Conveyors: power-driven – Conveyor section – Endless conveyor
Reexamination Certificate
1998-12-24
2001-02-20
Olszewski, Robert P. (Department: 3652)
Conveyors: power-driven
Conveyor section
Endless conveyor
C198S860300, C198S861300
Reexamination Certificate
active
06189684
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a sheet conveyor belt and in particular to a device for conveying printing substrates, sheets of paper, plastic or other materials which are to be printed and/or have been printed, the device including a frame, a plurality of spaced-apart and axially parallel cylindrical rollers which are supported on the frame, one of the rollers being a rotatably drivable drive roller, and the other rollers being freely rotatably supported, and an endless conveyor belt that wraps around all the rollers and in operation is in static-frictional contact with the drive roller.
A device of the foregoing general type heretofore known, for example, from the published European Patent Document EP-A 0 738 680, has some advantages over conventional belt conveyor devices with grippers which make it especially well suited for use in conjunction with electrographic printing units, ink jet printing units, or other printing units which are controllable pixel by pixel.
Belt conveyor devices for printing presses have been developed departing from the basic form thereof wherein two rotatable rollers, one of which is driven, are disposed at a spaced distance from one another corresponding to the conveying distance. A conveyor belt is wrapped around both rollers with initial tension. While printing substrates are fed from a feeder to a delivery along the upper portion of the belt, for multicolor printing in register they pass through a plurality of printing units, at each of which the various basic colors are applied successively. Except for the fact that additional rollers are often provided on the inner side of the conveyor belt in order to support or apply tension to the belt, this basic form has remained unchanged to the present day.
Between the drive roller and the conveyor belt entrained therewith by friction, there is intrinsically a variable amount of slip, which cannot be reduced arbitrarily, especially because it is desirable for the inner side of the conveyor belt to be as smooth as possible so as to keep the friction low in the overall system. In particular, this slip cannot be ignored if high-precision registration is demanded. Heretofore known slip compensating devices are relatively complicated and thus can be considered only for very high-quality printing presses. A proposal is made in the aforementioned published European Patent Document EP-A 0 738 680, for example, that the lagging of the conveyor belt be detected by a sensor and that the printing signals to the printing units be delayed accordingly, so that the accuracy of registration is preserved.
In addition to the aforedescribed problems of slip between the drive roller and the conveyor belt, a problem exists in the heretofore known belt conveyor devices for printing presses that changing a worn or defective conveyor belt is a difficult task. Attempts to solve this problem so far by adhesively fastening or gluing the conveyor belt in the press, partly dismantling the press, or using split shafts, provide only inadequate solutions to the problem.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a sheet conveyor belt that avoids the foregoing problems of the heretofore known conveyor belts of this general type by minimizing the difficulties in changing worn or defective conveyor belts.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for conveying printing substrates, comprising a frame, a plurality of spaced-apart and axially parallel cylindrical rollers supported on the frame, one of the rollers being a rotatably drivable drive roller, and the other rollers being freely rotatably supported, and an endless conveyor belt wrapped around all of the rollers and in operation being in frictional contact with the drive roller, two of the rollers being relatively closely adjacent one another, being spaced apart from one another a distance selected from the group thereof consisting of less than and not considerably greater than the diameter of the drive roller; the drive roller being movable in a direction towards and away from the two spaced apart rollers; and including a retaining device for firmly retaining the drive roller in an operating position wherein an outer side of the conveyor belt rests on the drive roller, the conveyor belt being wrapped around the drive roller over an angle on the order of magnitude of 180°, while the other rollers are in engagement with an inner side of the conveyor belt; and a free space provided on one side of the conveying device for retracting the conveyor belt in axial direction away from the rollers.
In accordance with another feature of the invention, the drive roller has two ends by which the drive roller is supported on respective levers having respective pivots fixed to the frame and spaced apart from the axis of the drive roller above a plane wherein the conveyor belt is disposed, for pivoting the drive roller axially parallel to the other rollers in a direction towards and between the two relatively closely adjacent rollers.
In accordance with a further feature of the invention, the frame has a first and a second side wall substantially parallel to and spaced apart from one another, and between which the rollers extend lengthwise, one end of each of the rollers being supported on the second side wall, at least one self-supporting side part being disposed in vicinity of the first side wall and being secured to cross beams extending as far as the second side wall and being joined thereto; the other end of each of the rollers being supported at a corner or edge of the at least one self-supporting side part; and the first side wall being formed with a recess having a perimeter which is larger than the perimeter of the conveyor belt.
In accordance with an added feature of the invention, two self-supporting side parts are provided in the vicinity of the first side wall, a first self-supporting side part thereof being connected via first cross beams to the second side wall, and a second self-supporting side part thereof being connected via second cross beams to a third side part located in the vicinity of the second side wall; a respective one of the two relatively closely adjacent rollers being supported between the second side wall and the first self-supporting side part, on the one hand, and between the second self-supporting side part and the third self-supporting side part, on the other hand; and the second and third side parts being pivotable jointly about an axis extending parallel to the shafts of the rollers, in the course of which the two relatively closely adjacent rollers are movable away from one another.
In accordance with an additional feature of the invention, the two relatively closely adjacent rollers are disposed in a portion of the conveyor belt whereon the printing substrates are disposed during operation.
In accordance with yet another feature of the invention, the portion of the conveyor belt whereon the printing substrates are disposed during operation includes two flat subportions having planes which intersect in a region between the two relatively closely adjacent rollers, at an angle of less than 180°.
In accordance with yet a further feature of the invention, the retaining device for firmly retaining the drive roller in an operating position includes at least one electrically controllable actuator with which at least one end of the drive roller is adjustable slightly in a direction towards the two relatively closely adjacent rollers and away therefrom; and a position detecting sensor disposed in the vicinity of an edge of the conveyor belt; the position detecting sensor controlling the at least one actuator for regulating straight-ahead travel of the conveyor belt.
In accordance with an alternative feature of the invention, the retaining device for firmly retaining the drive roller in an operating position includes the at least one electrically controllable actuator with which both ends of the drive roller are adjustabl
Greenberg Laurence A.
Heidelberger Druckmaschinen Aktiengesellschaft
Lerner Herbert L.
McAllister Steven B.
Olszewski Robert P.
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