WO1988004780A1

WO1988004780A1 - Optic-magnetic speed sensor

Info

Publication number: WO1988004780A1
Application number: PCT/US1987/002713
Authority: WO
Inventors: Stephen Michael Emo
Original assignee: Allied Corporation
Priority date: 1986-12-22
Filing date: 1987-10-20
Publication date: 1988-06-30

Abstract

An electro-optic speed sensor for sensing the speed of rotation of a rotating member includes a magnetic core and a coil coupled magnetically to the core for sensing disturbances in the magnetic field of the core caused by the rotation of the rotating member. The disturbances in the magnetic field generate an electrical pulse in the coil, which is transmitted to an electrical circuit including one or more light emitting diodes, which emit a pulse of light in response to the electrical pulses. The light pulses are transmitted to a resolution circuit through a fiber-optic cable.

Description

OPTIC-MAGNETIC SPEED SENSOR Background of the Invention The present invention relates to devices for sensing the speed of an object, typically a rotating object, and in particular to such a device operable without an external power source for generating a light pulse signal as a function of speed that is transmit- table by means of a fiber optic conductor to a remote display and/or control device.

Electronic devices are being increasingly uti¬ lized to sense and manage the operation of machinery. Iⁿ o^ne such application, such electronic devices are utilized in electronic engine controls for gas turbine engines. In another such application, such control de¬ vices are utilized to monitor the rotational behavior of a vehicle's wheels and to control the application of braking pressure to avert skids. In the case of an electronic engine control, it is increasingly desirable to limit if not eliminate the use of electrical conduc¬ tors between sensors and controllers and the electronic control units to reduce the effects of EMI and EMP, lightning and other induced electrical noise. In the case of automotive applications, fiber optic connec¬ tions substantially reduce the effect of the various sources of electronic noise such as alternators, igni¬ tion systems, and the like. One particular type of transducer utilized in such systems is a speed transducer, that is, a device which generates a signal proportional to the speed of a machine such as a turbine engine or the wheel of a motor vehicle. Heretofore, transducers for generating such a speed signal have used electrical conductors to communi¬ cate with a remote electronic control or display or, in the alternative, have incorporated relatively expensive circuits for generating a light pulse signal suitable for transmission to the-electronic control unit. There therefore exists a need for an improved speed transducer which will produce a speed signal suitable for trans- mission by means of fiber optics which device is oper¬ able without an external power source or wiring, is rugged, and is relatively inexpensive.

Broadly, the present invention is an electro- optic speed sensor which comprises a housing enclosing an electric coil means electro magnetically coupled to a core. The core is mounted adjacent a moving object to define a variable air gap with the core. One of the core and the moving object is magnetic such that rel¬ ative movement therebetween produces a speed dependent variable magnetic flux in the electric coil causing it to generate an electrical pulse. A light emitting diode is mounted in the housing and electrically connected to the coil means to generate a pulse of light in response to each electrical pulse generated by the coil. In a specific embodiment of the invention, the housing incorporates means for attaching same to a fiber optic conductor. In yet another specific embodiment of the invention, a diode circuit is provided between the light emitting diode and the electric coil to improve the electrical performance thereof.

It is therefore an object of the invention to provide an improved speed transducer.

Another object of the invention is to provide such a transducer which produces a light pulse signal proportional to speed of an object.

Yet another object of the invention is to pro¬ vide a self contained electro-magnetic pulse generator connected to a light emitting diode to produce a light pulse signal proportional to the speed on object. Still another object of the invention is to provide such a transducer which requires no external power source.

Yet another object of the invention is to pro- vide such a transducer that is small, rugged, self con¬ tained, and inexpensive while exhibiting a high degree of reliability.

Brief Description of the Drawings These and other objects of the invention and the invention itself will be best understood in view of the following detailed description thereof taken in con¬ junction with the appended drawings wherein:

Figure 1 is electrical schematic of an electro- optic speed transducer in accordance with the present invention; and

Figure 2 is sectional view of an electro-optic transducer in accordance with the invention.

Description of the Preferred Embodiment

Referring first to Figure 1, the electro-optic transducer 10 comprises an electric coil 12 wound on a core 14 and having terminals 16, 18. A load resistor 20 is connected to terminal 16 electrically in series with the anode 22 of a light emitting diode 24. The cathode 26 of diode 24 is connected to the opposite terminal 18 of coil 12. A diode 28 is connected in parallel with diode 24 but in reverse polarity. A second light emit¬ ting diode 30 may, optionally, be connected electrically in parallel with light emitting diode 24 for redundancy. A moving object, illustrated in the form of a rotating toothed wheel 32 is disposed adjacent the core 14. The wheel 32 is made of a magnetically permeable material and it will be seen that its toothed surface will produce a variable magnetic coupling with core 14 and a corresponding variation in magnetic flux in the core 14. It will be recognized, of course, that the core 14 can be manufactured of a magnetically permeable material and toothed wheel 32 of a magnetized material or of a non-magnetic material with appropriate magnetic elements affixed thereto to produce the same effect.

