Sheet feeding or delivering – Delivering – Rotary conveyor
Reexamination Certificate
2001-11-29
2004-04-06
Mackey, Patrick (Department: 3651)
Sheet feeding or delivering
Delivering
Rotary conveyor
C271S204000, C271S206000, C101S410000
Reexamination Certificate
active
06715751
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a device for adjusting the position of sheet material when a direction of motion thereof is reversed, for example when sheet material is turned or reversed between printing units in multi-color rotary printing machines.
The published German Patent Document DE 41 13 478 A1 is concerned with an electronic sheet inspection device for cylinders in sheet-fed rotary printing machines. Sensing elements including linear CCDs and a light source register the leading edge of the respective sheet-material and the correct position thereof for a register-maintaining sheet transfer. By this inspection device, curved regions of a sheet-material leading edge are detected, in order specifically to correct possible faults by changing printing parameters. This paper position inspection makes it possible to register the sheet leading edge in the gripper system of each printing unit in a printing machine, in order even to detect printed sheet positional changes in the gripper system during the sheet transfer from one cylinder to another cylinder. The determined measured values are fed out of the cylinder to an evaluation device and are held ready in a data storage device for interrogation when the cylinder is at a standstill.
The published German Patent Document DE 85 03 577 U1 describes a register rail or bar having rotatably motor-driven setting screws, for stopping the leading edge of a respective sheet. By the rotatably motor-driven setting screws, the register rail or bar can be given a slight curvature, in order to bow the sheet slightly during the sheet acceleration in order to improve the contact thereof with the outer cylindrical or jacket surface of a cylinder.
The published German Patent Document DE 44 06 740 A1 discloses a device for color register correction in a rotary printing machine. In this correction device, a sheet holder grips the sheet at an edge region thereof leading in the conveying direction, electronic measuring elements being provided for establishing the sheet position. Sheet holders are displaceably arranged and are connected to motorized actuating elements controlled by the measuring elements. According to this embodiment, the sheet holders are constructed so as to be movable in the conveying direction and transversely to the conveying direction of the sheet. Signals from a nominal/actual comparison of the measuring elements determining the sheet position control the associated actuating elements which influence the sheet position at a contact surface.
It has become known heretofore that the color register of sheet material to be reversed or turned is always determined by the position of the leading edge of the sheet material. The trailing edge of the sheet material cannot be used as a reference edge, because of cut tolerances on the printing materials, which occur during the production thereof. A precondition for a good color register, i.e., one which maintains tolerance, is the maintenance of tolerance of the transfer color register. This means that the leading edge of each individual copy of the sheet material is positioned within the transfer color register tolerance range in the gripper system of a storage drum or a machine component, for example, which is the last to carry the printing material at the leading edge thereof before the printing material is picked up at the trailing edge thereof. In order to achieve this, the sheet is tautened in various ways at the trailing edge on the outer cylindrical or jacket surface of a sheet-carrying cylinder. For this purpose, use is made, for example, of sucker systems, which are capable of performing a relative movement with respect to the circumferential direction of the respective sheet-carrying cylinder, and exert a pulling force on the copy of the sheet material. The respective gripped copy is completely smoothened thereby, i.e., tautened, before the printing material is transferred to a gripper system for fixing the printing-material trailing edge.
The quality of the tautening of the sheet material on the outer jacket surface of the sheet-carrying cylinder, respectively, carrying the sheet material controls the manner in which the perfecting register, i.e., the systematic deviation of each piece of sheet material from the nominal or desired position, results in each case, taking into account tautening faults which are always the same from sheet to sheet, and/or the perfecting register, i.e., a stochastic deviation from the nominal position, for example, of tautening faults which repeatedly occur irregularly from sheet to sheet. These printing quality criteria are always determined in the same way by the relative position of the tautening elements, for example, tautening elements which are displaceable from the circumferential direction thereof on the outer jacket surface, to the gripper system for fixing the trailing edge of the fixed sheet material. In this regard, the perfecting register is determined by the accuracy; the color register is determined by the precision of repetition. Both operations, and particularly the tautening operation, cannot be performed with the demanded precision at higher printing speeds and in the case of certain printing materials, so that this circumstance has to be taken into account when turning or reversing sheet material between printing units of rotary printing machines.
SUMMARY OF THE INVENTION
In view of the afore-discussed prior art and the aforementioned technical problem, it is an object of the invention to provide a device for adjusting the position of sheet material when a direction of motion thereof is reversed, wherein turned or reversed sheet material is optimally adjusted in the position thereof even during the turning or reversing operation.
With the foregoing and other objects in view, there is provided, in accordance with a first aspect of the invention, a method of correcting a position of sheet material on conveying elements, the sheet material extending from a surface of a first sheet-conveying element to a surface of a second sheet-conveying element following downline from the first sheet-conveying element, as viewed in a conveying direction of the sheet material, which comprises detecting an actual position of a leading edge of the sheet material by at least one sensor element disposed on the first sheet-conveying element; by a control unit, making a comparison between a nominal and the actual position of the sheet material; and, if the actual position deviates from the nominal position of the sheet material, causing an actuator to fix the sheet material to the following second sheet-conveying element so as to perform a correction of the position deviation.
In accordance with another mode, the method of the invention includes providing jacket surfaces of sheet-guiding cylinders as the conveying elements, the sheet material extending from the jacket surface of a first sheet-guiding cylinder to a jacket surface of a second sheet-guiding cylinder, as viewed in the travel direction of the sheet material.
In accordance with a further mode, the method of the invention includes registering, by the sensor element, a time offset between a start of the movement of an actuator-operated gripper system and a start of movement of the edge of the sheet material covering the sensor element.
In accordance with an added mode, the method of the invention includes measuring the time offset in degrees of machine angle.
In accordance with an additional mode, the method of the invention includes determining the time offset of the start of movement by a sensor element constructed as an edge sensor.
In accordance with yet another mode, the method of the invention includes determining the time offset of the start of movement by a sensor element constructed as a linear CCD.
In accordance with yet a further mode, the method of the invention includes performing the correction of the position of the sheet material based upon the laws of motion of an actuator-operated gripper system provided on the following second she
Greenberg Laurence A.
Heidelberger Druckmaschinen AG
Locher Ralph E.
Mackey Patrick
Stemer Werner H.
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