Patent Publication Number: US-6666122-B2

Title: Web or sheet-fed apparatus having high-speed mechanism for simultaneous X, Y and θ registration and method

Description:
RELATED APPLICATIONS 
     This is a continuation of application Ser. No. 08/825,368, filed Mar. 28, 1997, now abandoned, and entitled “Web or Sheet-Fed Apparatus Having High-Speed Mechanism For Simultaneous X, Y and θ Registration and Method.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is broadly concerned with improved, high speed web or sheet processing apparatus designed for extremely accurate registration and operation upon successive material segments fed to the apparatus. More particularly, the invention pertains to such apparatus, and corresponding methods, which are operable for initially gripping or holding a fed material segment, whereupon the gripped segment is essentially simultaneously shifted along orthogonal axes within the plane of the segment, and about a rotational axis transverse to the segment plane for accurate alignment purposes. The invention is particularly suited for high speed accurate die cutting operations. 
     2. Description of the Prior Art 
     Three-axis die cutting presses have been proposed in the past for processing of continuous webs. One such press is disclosed in U.S. Pat. No. 4,555,968. The press of this patent includes a shiftable die unit supported on a cushion of air, and the die unit is moved laterally of the direction of travel of the web as well as rotatably about an upright axis perpendicular to the web in order to bring the die unit into precise registration with the defined areas of the web to the die cut by the press. Automatic operation of the press described in the &#39;968 patent is provided by a control system having two groups of photo-optical sensors which are disposed to detect the presence of two T-shaped marks provided on opposite sides of the web adjacent each defined area to be cut. The control system is electrically coupled to a servomotor mechanism for adjustably positioning the die unit once advancement of the web is interrupted in a defined area on the web in a general proximity to work structure of the die unit. 
     As shown in U.S. Pat. No. 4,697,485, a die cutting press is provided with a registration system operable to provide precise alignment of a shiftable die cutting unit along two axes during the time that the web material is advanced along a third axis to the die unit, so that as soon as a defined area of the web reaches the die unit, the press can be immediately actuated to subject the material to the die cutting operation. Continuous monitoring of an elongated indicator strip provided on the material enables the die unit to be shifted as necessary during web travel to ensure lateral and angular registration prior to the time that web advancement is interrupted. 
     U.S. Pat. No. 5,212,647 describes a die cutting press provided with a registration system that quickly and accurately aligns defined areas of a web with a movable die unit without requiring the use of elaborate or continuous marks or more than two sensing devices for determining the location of the marks relative to the die unit. The registration system of the &#39;647 patent employs a pair of reference indicia fixed on a bolster of the press for indicating the position at which the indicia on the web of material appear when the defined areas of the web are in a desired predetermined relationship relative to the die unit supported on the bolster. 
     Application for U.S. Letters Patent Ser. No. 08/641,413 filed Apr. 30, 1996, now U.S. Pat. No. 5,644,979, describes an improved die cutting press wherein the entire die unit comprising a lower platen and a shiftable, upper die assembly is supported on a cushion of air. During operation when a defined area of the web is initially fed to the die cutting station, the target area is gripped via a vacuum hold-down and the entire die unit is simultaneous adjusted along three axes so as to achieve precise alignment between the target area on the web and the die cutting assembly. 
     Although the accuracy provided by such prior art die cutting registration systems is very good, such presses are relatively slow. For example, in the case of the press described in the &#39;413 patent application the necessity of moving the relatively heavy and bulky die assembly tends to slow the operation thereof. The earlier die presses are in general able to operate at speeds no faster than about 20 strokes per minute. 
     There is accordingly a need in the art for an improved web or sheet-fed processing apparatus, such as a die cutting press, which avoids the problems of prior units of this type and gives very high speed registration and operation. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the problems outlined above and provides an apparatus and method for the processing of successively fed segments (i.e., portions of a continuous web or discreet sheets) so that operations such as die cutting can be rapidly and accurately carried out. Broadly speaking, the apparatus of the invention includes an operating station, means for initially feeding a segment of material into the station, and positioning means for accurately positioning the segment in the station after such initial feeding and prior to processing in the station. The positioning means includes segment gripping or holding means for firmly holding the initially fed segment, means for determining the position of the held segment within the station as compared with a desired position thereof, and motive means coupled with the segment-holding means for moving the latter and the segment held thereby to locate the segment in the desired position. Generally speaking, the material segments carry at least one and preferably a pair of position-identifying indicia, and the positioning means includes a reference assembly providing reference data corresponding to the desired position for the segment indicia, together with means for comparing the location of the segment indicia with the reference data. 
     In another aspect of the invention, an apparatus and method for processing of individual segments of a continuous flexible web is provided wherein accurate adjustment of the position of successively fed web segments is provided by initially holding each successive segment and subjecting the held segment to adjusting motion while the segment remains a part of a continuous web. This adjusting motion is selected from the group consisting of motion along either or both of orthogonal axes in the plane of the segment and rotational motion of the segment about an axis transverse to segment plane, and combinations of the foregoing motions. It is to be understood that the invention provides such three-axis movement of individually held web segments while the respective segments remain a part of the continuous web. 
     In preferred forms, the web gripping or holding apparatus of the invention includes a relatively lightweight vacuum hold-down plate within the web or sheet processing station. In the case of a die cutting press, the vacuum hold-down plate is in the form of a centrally apertured body surrounding an essentially stationary floating die cutting anvil; the vacuum plate is shiftable as necessary in an axial direction (i.e., in the direction of web travel), a lateral direction (transverse to the axial direction), and/or rotationally about an upright rotational axis perpendicular to the axial and lateral directions and to a plane containing the segments. As used herein “die cutting” refers broadly to encompass various operations including but not limited to stamping, cutting, punching, piercing, blanking, and other similar operations. 
     The preferred motive means is coupled directly to the vacuum plate and includes a plurality of spaced apart motors such as bi-directional stepper motors, each of the later being translatable during movement of the vacuum hold-down plate. In order to achieve the most accurate and rapid plate movement, the motors are coupled via eccentrics to the plate so that operation of the motors will drive and move the plate as required. In the most preferred form, the motive means includes three such eccentrically coupled stepper motors, with the axes of the plate-connecting shafts lying in a single, common rectilinear line. 
