups by a second scanning device. 
     According to still another feature the apparatus according to the invention includes section reference marks which are disposed at the inside of the respective register mark lines facing the center of the sheet, the section reference marks including a plurality of individual identical line sections having section edges disposed perpendicular to the direction of movement of the printing material, and wherein the register marks are disposed between mutually facing section reference marks. 
     According to a concomitant feature the apparatus according to the invention includes that the section reference marks are disposed, respectively, within the register mark lines, wherein the individual register marks of respective register mark lines are disposed exactly within an individual section reference mark of the other register mark line, and wherein the individual register marks and the individual section reference marks are scanned substantially simultaneously by their respective scanning device, wherein each of the section references marks are formed as individual line sections having parallel edges disposed perpendicularly to the direction of movement of the printing material, and wherein the scanning width (B) of each reference mark is exactly equal to the distance (B) between the parallel edges of adjacent register marks, when the respective individual register marks are scanned in their nominal position. 
     Although the invention is illustrated and described herein as embodied in an arrangement for determining register deviations of a multicolor rotary printing machine, 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, in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a diagrammatic representation of the invention as applied to printed material moving through a printing machine, and signal processing components connected with register adjusting devices; 
     FIG. 2 shows a register mark line with trapezoidal register marks and section reference marks in a periodical line pattern; 
     FIG. 3 shows a register mark line with triangular register marks and section reference marks in a periodical line pattern; 
     FIG. 4 shows a section reference mark line as a row of right angle triangles; 
     FIG. 5 shows arrangements of register marks and section reference marks disposed in respective lines, each line in alignment with a respective mark sensor and light source; 
     FIG. 6 shows a single line arrangement of register marks and section reference marks formed as line sections; 
     FIG. 7 shows an alternating assignment of register marks each exactly aligned with a respective section reference mark; 
     FIG. 8 shows a mark arrangement with respective measuring edges, that are relevant to the measurements; 
     FIG. 9 shows two lines of integrated section reference marks and register marks, with exemplary ink colors from respective printing units designated next the register marks; 
     FIG. 10 is a block diagram showing the major blocks of the electronic apparatus of the invention; 
     FIG. 11 shows details of the electronic control apparatus according to FIG. 10; and 
     FIGS. 12 a ,  12   b  and  12   c  together show a flowchart of the steps of a method for practicing the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows in diagrammatic form elements of the apparatus according to the invention. The apparatus accordingly includes, for determining register deviations, two scanning devices  1 ,  2 , which can slide perpendicularly to the sheet move direction indicated by arrow  3  along a cross bar  4 . A sheet  5  is driven by a drive  6 , via a diagrammatically illustrated gear-wheel transmission  7 , and by transport cylinders  8 ,  9 , under scanning devices  1 ,  2 . 
     The scanning devices  1 ,  2  contain each a respective common light source  10 ,  11 , a register mark sensor  12 ,  13 , and a section reference mark sensor  14 ,  15 . The register mark sensors  12 ,  13  and the section reference mark sensors  14 ,  15  are connected to a machine control arrangement  16  which includes a signal processing device  22 , which has printing machine controls  23 ,  25 , which, among other tasks, operate to control register adjusting devices  24  for respective printing machine units (not shown). 
     In addition to the above-described on-line version of the invention, it is also possible to provide a version of the invention arranged externally to the printing machine. to that end, the sheet  5  is positioned fixedly on a measuring table, and the scanning devices  1 ,  2  are arranged so that they can move in direction  3  of the sheet  5  in order to determine the register deviations. 
     In accordance with the invention, the sheet  5  has thereon two lines of section reference marks  18 ,  19 , arranged along respective register mark lines  20 ,  21 , in parallel therewith. The signals generated by the section reference mark sensors  14 ,  15  and the register mark sensors  12 ,  13  by scanning of the section reference marks  18 ,  19  and the register marks  17 , are connected to a signal processing device  22  for processing of the register mark signals, which can be part of the aforesaid machine control arrangement  16 . Furthermore, the machine control arrangement  16  can include machine controls  23 ,  25 , to each of which is connected a respective register adjusting device  24   a  and  24   b  of the individual printing units of a multicolor rotary printing machine, and a display device  22   a  for displaying the register mark deviations. An incremental angle transmitter  26  connected to a respective printing cylinder  9  of the printing machine is not necessary for obtaining the register deviations according to the present invention. The section reference marks  18 ,  19  are advantageously printed by a respective printing unit with an ink color that is detected by the respective section register mark sensors  14 ,  15 . 
