ELECTROMAGNETIC SENSOR SYSTEMS

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. Patent Application S.N. 11/846,907, entitled ELECTROMAGNETIC SENSOR SYSTEMS, filed on August 29, 2007, which in turn claims priority of U.S. Provisional Patent Application S.N. 60/841,061, entitled INDUCTION LINEAR SENSOR SYSTEM, filed on August 30, 2006, of U.S. Provisional Patent Application S.N. 60/841,322, entitled HIGH TEMPERATURE INDUCTIVE SENSOR, filed on August 31, 2006, and of U.S. Provisional Patent Application S.N. 60/853,568, entitled BRAKE LINING THICKNESS SENSOR, filed on October 23, 2006, all of which are also incorporated by reference herein.

BACKGROUND OF THE INVENTION

These teachings relate to electro-mechanical measurement and control systems.

As digital electronic information processing has improved, the search has developed for digital signal sources to indicate physical parameters for measurement and system control. Interfaces have been developed that allow analog sensing devices to be used with digital controls. However, there remains a need for sensors that have digital output and integrate seamlessly with digital equipment.

When high-speed position measurement is made with conventional devices that employ a magnetic field there is a delay between the actual position and the indicated position. This delay is

referred as measurement hysteresis. This measurement hysteresis is undesirable in practice.

Material considerations have discouraged the use of inductive proximity sensors at temperatures above 26Oo C. Conventionally used copper magnet wire may experience oxidation of the wire and degradation of its insulation at high temperature. Some assembly techniques have used materials that are unsuitable for exposure to high temperatures.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, the system of these teachings includes an oscillator circuit. In one instance, the sensing element is a variable reactance element.

For a better understanding of these teachings, together with other and further needs thereof, reference is made to the accompanying drawings and detailed description and its scope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure Ia is a schematic representation of an embodiment of the system of these teachings;

Figure Ib is a schematic representation of another embodiment of the system of these teachings;

Figure Ic is a schematic representation of yet another embodiment of the system of these teachings;

Figure Id is a schematic representation of a further embodiment of the system of these teachings;

Figure Ie is a schematic representation of a yet a further embodiment of the system of these teachings; Figures 2a-2d depict an embodiment of a sensing element of these teachings,- Figures 3a-3d depict an embodiment of a component of a physical structure of these teachings;

Figures 4a-4c show another embodiment of a component of a physical structure of these teachings;

Figures 5a-5f and 6a-6c show another embodiment of a sensing element of these teachings; and

Figures 7 depicts a schematic representation of a further embodiment of the system of these teachings.

DETAILED DESCRIPTION An embodiment of the system of these teachings is shown in Fig. Ia. The circuit shown in Fig. Ia is a tuned oscillator circuit. The tuned oscillator circuit is comprised of an amplifier (UIa, UIb, and UIc) and two reactive components, an inductor Ll and a capacitor C4. Ll and C4 are in series connection with C4 connected to ground (return) and Ll connected to the output of the amplifier (UIa, UIb, and UIc) . The frequency of the oscillator is:

F=-

2WiI*C

In one embodiment, the inductor Ll is a variable inductor and is the sensing component. In that embodiment, the capacitor C4 is a fixed value capacitor (fixed capacitance) . In another

embodiment, the physical structure that comprises the inductor Ll also exhibits variable capacitance (as, for example, but not limited to, the situation in which the electric and magnetic fields of physical structure are modified while performing a measurement) . It should be noted that the conventional sources of DC and oscillator power are not shown in Figure Ia (or in the subsequent figures, Figures Ib, Ic, Id and Ie) . The placement and configuration of such sources is conventional .

In one embodiment, the amplifier (s) (having sections UIa, UIb, and UIc) shown in Fig. Ia is a high speed CMOS hex inverter. The resistor R2 can be used to bias the input of the amplifier to compensate for the leakage current. The resistor R3 and capacitor C3 provide the feedback path. The oscillator is AC coupled by capacitor C3 so that there is no DC voltage path through the oscillator. Resistor R2 can influence the feedback path of the circuit. In one embodiment, the resistance value of R2 can chosen so that when the variable reactance is obtained by placing a conducting non magnetic surface, such as, but not limited to, copper, in proximity to a magnetic field producing component, such of variation of reactance will cause will cause the frequency of the circuit to increase, while, when a ferromagnetic surface, such as, but not limited to, steel, is placed proximity to the magnetic field producing component, such a variation will cause the frequency to decrease .

