Method and apparatus for vibration detection Number:7,365,530 from the United States Patent and Trademark Office (PTO) owispatent

Title: Method and apparatus for vibration detection

Abstract: Apparatus for detecting vibration of an object adapted to rotate includes one or more vibration processors selected from: a direction-change processor adapted to detect changes in a direction of rotation of the object, a direction-agreement processor adapted to identify a direction of rotation of the object in at least two channels and identify an agreement or disagreement in direction of rotation identified by the at least two channels, a phase-overlap processor adapted to identify overlapping signal regions in signals associated with the rotation of the object, and a running mode processor adapted to identify an unresponsive output signal from at least one of the at least two channels. A method for detecting the vibration of the object includes generating at least one of a direction-change output signal with the direction-change processor, a direction-agreement output signal with the direction-agreement processor, a phase-overlap output signal with the phase-overlap processor, and a running-mode-vibration output signal with the running-mode processor, each indicative of the vibration the object.

Patent Number: 7,365,530 Issued on 04/29/2008 to Bailey,   et al.

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Inventors:	Bailey; James M. (Concord, NH), Doogue; Michael C. (Manchester, NH), Towne; Jay M. (Newbury, NH)
Assignee:	Allegro Microsystems, Inc. (Worcester, MA)
Appl. No.:	10/942,577
Filed:	September 16, 2004

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Related U.S. Patent Documents

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	Application Number	Filing Date	Patent Number	Issue Date
	10820957	Apr., 2004

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Current U.S. Class:	324/207.25 ; 324/207.26
Current International Class:	G01B 7/14 (20060101)
Field of Search:	324/207.25,207.26

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Primary Examiner: Aurora; Reena
Attorney, Agent or Firm: Daly, Crowley, Mofford & Durkee, LLP

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Parent Case Text

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CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of and claims the benefit under 35 U.S.C. .sctn.120 of U.S. patent application Ser. No. 10/820,957 filed Apr. 8, 2004, which application is incorporated herein by reference in its entirety.

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Claims

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What is claimed is:

1. Apparatus for detecting a vibration of an object adapted for rotation, comprising: a plurality of magnetic field sensors for generating an RDIFF signal proportional to a magnetic field at a first location relative to the object and an LDIFF signal proportional to a magnetic field at a second location relative to the object; at least two rotation detectors, wherein a first one of the rotation detectors is coupled to at least one of the magnetic field sensors and is responsive to the RDIFF signal for providing a first output signal indicative of rotation of the object and wherein a second one of the rotation detectors is coupled to at least one of the magnetic field sensors and is responsive to the LDIFF signal for providing a second output signal indicative of rotation of the object; and a vibration processor responsive to the first and second output signals from the at least two rotation detectors for detecting the vibration of the object, the vibration processor comprising one or more vibration detectors including: a phase-overlap processor to identify a first signal region associated with the RDIFF signal and a second signal region associated with the LDIFF signal, to identify a first overlap as an overlap of the first signal region and the second signal region, and to generate a phase-overlap output signal indicative of the vibration of the object in response to the first overlap.

2. The apparatus of claim 1, wherein the apparatus comprises two rotation detectors, each of a type selected from a peak-referenced detector and a threshold detector.

3. The apparatus of claim 1, wherein the apparatus comprises four rotation detectors, each of a type selected from a peak-referenced detector and a threshold detector.

4. The apparatus of claim 1, wherein the first signal region is associated with a percentage range of a peak-to-peak magnitude of the RDIFF signal and the second signal region is associated with a percentage range of a peak-to-peak magnitude of the LDIFF signal.

5. The apparatus of claim 4, wherein the percentage range of the peak-to-peak magnitude of the RDIFF signal is substantially equal to the percentage range of the peak-to-peak magnitude of the LDIFF signal.

6. The apparatus of claim 1, wherein the one or more vibration detectors includes another different type of vibration detector, the vibration processor further comprising a combining processor coupled to the one or more vibration detectors to combine output signals of the one or more vibration detectors to generate a vibration-decision output signal indicative of the vibration of the object.

7. The apparatus of claim 1, wherein the apparatus is configured for use in an automobile.

8. The apparatus of claim 1, wherein the first signal region is associated with a first percentage range spanning about seventy to eighty-five percent of a peak-to-peak magnitude of the RDIFF signal and the second signal region is associated with the first percentage range spanning about seventy to eighty-five percent of a peak-to-peak magnitude of the LDIFF signal.

9. The apparatus of claim 1, wherein the phase-overlap processor is also to identify a third signal region associated with the RDIFF signal and a fourth signal region associated with the LDIFF signal, to identify a second overlap as an overlap of the third signal region and the fourth signal region, and to generate the phase-overlap output signal indicative of the vibration of the object in response to the first and second overlaps.

