DD226985A1 - METHOD FOR DETERMINING THE POSITION OF A LINE MARK MARK - Google Patents

Abstract

The invention relates to a method for objectively determining the position of an optical bar code mark in three degrees of freedom by imaging the mark on an x, y-addressable image sensor. Compared to known solutions, a substantial saving of processing time and required storage capacity is achieved in the image processing units. This is possible by selecting from the image field of the sensor two lines at a distance u and two columns at a distance v using a picture field selection circuit. On these lines and columns, the crosshairs mark is displayed so that four intersections arise from which one can determine the position of the intersection of the lines of the mark with the help of the line equation and the tilt of the mark from the rise of one of the lines. An application of the invention would be z. B. the adjustment of optical and mechanical components by means of an optical mark.

Description

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Title of the invention

Method for determining the position of a bar code mark

Field of application of the invention

The invention relates to a method for the objective determination of the position of an optical bar code mark in three degrees of freedom by imaging the mark on an x-, y-addressable image sensor. In this context, the term "crosshair mark" denotes any optical mark which consists of two lines G 1, G 2 crossing each other at an arbitrary angle.

As the x-, y-addressable image sensor, a video image scanning camera such as a vidicon camera or a solid-state camera with matrix arrangement of the light sensor elements may be used in conjunction with an image signal preprocessing unit for conditioning the image signals, digitizing, formatting and selecting relevant image data, and an image signal processing unit used to calculate the position of the optical mark. An application would be, for example, the adjustment of optical and mechanical components by means of an optical mark.

Characteristic of known technical solutions

Various methods of optically measuring the location of e.g. known optical brands.

For determining the position of an object arranged in a plane, it is possible to use a device which is characterized by imaging optics for the real one

Illustration of the object and at least two non-parallel rows of photodiodes (DE-OS 2543545). The described device enables rapid and automatic measurement. The disadvantage is the use of several spatially separated photodiode rows and the associated difficulties of the positional stability of the photodiode rows to each other

 In another known solution (DE-AS 20591Q6) structures are measured by means of a device based on the propagation time measurement of the video signal. For this purpose, the structures are imaged onto an image pickup tube and optically inserted into the beam path measuring marks. The disadvantage here is the high optical and mechanical effort for the Einbrenner in the beam path and the known disadvantages of an image pickup tube, such as geometry error, low Dynamikbreich, Nachzieheffekte, break - in time, mechanical sensitivity, life, etc

 Furthermore, solutions are known which are characterized in that two-dimensional imagers (e.g., vidicon tubes) scan the image, digitize and store the complete image information in an image memory. (e.g., DE-OS 3111027). An evaluation unit, such as a digital computer then determines the required sizes from the stored image data. The disadvantage here is the memory overhead for a Komplettbildabspeicherung and the required processing time.

Aim of the invention)

The aim of the invention is to carry out the determination of the position of an optical crosshairs mark imaged on a sensor in three degrees of freedom objectively, quickly, with high accuracy and a large capture range.

Essence of the invention

The invention has for its object to make the workflow in a used for objectively determining the location of a bar code position detection system, which consists essentially of image pickup device with x-, y-addressable image sensor, Bildvorverarbeitungseinricntung and image processing device so that a

significant savings in processing time and required storage capacity is achieved. This is only possible if only the image data relevant for the recognition of the situation is included to determine the location of the mark. For this purpose, two lines at distance u and two gaps at distance ν are selected using an image field selection circuit from the image field of the sensor, to which the crosshair mark is imaged such that four intersections of the mark with the selected lines and columns are produced. The straight line equations of the parts Gl, G2 of the crosshairs are calculated from these intersections. By determining the intersection of the two straight line equations, the position of the intersection of the crosshairs in the x and y directions can be calculated. The tilting of the mark in the image field plane about the z-axis results from the rise of one of the straight lines. The advantage of the method is to be seen in the minimization of storage and processing time. The gross accuracy of the orientation is achieved when the fringes and margins of the image sensor are selected. By suitably dimensioning the crosshair mark, it is possible to expand the capture area beyond the active area of the image sensor. The largest capture range is achieved when the length of the mark in the x direction is one pixel smaller than twice the width of the sensor and the length of the mark in the y direction is one pixel smaller than twice the height of the sensor, where the dimensions of the mark should generally be between the single and double width or single and double height of the image sensor. When using imaging optics, the magnification of the dimensioning of the iVlarke must be taken into account.

