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

• US 8,360,316 B2
• Filed: 08/06/2008
• Issued: 01/29/2013
• Est. Priority Date: 08/10/2007
• Status: Active Grant

• Current Assignee: Sick AG (Sick)
• Original Assignee: Sick AG (Sick)
• Inventors: Gehring, Roland, Reichenbach, Jrgen, Wiegers, Michael, Reich, Jan
• Primary Examiner(s): Le, Thien M
• Assistant Examiner(s): JOHNSON, SONJI N
• Application Number:
  US12/222,285
• Publication Number:
  US 20090039157A1
• Time in Patent Office: 1,637 Days
• Field of Search: 348/159, 235/436, 235/462.11, 235/462.24, 235/462.23
• 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 for the taking of undistorted images of a surface of objects moved on a conveying device, comprising:

a geometry detection sensor configured to detect a geometry of the objects with reference to at least one of spacing data and remission behavior of the objects;

a line sensor configured to scan the objects linewise for the generation of image data of the surface in a linear reading window which forms an angle with the conveying direction; and

a control configured;

to extrapolate spacing profiles in lines in an environment of an object from spacing profiles of the object margin to allow a soft transition;

to generate, on the basis of geometrical data of the geometry detection sensor, a respective spacing profile of the surface over the reading window from the perspective of the line sensor and to vary a taking frequency for the line sensor from each spacing profile according to the geometry of the objects as taken from the perspective of the line sensor;

to set the line sensor to the associated taking frequency for the respective line of the objects 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 in accordance with claim 1, wherein the control is configured to set a zoom factor such that the reading window in each case has an extent which corresponds to a maximum object extent in a line direction over all scanned lines of an object.

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

4. An apparatus in accordance with claim 1, wherein the control is configured to set a focus setting of the line sensor 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 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 in accordance with claim 1, wherein the geometry detection sensor is integrated into the line sensor.

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

and

wherein the control is configured to calculate the spacing profile in advance in dependence on the conveying direction of the objects.

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

and

wherein the control is configured to 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 in accordance with claim 7, wherein the speed sensor is implemented as one of the following:

an incremental encoder at the conveying device; and

/or

a speed evaluation device at the geometry detection sensor or at the line sensor which is configured to evaluate a distortion of expected object contours; and

/or

a comparator configured to recognize an object feature in the geometry data and in the image data again and determine the speed from the time difference of the data taking and the spacing of the geometry detection sensor and the line sensor.

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

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

and

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

11. An apparatus in accordance with claim 1, wherein the configuration of the control to extrapolate spacing profiles in lines in an environment of an object from spacing profiles of the object margin to allow a soft transition extends object contours virtually, so as to allow guiding of the zoom or focus into a required location at an early time.

12. An apparatus in accordance with claim 1, wherein the control is configured to set the line sensor to a base taking frequency which corresponds 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 taking frequency.

13. An apparatus in accordance with claim 1, wherein the geometry detection sensor is selected from the group consisting of (a) a laser scanner, (b) an image sensor, and (c) a distance-resolving image sensor.

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

15. An apparatus in accordance with claim 1, wherein a postprocessing unit is configured for digital postprocessing for the further equalization of the image data;

and

wherein the control is configured for transferring parameters relevant to the distortion, in particular the slanted position of an object or the conveying speed.

16. An apparatus in accordance with claim 1, wherein the control is further configured to generate an associated zoom factor for the line sensor from each spacing profile.

17. A method for the taking of undistorted images of a surface of objects moved on a conveying device, comprising:

detecting a geometry of the objects with reference to at least one of spacing data and remission behavior of the objects;

extrapolating spacing profiles in lines in an environment of an object from spacing profiles of the object margin to allow a soft transition;

scanning the objects by a line sensor linewise for the generation of image data of the surface in a linear reading window which forms an angle with the conveying direction;

generating a respective spacing profile of the surface over the reading window from the perspective of the line sensor;

varying a taking frequency for the line sensor from each spacing profile according to the geometry of the objects as taken from the perspective of the line sensor;

scanning the respective line of the objects to be scanned at the associated taking frequency; and

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

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

19. A method in accordance with claim 17, wherein the spacing profile is calculated in advance in dependence on the conveying position of the objects;

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.

20. A method in accordance with claim 19, wherein spacing profiles are only calculated for marked conveying positions in which in particular corners or edges of an object 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.