WO1984004972A1

WO1984004972A1 - Transducer having fiber optic transmission system

Info

Publication number: WO1984004972A1
Application number: PCT/US1984/000871
Authority: WO
Inventors: Edgar A Hirzel
Original assignee: Crane Co
Priority date: 1983-06-10
Filing date: 1984-06-07
Publication date: 1984-12-20
Also published as: JP2554318B2; EP0146611A4; EP0146611A1; JPS60501571A

Abstract

An optical wheel speed transducer (20) having a first optical fiber (48) for transmitting light pulses of constant frequency and intensity to an interrupter (44) rotating at an angular velocity proportional to the angular velocity of the wheel (2). The intensity of the light pulses is modulated by the interrupter (44) as a function of the angular velocity of the wheel (2). A second optical fiber (49) transmits the intensity modulated light pulses passing through the interrupter (44) to a light-sensitive device (64) which converts the intensity modulated light pulses to amplitude modulated electrical pulses. A demodulator (68) converts the amplitude modulated electrical pulses to an electrical signal that represents the angular velocity of the wheel (2). The transmission of the light pulses through the system is used to test the continuity of the system and to discriminate light emitted by external sources. A pair of collimating lenses (50 and 52) is used to focus the light pulses transmitted between the two optical fibers (48 and 49) across the interrupter (44).

Description

TRANSDUCER HAVING FIBER OPTIC TRANSMISSION SYSTEM

BACKGROUND OF THE INVENTION

The present invention generally relates to an optical transducer system for accurately measuring the angular velocity of an optical wheel. Specifically, the present invention is directed to a wheel speed transducer system wherein the intensity of constant frequency light pulses is modulated as a function of the angular velocity of the wheel.

Prior art wheel speed transducer systems in- elude optical systems wherein a steady stream of light is transmitted through or reflected from an interrupter disc to a light-sensitive device adjacent the interrup¬ ter. An example of such a system is disclosed in U.S. Patent No. 3,698,772 issued October 17, 1972. While these optical systems are reasonably accurate, they cannot discriminate light entering the system from ex¬ ternal sources, such as landing lights, sunlight, etc., and light emitted by the system light source. These systems, therefore, are vulnerable to false wheel speed measurements caused by external light.

In fields other than wheel speed measurement, the prior art includes optical systems that test the continuity of light within the system, for example, U.S. Patent No. 4,091,280 issued May 23, 1978. These systems, however, are based on a constant light source so that continuity is checked by detecting the presence

OMPI _ of constant light. If applied to an optical wheel speed system, this type of continuity test could not discern constant light from an external source and, - therefore, would be susceptible to false wheel speed measurements caused by external light.

Prior art optical wheel speed systems are also prone to other problems which lessen their reli¬ ability and accuracy. In most systems, the light- sensitive device is located near the rotating wheel area and the necessary wires leading away from the light-sensitive device are highly sensitive to electro¬ magnetic interference, particularly since small signals are generally used in optical sensors. Such systems also have difficulty collecting light from the inter- rupter because of scattering. Finally, the location of the light source in close proximity to the associated rotating wheel subjects the system to light loss due to dust, dirt, and other foreign matter.

The prior art also includes magnetic or in- ductive wheel speed transducers, an example of which is disclosed in U.S. Patent No. 3,515,920, issued June 2, 1970. These magnetic systems are reasonably accurate and reliable at moderate wheel speeds but are particu- larly inadequate for measuring low and high wheel speeds. Low speeds are difficult to measure because the ampli¬ tude of the electrical signal generated to represent wheel speed is directly proportional to the angular velocity of the wheel. As the angular velocity of the wheel decreases to zero, the amplitude of the electri- cal signal also decreases to zero. These smaller ampli¬ tude signals are difficult to distinguish from signals caused by vibrations, electromagnetic interference, and other external stimuli. To overcome this problem, attempts have been made to increase the magnitude of

OMPI the magnetic flux of the system. The higher magnetic forces due to the cutting of the flux, however, can cause a resonance in the mechanical elements of the antiskid system that look like a wheel skid to the brake control system. Thus, present magnetic wheel speed transducers are not reliable for measuring low wheel speeds.