In another embodiment, a transistor amplifier or operational amplifier can be used in place of hex inverter UIa, UIb, and UIc. In one instance, two signals can be generated from the oscillator for use as output. One signal is a square wave and the other signal is a sine wave, both have the same frequency.

Another embodiment of the system of these teachings is shown in Fig. Ib. In Fig. Ib, Capacitors Cl and C2 replace capacitor C4 of Fig. Ia. Capacitors Cl and C2 are connected in parallel and have an equivalent capacitance equal to the sum of the capacitance of capacitors Cl and C2. In one instance, the two capacitors Cl and C2 provide temperature compensation in the circuit. In that instance, capacitor Cl has a capacitance vs. temperature relation that is positive. Capacitor C2 has a capacitance vs. temperature relation that is negative. By judicious choice of the capacitance values of Cl and C2 temperature induced frequency drift of the sensor output can be minimized. In another embodiment, the capacitance versus temperature relationship of each of the two capacitors Cl and C2 is selected such that a desired variation of the sensor output versus temperature can be obtained. In the embodiment shown in Fig. Ib, UIa, UIb, and UIc are three sections of a 74HC04 hex inverter.

Yet another embodiment of the system of these teachings is shown in Fig. Ic. In Fig. Ic, the variable reactance Ll of Fig. Ib is replaced by a number of variable reactances L2 , L3 , L4 , where each one of the variable reactances is connected in parallel to the other variable reactances. In the embodiment

of the system of these teachings shown in Fig. Ic, variation of any one of the variable reactances L2, L3 , L4 will result in a change in the oscillator frequency.

Further embodiments of the system of these teachings are shown in Figs. Id and Ie. Referring to Figure Id, the embodiment shown therein includes a first oscillator circuit 15, which in this embodiment is the circuit of Figure Ia, and a second oscillator circuit 35. The output of the first oscillator circuit 15 is a sensor output 25. The second oscillator circuit 35 has a substantially fixed (other than due to temperature variations) inductor L2 , a third capacitor C5 , the inductor L2 being separated from ground by the third capacitor C5, a fourth capacitor C6 located in the feedback path from the connection between the inductor L2 and the third capacitor C5 to a second amplifier (U2d, U2e, U2f) . The output 45 of the second oscillator circuit 35 is a compensation signal output. The first oscillator circuit 15 is located in substantial proximity to the second oscillator circuit 35 and both the first oscillator circuit 15 and the second oscillator circuit 35 experience substantially a same temperature {in some instances, the variable reactance Ll is located away from the rest of the first oscillator circuit 15) . A computer subsystem (such as, but not limited to, a microprocessor subsystem in one instance) receives the sensor output 25 and the compensation signal output 45. The computer subsystem includes one or more processors 55 and one or more computer readable media 65. The computer readable media 65 has computer readable code embodied therein for causing the

processors 55 to utilize the compensation signal output 45 in order to substantially compensate the sensor output 25 for temperature induced variations such as, but not limited to, temperature induced drift. The one or more processors 55 and are one or more computer readable media 65 are operatively connected by an interconnection component 67 (for example, a computer bus) . The compensation signal output 45 and the sensor output 25 are also provided to the interconnection component 67.

Depending on the nature of the compensation signal output 45 and the sensor output 25, the signals are provided to the interconnection component 67 by different means. If the signals can be provided directly to the digital circuit, a direct connection to the interconnection component 67 is possible. In other instances, the compensation signal output 45 and the sensor output 25 are provided to the interconnection component 67 by interface circuits. The interface circuits are conventionally determined by the nature of the compensation signal output 45 and the sensor output 25 and the digital circuit. The nature of the compensation signal output 45 and the sensor output 25 is determined by a variety of factors including, but not limited to, signal amplitude and signal range.

In one instance, the third capacitor C5 may be chosen with a capacitance versus temperature characteristics that results in a predetermined temperature variation of the compensation signal output 45. In one instance, a substantially large

(predetermined) change in output corresponds to to a change in temperature. In one instance, the amplifiers U2d, U2e, U2f are part of the same integrated circuit as the amplifiers U2a, U2b, U2c. (for example, a 74HC04) .

