Abstract:
An engraver having an engraving head is provided wherein replaceable components, such as tools, of the engraving head are formed with a cartridge-style construction. For example, in one aspect of the engraving head, a cartridge-type diamond stylus is provided having a trapezoidal cross-section for facilitating positive registration and positioning of the stylus within the engraving head. Other tools, such as a shoe and/or burr cutter may also be provided in a detachable cartridge arrangement to facilitate quick mounting and replacement of an existing shoe or burr cutter, respectively, such that the shoe or burr cutter also becomes aligned and registered on the engraving head.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an engraver, and more particularly, to an engraving head having components which are easily mounted to the head and which are easily aligned with a plated cylinder to be engraved. 
     2. Description of Related Art 
     The basic principle of electro-mechanical engraving of a gravure cylinder involves rotating a plated cylinder while actuating an electrically driven tool which cuts or engraves cells or lines into the surface of the plated cylinder. The engraved cylinder is normally used in a web-type gravure printing press for printing paper, plastic, metallic film material, or other printed material. 
     In the gravure printing process, the engraved cylinder is flooded with ink, and a doctor blade wipes off excess ink from the surface so that only the engraved cells contain ink which is transferred to the material being printed. To obtain a high quality print, it is necessary that the cells be very accurately placed or located on the cylinder surface, usually within one or two microns of a desired predetermined location. The depth of the engraved cells must also be accurately controlled since the depth determines the amount of ink transferred which, in turn, determines the shade of gray in a black/white print, for example. In a color print, the amount of ink transferred to the paper or materials is even more critical since multiple colors are typically mixed to produce various shades of all possible colors. A slight variation in the desired amount of ink effects not only the color, but, more importantly, the density of the desired color. 
     In order to properly control the depth of the cells, the relative location between the plated cylinder and the electrically driven tool, which is typically a diamond stylus, must be accurately controlled. In order to ensure that the stylus is maintained at a constant distance from the plated cylinder as the cylinder rotates in an engraving process, the engraving head containing the stylus is provided with a diamond shoe tool which contacts the cylinder to maintain a desired predetermined spacing between the stylus and the cylinder. In the past, a diamond shoe tool has been used incorporating either a single ball-shaped engaging surface or a flat diamond engaging surface which requires precise tangential alignment relative to the cylinder surface. The ball-shaped diamond shoe tool provides a relatively small radius providing a small contact area between the shoe tool and the cylinder such that the ball shoe tool typically follows the irregularities in the cylinder surface well. However, this small contact area also results in a relatively high force being applied at the point of contact and, as a result, a ball shoe tool cannot be used for multiple pass engraving processes in that the shoe tool tends to distort or otherwise damage the cell walls created by the stylus on earlier passes. The flat diamond shoe tool is normally formed with a size sufficient to permit a better distribution of forces. However, although the flat shoe tools provide better distribution of forces applied to the cylinder than ball shoe tools, the flat shoe design often does not intimately follow the contours of the cylinder surface. 
     The placement of the diamond stylus within the engraving head of the engraver is also critical to proper formation of the engraved cells. In the past the stylus was mounted to a tool holder which was then located within an elongated aperture formed in a stylus arm wherein the tool holder would be manually positioned at a selected location within the aperture to cause the stylus to project outwardly a desired distance. Once the stylus was located in the desired position, fasteners threaded into the stylus arm were moved into engagement with a clamp member which would then cause the tool holder to frictionally engage the walls defining the aperture in the stylus arm. Typically, the tool holder would be formed with a D-shaped cross section having a flat side and a curved side, wherein the clamping member would engage the flat side of the tool holder and the curved side thereof would be forced into engagement with a cooperating curved surface of the aperture in the stylus arm. Thus, mounting of the stylus within the stylus arm required an operator to perform an alignment procedure in order to ensure that the placement of the stylus within the stylus arm was accurate. 
     When the stylus exits an engraved cell, a burr of material is commonly created around the edges of the cell, and the burr material is removed by a diamond burr cutter mounted on the engraving head adjacent to the location of the stylus and the diamond shoe tool. Past burr cutters have comprised diamond tools having a cutting edge which was located over the center of an engraved cell or row of engraved cells to remove the burr material. The alignment between the burr cutter and the cylinder would vary with variations in the diameter of the cylinder such that it was necessary for an operator to perform an alignment operation to place the cutter in tangential engagement with the cylinder surface whenever the cylinder diameter was changed. 
