Sheet inspection apparatus for sheet-fed offset printing press

Abstract: A sheet inspection apparatus for a sheet-fed offset printing press includes an endless conveying unit (5), a plurality of gripper units (7;7a;7b;7c;7d), and an inspection unit (28). The conveying unit has a conveying path and a return path and conveys a sheet (10) delivered from a printing unit. The gripper units are supported by the conveying unit at a predetermined interval along a sheet conveying direction to grip one end of the sheet. The inspection unit is arranged on an opposite side of the conveying path with respect to the return path to optically inspect a printed state of the sheet conveyed on the conveying path. The inspection unit is arranged at a position where an optical inspection operation for the sheet at an inspection position on the conveying path is not impeded by the gripper units traveling on the return path.

Description: Background of the Invention The present invention relates to a sheet inspection apparatus for a sheet-fed offset printing press, which detects a misfed sheet in a defective printed state after printing of sheets. Generally, in a sheet-fed offset printing press of this type, to inspect the printed state of a sheet upon completion of all printing processes, the inspection process is provided after the operation of the impression cylinder of the final printing unit. In this case, when the printed state is to be inspected on the impression cylinder of the final printing unit, the trailing edge of the sheet which has passed between the impression cylinder and a blanket cylinder is pulled to the blanket cylinder side due to the viscosity of the ink on the blanket cylinder, and the sheet largely swings, resulting in so-called instability of sheets. For this reason, determination of properly conveyed sheets and misfed sheets cannot always be exactly performed. Therefore, as disclosed in Japanese Patent Laid-Open No. 63-64748, a frame is added in a delivery unit continuing to the printing unit. A support plate functioning as a printing paper stabilization means for straining a sheet conveyed by an ejector chain is arranged in this frame in correspondence with the inspection unit such that the sheet is inspected in the sheet conveying unit of the delivery unit. However, since the inspection unit is set between the impression cylinder of the final printing unit and the delivery unit, an inspection unit adjustment operation or maintenance operation for cleaning paper dust adhering to the detection unit of the inspection unit or anti-setoff powder can hardly be performed, and the maintenance operation takes a long time. Additionally, the sheet conveying unit of the delivery unit has a dryer unit for drying a printed sheet. When the inspection unit is set to be close to this dryer unit, an electronic circuit including electronic components constituting the inspection unit is adversely affected by heat generated by the dryer unit. As a result, the inspection unit erroneously operates to impede proper inspection of the printed state. Further, a sheet inspection apparatus according to the preamble of claim 1 is known from EP-A-0 527 453. Summary of the Invention It is an object of the present invention to provide a sheet inspection apparatus for a sheet-fed offset printing press, which can easily perform adjustment and maintenance operation. It is another object of the present invention to provide a sheet inspection apparatus for a sheet-fed offset printing press which inspects the printing state of a sheet with high accuracy. In order to achieve the above object, there is provided according to the present invention a sheet inspection apparatus for a sheet-fed offset printing press comprising endless conveying means for conveying sheets delivered from a printing unit, said endless conveying means having a conveying path and a return path; a plurality of gripper units, supported by said conveying means at a predetermined interval along a sheet conveying direction, for gripping one end of a sheet, respectively; and an inspection unit arranged on a side of said conveying path which opposes said return path to optically inspect a printed state of said sheet conveyed on said conveying path through said return path, wherein said inspection unit is positioned such that the length of a path between an inspection position on said conveying path and a position on said return path corresponding to a point at which a line connecting said inspection unit and said inspection position crosses said return path is an integer multiple of the interval between said gripper units, so that optical inspection of the sheet is not impeded by the gripper units traveling on the return path. Brief Description of