Measurement system of a light source in space

• US 9,103,661 B2
• Filed: 07/14/2011
• Issued: 08/11/2015
• Est. Priority Date: 07/16/2010
• Status: Active Grant

• Current Assignee: CSEM Centre Suisse d'Electronique et de Microtechnique SA Recherche et Développement
• Original Assignee: CSEM Centre Suisse D'Electronique et de Microtechnique SA
• Inventors: Grenet, Eric, Masa, Peter, Franzi, Edoardo, Hasler, David
• Primary Examiner(s): Punnoose, Roy M
• Application Number:
  US13/810,455
• Publication Number:
  US 20130120763A1
• Time in Patent Office: 1,489 Days
• Field of Search: 356/621, 356/623
• US Class Current: 1/1
• CPC Class Codes: G01B 11/14 for measuring distance or clearance between spaced objects or spaced apertures G01B11/26 takes precedence; rangefinders G01C3/00
• CPC Class Codes: G01C 3/085 with electronic parallax measurement
• CPC Class Codes: G01D 5/34 the beams of light being detected by photocells
• CPC Class Codes: G01D 5/38 by diffraction gratings
• CPC Class Codes: G01S 3/781 Details
• CPC Class Codes: G01S 3/7835 using coding masks

Abstract

A system measures the position of a light source in space using an imager and transparent surface with a pattern on top. The pattern consists of a repetitive pattern and a distinctive element. The system achieves sub-micron precision. It also handles the measurement of several light sources simultaneously, and the measurement of the position of a retroreflector instead of the light.

Claims

1. A measurement system comprising,

at least one imaging device composed of a plurality of sensitive pixels disposed in at least one dimension;

at least one punctual light source;

at least one component configured to cast a shadow on the imaging device, the position of the component being fixed with respect to the imaging device, the component being composed of repetitive patterns realized on a planar surface including a distinctive element, the component being configured to cast a shadow made of repetitive patterns and made of a distinctive element, the imaging device being configured to record an image of said shadow; and

computation means;

wherein the repetitive patterns are repeated at regular space intervals, and the computation means is configured to compute the elevation of the light source from the position of the distinctive element present in said image, and

wherein the computation means is configured to modify the computed elevation of the light source from the position of the repetitive patterns present in said image.

2. The measurement system of claim 1, wherein the component patterns are made of microlenses, and

the distinctive element is a set of at least one missing microlens region.

3. The measurement system of claim 1, wherein the component is a grating composed of opaque repetitive patterns realized on a planar surface including a distinctive element.

4. The measurement system according to claim 1, further comprising M imaging devices and M components,

wherein each component is attached between the light source and its respective imaging device,

wherein the relative position between each imaging-component couple is fixed and defined,

wherein M is an integer greater than or equal to two,

wherein the imaging devices are not all coplanar, and

wherein the computation means are designed to compute the three dimensional position of the light source.

5. The measurement system according to claim 1, wherein the imaging device is composed of a plurality of sensitive pixels disposed in two dimensions, and

wherein the computation means are configured to compute the elevation along the first dimension and the elevation along the second dimension of the light source from the repetitive patterns and from the distinctive element present in said image.

6. The measurement system according to claim 5, wherein the computation of the elevation value along the first dimension or the elevation value along the second dimension, or both at the same time, uses at least 80% of said pixels that record said image of the shadow.

7. The measurement system according to claim 6, wherein the distinctive element is a two-dimensional code interlaced with the repetitive patterns, any squared subset of the code which contains at least three by three elements of the code being unique.

8. The measurement system according to claim 6, wherein the component is aligned to a pixel matrix of the pixels in such a manner that a sum of pixel values over lines of the image and a sum of pixels values over columns of said image defines the position of the shadow with respect to the component.

9. The measurement system of claim 6, further comprising at least two punctual light sources emitting light at distinct wavelengths and at least two filters,

wherein the filters are configured to cover distinct locations of the component,

wherein each filter covers a surface which is at least nine times the surface area of a single pattern of the component,

wherein the filters are matched to the wavelengths of the light sources, and

wherein the imaging device is designed to deliver one image per area covered by the filters.

10. The measurement system of claim 6, further comprising a retroreflector,

wherein the light source is connected to the computing means and to the imaging device, and

wherein the computation means are configured to compute the elevation of the retroreflector.

11. The measurement system of claim 10, further comprising at least two retroreflectors reflecting light at distinct wavelengths and at least two filters,

wherein the filters are configured to cover distinct locations of the component,

wherein each filter covers a surface which is at least nine times the surface area of a single pattern of the component,

wherein the filters are matched to the reflecting wavelengths of the retroreflectors, and

wherein the imaging device is configured to deliver one image per area covered by the filters.

12. The measurement system according to claim 10, further comprising at least two punctual light sources emitting light at distinct wavelengths and comprising at least two filters,

wherein the filters are configured to cover distinct locations of the component,

wherein each filter covers a surface which is at least nine times the surface area of a single pattern of the component,

wherein the filters are matched to the wavelengths of the light sources,

wherein the imaging device is configured to deliver one image per area covered by the filters, and

wherein every light source is connected to the computing means and to the imaging device.

