AU596568B2

AU596568B2 - Method of positioning printing plates before cutting registration holes and apparatus for carrying out the method

Info

Publication number: AU596568B2
Application number: AU50298/85A
Authority: AU
Inventors: Klaus Reuter; Klaus-Peter Schoen
Original assignee: Hoechst AG
Current assignee: Hoechst AG
Priority date: 1984-11-27
Filing date: 1985-11-22
Publication date: 1990-05-10
Anticipated expiration: 2005-11-22
Also published as: EP0184063A2; DE3575481D1; JPS61143759A; AU5029885A; EP0184063A3; AU4991290A; EP0184063B1; DE3443178A1

Description

7- C0,11MONWEALTH OF'PUST~.

PATENTS 'ACT, '1952 1 CO1iPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE 9 6 5jI28a Short Titlei Int. Cl 4 Application Num~ber- 50 Lodgedc 2c) Complete Specification-Lodged- Accepted: Lapsedg Published: ,Vriority: SRe~lated Art: Got This document contains the amendmer-ts made under Section 49 and i~s corftet for prirnting.

TO BE COMPLETED BY APPLICiTT1 N~am~e of Applicant, Address of Applicant.,

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1 4t tl Inventor; A*.ddress for Se rvice: HOE CHST AKTI ESEISCHAFT 6230 Frankfurt/Main 80, Gernany Klaus-Peter SQIOEN and Klaus IER ARTHUR S. CAVE CO., Patent and Trade Mark Attorneys, 1 Alfred Street, Sydney, New South Wales, Australia, 2000.

Complete Specification for _The invention entitled: ".TETHOD OF ?obiTiON INGA DRINI)JW, PL19TC- 1-fo'E CuitIN~ 1t8&15TR.A-1ON ftLeS ANJ APPARA-TUS Foa CAt4NaI CLCT TMlE The following statement is a full description of this invention, including the best method of performing it known to mezmero ra O POSITIONING PRINTING PLATG BFp3 CItIJN& R lStlV.fTIO t"-OLrS NlhD APVAMAfUS FbZ CfqlR,\NG OUT ltf MEc-1TDD.

BACKGROUND OF THE INVENTION The invention relates to a process for the positioning of printing prior to the punching of register apertures.

e Following exposure and development in a tr Srftces Cte printing plate developing machine, printing such C C Sas for example, printing plates, are fed to automatic t c plate punches, in which register apertures are punched 10 in the individual printing plate; such apertures permit the printing plate in each instance to be clamped .in an accurately aligned configuration on a printing cylinder for the printing process.

In the case of known semi-automatic plate punches, such as those manufactured by the company Barenschee, Luneburg, Federal Republic of Germany, the plates are manually inserted and removed, while the S' punching process takes place automatically, being ini- C tiated by a three point contact device as soon as the S 20 printing plate rests against three contact positions of the device. The register apertures of printing plates o are inter alia also provided for the chamfering of the plates which defines the correct register and which is required for the clamping of the printing plates on the rotary press. The chamfering of plates in the correct register is in general carried out by means of an autopTai -lamatic chamfering machine, which is composed of a collecting unit, a cycle initiation unit and a chamfering unit. The collecting unit of the automatic machine is connected to the printing plate developing machine, from which the plates, depending upon the particular requirements in each instance, are accepted so as to be guided further along a straight path or with a change in direction. In the chamfering unit, the printing plate is very accurately positioned by means of register pins and subsequently chamfered accurately.

The punching of register apertures is in general carried out after the development of the printing plate, since punching prior to development of the printing plate renders application of toner thereto t€ more difficult and in certain circumstances can lead to the collapse of the charging vol.tage in consequence of C surface leakage currents, which are formed as a result of t* t Cthe punching from the layer of the printing plate to be 20 developed in the direction of the reverse side of the printing plate. Collapse of this charging voltage also *0 leads in general to an undesired discharge of carrier particles of the developer.

