Abstract:
A platform for supporting an engraving head in a manner accommodating translational movement without any associated rotation. The platform has a deck which is supported by a pair of flexible support columns. In operation the platform is situated alongside a rotating printing cylinder. The engraving head is mounted on the deck of the platform and is provided with a guide shoe which rides against the surface of the printing cylinder. As the cylinder rotates to angular positions having different radii, the engraving head responds with a purely linear reaction. Consequently the engraving head is able to engrave uniform-depth cavities in the surface of the printing cylinder. In two alternative embodiments the deck is driven by a resilient link arrangement which is coupled to a leadscrew and carriage assembly.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to electronic engraving devices for engraving ink-receiving cavities into the surface of a gravure printing cylinder. Such engraving devices commonly comprise an engraving head which includes a diamond stylus and a guide shoe. The guide shoe bears against the printing cylinder and provides a reference surface for the engraving process. An electromagnetic driver is mounted within the engraving head for oscillating the stylus into engraving contact with the printing cylinder. Meanwhile the printing cylinder rotates about its cylindrical axis. The engraving head is supported such that it moves parallel to the axis of the printing cylinder in synchronism with printing cylinder rotation. A typical prior art device is shown in Buechler U.S. Pat. No. 4,450,486. 
     A prior art device of the type disclosed in the Buechler patent supports the engraving head in a manner generally as illustrated in FIG. 1 hereof. Thus an engraving head 12 supports a guide shoe 13 against a print cylinder 10 which is rotating in the direction indicated by the arrow 11. Engraving head 12 rests upon a deck 16 which in turn is supported by a base 20. Base 20 is horizontally moveable as indicated by the arrow 15, while deck 16 is rotatable about an axis 18. Rotation of deck 16 about axis 18 produces rotational movement of engraving head 12 as indicated by the arrow 93. A diamond engraving stylus (not illustrated in FIG. 1) is mounted alongside guide shoe 13 and is brought into engraving contact against cylinder 10 by a combination of translational motion and rotary motion. During setup the rotational position angle of engraving head 12 is adjusted so as to align the guide shoe and engraving stylus to the cylinder surface and produce a desired printing cell depth for a predetermined stylus driving signal. Unfortunately the rotation of engraving head 12 changes the orientation of the stylus as well as its cutting depth. This produces unwanted engraving errors. 
     It is therefore seen that there is a need for engraving head support means capable of positioning a stylus against a printing cylinder by translational motion only. 
     SUMMARY OF THE INVENTION 
     In an engraving apparatus according to the present invention an engraving head translates a stylus, without rotation, into engraving contact with a rotating printing cylinder. The engraving head is mounted on a platform comprising a deck and a base joined by connection means which permit the deck to move relative to the base only by translation within a plane perpendicular to the axis of the printing cylinder. In one embodiment the connection means comprise a pair of parallel support columns. The support columns may be deflected in parallel fashion to enable movement of the deck relative to the base. However, the deck remains parallel to the base at all times. The engraving head rests on the deck and cannot rotate relative to the printing cylinder. 
     Preferably the support columns are secured fast to the deck and the base and accommodate translation of the deck by parallel flexing. The flexing occurs within a plane perpendicular to the axis of rotation of the printing cylinder, and a parallel relation between the deck and the base is maintained. The platform is so constructed as to prevent relative movement between the deck and the base in a direction parallel to the axis of the printing cylinder. 
     In alternate embodiments the connection means comprise a carriage driven by a motor and a leadscrew which are mounted in the base. A resilient link arrangement couples the carriage to the deck. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a side elevation sketch of a prior art support arrangement for an engraving head. 
     FIG. 2 is a side elevation sketch of a support arrangement for an engraving head according to the present invention. 
     FIG. 3 is an enlarged view of a portion of FIG. 2. 
     FIG. 4 is a top plan view illustrating the geometrical relationship between an engraving stylus and a guide shoe. 
