The invention relates to a method and device for separating sheets of paper from a sheet pile with the aid of at least one lifting suction device and for transporting the sheets to a sheet processing machine with the aid of at least one forwarding or pull suction device.
The published German Patent Document DE 43 24 552 A1 teaches the use of a pneumatically controlled lifting suction device and a pneumatically controlled forwarding or pull suction device. In this reference, the lifting suction device separates the sheet from a sheet pile by lifting the sheet to a transfer level. The forwarding or pull suction device takes the sheet from a return level to a lower-lying transport level during a return motion. To prevent tensions in the sheet, the lifting suction device must simultaneously release the sheet; i.e., only a very short time window is provided for releasing the sheet. Particularly in the case of changing machine speeds, the air inertia of pneumatic systems can lead to defective sheet transfers from the lifting suction device to the pull or forwarding suction device, because no assurance can be offered that the lifting suction device would let the sheet go precisely when the forwarding or pull suction device picks it up.
It is accordingly an object of the invention to provide a method and device for separating and transporting sheets whereby sheet transfer from a lifting suction device to a pull or forwarding suction device is improved over the prior art methods and devices.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method for separating a respective sheet from a sheet pile and transporting it to a sheet processing machine, wherein the respective sheet is lifted by at least one lifting suction device to a transfer level lying above a suction air intake level, and the respective sheet is taken over by at least one forwarding suction device at the transfer level, which comprises thereafter transporting the respective sheet by the forwarding suction device on the transfer level in a direction towards the sheet processing machine, and after transferring the sheet from the lifting suction device to the forwarding suction device, lifting the lifting suction device to an elevation level above the transfer level.
In accordance with another mode, the method of the invention includes, in a return motion, moving the forwarding suction device from one terminal location to another terminal location on a return level situated above the transfer level.
In accordance with a further mode of the method, the return level is the elevation level above the transfer level.
In accordance with an added mode, the method invention includes lowering the lifting suction device from the elevation level to the suction air intake level after transporting the respective sheet away.
In accordance with an additional aspect of the invention, there is provided a device for performing a method of separating and transporting a sheet from a sheet pile, comprising a lifting suction device for separating the sheet from a sheet pile, a forwarding suction device for transporting the sheet in a direction towards a sheet processing machine, and a cam mechanism for moving the lifting suction device to three different elevation levels.
In accordance with another feature of the invention, wherein one of the elevation levels is a suction air intake level, and the suction air intake level of the lifting suction device is adjustable.
In accordance with a further feature of the invention, the forwarding suction device is pneumatically adjustable to two different elevation levels of the three different elevation levels.
In accordance with yet another aspect of the invention, there is provided a sheet-fed rotary printing machine having a device for performing a method of separating and transporting a sheet from a sheet pile, the device comprising a lifting suction device for separating the sheet from a sheet pile, a forwarding suction device for transporting the sheet in a direction towards a printing unit, and a cam mechanism for moving the lifting suction device to three different elevation levels.
In accordance with a concomitant aspect of the invention, there is provided, in a method of operating a sheet-fed rotary printing press, a method for separating a respective sheet from a sheet pile and transporting it to a printing unit, wherein the respective sheet is lifted by at least one lifting suction device to a transfer level lying above a suction air intake level, and the respective sheet is taken over by at least one forwarding suction device at the transfer level, which comprises thereafter transporting the respective sheet by the forwarding suction device on the transfer level in a direction towards the printing unit, and after transferring the sheet from the lifting suction device to the forwarding suction device, lifting the lifting suction device to an elevation level above the transfer level.
The advantage of the inventive method is namely that a larger time window is provided for the sheet transfer from the lifting suction device to the forwarding suction device, while at the same time tension in the sheet and scratches or abrasions of the sheet by the lifting suction device during transport of the sheet by the forwarding suction device are prevented.
In addition, during its return, the forwarding suction device does not contact the sheet which has been lifted with the aid of the lifting suction device, either.
The advantage of the device according to the invention lies particularly in the combination of a mechanically elevation or height-controlled lifting suction device and a pneumatically elevation or height-controlled forwarding suction device.
This measure makes it possible to construct a sufficiently long time window for transferring the sheet and, as a result, the exact sheet transfer does not depend upon the inertia of the air control.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and a device for separating and transporting sheets, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: