Light spot position measuring method of detecting one-dimensional position by two-dimensional sensor

• US 5,640,241 A
• Filed: 02/21/1995
• Issued: 06/17/1997
• Est. Priority Date: 02/23/1994
• Status: Expired due to Fees

• Current Assignee: Kabushikikaisha Wacom
• Original Assignee: Kabushikikaisha Wacom
• Inventors: Ogawa, Yasuji
• Primary Examiner(s): Pham, Hoa Q.
• Application Number:
  US08/392,375
• Time in Patent Office: 847 Days
• Field of Search: 356/372, 356/375, 356/376, 356/218, 356/121-123, 356/141.5, 356/141.4, 250/559.29
• US Class Current: 356/615
• CPC Class Codes: G01S 3/784 using a mosaic of detectors

Abstract

A light spot position measuring method uses an optical converter such as a cylindrical lens, a two-dimensional image pickup device such as a CCD image sensor and an image processing or computing unit. The cylindrical lens converts a light spot to a linear image intersecting a reference axis direction. The image sensor captures the linear image and produces corresponding pixel data. The computing unit processes the pixel data and derives a position of the light spot along the reference axis direction. In the light spot position measuring method, an orthogonal coordinate system is first set relative to a pixel array of the image sensor. The coordinate system has main and auxiliary axes orthogonal to each other. Subsequently, the linear image is projected to be inclined relative to the coordinate system with an angle of the linear image relative to the auxiliary axis smaller than that relative to the main axis. Subsequently, the pixel data is processed to effect linear-approximation of the linear image to derive a corresponding straight line. Further, another one-dimensional position of the straight line in a direction of the main axis is detected in terms of a one-dimensional position in a direction of the auxiliary axis by a magnified scale. Finally, the position of the light spot is derived based on a result of the detection of the one-dimensional position of the straight line. This measuring method may also be applied to derivation of a two-dimensional position of the light spot.

Claims

1. A light spot position measuring method using an optical converter which converts a light spot of an object to be measured into a linear image extending substantially in a predetermined one-dimensional direction, using a two-dimensional image pickup device having a two-dimensional pixel array which captures said linear image to produce corresponding pixel data, and using an image processing unit which processes said pixel data to derive a position of said light spot along said one-dimensional direction, said method comprising:

a setting step for setting an orthogonal coordinate system relative to said pixel array, said orthogonal coordinate system having a main axis and an auxiliary axis, each of which is orthogonal to the other;

a projecting step for projecting the light spot onto the optical converter to convert the light spot into a linear image extending substantially in the predetermined one-dimensional direction and projecting said linear image onto the two-dimensional pixel array of the image pickup device so as to be inclined relative to said orthogonal coordinate system such that an angle of said linear image relative to said auxiliary axis is set smaller than that relative to said main axis;

a detecting step for processing said pixel data to effect linear-approximation of said linear image to derive a corresponding straight line and for detecting a one-dimensional position of said straight line in a direction of said main axis in terms of another one-dimensional position in a direction of said auxiliary axis by a magnified scale; and

a deriving step for deriving the position of said light spot based on a result of said detection of the one-dimensional position of said straight line.

2. A light spot position measuring method as set forth in claim 1;

wherein said projecting step includes projecting said linear image at an angle with respect to said auxiliary axis in a range between 0° and

25°

.

3. A light spot position measuring method as set forth in claim 1;

wherein said projecting step includes projecting said linear image using an optical converter comprising a cylindrical lens.

4. A light spot position measuring method as set forth in claim 1;

wherein said projecting step includes projecting said linear image using an optical converter having a slit.

5. A light spot position measuring method as set forth in claim 1;

wherein said deriving step includes deriving a one-dimensional position of said light spot along said main axis.

6. A light spot position measuring method as set forth in claim 1;

wherein said deriving step includes deriving a one-dimensional position of said light spot along a predetermined reference axis other than said main axis.

7. A light spot position measuring method as set forth in claim 1;

wherein said deriving step includes deriving a one-dimensional position of said light spot along a predetermined reference axis orthogonal to the straight line corresponding to the linear image.

8. A light spot position measuring method as set forth in claim 1;

wherein said setting step includes setting a pair of orthogonal coordinate systems having a common origin and turned by 90°

relative to each other, said projecting step includes projecting a pair of linear images so as to be inclined relative to said orthogonal coordinate systems, respectively, and said deriving step includes deriving a two-dimensional position of said light spot based on the pair of linear images.

9. A light spot position measuring method using an optical converter which converts a light spot of an object to be measured into linear images intersecting orthogonal to each other, using a two-dimensional image pickup device having a pixel array which captures said orthogonal linear images to produce corresponding pixel data, and using an image processing unit which processes said pixel data to derive a two-dimensional position of said light spot, said method comprising:

a setting step for setting an orthogonal coordinate system so as to match a desired lattice of said pixel array;

a projecting step for projecting the light spot onto the optical converter to convert the light spot into intersecting linear images which are orthogonal with respect to each other and projecting said orthogonal linear images so as to be inclined relative to said orthogonal coordinate system at an angle deviating from 45°

; and

a deriving step for processing said pixel data to effect linear-approximation of one of said orthogonal linear images, said one of the orthogonal linear images having an inclination greater than 45°

relative to said orthogonal coordinate system, effecting linear-approximation of the other of said orthogonal linear images, said other of the orthogonal linear images having an inclination greater than 45°

relative to another orthogonal coordinate system derived by turning said orthogonal coordinate system by 90°

, and deriving the two-dimensional position of said light spot based on results of said linear-approximations, said two-dimensional position corresponding to an intersection of said orthogonal linear images.