     The preferred positioning apparatus also makes use of a pair of CCD (charge coupled device) cameras mounted within the processing station, together with a pair of split prisms and fixed reference indices carried by the die assembly. In operation, when a material segment is fed to the processing station, each camera receives a combined image made up of an image of the fixed indicia as well as one of the fiducials carried by the material segment. This image data is then used to calculate registration error and distance of travel information which is in turn employed in the operation of the respective stepper motors, so as to move the vacuum plate and the material segment held thereby for accurate positioning of the segments. 
     The apparatus of the invention is similar to that described in U.S. Pat. Nos. 4,555,968; 4,697,485; 5,212,647 and pending application Ser. No. 08/641,41-3, all of which are incorporated by reference herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of the preferred web fed die cutting apparatus in accordance with the invention; 
     FIG. 2 is a plan view of the apparatus illustrated in FIG. 1, and illustrating in detail the feeding assembly and shiftable web-holding adjustment plate thereof; 
     FIG. 3 is a vertical sectional view with parts broken away for clarity illustrating the input end of the die cutting station forming a part of the apparatus illustrated in FIGS. 1-2; 
     FIG. 4 is fragmentary view with parts broken way for clarity of the shiftable segment-holding vacuum plate assembly of the invention; 
     FIG. 5 is a sectional view taken along line  5 — 5  of FIG.  4  and further depicting the construction of the shiftable plate and anvil assembly; 
     FIG. 6 is a sectional view taken along line  6 — 6  of FIG. 4 which illustrates the internal construction of the plate and anvil assembly; 
     FIG. 7 is a fragmentary view depicting the input end of the plate and anvil assembly, with the cooper able die assembly illustrated in phantom; 
     FIG. 8 is a sectional view taken along line  8 — 8  of FIG. 4 which illustrates the side panel members of the shiftable plate and the underlying anvil assembly; 
     FIG. 9 is an enlarged, fragmentary in partial vertical section which illustrates one of the eccentric drive motor units coupled with the shiftable segment-holding plate; 
     FIG. 10 is a schematic view of the die cutting station illustrating the orientation of the CCD cameras and the associated prisms used to sense web segment position; 
     FIG. 11 is a schematic block diagram illustrating th interconnection between the computer controller of the die cutting apparatus and the sensing cameras and stepper motor drive units; 
     FIG. 12 is an exploded perspective view of the components of a second embodiment of the invention, designed for sheet-fed operation; 
     FIG. 13 is a plan view with parts broken away for clarity of the apparatus of FIG. 12; 
     FIG. 14 is a vertical sectional view of the apparatus of FIGS. 12-13; 
     FIG. 15 is a fragmentary side view in partial vertical section of the sheet-fed apparatus of FIG. 12; 
     FIG. 16 is a plan view of the three-motor drive unit forming a part of the sheet-fed apparatus of FIG. 12; 
     FIGS. 17A and 17B are together a flow diagram of the preferred control software employed in the web-fed apparatus of FIG. 1 for accurate positioning of successive web segments within the die cutting station; 
     FIG. 18 is a schematic plan view of the X-Y-θ table and interconnected X 1 , X 2  and Y axis drive units of the invention; 
     FIG. 19 is a schematic representation of certain geometrical relationships of the X 1 , X 2  and Y drive units used in the development of the preferred control algorithm of the invention; 
     FIG. 20 is a schematic representation of certain additional geometrical relationships used in the development of the control algorithm; and 
     FIG. 21 is a fragmentary top view of a continuous web illustrating respective web segments along the length thereof, together with position-indicating fiducial for each such segment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings, and particularly FIG. 1, die cutting apparatus  30  is illustrated. The apparatus  30  broadly includes a die cutting press or station  32  equipped with a die set  34 , a material feeder assembly  36  for sequentially feeding stock to the station  32  for sequential die cutting of segments  38  thereof (FIG.  21 ), and segment positioning apparatus  40  adjacent die set  34  for accurate positioning of each respective segments  38  relative to the die set. 
     The assembly  30  is adapted for use in processing elongated webs which present successive segments  38  having target die-cutting regions  42  thereon and carrying imprinted indicia such as fiducials  44  (FIG.  21 ), the latter being in predetermined positions relative to the corresponding target regions. An example of material capable of being processed in assembly  30  is a flexible synthetic resin web. The die cutting of such material as a part of production of many devices may be highly critical and extremely close cutting tolerances are required. The assembly  30  is thus designed for high speed yet very accurate die cutting of the successive segments  38 . 
     In more detail, the station  32  includes a base  46  supporting a central, upstanding, generally rectangular platen  48  and spacer  50 . Four upstanding rods  52  are supported on platen  48  and support adjacent the upper ends thereof an upper frame member  54 . A ram platen  56  is reciprocally carried by the rods  52  below frame member  54  and is vertically shiftable by means of piston  58 . A micrometer unit  60  is mounted atop frame member  54  and permits selective adjustment of the extent of vertical shifting of ram platen  56 , and a sensing mechanism  62  such as a glass scale supported between the member  54  and platen  56  for providing feedback to a controller regarding the vertical position of the platen  56 . 
     As best seen in FIGS. 3 and 6, the die set  34  includes a bolster  64  supported on spacer  50  with a central piston-receiving recess  66  therein as well as a relatively wide, fore and aft extending slot  68 . An anvil assembly  70  is supported on bolster  64  between the upstanding sidewalls of slot  68 . The anvil assembly  70  includes a lowermost piston  72  adapted to fit within recess  66  (FIG.  6 ), as well as an upper anvil block  74 ; the piston  72  is secured to block  74  via bolts  74   b . The block  74  presents a planar uppermost anvil face  76  and a pair of relatively narrow, elongated fore and aft extending slots  74   a  astride surface  76 . The block  74  is also provided with four transverse openings  75  therethrough adapted for the receipt of electrical heating elements. Piston  72  is equipped with a circumferential seal  78  and a supply of leveling media or material is provided in recess  66 ; the piston  72  and thus the anvil assembly  70  is thus resiliently supported. A pair of alignment blocks  80  are positioned atop bolster  64  on either side of slot  68  and engage opposed sidewall surfaces of block  74 . 
     The die set  34  also includes an upper fixture-supporting plate  82  which is disposed beneath platen  56 . The plate  82  supports a central cutting die assembly  84  disposed above anvil surface  76  as well as a pair of positioning CCD cameras  86 ,  88  and other structure associated with positioning apparatus  40  later to be described. The assembly  84  includes a die unit  89  which contacts the underlying anvil assembly  70  during each stroke of the die assembly  84 . 
     A total of four telescoping guide units  90  are positioned between and operably coupled to plate  82  and bolster  64  to assist in guiding the up and down reciprocal movement of plate  82  and thus die unit  84 . One such spring biased cylinder  92  is positioned adjacent each unit  90  and are biased to normally hold unit  84  above anvil surface  76 . 
     As best seen in FIGS. 1 and 2, the upstream or input end of assembly  36  is supported on a shiftable carriage  94  for movement thereof in a direction transverse to the path of travel of web material through the station  32 . In this fashion, either one of two webs later to be described can be positioned relative to die set  34  for processing. The assembly  36  broadly includes a pair of side-by-side supply reels  96 ,  98  supporting first and second webs  100 ,  102  of stock material, with motors  104 ,  106  serving to drive the reels  96 ,  98 . The overall assembly  36  further has vacuum tensioning assemblies  108 ,  110  and guide roller sets  112 ,  114  for guiding the webs through the station  32 . As will be evident to those skilled in the art, the supply reels  96 ,  98  are driven by the associated motors  104 ,  106  to unwind the webs  100 ,  102  so that stock material is can be fed through the station  32  for die cutting thereof. The vacuum tensioning assemblies  108 ,  110  maintain a predetermined tension on the webs during feeding thereof while the guide roller sets  112 ,  114  guide the webs into the station  32 ; these components are set so as to allow slight adjusting movement of web segments within the station  32  as later described. 