In the event that punching takes place after the development of the printing plate, it is necessar, to locate the position of the printing plate during It S. exposure and punching with accuracy. In the case of known automatic punching machines, it is in general 11(CCC only possible with the use of an expensive mechanical system to observe the accuracy required. In this pro- S: cedure, there is a risk that instances of deformation of the plate edges will arise, since with the use of a Sthree point contact device the same contact points must in- 49 variably be approached, for example, in such a manner that the two longitudinal edges and one narrow edge are subjected to coarse -2- 71N alignment by mechanical displacement in one working procedure until they rest against the three contact points. In this procedure, mechanical forces are created, which can lead to deformations of the plate edges; as a result of this, different positions of the printing plate can arise at the contact points. In this event, the printing area of the printing plate is not in agreement with the register apertures. It is entirely obvious that in the case of printing in four colors errors take place if the printing area of only a single 9, printing plate is not in agreement with the register apertures.

The deformations principally occur by reason of the fact *099 S: that the three point contact device of conventional plate a punches aligns the printing plate as quickly as possible and with appropriate force in one operational step, in such a manner that the printing plate comes into contact with the contact points.

O S SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide a process and apparatus for the positioning of printing 9 plates with great accuracy.

69o *9e It is another objection of the invention to provide a S process and apparatus, as above, which operates without mechanical deformation of the plate edges of the printing plate.

:Tt is yet another object of the invention to provide a rpd as process and apparatus, as above, which operates at lest a conventional positioning processes and plate punches.

The objects of the invention are achieved by a process for the positioning of printing surfaces prior to the punching of S3 1853- RA 1853E i register apertures, comprising the steps of exposing a printing surface with a pattern having measurement marks in a predetermined position relative to the printing area of the pattern, the measurement marks being exposed simultaneously with the printing surface,, developing the printing surface and the measurement marks by means of a toner; optically measuring the developed measurement marks to produce measurement values indicative of the position of said rr,,asurement marks; and aligning the printing surface in response to said measurement go* values. The aligning step includes a coarse alignment step, Roe followed by a fine alignment step until a maximum value of said measurement values is achieved.

The objects of the jivention are also achieved by an apparatus for the positioning of printing surfaces prior to the punching of register apertures, comprising a laser light source t for producing a beam of laser light; a beam splitter positioned in the beam path of the laser for splitting the beam into two laser beams; a separate lens positioned in the path of each split laser beam; a deflecting mirror positioned in the path of the first split laser beam, the mirror deflecting the first split beam to a direction parallel to that of the second split beam; and a separate annular element having a light sensitive layer and positioned in the path of each split laser beam past AX the lenses, the annular elements being irradiated in the centers thereof by a respective split laser beam. The split laser beams passing through the centers of the annular elements impinge upon measurement marks of a printing surface, and are reflected off the measurement marks and back onto the light -4- 1853E sensitive layers.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in greater detail herein below, with reference to the drawings. In the drawings: Fig. 1 shows a plan view of a printing surface, for example in the shape of a printing plate, which exhibits measurement marks and register apertures; Fig. 2 shows a plan view of a circular measurement mark which is developed with toner and which is situated on the printing plate according to Fig. i, as well as the inter-relationship between a white surface of the measurement mark and the intensity distribution of a measurement light beam which illuminates the measurement mark; Fig. 3 shows a basic arrangement for the positioning of the printing plate; and Fig. 4 shows a schematic representation of details of the arrangement according to Fig. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In execution of the invention, at least two measurement o marks on the printing surface are exposed, of which one measurement mark consists of a circular black surface with a circular white surface in the center and the other measurement mark consists of two lines extending parallel to one edge of the printing surface with a white surface of from about 0.05 to about 0.4 mm width between the lines. Expediently, a respective measurement light beam illuminates the two developed o measurement marks; in this event, the light refle, ted by the i measurement marks is measured and the printing surface is 1 TN Oll,.' 1853E

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I ~L ii:irl illr._lrr~xrr. i positioned, in accordance with the intensity of the reflected light, until a maximum intensity of the reflected light is produced.

