Proximity sensor based on projection of structured light

• US 7,459,670 B2
• Filed: 11/11/2003
• Issued: 12/02/2008
• Est. Priority Date: 11/11/2002
• Status: Expired due to Fees

• Current Assignee: Google LLC (Alphabet Inc.)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Orchard, David A, Lewin, Andrew C
• Primary Examiner(s): Luu, Thanh X
• Application Number:
  US10/534,494
• Publication Number:
  US 20060163455A1
• Time in Patent Office: 1,848 Days
• Field of Search: 250/221, 250/222.1, 356 401- 409
• US Class Current: 250/221
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target

Abstract

This invention relates to a proximity sensor. An illumination means (2) projects an array of spots (40) towards a scene. Detector (8) looks towards the scene through a mask (6). The mask (6) is arranged such that light from a target at a certain range, for instance far object (14) is not transmitted to the detector. Light reflected from a close object (16) however passes through the mask (6) and is incident on the detector (8). A rise in the intensity of incident light at the detector (8) is determined by threshold detector (10) and used to operate an alarm (12).

Claims

1. A proximity sensor comprising:

an illumination means for illuminating a scene with an array of spots of light,

a detector arranged to receive light reflected from the scene and

a mask, located in the optical path of light from the scene to the detector, the mask having transmissive portions and non-transmissive portions and being arranged, together with the illumination means and detector such that light reflected from a target from within a first range of distances from the sensor is transmitted through the mask to the detector and light from a second range of distances is not transmitted through the mask, wherein the illumination means comprises a light source arranged to illuminate part of the input face of a light guide, the light guide comprising a tube having substantially reflective sides and being arranged together with projection optics so as to project an array of distinct images of the light source towards the scene.

2. A proximity sensor as claimed in claim 1 wherein the mask is arranged such that reflected light is transmitted to the detector if the target is within a predetermined distance of the sensor and reflected light is not transmitted if the target is outside of that predetermined distance.

3. A proximity sensor as claimed in claim 1 wherein the mask is adapted to transmit light reflected from a target more than a predetermined distance away from the sensor and not transmit light from within the predetermined distance.

4. A proximity sensor as claimed in claim 1 wherein the illumination means illuminates the scene with spots of infrared light.

5. A proximity sensor as claimed in claim 1 wherein the illumination means is modulated at a predetermined frequency and a filter is applied to the detector at the predetermined frequency.

6. A proximity sensor as claimed in claim 1 wherein the detector is adapted to receive ambient light from the scene and compensate for the effects of the ambient light.

7. A proximity sensor as claimed in claim 1 wherein the mask is adapted to define a plurality of ranges of distance from the sensor and transmit a different amount of reflected light from a target in each distance range.

8. A proximity sensor as claimed in claim 7 wherein the illumination means is adapted to project a plurality of spots at different modulated frequencies and the mask is adapted such that at each range of distance a different modulated frequency is transmitted to the detector.

9. A proximity sensor as claimed in claim 1 wherein the mask comprises a substantially non transmitting material having a plurality of transmissive windows.

10. A proximity sensor as claimed in claim 1 wherein the light guide comprises a tube with a square cross section.

11. A proximity sensor as claimed in claim 1 wherein the tube comprises a hollow tube having reflective internal surfaces.

12. A proximity sensor as claimed in claim 1 wherein the tube comprises a solid material, arranged such that a substantial amount of light incident at an interface between the material of the tube and surrounding material undergoes total internal reflection.

13. A proximity sensor as claimed in claim 1 wherein the light source comprises an LED.

14. A proximity sensor as claimed in claim 1 wherein the light source comprises an array of LEDs.