     In FIG. 2, a register mark line  20  is placed in rows of pair-wise arranged trapezoid-shaped register marks  17 , respectively positioned before or behind every two respective pairs of start and end marks  27 ,  28 , printed in the color of the respective printing unit on the sheet  5 . Adjacent to this register mark line  20 , there is a row of section reference marks  29 , which is advantageously printed in the color black, readily detectable by the respective section reference mark sensors  14  and  15 . The distance A between the respective mark lines  20  and  21  and the section reference mark lines  18  and  19  corresponds to the distance between the scanning points of the respective register mark sensors  12  and  13  and the respective section reference mark sensors  14  and  15 . The reference marks  18 ,  19  are forming a screen or raster of periodically appearing short line sections, wherein the width of the line sections of the reference marks  18  is equal to the space between the sections of the reference marks  18 . 
     FIG. 3 shows the register marks as pairs of triangles  17 , wherein each pair of triangles  17  are printed by a respective printing unit. The corresponding section reference mark line  29  is, as in FIG. 2, formed as a line section screen. A high degree of accuracy can be attained by increasing the number of section reference marks  18  per unit of length, and wherein the signal processing device can additionally perform position or speed interpolation of the section reference signals. 
     FIG. 4 shows a version of the section reference marks  18 , wherein the section register mark line  20  is an uninterrupted periodic screen formed as a row of right-angle triangles  17 . one of the short sides  30  of the triangles is perpendicular to the move direction  3  of the sheet  5 . The other short side is positioned in the move direction, and the long sides  32  are all parallel to each other. By arranging the layout of the scanning geometry of the section reference mark sensors  14  to cover the entire width of the section reference mark line  29 , the rise time of the scanning signal obtained by scanning the long sides  32  of the triangles, the resolution of the definition of the register marks  17  can be improved. 
     In the arrangement shown in FIG. 5, the required investment in the scanning devices  1 ,  2  is reduced due to placement of the section reference marks  18 ,  19  within the range of the register mark lines  20 ,  21 . Each scanning device  1 ,  2  requires then only one photo-electric sensor for each line  20 ,  21 , since the register marks  17  and the section reference marks  18 ,  19  can accordingly be scanned one after the other in time sequence. In FIG. 5, the register marks  17  and the section reference marks  18 ,  19  can be printed in both edge regions of the sheet  5 , so that the register marks  17  of the register mark line  20  can be scanned simultaneously with the section reference marks  19  of the register mark line  21  by the respective register mark sensors  12 ,  13 , and with the section reference sensors  14 ,  15 . 
     FIG. 6 shows the section reference marks  18  and the register marks  17  and also the start and end marks  27 ,  28 , similarly arranged along a register mark line  20 . The significance of this is that the start mark  27  follows a first individual section reference mark  33  in one color, and that next each pair of triangle-shaped register marks  34  in a certain ink color, each followed by an individual section reference mark  35  printed in the standard ink color. This line  20  ends with the end mark  28 . The signals from the individual section reference marks  33 ,  35  make it possible to perform an interpolation of the velocity of the sheet  5  in respective time intervals between the start mark  28  and the section reference mark  33  respectively between the individual section reference marks  33 ,  35 . Assuming that the velocity variations of the sheet  5  in the range between two individual section reference marks  33 ,  35  is negligible, it is possible to determine the position of the sheet by measuring its speed from the positions of the register marks  34 , and thereby make the necessary register corrections. 
     FIG. 7 shows a mark configuration wherein the section reference marks  18 ,  19  are placed along respective register mark lines  20 ,  21 . Each individual register mark  36 ,  37  of a pair of register marks of a certain ink color of one register mark line  20  performs exactly as a section reference mark  38 ,  39  in the other register mark line  20 ,  21 . For each ink color there is provided in each register mark line  20 ,  21  a pair of triangle-shaped register marks  17 , and a pair of section reference marks  18 ,  19  respectively. The individual register marks  36 ,  37  are scanned at substantially the same time by each respective register mark sensor  12 ,  13 . The section reference mark sensors  14 ,  15  are scanning the sheet edges in direction perpendicular to the move direction  3  of the sheet  5  at the same sheet latitude except for register deviations. In the exemplary embodiment described, the measures for measurements of the section reference marks  18 ,  19  and  38 ,  39  respectively, and their distances from each other are in millimeters. The section reference marks  19  are, as are start marks  40 , printed in the particular color printed by the respective printing unit, and are comprised of a single line section having a width of B, whose parallel edges are perpendicular to the move direction  3  of sheet  5 . Assuming that a single register mark  36  (or  37 ) is positioned in its proper position, then it has a scanning width in the direction of move which is also equal to value of B. This version of the invention requires the least investment in regard to scanning devices  1 , 2  and in the circuit arrangement  22 , and offers a high processing speed. 
     FIG. 8 is a fractional view of the mark arrangement according to FIG.  7 . The register marks  7  are shown located away from their proper positions. In the following the arrangement of the signal processing as performed by the circuit arrangement  22  will be described by reference to the scanning points designated with a “P—”. 
