Fiber optic displacement sensor

• US 5,808,730 A
• Filed: 04/08/1997
• Issued: 09/15/1998
• Est. Priority Date: 04/08/1997
• Status: Expired due to Fees

• Current Assignee: CeramOptec Industries Incorporated (Biolitec AG)
• Original Assignee: CeramOptec Industries Incorporated (Biolitec AG)
• Inventors: Danielian, George, Avacian, Alexej
• Primary Examiner(s): Font, Frank G.
• Assistant Examiner(s): Ratliff, Reginald A.
• Application Number:
  US08/826,933
• Time in Patent Office: 525 Days
• Field of Search: 356/73.1
• US Class Current: 356/73.1
• CPC Class Codes: G01D 5/34723 involving light-guides

Abstract

A device is provided for measuring angular displacement and rotational movement of a shaft or linear displacement of an object comprising a light source, a Multichannel Fiber Optic Bundle, an optical code wheel or linear scale with optical tracks for light modulation, including typically a raster and a reference mark, a system of photodetectors, amplifiers, comparators of analog signals and a digital electronic block. The device forms a sequence of electric pulses whose number is proportional to displacement, a set of pulses indicating zero position of the disk, and also a logic signal indicating the direction of the displacement. A multichannel fiber optic bundle provides channels for the transmission and collection of light from the light source to the sensing site and back to the photodetectors and for light intensity monitoring of the source. Special randomization of the fibers at the sensing element end of the multichannel fiber optic bundle into two or more channels and modulating the collected light signals by a raster splits the collected light signal into at least two channels and introduces a phase difference of 90° between the split channels. The electronic components of the device are connected with the sensing element with a multichannel fiber optic cable or the directly by the multichannel fiber optic bundle, which removes them from the often harsh environments surrounding the sensing element. This provides an important advantage for many practical applications over the prior art.

Claims

1. A fiber optic displacement sensor for indicating the angle displacement and the rotational movement of a shaft or linear displacement of an object, comprising:

a first multichannel fiber optic bundle (MFOB A) for light transmission, which is split at one end into at least two channels, with at least one Reference Fiber Optic Channel for monitoring light intensity level of a light source;

two optical tracks for light modulation, a first optical track having means for displacement modulation, and a second optical track having at least one section for detecting a reference position;

a second multichannel fiber optic bundle (MFOB B) for receiving modulated light having at least two channels to split said received light and to introduce a phase difference of about 90 degrees between said light in said at least two channels;

light detectors for receiving a modulated light and converting it into an electrical signal, said light detectors being connected to individual ends of said at least two channels of said second multichannel fiber optic bundle; and

wherein said second Multichannel Fiber Optic Bundle for receiving modulated light further comprises groups of optical fibers within each of said at least two channels, said fibers each having a fiber core with a diameter, D₁, such that D₁ <

W/2, where W is a period of modulation of said first type of optical track;

fiber core centers of said fibers are placed with spacing L₁ =m(W/4), m taking on integer values;

within one group (row) of fibers, fiber core centers of said fibers are placed within a light path of said optical track and have spacing between centers L₂ =n(W/2), n taking on integer values independently of m; and

distance L₃ between centers of said fibers included in different groups (rows) being given by L₃ =m(W/4).

2. A fiber optic displacement sensor according to claim 1, wherein said means for displacement modulation involves having alternating transmissive and non-transmissive sections on a raster illuminated by channels.

3. A fiber optic displacement sensor according to claim 1, wherein said means for displacement modulation involves having alternating reflective and non-reflective sections;

said first and second Multichannel Fiber Optic Bundles are joined in the receiving ends and light transmitting and light receiving make a reflective type of modulated light path;

fiber core centers of said fibers are spaced with step L₄ =m(W/4); and

receiving fibers are interlaced with transmitting fiber(s) at an end facing said optical tracks and all fibers are designed to snugly fit in a row or rows of said bundle.

4. A fiber optic displacement sensor according to claim 1, wherein each group of fibers bundled in one channel of said receiving bundle is connected with one single fiber, such that an opposite end of each said single fiber is connected with a light detector;

and said single fiber core has a diameter large enough to collect a majority of light which come from fibers within said attached channel of said bundle.

5. A fiber optic displacement sensor according to claim 2, wherein each group of fibers bundled in one channel of said receiving bundle is connected with one single fiber, such that an opposite end of each said single fiber is connected with a light detector;

and said single fiber core has a diameter large enough to collect a majority of light which come from fibers within said attached channel of said bundle.

6. A fiber optic displacement sensor according to claim 3, wherein each group of fibers bundled in one channel of said receiving bundle is connected with one single fiber, such that an opposite end of each said single fiber is connected with a light detector;

and said single fiber core has a diameter large enough to collect a majority of light which come from fibers within said attached channel of said bundle.

7. A fiber optic displacement sensor according to claim 1, wherein each group of fibers bundled in one channel of said transmitting bundle is connected with one single fiber, such that an opposite end of each said single fiber is connected with a light source;

and said single fiber core has a diameter large enough to transmit a majority of light from said source to said fibers within said attached channel of said bundle.

8. A fiber optic displacement sensor according to claim 2, wherein each group of fibers bundled in one channel of said transmitting bundle is connected with one single fiber, such that an opposite end of each said single fiber is connected with a light source;

and said single fiber core has a diameter large enough to transmit a majority of light from said source to said fibers within said attached channel of said bundle.

9. A fiber optic displacement sensor according to claim 3, wherein each group of fibers bundled in one channel of said transmitting bundle is connected with one single fiber, such that an opposite end of each said single fiber is connected with a light source;

and said single fiber core has a diameter large enough to transmit a majority of light from said source to said fibers within said attached channel of bundle.