Referring to Fig. Ie, the first oscillator circuit 15 in the embodiment shown therein is the same circuit as the circuit of Figure Ib. The two capacitors Cl and C2 can be selected such that a desired temperature variation of the sensor output 25 is obtained. In one instance, these teachings not being limited only to that instance, the first oscillator circuit 15 and the second oscillator circuit 35 are configured such that the (frequency) sensor output 25 and compensation signal output 45 increase with increasing temperature in a predetermined manner (in one instance, in substantially the same manner) . In one possible embodiment, the variable reactance Ll is obtained in a manner that the sensor output 25 (frequency) increases or decreases upon measurement. In that embodiment, a predetermined difference between the sensor output 25 (frequency) and the compensation signal output 45 (frequency) will indicate a predetermined measurement.

It should be noted that embodiments of the sensor circuits shown in Figs. Id and Ie in which the variable reactance Ll is located at a distance from the rest of the first oscillator circuit 15 (such as the embodiment shown in Figure 7 below) are within the scope of these teachings.

During measurement, when utilizing the embodiments shown in Fig. Id and Ie, a sensor output is obtained from a first oscillator circuit including a variable reactance, a compensation signal output is obtained from a second oscillator circuit having a substantially fixed inductor, and the compensation signal output is utilized in order to substantially compensate the sensor output for temperature variations. An exemplary embodiment is presented hereinabove. Other embodiments in which at least the temperature variation of the second oscillator circuit 35 is substantially predetermined (or designed to be substantially predetermined) are also possible.

Embodiments in which the temperature variation of the second oscillator circuit 35 (and the first oscillator circuit 15 in some instances) is predetermined by calibration or predetermined by design are both within the scope of these teachings .

In one embodiment the variable reactance is obtained from a physical structure. In one instance the physical structure includes a substantially linear element (substantially linear as used herein refers to material properties such as a substantially conducting element or a material having a substantially linear permeability; see, for example, the number of structures 9 in Fig. 3b) and a sensing element for generating electromagnetic fields (see, for example, the sensing element 4 in Fig. 3c) . The substantially linear element and the sensing element can move with respect to each

other and the spatial relationship between the substantially linear element and the sensing element determines the variable reactance. Embodiments in which the substantially linear element and a sensing element move in a direction substantially parallel to a central axis of the sensing element or move in a direction substantially perpendicular to the central axis of the sensing element are within the scope of these teachings .

One embodiment of the variable reluctance element (Ll in Fig. Ia, L2, L3 or L4 in Fig." Ic) is shown in Figures 2a-2d, Figures 3a-3d and Figures 4a-4c. Referring to Figures 2a-2d, the sensing element shown therein includes a first end portion, a second end portion and a central portion (labeled 3 in Figure 2a) disposed on a base portion (1, Figures 2a-2d) and a coil 2, capable of carrying an electrical current, disposed (or wound) around the central portion 3. The first end portion, the second end portion, the central portion and the base portion are comprised of a substantially magnetic material (a substantially magnetic material, as used herein, refers to a ferromagnetic or a ferrimagnetic material) . Fig 2a and Fig 2b are two elevations of a sensing element (ferrite core) 4 in a structure conventionally referred to as an E core. The structure shown therein has width dimension "A" and length dimension "B" . When the coil 2 is energized by an electrical current, an electromagnetic field is projected from the faces of the end portions and the central portion 3. In one instance, the core shown therein is comprised out of a ferrite material. Fig 2c and Fig 2d show two elevations of

the ferrite core with electrical coil 2 assembled into a sensing element 4.

In one embodiment, an exemplary instance of which is shown in Figures 3a-3d, the substantially linear element includes a number of substructures, where each substructure (5, Fig. 3a) is comprised of a substantially conductive material and a substrate 6, on which the substructures are disposed. In one instance the substrate 6 is comprised of a substantially magnetic material. Each substructure has a characteristic dimension representative of height above the substrate 6 (in the embodiment shown in Figures 3a-3d, the characteristic dimension is the thickness of the foil) . Each substructure 5 is disposed at a predetermined distance from the adjacent substructure (forming a linear array of substructures) .