In addition, magnetic systems are unreliable at high wheel speeds. The electrical connection cables of magnetic systems have an inherent capacitance that attenuates high frequency control signals associated with high speeds. As the signal gets increasingly smaller, it is harder to detect.

Finally, magnetic wheel speed transducers are susceptible to electromagnetic interference which im¬ pairs their reliability at all speeds. By their nature, these systems necessarily include high impedance induc- tors and associated electrical wires that generally are located near the wheel or other moving parts in the transducer system. The wires that connect these ele¬ ments to a remote control box are highly susceptible to electromagnetic interference (EMI) and radio frequency interference (RFI).

It is apparent that the foregoing shortcomings of prior art wheel speed transducer systems can create potentially dangerous situations in certain applications, such as vehicle antiskid systems.

SUMMARY OF THE INVENTION

The present invention is directed to an im- proved optical wheel speed transducer system which provides more accurate and reliable measurements of wheel speed.

According to this invention, electromagnetic radiation pulses of a predetermined carrier frequency and constant intensity are directed to an interrupter which is driven by the rotation of the wheel. The in¬ terrupter modulates the intensity of these radiation pulses as a function of the angular velocity of the wheel. The intensity modulated radiation pulses are then collected from the interrupter, and a wheel speed signal is derived from the intensity modulation of the radiation pulses. The interrupter is arranged so at least low intensity radiation pulses are always output from the interrupter. Using the predetermined fre¬ quency of these intensity modulated radiation pulses, the continuity of the optical system can be verified, and radiation emanating from external sources can be distinguished. In the preferred embodiment, a single optical fiber transmits infrared light pulses from a light pulse generator to a lens that expands the diameter of the light, collimates it, and directs it to a first side of an interrupter disc. ,The interrupter disc is comprised of alternating transparent and opaque areas. The inten¬ sity of the light is modulated by the interference of the opaque areas of the interrupter disc and the opaque areas of an adjacent, similarly constructed code disc. A second collimating-type lens receives the intensity modulated light pulses passing through the code disc and transmits them via a second single optical fiber to a photosensor. The photosensor generates electrical signals of varying amplitude in response to the varying intensity of the light pulses. A demodulator then con- verts the amplitude modulation of the electrical signals to an electrical signal representing the angular velocity of the wheel. The demodulator is capacitively coupled to the photosensor so that electrical signals generated that are not of the carrier frequency are discriminated. Finally, a continuity check circuit tests for the carrier frequency of the electrical signals output from the photosensor and sends a signal to a visual display indicating the continuity or discontinuity of the system. The collimating lenses of the preferred system provide more efficient transmission and collection of light across the interrupter and code discs. Without, such lenses, the light transmitted from the end of an optical fiber diffuses outwardly. This diffused light is difficult to collect across an interrupter. Single optical fibers are used to provide improved light trans¬ mission efficiency into and out of the collimating lenses and greater flexibility in the design, manufac¬ ture, and cost of the transducer. Optical fibers also provide electromagnetic shielding of sensitive electrical elements and wires of the system, thereby reducing the effects of electro¬ magnetic interference. Furthermore, fiber optics elimi¬ nate light loss problems caused by dirt and dust in systems where the system light source is located near the wheel.

In the preferred embodiment of the invention, the above described advantages are employed to improve the performance of vehicular antiskid systems. This invention, however, may provide other beneficial uses. For example, in an airplane, accurate^" measurements of low wheel speed could be combined with other data to calculate the position of an aircraft with respect to the runway. This information then could be used to compute stopping distances.

These and other advantages of the present invention will be best understood by reference to the following detailed description of the preferred embodi¬ ment, taken in connection with the accompanying draw- ings. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an antiskid brake system including an optical wheel speed transducer of this invention; FIG. 2 is a sectional and schematic represen¬ tation of the preferred embodiment of the optical wheel speed transducer of this invention;

FIG. 3 is a sectional view of the preferred embodiment taken along lines 3-3 of FIGURE 2. FIG. 4 is a sectional view of the preferred embodiment taken along lines 4-4 of FIGURE 2.

