Taking undistorted images of moved objects with uniform resolution by line sensor

• US 20090039157A1
• Filed: 08/06/2008
• Published: 02/12/2009
• Est. Priority Date: 08/10/2007
• Status: Active Grant

• Current Assignee: Sick AG (Sick)
• Original Assignee: Sick AG (Sick)
• Inventors: WIEGERS, Michael, REICHENBACH, Jurgen, REICH, Jan, GEHRING, Roland
• Granted Patent: US 8,360,316 B2
• Time in Patent Office: Days
• US Class Current: 235/436
• CPC Class Codes: G06K 7/10792 Special measures in relation to the object to be scanned
• CPC Class Codes: G06V 10/147 Details of sensors, e.g. sensor lenses fingerprint or palmprint sensors G06V40/13; vascular sensors G06V40/145; eye sensors G06V40/19
• CPC Class Codes: G06V 30/144 using a slot moved over the image; using discrete sensing elements at predetermined points; using automatic curve following means

Abstract

An apparatus (10), in particular a code reader, for the taking of undistorted images of a surface of objects (14) moved on a conveying device (12) is set forth, wherein the apparatus (10) has a geometry detection sensor (18) which is made for the detection of the geometry of the objects (14) with reference to spacing data and/or to the remission behavior of the objects (14) as well as a line sensor (20), in particular a line camera, which can scan the objects (14) linewise for the generation of image data of the surface in a linear reading window (22) which forms an angle with the conveying direction. In this connection, a control (24) is provided which is made to generate, on the basis of geometrical data of the geometry detection sensor (18), a respective spacing profile of the surface over the reading window (22) from the perspective of the line sensor (20) and to generate an associated zoom factor and/or a taking frequency for the line sensor (20) from each spacing profile; to set the line sensor (20) to the associated zoom factor and/or to the taking frequency for the respective line of the objects (14) to be scanned; and to compose the image data thus taken linewise in an undistorted manner to form a uniformly resolved total image of the surface.

Claims

1. An apparatus (10), in particular a code reader, for the taking of undistorted images of a surface of objects (14) moved on a conveying device (12),wherein the apparatus (10) has a geometry detection sensor (18) which is made for the detection of the geometry of the objects (14) with reference to spacing data and/or to the remission behavior of the objects (14) as well as a line sensor (20), in particular a line camera, which can scan the objects (14) linewise for the generation of image data of the surface in a linear reading window (22) which forms an angle with the conveying direction,

characterized in that

a control (24) is provided which is made to generate, on the basis of geometrical data of the geometry detection sensor (18), a respective spacing profile of the surface over the reading window (22) from the perspective of the line sensor (20) and to generate an associated zoom factor and/or a taking frequency for the line sensor (20) from each spacing profile;

to set the line sensor (20) to the associated zoom factor and/or to the taking frequency for the respective line of the objects (14) to be scanned; and

to compose the image data thus taken linewise in an undistorted manner to form a uniformly resolved total image of the surface.

2. An apparatus (10) in accordance with claim 1, wherein the control (24) is made to set the zoom factor such that the reading window (22) in each case has an extent which corresponds to the maximum object extent in the line direction over all the scanned lines (26) of an object (14).

3. An apparatus (10) in accordance with claim 1, wherein the control (24) is made to set the taking frequency such that the scanned lines (26) are distributed in a regular manner over the geometrical surface.

4. An apparatus (10) in accordance with claim 1, wherein the control (24) is made to set a focus setting of the line sensor (24)from a measure of the spacing profile, in particular from an extreme or a mean value;

and/or to set a brightness of the line sensor (20) via an exposure time or via an amplification factor to compensate changes which arise due to variation of the zoom factor and/or of the taking frequency.

5. An apparatus (10) in accordance with claim 1, wherein the geometry detection sensor (18) is integrated into the line sensor (20).

6. An apparatus (10) in accordance with claim 1, wherein the geometry detection sensor (18) is disposed in front of the line sensor (20) in the conveying direction;

and wherein the control (24) is made to calculate the spacing profile in advance in dependence on the conveying direction of the objects (14).