     The assembly  36  also provides takeup for the remainders of the die cut webs  100 ,  102  upon processing thereof in station  32 , and to this end includes a shiftable carriage  115  supporting output drive roller sets  116 ,  118  and takeup reels  120 ,  122 , the latter being powered by motors  124 ,  126 . A stepper motor  128  is provided for driving each set of drive rollers  116 ,  118  and function as a coarse feed means for quickly advancing either web  100  or  102  along a path of travel to successively feed defined segments  38  toward and into station  32 . 
     A pair of air cylinders  130 ,  132  are provided for respectively moving the carriages  94 ,  115  between a first position in which web  100  is aligned with station  32  and die set  34 , and a second position in which web  102  is similarly aligned. A pair of rotatable shafts  134  extend through platen  48  in a direction parallel to the path of travel of the webs  100 ,  102 , with each shaft  134  presenting a pair of opposed axial ends that extend beyond platen  48 . A pinion gear  136  is secured on each end of the shafts  134  so that rotation of either pinion on each shaft is transmitted to the other pinion on the opposite side of the base platen. A rack gear  138 ,  140  is supported on the underside of each carriage  94 ,  115  in engagement with the proximal pinion gears so that each carriage moves in alignment with the other upon actuation of the cylinders  130 ,  132 . 
     The positioning apparatus  40  is located adjacent anvil block  74  and is in surrounding relationship to surface  76 . The apparatus  40  broadly includes a vacuum plate element  142  as well as a motive assembly  144  operatively coupled to the element  142 . The purpose of apparatus  40  is to provide a fine and accurate adjustment of the position of each segment  38  within station  32  so that the target region  42  thereof is accurately die cut. 
     The vacuum plate  142  includes an uppermost plate  146  presenting a central, substantially square opening  148  adapted to receive the central portion of block  74  and thus expose surface  76 . The plate  142  includes a forward portion  150  provided with a series of vacuum apertures  152  therein together with a spaced, opposed rearward portion  154  likewise having vacuum apertures  156  therethrough. The portions  150 ,  154  are interconnected by side marginal portions  158 ,  160  each provided with vacuum apertures  162 ,  164 . 
     The overall plate  142  further includes a lower plate element  166  likewise having an opening  168  therein in registry with opening  148 ; the lower plate  166  is secured to upper plate  146  by fasteners  147 . As best seen in FIG. 6, elongated, internal plenums  170 ,  172  are provided between the plates  146  and  166 . Individual vacuum line couplers  174 ,  176  are operatively connected to the lower plate  166  in communication with the corresponding plenums  170 ,  172  for connection to a selectively operable vacuum system (not shown). These plenums are, via appropriate internal passageways, in communication with the vacuum apertures  152 ,  156 ,  162  and  164 . Again referring to FIG. 6, it will be observed that the aligned openings  148 ,  168  in the upper and lower plates  146 ,  166  are dimensioned to be somewhat larger than the adjacent block  74 ; the importance of this feature will be made clear hereinafter. 
     The vacuum plate  142  is supported for limited simultaneous axial, lateral and rotational movement thereof by receipt of the side marginal portions  158 ,  160  in the respective anvil block slots  74   a  (see FIG.  8 ). It will again be observed that the slots  74   a  are dimensioned to be somewhat wider than the associated side marginal portions  158 ,  160 , so as to accommodate limited shifting movement of the vacuum plate  142 . 
     The motive assembly  144  comprises three stepper motor units  178 ,  180 ,  182  each secured to the forward end of vacuum plate  142  (see FIG.  4 ). The units  178 - 182  are respectively referred to as the X 1 , Y and X 2  units. Each of the units  178 - 182  includes an electrically powered bidirectional stepper motor  184  equipped with an encoder  186  and having a rotatable output shaft  188 . In addition, each motor has a centrally apertured carriage  190 ,  192  or  194  secured to the upper end of each stepper motor  184 . Referring to FIGS. 7 and 9, it will be seen that the carriage  192  is an elongated, centrally apertured integral block member and has generally T-shaped side surfaces  196 ,  198 , with the block longitudinal axis oriented in a perpendicular transverse relation relative to the fore and aft web direction through station  32 . Depending, end marginal yoke bearings  199  are supported adjacent the extreme ends of the carriage  192 . In addition, the carriage  192  has a centrally apertured top surface  200 . In a similar fashion, the carriages  190  and  194  have spaced, somewhat T-shaped side surfaces and corresponding top surfaces  202  and  204 ; these carriages also have endmost yoke bearings  201  (see FIG.  5 ). In the case of carriages  190  and  194  however, the longitudinal axes thereof are oriented transverse to surfaces  196 ,  198 , i.e., they are in alignment with the fore and aft web direction through station  32 . 
     The units  178 - 182  are supported beneath vacuum plate  142  for limited translatory movement thereof during movement of plate  142 . Specifically, the units  178 - 182  are mounted on a transverse, somewhat L-shaped mounting rail  206  having three laterally spaced apart unit-receiving openings  208 ,  210  and  212  respectively receiving the stepper motor  184  of each unit  178 - 182 , respectively. The upper surface of rail  206  adjacent each of the openings  208 - 212  is provided with a pair of spaced apart rails or unit guides for each associated unit. That is, unit guides  214 ,  216  are located astride opening  208  and oriented transverse to the fore and aft direction through station  32 ; unit guides  218 ,  220  are provided adjacent opening  210  and are oriented in alignment with the fore and aft direction; and unit guides  222 ,  224  are provided adjacent opening  212  in parallel with the guides  214 ,  216 . The yoke bearings  201  forming a part of the carriages  190  and  194  receive the unit guides  214 ,  216  and  222 ,  224  respectively. Similarly, the yoke bearings  199  forming a part of carriage  192  receive the unit guides  218 ,  220 . In this fashion, each of the units  178 - 182  is translatable to a limited degree within the associated rail openings  208 - 212 . 
     The units  178 - 182  are coupled to vacuum plate  142  by means of identical, respective eccentric coupling assemblies  226 ,  228 ,  230 . These assemblies each include a fixed pin connector  232  secured to vacuum plate  142  above each underlying unit  178 - 182 . Each such connector includes a depending pin  234  as best seen in FIG.  9 . Connection between the individual stepper motor output shafts  188  and the associated pins  234  is accomplished by provision of eccentric blocks  236 , again best shown in FIG.  9 . The center-to-center distance between the pins  234  and  188  for each unit  178 - 182  defines the crank arm length for that unit. 
