Wireless system and method for collecting motion and non-motion related data of a rotating system

A wireless system for collecting data indicative of a tire's characteristics uses at least one open-circuit electrical conductor in a tire. The conductor is shaped such that it can store electrical and magnetic energy. In the presence of a time-varying magnetic field, the conductor resonates to generate a harmonic response having a frequency, amplitude and bandwidth. A magnetic field response recorder is used to (i) wirelessly transmit the time-varying magnetic field to the conductor, and (ii) wirelessly detect the harmonic response and the frequency, amplitude and bandwidth, associated therewith. The recorder is adapted to be positioned in a location that is fixed with respect to the tire as the tire rotates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to wireless sensing systems. More specifically, the invention is a wireless system for collecting data that can be used to determine multiple characteristics associated with a non-conductive rotating system such as tires, pulleys, propellers, etc. Collected data can be used to determine, for example, rotational speed, temperature of the rotating system, rotational direction, and conditions during manufacturing and/or rotational operation.

2. Description of the Related Art

Most vehicles use some type of inflated tire as the point-of-contact between the vehicle and a ground/road surface. The integrity of a vehicle's tires is critical to vehicle safety. Accordingly, a variety of sensor systems (e.g., surface acoustic wave transducers, radio frequency identification-based sensors, etc.) has been developed that provide for the monitoring of various tire parameters of interest. However, each of these systems requires a dedicated sensor for each type of parameter to be measured. This increases the complexity and cost of a tire health monitoring system.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a method and system for collecting data of rotating systems such as tires, pulleys and propellers.

Another object of the present invention is to provide a method and system for collecting tire data in a wireless fashion.

Still another object of the present invention is to provide a system and method for collecting a variety of types of tire data using a single sensor.

Yet another object of the present invention is to provide a system and method for collecting a variety of types of tire data using a single sensor that is a single component.

In accordance with the present invention, a wireless system for collecting data indicative of a tire's characteristics uses at least one electrical conductor having first and second ends and shaped to form a geometric pattern therebetween. The conductor so-shaped defines an open-circuit having no electrical connections that can store energy in a magnetic field and an electric field and transfer the energy between both fields. In the presence of a time-varying magnetic field, the conductor so-shaped resonates to generate a harmonic response having a frequency, amplitude and bandwidth. The conductor so-shaped is adapted to be positioned within a tire. A magnetic field response recorder is used to (i) wirelessly transmit the time-varying magnetic field to the conductor, and (ii) wirelessly detect the harmonic magnetic field response frequency, amplitude and bandwidth associated therewith. The recorder is adapted to be positioned in a location that is fixed with respect to the tire as the tire rotates.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings and more particularly toFIGS. 1 and 2, a wireless system for collecting tire data in accordance with an embodiment of the present invention is shown. InFIG. 1, a portion of a tire100is illustrated as it would appear if viewed from the center thereof whileFIG. 2is a cross-sectional view of tire100taken along line2-2inFIG. 1. Tire100has side walls102and a tread wall104that combine to define a generally U-shape cross-section as would be well understood in the art. The interior surface of tread wall104is referenced by numeral104A. In general, tire100is made from a rubber-based material and can have cords and/or metal belts (not shown) embedded therein as is well known in the art of tire construction. It is to be understood that the particular construction of tire100is not a limitation of the present invention.

In the illustrated embodiment, a wireless system for collecting tire data uses an open-circuit spiral trace sensor10and a magnetic field response recorder20. Although a spiral trace is shown, the sensor can be any open-circuit geometric pattern having no electrical connections that can store energy In a magnetic field and an electric field and transfer the energy between both fields. Sensor10is attached to interior surface104A of tread wall104so that sensor10is protected from elements outside of tire100. Details of sensor10are described in co-pending U.S. patent application Ser. No. 11/671,089, filed Feb. 5, 2007, the contents of which are hereby incorporated by reference and will be repeated herein to provide a complete description of the present invention.

