Abstract:
According to one exemplary embodiment of the present invention, a method for sensing the position of an edge of a stock being feed to a printing press is provided. The method includes the steps of providing a light source, utilizing the light source to illuminate with planar radiation a preselected area of the stock, and a preselected area adjacent to the stock, and further providing a retro-reflecting surface on at least a portion of the preselected area adjacent to the stock illuminated by the light source. According to a feature of the present invention, a measuring device is provided and utilized to measure radiation reflected by the retro-reflecting surface.

Description:
[0001]     This application claims priority to German Patent Application 103 25 377.7, filed Jun. 5, 2003, which is hereby incorporated by reference herein.  
       BACKGROUND  
       [0002]     The present invention is directed a device for sensing the position of an edge of a product, as well as to a method for sensing the position of an edge of a product.  
         [0003]     During the process of printing sheets, in particular in a sheet-fed offset press, the sheets are supplied to the press from a sheet stack. When a single sheet is fed to the printing press, known methods heretofore provide for the sheet to be laterally aligned at the feeder along a guide edge. However, it is also possible for the sheet to be laterally aligned by actuator-driven displacement of the front sheet edge on the cylinder, thus during conveyance of the sheet. Such actuator-driven displacement is known, for example, from the German Application DE 196 18 030 and related U.S. Pat. No. 6,264,196, which is hereby incorporated by reference herein. In response to the actuator-driven displacement, the sheet is guided to a defined setpoint position, the actual position of the sheet being detected by sensors.  
         [0004]     To ensure exact alignment of the sheet, the actual position of the sheet edge must be precisely determined. A device for sensing and controlling the edge position of a continuous web is already known from the German Application DE 36 37 874. When working with this device, a web is irradiated by an illuminating device that extends over a planar area. The light beams striking the web are reflected from there in accordance with the laws of reflection and fed to an electro-optical image sensor. The electro-optical image sensor scans a strip on the web by sequential lines, the strip also encompassing a partial area situated outside of the web. In this way, the width of the area situated outside of the web can be determined and, from this, in turn, the position of the web. However, this method can only be applied when the material web used is a material web that is sufficiently reflective in accordance with the laws of reflection. This is particularly not the case when working with transparent films.  
         [0005]     From the German Application DE 101 36 871, a device is known for sensing the position of an edge of a sheet that is fed to a printing press. In this case, an opto-electronic measuring device is used, which is oriented orthogonally to the conveyance direction of the sheet.  
         [0006]     The measuring device is mounted above the feedboard and has reflecting arrays which are able to detect a reflected beam. To enable problematic sheets to be detected, in particular transparent or high-gloss materials, the surface of the feedboard is additionally provided with contrast-enhancing means. To this end, the feedboard is specially finished in one partial area, in particular highly polished, chromium-plated, or provided with a reflective layer. However, the drawback when working with this device is that it is no longer possible to distinguish the materials themselves from the contrast-enhancing layer when the sheets to be measured have surface properties which correspond or nearly match those of a highly polished or chromed surface.  
       SUMMARY OF THE INVENTION  
       [0007]     An object of the present invention is to provide a device and a method for sensing the position of an edge of a stock material, such as, for example, printing substrate, which are further optimized with regard to the measurability of various types of stock.  
         [0008]     In one preferred embodiment of the present invention, a device for sensing a position of an edge of a stock being feed to a printing press is provided. The device comprises a light source arranged to illuminate a preselected area of the stock, and a preselected area adjacent to the stock, and a measuring device for recording reflected radiation caused by reflection of radiation of the illumination of the light source. In accordance with a feature of the present invention, at least a portion of the preselected area adjacent to the stock that is being illuminated by the light source, comprises a retro-reflecting surface. The light source includes a planar illumination source.  
         [0009]     In another preferred embodiment of the present invention, a method for sensing the position of an edge of a stock being feed to a printing press is provided. The method includes the steps of providing a light source, utilizing the light source to illuminate with planar radiation a preselected area of the stock, and a preselected area adjacent to the stock, and further providing a retro-reflecting surface on at least a portion of the preselected area adjacent to the stock illuminated by the light source. According to a feature of the present invention, a measuring device is provided and utilized to measure radiation reflected by the retro-reflecting surface. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a schematic representation of a printing press arrangement having a feeder for feeding sheets of stock to the printing press.  
         [0011]      FIG. 2  is a schematic representation of a plan view of a portion of the feeder of  FIG. 1 .  
         [0012]      FIG. 3  is a schematic representation of a device for measuring the position of an edge of a stock being feed to a printing press, and having a CCD array according to a feature of the present invention.  