A laser beam with a Gaussian intensity distribution is preferably employed as a measurement light beam. In this event, the diameter or the breadth of the white surface of each measurement mark is chosen to be equal to a beam width of the measurement light beam which is between the level of the half width of the measurement light beam and the breadth of the measurement light beam at a level which corresponds to the l/e 2 intensity of the measurement light 4 4* *r 4 44,, 4 44 04 *r 4 *4* 4.

*s 4 4* 4 44 44 4 44 4o .4444 .444 4444 5a 1853E 1.

i,? i beam.

In the arrangement for carrying out the process, a laser of fixed position, a beam splitter in the beam path of the laser to split the beam into two laser beams, lenses and a deflecting mirror are present in the beam paths of the laser beams, each laser beam passes through an annular light-sensitive element in the center, the light-sensitive layer of which faces the printing and the laser beams impinge on the measurement marks and are reflected by these onto the light-sensitive layer bf the pertinent annular element.

A printing plate 5 shown in Fig. 1 exhibits along its narrow sides register apertures 18, 20 and 19, which have different shapes. A measurement mark 21 near to one register aperture 20 consists of a circular r black surface having a diameter of from about 1 to about 3 mm, which exhibits in the center a white surface having a diameter of from about 0.05 to about 0.4 mm. A measurement mark 22 situated opposite to

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tVz 20 this measurement mark 21 consists of two lines, extending parallel to the longitudinal edge of the c E :4 printing plate 5, having a length of from about 2 to about 5 mm, which in the case of a breadth of 1 to 3 mm include a white surface of from about 0.05 to about 0.4 mm. The breadth of this white surface or the spacing between the two lines of this measurement mark 22 is equal to the diameter of the white surface of the

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F other measurement mark 21. Although this is not shown, C, t'i r it is also possible for more than two measurement marks AlCa: 30 to be disposed on the printing plate 5. Opposite to C the measurement marks 21 and 22 there are situated the ILtwo surfaces for chamfering of the printing plate es in which the register apertures 18, 20 and 19, respectively are also situated. When the plate is chamfered to register, which is in general necessary for the clamping of the printing plate on the rotary press, -6-

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i pl-- d- arrraaspr~ a~ these surfaces are chamfered in the chamfering unit of an automatic chamfering machine along the lines shown dotted in Fig. 1 parallel to the narrow sides of the printing plate 5, after the printing plate has previously been positioned with great accuracy by means of register pins which pass through the register apertures 18, 20 and 19 respectively.

The measurement marks 21 and 22 are exposed in a predetermined position in relation to the printing area of the pattern, which is projected onto the charged printing plate 5, and subsequently the printing plate 5 is developed with toner. Subsequently, the developed measurement marks 21 and 22 are fixed and the coating is removed, and they are correlated with the printing area with accuracy in terms of position. The patterns for the measurement marks 21, 22 are situated Icc for example on the glass plate of a pattern holder, I- r into which the pattern to be exposed on the printing plate 5 is inserted. Another possibility for the expo sure of the measurement marks consists in printing the latter onto a measurement foil or a mounting foil, a C which prior to exposure is placed on the pattern in the a i t pattern holder. As will be described in greater detail hereinbelow, the developed measurement marks 21, 22 are measured optically, in order to position the printing C plate 5 with great accuracy for the punching of the register apertures 18, 20 and 19 respectively. The alignment of printing plate 5 takes place in the first E instance by a coarse displacement, which is followed by 30 a fine displacement, which takes place on the basis of the measured values received from the measuring marks 0 of the reflected measurement light beams until such o time as the measurement values have reached a maximum value.