     The overall positioning apparatus  40  also includes the aforementioned CCD cameras  86 ,  88  which are supported on mounts  242 ,  244  depending from plate  82  (FIG.  10 ). The cameras  86 ,  88  are provided with associated prisms  246 ,  248  mounted on die set  34 , the latter also including fixed positional indicia  250 ,  252 . Preferably, each indicium  250 ,  252  includes a closed line forming a square, wherein the open area of the square corresponds to the size of one of the fiducial indicia  44  on each segment  38 . For example, where solid, circular fiducials are printed on web, the reference indicia  250 ,  252  would include a square having an inner area equal in width and height to the diameter of the circular fiducials. A clear line of sight extends between each reference indicium  250 ,  252  and the desired location of the corresponding indicium  44 , with an associated split prism  246  or  248  along the line of sight. The images projected along the line of sight from above and below the split prism are both reflected laterally as a single compound image within which both the reference indicium and the fiducial indicium on the web are visible. The cameras  86 ,  88  are thus aligned vertically with an associated split prism  246 ,  248  so that each camera receives the compound image reflected by the prism. By way of example, each CCD camera may be provided with a two-dimensional array made up of 512×489 pixels and outputs analog signals representative of the image. These signals are converted to digital data by conventional analog-to-digital conversion mechanism. Lenses forming a part of each CCD camera are also provided for focusing the camera on the corresponding split prism. Preferably, the lenses focus the array on an area of about ⅙ of an inch square to provide the desired resolution for registering the die unit and target area  42  of each segment  38  to within about {fraction (2/10,000)}ths of an inch. 
     As illustrated in schematic FIG. 11, a computer controller  254  is provided as a part of the apparatus  40 , which would typically include a central processing unit, an input device, display means and a memory for storing data and suitable software. As shown, the cameras  86 ,  88  are coupled to the controller, which also has connections to the stepper motor units  178 - 182 . In addition, the controller  254  is connected to the reel motors  104 ,  106  and  124 ,  126 , tensioning units  108 ,  110 ,  116  and  118  and stepper motors  128  for controlling the webs  100 ,  102 . Broadly speaking, once a given segment  38  is initially and coarsely positioned within station  32  by appropriate actuation of feeder assembly  36  to move the web  100  or  102  a predetermined axial distance, the vacuum system associated with the plate  142  is actuated to firmly grip the segment  38  to the plate  142 . The appropriate downstream takeup reel motor  124  or  126  and the associated drive roller sets  116 ,  118  are then reversed to slightly slacken the web  100  or  102  downstream of the station, thus reducing the web tension. This feature, together with the settings of the upstream web tensioning units  108 ,  110  allowing slight web movement, together permit web segment adjustment along the orthogonal X and Y axes, and web rotation, without fear of splitting or tearing the web. 
     The cameras  86 ,  88  are next actuated to generate image data. The controller  254  receives such image data from the cameras  86 ,  88  and compares the relative positions of the reference indicia  250 ,  252  and the indicia  44  for the segment  38  and generates appropriate error data representative of the difference between the actual X, Y and θ positions of the indicia  44  and their desired positions as represented by the reference indicia  250 ,  252 . The position of plate  142  is also known via the encoders  186  of each stepper motor  184 . The difference data is then used by the controller in the manner to be described to selectively energize the units  178 - 182  to change the position of the vacuum plate  142  and thus the segment  38  until the indicia  44  are aligned (within preselected tolerances) with the associated reference indicia. For course, the adjustment of the segment  38  occurs while the segment remains a part of the web, the latter accommodating the slight degree of adjustment required owing to the described web slackening. At this point, die cutting can be commenced in the usual way by lowering of the upper die-carrying portion of die set  34  into cutting contact with the segment  38 . After such cutting, the assembly  36  is actuated to move the next segment  38  into station  32 , where the process is repeated. 
     The controller  254  also employs the calculated difference between the actual axial or longitudinal distance between fiducials  44  and the indicia  250 ,  252  to control the feeding assembly  36 . That is, after each segment feeding operation, the axial distance of the web feeding for the next operation of assembly  36  is varied to compensate for the determined axial distance error. In this way, initial web feeding is controlled to prevent inaccuracies in the initial feeding step from accumulating to a point where successive segments  38  would no longer be brought into a sufficiently close alignment so that the cameras  86 ,  88  could simultaneously view an image including the fixed indicia  250 ,  252  and fiducials  44 . The controller  254  thus controls the operation of the motors of drive assembly  36  in response to the axial difference data calculated during the preceding operational sequence. 
     In order to better understand the method and algorithm by which the vacuum plate  142  is adjusted in order to insure accurate alignment of each respective segment  38  in station  32 , attention is directed to FIGS. 18 and 19, which are, respectively, a schematic representation of an X-Y-θ table representative of vacuum plate  142 , and a schematic representation showing movements of the respective drive units  178 - 182 . In these Figures, the symbols have the following definitions: 
     X 1 =drive unit  178 ; 
     Y=drive unit  180 ; 
     X 2 =drive unit  182 ; 
     T=distance between fiducials; 
     C x1 =the radial eccentric or crank length of drive unit X 1  (drive unit  178 ); 
     C y =the radial eccentric or crank length of drive unit Y (drive unit  180 ); 
     C x2 =the radial eccentric or crank length of drive unit X 2  (drive unit  182 ); 
     α=the angle between the Y axis and the drive unit X 1  crank length; 
     γ=the angle between the X axis and the drive unit Y crank length; 
     β=the angle between the Y axis and the drive unit X 2  crank length; and 
     M=the length between the axes of the plate pins  234 . 
     As is evident from these Figures, the X-Y-θ table (i.e., vacuum plate  142 ) is attached via the three pins  234  through radial eccentric lengths or crank arms C x1 , C y  and C x2  which are driven by the corresponding stepper motors. The units X 1  and X 2  slide along the Y axis, whereas unit Y slides along the orthogonal X axis. The central axes of all of the pins  234  lie on a common rectilinear line, with the three pins preferably being equidistantly spaced. Units X 1  and X 2  have the same crank length, but the crank length C y  can be different. 
     There are two types of motion associated with each crank: active rotation of the motor shafts  188  which, through the effective crank arms of the eccentrics  236 , move vacuum plate  142 ; and passive translation (sliding) of the individual drive units to accommodate such plate movement. To achieve translation of the table or plate  142  along the X axis, the crank arms associated with units X 1  and X 2  rotate in opposite directions (one clockwise, the other counterclockwise or vice versa), while the Y unit slides up or down. Table rotation (about an axis transverse to the plane of the segment) is effected by rotating both of the X 1  and X 2  crank arms in the same direction (clockwise for table counterclockwise or counterclockwise for table clockwise) without any translation of the Y unit. Translation of the table or plate  142  along the Y axis is obtained by rotation of the Y crank arm with both the X 1  and X 2  units sliding left or right together. Any time the X 1  or X 2  crank arms rotate away from the Y axis, the X 1  or X 2  drive units slide inward; any time the X 1  or X 2  crank arms rotate toward the Y axis, the X 1  or X 2  drive units slide outward. If the Y crank arm rotates away from the Y axis, the Y unit slides up; if the Y crank arm rotates towards the X axis, the Y unit slides down. Since the system is nonlinear, for the same amount of table translation or rotation, the amount of each individual crank arm movement will be different at different crank angles. For the same reason, for a single translation along the X axis or table rotation, the rotation of the X 1  and X 2  crank arms are not necessarily the same amount, but depend upon the crank angles. 
     Referring specifically to FIG. 19, it will be seen that at any given time, the following holds: 
     