the Drawings Fig. 1 is an enlarged side view showing the main portion of a sheet conveying unit shown in Fig. 3; Fig. 2 is a view for explaining the relationship between the inspection operation of an inspection unit shown in Fig. 1 and movement of gripper bars; and Fig. 3 is a schematic view showing the arrangement of a delivery unit for a sheet-fed offset printing press according to an embodiment of the present invention. Description of the Preferred Embodiment An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. Fig. 3 shows the schematic arrangement of a delivery unit for a sheet-fed offset printing press according to an embodiment of the present invention. Referring to Fig. 3, reference numeral 1 denotes a sheet conveying unit 1 constituting the delivery unit. A final printing unit 50 having an impression cylinder 2 is arranged upstream in the sheet conveying direction of the sheet conveying unit 1. A pile board 60 on which a printed sheet 10 is stacked is arranged downstream in the sheet conveying direction of the sheet conveying unit 1. A pair of left and right sprockets 3a are arranged at an end upstream in the sheet conveying direction of the sheet conveying unit 1. A pair of left and right sprockets 3b are arranged at an end downstream in the sheet conveying direction of the sheet conveying unit 1. A pair of left and right delivery chains 5 as conveying means extend between the sprockets 3a and 3b. When the sprockets 3a rotate, the delivery chains 5 supporting grippers 71 travel in the direction for delivering the sheet 10. In the delivery unit with the above arrangement, the sheet 10 with its leading edge being gripped by the grippers 71 of the delivery chains 5 is delivered from the impression cylinder 2 of the printing unit 50 and conveyed onto the pile board 60 through the sheet conveying unit 1. When the grippers 71 are opened by a cam mechanism 61, the sheet 10 conveyed onto the pile board 60 is released and stacked on the pile board 60. Fig. 1 shows the main portion of the sheet conveying unit 1 shown in Fig. 3. Referring to Fig. 1, the sheet conveying unit 1 has a pair of left and right delivery frames 4 each standing on the floor base through a column (not shown) and having a rectangular window 4a. The above-described sprockets 3a and 3b are rotatably supported by the pair of delivery frames 4 through bearings. Rotation of a motor is transmitted to the delivery chains 5 through a driving gear (not shown) axially mounted on the shaft of the sprockets 3a so that the delivery chains 5 travel in the sheet conveying direction indicated by an arrow A. A plurality of gripper bars 7 each having the above-described grippers 71 are arranged between the pair of delivery chains 5 at a predetermined interval in the conveying direction of the sheet 10. Each of the gripper bars 7 is constituted by a gripper shaft 8 and a gripper pad shaft 9 which are axially and parallelly held by the delivery chains 5, and a plurality of sets of grippers 71 and gripper pads 72 which are arranged on the axes 8 and 9, respectively, to oppose each other. The sheet 10 delivered from the impression cylinder 2 of the printing unit 50 is gripped by the grippers 71 and the gripper pads 72 and conveyed by the delivery chains 5 traveling in the direction indicated by the arrow A. A plurality of tie-bars 11 span between the delivery frames 4. Guide rails 12 and 13 are fixed on the upper and lower sides of the delivery frames 4 through stepped studs 14 such that the delivery chains 5 are guided between the rails 12 and 13. A pair of left and right semicircular guide rails 15 are fixed on the left and right delivery frames 4, respectively, through stepped studs 16 along the outer circumferences of the sprockets 3a. Reference numeral 17 denotes a missing sheet regulation member fixed to the guide rails 15. The missing sheet regulation member 17 is arranged below the opposing position of the sprockets 3a and the impression cylinder 2 to prevent the sheet 10 that the grippers 71 of the gripper bar 7 have failed to grip from falling in the apparatus. A plurality of paper guides 18 each having an arcuate section are arranged between the delivery frames 4 at a predetermined interval. The paper guides 18 are separated from the outer circumferences of the sprockets 3a by a predetermined distance and regulate the instability of the trailing edge of the sheet 10 transferred from the grippers of the impression cylinder 2 to the grippers 71 of the gripper bar 7. A paper guide plate 20 is horizontally arranged under the delivery chains 5 downstream in the sheet conveying direction from the paper guides 18 while being separated from the delivery chains 5 by a predetermined distance over the range where an inspection