Before details are given concerning the measurement procedure or concerning the positioning of -7- ,i L~~~~~lii~llC~bU1- I; i a~: the printing plate 5, an explanation will be given, with reference to Fig. 2, of the inter-relationship between the circular measurement mark 21 and the intensity distribution of the measuring light beam which illuminates the measurement mark 21. A laser beam with a Gaussian intensity distribution is employed as a measurement light beam which illuminates the measurement mark 21. The diameter d of the white surface of the measurement mark 21, 22 is on the one hand greater than the half width of the measurement light beam and on the other hand is smaller than the breadth of the measurement light beam at a level which corresponds to the l/e 2 intensity of the measurement light beam. It is also true in an analogous manner, although this is not represented, in the case of the measurement mark 22 that the spacing or the breadth of the white surface between the two lines of this measurement mark which r rr are parallel to one another is on the one hand greater Sr than the half width of the measurement light beam and on the other hand smaller than the breadth of the Smeasurement light beam at a level equal to the l/e 2 intensity of the measurement light beam. For the positt C Ftioning of the printing plate 5, a respective measurement light beam illuminates the two developed measurement marks 21 and 22, and the light reflected c from the measurement marks is measured and the printing Splate is positioned, in dependence upon the intensity of the reflected light, until a maximum intensity of the reflected light is achieved. In this connection, use is made of the fact that the reflectivity of the white surface of the measurement marks is approximately equal to 20 times the amount of the reflectivity of the black surfaces, of the sllrfaces developed with toner, of the measurement marks. If the individual light beam is reflected in part by the black surface and in part by the white surface, then the intensity of -8the reflected measurement light beam adopts a specific value which becomes greater with an increasing proportion of the white surface in the illumination of the measurement mark or in the reflection of the light measurement beam and reaches a maximum value in circumstances in which the white surface of the measurement mark is centered in relation to the measurement light beam as a result of an alignment corresponding to the increase in the measured intensity of the reflected light measurement beam.

Fig. 3 shows schematically a basic arrangement for the positioning of the printing plate 5, while details of this arrangement are schematically represented in Fig. 4. The arrangement comprises a laser 1 of fixed position, a beam splitter 2 in the beam path of the output beam of the laser 1, which splits the output beam into two laser beams 6 and 8 which extend in the first instance perpendicular to one another and Cr of which the laser beam 6 is directed by means of a deflecting mirror 7 parallel to the other laser beam 8.

IV C r In the beam paths of the laser beams 6 and 8 there are 4 situated lenses 3 and 4, which are disposed in front of 4 annular light-sensitive elements 9 and 10. These annular elements 9 and 10 are irradiated at the center by the respective laser beams 6 and 8 and their lightsensitive layers face the printing plate 5. The laser beams 6 and 8 impinge upon the measurement marks 21 and 22 and are reflected by these onto the light-sensitive St t layer of the respective pertinent annular elements 9 and 30 10. The annular elements 9 and 10 can be photodetectors, which consist of a number of photocells, which are disposed in an annular configuration about the It laser beam. The photocells can, for example, be large area silicon cells. In place of a single laser, the beam of which is split by means of a beam splitter into two laser beams, it is also possible for two lasers to -9r be provided, each of which directs a measurement light beam directly onto the printing plate 5. If more than two measurement marks are present on the printing plate then a corresponding number of laser beams must be provided. The intensity distribution in each individual laser beam is Gaussian. As has already be!en mentioned previously, the diameter of the individual measurement light beam which is used is greater than the diameter or the breadth of the white surface of the measurement marks. In this procedure, preference is given to a beam width at which the diameter or the breadth of the white surface of the individual measurement mark cuts the measurement light beam between the 1/e 2 and the half intensity level. The measurement light beams impinge perpendicularly on the printing plate 5, and are disposed in a positionally fixed relation to the punching tool in the chamfering unit of an automatic chamfering machine.

