Optical position sensor

• US 3,918,814 A
• Filed: 05/13/1974
• Issued: 11/11/1975
• Est. Priority Date: 05/13/1974
• Status: Expired due to Term

• Current Assignee: Sidney Weiser
• Original Assignee: Sidney Weiser
• Inventors: Weiser, Sidney
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Rosenberger, Richard A.
• Application Number:
  US05/469,708
• Time in Patent Office: 547 Days
• Field of Search: 356/138,153,156,162,172,209 350/55 250/23R,211R
• US Class Current: 356/620
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates

Abstract

An optical position sensor includes a light source, a lens system and a four quadrant photo-sensitive detector, all located in a compact housing. Light from the source emanates from the principal focus of the lens system which therefore collimates the sensing beam emitted from the housing. The four quadrant detector is positioned to receive light reflected by an external object back through the lens system. In a preferred embodiment the light source is an inexpensive low power lamp; the flux density of the light from the lamp is increased by a tapered fiber optic pipe whose output end is positioned at the principal focus of the lens system. The fiber optic pipe also acts to eliminate the image of the lamp filament from the sensing beam. The four quadrant detector may be located on or off the lens system axis, depending upon whether or not a suitable reflector element is used for the return light energy. Differences between energy levels detected in the four quadrants indicate the X-Y position of the external object relative to lens axis. Z position of the object is manifested by the size of the image reflected onto the detector and therefore is measurable by radially segmenting the detector and sensing the presence of an image in different radial segments.

Claims

1. An optical position sensor for determining the position of an object, said sensor being characterized by a common housing for all sensor components and including:

a low power lamp;

a tapered fiber optic pipe having a wider end positioned adjacent said lamp to receive light emitted from said lamp, the opposite end of said pipe being narrow such that light from said lamp has a greater flux density at said narrow end than at said wider end;

a lens system having a point of principal focus and a predetermined optical axis, said lens system positioned relative to said fiber optic pipe such that the narrow end of said pipe resides at the principal focus of said lens system, said lens system being arranged to collimate substantially all of the light emitted from the narrow end of said pipe into a sensing beam directed out of said housing and imaged substantially at infinity; and

a photo-sensitive detector positioned within said housing to intercept light reflected from said object back through said lens system and into said housing, said photo-sensitive detector including means for providing electrical signals indicative of the position of said object.

2. The sensor according to claim 1 wherein said photo-sensitive detector is positioned between said lamp and said lens system and includes an aperture through which said fiber optic pipe extends.

3. The sensor according to claim 2 wherein said photo-sensitive detector is a four-quadrant detector having four photo-sensitive elements of the same configuration disposed in a common plane about said aperture, each element subtending an angle of approximately 90* and arranged to provide a voltage proportional to the light energy impinging thereon.

4. The sensor according to claim 3 wherein said lamp and said fiber optic pipe are positioned along said predetermined axis.

5. The sensor according to claim 1 wherein said housing is metal and further comprising:

a heat sink disposed within said housing about said lamp; and

means for conducting heat between said heat sink and said housing.

6. The sensor according to claim 1 wherein said narrow end of said fiber optic pipe is configured such that all of the light emitted therefrom impinges upon said lens system, and wherein the outer surface of said fiber optic pipe bears a light absorbant coating.

7. The sensor according to claim 1 wherein said housing includes a longitudinally-extending generally cylindrical bore within which said lamp, said fiber optic pipe, said photo-sensitive detector and said lens system are removably disposed.

8. The sensor according to claim 1 wherein said photo-sensitive detector is positioned off-axis with respect to said sensing beam, and further comprising a reflector positioned to direct toward said detector the light reflected by said body back through said lens system.

9. The sensor according to claim 8 wherein said reflector includes an aperture through which said fiber optic pipe projects.

10. The sensor according to claim 1 wherein said sensing beam is directed along said predetermined axis, and wherein said photo-sensitive detector includes means for providing signals having amplitudes proportional to displacement of said object normal to said predetermined axis.

11. The sensor according to claim 10 wherein said photo-sensitive detector is a four-quadrant detector having four photo-sensitive elements of the same configuration disposed in a common plane about said aperture, each element subtending an angle of approximately 90* and arranged to provide a voltage proportional to the light energy impinging thereon.

12. The sensor according to claim 11 wherein said four photo-sensitive elements are each segmented into plural indepEndent photo-sensitive segments positioned at different radial locations about the center of said detector, whereby the presence of reflected object image on different segments indicates different positions of said object along said predetermined axis.

13. The sensor according to claim 1 wherein said sensor beam is directed along said predetermined axis, and whrein said photo-sensitive detector includes means for providing signals as a function of the position of said object along said predetermined axis.

14. A sensor for determining the position of a body having a diffuse regularly configured surface, said sensor comprising:

lens means having an optical axis and a point of principal focus, said lens system being configured to transmit light emanating from said point of principal focus, the transmitted light taking the form of a sensing beam disposed concentrically about said optical axis and imaged at infinity;

source means for providing light which emanates from said point of principal focus and is substantially entirely received and transmitted by said lens system;

detector means for intercepting light of said sensing beam reflected by said diffuse surface back through said lens means and for providing an electrical signal indicative of the position of said diffuse surface, said detector means being located substantially further from said lens means than said point of principal focus; and

a common compact housing containing said lens means, said source means and said detector means.

15. The sensor according to claim 14 wherein said source means comprises a laser arranged to emit a coherent beam of light and a decollimating lens arranged to focus said coherent beam of light at said point of principal focus.

16. The sensor according to claim 14 wherein said electrical signal has an amplitude and polarity indicative of the asymmetry of said diffuse surface about said optical axis.

17. The sensor according to claim 14 wherein said electrical signal is indicative of the position of said diffuse surface along said optical axis.