The invention relates to a method for conveying a sheet, in which an electrically charged sheet is guided pneumatically along a desired path. The invention also relates to an apparatus for carrying out the method.
German Published, Non-Prosecuted Patent Application DE 43 36 479 A1 discloses a control device for the transport of workpieces in a printing machine. The control device includes an electrification configuration for the workpieces and a configuration for measuring field strength. Changes in the field strength occurring as a workpiece edge passes through are detected and used in generating actuating signals for a sheet transport apparatus.
According to German Published, Non-Prosecuted Patent Application DE 22 42 948 A1, corresponding to U.S. Pat. No. 3,868,666, a stream of ions is led through a transport path in order to detect sheet material which is transported wrongly. The stream of ions is interrupted when a sheet is conveyed past. A switch of a sheet-processing machine is controlled on the basis of the magnitude of the stream of ions.
German Published, Non-Prosecuted Patent Application DE 199 38 600 A1 discloses a device for processing a material web, in which electrostatic charging of the material web is detected by a sensor and the charge is dissipated through the use of a discharging rod on the basis of the sensor signal. The discharging rod is connected to a controllable high voltage source. The device can be used only at low transport speeds.
According to German Published, Non-Prosecuted Patent Application DE 195 36 248 A1, a linear configuration of discharging points is used for the purpose of passive discharging of a statically charged recording medium in a printing device. The discharging points are disposed at a distance from the recording medium being conveyed past.
According to German Published, Non-Prosecuted Patent Application DE 197 30 042 A1, an actual position of a sheet is detected by a distance sensor measuring without contact and is compared with a reference position, in an apparatus for regulating a blown air rate in a sheet-fed printing machine in a region of sheet guidance. Reference-actual deviations of the position are compensated for by driving actuating elements for the blown air rate. The distance sensor proposed is an optical triangulation sensor or an ultrasonic distance sensor. The influence of static electricity on the position of the sheets is not taken into account directly.
It is accordingly an object of the invention to provide a method for conveying a sheet and an apparatus for carrying out the method, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and apparatuses of this general type and which permit a sheet to be guided with small deviations from a desired path.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for conveying a sheet. The method comprises pneumatically guiding an electrically charged sheet along a desired path, continuously detecting a charge distribution on the sheet, and reducing a deviation in a position of the sheet from a desired path by actuating at least one actuating element influencing the position in dependence on a charge distribution.
With the objects of the invention in view, there is also provided an apparatus for carrying out the method. The apparatus comprises a control device for controlling the position of the sheet, and a sensor connected to the control device for detecting the electric field present on the sheet.
Therefore, according to the invention, a charge distribution on a sheet is detected continuously by a sensor. In order to reduce the positional deviation of the sheet from a desired path, at least one actuating element influencing the position is actuated on the basis of the charge distribution.
In accordance with another feature of the invention, the actuating element is a configuration forming ions, such as a rod forming corona ions. Furthermore, a blown air and/or vacuum device can be used as the actuating element.
In accordance with a further feature of the invention, the sheet is held in grippers on a revolving drum, a sheet guide plate and a blown air device are disposed along a circumferential contour of the drum, and a sensor for detecting an electric field present on the sheet is integrated into the sheet guide plate. The floating height of the sheet above the guide plate can be controlled or regulated with an additional distance sensor.
In accordance with a concomitant feature of the invention, the sensor used to detect the electric charge present on the sheet is an electric field meter or a sensor for a variable proportional to the electric charge, in particular paper moisture.
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 for conveying a sheet and an apparatus for carrying out the method, 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.
Referring now to the figures of the drawings in detail and first, particularly, to
If designations which have already been used are used in the following description, they are elements or symbols with an equivalent function or equivalent meaning.
In the apparatus according to
If the sheet 1 has a residual charge after the discharging rod 10, then the sheet 1 could come into contact with the metallic surface of the sheet guide plate 6 as a result of electrostatic forces, and a printed image located thereon could be damaged. The residual charge can be measured with the electric field meter 7. The output signals from the electric field meter 7 are supplied to the control device 8. An opposing force which is required in order to bring the sheet 1 onto the desired path is determined in the control device 8 from the electric field meter signals with the aid of characteristic curves which contain a relationship between field strength and grammage of the sheet 1. The opposing force is applied by driving the blown air source 12 in such a way that the carrying air cushion keeps the sheet 1 on the desired path.
This application claims the priority, under 35 U.S.C. ยง119, of German Patent Application DE 10 2005 044 995.6, filed Sep. 21, 2005; the prior application is herewith incorporated by reference in its entirety.
Number | Date | Country | Kind |
---|---|---|---|
10 2005 044 995.6 | Sep 2005 | DE | national |