As is evident from Fig. 4, the electrical outputs of the annular elements 9 and 10 are connected with C current/voltage converters 11 and 12. In the voltage converters, the photoelectric current generated by the reflected measurement light beam in the respective annular light-sensitive element is converted into a direct current voltage which is supplied to the control circuits 13 and 14. The control circuit 13 is connected with linear displacement elements 15 and 16 for the positioning of the printing plate 5Sin the x and y C C, direction. The control circuit 14 is connected with a rotary displacement element 17 for the positioning of the printing plate 5 with reference to an angle of '.rotation'1' in the x-y plane. The linear displacement elements and the rotary displacement element comprise known components; in this connection, a chain of movement consists in general of a motor, rotary sensor, reduction gear and a shaft-nut-gear.

The coarse poitioning of a printing plate takes place along a narrow side and a longitudinal side to an accuracy of approximately 0.2 to 0.3 mm. In this proceduze, the measurement marks 21 and 22 are in part illuminated by the respective lser beams 6 and 8. For the fine positioning, for example in the first instance the measurement mark 21 is aligned by means of the linear displacement elements 15 and 16 with great accuracy; in this connection, this measurement mark forms the fulcrum for the subsequent fine displacement with the aid of the rotary displacement element 17. To this end, the rotary displacement element 17 is actuated until such time as the measurement light beam reflected by the measurement mark 22 has reached a maximum.

E The white surfaces of the measurement marks 21 and 22 are in general formed by the anodized aluminum

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C of the printing plate 5; this possesses a reflection which is substantially increased in relation to the r 20 toner-developed positions of the printing plate 5. The rlaser beams are reflected at various angles by the ,rough surface of the printing plate 5, so that it is ensured that the reflected laser beam impinges on the pertinent light-sensitive element 9 or 10 respectively and is not precisely reflected back into its beam path.

The measurement marks can also be reflected C tonto the printing plate 5 with the aid of a suitable optical system, in the event that the mounting foil haF no further place for the application of the measurement 30 marks. A further possibility for the application of the measurement marks consists in that the patterns for es the measurement marks to be projected onto the printing 00 plate are disposed on the end surfaces of the register pins for the printing pattern in the pattern holder.

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Claims

1. A process for the positioning of printing surfaces prior to the punching of register apertures, comprising the steps of: exposing a printing surface with a pattern which has measurement marks in a predetermined position relative to the printing area of said pattern, said measurement marks being exposed simultaneously with said printing area; developing said printing surface including said measurement marks; illuminating said measurement marks with measurement light beams and measuring the intensity of light reflected from the measurement marks to obtain measurement values indicative of the position of said measurement marks; and t positioning by aligning said printing surface in response to said measurement values, wherein said aligning step includes a coarse alignment step followed by a fine alignment step until an optimum value of said measurement values is achieved.

2. The process as claimed in Claim 1, wherein said exposing step includes exposing at least two measurement marks on said printing surface, one said measurement mark consisting of a circular black surface having a circular white surface in the center thereof, and said other measurement mark consisting of two lines extending parallel to one edge of sQ3d printing

