Sheet Inverting

This invention relates generally to a method and apparatus for sequentially working on a sheet with first one side up and then the other using a pair of work units while the same edge of the sheet leads as the sheet passes through each of the work units. The particular application for which the invention is intended, involves printing equipment for printing on both sides of a sheet, and the following description is expressed primarily in terms of that environment. It will however be readily apparent that sheet handling equipment of this nature will be equally applicable in other situations.

There are known printing systems which are effective to simultaneously print on opposite sides of a sheet. These known printing systems are rather complicated in their mode of operation. Somewhat simplier printing systems have been used which are effective to print on only one side of a sheet. Still other printing systems have utilized a pair of printing units to sequentially print on opposite sides of a sheet.

Some of the known printing units which sequentially print on opposite sides of a sheet have utilized inverters to invert the sheet between the printing units. When these known inverters are utilized to invert a sheet, a first edge of the sheet leads as it passes through the first printing unit and the second edge of the sheet leads as it passes through the second printing unit. Some of these known inverters have utilized cylinders which have relatively complicated gripper arrangements to effect a turning over or inverting of the sheet.

The present invention relates to a printing apparatus and method which inverts a sheet between a pair of printing units in such a manner that the same edge of the sheet leads as it passes through the two printing units. After a sheet has been printed on an upwardly facing side with a head edge leading by the first printing unit, a first conveyor between the printing units receives the sheet with the head edge of the sheet leading. When the sheet has been moved by the first conveyor to a first readiness position at the entrance of a turnover mechanism, the head edge of the sheet engages a stop. A pusher then engages a side edge of the sheet and moves the sheet into the turnover mechanism with the opposite side edge of the sheet leading.

The turnover mechanism moves the sheet along a generally U-shaped path from an orientation in which the side of the sheet printed on by the first printing unit faces upwardly to an orientation in which the side of the sheet printed on by the first printing unit faces downwardly. At the end of this generally U-shaped path, the sheet enters a second readiness position, and its leading side edge engages stops to register the sheet relative to the second printing unit. A second conveyor is then effective to move the sheet into the second printing unit with the head edge of the sheet leading and the unprinted or blank side of the sheet facing upwardly.

Accordingly, it is an object of this invention to provide a new and improved system which acts on sheets moving in a predetermined direction and which inverts a sheet from a first orientation in which a first side of the sheet faces in one direction to a second orientation in which the opposite side of the sheet faces in the one direction, and continues to move the sheet in the same general direction with the same edge of the sheet leading as was leading initially.

It is also an object of this invention to provide a new and improved printing system which inverts a sheet from a first orientation in which a printed side of the sheet faces in one direction to a second orientation in which the opposite side of the sheet faces in the one direction, and moves the sheet through a second printing unit with the same edge of the sheet leading as was leading as the sheet passed through the first printing unit.

Another object of this invention is to provide a new and improved apparatus to sequentially print on opposite sides of a sheet with the same edge leading and wherein the apparatus includes an inverter assembly between first and second printing units to change the orientation of the sheet from an orientation in which a first or printed side of the sheet faces in one direction to an orientation in which a second or blank side of the sheet faces in the one direction by moving the sheet along a path which extends transversely to the direction of movement of the sheet through the printing units.

Another object of this invention is to provide a new and improved apparatus for printing on opposite sides of a sheet with the same edge of the sheet leading and wherein a sheet printed on one side by a first printing unit is moved by an inverter along a generally U-shaped path to a conveyor which moves the sheet to a second printing unit with the same edge leading as was leading as the sheet passed through a first printing unit.

Another object of the invention is to provide a new and improved method of sequentially working on opposite sides of a sheet and wherein the method includes the steps of working on a first side of the sheet in a first work unit with a first edge of the sheet leading, inverting the sheet, and working on the second side of the sheet with a second work unit as the sheet moves through the second work unit with the first edge of the sheet leading.

The foregoing and other objects and features of the present invention will become more apparent of a consideration of the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of a printing system constructed and operated in accordance with the present invention and illustrating the relationship between a pair of printing units and an inverter;

FIG. 2 is an enlarged elevational side view of a sheet inverter and conveyors constructed in accordance with the present invention;

FIG. 3 is a fragmentary elevational view of cams which activate pusher linkages in the inverter;

FIG. 4 is a fragmentary plan view taken on line 4--4 of FIG. 2, illustrating a pusher member and linkage activated by one of the cams of FIG. 3;

FIG. 5 is a sectional elevation taken generally on line 5--5 of FIG. 2;

FIG. 6 is a fragmentary plan view, with parts broken away, taken generally on line 6--6 of FIG. 2, illustrating a pusher member and a portion of the linkage activated by the other of the cams in FIG. 3.