10. The apparatus of claim 9, wherein the first signal region is associated with a first percentage range spanning about seventy to eighty-five percent of a peak-to-peak magnitude of the RDIFF signal, the second signal region is associated with the first percentage range spanning about seventy to eighty-five percent of a peak-to-peak magnitude of the LDIFF signal, the third signal region is associated with a second percentage range spanning about fifteen to about thirty percent of a peak-to-peak magnitude of the RDIFF signal, and the second signal region is associated with the second percentage range spanning about fifteen to about thirty percent of a peak-to-peak magnitude of the LDIFF signal.

11. The apparatus of claim 1, further comprising an output protocol processor coupled to the vibration processor, the output protocol processor for providing an output signal indicative of the vibration of the object and also indicative of the rotation of the object.

12. The apparatus of claim 11, wherein the output signal provided by the output protocol processor is indicative of the rotation of the object when no vibration is detected by the vibration processor, and wherein the output signal provided by the output protocol processor achieves a substantially static signal value when a vibration is detected by the by the vibration processor.

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Description

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to vibration detection, and in particular, to vibration detection methods and apparatus that can identify a vibration in an object adapted to rotate in normal operation.

BACKGROUND OF THE INVENTION

Proximity detectors (also referred to herein as rotation detectors) for detecting ferrous or magnetic objects are known. One application for such devices is in detecting the approach and retreat of each tooth of a rotating ferrous object, such as a ferrous gear. The magnetic field associated with the ferrous object is often detected by one or more magnetic field-to-voltage transducers (also referred to herein as magnetic field sensors), such as Hall elements or magnetoresistive devices, which provide a signal proportional to a detected magnetic field (i.e., a magnetic field signal). The proximity detector processes the magnetic field signal to generate an output signal that changes state each time the magnetic field signal crosses a threshold. Therefore, when the proximity detector is used to detect the approach and retreat of each tooth of a rotating ferrous gear, the output signal is a square wave representative of rotation of the ferrous gear.

In one type of proximity detector, sometimes referred to as a peak-to-peak percentage detector (also referred to herein as a threshold detector), the threshold signal is equal to a percentage of the peak-to-peak magnetic field signal. One such peak-to-peak percentage detector is described in U.S. Pat. No. 5,917,320 entitled DETECTION OF PASSING MAGNETIC ARTICLES WHILE PERIODICALLY ADAPTING DETECTION THRESHOLD, which is assigned to the assignee of the present invention.

Another type of proximity detector, sometimes referred to as a slope-activated or a peak-referenced detector (also referred to herein as a peak detector) is described in U.S. Pat. No. 6,091,239 entitled DETECTION OF PASSING MAGNETIC ARTICLES WITH A PEAK-REFERENCED THRESHOLD DETECTOR, which is assigned to the assignee of the present invention. Another such peak-referenced proximity detector is described in U.S. Pat. No. 6,693,419 entitled PROXIMITY DETECTOR, which is assigned to the assignee of the present invention. In the peak-referenced proximity detector, the threshold signal differs from the positive and negative peaks (i.e., the peaks and valleys) of the magnetic field signal by a predetermined amount. Thus, in this type of proximity detector, the output signal changes state when the magnetic field signal comes away from a peak or valley by the predetermined amount.

In order to accurately detect the proximity of the ferrous object, the proximity detector must be capable of closely tracking the magnetic field signal. Typically, one or more digital-to-analog converters (DACs) are used to generate a DAC signal, which tracks the magnetic field signal. For example, in the above-referenced U.S. Pat. Nos. 5,917,320 and 6,091,239, two DACs are used; one to track the positive peaks of the magnetic field signal (PDAC) and the other to track the negative peaks of the magnetic field signal (NDAC). And in the above-referenced U.S. Pat. No. 6,693,419, a single DAC tracks both the positive and negative peaks of the magnetic field signal.

The magnetic field associated with the ferrous object and the resulting magnetic field signal are proportional to the distance between the ferrous object, for example the rotating ferrous gear, and the magnetic field sensors, e.g., the Hall elements, used in the proximity detector. This distance is referred to herein as an "air gap." As the air gap increases, the magnetic field sensors tend to experience a smaller magnetic field from the rotating ferrous gear, and therefore smaller changes in the magnetic field generated by passing teeth of the rotating ferrous gear.