       
         2  M  sin θ= C   x (sin α+sin β)  (1) 
       
     
     
       
           Y=C   y  sin γ  (2) 
       
     
     1. For a pure T rotation (pivoting at the center pin) with (+) Δθ 
     
       
           C   x (sin α 2 −sin α 1 )= M (sin θ 2 −sin θ 1 ) 
       
     
     therefore          sin                   α   2       =         M     C   x            (       sin                   θ   2       -     sin                   θ   1         )       +     sin                   α   1                         
     From (1) we have                  sin                   θ   1       =         C   x     M              sin                   α   1       +     sin                   β   1         2              
        and           (   3   )                 θ   1     =       sin     -   1            (         C   x     M              sin                   α   1       +     sin                   β   1         2       )               (   4   )                         
     upon given Δθ and using (3) and (4)                          α   2     =                  sin     -   1            (         M     C   x            (       sin        (       θ   1     +   Δθ     )       -     sin                   θ   1         )       +     sin                   α   1         )                   =                  sin     -   1       (       M     C   x            (       sin        (         sin     -   1            (         C   x     M                         sin                   α   1       +     sin                   β   1         2       )       +   Δθ     )       -                                              C   x     M        sin                   α   1       +       sin                   β   1       2       )     +     sin                   α   1         )                
          Similarly   ,     
                             =                  sin     -   1       (       M     C   x            (     sin        (         sin     -   1            (         C   x     M                         sin                   α   1       +     β   1       2       )       +   Δθ     )                                              C   x     M                         sin                   α   1       +     sin                   β   1         2       )     +     sin                   β   1         )           -              
             (   5   )                 β   2     =                  sin     -   1       (         M     C   x            (       sin        (       θ   1     +   Δθ     )       -     sin                   θ   1         )       +     sin                   β   1                   (   6   )                         
     2. For a pure X translation with (+)Δx, from (1) 
     
       
         sin α 1 +sin β 1 =sin α 2 +sin β 2   (7) 
       
     
     
       
         ∵ C   x  sin α 2   =C   x  sin α 1   +Δx   
       
     
     
       
         
           
             
               
                 
                   
                     ∴ 
                     
                       sin 
                        
                       
                           
                       
                        
                       
                         α 
                         2 
                       
                     
                   
                   = 
                   
                     
                       sin 
                        
                       
                           
                       
                        
                       
                         α 
                         1 
                       
                     
                     + 
                     
                       
                         
                           Δ 
                            
                           
                               
                           
                            
                           x 
                         
                         
                           C 
                           x 
                         
                       
                        
                       
                           
                       
                        
                       and 
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
             
               
                 
                   
                     
                       α 
                       2 
                     
                     = 
                     
                       
                         sin 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             sin 
                              
                             
                                 
                             
                              
                             
                               α 
                               1 
                             
                           
                           + 
                           
                             
                               Δ 
                                
                               
                                   
                               
                                
                               x 
                             
                             
                               C 
                               x 
                             
                           
                         
                         ) 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     Similarly 
                     , 
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
             
               
                 
                   
                     sin 
                      
                     
                         
                     
                      
                     
                       β 
                       2 
                     
                   
                   = 
                   
                     
                       sin 
                        
                       
                           
                       
                        
                       
                         β 
                         1 
                       
                     
                     - 
                     
                       
                         
                           Δ 
                            
                           
                               
                           
                            
                           x 
                         
                         
                           C 
                           x 
                         
                       
                        
                       
                           
                       
                        
                       and 
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
             
               
                 
                   
                     β 
                     2 
                   
                   = 
                   
                     
                       sin 
                       
                         - 
                         1 
                       
                     
                      
                     
                       ( 
                       
                         
                           sin 
                            
                           
                               
                           
                            
                           
                             β 
                             1 
                           
                         
                         - 
                         
                           
                             Δ 
                              
                             
                                 
                             
                              
                             x 
                           
                           
                             C 
                             x 
                           
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
         
         
             
         
       
     
     Substituting sin β 2  in (7) with that of in (10), (8) can also be obtained. 
     3. For a pure Y translation with (+) Δy, from (2) we have                γ   2     =       sin     -   1            (       sin                   γ   1       +       Δ                 y       C   y         )               (   12   )                         
     4. Composite Move 
     From (1), (2), (9), (11) and (12), it is seen that Y movement is independent of X-T movement; therefore the following discusses an X-T move only. 
     Assume initial position α 0 , β 0 , desired translation Δx and rotation Δθ, resulting position α 2 , β 2 . 
     Even though it is a non-linear system, a simultaneous, 3-axis movement can be obtained if the following is established: 
     a. Δx first, arrived at α 1 , θ 1 , then Δθ, from (5) and (8) giving                      sin                   α   2       =         M     C   x            (       sin        (       θ   1     +   Δθ     )       -     sin                   θ   1         )       +     sin                   α   1                     =         M     C   x            (       sin        (       θ   0     +   Δθ     )       -     sin                   θ   0         )       +     sin                   α   0       +       Δ                 x       C   x                       (   14   )                         
     From (3) or (4), (14) can be written as 
     