FIG. 5 is a circuit diagram of a light pulse generator that may be used in the preferred embodiment of FIG. 2. FIG. 6 is a circuit diagram of a photosensor, amplifier, demodulator, continuity check, and display that may be used in the preferred embodiment of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, a preferred embodiment of the improved wheel speed transducer sys¬ tem of the present invention will be described in con¬ nection with the brake control system for an aircraft ^• wheel as shown in FIGURE 1. FIGURE 1 shows the major components of the antiskid brake control system which provides brake control for the brake 3 of a rotatable wheel 2. In this system, the wheel 2 is provided with an optical wheel speed sensor 4 which generates an electrical signal on a line 5 corresponding to the wheel speed of the wheel 2 and an electrical signal on a line 7 corresponding to the continuity of the optical system. The sensor 4 includes an optical wheel speed transducer 20, an optical signal processor 60, and single optical fibers 48 and 49 which pass optical signals between the processor 60 and transducer 20. A detailed description of the preferred embodiment of the wheel speed sensor 4 will be provided below in connection with FIGURES 2-6. The wheel speed signal on line 5 is passed to a skid control circuit 6 which is designed to use this information to control a servo valve 8 to prevent the wheel from skidding. The servo valve 8, which is also responsive to braking commands supplied by the pilot via the pilot transducer 10 and brake control circuit

12, operates to valve high pressure fluid from an input pressure line 13 to a wheel brake 3 via a brake line 17. The signal on line 7 is transmitted to a dis¬ play 14 in the cockpit to visually indicate the continu- ity or discontinuity of the system.

Referring now to FIGURE 2, the preferred embodi¬ ment of the optical wheel speed sensor 4 includes single optical fibers -48 and 49 connecting the optical. wheel speed transducer 20 to, a remotely located optical signal processor 60.

The transducer 20 includes a nonrotating adaptor assembly 22 which is secured to the axle of the wheel (not shown) . The body assembly 32 of the transducer is attached to the adaptor assembly 22 so that it also does not rotate, although the body assembly is removable and can be fixed to the adaptor assembly of any vehicle. An end cap 42 is fastened to the body assembly 32 by the alignment pins and locking helical coil 41.

A wheel drive coupling 24 is attached to the wheel so that it rotates at the same angular velocity as the wheel. The wheel drive coupling 24 is attached to a shaft drive coupling 26 by a screw 21 and flat washer 23. A lock wire 25 prevents the screw 21 from unthreading. The wheel drive coupling is positioned within the adapter assembly 22 by bearings 27, and the

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OMPI v WIPO ,Λ shaft drive coupling 26 is positioned within the adaptor ' assembly 22 by bearings 28. An annular retainer 30 positions the bearings 28 within the adaptor assembly 22. The shaft drive coupling 26 is connected to a drive coupling 34 by a screw 33. The drive coupling 34 in turn is attached to a drive coupling rotor 36, which is secured to a rotor assembly 40 by the hex socket set screw 35. The rotor 40 is positioned between the body assembly 32 and the end cap 42 by a wave washer. and bearings 39. All these elements cooperate to drive the rotor 40 at the same angular velocity as the wheel.

An annular interrupter disc 44 is secured to the perimeter of the rotor 40 so that it rotates at the same angular velocity as the wheel. FIG. 4 shows the face of this disc which comprises regularly spaced, alternating transparent and opaque areas. A nonrotat- ing, annular code disc 46 is secured to the end cap 42, adjacent the interrupter disc 44. The face of the code disc 46 contains the same pattern of transparent and opaque areas shown in FIG. 4 for the interrupter disc 44. The opaque areas of these two discs interact to vary the intensity of light pulses passing through the discs as a function of the rotation of the interrupter disc 44 and, therefore, as a function of the anguiar veloc- ity of the wheel. That is, the degree of overlap be¬ tween the opaque areas of the discs 44 and 46 determines the intensity of the light passing through the disc 46. When the transparent areas of the two discs are com¬ pletely aligned, fifty percent of the light incident to the interrupter disc 44 will be transmitted through the code disc 46--the other fifty percent will be absorbed by the opaque areas of the interrupter disc 44. When the opaque areas of the interrupter disc 44 completely coincide with the transparent areas of the code disc

OMPI ^/VATlO 46, virtually no light passes through the code disc 46 (although it is important that some light trickles through for reasons that will be explained below) . The rate at which the opaque areas modulate the intensity of light passing through the discs between full on and full off will correspond to the angular velocity of the wheel.