Proximity detectors have been used in systems in which the ferrous object (e.g., the rotating ferrous gear) not only rotates, but also vibrates. For the ferrous gear capable of unidirectional rotation about an axis of rotation in normal operation, the vibration can have at least two vibration components. A first vibration component corresponds to a "rotational vibration," for which the ferrous gear vibrates back and forth about its axis of rotation. A second vibration component corresponds to "translational vibration," for which the above-described air gap dimension vibrates. The rotational vibration and the translational vibration can occur even when the ferrous gear is not otherwise rotating in normal operation. Both the first and the second vibration components, separately or in combination, can generate an output signal from the proximity detector that indicates rotation of the ferrous gear even when the ferrous gear is not rotating in normal operation.

Proximity detectors have been applied to automobile antilock brake systems (ABS) to determine rotational speed of automobile wheels. Proximity detectors have also been applied to automobile transmissions to determine rotating speed of transmission gears in order to shift the transmission at predetermined shift points and to perform other automobile system functions.

Magnetic field signals generated by the magnetic field sensors during vibration can have characteristics that depend upon the nature of the vibration. For example, when used in an automobile transmission, during starting of the automobile engine, the proximity detector primarily tends to experience rotational vibration, which tends to generate magnetic field signals having a first wave shape. In contrast, during engine idle, the proximity detector primarily tends to experience translational vibration, which tends to generate magnetic field signals having a second wave shape. The magnetic field signals generated during a vibration can also change from time to time, or from application to application, e.g., from automobile model to automobile model.

It will be understood that many mechanical assemblies have size and position manufacturing tolerances. For example, when the proximity detector is used in an assembly, the air gap can have manufacturing tolerances that result in variation in magnetic field sensed by the magnetic field sensors used in the proximity detector when the ferrous object is rotating in normal operation and a corresponding variation in the magnetic field signal. It will also be understood that the air gap can change over time as wear occurs in the mechanical assembly.

Some conventional proximity detectors perform an automatic calibration to properly operate in the presence of manufacturing tolerance variations described above. Calibration can be performed on the magnetic field signal in order to maintain an AC amplitude and a DC offset voltage within a desired range.

Many of the characteristics of a magnetic field signal generated in response to a vibration can be the same as or similar to characteristics of a magnetic field signal generated during rotation of the ferrous object in normal operation. For example, the frequency of a magnetic field signal generated during vibration can be the same as or similar to the frequency of a magnetic field signal generated during rotation in normal operation. As another example, the amplitude of a magnetic field signal generated in response to a vibration can be similar to the amplitude of a magnetic field signal generated during a rotation in normal operation. Therefore, the conventional proximity detector generates an output signal both in response to a vibration and in response to a rotation in normal operation. The output signal from the proximity detector can, therefore, appear the same, whether generated in response to a vibration or in response to a rotation in normal operation.

It may be adverse to the operation of a system, for example, an automobile system in which the proximity detector is used, for the system to interpret an output signal from the proximity detector to be associated with a rotation in normal operation when only a vibration is present. For example, an antilock brake system using a proximity detector to detect wheel rotation may interpret an output signal from the proximity detector to indicate a rotation of a wheel, when the output signal may be due only to a vibration. Therefore, the antilock brake system might not operate as intended.

It may also be undesirable to perform the above-described proximity detector calibration in response to a vibration rather than in response to a rotation in normal operation. Since the conventional proximity detector cannot distinguish a magnetic field signal generated in response to a rotation in normal operation from a magnetic field signal generated in response to a vibration, the proximity detector may perform calibrations at undesirable times when experiencing the vibration, and therefore, result in inaccurate calibration.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for detecting a vibration of an object adapted to rotate in normal operation.

In accordance with the present invention, an apparatus for detecting a vibration in an object adapted to rotate includes a plurality of magnetic field sensors for generating an RDIFF signal proportional to a magnetic field at a first location relative to the object and an LDIFF signal proportional to a magnetic field at a second location relative to the object. The apparatus also includes at least two rotation detectors (also referred to alternatively as proximity detectors), one of which is coupled to at least one of the magnetic field sensors and is responsive to the RDIFF signal to provide a first output signal indicative of rotation of the object and the second one of which is also coupled to at least one of the magnetic field sensors and is responsive to the LDIFF signal to provide a second output signal indicative of rotation of the object. A vibration processor is responsive to the first and second output signals from the at least two rotation detectors for detecting the vibration of the object.

In one embodiment, the vibration processor includes at least one of a direction-change processor, a phase-overlap processor, and a direction-agreement processor. The direction-change processor is coupled to at least one of the rotation detectors to detect the vibration of the object in response to a change in the direction of rotation of the object as indicated by the output signal of the at least one rotation detector and to generate a direction-change output signal in response to the vibration. The phase-overlap processor identifies a first signal region associated with the RDIFF signal and a second signal region associated with the LDIFF signal, identifies an overlap of the first signal region and the second signal region, and generates a phase-overlap output signal in response to the overlap. The direction-agreement processor is coupled to the at least two rotation detectors to detect the vibration of the object in response to a disagreement in the direction of rotation of the object as indicated by output signals of the at least two rotation detectors and to generate a direction-agreement output signal in response to the vibration.

