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:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of Ser. No. 08/474,104, filed Jun. 7, 1995 now U.S. Pat. No. 5,767,981, which is a continuation of Ser. No. 08/091,302, filed Jul. 12, 1993, now U.S. Pat. No. 5,454,306. 
    
    
     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. 4 a  is a schematic illustration of the engraving action of the present invention. 
     FIG. 4 b  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 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. 4 a.    
     As shown in FIG. 4 a , 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 ½ milliradian. This is illustrated in exaggerated form by the angle A of FIG. 4 b . Such rotation of stylus  14  causes an alteration of the engraving action. Thus, stylus  14  may engrave cavities as illustrated by the phantom line  32   a  whereas cavities  32  are desired. 
     Platform  50  comprises a deck  15  supported upon a base  24  by a front support column  22   a  and a rear support column  22   b . Preferably the support columns are secured fast to the deck  20  and base  24  at fixed points of attachment. Support columns  22   a  and  22   b  are of matching construction and may be flexed to accommodate parallel motion of engraving head  12 . In the unstressed or rest position, columns  22   a  and  22   b  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  22   a  in more detail. In the illustrated embodiment, support column  22   a  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  22   a ,  22   b  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  108  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.