Abstract:
To determine the thickness of a liquid layer, particularly that of an oil film, on a roller in a simple manner that saves time and that is cost-effective. To achieve this task, a procedure and a device are provided in which the thickness of the liquid layer is measured by a measuring device in the printing press. In addition, a delivery device for liquid is controlled on the basis of the measured thickness of the liquid layer.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a procedure and a device for measuring the thickness of a liquid layer.  
           [0002]    A toner material is applied to a paper sheet by an electrophoto-graphic printing press and subsequently set in the paper sheet. For this purpose, highly heated rollers are used, which grip the paper sheet from above and below to effectively set the toner material with high pressure and heat by embossing. The problem with this customary procedure is that between the heated rollers and the paper sheet stock, adhesive forces are produced, particularly with respect to the toner material, which hinder the separation of the heated rollers from the stock. As a remedy, an oil layer is applied to the heated rollers by metering and donor rollers, which ensures a loosening of the heated rollers from the stock following the setting of the toner material.  
           [0003]    In order to avoid any adverse effects, it must be ensured that the oil layer thickness always lies within a specified range and that such thickness is neither too large nor too little. If the values of the oil layer thickness are too small, the adverse effects mentioned above occur. On the other hand, if the values of the oil layer thickness are too large, the disadvantages lie in the resulting prints being oily or too shiny, and particularly with two-sided printing, in the soiling of the printing press due to the used oil. It is thus desirable that the oil layer thickness on the heated rollers for setting the paper sheets or on setting rollers or on metering or donor rollers, which apply the oil to the heated roller, be set at a specified value.  
           [0004]    Up until now oil layer thickness has been determined by applying the heated setting rollers, with an oil layer, on the paper sheet in the printing press for test purposes, and measuring the oil layer thickness on this paper sheet in the laboratory by a spectroscopic procedure. Apart from this costly procedure, an oiling system is set up by the operator, who uses a delivery device and metering or donor rollers to apply an oil layer based on the oil layer thickness estimated by the paper sheet and the metering or donor rollers. It is expected that an oil layer thickness in the order of several hundred nanometers delivered the best results.  
         SUMMARY OF THE INVENTION  
         [0005]    The task of the invention is to determine the thickness of a liquid layer, in particular that of an oil layer on a roller, in a simple manner that would save time and be cost-effective. To achieve this task, a procedure and a device are provided in which the thickness of a liquid layer in the printing press is measured by a measuring device. In a particularly advantageous manner, a control device to control a delivery device is provided for delivering liquid based on the calculated thickness. The rollers, as carriers of the thickness of the liquid layer to be measured, may be measured prior to the procedure according to the invention and the measuring results stored in the computer. In this manner, the unevenness of the roller surfaces, which can lead to measuring errors during the procedure according to the invention, is determined.  
           [0006]    The thickness of the liquid layer is calculated by the measuring device as the value resulting from a variable value that is dependent on the roller surface and from the thickness of the liquid layer calculated on the basis of an even roller surface. In this connection, the measuring device may contain a rotary encoder, which calculates the rotational angle of the rollers as a function of the distances measured. Advantageously, several measuring devices may be used to increase the precision and to simultaneously measure various roller areas. These are connected to the computer and the control unit. Specific measuring points on the roller surfaces are provided, which are sufficiently smooth enough for the measurements and which have a high reflectivity, thus making measurements easier.  
           [0007]    In a further development, the measuring device contains an interferometer, with which, for example, the thickness of the liquid layer is measured either by a change in the intensity brought about by the interference of rays of the interferometer, or by a phase difference in the rays, which depends upon the thickness of the liquid layer. When the surface of the roller is rough, the use of radiation in the infrared spectrum for measuring the thickness of the liquid layer produces particularly good results. In particular, an infrared sensor may be used.  