In accordance with yet another aspect of the present invention, a method for detecting a vibration in an object adapted to rotate includes providing a first output signal indicative of a rotation of the object with a first rotation detector, providing a second output signal indicative of the rotation of the object with a second rotation detector, detecting a change in direction of rotation of the object from the first and the second output signals, and generating a direction-change output signal in response to the change in direction

In one particular embodiment, the method can also include providing a third output signal indicative of the rotation of the object with a third rotation detector, providing a fourth output signal indicative of the rotation of the object with a fourth rotation detector, detecting a first direction of rotation of the object with the first rotation detector and with the second rotation detector, detecting a second direction of rotation of the object with the third rotation detector and with the fourth rotation detector, determining whether the first direction of rotation is the same as the second direction of rotation, and generating a direction-agreement output signal in response to the determination.

In yet another particular embodiment, the method can include detecting a magnetic field with a first magnetic field sensor at a first location relative to the object to provide an RDIFF signal, detecting a magnetic field with a second magnetic field sensor at a second location relative to the object to provide an LDIFF signal, identifying a first signal region associated with the RDIFF signal and a second signal region associated with the LDIFF signal, identifying an overlap of the first signal region and the second signal region, and generating a phase-overlap output signal in response to the overlap.

In accordance with yet another aspect of the present invention, the vibration processor includes a running mode processor and at least one of the direction-change processor, the phase-overlap processor, and the direction-agreement processor. The running-mode processor is coupled to the rotation detectors to detect the vibration of the object in response to an unresponsive one of the first and second output signals from a respective one of the first and second rotation detectors and to generate a running-mode-vibration output signal indicative of the vibration.

In accordance with yet another aspect of the present invention, a method for detecting a vibration in an object adapted to rotate includes providing a first output signal indicative of a rotation of the object with a first rotation detector and providing a second output signal indicative of the rotation of the object with a second rotation detector. The method further includes detecting an unresponsive output signal from among the first and second output signals and generating a running-mode-vibration output signal in response to the unresponsive output signal.

With these particular arrangements, the apparatus and method can discriminate a vibration from a rotation of the object.

In accordance with yet another aspect of the present invention, a peak-referenced detector for detecting rotation of an object adapted to rotate includes a DIFF signal generator adapted to generate a DIFF signal associated with a varying magnetic field generated by the object when rotating. The peak-referenced detector also includes mean for identifying a positive peak value corresponding to a positive peak of the DIFF signal, means for identifying a negative peak value corresponding to a negative peak of the DIFF signal, means for generating a first threshold as a first predetermined percentage below the positive peak value, and means for generating a second threshold as a second predetermined percentage above the negative peak value. A comparator can be used for comparing the first and second thresholds to the DIFF signal to generate an output signal indicative of the rotation of the object. In one particular embodiment, the first and second predetermined thresholds can each be about fifteen percent.

With this particular arrangement, the peak-referenced detector can use thresholds that are predetermined percentages away from the positive and negative peaks of the DIFF signal, unlike a conventional peak-referenced detector that uses thresholds that are a predetermined value away from the positive and negative peaks of the DIFF signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which:

FIG. 1 is a block diagram of a sensor containing a vibration processor according to the invention;

FIG. 2 is a block diagram showing rotation detectors that can be used in the sensor of FIG. 1 in greater detail;

FIG. 2A shows a series of waveforms associated with the rotation detectors of FIG. 2;

FIG. 2B is a block diagram of a circuit used to provide control signals to the rotation detectors of FIG. 2;

FIGS. 3-3B show a series of waveforms including magnetic fields, corresponding output signals of magnetic field sensors, corresponding output signals associated with rotation detectors, and corresponding output signals associated with a direction-change processor of FIG. 1 in response to a vibration of an object;

FIG. 4-4B show a series of waveforms including magnetic fields, corresponding output signals of magnetic field sensors, corresponding output signals associated with rotation detectors, and corresponding output signals associated with the direction-change processor of FIG. 1 in response to a rotation of the object in normal operation;

FIG. 5 shows a series of waveforms including magnetic fields, corresponding output signals associated with rotation detectors, and corresponding output signals associated with a direction-agreement processor of FIG. 1 in response to the vibration of the object and in response to the rotation of the object in normal operation;

FIG. 6 is a graph showing magnetic fields associated with a phase-overlap processor of FIG. 1 in response to the rotation of the object in normal operation;

FIG. 7 is a graph showing magnetic field signals and other signals associated with the phase-overlap processor of FIG. 1 in response to a vibration;