     Accordingly, there is a need for an improved engraving head which provides for simplified mounting and alignment of the stylus within the engraving head, and including a simplified mounting for a self-aligning shoe which provides for improved alignment of the engraving head relative to the cylinder. In addition, there is a need for a burr cutter for use on an engraving head wherein the burr cutter may be used on a variety of cylinder diameters without requiring adjustment of the burr cutter to obtain tangential alignment with the cylinder. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved engraving head which includes a stylus adapted to be quickly aligned within the engraving head, a diamond shoe tool which is adapted to align itself to a surface of a cylinder and a burr cutter which is adapted to be used with a plurality of cylinders having different diameters without requiring manual alignment to accommodate the different cylinder diameters. 
     In one aspect of the invention, a stylus assembly is provided for use in an engraving apparatus wherein the stylus assembly comprises stylus means and mounting means for receiving the stylus means, the mounting means including positioning means for cooperating with the stylus means to define a predetermined stop position for the stylus means. The mounting means includes a stylus arm including means defining an aperture for receiving the stylus means and the stylus means is preferably in the form of a stylus cartridge including a stylus mounted to a stylus holder. 
     The aperture in the stylus arm includes an integral end wall for engaging an end of the stylus holder in abutting contact whereby the stylus is caused to project from the stylus arm a predetermined distance toward a cylinder to be engraved. 
     In addition, the stylus holder is formed having a trapezoidal cross-section wherein opposing angled walls of the stylus holder are adapted to engage cooperating walls within the aperture. The engagement between the walls of the stylus holder and the walls of the aperture cause the stylus cartridge to be angularly oriented and positively positioned within the aperture of the stylus arm. 
     In another aspect of the invention, a shoe tool assembly is provided which is adapted to engage a surface to be engraved to maintain a predetermined spacing between the engraving head and the surface to be engraved wherein the shoe assembly comprises a support means and shoe means supported by the support means and including at least one non-planar contact means adapted to engage the surface to be engraved. The support means includes a support arm pivotally mounted to the engraving head and the shoe means preferably includes first and second non-planar contact surfaces defined by omni-directional convex diamonds. 
     The shoe means is mounted in pivotal relationship to the support arm whereby the shoe means may pivot to accommodate surface irregularities in the surface to be engraved such that the shoe tool assembly is self aligning. In addition, the omni-directional convex diamonds provide two distinct contact points for contacting the surface to be engraved to facilitate distributing the contact force exerted on the cylinder surface. Thus, the shoe means may move in contact with previously engraved cells on an engraved cylinder wherein the omni-directional convex diamonds facilitate distributing the contact pressure on the cell walls, thereby preventing the cell walls from being damaged during a multiple pass engraving process. 
     In yet another aspect of the invention, a burr cutting assembly is provided for use in the engraving apparatus, the cutting assembly comprising tool means having a cutting edge for engaging and cutting burrs on an engraved surface wherein the cutting edge is curved. By providing a curved cutting edge, the cutting assembly is capable of being used with a plurality of cylinders having different diameters wherein the cutting edge will engage each cylinder surface in tangential relationship such that it is not necessary to perform a manual alignment operation in order to obtain proper alignment between the cutting edge and the cylinder surface. 
     The tool means is supported by a support in fixed relationship thereto and the support is pivotally mounted to the engraving head whereby the tool means may follow any surface irregularities in the cylinder surface. 
     Further, the stylus assembly, shoe assembly and burr cutting assembly each include surface engaging diamond elements which are cartridge mounted whereby the surface engaging elements may be easily replaced. 
     Therefore, it is an object of the present invention to provide an engraving head having an improved stylus assembly whereby the stylus may be easily mounted into a predetermined position within the engraving head. 
     It is another object of the invention to provide an engraving head with an improved shoe assembly for maintaining a predetermined spacing between an engraving head and a surface to be engraved wherein the shoe assembly is self-aligning relative to the surface to be engraved and also permits multi-pass engraving to be performed. 
     It is yet another object of the present invention to provide a burr cutting assembly wherein alignment of a burr cutter to a cylinder surface is not required in order to obtain tangential contact between the burr cutter and the cylinder surface. 
     Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS 
     FIG. 1 is an elevational view of an engraver incorporating the engraving head of the present invention; 
     FIG. 2 is a perspective view of the engraving head of the present invention showing the cylinder engaging components thereof; 
     FIG. 3 is a perspective view of the stylus arm showing details relating to the mounting of the stylus; 
     FIG. 4 is a perspective view of the stylus; 
     FIG. 5 is a perspective view of a first embodiment of the self-aligning shoe tool; 
     FIG. 6 is a perspective view of the servo drive mechanism for moving the self-aligning shoe tool; 
     FIG. 7 is a perspective view of a second embodiment of the self-aligning shoe tool; 
     FIG. 8 is an elevational view of the burr cutter and associated mounting assembly for the present invention; 
     FIG. 9 is a perspective view of the cartridge holder and cartridge style tool holder assembly for the burr cutter; and 
     FIG. 10 is an elevational view of the cartridge holder and tool holder assembly of FIG. 9 taken from the tool side of the tool holder. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to Fig, 1, the engraving head of the present invention is shown mounted within an engraver 10 which includes a headstock 12 and a tailstock 14 wherein the headstock 12 and the tailstock 14 are adapted to support a plated cylinder 16 therebetween, The engraving head 18 of the present invention is mounted in front of the cylinder 16 for movement longitudinally of the cylinder 16 during an engraving process, In addition, the engraver 10 is provided with a driver, illustrated diagrammatically as element 19, for moving the engraving head toward and away from the cylinder 16, 
     Fig, 2 illustrates the side of the engraving head 18 which faces toward the cylinder 16, The engraving head 18 includes a stylus arm 20 for mounting a stylus cartridge 22 wherein the stylus arm 20 is mounted on an engraving head base 24 and is actuated by a torque motor shaft 21 to move the stylus cartridge 22 toward and away from the cylinder to form engraved cells. 
     The engraving head 18 further includes a selfaligning shoe tool assembly 26 pivotally mounted to the engraving head base 24, The shoe tool assembly 26 is adapted to contact the cylinder 16 to accurately place the tip of the stylus cartridge 22 at a predetermined location relative to a point of contact between the assembly 26 and the cylinder 16. 
     Additionally, a burr cutter assembly 28 is provided for removing a burr of material created when the stylus exits the engraved cells. The burr cutter assembly 28 is mounted for movement in an axial direction relative to the cylinder 16 whereby a cutting edge of the burr cutter assembly 28 may be centered over any desired cell or row of cells, such as the next-to-last engraved cell, as will be described in detail below. 
     Referring to FIGS. 3 and 4, the stylus cartridge 22 of the present invention comprises a diamond stylus 30 anchored to an elongated tool holder 32 having a predetermined length. The diamond stylus 30 defines a conventional pointed tip for engaging a workpiece, such as the surface of a cylinder. The tool holder 32 is formed with a trapezoidal cross-section which is received within a corresponding elongated trapezoidally-shaped aperture 34 formed in the stylus arm 20. During mounting of the stylus cartridge 22 into the aperture 34, the tool holder 32 is moved into the aperture until a rear wall 36 of the tool holder 32 abuts against a stop 38 defined by a rear wall of the aperture 34. Thus, the stylus 30 is positioned to extend a predetermined distance from the stylus arm 20 by simply inserting the stylus cartridge 22 into the aperture 34 until the tool holder 32 engages the stop 38 wherein the amount of extension is controlled by the length of the tool holder 32. Once the cartridge 22 is in position, a pair of fasteners, such as set screws 40, 42, extending transverse to the longitudinal axis of the stylus cartridge 22 and engaged within threaded apertures 44, 46 of the stylus arm 20, may be turned into engagement with the side wall 48 of the tool holder 32. As the screws 40, 42 are tightened down on the tool holder 32, opposing upper and lower tool holder surfaces 50, 52, which are angled toward each other to form the trapezoidal shape, will move into wedging frictional engagement with respective angled upper and lower surfaces 54, 56 of the aperture 34 to firmly lock the cartridge 22 into position and to establish the angular orientation of the stylus 30 relative to the stylus arm 20. 
     When it is desired to remove the cartridge 22 from the stylus arm 20, a tool (not shown) may be inserted into an elongated slot 58 formed in the top surface of stylus arm 20 above the aperture 34 to engage within a recess 60 formed in the tool holder 32. The tool may then be moved forwardly in the slot 58 to guide the stylus cartridge 22 forwardly out of the aperture 34. 
     It should be apparent from the above description that by providing a stop 38 formed integrally with the stylus arm 20, a positive stop position is defined for registering with the stylus cartridge 22 to thereby facilitate loading or replacement of the cartridge 22. Further, the trapezoidal geometry for the tool holder 32 and associated stylus arm aperture 34 provides for positive angular positioning of the stylus cartridge 22 relative to the axis of the cylinder 16 and additionally reduces the number of clamp elements required for locking the stylus cartridge 22 in position. 
     Referring to FIGS. 2 and 5, the shoe tool assembly 26 of the present invention includes a support arm 62 which is mounted for pivotal movement relative to the engraving head base 24 and which is adapted to support a shoe cartridge 64 carrying a diamond shoe 66 adjacent to the stylus cartridge 22. 
     As may be seen in FIG. 5, the diamond shoe 66 includes first and second omni-directional diamonds 68,70 which define non-planar or convex surfaces for providing two spaced contact points in engagement with the cylinder. It should be noted that the diamonds 68, 70 may be either natural or formed of a synthetic material having equivalent characteristics. 
     The diamond shoe 66 is attached to a shoe holder 72 of the cartridge 64 through a pivot connection formed by a pivot pin 74 whereby the diamond shoe 66 is pivotable about a vertical axis in a substantially horizontal plane containing the first and second diamonds 68,70. In addition the shoe cartridge 64 is detachably fastened to the support arm 62 by a pin 76 which immovably registers the shoe holder 72 with a datum shelf 78 on the support arm 62. 
     The pivot formed by the pin 74 is such that the diamond shoe 66 is capable of pivotal movement relative to the shoe holder 72 to permit the omni-directional convex diamonds 68, 70 to follow irregularities in the surface of the cylinder 16 as it rotates. The support arm 62 pivots about a pivot axis 80, parallel to the axis of the cylinder 16 and perpendicular to the pivot axis of the shoe 66, on a pivot pin (not shown) supported by the engraving head base 24. In addition, the pivot pin (not shown) is preloaded by a bevel spring 82 (see FIG. 2) to eliminate rotational backlash, and the support arm 62 is captured against a bearing surface 84 whereby the support arm 62 is located in an axial direction. 
     Referring to FIG. 6, the support arm 62 is rotated toward and away from the cylinder 16 by means of a servomotor 86 having an integral gear reducer (not shown) and having additional gear reduction through spur gears 88 and 90 to rotate a threaded spindle 92 mounted to the spur gear 90. The threaded spindle 92 is threadably engaged with a barrel 94 which is rigidly mounted relative to the engaging head base 24. The threaded spindle 92 is attached to the support arm 62 such that threaded movement of the spindle relative to the barrel 90 will cause the support arm 62 to move toward and away from the cylinder 16. During an engraving process, such as a set-up engraving process, the engraved cell on the cylinder 16 is measured optically and a motor signal is generated to cause the motor 86 to move the shoe 66 within a plane intersecting the tip of the stylus 30 whereby the engraving head 18 may be located at a predetermined distance from the cylinder 16 to accurately obtain a desired cell depth. 
     It should also be noted that a control for detecting the travel limits of the spindle 92 is provided and includes a disc 98 mounted integrally with the end of the spindle 92 which is sensed by fore and aft proximity switches 100 and 102 for detecting the presence of the disc 98 at its extreme fore and aft positions. 
     FIG. 7 illustrates an alternative configuration for the cartridge wherein the shoe tool assembly 26 is shown including a cartridge 104 carrying a diamond shoe 06 mounted to a shoe holder 108 by means of a horizontal pivot pin 110 whereby the diamond shoe 106 may pivot in a vertical plane. As with the diamond shoe 66, the present diamond shoe 106 includes first and second omnidirectional convex diamonds 112, 114. In addition, the cartridge 104 is detachably mounted to the support arm 62 by means of a pin 116. 