           [0008]    The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is a schematic drawing of the side view of a roller, an oiling system, a measuring device and a computer as well as a control unit in a circuit block;  
         [0011]    [0011]FIG. 2 is an alternate embodiment a variant of the invention with a top view of the roller similar to FIG. 1 with two measuring devices, whereby one of the measuring devices is arranged at the measuring point with a liquid layer and the other measuring device is arranged at the measuring point without a liquid layer;  
         [0012]    [0012]FIG. 3 is a further development of the invention similar to FIG. 2 with two measuring devices, whereby one of the measuring devices determines the liquid layer thickness according to the delivery device and the second measuring device determines the oil layer thickness according to a stock;  
         [0013]    [0013]FIG. 4 is a top view of a roller with a measuring device and the assigned measuring points in the form of strips on the roller surface; and  
         [0014]    [0014]FIG. 5 is a view according to FIG. 4, in which the measuring points take the form of rectangles.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    [0015]FIG. 1 illustrates a schematic drawing of a side view of a roller with an oil delivery device  55  and an oil layer thickness-measuring device  20 . Computer  41  and control unit  42  are shown in a circuit block and are subsequently indicated as a combined computer and control unit  40 . In the customary manner, an oil film is provided as liquid layer  12  by the delivery device  55  via a donor roller  60  and a metering roller  50  that are contained in the delivery device  55 . The oil to be applied to roller  10  for setting toner material on a stock is located in a container of the delivery device  55  and is absorbed by the surface of the rubber-sheathed donor roller  60 , which moves in the direction of the arrow. By contact of the metering roller  50  with the donor roller  60 , the oil is rolled onto the latter. Metering roller  50 , which rotates in an oil bath of delivery device  55  on a bonded fabric, moves in the direction of the arrow opposite to that of the donor roller  60  and transfers an oil film on roller  10  by contact. For clarity purposes, the oil film or the liquid layer  12  has been represented as being considerably thicker in relationship to roller  10 . Another possibility of applying the oil film to roller  10  includes passing an oil-soaked cloth over roller  10 .  
         [0016]    A measuring device  20  has been arranged next to roller  10 . The measuring device  20  contains a capacitive sensor that can determine the known distances on the basis of capacitive changes in the environment of its measuring transducer. Inductive or electro-optical sensors can likewise be used. Measuring device  20  is connected with a combined computer-control unit  40 . In order to measure the thickness c of liquid layer  12 , in this case the oil film, the electrical capacitance between a measuring transducer of the sensor and the roller surface without a liquid layer  12 , represented by the line segment a, is measured with a capacitive sensor of the measuring device  20 . The electrical capacitance between the roller surface and the measuring transducer is now clearly determined and is stored in the computer  41 .  
         [0017]    The next step, as described above, is to apply the liquid layer  12  of the oil film to the roller  10 . The relative permittivity ε of liquid layer  12  is different from that of the roller surface, so that the measurement of the capacitive sensor now detects another capacitance between the measuring transducer of the sensor of measuring device  20  and the surface of liquid layer  12 , represented by the line segment b. For example, capactitive sensors as path measuring systems achieve a dissolution of 2 nm. To strengthen the capacitance change with and without liquid and subsequently the sensor signal of the measuring device  20 , an additive can be added to the oil to increase the relative permittivity ε. Based on both the above-mentioned capacitances, the value c as the thickness of the liquid layer  12  is determined in the computer-control unit  40  by comparison with the values stored therein.  
         [0018]    In this manner, any capacitance change that is equal to the thickness of liquid layer  12  on roller  10  can be clearly assigned a length value. As can be easily understood, the length c describes the thickness of the liquid layer  12 . If the thickness of liquid layer  12  does not lie in a particular desired range, the computer-control unit  40  transmits control signals to the delivery device  55 . The control signals cause the amount of the liquid layer dispensed to be increased or decreased in the appropriate manner.  