     In regard to FIG. 6, if the section reference and register marks  33 ,  34  are printed in their precise registration, then the scanning devices  1 ,  2  (FIG. 1) will generate identical signal time sequences. Beginning with a leading signal edge P of a start mark  27 , high frequency timing pulses generated by a precise quartz crystal generator  51  (FIG. 10) are counted in reference counter  52 . The states of counter  52  for the occurrence of each of the edges designated with a “P—” of the register marks  17  in FIG.  8  and the reference register marks  18  or  19  are recorded in a memory, i.e. storage units  56   a ,  56   b . Next these counter states are processed in a computer (CPU)  53 , FIG. 10, which is a part of the signal processing device  22 , and register errors, if required, are corrected by the register adjusting devices  24   a ,  24   b  (FIG.  1 ). The circumferential register deviations UR 1 and UR   2  for register mark lines  20 ,  21  (FIG. 8) are determined for example as follows:                  UR   1     =         (       P   11     -     P   21       )     +     (       P   14     -     P   24       )       2                     and           (   a   )                 UR   2     =         (       P   25     -     P   15       )     +     (       P   28     -     P   18       )       2             (   b   )                                
     wherein Pn is equal to the count of timing pulses received in the reference counter  52  (FIG.  10 ), as described in more detail below, and wherein the subscript n relates to the respective edge of a register mark or reference mark. For example, in equation (a) P 11  represents the count in counter  52  at the moment the leading edge of register mark  36  is recorded in storage unit  1 . An edge detector detects the moment the edge of the mark passes under the respective register mark sensor  1 ,  2  (FIG.  1 ). 
     It follows that in equation (a), the difference P 11 -P 21  represents the time difference between the passing of the respective leading edge of register mark  36 , and the leading edge of reference mark  38 , and the difference P 14 -P 24  represents the time difference between the respective trailing edges of register mark  37  and reference mark  39 . As seen in equation (a) the sum of the differences is divided by  2  to give a mean value UR, of the time difference between the respective leading edges and the trailing edges for mark line  20 . Equation (b) performs the same operation on mark line  21  to give a means value UR 2 . 
     The diagonal register deviation can now be determined as: 
     
       
         SchRR=U R2 -U R1   (c) 
       
     
     To that end it is necessary that the register mark lines  20 , 21  are located on the respective edge of the sheet  5 . 
     The side register deviations can be determined by equation (d) as:                    SR   =                      (       (       P   12     -     P   11       )     -     (       P   22     -     P   21       )       )     +     (       (       P   24     -     P   23       )     -     (       P   14     -     P   13       )       )       4     +                                  (       (       P   26     -     P   25       )     -     (       P   16     -     P   15       )       )     +     (       (       P   18     -     P   17       )     -     (       P   28     -     P   27       )       )       4                   (   d   )                                
     The above values indicated by P(I,K) represent the Ith line as determined at the sides of the edges. The advantage of the mark arrangement according to FIGS. 6,  7  and  8  is the complete independence of the determination of the register deviations from changes in the velocity of the sheet  5 . While, in the arrangement according to FIGS. 2-5, it must be assumed that the velocity of the sheet  5  is consistent, and determined by the geometry of the respective arrangement of the section reference marks  18 ,  19 , the section length is shortened in the arrangement according to FIGS. 7 and 8, due to their closer approximation to the proper register adjustment. Determination of the register deviations is always more correct, if obtained as the value close to the correct position. Since only the counter states P(I,K) of the respective absolutely necessary edges are stored, the amount of information to be processed is minimal. 
     It follows that the values from equations (c) and (d) represent counts of pulses from the frequency generator  51 , as recorded in storage units  1  and  2  ( 56   a ,  56   b ). In order to obtain the actual register errors in units of length, the respective counts must be multiplied in the central processing unit  56  by the distance the printing material moves during two counts of the frequency generator  51 . 
     In FIG. 10, the reference frequency generator is a very stable and precise pulse generator which generates a precise reference of e.g. one megahertz or any other suitable frequency high enough to define the movement of the printing material in sufficiently small increments as required for determining a high degree of definition of the register deviations. The program memory  57  contains in storage the control program for the CPU  53 , which are structured according to the flow charts shown in FIGS. 12 a, b  and  c , as described in more detail below. The data memory  58  serves to contain fixed and variable data as required for the operation of the CPU  53  in conventional manner. 
     The data bus  59  operates to transmit data between the various blocks  56   a ,  56   b ,  57 ,  58  and CPU  53  as required according to the control program. The CPU  53  is connected via an output bus  61  to a motor actuation unit  62 , which represents each register motor for each register, i.e. the circumferential, side, and diagonal register motor (M)  63  for each printing unit. Such motors are quite conventional and are well known in the printing art. The motor  63  can, for example, be realized as stepping motors that are set back or forward by step pulses generated by the CPU  53  and transmitted via motor actuation circuit  62  by a bus  65  to each register motor  63  so that any register deviation determined by the CPU  53  is corrected. 