unit 28 (to be described later) inspects the printed surface of the sheet 10. The paper guide plate 20 is fixed, with bolts, to tie-bars 21 fixed between the delivery frames 4 with bolts such that the surface of the paper guide plate 20 becomes close to the gripping surface of the gripper pads 72 of the gripper bar 7. A plurality of juxtaposed paper guides 22 are horizontally attached between the delivery frames 4 at a position close to the downstream side of the sheet conveying direction of the paper guide member 20. Reference numeral 23 denotes a grease receiving tray fixed to the lower portion of the upper guide rail 13 with bolts. Reference numeral 25 denotes a dryer unit having an UV irradiation unit and fixed, above the paper guides 22, to a rest 26 attached between the delivery frames 4. The dryer unit 25 can be extracted/inserted through the window 4a of the delivery frame 4. The inspection unit 28 having a camera or the like is supported and fixed on the upper end portions of the delivery frames 4 through a bracket 29, i.e., arranged above the delivery chains 5. The inspection unit 28 optically measures the printing density value of the printed surface of the sheet 10 conveyed on the paper guide plate 20 and compares the measurement value with the density value of a standard image, thereby detecting a misfed sheet. According to the above arrangement, since the inspection unit 28 is arranged above the delivery chains 5, the adjustment operation and the maintenance operation can be easily performed, as compared to the conventional arrangement in which the inspection unit is arranged between the upper and lower delivery chains 5. In addition, since the inspection unit 28 is separated from the dryer unit 25, the inspection unit 28 is not adversely affected by heat generated by the dryer unit 25. Therefore, highly accurate inspection is performed while preventing the erroneous operation of the inspection unit 28. As shown in Fig. 2, the inspection unit 28 inspects the printed surface of the sheet 10 which is being conveyed while being gripped by a gripper bar 7a at an inspection position B on lower delivery chains (conveying path) 5b. A point at which the optical path connecting the inspection unit 28 and the inspection position B crosses upper delivery chains (return path) 5a constituting the conveying path is represented by C. The inspection unit 28 is positioned with respect to the sheet conveying direction such that, when the inspection unit 28 starts to inspect the gripped end portion of the sheet 10 at point B, a gripper bar 7c supported by the upper delivery chains 5a passes point C, and after inspection of the trailing edge portion of the sheet 10 is ended at point B, a next gripper bar 7d passes point C. In other words, the inspection unit 28 is positioned with respect to the sheet conveying direction on the basis of the interval of the gripper bars 7a, 7b, 7c and 7d such that, while the sheet 10 gripped by the gripper bar 7a is being optically inspected by the inspection unit 28 at the inspection position B, the gripper bars 7c and 7d supported by the upper delivery chains 5a do not shield the optical path of the inspection unit 28, i.e., do not impede the optical inspection operation of the inspection unit 28. More specifically, the inspection unit 28 is positioned such that the length of the delivery chain from the inspection position B to the intersection C via the sprocket 3a becomes an integer multiple of the interval of the gripper bars 7a, 7b, 7c and 7d. A sheet printed state inspection operation of the inspection unit 28 having the above arrangement will be described next. The sheet 10 printed by the printing unit 50 is transferred from the grippers of the impression cylinder 2 to the grippers 71 and the gripper pads 72 of the gripper bar 7 and conveyed onto the paper guide plate 20 by the delivery chains 5 traveling in the direction indicated by the arrow A. Since the surface of the paper guide plate 20 is set close to the gripping surface of the gripper pads 72 of the gripper bar 7, the sheet 10 gripped by the grippers 71 and the gripper pads 72 is conveyed while horizontally sliding on the paper guide plate 20. The printing density value of the printed surface of each sheet 10 which has conveyed while sliding on the paper guide plate 20 is optically measured by the inspection unit 28 at the inspection position B. When the measurement value differs from the density value of the standard image due to smear, setoff, misregistration, or the like, the inspection unit 28 outputs a misfed sheet detection signal. At this time, the inspection operation on the optical path of the inspection unit 28 is not shielded by the gripper bar 7 traveling with the upper delivery