         [0019]    [0019]FIG. 2 indicates a schematic drawing of an alternate embodiment of the invention. Two measuring devices  20 ,  20 ′ are arranged in the vicinity of roller  10 . These contain a reflectometer in this example. Reference numeral  15  shows a shaft of roller  10 . The procedure performed according to FIG. 2 is similar to the procedure according to FIG. 1. In this case, contrary to the procedures in FIG. 1, the measurements of the thickness of the liquid layer  12  are not performed successively, but are instead performed simultaneously with the measuring devices  20 ,  20 ′. To this end, an area  12  of roller  10  is not supplied with liquid, in this case an oil film, while the other area  14  is supplied with liquid in the customary manner. As is evident in FIG. 2, the two areas are separated from each other by a dotted line for clarity purposes. The advantage of this modified procedure is that no measurement is required prior to the operation of roller  10  with the printing press (not shown). The measuring procedure can be fully carried out during the operation of the printing press. The computer-control unit  40  controls the delivery device  55  according to the calculated values of the oil layer thickness c. As a result, the delivery device  55  supplies a suitable amount of liquid or oil to roller  10 .  
         [0020]    [0020]FIG. 3 shows another embodiment of the invention similar to that in FIGS. 1 and 2. Two measuring devices  20 ,  20 ′ are arranged close to roller  10  in such a way, that the measuring device  20 ′ directly determines the thickness of the liquid layer  12  following the application of the oil film to roller  10  by delivery device  55  with the metering and donor rollers  50  and  60 , while the second measuring device  20  determines the thickness of the liquid layer  12  after roller  10  has applied and set the toner material (not shown) on stock  5 . Normally another roller is arranged below stock  5  to provide a counteracting force to the compressive force of roller  10 , but this was not done in this case. This process is based on the idea that by the measurement of the two known thicknesses and with the knowledge of the circumference of roller  10  before and after the stock  5 , it can be determined what the thickness of the liquid layer  13  on the stock  5  is after the setting and application on roller  10 . The thickness of the liquid layer  12  or the oil film following the passing over of roller  10  over the stock  5 , which is determined with the measuring device  20  and the computer-control unit  40 , is equal to the thickness of the liquid layer  12  or the oil film prior to the passing of roller  10  over the stock  5 , i.e., directly following the application of the liquid layer  12 , together with the thickness of the oil layer  13 , which is transferred during the setting process of roller  10  for setting the stock  5 .  
         [0021]    The thicknesses of the oil layer  12  calculated are transferred via the lines of the computer-control unit  40  as illustrated in FIG. 3, and by the comparison of the stored values to the values calculated, as described above, the desired quantity and the thickness of the liquid layer  13  on the stock  5  is determined. If this quantity is within a specified tolerance range, the delivery device  55  is operated unchanged. If the value is outside the tolerance range, however, the computer-control unit  40  controls the delivery device  55  in such a way that a decreased or increased amount of liquid or oil is dispensed by the delivery device  55 .  
         [0022]    Furthermore, roller  10  in FIG. 3 is provided with a rotary encoder  30 , which can be used to precisely determine the rotational angle of roller  10 . The rotary encoder  30  is connected with the computer-control unit  40 . The measurement of the distance between the measuring transducers of the measuring devices  20 ,  20 ′ and the surface of roller  10  is carried out in certain short intervals. With the help of the rotary encoder  30 , the measuring devices  20 ,  20 ′ can allocate the above-mentioned distances of the specified rotational angles, which are allocated to the corresponding positions determined on the surface of roller  10 . This is advantageous, since, in this manner, the unevenness of the roller surface during measurements and calculations can be taken into consideration. Without the allocation of rotational angles at specified positions on the surface of roller  10 , the measurements are independent of the measured positions on the surface, i.e., unevenness in the range of micrometers and nanometers of the configuration of the roller surface are included in the measurements and degrade the measurement results.  