     The shoe cartridge 104 provides advantages similar to the previously described shoe cartridge 64 in that the diamond shoe 106 may pivot to automatically align with the surface of a cylinder 16 as the shoe 106 is moved into contact with the surface. In addition, the shoe 106 will follow circumferential irregularities in the cylinder whereby the circumferential following of the diamond shoe 106 over the cylinder 16 is significantly improved. Further, the cartridge design for supporting the diamond shoes 66, 106 of the present invention facilitates alternative use of the diamond shoes 66,106, without requiring replacement of parts other than the cartridges 64, 104 associated with the diamond shoes 66, 106. For example, the cartridge 64 may be detached from the arm 62 at the pin 76 and replaced by the cartridge 104. 
     It should be noted that in addition to providing better following of the cylinder, the present shoe design incorporating two omni-directional convex diamonds eliminates the need to align the shoes 66, 106 to the cylinder surface in that the shoes 66, 106 are self-aligning on their pivot axes, whereas in prior art devices it was necessary to manually align the single flat diamond shoe to be tangential to the cylinder surface in order to avoid scoring. Further, by incorporating two spaced convex contact surfaces for engaging the cylinder surface, it is now possible to perform multi-pass engraving operations without crushing or otherwise damaging the walls of cells formed on a previous pass of the engraving head, as could occur with the prior art ball-shaped shoe design. 
     It should be understood that the convex surfaces defined by the diamonds 68, 70, 112, 114 have a relatively large radius of curvature at any given point on the convex surfaces such that, when the diamonds 68, 70, 112,114 contact cells on the cylinder surface, the angle of contact is small and the diamonds will span a greater area than the prior ball shoe tools and will easily pass over the cell walls. In addition, the curvature of the diamonds ensures that the shoe will accurately follow small variations in the contour of the cylinder surface. Thus, the present shoe design provides for a distribution of forces exerted on the cylinder surface, thereby avoiding the damaging effects associated with prior shoe designs. 
     Referring to FIGS. 2 and 8-10, the burr cutter assembly 28 comprises a tool holder cartridge 118 which includes a diamond tool 120 for engaging and cutting away burrs of material created when the stylus 30 exits an engraved cell in the cylinder 16. The burr cutter assembly 28 further includes a cartridge holder 122 which is rigidly mounted to a support member or yoke 124 and which rigidly supports the tool holder cartridge 118 on the engraving head 18. In addition, the yoke 124 is supported for pivotal movement on the engraving head base 24 by means of pivot pins 125 and 127 to permit the tool 120 to follow any irregularities in the cylinder 16. 
     Referring to FIGS. 9 and 10, the diamond tool 120 includes a substantially planar facing surface 129 oriented perpendicular to the surface of the cylinder 16, in a radial direction, and extending at an acute angle relative to the axis of the cylinder, in an axial direction. One edge of the facing surface 129 defines an inclined cutting edge 126 for engaging the surface of the cylinder 16 at an acute angle. Further, the cutting edge 126 is convexly curved or radiused in order to accommodate a large range of cylinder diameters. Specifically, the cutting edge 126 is curved within a plane defined by the facing surface 129 such that as various cylinders of differing diameters are engraved, wherein the yoke 124 pivots toward or away from the cylinder depending on the cylinder diameter, the engagement point between the cylinder and the cutting edge 126 will move up or down the cutting edge 126 as a function of the diameter of the cylinder being engraved. By providing a radiused cutting edge 126, a tangential contact point will be established between the cutting edge 126 and the surface of the cylinder 16 regardless of the diameter of the cylinder. Thus, the present cutting edge 126 eliminates the need to manually align the burr cutter to be aligned tangential to the cylinder circumference, as would be required with a flat cutting edge, and permits the burr cutter to be used with a wide range of cylinder diameters. 
     The yoke 124 is provided with means to linearly move the diamond tool 120 axially of the cylinder 16 into alignment with the center of a desired cell or row of cells, such as the next-to-last row of engraved cells, on the cylinder 16. The means for locating the yoke 124 in a desired location includes a motor 128 and associated gear box 130 for rotating a bevel gear 132. The bevel gear 132 drives an associated bevel gear 134 which is fastened to a threaded spindle 136. The threads on the spindle 136 are engaged with the pivot pin 127 such that rotation of the spindle 136 causes the spindle 136 to move relative to the pin 127. In addition, a flanged head 138 of the spindle 136 is axially fixed in position relative to the yoke 124 and is free to rotate in a space defined between stop portions 140 and 142. Thus, as the motor 128 drives the gears 132 and 134, the yoke 124 will slide axially along the pivot pins 125 and 127. 