     FIG. 11 shows further circuit details of the block diagram shown in FIG.  10 . 
     The pre-processing circuit  54  includes two differentiating circuits  71 ,  72  of conventional construction, with a common input  66  connected via signal line  66  to optical scanning device  1  (FIG.  1 ), while pre-processing unit  54 ′ is connected to scanning unit  2  via line  67 . When the scanning signal on signal line  66  goes active as a leading edge P 11 , P 13 , P 15  or P 17  (FIG. 8) of a register or reference mark is detected, a positive start pulse is generated on the differentiating circuit&#39;s output lead  73 , and when subsequently the trailing edge of the mark is detected, a positive end pulse is generated on the output lead  74 . The reference frequency circuit  51 , described above, drives a continuously running reference counter  52  formed of a counting chain of series-connected counters  76  of conventional construction. In other words, the reference counter  52  is a continuously running clock. A time difference circuit  60  is composed of storage units  1  and  2 . The reference counter  52  is coupled to storage units  1  and  2  by means of respective blocks of AND-gates  77 ,  78 . At the moment the leading edge of a register or reference mark is detected the contents of the reference counter of that moment is transferred via AND-gates  77 , all being activated simultaneously by the leading edge pulse on line  73 , to corresponding registers  79  in storage unit  1 . The contents of storage unit  1  is next transmitted via CPU bus  59  to the CPU  53 . Similarly, when the trailing edge of the register or reference mark is detected, a trailing edge pulse is transmitted from differentiating circuit  72  via lead  74 , which activates AND-gates  78 , causing the contents of reference counter  52 , at that moment to be transferred into storage registers  81  of storage unit  2 . The contents of storage unit  2  is subsequently transferred via CPU bus  59  to CPU  53 . The CPU can next compute the time difference between the respective leading and trailing edges of each register and reference mark. It should be noted that counters  76 , the AND-gates  77 ,  78  and storage registers  79 ,  81  are shown only diagrammatically, and that several conventional details, such as reset functions, couplings  76  and data transfer gates etc. have not been shown in complete detail for the sake of clarity, since such details would be readily provided by a person having ordinary skills in design of electronic circuits. 
     The corresponding circuits for the other optical scanning device  2  (FIG. 1) are shown in the bottom part of FIG. 11 with the same parts marked with the same reference numerals with a prime, e.g. the pre-processing circuit is shown as box  54 ′, which constructed and operates in the same manner as pre-processing circuit  54 . The same remarks apply to storage units  56 ′ and  56   b ′, that are part of time difference circuit  60 ′. 
     FIGS. 12 a ,  12   b  and  12   c  show a flowchart describing the operation of the CPU in determining the register deviations, i.e. register errors, which are to be connected for the printing units. 
     The flowchart is described only briefly since the labels in each block are shown in sufficient detail to enable a person having ordinary skills in designing computer programs to provide a complete working program for the operation of the invention. The small numbered circles identify connections to parts of the flowchart shown on other sheets of the flow chart. 
     After start  100 , the register and reference marks are scanned and the leading and trailing edges P(I,K) are timed in steps  101  and  102 , until the marked edges for a respective unit are detected. Once a first leading edge is formed, a step counter is set for a first selected color n=O in step  103 . In step  104 , after the first color is selected, the edges P 11 -P 18  (FIG. 8) for storage unit  1  are searched. If no edges are found, an error or continue message is received in step  107 . Next the same color marks are searched in storage unit  2  in step  106 , and if not found an error message is again issued in step  107 . 
     When the edges are detected and their times are determined in the side register deviation equations SR 1  and SR 2 , if any, are computed by the CPU in step  108 , and the mean side register deviation SR is determined in step  109 . In step  111  the register deviations are normalized or standardized, i.e. converted from pulse count deviations to standard register deviations measured in e.g. millimeters in step  111 . 
     In step  112 , the circumferential deviation UR 1  is computed for storage unit  1 , and in step  113  for storage unit  2 , and standardized into millimeters in step  114 . 
     In step  116 , the diagonal register deviations DR are determined in normalized form as the difference between the respective circumferential register values UR 1  and UR 2 , and next, in step  117 , all register deviations in the first selected color are stored in memory of the CPU for subsequent execution, if necessary. 
     In step  118 , a test is made to determine if all colors have been scanned. If the answer is “no”, n is incremented by one in step  119 , returning the process to step  104 , and if the answer is “yes”, all register motors are activated to perform the required register corrections in step  121 .