FIG. 8 is a flow chart showing a process of generating a direction-change output signal associated with the direction-change processor of FIG. 1;

FIGS. 8A and 8B together are a flow chart showing further details of the process of FIG. 8;

FIG. 9 is a flow chart showing a process of generating a direction-agreement output signal associated with the direction-agreement processor of FIG. 1;

FIG. 10 is a flow chart showing a process of generating a phase-overlap output signal associated with the phase-overlap processor of FIG. 1;

FIG. 11 is a block diagram of an alternate sensor containing a vibration processor according to the invention;

FIG. 12-12B show a series of waveforms including magnetic fields, corresponding output signals of magnetic field sensors, corresponding output signals associated with rotation detectors, and corresponding output signals associated with a running-mode processor of FIG. 11 in response to a vibration of an object;

FIG. 13 is a block diagram of a circuit that can be used to provide the running-mode processor of FIG. 11;

FIG. 14 is a flow chart showing a process of generating a running-mode-vibration output signal associated with the running-mode processor of FIGS. 11 and 13; and

FIG. 14A is a flow chart showing further detail associated with the process of FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION

Before describing the present invention, some introductory concepts and terminology are explained. As used herein, the term "rotational vibration" refers to a back and forth rotation of an object about an axis of rotation, which object is adapted to rotate in a unidirectional manner about the axis of rotation in normal operation. As used herein, the term "translational vibration" refers to translation of the object and/or of magnetic field sensors used to detect magnetic fields generated by the object generally in a direction perpendicular to the axis of rotation. It should be recognized that both rotational vibration and translational vibration can cause signals to be generated by the magnetic field sensors.

Referring now to FIG. 1, an exemplary sensor 10 includes a plurality of magnetic field sensors 14a-14c for generating an RDIFF signal 28 proportional to a magnetic field at a first location relative to an object 11 and an LDIFF signal 58 proportional to a magnetic field at a second location relative to the object 11. As described more fully below, the first and second locations correspond to right and left channels. The object 11 can be an object adapted to rotate, for example, a ferrous gear, which, in addition to unidirectional rotation in normal operation, is also subject to undesirable rotational and translational vibrations. The sensor 10 includes a right channel amplifier 16 providing the RDIFF signal 28 and a left channel amplifier 50 providing the LDIFF signal 58.

The sensor 10 also includes rotation detectors 12, including at least two rotation detectors as at least one of a right channel threshold detector 22 and a right channel peak-referenced detector 20, and at least one of a left channel threshold detector 56 and a left channel peak-referenced detector 54.

The right channel threshold detector 22 is responsive to the RDIFF signal 28 and provides a first output signal 26 (RThreshOut) indicative of a rotation of the object. The left channel threshold detector 56 is responsive to the LDIFF signal 58 and provides a second output signal 62 (LThreshOut) also indicative of the rotation of the object. The right channel peak-referenced detector 20 is responsive to the RDIFF signal 28 and provides a third output signal 24 (RPeakOut) further indicative of the rotation of the object. The left channel peak-referenced detector 54 is responsive to the LDIFF signal 58 and provides a fourth output signal 62 (LThreshOut) still further indicative of the rotation of the object.

The designations "left" and "right" (also L and R, respectively) are indicative of physical placement of the magnetic field sensors 14a-14c relative to the object 11 and correspond to left and right channels, where a channel contains the signal processing circuitry associated with the respective magnetic field sensor(s). For example, the magnetic field sensors 14a, 14b differentially sense the magnetic field at a location to the right of the object 11 and the right channel contains circuitry for processing the magnetic field thus sensed (e.g., right channel amplifier 16, R Peak-referenced detector 20, and R threshold detector 22). In the illustrative embodiment, three magnetic field sensors are used for differential magnetic field sensing, with the central sensor 14b used in both channels. While three magnetic field sensors 14a-14c are shown, it should be appreciated that two or more magnetic field sensors can be used with this invention. For example, in an embodiment using only two magnetic field sensors 14a, 14b, magnetic field sensor 14a can be coupled to the right channel amplifier 16 and magnetic field sensor 14b can be coupled to the left channel amplifier 50. The right channel includes magnetic field sensors 14a and 14b, the right channel amplifier 16, the right channel peak-referenced detector 20, and the right channel threshold detector 22. The left channel includes magnetic field sensors 14b and 14c the left channel amplifier 50, the left channel peak-referenced detector 54, and the left channel threshold detector 56. It will be appreciated that right and left are relative terms, and, if reversed, merely result a relative phase change in the magnetic field signals. This will become more apparent below in conjunction with FIGS. 8A and 8B.