The number of opaque areas of the discs (along with the rotational speed of the wheel) determines the light pulse intensity modulation frequency. Increasing the number of opaque areas increases the sampling fre¬ quency and the resolution of the system. The present embodiment uses 200 opaque areas to be compatible with existing parameters but is not limited in principle. A single optical fiber 48 directs light from a light pulse generator 62 to a first side of the in¬ terrupter disc 44. This fiber is only about 100 micro¬ meters in diameter and is encased in a protective covering^' 53. The fiber is secured through the end cap 42 by a -split ring 45 and potting compound 47. As better shown in FIG. 3, a coupling shield 38, attached to the body assembly 32 by screws 37, guides the fiber optic 48 around the previously described rotating ele¬ ments. A lens 50 is connected to the terminal end of the fiber 48. This lens is enclosed in a metal jacket 51 which is fastened by its flange 54 to the body assembly 32 by screws 55. It is preferred that lens 50 is a SELFOC™ lens manufactured by Nippon Electric Co., America, Inc., Electron Devices Division, 3070 Lawrence Expressway, Santa Clara, California, United States of America. Though this type of lens is ordinarily used as a connector, in the present embodiment it is used as a lens to collimate the light transmitted by single

OMPI ξ NAT\C fiber 48 into a plurality of parallel beams that minimize the scattering losses that would otherwise occur from the end of single fiber 48.

One end of a second lens 52 is located adja- cent the output side of the code disc 46. The other end of this lens is attached to the single fiber optic 49. The lens also is enclosed in a metal jacket 51 and, preferably, is a SELF0C^w lens. This lens 52 co¬ operates with lens 50 to align the collimated light transmitted through the discs 44 and 46, and focuses the expanded light passing through the disc 46 down to the single fiber 49.

The collimating lenses 50 and 52, in connec¬ tion with the ^"single optical fibers 48 and 49, provide significant advantages over fiber optic bundles with respect to light transmission efficiency and the de¬ sign, manufacture, and cost of the transducer. Without these lenses, it is difficult to align light across the discs 44 and 46 because of diffusion of the light emitted from the fibers and because of scattering caused by the discs. The lenses overcome this problem by transmitting a collimated beam of light across the discs. The single optical fibers make it easier to couple light to and from these lenses due to the physi- cal nature of the lenses.

The light input to the interrupter disc 44 originates from the light pulse generator 62 located in the optical processor 60. This light pulse generator can be comprised of any conventional radiation pulse generator that emits pulses of electromagnetic radia¬ tion at a constant carrier frequency and intensity. A typical generator may be comprised of a square wave generator coupled to a light emitting diode (LED), as shown in FIG. 5. The square wave generator of FIG. 5

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^? AT_C≤> comprises an LM 193 amplifier and the Darlington tran¬ sistor pair Q^ -Qy , both of which cooperate to produce a 200 KHz current pulse train. These current pulses drive the LED to generate radiation pulses of constant intensity at a rate of 200 KHz. Fiber optic 48 is directly coupled to the LED to transmit these radiation pulses. It is preferred that the LED is easily coupled to the current pulse generator and that the LED emits ^'light in the infrared or near infrared region since presently available optical fibers and electro-optical devices are very efficient with these wavelengths.

It is also preferred that the light pulse generator 62 emits light pulses at a carrier frequency that is at least ten times greater than the highest frequency anticipated for the intensity modulation of the light pulses. The maximum intensity modulation frequency can be determined from the number of opaque areas on the interrupter disc 44, the number of revolu¬ tions of the interrupter disc 44 per foot (30 cm) traveled by the wheel, and the greatest anticipated braking speed of the vehicle. High ratios of the carrier frequency to the intensity modulation frequency are desirable because they provide more reference points to measure, Which improves the reliability of the measurements. On the other hand, a carrier frequency/intensity modulation frequency ratio below ten is too susceptible to error for safe operation of the transducer in an antiskid system.

