Method and device for the detection of a substrate edge in a printing machine
View Patent ↗The present invention relates to a method and a device for the detection of a substrate edge in a printing machine comprising a substrate transport unit that defines a substrate transport path ( 8 ). In this method, at least one light value of a first section of a sensor line ( 10 ) and a dark value of a second section of the sensor line are determined, and a threshold value is calculated based thereon. When the threshold value on one pixel is exceeded and the threshold value on another pixel is not reached, it is possible to calculate a position of the substrate edge. The device comprises a light source arrangement ( 5 ) for generating diffuse light, and comprises a sensor line for the detection of light from the light source arrangement. Furthermore, a gradient lens arrangement ( 15 ) is provided, said gradient lens arrangement being arranged between the light source and the sensor line in such a manner that, on the one hand, a focus is located on a central position of the substrate transport path between the light source and the gradient lens arrangement, and, on the other hand, on the sensor line.
1. A method for detecting a substrate edge in a printing machine comprising a substrate transport unit that defines a substrate transport path, said method comprising:
determining a light value by collecting measured data of a first section of a sensor line, said first section not being covered by the substrate and said sensor line having a plurality of discrete pixels;
determining a dark value by collecting measured data of a second section of the sensor line, said sensor line being covered by the substrate;
calculating a threshold value based on the light and dark values of the sensor line;
collecting measured data of the sensor line, wherein, when the threshold value on a pixel is exceeded, determining that said pixel is not covered by the substrate, and when the threshold value on a pixel is not reached, determining that said pixel is covered by the substrate; and
calculating a position of the substrate edge based on the collected measured data, wherein based on the measured data of the first and the second sections, correction data are determined for the adaptation of all the pixels of the sensor line, and wherein a correction of the dark values of all the pixels of the sensor line by means of the correction data includes a compensation of an offset of an output signal of the sensor line.
2. The method of claim 1 , wherein the threshold value is calculated in such a manner that said threshold value corresponds to the mean value of the light and dark values.
3. The method of claim 1 , wherein the step of collecting the measured data in the first section of the sensor line comprises an outer region, relative to a transport direction of the substrate, of the sensor line, and that the step of collecting the measured data in the second section of the sensor line comprises an inner region of the sensor line.
4. The method of claim 3 , wherein a maximum light value is determined based on the measured data of the first section.
5. The method of claim 1 , wherein a correction of the light values of all the pixels of the sensor line by means of the correction data includes an adjustment of all the pixels to the maximum light value.
6. The method of claim 1 , wherein the calculating of the position of the substrate edge, takes into consideration distances between the pixels.
7. The method of claim 6 , wherein imaging of the substrate edge is upright and true to side.
8. The method of claim 1 , wherein an image of the substrate edge is projected via a gradient lens arrangement on a scale of 1:1 onto the sensor line.
9. The method of claim 1 , wherein said steps are performed during a transport of the substrate past the sensor line.
10. A device for the detection of a substrate edge in a printing machine comprising:
means for determining a light value by collecting measured data of a first section of a sensor line that is not covered by the substrate;
means for determining a dark value of a second section of the sensor line that is covered by the substrate;
means for calculating a threshold value based on the light and dark values of the sensor line;
means for collecting measured data of the sensor line, this indicating, when the threshold value on a pixel is exceeded, that the pixel is not covered by the substrate, and indicating, when the threshold value on a pixel is not reached, that the pixel is covered by the substrate; and
means for calculating the position of the substrate edge based on the collected measured data and means for determining light and dark value correction data from the collected measured data for adapting all the pixels of the sensor line,
wherein a correction of the dark values of all pixels of the sensor line by the correction data includes a compensation of an offset of an output signal of the sensor line.
11. The device of claim 10 , comprising a means for taking into consideration distances of the pixels and distances of the elements within the sensor line for calculating the position of the substrate edge.