The sensor 10 also includes a vibration processor 13 responsive to output signals from at least two rotation detectors 20, 22, 54, 56 for detecting the vibration of the object. The vibration processor 13 includes at least one of a peak direction-change processor 30, a threshold direction-change processor 36, a direction-agreement processor 40, and a phase-overlap processor 46. In one particular embodiment, the vibration processor 13 contains the threshold direction-change processor 36, the direction-agreement processor 40, and the phase-overlap processor 46.

The threshold direction-change processor 36 is described in greater detail in conjunction with FIGS. 3-4B, the peak direction-change processor 30 and the threshold direction-change processor 36 are described in greater detail in conjunction with FIGS. 8 and 8A, the direction-agreement processor 40 is described in greater detail in conjunction with FIGS. 5 and 9, and the phase-overlap processor 46 is described in greater detail in conjunction with FIGS. 6, 7, and 10. However, let it suffice here to say that the peak direction-change processor 30 and the threshold direction-change processor 36 detect the vibration of the object and generate respective direction-change output signals 32, 38 in response to the vibration. The direction-agreement processor 40 detects the vibration of the object and generates a direction-agreement output signal 42 in response to the vibration. The phase-overlap processor 46 also detects the vibration of the object and generates a phase-overlap output signal 48 in response to the vibration.

A combining processor 34 logically combines at least two of the direction-change output signal 38, the second direction-change output signal 32, the direction-agreement output signal 42, and the phase-overlap output signal 48 to provide a vibration-decision output signal 80 indicative of whether or not the object is vibrating. For example, in one particular embodiment, the logical combining is an OR function providing that if any of the direction-change output signal 38, the direction-change output signal 32, the direction-agreement output signal 42, and the phase-overlap output signal 48 indicates a vibration of the object, then the vibration-decision output signal 80 indicates the vibration accordingly, for example, as a high logic state.

However, in an alternate arrangement, the sensor 10, has one vibration processor, selected from among the peak-direction change processor 30, the threshold direction-change processor 36, the direction-agreement processor 40, and the phase-overlap processor 46, the selected one of which provides the vibration decision output signal 80.

It will become apparent from discussion below that the threshold direction-change processor 38, the peak direction-change processor 30, the direction-agreement processor 40, and the phase-overlap processor 46 can detect rotational vibration of the rotating object, for example, the rotating ferrous gear described above. It will also be apparent that the phase-overlap processor 46 can detect translational vibration of the object and/or of the magnetic field sensors 14a-14c. However, in other embodiments, any of the above-identified processors can be adapted to detect either the rotational vibration or the translational vibration or both.

The exemplary sensor 10 can also include a speed detector 64 to detect a rotational speed of the object and provide a corresponding speed output signal 66 indicative of a speed of rotation of the object, a direction detector 68 to detect a direction of rotation of the object and provide a corresponding direction output signal 70 indicative of the direction of rotation of the object, an air gap detector 72 to detect an air gap between one or more of the magnetic field sensors 14a-14c and the ferrous object and provide a corresponding air gap output signal 74 indicative of the air gap, and a temperature detector 76 to detect a temperature and provide a corresponding temperature output signal 78 indicative of the temperature.

An output protocol processor 82 is responsive to one or more of the output signals 66, 70, 74, 78 and to the vibration-decision output signal 80 for generating a sensor output signal 84 in accordance with the received signals. In one particular embodiment, for example, the output signal 84 has a first characteristic when the vibration-decision output signal 80 indicates a vibration, and a second characteristic when the vibration-decision output signal 80 indicates no vibration. For example, in one particular embodiment, the output signal 84 can be static (i.e., statically high or low) when the vibration-decision output signal 80 indicates the vibration, and can be active (e.g., an AC waveform having a frequency proportional to the speed output signal 66) when the vibration-decision output signal 80 indicates no vibration. In other embodiments, the output protocol processor 82 provides an encoded output signal 84 in accordance with one of more or output signals 66, 70, 74, 78, 80.

Referring now to FIG. 2, exemplary rotation detectors 102, which correspond to the rotation detectors 12 of FIG. 1, are shown in greater detail. A right channel corresponds to an upper half of FIG. 2 and a left channel corresponds to a lower half of FIG. 2. It will be appreciated that the left channel has characteristics similar to the right channel. For simplicity, only the right channel is described herein.

An input signal 104 from a right channel amplifier, e.g., the right channel amplifier 16 of FIG. 1, can include an undesirable DC offset. A right channel auto offset controller 106, a right channel offset digital-to-analog converter (DAC) 108 and a summer 110 are provided in order to eliminate the DC offset by known techniques. A right channel automatic gain controller (RAGC) 114 provides an RDIFF signal 136 having an amplitude within a predetermined amplitude range. Control of the RAGC 114 is further described below. It should be understood that the RDIFF signal 136 is representative of the magnetic field experienced by one or more magnetic field sensors, for example, the magnetic field sensors 14a, 14b of FIG. 1.