Spiral trace sensor10is made from an electrically-conductive run or trace that can be deposited directly onto interior surface104A. Sensor10could also be deposited onto a substrate material (not shown) that is electrically non-conductive and can be sufficiently elastically flexible to facilitate mounting to the curved interior surface104A. The particular choice of the substrate material will vary depending on how it is to be attached to interior surface104A. In either case, sensor10is a spiral winding of conductive material with its ends10A and10B remaining open or unconnected. Accordingly, sensor10is said to be an open-circuit. Techniques used to deposit sensor10either directly onto interior surface104A or on a substrate material can be any conventional metal-conductor deposition process to include thin-film fabrication techniques. In the illustrated embodiment, sensor10is constructed to have a uniform trace width throughout (i.e., trace width W is constant) with uniform spacing (i.e., spacing d is constant) between adjacent portions of the spiral trace. However, as will be explained further below, the present invention is not limited to a uniform width conductor spirally wound with uniform spacing.

As is well known and accepted in the art, a spiral inductor is ideally constructed/configured to minimize parasitic capacitance so as not to influence other electrical components that will be electrically coupled thereto. This is typically achieved by increasing the spacing between adjacent conductive portions or runs of the conductive spiral trace. However, in the present invention, sensor10is constructed/configured to have a relatively large parasitic capacitance. The capacitance of sensor10is operatively coupled with the sensor's inductance such that magnetic and electrical energy can be stored and exchanged by the sensor. Since other geometric patterns of a conductor could also provide such a magnetic/electrical energy storage and exchange, it is to be understood that the present invention could be realized using any such geometrically-patterned conductor and is not limited to a spiral-shaped sensor.

The amount of inductance along any portion of a conductive run of sensor10is directly related to the length thereof and inversely related to the width thereof. The amount of capacitance between portions of adjacent conductive runs of sensor10is directly related to the length by which the runs overlap each other and is inversely related to the spacing between the adjacent conductive runs. The amount of resistance along any portion of a conductive run of sensor10is directly related to the length and inversely related to the width of the portion. Total capacitance, total inductance and total resistance for spiral trace sensor10is determined simply by adding these values from the individual portions of sensor10. The geometries of the various portions of the conductive runs of the sensor can be used to define the sensor's resonant frequency.

Spiral trace sensor10with its inductance operatively coupled to its capacitance defines a magnetic field response sensor. In the presence of a time-varying magnetic field, sensor10electrically oscillates at a resonant frequency that is dependent upon the capacitance and inductance of sensor10. This oscillation occurs as the energy is harmonically transferred between the inductive portion of sensor10(as magnetic energy) and the capacitive portion of sensor10(as electrical energy). In order to be readily detectable, the capacitance, inductance and resistance of sensor10and the energy applied to sensor10from the external oscillating magnetic field should be such that the amplitude of the sensor's harmonic response is at least 10 dB greater than any ambient noise where such harmonic response is being measured.

The application of the magnetic field to sensor10as well as the reading of the induced harmonic response at a resonant frequency is accomplished by magnetic field response recorder20. The operating principles and construction details of recorder20are provided in U.S. Pat. Nos. 7,086,593 and 7,159,774, S. E. Woodard, S. D. Taylor, “Measurement of Multiple unrelated Physical Quantities Using a Single Magnetic Field Response Sensor,” Meas. Sci. Technol. 18 (2007) 1603-1613, and S. E. Woodard, B. D. Taylor, Q. A. Shams, R. L. Fox, “Magnetic Field Response Measurement Acquisition System,” NASA Technical Memorandum 2005-213518, the contents of each being hereby incorporated by reference m their entirety. Briefly, as shown inFIG. 3, magnetic field response recorder20includes a processor22and a broadband radio frequency (RF) antenna24capable of transmitting and receiving RF energy. Processor22includes algorithms embodied in software for controlling antenna24and for analyzing the RF signals received from the magnetic field response sensor defined by sensor10. On the transmission side, processor22modulates an input signal that is then supplied to antenna24so that antenna24produces either a broadband time-varying magnetic field or a single harmonic field. On the reception side, antenna24receives harmonic magnetic responses produced by sensor10. Antenna24can be realized by two separate antennas or a single antenna that is switched between transmission and reception. For an operational scenario where tire100is mounted on a vehicle, recorder20is typically attached to the vehicle in a fixed location200, such as the vehicle's wheel well. Another option is to fixedly mount just antenna24in proximity to the tire while mounting processor22at another location in the vehicle.