Ausfuhrunqsbeispiel

The method according to the invention is explained below using the example of a position detection system with a CCD matrix sensor according to FIG. 1 and an optical mark in form of a reticule for adjusting optical components according to FIG. 2

 The position detection system consists of an image pickup device 0, which 'the image sensor 1 including the drive

electronics, an image processing control circuit 2, an image processing circuit 3, a monitor 4, a digitizing circuit 5, a fora dating circuit 6, a direct memory access circuit 7, an image field selection circuit S, a processing device 9, a memory circuit 10 and a control module 11. The situation the optical mark imaged on the image sensor is determined in the coordinate system of FIG. The image sensor consists of ra times η picture elements BE, which are arranged in a matrix on it. Where m is the width of the image sensor in pixels and η is the height of the image sensor in pixels. A picture element has the dimensions BE _x times BEy. To increase the capture range of the position detection system, it is convenient, the dimensions of the optical mark in the image plane

a = (2ra-l) BE _x b = (Zn)

to choose. The capture area can thereby increase to a multiple of the sensor area, since the adjacent to the four sides of the image sensor surfaces allow a rough orientation of the optical mark. However, this orientation is initially only in the determination of one of the four adjacent surfaces in which the intersection of the optical mark is located. It is thus a first 3ustierbewegung in the direction of the sensor surface and possibly v / eitere Oustierbewegungen necessary until the optical mark is so imaged on the sensor surface, that the 1st and ro-th column, as well as the 1st and nth line of Image sensor are cut by the crosshairs brand. With the resulting four intersection coordinates χ, /, κ ^ ΎνΎζ, the straight line equations Q _-1 and g _{z of} the two parts Gl and G2 of the bar code mark can be determined. From the linear equations g and g can be determined by intersection determination, the position of the intersection of the optical mark in the x and y direction and the tilt of the optical rake to the. Determine z-axis in a known manner. The coordinates X ₀ , y _{0 of} the intersection P of the two straight lines Gl, G _{2 are} determined to be:

Cy ₁ - Ό

(η - DBE "*" ^w ^ ^ ö

(η - 1) BE

α-1) ΒΞ _χ

y ₂ - 1λ

⁰ (m1) BE °

The tilt angle * f is determined to be

f = arctane

Claims (4)

* ra V ^ J ^ J \ J Al J L 1) A method for determining the position of a Strickreuzrnarke by imaging the mark on an x-, y-addressable image sensor, characterized in that selected from the image field of the sensor two lines at a distance u and two columns at a distance v, the bar cross mark so on the sensor is shown that four intersection points of the mark with the selected rows and columns arise, from which the straight line equations of the cross can be calculated and that by intersection of the two straight equations the position of the mark in the x and y direction and from the rise of a the straight line, the rotation of the mark in the image field plane of the sensor is determined about the z-axis. 2) Method according to item 1, characterized in that the edge lines and edge columns of the image sensor are selected for determining the position of the bar code mark. 3) Method according to item 1, characterized in that the stroke lengths of the line cross mark or its image are selected so that they are in the range of single and double the width and the single and double the height of the image sensor. 4) Method according to item 3, characterized in that the stroke lengths of the crosshairs mark in the x direction a pixel less than twice the width of the sensor and the stroke length in the y direction a Bildeleraent less than twice the height of the sensor selected v / ground. For this 1 page drawing.