The light passing through the output side of the code disc 46 is transmitted by the fiber 49 to a photosensor 64 located inside the optical processor 60. The photosensor generates electrical signals of varying amplitude in response to the varying intensity of the light transmitted by fiber optic 49. The electrical signals generated will be of the same carrier frequency and amplitude (intensity) modulation frequency as the optical pulses sensed by the photosensor. Thus, the amplitude modulation of the electrical signals repre- sents the angular velocity of the wheel and can be pro¬ cessed by conventional electrical circuits to derive the actual wheel speed.

The optical processor 60 also includes an amplifier 66 which amplifies electrical signals from the photosensor 64. Demodulator 68 demodulates the amplitude modulation of these signals to provide an electrical signal that is transmitted to a standard velocity converter 70. From this input, the velocity converter 70 generates a wheel speed signal in a well known manner.

The electrical signals leaving the -amplifier 66 are also input to a continuity check circuit 72, which checks the continuity of the system based on the carrier frequency of the opti-cal pulses. -Assuming for a moment that the optical system is intact, the discs

44 and 46 interact so that at least low intensity light pulses pass through the code disc 46, even when the transparent areas of the interrupter disc 44 are aligned with the opaque areas of^' the code disc 46. Thus, the photosensor 64 will always generate at least low-level electrical signals at the carrier frequency. The con- ■ tinuity check 72 detects the presence of the carrier frequency in the electrical signals and sends a signal over line 7 to the display 14 indicating the continuity of the system. Conversely, if the continuity circuit does not detect the carrier frequency, it will send a signal indicating the discontinuity of the system.

The performance of the elements of the opti¬ cal processor 60 may be affected by electromagnetic interference. Therefore, an electromagnetic shield 80 is provided for protection. In addition, the fiber optics 48 and 49 each can be as long as 50 feet, thereby physically isolating the optical processor 60 from the proximate area of the rotating wheel where it is difficult to shield the optical processor from electromagnetic interference.

For the present invention, any conventional photosensor 64, amplifier 66, demodulator 68, continu- ity check 72 and display 14 can be used. FIG. 6 illus¬ trates one embodiment of these elements, which will be described now.

Photosensor 64 is comprised of a reverse- biased photodiode D.. It is preferred that the photo- diode D- is a PIN photodiode because of its high frequency characteristics. This photodiode, however, has an inherent capacitance. Incident light generates a current in the photodiode which causes the voltage across the diode to vary. This changing voltage- charges and discharges the capacitance of the photo¬ diode, thereby limiting the high frequency response of the system. To overcome this limitation, the photo¬ diode D. is connected to the inverting input of a transimpedance amplifier A, as shown in FIG. 6. In this arrangement, the inverting input of amplifier A., is held at a virtually constant potential, even in the face of fluctuating photodiode current. Thus, the potential across the photodiode D. remains nearly constant. As a result, the voltage output of ampli¬ fier A. is directly proportional to the current generated in the photodiode D- .

The output of the amplifier A., is connected to the inverting input of an amplifier A_ which ampli¬ fies the input signal in a conventional manner. The amplifier A« also receives offset correction from an amplifier A₃ to eliminate drift in the system. This is accomplished by holding reference points T.. and T~ at the same potential. The output of the amplifier Ay is directed to the demodulator 68 and continuity circuit 72.

The demodulator 68 is comprised of a conven¬ tional diode and filter network which demodulates the amplitude modulation frequency of the signal output from amplifier A₂ in a manner similar to an AM radio. This demodulator also discriminates signals generated from external sources .because it is A/C coupled to amplifier A« via a capacitor C.._ . This capacitor is responsive to the carrier frequency of the light pulses generated by the light pulse generator 62. Thus, electrical signals generated by light from external sources are not coupled to the demodulator. The de¬ modulated output of the-.demodulator 68 is fed into a unity gain, voltage follower amplifier A_ς which'drives the signal to a standard antiskid velocity converter 70.

Since the interference of the rotating disc 44 and code disc 46 is never total, there will always be at least a low-level carrier frequency ripple at the non-inverting input of the amplifier A₄ if the optical system is intact. If, however, there is a break in the system, this signal will disappear. The amplifier A₄ is a conventional selective frequency trap-type circuit which is designed to detect the presence of the carrier frequency. For example, in the circuit shown in FIG. 6, the amplifier A₄ is a 200 KHz trap circuit which is set to detect the 200 KHz carrier frequency generated by the light pulse generator shown in FIG. 5.