As mentioned above, both the width of the sensor's conductive trace and the spacing between adjacent portions of the conductive trace can be uniform as shown inFIG. 1. However, the present invention is not so limited. For example,FIG. 4illustrates a sensor40in which the width of the conductive trace is non-uniform while the spacing between adjacent portions of the conductive trace is uniform. The lengths of the outer portion of the spiral trace are also annotated.FIG. 5illustrates a sensor50in which the width of the conductive trace is uniform, but the spacing between adjacent portions of the conductive trace is non-uniform. Finally,FIG. 6illustrates a sensor60having both a non-uniform width conductive trace and non-uniform spacing between adjacent portions of the conductive trace.

As described above, the length/width of the conductive t race and the spacing between adjacent portions of the conductive trace determine the capacitance and inductance (and, therefore, the resonant frequency) of a spiral trace sensor in the present invention. In addition, the sensor's resonant frequency can be modified by providing a dielectric material (i) that resides between adjacent portions of the sensor's conductive trace, or (ii) that encases the sensor's conductive trace. This is illustrated inFIGS. 7A and 7Bwhere a cross-sectional view of a sensor in accordance with the present invention (e.g., sensor10) has been embedded in tire100which comprises a dielectric material. For example, inFIG. 7A, sensor10is embedded in tread wall104such that it is flush with interior surface104A so that the dielectric material of tire100is under and between the conductive traces of sensor10. InFIG. 7B, sensor10is fully embedded/encased in tread wall104so that the dielectric material of tire100fully encases and protects sensor10. Placing sensor10on the inner wall of the tire also protects the sensor.

The completely wireless system having only one sensor as described above can be used to collect/record data about a tire. The sensor installed or embedded in the tire is powered and read by a magnetic field response recorder as the tire rotates during vehicle operation. As a result of being powered by a time-varying magnetic field from the recorder, the sensor resonates and the recorder collects/records the frequency, amplitude and bandwidth of the sensor's harmonic response. The present invention uses the attributes of the sensor's harmonic resonance to provide information about the tire. For example, the amplitude of the harmonic response can be used to determine the tire's rotation rate which, in turn, is indicative of vehicle speed and distance traveled. More specifically, since amplitude of the sensor's harmonic response will peak, at its point of closest approach10the magnetic field response recorder's antenna, one revolution of tire100is indicated each time the peak (or a threshold revel near the peak) is recorded. The time between such peak/threshold level detections can be used in a straight forward fashion to determine tire rotation rate and distance traveled.

The present invention can also be used to determine a number of attributes indicative of the tire's health. If the sensor is embedded within the dielectric material of the tire, tire monitoring in accordance with the present invention can begin daring the manufacture of the tire. That is, if a geometric-patterned sensor in accordance with the present invention is embedded in a tire prior to the curing thereof, the present invention can be used to monitor curing and establish a baseline harmonic response that can be used as a reference measurement for later operational monitoring of the tire. Furthermore, with the sensor embedded in the tire's dielectric material, the sensor is protected from damage, corrosion, etc.

Assuming a sensor of the present invention is embedded in the tire's dielectric material, the present invention can track the curing process by wirelessly powering the sensor and then periodically recording amplitude and frequency of the sensor's harmonic response. Until the tire's dielectric material cures, the embedded sensor's resonant frequency will change with phase changes in the curing dielectric material. Accordingly, the curing process is considered to be active until such time that the sensor's amplitude and frequency stabilize. At this point, the amplitude, frequency and bandwidth of the sensor's harmonic response define a baseline harmonic response that can be used when monitoring the tire during its useful life as will now be described.

A tire that includes a geometric-patterned sensor of the present invention is mounted on a vehicle's wheel (not shown) some time after the tire has cured. A magnetic field response recorder is also mounted on the vehicle in a fixed location that will allow the recorder to power the sensor and collect the harmonic response generated thereby as described above. By way of example,FIGS. 1 and 2will be referred to again where tire100includes sensor10and recorder20is fixed to a portion200of the vehicle (e.g., a wheel well) on which tire100is mounted.

As tire100rotates, recorder20wirelessly transmits a time-varying magnetic field that causes sensor10to resonate. Recorder20also wirelessly detects the sensor's harmonic response resulting from such resonation. Recorder20compares the cured tire's baseline frequency, amplitude and bandwidth to the sensor's current harmonic response attributes. By virtue of these comparisons, a number of physical attributes can be determined using just one sensor. For example, strain changes in the tire are indicated when there is a frequency change (relative to the baseline frequency) without a corresponding change in the bandwidth. Since stress is proportional to tire strain and since tire pressure is proportional to stress in the tire, strain can be used to indicate tire pressure.

Tire damage is indicated when the sensor's frequency is permanently shifted relative to the baseline frequency. That is, the permanent frequency shift indicates that the sensor's conductor is damaged (e.g., via a tire puncture or crack). Tire wear is indicated by gradual changes in frequency and amplitude relative to the tire's baseline frequency and baseline amplitude. If the tire includes steel belts in its construction, the present invention can also be used to monitor the tire for delamination, i.e., tire rubber and steel belt separation. More specifically, tire delamination is indicated when frequency decreases relative to the tire's baseline frequency while amplitude increases relative to the tire's baseline amplitude.

Tire temperature can also be monitored by comparing the bandwidth of the sensor's harmonic response (while the tire is being used) to the tire's baseline bandwidth. This can be explained briefly as follows. The sensor's resistance R is dependent upon temperature T, and can be referenced to a baseline resistance R0by the following relationship
R=R0(1+αT)  (1)
where
α=0.00427 and R0=R(0° C.)
or more generally
R2=R1[1+α1(T1−T2)]  (2)
where

When a sensor is electrically excited via Faraday induction at 0° C., the current in the sensor I0is

The inductance and resistance are the sum of the inductance and resistance, respectively, of all sensor portions. The capacitance is the sum of the capacitance from the spacing between the traces. Therefore, for n sensor portions,

The interrogation antenna (i.e., antenna24in recorder20) transmits a magnetic field of frequency ω, and the sensor has capacitance C and inductance L. The magnetic field response BRX(0° C.) produced by the geometric pattern at any point in space is

where the magnetic flux, ΦBTX, from the external transmitting antenna acting on the sensor is
ΦBTX=∫BTX·dS.(10)

BTXis a vector whose direction and magnitude are those of the magnetic field from the transmitting antenna. S is a surface vector whose direction is that of the surface normal and whose magnitude is the area of the sensor surface. In accordance with Faraday's law on induction, the induced electromotive force ∈ on the sensor is

The sensor trace is a series of portions with each portion having a length lias shown inFIG. 4. The responding magnetic field BRX(T) of the geometric pattern (sensor) is due to the combined response of each element dlialong all the sensor portions li. Each element dliis at a distance r from a point on the receiving antenna. The sensor response BRX(T) at any temperature T in degrees Celsius, in terms of the sensor electrical resistance at 0° C., is

BRX⁡(T)=[μ4⁢π][ⅆΦBTXⅆt⁢|t0S2+(1+0.00427⁢T)2⁢R2⁡(0⁢°⁢⁢C.)]⁢∑i=1n⁢∫li⁢⁢ⅆli⁢sin⁢⁢θr2.(12)
BRX(T) is dependent on temperature for fixed values of T, L and C and a reference response BRX(0° C.) . Note that any temperature could be used to establish a reference. Using this relationship, one can readily see that the bandwidth increases monotonically with temperature. The total sensor response received by the receiving antenna would be the summation of the response for each point on the antenna.

