Structured light projection through the minimization of visual artifacts by way of deliberately introduced optical aberrations

Patent metadata

Field	Value
Publication number	US-12025470-B2
Application number	US-202117318311-A
Country	US
Kind code	B2
Filing date	May 12, 2021
Priority date	May 12, 2020
Publication date	Jul 2, 2024
Grant date	Jul 2, 2024

Abstract

A triangulation device for measuring a measurement object by a projection of a structured light pattern onto the measurement object. The triangulation device includes a projector projecting the structured light pattern decomposable into different spatial frequencies onto the measurement object. The projector comprises a matrix of pixel elements and a lens system which determines a wavefront with a wavefront aberration from a reference wavefront, and a camera including a lens system and an imaging sensor, the camera being configured to receive the structured light pattern projected by the projector onto the measurement object, and a processing unit configured to provide distance information by evaluating imaging information provided by the camera. The wavefront aberration comprises a primary spherical aberration coefficient Z 9 , wherein the primary spherical aberration coefficient Z 9 is larger than 0.5λ, wherein λ is a wavelength of the projected structured light pattern.

First claim

What is claimed is:

1. A triangulation device for measuring a measurement object by a projection of a structured light pattern onto the measurement object, the triangulation device comprising:
a projector configured to project the structured light pattern with projection light, the projection light comprising at least one wavelength λ, onto the measurement object, the structured light pattern being decomposable into different spatial frequencies, the projector comprising:
a matrix of pixel elements, wherein an artifact pattern is defined by artifact regions between neighboring pixel elements, and
a lens system, wherein the lens system is arranged so that the projection light passing through the lens system defines a wavefront with a wavefront aberration from a spherical reference wavefront;

a camera comprising a lens system and an imaging sensor, wherein the camera is configured to receive the structured light pattern projected by the projector ( 8 ) onto the measurement object; and
a processing unit configured to provide distance information by evaluating imaging information provided by the camera,
wherein the wavefront aberration is defined by a primary spherical aberration coefficient Z 9 of a Zernike decomposition, wherein Zernike polynomials defining the Zernike decomposition are ordered according to the Fringe Zernike coefficient ordering, wherein the primary spherical aberration coefficient Z 9 is larger than one fourth of the wavelength λ.

2. The triangulation device according to claim 1 , wherein the primary spherical aberration coefficient Z 9 is larger than one third of the wavelength λ or larger than one half of the wavelength λ.

3. The triangulation device according to claim 1 , wherein the primary spherical aberration provides a low pass filter.

4. The triangulation device according to any claim 1 , wherein the structured light pattern is embodied as a sinusoidal pattern.

5. The triangulation device according to claim 1 , wherein the Modulation Transfer Function (MTF) of the projector lens system is closer to diffraction MTF values than to zero at the spatial frequencies of the structured light pattern, and closer to zero than to diffraction MTF values at the spatial frequencies of the neighboring pixel element artifact pattern.

6. The triangulation device according to claim 1 , wherein the largest ratio between the MTF values of the projector lens system at the spatial frequencies of the neighboring pixel element artifact pattern to the MTF values of the projector lens system at the spatial frequencies of the structured light pattern is smaller than 0.5.

7. The triangulation device according to claim 1 , wherein the MTF value of the projector lens system at a spatial frequency of the neighboring pixel element artifact pattern is smaller than one half of the MTF value of the projector lens system at a spatial frequency of the structured light pattern.

8. The triangulation device according to claim 5 , wherein the MTF values are related to a point along the optical axis of the projector lens system, wherein the point lies in a pre-defined measurement range.

9. The triangulation device according to claim 1 , wherein the MTF 15 preserved across the entire projected structured light pattern, and wherein any two arbitrary points on the measurement object onto which the structured light pattern is projected possess substantially equal MTF curves, the arbitrary points lying on a portion of the surface of the measurement object illuminated by the structured light pattern.

10. The triangulation device according to claim 1 , wherein the lens system of the projector is focused with respect to a pre-defined measurement range.

11. The triangulation device according to claim 10 , wherein the surface of the measurement object onto which the structured light pattern is projected is located within the pre-defined measurement range.

12. The triangulation device according to claim 1 , wherein the projector is embodied as a digital light processing projector, using a digital mirror device (DMD), or as an LCD projector, or as an OLED projector, with an artifact region between two neighboring pixel elements having an extent of at most 15% of the individual pixel element width.

13. The triangulation device according to claim 1 , wherein the triangulation device comprises a second camera, the second camera comprising a lens system and an imaging sensor, and the camera of the triangulation device and the second camera are placed symmetrically around the projector, wherein the processing unit is configured to provide distance information by evaluating imaging information provided by the camera and the second camera.

14. The triangulation device according to claim 1 , wherein the structured light pattern is designed to contain spatial frequencies whose average value is smaller than a smallest spatial frequency of the neighboring pixel element artifact pattern.

15. The triangulation device according to claim 14 , wherein the smallest spatial frequency is a lower bound for the set of spatial frequencies of the neighboring pixel element artifact pattern, or the spatial frequencies of the structured light pattern are disjunct from the spatial frequencies of the neighboring pixel element artifact pattern.

Assignees

• Hexagon Technology Ct Gmbh

Inventors

• Schwendener Andreas
• Jensen Thomas
• Stigwall Johan

Classifications

• G01C3/18

  with one observation point at each end of the base (G01C3/20 takes precedence) · CPC title

• G01B11/2545

  with one projection direction and several detection directions, e.g. stereo · CPC title

• G06T7/66

  of image moments or centre of gravity · CPC title

• G06T7/70

  Determining position or orientation of objects or cameras (camera calibration G06T7/80) · CPC title

• G01C3/08 Primary

  Use of electric radiation detectors · CPC title