Optical displacement sensor

• US 20020167677A1
• Filed: 03/22/2002
• Published: 11/14/2002
• Est. Priority Date: 03/25/2001
• Status: Active Grant

• Current Assignee: Omron Corporation
• Original Assignee: Omron Corporation
• Inventors: Mano, Mitsuharu, Kawachi, Masahiro, Matsunaga, Tatsuya, Okada, Michitoshi
• Granted Patent: US 6,839,144 B2
• Time in Patent Office: Days
• US Class Current: 356/602
• CPC Class Codes: G01B 11/25 by projecting a pattern, e.g. one or more lines, moiré fringes on the object G01B11/255 takes precedence ; image analysis for depth or shape recovery G06T7/50

Abstract

An optical displacement sensor takes in a plurality of images of a target object by projecting a slit beam of light and using a two-dimensional image taking element by changing the image taking conditions each time. Parameters defining these conditions affecting the brightness of the obtained image are varied. From each of these images including an image of a portion of the sectional contour line of the target object, a segmented image satisfying a specified maximum brightness condition is extracted and a synthesized image is generated by gathering such segmented images. The target object is inspected from such synthesized image.

Claims

1. An optical displacement sensor comprising:

multi-imaging means including a light projecting means, an image taking means and a parameter scanning means, said light projecting means being for providing a slit beam of light and projecting said slit beam of light onto a target surface of a target object at a specified angle, said image taking means being for obtaining contour-including images including an image of a sectional contour line by an optical sectional surface by using a two-dimensional image taking element at another angle different from said specified angle to photograph said target surface where said slit beam of light is made incident, said parameter scanning means being for scanning the brightness of said contour-including images by varying the value of at least one of parameters that define image taking conditions affecting the brightness of said contour-including images obtained through said image taking means, said multi-imaging means serving to obtain a plurality of said contour-including images under different image taking conditions;

image synthesizing means for extracting from a plurality of said contour-including images obtained by said multi-imaging means a segmented image satisfying a specified maximum brightness condition for each of predetermined segments and generating a synthesized image including a series of portions of the image of said sectional contour line by gathering said extracted segmented images; and

measuring means for carrying out a specified measuring process based on said series of portions of the images of said sectional contour line and generating a value representing a result obtained by said specified measuring process.

2. The optical displacement sensor of claim 1 wherein said measuring means measures the distribution of distance between said multi-imaging means and said target surface along a line including where said slit beam is made incident.

3. The optical displacement sensor of claim 1 wherein said parameters include shutter time of said two-dimensional image taking element.

4. The optical displacement sensor of claim 1 wherein said parameters are changed in variable units.

5. The optical displacement sensor of claim 1 wherein said parameters are changed within a variable maximum range.

6. The optical displacement sensor of claim 1 wherein said parameters are changed within a maximum range, said maximum range being automatically set according to results of a test measurement.

7. The optical displacement sensor of claim 1 wherein said parameters are changed within a maximum range in specified units, said sensor including means for automatically adjusting said maximum range and said specified units according to the brightness of the image of said sectional contour line taken by said sensor.

8. The optical displacement sensor of claim 1 wherein said predetermined segments each consist of an area including one or more mutually adjacent horizontal scan lines on an image obtained by said two-dimensional image taking element.

9. The optical displacement sensor of claim 1 wherein said image synthesizing means includes:

an image memory for storing image of one screen portion of said two-dimensional image taking element, said image memory being divided into segments;

a flag memory for storing write-control flags indicating whether or not a write-in is allowed to each of these segments of said image memory;

an image recording means or recording images obtained by said multi-imaging means into said image memory in units of the segments according to said write-control flags; and

a flag control means for controlling said write-control flags such that after a segmented image satisfying said specified maximum brightness condition is recorded in each of the segments of said image memory, the write-in into the corresponding segment is inhibited.

10. The optical displacement sensor of claim 9 wherein said multi-imaging means stops obtaining said contour-including images when the segmented images satisfying said specified maximum brightness condition have been recorded into all of specified ones of said segments of said image memory.

11. The optical displacement sensor of claim 9 wherein said predetermined segments each consist of an area including one or more mutually adjacent horizontal scan lines.

12. The optical displacement sensor of claim 1 wherein said multi-imaging means is contained in a housing structure to form a sensor head unit and said image synthesizing means and said measuring means are contained in another housing structure to form a signal processing unit.

13. The optical displacement sensor of claim 1 further comprising an image monitor which is externally connected to said signal processing unit.