The RDIFF signal 136 is provided to a right channel peak (RPeak) comparator 116 and to a right channel threshold (RThresh) comparator 138. The RPeak comparator 116 also receives a threshold voltage 134 and the RThresh comparator 138 receives a threshold voltage 135. Generation of the threshold voltages 134, 135 is further described in conjunction with FIGS. 2A and 2B.

The threshold voltage 134 switches between two values, a first one of which is a first predetermined percentage below a positive peak of the RDIFF signal 136 and a second one of which is a second predetermined percentage above a negative peak of the RDIFF signal 136. In one particular embodiment, the first and second predetermined percentages are each about fifteen percent. The first threshold voltage 134 is, therefore, relatively near to and below a positive peak of the RDIFF signal 136 or relatively near to and above a negative peak of the RDIFF signal 136. Therefore, the RPeak comparator 116 generates an RPeakOut signal 118 having edges closely associated with the positive and negative peaks of the RDIFF signal 136.

The threshold voltage 135 also switches between two values, a first one of which is a first predetermined percentage of the peak-to-peak amplitude of the RDIFF signal 136 and a second one of which is a second predetermined percentage of the peak-to-peak amplitude of the RDIFF signal 136. In one particular embodiment, the first predetermined percentage is about sixty percent and the second predetermined percentage is about forty percent of the peak-to-peak amplitude of the RDIFF signal 136. Therefore, the RThresh comparator 138 generates an RThreshOut signal 140 having edges relatively closely associated with the midpoint, or fifty percent point, between the positive peak and the negative peak of the RDIFF signal 136.

The threshold voltages 134, 135 are generated by counters 124, 125, logic circuits 123, 127, a right channel PDAC 126, a right channel NDAC 128, comparators 122, 130, a resistor ladder 132 and transmission gates 133a-133d. The comparator 122 receives the RDIFF signal 136 and an output from the right channel PDAC 126, and, by way of feedback provided by the logic circuit 123 and the counter 124, causes the output of the PDAC 126 (i.e., the PDAC voltage) to track and hold the positive peaks of the RDIFF signal 136. Similarly, the comparator 130 receives the RDIFF signal 136 and an output from the right channel NDAC 128, and, by way of feedback provided by the logic 127 and the counter 125, causes the output of the NDAC 128 (i.e., the NDAC voltage) to track and hold the negative peaks of the RDIFF signal 136. Therefore, the differential voltage between the output of the PDAC 126 and the output of the NDAC 128 represents the peak-to-peak amplitude of the RDIFF signal 136. The outputs of the PDAC 126 and the NDAC 128 are described below in greater detail in conjunction with FIG. 2A.

The PDAC and NDAC voltages are provided to opposite ends of the resistor ladder 132. The transmission gates 133a, 133d provide the threshold voltage 134 as one of two voltage values as described above, depending upon the control voltages RPeakHyst and its inverse RPeakHystN applied to the transmission gates 133a, 133d respectively. Similarly, the transmission gates 133b, 133c provide the threshold 135 voltage as one of two voltage values as described above, depending upon the control voltages RThreshOut 140 and its inverse RThreshOutN applied to the transmission gates 133c, 133b respectively.

It should be recognized from the discussion above that the two states of the threshold voltage 134 are closely associated with the positive peak and the negative peak of the RDIFF signal 136, while the two states of the threshold 135 are closely associated with a midpoint of the RDIFF signal 136. This difference is accomplished by way of the control signals applied to the transmission gates 133a, 133d compared to control signals applied to the transmission gates 133b, 133c. The control signals are further described below in conjunction with FIGS. 2A and 2B.

A shared AGC DAC 152 is shown in the lower half of FIG. 2, providing a shared AGC DAC output signal 154 to control the gain of both the RAGC 114 and LAGC 156 amplifiers. The shared AGC DAC output signal 154 causes both the right and the left channels to have the same gain. One of ordinary skill in the art will understand how to set the shared AGC DAC 152 to provide and appropriate shared AGC DAC output signal 154.

Referring now to FIG. 2A, an RDIFF signal 186 can correspond, for example to the RDIFF signal 28 of FIG. 1 and the RDIFF signal 136 of FIG. 2. The RDIFF signal 186 is shown to have a shape of a simple sine wave for clarity. However, it will be recognized that the RDIFF signal 186 can have various shapes.