General Description

Referring to the schematic showing in FIG. 1, a sheet printing system 8 constructed in accordance with the present invention is illustrated schematically in FIG. 1 and includes a first printing unit 10. The printing unit 10 prints on an upwardly facing first major side surface 14 of a sheet 12 as it passes through the first printing unit with the head edge 16 of the sheet leading and a foot edge 18 of the sheet trailing. As the sheet 12 moves out of the first printing unit 10, the sheet moves through pull out rolls 74, 76 and along guide means 70, 78 onto a conveyor which constitutes the initial station of an inverter 24.

As the sheet 12 enters the inverter 24, the leading head edge 16 of the sheet engages a stop 28 which stops the sheet in a predetermined position relative to a turnover mechanism 39. A pusher member 32 then engages a first side edge 34 of the sheet 12 and pushes it into engagement with lower conveyor belts 38 of the turnover mechanism. The conveyor belts 38 are effective to move the sheet along the lower leg of a generally U-shaped path with a second side edge 42 of the sheet 12 leading. An arcuate surface 40 guides movement of the sheet along the curved portion of the U-shaped path. Upper turnover conveyor belts 41 then move the sheet along the upper leg of the U-shaped inverter path.

As the sheet 12 moves through the turnover mechanism 39, the orientation of the sheet is changed from an orientation in which the printed major side surface 14 faces upwardly to an orientation in which a blank opposite major side surface 44 faces upwardly. When the sheet 12 has moved to a position substantially over the position in which it entered the inverter 24, the leading side edge 42 of the sheet engages a stop 46 which interrupts movement of the sheet at a second readiness position on a platform 132. Engagement of the sheet with the stop 46 registers the sheet relative to a second printing unit 50.

The sheet 12 is then started to the second printing unit 50 by a pusher member 56 which pushes against the trailing foot edge 18 of the sheet 12 to push the sheet into a nip between a roller 150 and conveyor belts 58. The conveyor belts 58 feed the sheet into the second printing unit 50 with the head edge 16 of the sheet leading. The printing unit 50 is then effective to print on the blank upwardly facing major side 44 of the sheet as the sheet passes through the printing unit. It should be noted that the opposite sides 14 and 44 of the sheet were sequentially printed on by the two printing units 10 and 50 with the same edge of the sheet leading, that is the head edge 16.

As the sheet 12 passes through a printing nip 62 formed in the first printing unit 10 between a plate or master cylinder 64 and an impression cylinder 66, the upwardly facing major side surface 14 of the sheet 12 is printed on by a master 67. As the sheet 12 exits from the printing nip 62 with the head edge 16 leading, the sheet moves onto a guide surface 70 (FIG. 2) and is directed into a feed nip 72 formed between a pair of feed rollers 74 and 76. The feed rollers 74 and 76 feed the sheet along a support surface 78 downwardly onto a belt conveyor 80 forming the input stage of the inverter 24.

The belt conveyor 80 has a horizontal upper run 84 which engages the downwardly facing blank side 44 of the sheet and moves the sheet toward the left (as viewed in FIG. 2). At the end of the conveyor 80, the leading head edge 16 of the sheet moves into engagement with the face surface 48 of the stop 28. The sheet is held from bouncing back away from the vertical face surface 48 on the stop 28 by one or more brushes 88 (FIGS. 2 and 5) which extend forwardly and downwardly from an upper level platform 90 of the inverter assembly 24. The brushes 88 slope toward the stop 28 so that the bristles of the brushes engage the printed upwardly facing surface 14 of the sheet 12 to hold the sheet against rebounding.

Once the sheet 12 has moved into engagement with the stop 28, the pusher 32 is actuated to initiate movement of the sheet onto the parallel lower conveyor belts 38 of the turnover mechanism 39. The pusher member 32 has a vertical face surface which engages the side edge 34 of the sheet 12 as the pusher member is moved along a horizontal path extending perpendicular to the longitudinal central axis of the conveyor 80. This movement of the pusher member 32 is effected by a cam 94 (FIG. 3). The cam 94 is mounted on a horizontal shaft 96 which is rotated under the influence of the drive for the two printing units 10 and 50. Therefore, the cam 94 rotates in a timed relationship with the movement of sheets through the printing units. Preferably the shaft 96 makes one revolution for each rotation of the printing cylinders.