     FIG. 4a is a schematic illustration of the engraving action of the present invention. 
     FIG. 4b is a schematic illustration of the engraving action which results when engraving head rotation is permitted to occur. 
     FIG. 5 is a perspective view of the upper end of a front support column. 
     FIG. 6 is a cross-sectioned side elevation view of a second embodiment of an engraving head support arrangement. 
     FIG. 7 is a cross-sectioned side elevation view of a third embodiment of an engraving head support arrangement. 
     FIG. 8 is a perspective drawing of the support arrangement of FIG. 6. 
     FIG. 9 is a perspective drawing of the support arrangement of FIG. 7. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A support platform 50 according to the present invention may be configured as illustrated generally in FIG. 2. Platform 50 supports an engraving head 12 for translational movement between a position illustrated in solid lines and another position illustrated in dotted lines. A bias mechanism, such as a compression spring 26, urges engraving head 12 toward a normal operating position wherein a guide shoe 13 is in surface-to-surface contact with printing cylinder 10. A second such compression spring may be installed at the remote end of platform 50. The movement is two-dimensional and parallel; no rotation being permitted. The plane of movement is perpendicular to the axis of rotation 45 of printing cylinder 10. Referring now to FIG. 4, there is shown a top plan view of an engraving stylus 14 and a guide shoe 13. When guide shoe 13 is ideally positioned, as illustrated in FIG. 4, it contacts printing cylinder 10 along a contact line 34. Cutting tip 98 of stylus 14 cuts into printing cylinder 10 along an extension of contact line 34. The engraving action thereof is illustrated in FIG. 4a. 
     As shown in FIG. 4a, cutting tip 98 oscillates in the direction of the double headed arrow 17 so as to cut into the surface 30 of printing cylinder 10. Printing cylinder 10 moves in a direction as indicated by the arrow 11, and the oscillating stylus cuts a channel indicated by the profile 32. 
     During engraving the guide shoe 13 and stylus 14 may move radially toward and away from the axis of the printing cylinder 10 to accommodate for runout due to the surface condition of the printing cylinder 10. In the embodiment being described, this radial movement is in the order of about 0-0.01 inch, but it could be less or greater if desired. A prior art arrangement as illustrated in FIG. 1, the distance between stylus 14 and axis 18 may be in the order of about 6 inches. Therefore stylus 14 rotates relative to cylinder 10 through an angle of about 1/2 milliradian. This is illustrated in exaggerated form by the angle A of FIG. 4b. Such rotation of stylus 14 causes an alteration of the engraving action. Thus, stylus 14 may engrave cavities as illustrated by the phantom line 32a whereas cavities 32 are desired. 
     Platform 50 comprises a deck 15 supported upon a base 24 by a front support column 22a and a rear support column 22b. Preferably the support columns are secured fast to the deck 20 and base 24 at fixed points of attachment. Support columns 22a and 22b are of matching construction and may be flexed to accommodate parallel motion of engraving head 12. In the unstressed or rest position, columns 22a and 22b extend perpendicularly between deck 15 and base 24. Base 24 is connected to a suitable driving mechanism (not illustrated) operative in the direction indicated by the double arrows 25 for driving platform 50 from a rest position to an operating position shown in solid lines in FIG. 2. A compression spring 26 maintains guide shoe 13 in contact with printing cylinder 10 during normal operation. Thereafter guide shoe 13 maintains contact with the surface of cylinder 10 by linear movement only (as shown in exaggerated form by the dotted lines in FIG. 2). 
     FIG. 3 illustrates front support column 22a in more detail. In the illustrated embodiment, support column 22a comprises a beam 40, an upper leaf spring 42 and a lower leaf spring 44. Upper leaf spring 42 may be fabricated from spring steel and joins deck 15 to beam 40. Lower leaf spring 44 is likewise of spring steel construction and joins beam 40 to base 24. Beam 40 may be a rigid member, if desired. Alternatively, beam 40 and leaf springs 42,44 could be replaced by a single leaf spring. During translation of deck 15, leaf springs 42,44 are flexed as indicated by the dotted lines in FIG. 3. 