Refering now to Figure 2, the magnetic core 14 and coil 12 are disposed within a housing 34 and the resistor 20 and diodes 22, 28 are similarly mounted within the housing 34. A fiber optic coupler 36 is de- tachably secured to the housing 34 by means of threads 38 and threads 40 are formed on the outer surface of the housing 34 to facilitate attachment thereof to a suit- able mounting bracket (not shown in the drawings) adja¬ cent the wheel 32. A fiber optic conducter 42 extends from the fiber optic coupler 36, the fiber optic conduc¬ ter 42 including a lens as at 44 positioned to receive the light from the light emitting diode 22 and conduct same to a remote electronic circuit (not shown in the drawings) .

In operation, it will be seen that as the wheel 32 or magnetic elements 33 move past the core 14, a mag¬ netic disturbance is created in the latter. This magne- tic disturbance produces a pulse of electrical energy in the coil 12. This pulse of electric energy passes via load resistor 20 through the light emitting diode 22 causing same to produce a pulse o radiant energy, typi¬ cally visible light, in response to each disturbance of the magnetic field in the core 14. This pulse of light is then transmitted via the fiber optic conductor 42 to a remote circuit where it can be sensed by a suitable photo detector. Since the pulses are directly propor¬ tional to the disturbances in the magnetic core 14, it will be recognized that these pulses are directly pro¬ portional to the speed of the element 32. In some em¬ bodiments, where extreme reliability is required, a redundant light emitting diode 46 may be provided in parallel with the light emitting diode 24.

The entire assembly is small and compact and will be seen to require no external power source. The light pulse, because it is transmitted via an optic conductor can be transmitted to a remote electronic circuit via a medium that does not respond to elec¬ tronic, magnetic, or similar electrical and radiation disturbances. The device requires no external source of energy. The device can be manufactured of various mate¬ rials thereby providing a device having high temperature resistance. In a working embodiment of the invention, the device provides a suitable pulse signal at a pulse frequency of 5 kHz to as high as 5500 kHz.

Although the present invention has been illus¬ trated and described in connection with example embodi- ments, it will be understood that this is illustrative of the invention, and is by no means restrictive, there¬ of. It is reasonable to be expected that those skilled in the art can make numerous revisions and additions to the invention and it is intended that such revisions and additions will be included in the scope of the following claims as equivalents of the invention.

Claims

CLAIMS What I claim is:

1. An electro-optic speed sensor comprising a housing, magnetic core means mounted in said housing means for generating a magnetic field therein, means for producing a disturbance in said magnetic field, coil means mounted i said housing and electro magnetically coupled to said core for generating an electrical pulse in response to each disturbance of the magnetic field of said core, a light emitting diode fixedly mounted in said housing, and circuit means electrically connecting said diode to said coil means, said diode emitting a pulse of light in response to each said electrical pulse.

2. The sensor of claim 1 wherein said magnetic core means includes a cylindrical magnet, said housing being an elongated cylindrical body, said magnet being disposed axially therein, said means for producing a disturbance in said magnetic field including a body of magnetically permeable material having an irregular surface movable in variable proximity with respect to said magnetic core.

3. The sensor of claim 1 wherein said core means includes a cylindrical element of magnetic mate¬ rial having said coil wound thereon, said means for pro¬ ducing a disturbance in said core including a movable body having at least one magnetic element fixedly secured in the surface thereof and movable into and out of proximity with said core.

4. The sensor of claim 1 further including a fiber optic conductor connected to said housing adjacent said light emitting diode and in optical connection therewith.

5. The sensor of claim 4 further including lens means disposed between said light emitting diode and said fiber optic conductor for concentrating the light emitted by said light emitting diode into said fiber optic conductor.

6. The sensor of claim 5 wherein said housing is an elongated, hollow cylindrical body, said core means comprising a cylindrical body of magnetized mate¬ rial disposed coaxially within said housing, said coil surrounding said core, one end of said core being con¬ tiguous with one end of said housing, said light emittrng diode being mounted within said housing at the end there¬ of opposite said core end, and further including coupling means for connecting said fiber optic conductor and said lens to said housing.