The output of A₄ is input into the display board 14 to indicate the continuity or discontinuity of the optical system. When the output is high (system intact), the green LED is on and the red LED is off.^' Conversely, when the output goes low, the red LED is illuminated and the green LED is off. The circuits disclosed in FIGS. 5 and 6 are intended to be exemplary and should not limit the pre¬ sent invention in any way. A table of exemplary values for the components shown in these circuits is set out below. Other types of circuits could be readily adapted by one skilled in the art to perform the functions of the elements of the optical processor 60. For example, the demodulator 68 could derive a wheel speed signal from the amplitude modulation signal using a counter- type circuit to compute the rate of full intensity pulses passing through the code disc 46. The continuity check circuit 72 could detect the carrier frequency with a phase lock loop or a band pass filter.

TABLE

R_χ ^' ' 100K R₂ 294K

R₃ 100K

R₄ 4.32K-

R_? 340 ohms (2 W)

R₈ 85 ohms (6 W)

R_g 100K

R₁₀ 50K

R₁₁ 100K R 50K

R₁₃ 10K

R₁₄ 10K

R₁₅ 100K

R 10K

R_1Q 22M TABLE Cont'd)

R 10K

19 ^20 10K ^l21 3OK

301 ohms

^{^}22 • 361 ohms ^l23 435K ^l24 5IK ^l25

R 50 ohms 26 IK

27

22pF

47pF

22pF lOOpF

22μF

O.lμF

5pF

O.lμF

'8

0. lμF

O.lμF _.

'10

^:ιι O.lμF

O.lμF

^:12^' lOOOpF ^;13

15μF ^:14

33μF ^:15

2N2222A

2N3506 (heat sink)

2N2222 4 2N2222

LED OPCV 20H-P-100 (1)

MF0D104F (2)

(1) Manufactured by Nippon Electric Co.,

America, Inc., Electron Devices Div. , 3070 Lawrence Expressway, Santa Clara,

California, United States of America.

(2) Manufactured by Motorola, P.O. Box 20912,

Phoenix, Arizona, United States of America.

TABLE Cont'd)

^D2 1N914

^D3 1N914

^D4 3x 1N914 ( 3 )

^A1^"A5 CA3140

The device illustrated in FIGS. 2-6 operates as follows. The wheel drive coupling 24 is attached directly to the wheel so that it rotates at the same angular velocity as the wheel. This wheel drive^ coupl- ing 24 then cooperates with the shaft drive coupling

26, the drive coupling 34, the drive coupling rotor 36, and the rotor 40 to drive the interrupter disc 44 at the same angular velocity as the wheel.

The light pulse generator 62 of the optical processor 60 generates constant intensity infrared light pulses at a 200 KHz carrier frequency. These light pulses are transmitted to the SELFOC™ lens 50 via the single optical fiber optic 48. This lens expands . the diameter of the light pulses, collimates them, and directs them towards the face of the interrupter disc 44.

The opaque areas of the interrupter disc 44 cooperate with the opaque areas of the code disc 46 to modulate the intensity of the incident light pulses at their carrier frequency. That is, the rotation of the interrupter disc 44 relative to the code disc 46 will vary the degree of overlap of the opaque areas of both discs, thereby modulating the intensity of the light passing through the discs. Since the angular velocity of the interrupter disc 44 corresponds to the angular velocity of the wheel, the frequency at which the intensity of these light pulses is modulated will represent the angular velocity of the wheel.

(3) Three 1N914 diodes in series.

OMPI The SELFOC™ lens 52, located adjacent the output side of the code disc 46, receives the intensity modulated light pulses passing through the code disc 46 and focuses them down to the single optical fiber 49. This lens also cooperates with lens 50 to align the light pulses passing through the discs 44 and 46.