10. A light spot position measuring method as set forth in claim 9;

wherein said projecting step includes projecting the orthogonal linear images using an optical converter having divided cylindrical lens surfaces, said cylindrical lens surfaces having their cylinder axes orthogonal to each other.

11. A light spot position measuring method as set forth in claim 9;

wherein said projecting step includes projecting the orthogonal linear images using an optical converter having slits arranged orthogonal to each other.

12. A light spot position measuring apparatus comprising:

an optical converter for converting a light spot into a linear image and projecting the linear image;

a two-dimensional image pickup device having a two-dimensional pixel array for receiving the projected linear image and producing corresponding pixel data, the pixel array being set with an orthogonal coordinate system having an orthogonal pair consisting of a main axis and an auxiliary axis such that an angle of the projected linear image relative to the auxiliary axis is set smaller than that relative to the main axis; and

an image processing unit for processing the pixel data to effect linear-approximation of the linear image to derive a corresponding straight line, and for computing a first intercept of the straight line at the main axis by a magnified scale in terms of a second intercept of the same straight line at the auxiliary axis so as to determine a one-dimensional position of the light spot correlated to the first intercept.

13. A method for determining the position of a light spot, comprising the steps of:

converting a light spot into a linear image using an optical converter;

providing an image pick-up device having a two-dimensional pixel array for receiving an image and producing corresponding pixel data;

setting up an orthogonal coordinate system relative to the pixel array, the coordinate system having a main axis and an auxiliary axis orthogonal thereto;

projecting the linear image onto the pixel array so as to be inclined with respect to the orthogonal coordinate system such that an angle of the linear image with respect to the auxiliary axis is smaller than an angle of the linear image with respect to the main axis;

processing the pixel data output by the pixel array in response to the projected linear image to perform linear approximation to determine a straight line corresponding to the linear image, and determining the position of the straight line with respect to the orthogonal coordinate system in accordance with an intercept of the straight line with the main axis and an intercept of the straight line with the auxiliary axis; and

determining a location of the light spot on the straight line in accordance with the position of the straight line.

14. A method for determining the position of a light spot according to claim 13;

wherein the step of projecting the linear image onto the pixel array comprises the step of projecting the linear image at an angle with respect to the auxiliary axis in the range of 0° and

25°

.

15. A method for determining the position of a light spot according to claim 13;

wherein the step of converting the light spot into a linear image includes using an optical converter comprising a cylindrical lens.

16. A method for determining the position of a light spot according to claim 13;

wherein the step of converting the light spot into a linear image includes using an optical converter having a slit.

17. A method for determining the position of a light spot according to claim 13;

wherein the step of determining a location of the light spot on the straight line includes determining a position of the light spot along the main axis based on the position of the straight line.

18. A method for determining the position of a light spot according to claim 13;

wherein the step of determining a location of the light spot on the straight line includes determining a position of the light spot along a predetermined reference axis other than the main axis based upon the position of the straight line.

19. A method for determining the position of a light spot according to claim 13;

wherein the step of determining a location of the light spot on the straight line includes determining a position of the light spot along a predetermined reference axis orthogonal to the straight line corresponding to the linear image based on the position of the straight line.

20. A method for determining the position of a light spot according to claim 13;

wherein the step of setting up an orthogonal coordinate system includes setting up a pair of orthogonal coordinate systems having a common origin and offset by 90°

with respect to each other, the step of projecting the linear image onto the pixel array includes projecting a pair of linear images so as to be inclined with respect to the orthogonal coordinate systems, respectively, and the step of determining the location of the light spot on the straight line includes determining a two-dimensional position of the light spot based on the pair of linear images.

21. A method for determining the position of a light spot according to claim 20;

wherein the step of projecting the pair of linear images is performed using an optical converter having divided cylindrical lens surfaces, the cylindrical lens surfaces having cylinder axes which are orthogonal to each other.

22. A method for determining the position of a light spot according to claim 20;

wherein the step of projecting the pair of linear images is performed using an optical converter having slits arranged orthogonal to each other.

23. An apparatus for determining the position of a light spot, comprising:

an optical converter for converting a light spot into a linear image and projecting the linear image;

an image pickup device having a two-dimensional pixel array for receiving the projected linear image and producing corresponding pixel data, the pixel array being set with an orthogonal coordinate system having a main axis and an auxiliary axis orthogonal with respect thereto such that an angle of the projected linear image with respect to the auxiliary axis is smaller than an angle of the projected linear image with respect to the main axis; and

image processing means for processing the pixel data by performing a linear-approximation of the linear image to derive a corresponding straight line and for computing a first intercept of the straight line at the main axis by a magnified scale in terms of a second intercept of the same straight line at the auxiliary axis so as to determine a one-dimensional position of the light spot correlated to the first intercept.