13. The measurement system of claim 12, further comprising several identical copies of said light sources,

wherein every light source is addressable individually, and

said copies of the light sources are positioned at increasing distance from the imaging device.

14. The measurement system of claim 6, wherein the computation means are configured so that the elevation along both dimensions are defined in at least two distinct locations of the same imaging device, and so that the combination of all said elevations defines the three-dimensional position of the punctual light source.

15. The measurement system of claim 6, comprising N imaging devices and N components,

wherein each component is attached between the light source and its respective imaging device,

wherein the relative position between each imaging-component couple is fixed and defined,

wherein N is an integer greater than or equal to two, and

wherein the computation means are designed to compute the three dimensional position of the light source.

16. The measurement system of claim 6, further comprising control means arranged to switch the light source(s) on-and-off according to a predefined timed sequence.

17. The measurement system of claim 6, further comprising a modulation circuit configured to modulate the power of the light in a repetitive manner.

18. A method for the measurement of the position of a light source, for implementing a measurement system including

at least one imaging device composed of a plurality of sensitive pixels disposed in at least one dimension,

at least one punctual light source,

at least one component configured to cast a shadow on the imaging device, the position of the component being fixed with respect to the imaging device, the component being composed of repetitive patterns realized on a planar surface including a distinctive element, the component being configured to cast a shadow made of repetitive patterns and made of a distinctive element, and

computation means,

the method comprising:

recording, by the imaging device, the image of the shadow; and

computing, using the image of the shadow, the position of the shadow with respect to the component,

wherein the repetitive patterns are repeated at regular space intervals, the computation means are configured to compute the elevation of the light source from the position of the distinctive element present in said image, the computation means being configured to modify the computed elevation of the light source from the position of the repetitive patterns present in said image,

the imaging device is composed of a plurality of sensitive pixels disposed in two dimensions,

the computation means are configured to compute the elevation along the first dimension and the elevation along the second dimension of the light source from the repetitive patterns and from the distinctive element present in said image,

the computation of the elevation value along the first dimension or the elevation value along the second dimension, or both at the same time, uses at least 80% of said pixels that record said image of the shadow, and

the elevation of the light source or of a retroreflector along the first dimension and along the second dimension of the imaging device is computed using the position of the shadow.

19. The measurement method of claim 18, wherein the position of the shadow of the component is obtained as the sum of an approximate position value computed from the distinctive element and a phase position value computed from the repetitive patterns.

20. The measurement method of claim 19, wherein the position of the shadow of the component is computed from a sum of pixel values over the lines of the image and from a sum of pixel values over the columns of the image of the shadow.

21. The measurement method of claim 18, wherein the position of the shadow of the component is computed from a sum of pixel values over the lines of the image and from a sum of pixel values over the columns of the image of the shadow.

22. The measurement method according to claim 18, wherein the position of the shadow with respect to the component is computed in at least two distinct locations of the imaging device, and

the combination of said positions is used to compute the three-dimensional position of the light source or of the retroreflector.

23. The measurement method according to claim 18, wherein, the measurement method is for implementing a measurement system that further comprises a modulation circuit configured to modulate the power of light in a repetitive manner, the method further comprising:

modulating, by the modulation circuit, the intensity of the light source;

recording the image of the shadow at least twice;

combining said recorded images to deliver a new image of the shadow, the combining the recorded images cancelling the effect on said new image of any other light source present in the measurement system environment and whose modulation differs from the light source modulated by said modulation circuit; and

computing the position of the shadow with respect to the component from said new image of the shadow.

24. The measurement method according to claim 18, wherein, the measurement method is for implementing a measurement system that further comprises:

(i) a retroreflector, the light source being connected to the computing means and to the imaging device, the computation means being designed to compute the elevation of the retroreflector,

(ii) at least two punctual light sources emitting light at distinct wavelengths, and

(iii) at least two filters, the filters being configured to cover distinct locations of the component, each filter covering a surface which is at least as big as nine times the surface of a single pattern of the component, the filters being matched to the wavelengths of the light sources, the imaging device being configured to deliver one image per area covered by the filters, every light source being connected to the computing means and to the imaging device; and

the method further comprising

computing the position of the shadow with respect to the component at least once per area covered by the filters, and

computing, using the positions computed at least one per area covered by the filters, the three-dimensional position of the retroreflector.

25. The measurement method according to claim 24, wherein, the measurement method is for implementing a measurement system that further comprises several identical copies of said light sources, every light source being addressable individually, said copies of the light sources being positioned at increasing distance from the imaging device, and

the position of the three-dimensional position of the retroreflector is first computed using a light first source and a second light source that are close to the sensor, followed by a computation using a copy of light the first light source and a copy of the second light source that are positioned further apart from the sensor.