       
         ƒ(α 2 )=ƒ x (α 0 ,β 0   ,Δx )+ƒ 0 (α 0 ,β 0 ,Δθ)+Const  (15) 
       
     
     here                f   x     =       Δ                 x       C   x               (   16   )                 f   x     =       Δ                 x       C   x               (   17   )                 f   0     =       M     C   x            (       sin        (       θ   0     +   Δθ     )       -     sin                   θ   0         )               (   18   )                        Const=sin α 0   (19) 
     b. Δθ first, arrived at α 1 , θ 1 , then Δx, from (8) and (5) giving                      sin                   α   2       =                  sin                   α   1       +       Δ                 x       C   x                     =                    M     C   x            (       sin        (       θ   0     +   Δθ     )       -     sin                   θ   0         )       +     sin                   α   0       +       Δ                 x       C   x                       (   20   )                         
     (14), (15) and (20) shows the independence of the move sequence. 
     From (3), (4) and (18) giving            M     C   x            (       sin        (       θ   0     +   Δθ     )       -     sin                   θ   0         )       =       M     C   x            (       sin        (         sin     -   1            (         C   x     M              sin                   α   0       +     sin                   β   0         2       )       =   Δθ     )       -         C   x     m              sin                   α   0       +     sin                   β   0         2         )                       
     Thus, the following motion equations are derived: 
     
       
         α 2 =sin −1 (ƒ x +ƒ θ +sin α 0 )  (21) 
       
     
     
       
         β 2 =sin −1 (−ƒ x +ƒ θ +sin β 0 )  (22) 
       
     
     
       
         γ 2 =sin −1 (ƒ y +sin γ 0 )  (23) 
       
     
     here                f   x     =       Δ                 x       C   x               (   24   )                 f   y     =       Δ                 y       C   y               (   25   )                 f   θ     =       M     C   x            (       sin        (         sin     -   1          ϕ     +   Δθ     )       -   ϕ     )               (   26   )                         
     with              ϕ   =         C   x     M              sin                   α   0       +     sin                   β   0         2               (   27   )                         
     5. Determination of ΔX, ΔY and Δθ. 
     The position differences in camera  86  and camera  88  can be translated into physical error. 
     The coordinate system rotation transformation is          [           x   ′               y   ′           ]     =       [           cos                 Θ           sin                 Θ                 -   sin                   Θ           cos                 Θ           ]                [         x           y         ]                     
     So the increment equation can be derived as                [           Δ                   X   i                 Δ                   Y   i             ]     =           [           K                   x   i           0           0         K                   y   i             ]                [           cos                   Θ   i             sin                   Θ   i                   -   sin                     Θ   i             cos                   Θ   i             ]                [           Δ                   x   i                 Δ                   y   i             ]     =       [           a   i           b   i               -     c   i             d   i           ]                [           Δ                   x   i                 Δ                   y   i             ]               (   28   )                         
     here                K                   x   i       =       C                 a                 l                 i                 Δ                   X   i           Δ                   x   i        cos                 Θ     +     Δ                   y   i        sin                 Θ                 (   29   )                 K                   y   i       =       C                 a                 l                 i                 Δ                   Y   i             -   Δ                     x   i        sin                 Θ     +     Δ                   y   i        cos                 Θ                 (   30   )                         a   i   =Kx   i ·cos Θ  (31) 
     
       
           b   i   =Kx   i ·sin Θ  (32) 
       
     
       c   i   =Ky   i ·cos Θ  (33) 
     
       
           d   i   =ky   i ·cos Θ  (34) 
       
     
     Θ i  is the angle between camera I coordinate system and the physical table coordinate system. 
     Kx 1 , Kx 2 , Ky 1 , Ky 2  are the camera-motion scale factors of X and Y axis of camera  86  and camera  88  coordinate system unit vs. table coordinate system unit. 
     The average approach is used to measure the physical error which is demonstrated by the following. Assume line I and line I′ are to be aligned. 
     The center point of line I is determined by        [           x   1     +     x   2       2     ,         y   1     +     y   2       2       ]                   
     and the center point of line I′ is determined by        [           x   1   ′     +     x   2   ′       2     ,         y   1   ′     +     y   2   ′       2       ]                   
     Therefore the center point displacement between two lines is                Δ                 X     =             X   1     +     X   2       2     -         X   1   ′     +     X   2   ′       2       =         Δ                   X   1       +     Δ                   X   2         2               (   35   )                 Δ                 Y     =             Y   1     +     Y   2       2     -         Y   1   ′     +     Y   2   ′       2       =         Δ                   Y   1       +     Δ                   Y   2         2               (   36   )                         
     The theta error can be found by              Δθ   =     2          sin     -   1       (             (     Δ                   X   12       )     2     +       (     Δ                   Y   12       )     2           2      T       )               (   37   )                         
     here, 
     T is the distance between target 1 and target 2, 
     
       
         Δ X   12   =ΔX   1   −ΔX   2   
       
     
     
       
         Δ Y   12   =ΔY   1   −ΔY   2   
       
     
     
       
         for Δθ&lt;&lt;1 , ΔX   12   &gt;&gt;ΔY   12 , 
       
     
     
       
         
           
             
               
                 
                   Δθ 
                   = 
                   
                     2 
                      
                     
                       
                         sin 
                         
                           - 
                           1 
                         
                       
                        
                       
                         ( 
                         
                           
                             Δ 
                              
                             
                                 
                             
                              
                             
                               X 
                               12 
                             
                           
                           
                             2 
                              
                             T 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   38 
                   ) 
                 
               
             
           
         
         
         
             
         
       
     
     Since the target line to be registered is off the pivot center, additional translation error will be introduced bye θ correction. The additional X error will be canceled out. The additional Y error can be determined by reference to FIG. 20, where: D=the distance between the Y axis and the fiducial line T; R=the distance from the origin to the fiducial; Δθ=rotation error; and ΔY′=the distance of Y axis offset generated by rotation through Δθ. 
     Thus, 
     
       
         Δ Y′=Δθ·R ·sin α=Δθ· D   (39) 
       
     
     here D is the distance between Y axis and the target line T. 
     Therefore total Y move needed is the sum of (29) and (39). 
     Thus, we have              Δθ   =     2          sin     -   1            (         (           a   1     ·   Δ                     x   1       +         b   1     ·   Δ                     y   1         )     -     (           a   2     ·   Δ                     x   2       +         b   2     ·   Δ                     y   2         )         2      T       )                 (   40   )               X   =         (           a   1     ·   Δ                     x   1       +         b   1     ·   Δ                     y   1         )     +     (           a   2     ·   Δ                     x   2       +         b   2     ·   Δ                     y   2         )         2      T               (   41   )                     Δ                 Y     =         (           -     c   1       ·   Δ                     x   1       +         d   1     ·   Δ                     y   1         )     +     (           -     c   2       ·   Δ                     x   2       +         d   2     ·   Δ                     y   2         )         2      T         )     +     Δθ   ·   D             (   42   )                         
     The resolution and range of travel of the preferred apparatus  40  is determined as follows. The discussion can be limited within        [     0   ,     π   2       ]                   
     since it is symmetrical. 
     The following parameter design values are used for verification. 
     All motor encoders in the preferred embodiment are 4000 pulse/rev. so that one encoder pulse generates Δα=Δβ=Δγ=0.09°. M=3.0″, C x =C y =0.050″, T=5.562″, D=7.09″. 
     1. Resolution 
     a. X axis 
     From (8), we have 
     