When the leading head edge 16 of the sheet 12 has moved into engagement with the stop 28, the cam 94 effects movement of a cam follower lever 100 to cause a horizontal link 102 to move to the left. This link is connected with a bell crank lever 104. (See FIG. 4.) The bell crank lever 104 is pivotally mounted at 106 for movement about a vertical axis. As the link 102 is moved to the left, the bell crank 104 is pivoted in a counterclockwise direction (as viewed in FIG. 4), and the pusher member 32 is moved along a horizontal path extending perpendicular to a horizontal longitudinal edge 107 of the conveyor belt 80. It should be noted that the stroke of the crank actuator rod 102 is relatively short so that the pusher 32 is moved from an initial position shown in solid lines in FIG. 4 to the position shown in dash lines in FIG. 4 in which an upwardly projecting body section 108 of the pusher member 32 is disposed adjacent to a longitudinally extending side edge 107 of the conveyor belt 80. A spring 105 serves to restore the pusher to home position and maintains the follower 100 in contact with its cam 94.

As the sheet moves into the lower portion of the turnover mechanism 39, the leading side edge 42 of the sheet moves onto the continuously driven feed belts 38 (FIG. 5). The horizontal blank lower major side 44 of the sheet is urged downwardly into engagement with the feed belts 38 by suction applied to the lower side surface 44 of the sheet by a vacuum box 112 which is connected with a source of low pressure through a conduit 114. The upper run of the feed belt 38 is driven toward the left (as viewed in FIG. 5) to move the leading side edge 42 of the sheet along the horizontal lower leg of a generally U-shaped path along which the sheet travels in moving through the turnover mechanism 39.

As the sheet 12 continues to move through the turnover mechanism, the leading side edge 42 of the sheet moves along a semi-circular guide surface 40. The leading edge 42 of the sheet then moves into engagement with the upper feed belts 41. The now upwardly facing major blank side surface 44 of the sheet is drawn into engagement with the belts 41 under the influence of suction applied against the side surface 44 of the sheet by a second vacuum box 122 which is connected with a source of low pressure by a conduit 124.

The lower runs of the continuously driven feed belts 41 are effective to move the sheet toward the right (as viewed in FIG. 5) along the upper leg of the generally U-shaped inverter path. At this time the side edge 42 of the sheet is leading and the blank major side surface 44 of the sheet is facing upwardly. In moving from the conveyor belts 38 to the conveyor belts 41, the sheet is moved along a path which turns back on itself so that the blank major side 44 of the sheet which was facing downwardly when the sheet initially engaged the belts 38, is facing upwardly when the sheet moves into engagement with the belts 41. It should be noted that the width of the sheet, that is, the distance between the two side edges 34 and 42 of the sheet, is such that the leading edge 42 of the sheet moves into engagement with the conveyor belts 41 before the trailing edge 34 of the sheet moves out of engagement with the conveyor belts 38. Therefore, the sheet is continuously maintained in engagement with either the conveyor belts 38 or the conveyor belts 41 as the sheet moves along the U-shaped path through the inverter unit 24.

As the leading side edge 42 of the sheet moves rightwardly (as viewed in FIG. 5) away from the belts 41, it gradually droops down onto a support tray 132, and it also moves toward a sloping deflector plate 130 which is effective to insure deflection of the sheet downwardly onto the support tray. Thus, as the sheet leaves the conveyor belts 41, it moves toward the right (as viewed in FIG. 5) and the lead edge 42 is driven against the stop member 46 by the action of the conveyor belts 41. A plurality of brushes 138 (FIGS. 5 and 6) extend through openings in the deflector 130 into engagement with the upper side 44 of the sheet to prevent it from rebounding from the stop 46.

The support tray 132 forms part of the upper platform 90 of the inverter 24 and extends parallel to the upper run 84 of the conveyor belt 80 which is disposed directly beneath the tray. As the sheet engages the stop surface 46, the printed side 14 of the sheet faces downwardly toward the support tray 132. To prevent smudging of the ink on the printed side surface 14 of the sheet, a plurality of parallel ribs or ridges 139 (FIG. 6) are formed in the support tray 132. The ribs 139 engage a relatively long narrow area on the printed major side 14 of the sheet and prevent widespread contact with the sheet surface.

After the side edge 42 of the sheet has been moved into engagement with stop surface 46, the pusher 56 is moved along the tray 132 toward the printing unit 50. The pusher 56 is mounted on a carriage 142 which is disposed on the platform 90 beneath the support tray 132. The carriage 142 and pusher member 56 are moved along a horizontal path extending parallel to the longitudinal central axis of the upper run 84 of the conveyor belt 80.

Upon movement of the carriage 142 and pusher 56 toward the printing unit 50, an upright face surface 146 of the pusher 56 engages the foot edge 18 of the sheet and pushes the sheet into a nip formed between the belts 58 of conveyor 54 at pulley 148, and a feed roller 150 (see FIGS. 1 and 2).