     The geometry of the diamond tool 120 is such that an exponential relationship exists between the cylinder diameter and the location of contact between the cutting edge 126 and the surface of the cylinder 16. Positioning of the diamond tool 120 over the center of the desired cell or row of cells, such as the next-to-last row of cells, is determined as a function of the motor speed, the gear reduction, and the time required to move the yoke 124 to locations spaced from proximity detectors 144, 146, which operate in conjunction with a sensor or sensors mounted in stationary relationship to the engraving head base 24. 
     In the preferred embodiment, the diameter of the cylinder being engraved is input to a controller, illustrated diagrammatically as element 148, for controlling the movement of the yoke 124, as well as the other aspects of the engraving process. The controller 148 includes a preprogrammed look-up table which correlates the desired point of contact between the diamond tool 120 and the cylinder surface to the cylinder diameter. The look-up table for the controller 148 may be established empirically and the values in the table are used to control actuation of the motor 128. For example, during positioning of the diamond tool 120 in the axial direction, the diameter of the cylinder being engraved is input to the controller 148, either manually by an operator or by means of an automatic system for sensing the cylinder diameter, and the controller 148 then moves the yoke 124 axially to an end or home position, as determined by one of the proximity detectors 144, 146. Using a value provided by the look-up table and corresponding to the cylinder diameter, the controller 148 then actuates the motor 128 for a predetermined time period and at a predetermined speed, which in turn results in the yoke moving axially to a desired location for precisely positioning the diamond tool 120. 
     In an alternative embodiment, the motor 128 may be provided with an encoder or a potentiometer, indicated diagrammatically by 128A, to provide the controller 148 with direct feedback as to the axial position of the yoke 124. Alternatively, a stepper motor may be used to rotate the bevel gear 132 by a predetermined angular amount whereby the location of the yoke 124 may be precisely controlled. 
     It should be noted that an advantage associated with the present burr cutter assembly 28, in addition to not requiring alignment relative to the surface of the cylinder 16, resides in the use of the tool holder cartridge 118 for holding the diamond tool 120 in that the cartridge 118 may be easily attached to and detached from the cartridge holder 122 at the pin 123 to thereby facilitate replacement of the diamond tool 120. In addition, the tool holder cartridge 118 and cartridge holder 122 have cooperating abutting surfaces engaged with each other at joint locations 150 such that the cartridge holder 122 includes datum surfaces for precisely locating the tool holder cartridge 118. Thus, the process of replacing the cartridge 118 is facilitated in that the cartridge holder 122 provides for automatic alignment of the cartridge 118 and associated diamond tool 120 relative to the engraving head 18 during installation of the cartridge 118. 
     As noted above, the controller 148 may be used for controlling various aspects of the engraving process, including positioning of the engraving head 18 at desired locations relative to the cylinder 16. To this end, the controller 148 may comprise a numerical control system and the engraving head may be provided with right and left optical proximity sensors 152, 154 for sensing the right and left ends of the cylinder 16, as well as the distance between the engraving head 18 and the cylinder 16. In addition, the driver 19 preferably includes a stepper motor or equivalent drive means controlled by the controller 148 to move the engraving head into operative relationship with the cylinder 16. 
     Thus, during a set-up operation, the head 18 would be actuated to move toward the cylinder 16 and, as the sensors 152, 154 sense the head 18 moving into close proximity with the cylinder 16, the movement of the head 18 may be slowed and stopped to provide for gentle engagement between the shoe tool assembly 26 and the cylinder 16. Further, the controller 148 is adapted to operate in conjunction with the sensors 152, 154 to sense the ends of the cylinder 16 for providing the controller 148 with a reference location whereby the controller 148 may determine where to begin a test cut at the initiation of the engraving process. 
     In addition, the controller 148 is also adapted to control the servomotor 86 for the shoe tool assembly 26 to locate the engraving head 18 at a predetermined distance from the cylinder 16, such that the operation of positioning the head 18 relative to the cylinder is substantially automated and requires a minimum of operator input. 
     While the forms 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.