     FIG. 5 illustrates the front upper leaf spring 42 in perspective. It will be seen that leaf springs 42,44 and beam 40 extend a substantial distance in a direction parallel to cylinder axis 45 so as to inhibit flexing of support columns 22a, 22b in that direction. It will be understood, however, that base 24 is attached to a carriage (not illustrated) which is driven in a controlled manner in a direction parallel to the axis 45. It is desired that motion of stylus 14 in the direction of the cylinder axis be restricted to that which is imparted by a carriage 27 (FIG. 2) on which the base 24 is mounted. 
     A second embodiment of the invention may be constructed as generally illustrated in FIGS. 6 and 8. In this embodiment the engraving head 12 is supported by a platform 150 having a base 124 in the form of a track channel. A leadscrew 108 is mounted in base 124 and is driven by a motor 110. A carriage 102 is threadably engaged by leadscrew 108 for horizontal movement in response to rotation of motor 110. Carriage 102 supports a guideway 104 having end walls 132 and 134. Engraving head 12 rests upon a deck 115 supported within guideway 104. A pair of compression springs 106,107 are compressed between deck 115 and end walls 132,134 respectively of guideway 104. As illustrated in FIG. 8, a pair of fingers 112,114 are mounted on a side wall of guideway 104 and are sensed by a proximity sensor 116 supported on deck 115. 
     The embodiment of FIGS. 6 and 8 is set up by operating motor 110 to move engraving head 12 in a direction toward printing cylinder 10. When guide shoe 13 comes into engagement against the surface of printing cylinder 10, compression-spring 106 begins compressing, and fingers 112,114 begin moving relative to proximity sensor 116. Proximity sensor 116 is connected to terminate power to motor 110 when a predetermined movement of fingers 112,114 has been sensed. This causes guide shoe 13 to ride against printing cylinder 10 with a predetermined contact force. The contact force is a function of the spring constants of compression springs 106,107. Preferably, one of springs 106,107 has a stiffness slightly greater than the other, so that a finite contact force is maintained. Preferably, base 124 incorporates bearing tracks (not illustrated) for providing guided linear movement of carriage 102. In the embodiment being described, the bearing tracks may be conventional linear bearing tracks. 
     A third embodiment of the invention is illustrated in FIGS. 7 and 9. The embodiment of those figures is similar to the embodiment of FIGS. 6 and 8 in that it employs a base 124 fitted with a leadscrew 100 driven by a motor 110. A carriage 202 is threadably engaged by leadscrew 108. Carriage 202 drives an upstanding arm 213 which extends upwardly into an opening 211 in deck 204. Deck 204 is mounted on a table 205 which receives, but does not engage, leadscrew 108. Carriage 202 and table 205 may have bearings 264,266 respectively which ride within a track 260 in base 124. A second track and other bearings (not illustrated) may be provided opposite track 260 and bearings 264,266. 
     Deck 204 supports engraving head 12 and is driven by forces exerted upon a pair of compression springs 206,207 by arm 213. Arm 213 is upwardly terminated by a pair of fingers 212,214 which are sensed by a proximity sensor 216. Proximity sensor 216 is supported by deck 204 so as to sense relative movement of fingers 212,214 which occurs during setup when guide shoe 13 comes into contact with the surface of printing cylinder 10. As with the previously discussed embodiment, a predetermined relative movement of fingers 212,214 causes proximity sensor 216 to disconnect power from motor 110. Again, guide shoe 13 rests against the surface of cylinder 10 with a predetermined force. 
     An engraving head platform according to the present invention eliminates the prior art head pivoting mechanism while improving engraving accuracy. Advantageously, the guide shoe may be brought into direct contact with a rotating printing cylinder without any need for manual setup. 
     While the form of apparatus herein described constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to these precise forms of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.