Fiber 49 transmits the light collected by lens 52 to the photosensor 64 located in the optical processor 60. The photosensor senses the photons transmitted by fiber 49 and generates electrical sig¬ nals of varying amplitude corresponding to the varying light intensity of the sensed light pulses. These electrical signals will be of the same carrier fre¬ quency and amplitude (intensity) modulation frequency as the light pulses. The amplifier 66 amplifies the signals generated by the photosensor 64 and sends them to the demodulator 68 and continuity check 72.

The demodulator 68 demodulates the amplitude modulation frequency of the electrical signals to deter- mine the angular velocity of the wheel. The demodulator is capacitively coupled to the amplifier 66 so that it also discriminates electrical signals generated by light from external sources. The signal from the demodulator 68 is input to the velocity converter 70 which- generates a wheel speed signal in a well known manner.

The continuity check circuit 72 detects the presence of the 200 KHz carrier frequency of the signals output from the amplifier A_ . As previously explained, the carrier frequency will always be present at the input of the continuity check 72 as long as the system is intact because at least low intensity light pulses always will pass through the discs 44 and 46. If the continuity circuit 72 detects the 200 KHz carrier fre¬ quency, it sends a signal to the display 14 indicating

OMPI that the system is intact. Conversely, if the continu¬ ity circuit 72 does not detect the 200 KHz carrier fre¬ quency, it sends a signal to the display 14 indicating that there is a break in the system. By using a 200 KHz carrier frequency, this system is able to discriminate light from external sources that is not of the carrier frequency. Thus, the wheel speed and continuity of the system can be measured vir¬ tually free of errors caused by external light. Of course, it should be understood that vari¬ ous changes and modifications to the preferred embodi¬ ment described above will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the pre- sent invention, and without diminishing its attendant advantages. It is, therefore, intended that all such changes and modifications be covered by the following claims.

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Claims

CLAIMS :

1. In an optical system for measuring the angu¬ lar velocity of a rotating wheel which can discriminate radiation from external sources, the combination com- prising: means for generating pulses of radiation at a selected frequency and constant intensity; interrupter means for modulating the ^'intensity of said radiation pulses; means responsive to the rotational movement of said wheel for driving said interrupter means at a rate that is a function of the angular velocity of said whee1; means for directing radiation pulses from said pulse generating means to an input side of said interrupter means; means for receiving from an output side of said interrupter means the radiation pulses modulated by said interrupter means, wherein the intensity of said radiation pulses is modulated by said interrupter means at a frequency that is a function of the angular velocity of said wheel; means for deriving from said intensity modu¬ lated radiation pulses received by said receiving means a signal that represents the angular velocity of said wheel; and means for discriminating radiation emanating from outside said optical system.

2. The invention of claim 1 wherein said direct- ing means comprises a first optical fiber having its distal end adjacent said pulse generating means and its proximal end adjacent said input side of said interrup¬ ter means.

3. The invention of claim 2 wherein said receiv¬ ing means comprises a second optical fiber having its proximal end positioned relative to said output side of said interrupter means to receive a portion of the radia- tion pulses modulated by said interrupter means and its distal end adjacent said deriving means.

4. The invention of claim 3 wherein said given frequency is at least one and one-half times the fre¬ quency of said intensity modulation.

5. The invention of claim 4 wherein said inter¬ rupter means comprises alternating regularly spaced radiation transmitting and opaque areas.

6. In an optical system for measuring the angu¬ lar velocity of a rotating wheel which can discriminate radiation emitted by external sources, the combination comprising: means for generating pulses of radiation at a predetermined frequency and constant intensity; interrupter means for modulating the inten- sity of said radiation pulses; means responsive to the rotation of said wheel for driving said interrupter means at a rate that is a function of the angular velocity of- said wheel; means for transmitting radiation having a first end adjacent said pulse generating means and a terminal end adjacent an input side of said interrupter means, whereby radiation pulses are transmitted from said pulse generating means to said input side of said interrupter means; first means for collimating radiation pulses transmitted to said input side of said interrupter means; means for receiving radiation having a receiv¬ ing end positioned relative to an output side of said interrupter means to receive a portion of the collimated radiation pulses modulated by said interrupter means, wherein the intensity of said radiation pulses is modu¬ lated by said interrupter means at a frequency that is a function of the angular velocity of said wheel; means for deriving from said intensity modu¬ lated radiation pulses a signal that represents ^'the angular velocity of said wheel, said deriving means located adjacent the other end of said receiving means; means for discriminating radiation emitted by external sources; and means for testing the continuity of said radia- tion pulses transmitted through said optical system between said pulse generating means and said deriving means.