       
         Δ X=C   x (sin(α 1 +Δα)−sin α 1 ) 
       
     
     Apply the first and the second derivative and use them                  ∂     (     Δ                 X     )         ∂     (   Δα   )         =         C   x          cos        (       α   1     +   Δα     )         =   0             (   43   )                     ∂   2          (     Δ                 X     )         ∂       (   Δα   )     2         =         -     C   x            sin        (       α   1     +   Δα     )         &lt;   0             (   44   )                         
     From (43), the extreme value is achieved at            α   1     +   Δα     =     π   2                     
     or 
     
       
         α 1 =90°−Δα 
       
     
     From (44), it indicates that it is a monotonous decreasing function, 
     Thus 
     
       
         minimum Δ X=C   x (1−sin(90°−Δα))  (45) 
       
     
     The maximum is achieved at 
     
       
         α 1 =0 
       
     
     
       
         maximum Δ X=C   x  sin(Δα)  (46) 
       
     
     In this design, 
     
       
           X  Resolution=0.05 sin(0.09°)=0.000078539″ 
       
     
     b. Y axis 
     Similarly, 
     
       
         minimum Δ Y=C   y (1−sin(90°−Δα))  (47) 
       
     
     
       
         maximum Δ Y=C   y  sin(Δγ)  (48) 
       
     
     In this design, 
     
       
           Y  Resolution=0.000078539″ 
       
     
     c. T axis 
     From (5),                sin                   α   2       =             M     C   x            (       sin        (       θ   1     +   Δθ     )       -     sin                   θ   1         )       +     sin                   α   1              
     ∴   Δθ     =         sin     -   1            (           C   x     M          (       sin        (       α   1     +   Δα     )       -     sin                   α   1         )       +     sin                   θ   1         )       -     θ   1                 (   49   )                         
     Apply the first derivative and use it            ∂     (   Δθ   )           ∂   Δα     )       =             C   x     M          cos        (       α   1     +   Δα     )             1   -       (           C   x     M          (       sin        (       α   1     +   Δα     )       -     sin                   α   1         )       +     sin                   θ   1         )     2           =   0                     
     It can be found, with (49), (3) and (4), that at 
     
       
         α 1 =90°−Δα 
       
     
     minimum              Δθ   =         sin     -   1            (       C   x     M     )       -       sin     -   1            (         C   x     M          sin        (       90   ∘     -   Δα     )         )                 (   50   )                         
     Similarly, the maximum obtained at 
     
       
         α 1 =0 
       
     
     maximum              Δθ   =       sin     -   1            (         C   x     M     -     sin                   (     Δ                 α     )         )               (   51   )                         
     In this design, 
     T Resolution        θ   =         sin     -   1            (       0.005   3          sin        (     0.09      °     )         )       =     0.0015      °                 AX   θ     =         sin        (     Δθ   2     )          T     =         sin        (     0.0015   /   2     )       ·   5.562     =     (     0.000072806   ″                           
     2. Travel range 
     a. X axis 
     From (8) 
     
       
         Δ X=C   x (sin(α 1 +Δα)−sin α 1 ) 
       
     
     For 
     
       
         α=−90° 
       
     
     
       
         α 1 +Δα=90° 
       
     
     X travel range 
     
       
         Δ X =2 C   x   (52) 
       
     
     In this design, maximum X travel=0.1″ 
     b. Y axis 
     Similarly, Y travel range 
     
       
         Δ Y =2 C   y   (53) 
       
     
     In this design, maximum Y travel=0.1″ 
     c. θ axis 
     From (49)                Δ                 θ     =                    sin     -   1            (           C   x     M          (       sin        (       α   1     +   Δα     )       -     sin                   α   1         )       +     sin                   θ   1         )       -     θ   1                                  sin     -   1       (           C   x     M          (       sin                   (       α   1     +   Δα     )       -     sin                   α   1         )       +                                      C   x     m              sin                   α   1       +     sin                   β   1         2       )     -       sin     -   1            (         C   x     M              sin                   α   1       +     sin                   β   1         2       )                             
     For 
     
       
         α=−90° 
       
     
     
       
         β 1 =−90° 
       
     
     