7. An apparatus (10) in accordance with claim 6, wherein a speed sensor is provided which can determine the conveying speed;

and wherein the control (24) can convert the zoom factors and/or taking frequencies dependent on the conveying position by means of the conveying speed into time-dependent zoom factors and/or taking frequencies.

8. An apparatus (10) in accordance with claim 7, wherein the speed sensor is implemented as one of the following:

an incremental encoder at the conveying device (12);

and/or a speed evaluation device at the geometry detection sensor (18) or at the line sensor (20) which can evaluate a distortion of expected object contours;

and/or a comparator which recognize an object feature in the geometry data and in the image data again and determines the speed from the time difference of the data taking and the spacing of the geometry detection sensor (18) and the line sensor (20).

9. An apparatus (10) in accordance with claim 6, wherein the control (24) is made to calculate the spacing profiles for each conveying position corresponding to a maximum or preset constant taking frequency of the line sensor (20).

10. An apparatus (10) in accordance with claim 6, wherein the control (24) is made to calculate spacing profiles only for marked conveying positions (32) in which in particular corners or edges of an object (14) are located in the reading window (22);

and to interpolate the conveying positions disposed therebetween in step form or linearly, with in particular the control (24) also being able to track the zoom factors and/or the taking frequency in step form or linearly.

11. An apparatus (10) in accordance with claim 1, wherein the control (24) is made to extrapolate spacing profiles in lines in the environment of an object (14) from spacing profiles of the object margin to allow a soft transition.

12. An apparatus (10) in accordance with claim 1, wherein the control (24) is made to set the line sensor (20) to a base zoom factor and/or to a base taking frequency which correspond to a reference spacing profile and to set differences from line to line differentially with respect to the preceding line or with respect to the base zoom factor and/or the base taking frequency.

13. An apparatus (10) in accordance with claim 1, wherein the geometry detection sensor (18) is a laser scanner or image sensor, in particular a distance-resolving image sensor.

14. An apparatus (10) in accordance with claim 1, wherein the control (24), when a plurality of objects (14) are present in the reading field, to relate the spacing profile to the foremost object (14) or hindmost object (14) from the line sensor (20 or to calculate the foremost spacing profile in each case with an incomplete detection of the object (14).

15. An apparatus (10) in accordance with claim 1, wherein a postprocessing unit is provided which is made for digital postprocessing for the further equalization of the image data;

and wherein the control (24) transfers parameters relevant to the distortion, in particular the slanted position of an object (14) or the conveying speed.

16. A method for the taking of undistorted images of a surface of objects (14) moved on a conveying device (12),wherein the geometry of the objects (14) is detected with reference to spacing data and/or to the remission behavior of the objects (14) and the objects are scanned by a line sensor (20), in particular a line camera linewise for the generation of image data of the surface in a linear reading window (22) which forms an angle with the conveying direction,

characterized in that,

on the basis of geometrical data, a respective spacing profile of the surface is generated over the reading window (22) from the perspective of the line sensor (20) and an associated zoom factor and/or a taking frequency for the line sensor is generated from each spacing profile. with the line sensor (20) scanning the respective line of the objects (14) to be scanned at the associated zoom factor and/or taking frequency composing the image data thus taken linewise in an undistorted manner to form a uniformly resolved total image of the surface.

17. A method in accordance with claim 16, wherein the zoom factor is set in each case such that the reading window (22) has an extent of the absolute maximum object extent in the line direction over all scanned lines of an object (14) and/or the taking frequency is set such that the scanned lies are disposed regularly over the geometrical surface.

18. A method in accordance with claim 16, wherein the spacing profile is calculated in advance in dependence on the conveying position of the objects (14);

and

wherein the conveying speed is determined to convert the zoom factors and/or taking frequencies dependent on the conveying position into time-dependent zoom factors and/or taking frequencies.

19. A method in accordance with claim 18, wherein spacing profiles are only calculated for marked conveying positions (32) in which in particular corners or edges of an object (14) are located in the reading window and the conveying positions disposed therebetween are interpolated in step form or linearly and the zoom factors and/or the taking frequency being tracked accordingly in step form or linearly.