chains 5a. The detection signal output from the inspection unit 28 is sent to the gripping releasing unit of the delivery unit via, e.g., a delay circuit and used as a control signal for delivering the misfed sheet whose printed surface is being dried by the UV irradiation unit 27 of the dryer unit 25 to a route different from that to the pile board 60 on which normal papers are stacked. Alternatively, the detection signal is used as a control signal for inserting a tape under the misfed sheet stacked on the pile board 60 to discriminate the misfed sheet from normal sheets. In the above embodiment, the delivery chains 5 are horizontally set. However, the present invention is not limited to this, and the delivery chains 5 may be set at an angle or in the vertical direction. In the above embodiment, the sheet 10 is conveyed from the final printing unit 50 to the pile board 60. However, the present invention is not limited to this and can also be applied to inspect the printed state of the sheet among a multiple of printing units. As has been described above, according to the present invention, since the inspection unit is arranged above the movement locus of the gripper bar, the adjustment and maintenance operations of the inspection unit are facilitated. In addition, proper inspection is performed while preventing the inspection operation from being impeded by the gripper bar supported by the upper chains. Furthermore, since the influence of heat generation by the dryer unit on the inspection unit is eliminated, erroneous operation of the inspection unit can be prevented to perform highly accurate inspection.

Claims: A sheet inspection apparatus for a sheet-fed offset printing press comprising: endless conveying means (5) for conveying sheets (10) delivered from a printing press unit (50), said endless conveying means having a conveying path (5b) and a return path (5a); a plurality of gripper units (7, 71, 7a, 7b, 7c, 7d), supported by said conveying means at a predetermined interval along a sheet conveying direction, for gripping one end of a sheet, respectively; and an inspection unit (28) arranged on a side of said conveying path which opposes said return path to optically inspect a printed state of said sheet conveyed on said conveying path through said return path, characterized in that said inspection unit is positioned such that the length of a path between an inspection position (B) on said conveying path and a position (C) on said return path corresponding to a point at which a line connecting said inspection unit and said inspection position crosses said return path is an integer multiple of the interval between said gripper units, wherein said inspection unit is being adapted to inspect said sheet conveyed to the inspection position on said conveying path from a leading edge to a trailing edge within a period after a preceding gripper unit crosses the intersection on said return path unit until a next gripper unit crosses the intersection, so that optical inspection of the sheet is not impeded by the gripper units travelling on the return path. An apparatus according to claim 1, wherein said inspection unit is positioned on the basis of the intervals of said gripper units. An apparatus according to claim 1, wherein said conveying path is horizontally arranged, said return path is arranged above said conveying path to be parallel to said conveying path, and said inspection unit is arranged above said return path. An apparatus according to claim 3, further comprising a pair of frames (4) opposing each other through said conveying means and supporting said conveying means therebetween along the sheet conveying direction, and wherein said inspection unit is supported at an upper end portion of at least one of said frames positioned above said return path. An apparatus according to claim 1, wherein said conveying means comprises a pair of delivery chains arranged at an interval larger than the width of said sheet, and two ends of said gripper units are supported by said delivery chains. An apparatus according to claim 1, further comprising dryer means (25), arranged downstream from the inspection position (B) on said conveying path along the sheet conveying direction, for drying said sheet between said conveying path and said return path, and wherein said conveying means is arranged between said printing unit and a pile board (60) to convey said sheet delivered from said printing unit, inspected by said inspection unit, and dried by said dryer means onto said pile board.

Inventors: SHIBATA SATOSHI, SHIBATA, SATOSHI, SHIBATA, SATOSHI, C/O TORIDE PLANT
Applicants: KOMORI PRINTING MACH, KOMORI CORPORATION
Application year: 1997
Main classification: B41F21
IPC codes: B41F21, B41F33