7. The invention of claim 6 wherein said trans¬ mitting means comprises a first optical fiber having a first end adjacent said pulse generating means and a terminal end adjacent said input side of said inter¬ rupter means.

8. The invention of claim 7 wherein said receiv¬ ing means comprises second means for collimating radia- tion positioned relative to said output side of said interrupter means for receiving a portion of the radia¬ tion pulses modulated by said interrupter means, and a second optical fiber having a receiving end adjacent said second collimating means and its other end adja- cent said deriving means.

9. The invention of claim 8 wherein said given frequency is at least one and one-half times the fre¬ quency of said intensity modulation.

10. The invention of claim 9 wherein said inter- rupter means comprises alternating regularly spaced radiation transmitting and opaque areas.

11. In an optical system for measuring the angu¬ lar velocity of a rotating wheel which can discriminate radiation emanating from external sources and which is not sensitive to electromagnetic interference, the com¬ bination comprising: means for generating radiation pulses of a predefined carrier frequency and constant intensity physically located remote from said wheel; interrupter means for modulating the inten¬ sity of said radiation pulses mounted adjacent said wheel and having alternating regularly spaced opaque and radiation transmitting areas; means responsive to the rotation of said wheel for driving said interrupter means at a rate that is a function of the angular velocity of said wheel; first means for transmitting radiation having an input end adjacent said pulse generating means and an output end adjacent a first side of said interrupter means, whereby radiation pulses are transmitted from said pulse generating means to said first side of said interrupter means; first means for collimating radiation trans¬ mitted from said output end of said first transmitting means to said first side of said interrupter means; second means for collimating intensity modu¬ lated radiation pulses passing through said interrupter

J 3 EΛ

O PI Zπc means, wherein the intensity of said radiation pulses is modulated by said interrupter means at a frequency that is a function of the angular velocity of said wheel; second means for transmitting radiation having a receiving end adjacent said second collimating means and a terminal end located remotely from said wheel, whereby said intensity modulated radiation pulses are transmitted from said second collimating means to said terminal end; means for sensing said intensity modulated radiation pulses transmitted to said terminal end and for generating electrical signals having the same carrier frequency as said radiation pulses and an ampli¬ tude modulation frequency corresponding to the frequency of the intensity modulation of said radiation pulses, said sensing means located adjacent said terminal end of said second transmitting means; means for demodulating said amplitude modu¬ lated electrical signals to provide a signal that repre- sents the angular velocity of said wheel, wherein said demodulating means discriminates electrical signals generated by radiation from external sources; means for testing the carrier frequency of radiation incident -to said sensing means to check the continuity of said radiation pulses transmitted through said optical system between said pulse generating means and said sensing means; means for indicating when the continuity of said optical system has been broken; and means for shielding said pulse generating means, said sensing means, said demodulating means, and said testing means from electromagnetic interference.

12. The invention of claim 11 wherein said first transmitting means comprises a first optical fiber hav¬ ing an input end adjacent said pulse generating means and an output end adjacent said first collimating means, and wherein said first collimating means is located adjacent said first side of said interrupter means.

13. The invention of claim 12 wherein said second transmitting means comprises a second optical fiber having a receiving end adjacent said second collimating means and a terminal end adjacent said sensing means, and wherein said second collimating means is. located adjacent a second side of said interrupter means.

14. The invention of claim 13 wherein said carrier frequency is at least one and one-half times as great as the highest frequency anticipated for said intensity modulation.

15. The invention of claim 14 wherein said pulse generating means comprises means for generating pulses of infrared or near infrared light.

16. In an optical measurement system, the com¬ bination comprising: means for transmitting radiation; means for receiving radiation transmitted from said transmitting means; means for varying the intensity of radiation received by said receiving means in response to an ex¬ ternal stimulus; and collimating means for collimating radiation transmitted by said transmitting rr.eans.

17. The invention of claim 16 further comprising second collimating means for collimating radiation in¬ cident to said receiving means.