In one exemplary embodiment, these teachings not be limited only to that exemplary embodiment, each substructure is a rectangle of metal foil (a substructure having a substantially planar rectangular surface and another substantially planar surface, the two surfaces being disposed at a predetermined distance from each other) that has width dimension "C" and length dimension "D" . The metal foil is made of non magnetic electrically conducting material, such as, but not limited to, copper or aluminum and may, in an exemplary embodiment, have thickness of 0.003 inches. Width dimension "C" is, in one exemplary instance, the same or greater than dimension "A" of sensing element 4 shown in Fig 2c. Length dimension ^λλ D" may, in an exemplary instance, be equal to length dimension "B" of

sensing element 4. Length dimension "D" may also be greater than length dimension "B" in which case the increased length dimension "D" may compensate for lateral misalignment of sensor 4 in its travel. Fig 3b shows an array of sensor target elements in relation to each other for use in one embodiment of these teachings. In general the elements 5 are arranged to make a uniform pattern (in one instance, similar to teeth of a rack gear) . The distance "E" between each element 5 may be equal to or greater than dimension "C" . Fig 3c and Fig 3d show the substructures 5 in relation to substrate 6 and sensing element 4 as used in one embodiment of these teachings. Elements 5 are fixed to substrate 6 in the pattern shown in Fig 2b. In one instance, the substrate 6 is a substantially magnetic material as steel, iron, or ferrite. Sensing element 4, in one instance, is positioned so that face of sensing element 4 is substantially parallel to the substructures 5 on substrate 6. The sensing element 4, in one embodiment, moves in a direction substantially perpendicular to dimension "D" of substructures 5, as indicated in Fig 3d, in such a manner as to traverse over the substructures 5.

In another embodiment, shown in Figures 4a-4c, the substantially linear element includes a first laminate layer 7 having a substantially adhesive surface. The first laminate layer 7 is disposed over the substructures 5. The substantially adhesive surface is adjacent to the substructures 5. The substantially linear element also includes a second laminate layer 8 having two substantially adhesive surfaces. The substructures 5 are disposed over one

of the two substantially adhesive surfaces. Another one of the two substantially adhesive surfaces is disposed over the substrate 6. In one exemplary embodiment, not a limitation of these teachings, the first laminate layer 7 may be a self- adhesive flexible polyester tape with glass filament reinforcements. The second laminate layer 8 may be self- adhesive tape with adhesive on both surfaces (for example, double-sided adhesive tape) . One adhesive surface is applied to the substructures. The other adhesive surface is applied to a substrate 6, which in one embodiment is comprised of a substantially magnetic material.

In an exemplary application of the circuit of these teachings shown in Figs. Ia or Ib, and the sensing element and substantially linear element shown in Figs. 3a-3d, the frequency output of the circuit of Figs. Ia or Ib can be provided as input to a microprocessor. In one instance, the output is utilized by the microprocessor in order to count each time the frequency attain some value in the midpoint of the range of frequencies. In one exemplary embodiment (not a limitation of these teachings) , if the frequency attains a value of 74 kHz when the face of the sensing element 4 is adjacent to a substructure 5 and the frequency attains a value of 66 kHz when the face of the sensing element 4 is adjacent to a region of the substrate 6 between two substructures 5, then a count or pulse {indicative that the sensing element 4 is at a location near the edge of the substructure 5) can be generated when the frequency attains a value of 69 kHz . The counts can be summed and from knowledge of the distance

between the substructures, an indication of distance can be determined from the sum.

in order to better illustrate the present teachings, another exemplary embodiment is disclosed hereinbelow. In the exemplary embodiment, not a limitation of these teachings, a coil of 170 turns of 34 AWG wire is assembled into a ferrite core of dimension 1/8 inch width and % inch length in order to form the sensing element 4. Copper elements comprising the substructures 5 have dimension 1/8 inch X ¹ A inch each and each element has thickness of 0.003 inch. The glass re enforced polyester lamination 9 has thickness 0.012 inches and is attached to a mild steel substrate 6.

In yet another embodiment of the system of these teachings, in order to operate above a predetermined temperature, the sensing element is comprised of a material having a Curie temperature above the predetermined temperature . In one instance, the coil 2 of Fig. 2d is encapsulated in a ceramic material. In another instance, after placing the encapsulated coil around the center portion of the core {as in Fig. 2d) , the sensing element 4 is encapsulated in a ceramic material.