15. The multiple image taking device of claim 14 contained in a housing structure to form a sensor head unit.

17. The signal processing unit of claim 16 contained in a housing structure to be formed as a signal processing unit.

18. The optical displacement sensor of claim 1 further comprising image repairing means for repairing a missing portion of the image of said sectional contour line in said synthesized image generated by said image synthesizing means.

19. The optical displacement sensor of claim 18 wherein said image repairing means sequentially detects the presence or absence of the image of a portion of said sectional contour line on each of scan lines forming said synthesized image and replaces the image of a scan line with missing image of said sectional contour line with the image of the scan line immediately before.

20. The optical displacement sensor of claim 18 wherein said image repairing means sequentially detects the presence or absence of the image of a portion of said sectional contour line on each of scan lines forming said synthesized image and replaces the image of a scan line with missing image of said sectional contour line by using the images of the scan lines before and after.

21. The optical displacement sensor of claim 18 wherein said image repairing means sequentially detects the presence or absence of the image of a portion of said sectional contour line on each of scan lines forming said synthesized image and replaces or does not replace the image of a scan line, depending on the continuity of brightness with the images of said sectional contour line on lines before and after.

22. The optical displacement sensor of claim 1 further comprising monitor output means for generating output signals for displaying a specified image on an image monitor.

23. , The optical displacement sensor of claim 22 wherein said specified image includes said synthesized image.

24. The optical displacement sensor of claim 23 wherein said specified image includes a cursor which indicates one of horizontal scan lines forming said synthesized image and a brightness distribution curve of one of said scan lines selected by said cursor.

25. The optical displacement sensor of claim 23 wherein said specified image includes a cursor which indicates one of horizontal scan lines selected from said synthesized image and image taking conditions for one of said scan lines selected by said cursor.

26. The optical displacement sensor of claim 23 wherein said specified image includes a mark on each of horizontal scan lines forming said synthesized image indicating absence of image of said sectional contour line.

27. The optical displacement sensor of claim 23 wherein said specified image includes a mark on each of horizontal scan lines forming said synthesized image indicating presence of image of said sectional contour line.

28. The optical displacement sensor of claim 22 further comprising a graphical user interface for holding conversation between an operator and said image monitor through a pointing device

29. The optical displacement sensor of claim 1 further comprising tracking control means for changing target position for measurement according to relative motion of said target object.

30. The optical displacement sensor of claim 29 wherein said target position is for measuring the distance between said multi-imaging means and said target surface and wherein said relative motion is perpendicular to the direction in which said distance changes.

31. The optical displacement sensor of claim 29 wherein said target position is for measuring the distance between said multi-imaging means and said target surface and wherein said relative motion is in the direction in which said distance changes.

32. The optical displacement sensor of claim 29 wherein said target position is for measuring the distance between said multi-imaging means and said target surface and wherein said relative motion is both in and perpendicular to the direction in which said distance changes.

14. A multiple image taking device comprising:

light projecting means for providing a slit beam of light and projecting said slit beam of light onto a target surface of a target object at a specified angle;

an image taking means for obtaining contour-including images including an image of a sectional contour line by an optical sectional surface by using a two-dimensional image taking element at another angle different from said specified angle to photograph said target surface where said slit beam of light is made incident; and

a parameter scanning means for scanning the brightness of said contour-including images by varying the value of at least one of parameters that define image taking conditions affecting the brightness of said contour-including images obtained through said image taking means;

said multiple image taking device serving to obtain a plurality of said contour-including images under different image taking conditions

16. A signal processing device to be connected to a multi-imaging means, said multi-imaging including a light prejecting means, an image taking means and a parameter scanning means, said light projecting means being for providing a slit beam of light and projecting said slit beam of light onto a target surface of a target object at a specified angle, said image taking means being for obtaining contour-including images including an image of a sectional contour line by an optical sectional surface by using a two-dimensional image taking element at another angle different from said specified angle to photograph said target surface where said slit beam of light is made incident, said parameter scanning means being for scanning the brightness of said contour-including images by varying the value of at least one of parameters that define image taking conditions affecting the brightness of said contour-including images obtained through said image taking means, said multi-imaging means serving to obtain a plurality of said contour-including images under different image taking conditions;

said signal processing unit comprising;

image synthesizing means for extracting from a plurality of said contour-including images obtained by said multi-imaging means a segmented image satisfying a specified maximum brightness condition for each of predetermined segments and generating a synthesized image including a series of portions of the image of said sectional contour line by gathering said extracted segmented images; and

measuring means for carrying out a specified measuring process based on said series of portions of the images of said sectional contour line and generating a value representing a result obtained by said specified measuring process;

said signal processing device measuring a cross-section of said target object.