         [0013]      FIG. 4  is a schematic representation of a device for measuring the position of an edge of a stock being feed to a printing press, and having a CMOS matrix according to a feature of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     Referring now to the drawings, and initially to  FIG. 1 , there is illustrated a schematic representation of a printing press arrangement having a feeder for feeding sheets of stock to the printing press.  FIG. 1  depicts a print unit  10  having a drive unit  12  assigned thereto which is controlled or regulated by a control electronics  14  associated with the print unit. With the aid of a feeder  16 , which may include a suction band  18 , for example, stock such as paper sheets  20  are fed to the print unit  10  in a conveyance direction T. The paper sheets  20  are supplied from a paper stack with the aid of a lifting suction device  28  and a forwarding suction device  26 , in a paced feeding sequence to the feeder  16 . In the feeder  16 , a feed board  22  (see  FIG. 2 ) is provided, on which a retro-reflecting surface  30  may be applied in accordance with the present invention.  
         [0015]     Thus, the device according to the present invention is distinguished in that a retro-reflecting surface area is used to sense the position of an edge of a stock. This retro-reflecting area is provided at a location where the stock  20  is fed to the printing press. By illuminating both the stock, as well as the adjacent retro-reflecting surface area, the edge of the stock may be ascertained even in cases where the stock itself reflects specularly. This is because the retro-reflecting surface area reflects the incident light back in the direction of the incident radiation. If a sensor is provided in this direction for detecting the retro reflected radiation, then the radiation that is reflected outside of the stock into the retro-reflecting sensor system, may be uniquely detected. The stock itself, on the other hand, does not reflect any radiation into the sensor, since it either scatters the radiation or reflects the incident radiation specularly, in a different solid angle, in accordance with the laws of optics.  
         [0016]     As shown schematically in the plan view of  FIG. 2 , the sheet  20 , which is to be fed to the print unit  10  in direction T, is present on feed board  22 . At a suitable location on the feed board  22 , a retro-reflecting surface  30  is provided in such a way that a sheet  20  conveyed in the direction T only partially covers the retro-reflecting surface  30 . This partial covering may be ensured, for example, by providing the entire feed board  22  with a retro-reflecting surface. Of course, as shown in  FIG. 2 , it is also possible to provide a partial region of the feed board  22  with the retro-reflecting surface  30 .  
         [0017]     According to a feature of the present invention, CMOS matrix elements or CCD matrices, arranged in a two-dimensional array, may be used as a stock image sensor. The imaging quality may be further improved, in particular the imaging contrast enhanced, when working with films, in that light that is linearly polarized in a suitable direction is used to illuminate the stock or sheet and the retro-reflecting area adjacent to the sheet. By using CMOS matrix elements as image sensors and with the aid of fast readout algorithms, it is possible to increase the measuring frequency. For example, the article entitled “CMOS Image Sensor with Cumulative Cross Section Readout” by Bums and Homsey (www.cs.yorku.ca/˜visor/pdf/CCDAIS03_CCS.pdf) and “A 640×512 CMOS Image Sensor with Ultrawide Dynamic Range Floating-Point Pixel-Level ADC” by Yang, Gamal, Boyd and Tian (IEEE Journal of Solid-State Circuits, Vol. 34, No. 12, December 1999) describe CMOS readouts, and are hereby incorporated by reference herein. This enables a plurality of measured values to be recorded per sheet, from which an average value may then be calculated, thereby enabling error measurements to be minimized.  
         [0018]     Referring now to  FIG. 3 , there is illustrated a device for sensing the position of an edge of a sheet which is to be fed to a printing press, according to a preferred embodiment of the present invention. Via a light source  32 , which is disposed downstream from an optics arrangement  34 , a parallel light beam  31  is fed to a semi-reflective mirror  38 . Upstream from where the light beam  31  strikes the semi-reflective mirror  38 , a polarization filter  36  may also be provided for linearly polarizing the light. The illuminating device is preferably mounted in such a way that light beam  31  is oriented in parallel to the xz plane and forms an angle α of greater than 0° with the z-axis. In addition, light source  32  is positioned in such a way that sheet  20  is partially situated in the light path ray trajectory of the illumination. The sheet  20  is present on the a feed board  22 . The retro-reflecting surface  30  is provided, in particular as a retro-reflecting film or retro-reflecting coating, at least in one partial region on the feed board  22 . This retro-reflecting surface has the property of reflecting back an incident light beam  33  precisely in the direction of incidence. Consequently, light  35  reflected by the retro-reflecting surface  30  is fed again to semi-reflective mirror  38 . The light beams  35  are able to partially penetrate mirror  38 , depending on its transmittance. These component beams of light, at this point characterized as measuring beams  37 , are fed via a lens  42  and a cylindrical lens  44  to a CCD array  46 . By using the cylindrical lens  44 , it is ensured that the light beams are only imaged in one direction. As a result, the measuring beams  37  striking the cylindrical lens  44  are refracted in such a way that they intersect in one line. Since the cylindrical lens  44  is positioned in such a way that cylinder axis  45  runs in parallel to the y-axis and the distance between the cylindrical lens and CCD array  46  is equal to the focal length of the cylindrical lens, the image of the rectangular illumination cross-section is formed in one line in the x-direction, i.e., on CCD array  46 . It is, thus, possible to obtain an optical averaging over one defined length of the sheet edge. Using this arrangement in this way, the lateral position of a sheet  20  resting against front guides  40  may be precisely determined, the averaging being carried out over one defined area of the sheet edge, which may then be established as an image of sheet edge, designated by reference numeral  48 .  