         [0023]    With the use of the rotary encoder  30 , the measurements of unevenness on the surface of roller  10  are not affected, since the distances and the thicknesses of the oil layer  12  are measured by the respective measuring devices  20 ,  20 ′ at each of the same positions on roller  10 . For example, in FIG. 3, this means that the two values measured in the previously determined moment by the measuring devices  20 ,  20 ′ at positions C and D are not compared and no calculation is performed with these two values. Rather, the two values measured at positions C and D are transferred to the computer-control unit  40 , and the position D indicated by the cross drawn, whose value was calculated by measuring device  20 ′, is compared with the value that was calculated at the same position D on roller  10  by the other measuring device  20 , after roller  10  has moved to the rotational angle α in the direction of the arrow. Accordingly, the line segment on the surface of roller  10  between C and D is allocated to the rotational angle α in order to identify the position D in the computer-control unit  40  in a clear manner.  
         [0024]    [0024]FIG. 4 shows a side view of a roller  10  with a shaft  15  and allocated measuring locations  70  in the form of strips on the roller surface. A measuring device  20  is allocated to the measuring locations  70 , whereby the measurements are carried out at the measuring locations  70 . The measuring device  20  is illustrated with a portion of its connection to the computer-control unit  40 . The measuring locations  70  have a smooth surface that reflects the signals of the measuring device  20 . The direction of a signal process of the measuring device  20  is illustrated in an exemplary fashion with a thin dotted line. The use of the measuring locations  70  is particularly advantageous, since the surface of setting rollers often does not have the required prerequisites for sensor measurements concerning smoothness and reflecting capacity. Accordingly, a higher measurement sensitivity is achieved in this manner.  
         [0025]    It was discovered that the use of optical sensors as a component of the measuring device  20  required an especially smooth surface of roller  10  that had reflection capability, since with optical rays hitting rough and poorly reflecting surfaces, their reflections experience path deviations. The measuring locations  70  may be produced by the vaporization of thin metallic layers. It must be ensured that the measuring locations  70  adhere sufficiently to the roller surface and that they are sufficiently malleable, abrasion-resistant and temperature-resistant.  
         [0026]    The measuring locations  70  are as small as possible in order to preserve the surface characteristics of roller  10  with respect to setting regarding oil absorption and sheet removal. The minimal width of the measuring locations  70  is equal to the ray cross-section of the sensor signal of the measuring device  20 . It is understood that the measuring locations  70  in FIG. 4 are shown considerably enlarged in comparison to roller  10 . With the embodiment according to FIG. 4 the oil film thickness is measured with the optical electronic sensors. Particularly with insufficiently smooth surfaces of the roller  10  or the measuring locations  70 , the use of radiation in the infrared spectrum has proved to be useful. The measuring procedure corresponds to that described above.  
         [0027]    With a further development according to FIG. 5, the measuring locations  70  are configured as rectangles. In this case, the measurements of the distances are only carried out with rectangles. This requires rotary control of roller  10 , which ensures that the sensor signals of the measuring devices  20 ,  20 ′,  20 ″, which are shown here with lines to the signal transfer to the computer-control unit  40 , are sent at the desired time. Rotary control is produced by the rotary encoder  30 , which determines the rotational angle of roller  10  with the appropriate sensitivity and transfers it to the computer-control unit  40 .  
         [0028]    When a given rotational angle is present that has been allocated to a position on the roller surface on which a rectangle is located, the computer-control unit  40  transmits a trigger signal to the measuring devices  20 ,  20 ′,  20 ″, which triggers a sensor signal. The measurement is then carried out as described. In a variation, the described procedure can be also be used to determine and to control the oil layer thickness on metering or donor rollers  50  and  60  in a similar manner. In a modification, the procedure can further be used to determine and control the oil layer thickness on the metering and donor rollers  50  and  60 . Further applications of the invention are, for example, the measurement and control of the thickness of a color layer or a moisturizing layer in a printer of a printing press.  
         [0029]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.