The advantages of the present invention are numerous. A single, geometric-patterned, open-circuit sensor mounted in a tire can provide a variety of tire data when wirelessly powered and read by a magnetic field response recorder. When the sensor is embedded in the tire during its manufacture, the present invention can also be used to monitor the tire's curing process. The sensor can be made from a lightweight conductive trace and will, therefore, not affect a tire's rotational balance. The present invention can be readily extended to work with any non-conducting rotating system such as pulleys, propellers, etc.

Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. For example, as shown inFIG. 8, a second sensor12having a unique resonant frequency can be positioned in tire100. Sensor12is spaced apart from the first sensor10in the direction of tire rotation. Using two sensors having unique resonant frequencies, the present invention can also be used to indicate a rotational direction of the tire. That is, if the resonant frequency of sensor10is f10and the resonant frequency of sensor12is f12where f10≠f12, the tire's direction, of rotation is indicated by the order in which the amplitudes of the two sensors' harmonic responses increase.FIG. 9illustrates a further embodiment of the present invention having an array300of spiral trace sensors (10a-10g). Other geometric patterns could also be used in the array. Sensor array300has all but two sensors (10aand10g) aligned. Although five aligned sensors (10b-10f) are shown, the present invention is not limited to a particular number. Any number of aligned sensors can be used. The two sensors10aand10gare placed adjacent to the aligned sensors so that they are inductively coupled to the aligned sensors, but not positioned along the same line. Although the non-aligned sensors are shown on opposite sides of the aligned sensors, they could be positioned along either side. The response recorder20with external antenna24is positioned to power and receive the responses from sensors10aand10g. Because sensors10b-10fare inductively coupled to sensors10aand10g, their responses will be superimposed upon both sensor10aand sensor10g. For an operational scenario where tire100is mounted on a vehicle, recorder20with external antenna24is typically attached to the vehicle in a fixed location200, such as the vehicle's wheel well. Alternatively, antenna24can be mounted in proximity to the tire while processor22is mounted at another location in the vehicle.FIG. 10illustrates sensor array300placed inside the tire. The array300is positioned so that sensors10aand10gare completely placed on the inner tire sidewall104b, therefore allowing their responses to not be attenuated by the tire's steel belts. Sensors10b-10fare positioned on the inner wall bottom surface104a, with a portion of each sensor placed upon the tire inner sidewall.FIG. 11illustrates a cross-sectional view of sensor array300placed inside the tire100. If any sensor in the array300should have its response change (as result of the change in a physical quantity that it is measuring), the change will manifest Itself in the responses of sensors10aand10g.

The array300is applicable to either steel belted or non-steel belted tires. Sensor10aand10ghave response frequencies ωaand ωgwhich are unique and separated in value from those of sensors10b-10f. Sensors10aand10gcan be used to determine wheel speed and direction. All sensors (10a-10g) can be used to measure rubber curing, tire pressure, rubber delamination, tire wear, tire damage and inner tire temperature. Sensor array300is placed along the inner wall of the tire in a manner that allows sensors10b-10fto extend beyond the tire's inner bottom wall onto the tires inner side wall. All sensors10a-10gare inductively coupled so that any damage such as puncture, tear or wear to either sensor will be discernable by measuring change in response to any sensor. The sensors generally to be measured are10aand10g. Each sensor (10a-10g) can have a unique frequency range that does not overlap with the other sensors. In an even further embodiment, sensor10aand10ghave unique frequency ranges, and sensors10b-10fhave the same frequency. Multiple arrays300can be placed along the inner wall of the tire so that the entire inner wall is completely covered with the sensors. Sensors10aand10gcan be interrogated using a recorder20whose antenna24is placed in the wheel well of a vehicle.

It is therefore to re understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.