9- surface with a white surface of from 0.05 to 0.4 mm breadth between said lines. 3. The process as claimed in Claim 2, wherein respective measurement light beams illuminate each of said two developed measurement marks, the light reflected from said measurement -12- V- 08 6e/AC 2 I, Y marks being measured, and the printing surface positioned, as a function of the intensity of the reflected light, until a maximum intensity of the reflected light is reached. 4. The process as claimed in Claim 3, wherein a laser beam with a Gaussian intensity distribution is employed as a measurement light beam. The process as claimed in Claim 4, wherein the diameter or the breadth of the white surfPce of each measurement mark is selected to be between the half width of the measurement light beam and the breadth of the measurement light beam at a level which corresponds to 1/e 2 of the intensity of the measurement light beam. 6. An apparatus for the positioning of a printing surface prior to the punching of register apertures which comprises: r a printing surface with an exposed pattern, said pattern comprising measurement marks in a predetermined position relative to the printing area of said pattern, said printing surface having also been developed; one or more laser light sources for producing one or more beams of laser light, each of said laser light sources dire ting a measurement beam directly onto said printing surface, whereby the number of measurement beams corresponds to the number of said measurement marks; a separate lens positioned in the path of each said measurement laser beam; a separate annular element having a light-sensitive layer and positioned in the path of each said measurement laser beam between said lens and said printing surface, wherein each said 13 0186e/AC 'j t 6 S- measurement laser beam passes through the centre of said annular element and impinges upon said measurement marks on kaid printing surface, each said measurement laser beam being reflected off said measurement marks and back onto said light sensitive layer of the annular element, whereby the intensity of light reflected from the measurement marks is measured to obtain measurement values indicative of the position of said measurement marks; and positioning means to align said printing surface in response to said measurement values by a coarse alignment followed by a fine alignment until an optimum value of said measurement values is achieved. 7. An apparatus for the positioning of a printing surface r* 9 I prior to the punching of register apertures which comprises: a printing surface with an exposed pattern, said pattern comprising measurement marks in a predetermined position relative to the printing area of said pattern, said printing surface having been developed; 0" one laser light source having a beam splitter positioned in the beam path of said laser source for splitting the beam into two split laser beams being measurement beams directed o onto said printing surface; t 'a deflecting mirror positioned in the path of a first said split laser beam, said mirror deflecting said first split beam to a direction parallel to that of the second said split beam; a separate lens positioned in the path of each said split laser beam; 14 I t\Sl0186e/AC >I- a separate annular element having a light-sensitive layer and positions in the path of each said split laser beam between said lens and said printing surface, wherein each said split laser beam passes through the centre of said annular element and impinges upon said measurement marks on said printing surfaces, each said split laser beam being reflected off said measurement marks and back onto said light sensitive layer of the annular element, whereby the intensity of light reflected from the measurement marks is measured to obtain measurement values indicative of the position of said measurement marks; and positioning means to align said printing surface in Sresponse to said measurement values by a coarse alignment followed by a fine alignment until an optimum value of said 4444 S* measurement values is achieved. 8. The apparatus as claimed in claim 6 or claim 7, wherein each annular element comprises a plurality of photocells as photosensitive elements. moar 9. The apparatus as claimed in claim 6 or claim 7, wherein .9 the electrical outputs of the annular elements are connected with a pair of current/voltage converters. The apparatus as claimed in Claim 9, wherein one of said current/voltage converters is connected with a control circuit, which co-operates with the linear displacement elements for the positioning of said printing surface in the x and y direction, and wherein the other said current/voltage converter is connected with a control circuit which is connected with the rotary displacement element for the positioning of the printing

86- 01TeA 0186e/AC Vz i_ ;I :----LI~1IYL~L IIU~~ -P I*I~YI~-ill-t T IXI X l_(_il surface with reference to an angle of rotation in the x-y plane. 11. The apparatus as claimed in claim 6 or claim 7, wherein the'patterns for the measurement marks are disposed on a glass plate of said pattern holder for the patterns to be exposed on the printing surface, on a measurement foil, or on a mounting foil. 12. The apparatus as claimed in claim 6 or claim 7, wherein said patterns for the measurement marks to be piojected on said printing plate are disposed on the end surfaces of register pins which register the printing patterns in said pattern holder. 13. A process for the positioning of printing surfaces prior to the punching of register apertures, substantially as herein described with reference to the drawings. 14. An apparatus for the positioning of printing surfaces prior to the punching of register apertures, substantially as herein described with reference to the drawings. *4 4 DATED this 15th day of February, 1990. S" I C HOECHST AG By Its Patent Attorneys ARTHUR S. CAVE CO. 16 0 18 6e/AC r