An embodiment of an encapsulated sensing element is shown in Figures 5a-5f and 6a-6c. Referring to Figures 5a-5f, a core is shown therein having a first side portion 12, a second side portion 12, a center portion 14 and a base portion 16. The base portion 16 has a surface with a substantially circular area. Each of the side portion 12 are disposed along a

portion of the half-circumference of the substantially circular area and the center portion 14 has a cross- sectional area that is smaller than the substantially circular area of the base portion 16. The coil 20 is disposed around the center portion 14 and between the center portion 14 and the side portions 12. The wire comprising the coil 20 is encapsulated in a ceramic material. Leads 30 allow providing an electrical current to the coil 20.

In one exemplary embodiment, these teachings not being limited only to the exemplary embodiment, the coil 20 is made by winding aluminum magnet wire that has been anodized. The anodized surface on the wire provides electrical insulation for the wire. As the wire is wound onto a form to make the coil, ceramic cement is applied to the wire. The cement is allowed to cure and then the coil is removed from the winding tool. The cement used may be one of a number of conventional cements used for encapsulating or joining electrical heating elements and electrical lighting elements. (For example, these teachings not being limited only to this example, one source for the cement is Sauereisen.)

The material of the core 10 is chosen to have a Curie temperature above the temperature at which the sensing element will operate. In an exemplary embodiment (not a limitation of these teachings), the core 10 is a ferrite core. Many types of soft ferrite are conventionally available. For any particular sensing element, a ferrite material is chosen that has at least a predetermined magnetic permeability at the temperature

at which the sensing element will operate. For a high temperature sensing element, a material is chosen with a Curie temperature above the temperature at which the sensor will operate. There are various NiZn ferrite materials that have a Curie temperature above 32Oo C. These ferrite materials can be used to make inductive proximity sensors that will operate at these high temperatures. (In one exemplary embodiment, these teachings not being limited to only that embodiment, one source for the ferrite material is Ferroxcube) .

In the embodiment shown in Figures 5e and 5f , the coil 20 is assembled onto/into the core 10 of Figure 5a. The assembled sensing element is then encapsulated in a ceramic material. Figures 6a- 6c show and embodiment of the encapsulated sensing elements corresponding to the sensing element of Figures 5a- 5f. - The encapsulated sensing element includes the sensing elements 40 that has been encapsulated in a shell 80 of ceramic cement. Coil leads 30 may be joined to sensor leads 50 by crimping, welding, or brazing connections 60. The shell 80 encloses the sensing element 40 of Figures 5e and 5f and wire connections 60 and substantially prevents air (ambient gas) from coming in contact with the contents of the shell 80. In one instance, not a limitation of these teachings, shell 80 is formed by suspending the sensing element 40 with attached connections 60 to sensor leads 50 in a mold and filling the mold cavity with ceramic cement.

Figure 7 shows the embodiment shown in Figure Ib of the sensor circuit of the present teachings with the encapsulated sensing

element 70 of Figure 6c. It should be noted that these teachings are not limited only to the embodiment shown in Figure Ib. Other embodiments, for example, such as those shown in Figures Ia or Ic, are also within the scope of these teachings. In the embodiment shown in Figure 7, the sensing element 70 is separated from the rest of the sensor circuit by cable 90 so as to prevent the high temperature that affects the sensing element 70 from affecting the other components in the circuit.

While exemplary embodiments including specific materials have been disclosed hereinabove, it should be noted that these teachings are not limited to only those embodiments and all our exemplary embodiments are also within the scope of these teachings.

Not desiring to be bound by theory, the embodiments described above are not limited by the description of the physical mechanisms detailed above.

Elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same functions.

Each computer program within the scope of the claims below may be implemented in any programming language, such as assembly language, machine language, a high-level procedural programming language, or an object-oriented programming

language. The programming language may be a compiled or interpreted programming language .

Each computer program may be implemented in a computer program product tangibly embodied in a computer-readable storage device for execution by a computer processor. Method steps of the invention may be performed by a computer processor executing a program tangibly embodied on a computer-readable medium to perform functions of the invention by operating on input and generating output.

Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CDROM, any other optical medium, punched cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, or any other medium from which a computer can read. From a technological standpoint, a signal or carrier wave (such as used for Internet distribution of software) encoded with functional descriptive material is similar to a computer-readable medium encoded with functional descriptive material, in that they both create a functional interrelationship with a computer. In other words, a computer is able to execute the encoded functions, regardless of whether the format is a disk or a signal.

Although these teachings have been described with respect to various embodiments, it should be realized these teachings are also capable of a wide variety of further and other

embodiments within the spirit and scope of the appended claims .

What is claimed is: