Optical positioning device using telecentric imaging
View Patent ↗One embodiment relates to an optical displacement sensor for sensing movement of a data input device across a surface by determining displacement of optical features in a succession of frames. The sensor includes at least an illuminator, telecentric imaging optics on the object (scattering surface) side, and an array of photosensitive elements. The illuminator is configured to illuminate a portion of the surface. The telecentric imaging optics is configured to image the optical features emanating from the illuminated portion of the surface, and the array of photosensitive elements is configured to detect intensity data relating to the optical features imaged by the telecentric imaging optics. Other embodiments are also disclosed.
1. An apparatus, comprising:
an illuminator configured to illuminate a portion of a surface using a coherent light source;
object-side telecentric imaging optics configured to reduce speckle boiling of optical features of a speckle pattern generated by the coherent light source and emanating from the illuminated portion of the surface; and
an array of photosensitive elements comprising a comb array, wherein the array of photosensitive elements is configured to detect intensity data relating to the optical features imaged by the object-side telecentric imaging optics.
2. The optical displacement sensor according to claim 1 , wherein the optical features imaged by the object-side telecentric imaging optics are substantially invariant during translation of the surface with respect to the data input device.
3. The optical displacement sensor according to claim 1 , wherein the coherent light source comprises a Vertical Cavity Surface Emitting Laser (VCSEL), and wherein the photosensitive elements comprise photodiodes.
4. The optical displacement sensor according to claim 1 , wherein the object-side telecentric imaging optics is configured such that chief rays from points on the surface in a field of view are substantially parallel when the chief rays leave the surface.
5. The optical displacement sensor according to claim 4 , wherein the chief rays are normal to the surface when the chief rays leave the surface.
6. The optical displacement sensor according to claim 4 , wherein the chief rays leave the surface at an angle which is not normal to the surface.
7. The optical displacement sensor according to claim 1 , wherein the object-side telecentric imaging optics comprises:
an aperture; and
a first lens located between the aperture and the illuminated portion of the surface.
8. The optical displacement sensor according to claim 7 , wherein the first lens has a focal length substantially equal to an optical distance between the first lens and the aperture.
9. The optical displacement sensor according to claim 8 , further comprising image-side telecentric imaging optics which comprises:
a second lens located between the aperture and the photosensitive elements, wherein the second lens has a focal length substantially equal to the optical distance between the second lens and the aperture.
10. The optical displacement sensor according to claim 7 , wherein the aperture comprises an optical element which defines a numerical aperture of light which is detected by the photosensitive elements.
11. The optical displacement sensor according to claim 10 , wherein the aperture further comprises an optical element which has both a substantially transparent section and a substantially opaque section.
12. The optical displacement sensor according to claim 11 , wherein the aperture has a substantially transparent section which is circular in shape.
13. The optical displacement sensor according to claim 1 , wherein the optical features comprise speckle, a complex interference pattern created by light reflected from the surface, and wherein the optical displacement sensor comprises a speckle-based displacement sensor adapted to sense movement of the data input device across the surface based on displacement of the speckle pattern.
14. A method comprising:
illuminating a portion of a surface using coherent light;
reducing speckle boiling of a speckle pattern generated by the coherent light using object-side telecentric imaging optics;
mapping images of the speckle pattern to an array of photosensitive elements comprising a comb array using the telecentric imaging optics; and
determining displacement of optical features of the speckle pattern emanating from the illuminated portion of the surface in a succession of frames to sense movement of the data input device across the surface in at least one dimension.
15. The method according to claim 14 , wherein the illuminating is performed by using a laser.
16. The method according to claim 14 , further comprising detecting intensity data of the optical features.
17. The method according to claim 14 , further comprising sensing movement of an input device relative to a surface based on the displacement of the optical features.
18. An optical positioning device comprising:
a laser configured to illuminate a portion of the surface;
an array of photosensitive elements;
telecentric imaging optics on an object side configured to reduce speckle boiling of a speckle pattern from the illuminated portion of the surface and to focus the speckle pattern to the array of photosensitive elements, wherein the array of photosensitive elements comprises a comb array; and
a signal processor configured to determine displacement of the speckle pattern in a succession of frames.
19. The optical positioning device of claim 18 , wherein the object-side telecentric imaging optics comprises:
an aperture; and
a lens located between the aperture and the illuminated portion of the surface.
20. The optical positioning device of claim 18 , wherein the illumination has a substantially uniform wave front before impinging upon the surface.