         [0019]     Another exemplary embodiment of the present invention is shown in  FIG. 4 . In contrast to the embodiment shown in  FIG. 3 , in the embodiment of  FIG. 4 , a CMOS matrix  47  is used as an image sensor. Using CMOS matrix  47  eliminates the need for a cylindrical lens. Light  35  reflected by the retro-reflecting surface  30  penetrates, in turn, the semi-reflective mirror  38 . These measuring beams  37  are imaged via lens  42  onto a CMOS matrix  47 . In this context, CMOS matrix  47  is composed of very small photosensitive elements, which are arrayed in the manner of elements of a matrix. However, in contrast to a CCD matrix, each individual photosensitive element may be optionally read out. Thus, by using this arrangement, an image of the sheet, i.e., of lateral sheet edge  48 , is formed on CMOS matrix  47 . By evaluating the pixels of the matrix, an averaged lateral position, i.e., a position in the y-direction of the sheet edge is calculated.  
         [0020]     Since it is possible to read out the individual photosensitive elements of the CMOS matrix  47 , the number of pixels to be read out may be decidedly reduced by using fast readout algorithms, thereby enabling the measuring frequency to be clearly increased in comparison to a CCD matrix have the same number of pixels. By using parallel light, which is oriented in parallel to the x-z plane, disadvantageous influences caused by a sheet edge that is slightly curved in the z-direction, may be kept to a minimum; the quality, and the y-position of the shadow of the sheet edge cast on the retro reflecting surface  30 , being only slightly affected. Moreover, optical power losses occurring within the system are minimized by using parallel light.  
         [0021]     In addition to the embodiments illustrated in  FIGS. 3 and 4 , it is also possible, instead of a CCD array or a CMOS matrix, to use a CCD matrix or a photo diode to detect the measuring beams  37 . When a photo diode is used, the light, which is reflected by the retro reflecting surface  30  and has penetrated the semi reflective mirror  38 , is focused via a lens at a photo diode, and the intensity of the diode&#39;s photoelectric current is measured. To determine the y-position of a lateral sheet edge, the entire sensor is moved via a guide in the y-direction, and the y-position of the light beam is continuously recorded by a position-measuring system. When the lateral sheet edge is crossed in the y-direction, the intensity of the diode&#39;s photoelectric current changes almost abruptly, so that the sheet edge is able to be determined, in turn.  
         [0022]     In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.  
       REFERENCE NUMERAL LIST  
       [heading-0023]      10  print unit  
         [heading-0024]      12  drive unit  
         [heading-0025]      14  control  
         [heading-0026]      16  feeder  
         [heading-0027]      18  suction band  
         [heading-0028]      20  sheet  
         [heading-0029]      22  feed board  
         [heading-0030]      24  stack  
         [heading-0031]      26  forwarding suction device  
         [heading-0032]      28  lifting suction device  
         [heading-0033]      30  retro reflecting surface  
         [heading-0034]      31  light beam  
         [heading-0035]      32  light source  
         [heading-0036]      33  incident light beam  
         [heading-0037]      34  optics  
         [heading-0038]      35  retro reflecting light beam  
         [heading-0039]      36  polarization filter  
         [heading-0040]      37  measuring beam  
         [heading-0041]      38  semi reflective mirror  
         [heading-0042]      40  front guide  
         [heading-0043]      42  lens  
         [heading-0044]      44  cylindrical lens  
         [heading-0045]      45  cylinder axis  
         [heading-0046]      46  CCD array  
         [heading-0047]      47  CMOS matrix  
         [heading-0048]      48  image of the sheet edge