Two fill cycles of the RDIFF signal 186 are shown, however, relationships of the RDIFF signal 186 to other waveforms is described beginning at a point 186a. The point 186a and another point 186n each correspond to negative peaks of the RDIFF signal 186. Points 186b, 186m, 186p each correspond to the RDIFF signal 186 having reached about fifteen percent of its peak-to-peak amplitude. Points 186c, 186j, 186q each correspond to the RDIFF signal 186 having reached about forty percent of its peak-to-peak amplitude. Points 186d, 186i, 186r each correspond to the RDIFF signal 186 having reached about sixty percent of its peak-to-peak amplitude. Points 186f, 186h each correspond to the RDIFF signal 186 having reached about eighty five percent of its peak-to-peak amplitude. While particular percentages are described above, other percentages can also be used. However, the points 186b, 186e, 186h, 186k, and 186p will be seen to be associated with a peak-referenced detector, and therefore, are selected to be relatively near to a positive of a negative peak of the RDIFF signal 186.

A PDAC signal 184 corresponds to the PDAC output signal label in FIG. 2 and an NDAC signal 185 corresponds to the NDAC output signal label in FIG. 2. As seen in FIG. 2, the PDAC and NDAC output signals are applied to the resistor ladder 132, which can provide outputs at a variety of percentages of a difference between the PDAC output signal 184 and the NDAC output signal 185.

Presuming steady state conditions, at a time associated with the point 186a, the PDAC output signal 184 is at a steady state relatively high level corresponding to a positive peak of the RDIFF signal 186, where it remains until a time associated with the point 186d, corresponding to a sixty percent level. At this time, the PDAC output signal 184 counts down until the PDAC output signal 184 intersects the RDIFF signal 186 at the point 186e, at which point, the PDAC output signal 184 reverses direction and counts up to track the RDIFF signal 186 to its next positive peak at the point 186g. Upon reaching the point 186g, the PDAC output signal 184 again holds its value at the positive peak of the RDIFF signal 186.

At the point 186a, the NDAC output signal 185 is at a steady state relatively low level corresponding to a negative peak of the RDIFF signal 186, where it remains until a time associated with the point 186j, corresponding to a forty percent level. At this time, the NDAC output signal 185 counts up until the NDAC output signal 185 intersects the RDIFF signal 186 at the point 186k, at which point, the NDAC output signal 185 reverses direction and counts down to track the RDIFF signal 186 to its next negative peak at the point 186n. Upon reaching the point 186n, the NDAC output signal 185 again holds its value at the negative peak of the RDIFF signal 186. The above-described behavior of the PDAC signal 184 and the NDAC signal 185 repeats on each cycle of the RDIFF signal 186.

An RThreshOut signal 187 corresponds to the RThreshOut signal 26 of FIG. 1 and the RThreshOut signal 140 of FIG. 2. The RThreshOut signal 187 is a digital signal that, due to transitions of a threshold signal 188 described below, switches states at times corresponding to points 186d (sixty percent), 186j (forty percent), and 186r (sixty percent).

In order to achieve the desired edge time placement of the RThreshOut signal 187, a threshold signal 188 is generated, for example, the threshold signal 135 of FIG. 2 with the ladder network 132 of FIG. 2. As shown in FIG. 2 and as will be understood from the waveforms 184, 185, 186, 187, of FIG. 2A, using the RThreshOut signal 187 (140, FIG. 2) to control the transmission gate 133c of FIG. 2 and its inverse to control the transmission gate 133b, results in the threshold signal 188 (signal 135, FIG. 2). The resistor ladder 132 of FIG. 2 is scaled to provide transitions of the threshold 188 (signal 135, FIG. 2) between levels at about forty percent and about sixty percent of the peak-to-peak amplitude of the RDIFF signal 186 (signal 136, FIG. 2).

Taking edge 187a as representative of a positive edge in the RThreshOut signal 187 occurring at a time associated a the sixty percent point, e.g., the point 186d, it can be seen that the edge 187a is generally coincident with the downward edge 188a of the threshold signal 188. It will be understood that the transition 188a of the threshold 188 acts to provide hysteresis, for example, to the comparator 138 of FIG. 2. Following the edges 187a, 188a, which occur at the sixty percent point of the RDIFF signal 186, the next desired switch point is at the forty percent level of the RDIFF signal 186. Following the edges 187a, 188a, a switch point at the forty percent level does not occur until a time corresponding to the point 186j, where the RThreshOut signal 187 has transition 187b and the threshold signal 188 has transition 188b, again providing hysteresis.

It should be apparent that waveforms 187, 188 apply to a threshold detector, for example, a threshold detector associated with the RThresh comparator 138 of FIG. 2. Similar waveforms apply to a peak-referenced detector, for example a peak-referenced detector associated with the RPeak comparator 116 of FIG. 2. However, in order to generate a