The conveyor belts 58 feed the sheet 12 into the printing unit 50 with the head edge 16 of the sheet leading and the blank side 44 of the sheet facing upwardly. As the sheet passes through a printing nip 154, a master 156 (FIG. 1) on a plate or master cylinder 158 prints on the upper side 44 of the sheet. As the sheet passes through the printing nip 154, the previously printed side 14 of the sheet is supported by an impression cylinder 160.

Although the pusher 56 (FIG. 6) could be driven in many different ways to effect movement of a sheet from the inverter 24 toward the printing unit 50, the pusher member 56 is advantageously driven in timed relationship with the operation of the printing units 10 and 50 by a cam 164 (see FIG. 3) which is connected with the shaft 96 and rotates with the cam 94. The cam 164 pivots the cam follower lever 166 to effect movement of a horizontal link 168 connected with a link 170 (FIG. 2) which is pivotally mounted on a base frame at 172. Pivotal movement of the link 170 moves a link 174 to cause a lever arm 176 (FIG. 6) to pivot about vertical axis 178 (FIG. 6). The lever arm 176 has a pin and slot connection 180 with the pusher carriage 142 so that pivotal movement of the arm 176 in a counterclockwise direction (as viewed in FIG. 6) about the pivot 178 under the influence of the cam 164 causes the pusher 56 to push against the foot edge 18 of the sheet 12 to move the sheet toward the printing unit 50. The pusher 56 is moved against a return spring 184. When the pusher 56 reaches the end of its stroke, the cam 164 allows the follower lever 166 to pivot in a counterclockwise direction (as viewed in FIG. 3) and the spring 184 acts to return the carriage 142 and the pusher 56 to the initial position shown in solid lines in FIG. 6.

In order to make the Figures consistent, FIG. 6 shows the parts in positions corresponding contemporaneously to the positions in FIGS. 3 and 4; i.e., with the pusher 32 retracted and the pusher 56 substantially extended. Of course, by the time the cam 94 has moved to a location causing extension of the pusher 32 to start turnover action of the sheet, cam 164 will have moved counterclockwise to a position perhaps 80.degree. from that shown, so that at this time the pusher 56 will be substantially in its dotted or retracted position in FIG. 6, ready to receive the sheet as it approaches from the turnover mechanism 39. Projection of the sheet by means of pusher 56 will then occur when the lobe of cam 164 activates its follower 166 on the succeeding cycle.

In accordance with a feature of the present invention, the turnover mechanism 39 may be bypassed so that a sheet passing through the printing unit 10 is conducted directly to the printing unit 50 without being turned over. At this time, the printing unit 50 would either be in a thrown-off or ineffective condition in which the sheet would pass through the printing unit 50 without the occurrence of a printing operation, or would be arranged to make an impression of a different character (e.g., a different color) on the face of the sheet already printed.

To move the conveyor 22 to a bypass condition, a handle 190 (see FIG. 2) is rotated in a clockwise direction about a pivot connection 192. This causes a main lever 194 to actuate a link 196 to move one end of a frame member 198 carrying the conveyor 80 upwardly from the position shown in FIG. 2. By virtue of the link 199, the upper platform 90 is also pivoted upwardly to the dotted line position to make room for frame 198. This results in the upper run of the conveyor belt 80 being disposed with its left-hand end in line with the nip 148, 150, above the upper edge of the stop 28 and above the path of the pusher 32, both of which are mounted on the base frame. Therefore, the conveyor 80 is operable to feed a sheet directly into the feed nip between the rollers 148 and 150 without inverting the sheet.

In view of the foregoing description it can be seen that the present invention provides an apparatus and method which inverts a sheet 12 between a pair of work units or printing heads 10 and 50 in such a manner that the same edge 16 of the sheet leads as it passes through the two units. After a sheet 12 has been acted on by the first work unit 10 with the side 14 facing up, with a head edge 16 leading, a first conveyor 80 between the work units 10 and 50 receives the sheet 12 with the head edge 16 of the sheet leading. When the sheet 12 has been moved by the first conveyor 80 to a first ready position, the head edge 16 of the sheet engages a stop 28. A pusher 32 then engages a side edge 34 of the sheet and moves the sheet into the turnover mechanism 39 with the opposite side edge 42 of the sheet leading.

The turnover mechanism moves the sheet 12 along a generally U-shaped path from an orientation in which the printed side 14 of the sheet faces upwardly to an orientation in which the blank side 44 of the sheet faces upwardly. At the end of this generally U-shaped path, the leading side edge 42 of the sheet 12 engages a stop 46 to register the sheet relative to the second work unit 50 at a second ready position. A pusher 56 then introduces the sheet along a substantial extension of its original path to a conveyor 54 which is effective to move the sheet into the second work unit 50 with the head edge 16 of the sheet leading and the side 44 of the sheet facing upwardly.