       
         α 1 +Δα=90° 
       
     
     θ travel range              Δθ   =       -       sin     -   1            (       -     C   x       M     )         =       sin     -   1            (       C   x     M     )                 (   54   )                         
     In this design, maximum θ travel=0.9549738730°         Δ                   X   θ       =         sin        (     Δθ   2     )          T     =         sin        (     0.955   /   2     )       ·   5.562     =     0.04635   ″                         
     Attention is next directed to FIGS. 17A and 17B which is a flow chart of the preferred software incorporating the above-described algorithm. This software is stored in computer controller  254 , the latter being connected to the drive unit encoders and stepper motors, as well as to the cameras  86 ,  88  (see FIG.  11 ). 
     In the first step, the segment registration operation is started as at  256  by acquiring images from the cameras  86 ,  88 . As explained previously, such images include data respecting the reference indicia  250 ,  252 , as well as the actual locations of the fiducials  44  on the segment  38 . These acquired images are then searched (step  258 ) to determine the fiducial images therein. A first search (step  260 ) initiates this determination. In the initial subroutine, the data respecting the reference indicia  250 ,  252  is obtained (step  262 ) and the actual locations of the fiducials  44  is fixed as compared with the location of reference indicia  250 ,  252  (step  264 ). In subsequent determinations, the step  262  may be dispensed with, owing to the fact that the reference indicia  250 ,  252  are fixed. 
     In the next step  266 , the program determines the differences between the desired and actual locations of the fiducials  44 . This data is then manipulated to convert the X-axis differences and Y-axis differences to physical error as described in the algorithm above (steps  268 ,  270 ). The determination made in these latter steps is then employed to calculate the θ error ( 272 ), followed by calculation of additional Y-axis error caused by θ correction, step  274 , see FIG.  20  and associated discussion above. 
     The program next determines if the X, Y and θ values for the fiducials  44  are within preselected tolerances (step  276 ). If these values are within tolerance, the registration operation is complete as shown in step  278 , and no adjustment of the segment  38  through the medium of vacuum plate  142  is required. However, if any of these values are outside of tolerance, the program next determines how and to what extent vacuum plate  142  must be moved to correct the registration. 
     In the first step, the motion parameters are initialized (step  280 ), and the Y-axis error is determined as the sum of the original error plus any additional error caused by rotation (step  282 ). Next, the program determines whether there is any X-axis or θ error (step  284 ). If no such error is determined, the program advances to step  286  and determines if there is any Y-axis error. If the answer is no, the program next performs step  288  and calculates the necessary Y-axis translation component. The final step is the execution of positioning instructions as necessary to the stepper motors  184  of the respective drive units  178 - 182  (step  290 ) and a return to the starting point for the next determination. 
     On the other hand, if in step  284  X-axis and/or θ error is determined, the X 1  and X 2  crank angles are read via the stepper motor encodens (step  286   a ) and X-axis and θ translation and rotation components are calculated (steps  292 ,  294 ). The program then proceeds to step  286  as previously mentioned. Again, if no Y-axis error is ascertained in step  286 , the program proceeds to execute steps  288 ,  290 . However, if such error is determined, the program calculates the desired crank positions for the X 1 , X 2  and Y drive units (step  296 ) and the Y crank angle is read (step  298 ). Upon completion of these routines, the program then proceeds to completion through steps  288  and  290  as shown. 
     Attention is next directed to FIGS. 12-16 which illustrate another embodiment in accordance with the invention wherein segments in the form of sheets can be processed (as used herein, the term “segment” with reference to material to be processed in the devices of the invention is intended to cover both portions of a continuous web and discrete sheets). As shown in FIG. 13, the positioning assembly  300  of a sheet fed processing apparatus such as a die cutter or laminating unit is depicted. The assembly  300  broadly includes a sheet of segment support  302  having a central, generally rectangular opening  304 , with a vacuum hold-down plate  306  disposed within the opening  304 , a motive assembly  308  operatively coupled with the plate  306 , and a sheet feeder assembly  310 . 
     In more detail, the support  302  is in the form of a metallic plate  312  having two pairs of beltway slots  314 ,  316  and  318 ,  320  respectively disposed on opposite sides of the opening  304 . The support  302  also includes a pair of elongated, bar-like elements  322 ,  324  secured to the underside thereof adjacent the side margins of opening  304  and extending inwardly as best seen in FIG.  14 . The elements  322 ,  324  are secured to plate  312  by means of fasteners  326 . A nose member  328  is similarly secured to the underside of plate  312  adjacent the leading transverse edge thereof. 
     The hold-down plate  306  includes an uppermost metallic plate  330  having a series of vacuum apertures  332  therethrough. The plate  330  is secured to an underlying block  334  which cooperatively define a plenum  336  directly beneath plate  330  (see FIG.  14 ). A pair of vacuum ports  338 ,  340  are provided in block  334 , these communicating with plenum  336  via vertical passageways  342  (FIG.  15 ). The ports  338 ,  340  are adapted for connection with a vacuum system, not shown. The plate  330  and block  334  are supported within opening  304  by means of the elements  322 ,  324 . As illustrated in FIG. 13, the opening  304  is sized to be somewhat larger than the plate  330 , so as to permit limited movement of the latter within the confines of the opening  304 . 
     The motive assembly  308  includes an elongated channel  344  disposed beneath block  334  and supports three spaced apart stepper motor drive units  346 ,  348  and  350 . To this end, the channel  344  has three generally rectangular openings provided therethrough, namely endmost openings  352  and  354  oriented with the longitudinal axes transverse relative to the longitudinal axis of channel  344 , and central opening  356  oriented with its longitudinal axis parallel to that of the channel  344 . Each of the drive units includes a stepper motor  358  as well as an associated encoder  360  and a rotatable output shaft  362 . In addition, each of the units has a carriage  364 ,  366  or  368  allowing the unit to translate during operation of assembly  30 . Each such carriage is in the form of a centrally apertured block having generally T-shaped sidewall surfaces  370  and an apertured top wall surface  372 . Each carriage  364 - 368  is provided with a pair of depending yoke bearings  374 ,  376 . In the case of endmost carriages  364  and  368 , such yoke bearings are oriented parallel to the longitudinal axis of channel  344 , whereas with central carriage  366 , the yoke bearings are oriented perpendicular to this longitudinal axis. A pair of rail-type guides  378 ,  380  are affixed to channel  344  on opposite sides of each opening  352 - 356  and mate with the described yoke bearings for each carriage  364 - 368 . Thus, the guides  378 - 380  for the endmost carriages  364 - 368  are aligned with the longitudinal axis of the channel  344 , with the guides for the central carriage  366  being perpendicular to this axis. 
     The stepper motors  358  of each drive unit  346 - 350  is operatively coupled to the underside of block  334  through an eccentric coupling mechanism. An eccentric block  382  is secured to each motor output shaft  362  as best seen in FIG.  12 . The block  334  is equipped with three spaced apart stationary couplers  384  each having a downwardly projecting pin  386 . The pins  386  are received with appropriate offset openings in the corresponding eccentric block  382 . The center-to-center distance between the pins  362 ,  386  for each unit define the crank length for that unit. Also, the axes of the three pins  386  lie in a common rectilinear line. 
     The feeder assembly  310  includes a total of four continuous belts  388 ,  390 ,  392   394  mounted on pulleys  396 . The pulleys  396  are rotationally mounted on appropriate cross-shafts  398 ,  400 . The upper stretches of each of the belts  388 - 394  are received within the corresponding beltway slots  314 - 320 , as will be understood from a consideration of FIGS. 13 and 15. 
     In the operation of assembly  300 , a sheet is initially fed via the belts  388 - 394  for coarse positioning on plate  312 . At this point, the vacuum system is actuated so that a vacuum is drawn through apertures  332  to thus hold the sheet. The drive units  346 - 350  are then actuated as necessary so as to shift the plate  306  and block  334  within opening  304  so as to accurately position the sheet within the assembly  300 . A die cutting or laminating or other operation can then be performed on the accurately positioned sheet, whereupon the assembly  310  can again be actuated to move the processed sheet out of the assembly. 
     It will be understood that the motive assembly  308  can be controlled in a manner similar to that described in connection with the first embodiment; or by any other equivalent means. In general, all that is required is that reference data be provided which corresponds to the desired final position for the sheet, together with means for comparing the actual initial location of the sheet with this reference data. With this information, the drive units  346 - 350  can be appropriately operated for the final accurate positioning of the sheet. 
     Use of the invention allows high speed operations on the order of 40-45 strokes/minute with 200 millisecond dwell times between strokes. 
     Although the invention has been described in detail in the content of die cutting apparatus, the invention is not so limited. Rather, the invention may find utility in a number of applications requiring high speed, high accuracy repeat operations, such as various painting techniques.