Device for measuring small distances

• US 4,717,255 A
• Filed: 07/09/1986
• Issued: 01/05/1988
• Est. Priority Date: 03/26/1986
• Status: Expired due to Fees

• Current Assignee: Hommelwerke, GmbH (Jenoptik AG)
• Original Assignee: Hommelwerke, GmbH (Jenoptik AG)
• Inventors: Ulbers, Gerd
• Primary Examiner(s): Willis, Davis L.
• Assistant Examiner(s): Koren, Matthew W.
• Application Number:
  US06/883,553
• Time in Patent Office: 545 Days
• Field of Search: 356/345, 356/358, 356/359, 356/360, 350/96.11, 350/96.12
• US Class Current: 356/501
• CPC Class Codes: G01B 11/303 using photoelectric detection means

Abstract

A device for measuring small distances, provided with a sensing tip mounted to be movable in the direction of the length to be measured, a transducer for converting the movements of the sensing tip into corresponding electric signals, and indicating means to indicate such signals. The transducer comprises an optical interferometer provided with a measuring waveguide. One end of the waveguide is connected to a laser and the other end to optical means for directing the light onto a measuring mirror disposed at a distance. The light is reflected by the mirror back to the optical means. The measuring mirror is connected to the sensing tip. The interferometer further includes a reference waveguide linked to the measuring waveguide. The reference waveguide has a mirror disposed at one end and a photoelectric transducer at the other end. The transducer is connected to the indicating means for indicating the output signals of the transducer. The device permits a cost-effective and uncomplicated construction as an integrated unit. The device affords precision measurements at accuracies in the range of one half of the wavelength of the laser beam, or even far below such a value. The device also exhibits a high linearity for substantially greater distances. The device is also suitable for measuring extremely rapid changes in length while using a small bearing pressure on the sensing tip.

Claims

1. A device for measuring small distances, said device including a sensing tip mounted to be movable in the direction of the distance to be measured, a transducer for converting the movements of said sensing tip into corresponding electric signals, and indicating means for indicating said electrical signals, characterized in that said transducer comprises:

a laser for emitting light;

an optical interferometer, said interferometer including first and second ends and a measuring waveguide, said first end interconnected to said laser;

optical means, interconnected to said second end of said measuring waveguide, for focusing said light; and

a measuring mirror, disposed at a distance from said optical means, for receiving said focused light and reflecting said light back to said optical means, said mirror being interconnected to said sensing tip;

said interferometer further including a reference waveguide coupled to said measuring waveguide, at one end having disposed a mirror and at its other end having disposed a photoelectric transducer connected to said indicating means for indicating the electric output signal of the photoelectric transducer.

2. A device as claimed in claim 1, wherein said optical means comprises a diffraction grating for deflecting the light substantially parallel onto the mirror.

3. A device as claimed in claim 1, wherein said measuring mirror is secured at one end to a two-arm lever, the other arm of which carries said sensing tip.

4. A device as claimed in claim 1, wherein said measuring mirror is secured to one end of a parallel extending measuring rod, the other end of which carries said sensing tip.

5. A device as claimed in claim 1, wherein said measuring mirror is comprised of a plane mirror.

6. A device as claimed in claim 1, wherein said measuring mirror is comprised of a triple mirror.

7. A device as claimed in claim 1, wherein said measuring mirror is comprised of a glass sphere.

8. A device as claimed in claim 1, wherein said indicating means consists of a counter.

9. A device as claimed in claim 8, wherein said reference waveguide is linked to a branch waveguide, one end of said waveguide being interconnected to another photoelectric transducer and being provided with phase adjusting means for adjusting the phase at said other photoelectric transducer, such that the phase of the light at said other photoelectric transducer is displaced by 90°

with respect to the phase of the light at the photoelectric transducer interconnected to said reference waveguide, whereby a rotating field is formed, and

means for determining the direction of rotation of the rotating field and, consequently, the direction of counting of the counter, said counter being constructed as an up and down counter.

10. A device as claimed in claim 9, wherein division means are provided for subdividing a cycle of the rotating field into a number of separate values, and wherein said separate values are counted by said up and down counter.

11. A device as claimed in claim 1, wherein the measuring waveguide, reference waveguide, and the branch waveguide are formed about the surface of a common plate, wherein the laser and the photoelectric transducer are directly disposed at an edge of the plate, at which edge the respective ends of the said waveguides terminate, and wherein the mirror disposed at one end of the reference waveguide is comprised of a reflecting coating applied to the lateral edge of the plate up to which said reference waveguide extends.

12. A device as claimed in claim 9, wherein the measuring waveguide, reference waveguide, and the branch waveguide are formed about the surface of a common plate, wherein the laser and the photoelectric transducers are directly disposed at an edge of the plate, at which edge the respective ends of the said waveguides terminate, and wherein the mirror disposed at one end of the reference waveguide is comprised of a reflecting coating applied to the lateral edge of the plate up to which said reference waveguide extends.

13. A device as claimed in claim 11, wherein said phase adjusting means consist of two electrodes which extend on each side of the branch waveguide and are connected to an adjustable direct voltage source.

14. A device as claimed in claim 12, wherein said phase adjusting means consist of two electrodes which extend on each side of the branch waveguide and are connected to an adjustable direct voltage source.

15. A device as claimed in claim 11, wherein said optical means focusing the light onto said measuring mirror consists of a diffraction grating disposed on the surface of the plate.

16. A device as claimed in claim 12, wherein said optical means focusing the light onto said measuring mirror consists of a diffraction grating disposed on the surface of the plate.

17. A device according to claim 1, wherein said photoelectric transducers and laser are integrated in the plate.