Abstract:
A system for sensing vibration of a machine is provided. A light source directs a beam of light toward a light receiving system adapted to receive at least a portion of the beam of light. A light modulating system modulates the light beam received by the light receiving system so as to correspond to vibration of the machine. A processing system operatively coupled to the light receiving system processes data received from the light receiving system to facilitate determining vibration of the machine.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to a system and method for obtaining vibration data from vibrating structures for diagnosis and failure analysis. In particular, the present invention employs an optical sensing system to acquire vibration data to diagnose the state of a structure subject to vibrational forces. 
   BACKGROUND OF THE INVENTION 
   Vibrating structures, including electric machines such as motors and generators, are widely employed in industrial and commercial facilities. These machines are relied upon to operate with minimal attention and provide for long, reliable operation. Many facilities operate several hundreds or even thousands of such machines concurrently, many of which are integrated into a large interdependent process or system. Like most machinery, at least a small percentage of such are prone to failure. The majority of such failures can be attributed to either mechanical failures and/or thermal failures of the machine insulation. 
   Other than normal aging, failures are typically due to: poor or no maintenance; improper application (e.g., wrong enclosure, excessive loading, etc.); and improper installation (e.g., misalignment, bad power, inverter mismatch, etc.). Even with normal aging failures, it is desirable to provide low cost failure prediction information for such machines. 
   Depending on the application, the failure of a machine in service can possibly lead to system or process down time, inconvenience, and possibly even a hazardous situation. Thus, it desirable to diagnose the machinery for possible failure or faults early in order to avoid such problems. 
   Vibration analysis is an established technique for determining the health of mechanical components in rotating machinery such as motors. To obtain vibration data from machinery and other structures, accelerometers as well as associated sampling and filtering techniques are often employed. Larger machines and/or systems may also employ proximity detectors in addition to or instead of accelerometers to determine vibration. 
   In structures such as electric machines, multiple axis detection and multiple location sensing typically are necessary to properly diagnose vibration in the machine. Thus, in many cases, multiple sensors and detectors are required to be located on the machine. As more and more sensing elements are added to the machine, cost associated therewith increases. Also, for critical machines, additional failure detection mechanisms may be needed because the sensing elements themselves can fail. 
   The accelerometers typically employed utilize a moving mass which is coupled with other mechanical and electrical components to generate an electrical signal (e.g., magnetically or capacitively coupled). The resulting electrical signal must then be transmitted via electrical wires where it may be filtered, digitized, analyzed (e.g., FFT analysis) and appropriate control and data recording performed. Due to the low signal levels and the amount of data to be transferred, the length of the signal wires are generally limited and the wire lengths are minimized where possible. In an electrically noisy environment, such as an electric motor, more costly shielded cables are used and there will be further processing performed very near the sensor or integral with the sensor. 
   Typical accelerometers will therefore employ signal wires which contain a varying voltage or current which indicate the vibration experienced at the sensor. In addition, several more wires must also be routed to the sensor to provide power to the accelerometer. The additional wires must be routed through and attached to the structure and represent a possible location for shorting or sparking or for picking up electrical noise which may influence the sensor readings. 
   Consequently, there is a strong need in the art for a system and/or method for detecting vibrations in structures that requires minimal components, requires less wiring, provides for high noise immunity, provides for lower maintenance, and provides for lower costs. 
   SUMMARY OF THE INVENTION 
   The present invention provides for a system and method for acquiring vibration data using optical sensing. It has been found that vibration data relating to the state of a machine or structure may be acquired by employing light modulating systems to minimize components. Also, it has been found that waveguide technology employing evanescent coupling may be used for optical vibration sensing eliminating additional field excitation components. Additionally, it has been found that precise vibration data can be achieved using optical resonators. Thus, the present invention provides for a system and method to obtain optical vibration data via optics, which typically employs fewer components and sensors than conventional vibration sensing systems. 
   More particularly, in a preferred embodiment, the present invention includes light modulating systems employing cantilevered obstruction modulators and/or suspended portal modulators requiring minimal components. Thus, light modulating systems mitigate the need to enter a complex machine or structure to replace sensors and mitigates additional wiring in the machine. Additionally, light modulating systems are noise immune in harsh electrically noisy environments, and they are conducive for use in explosive environments where a small spark may have catastrophic consequences. In another embodiment, the present invention includes optical waveguide technology employing a variable separation distance between waveguides to mitigate the need for external vibration sensing elements. In yet another embodiment, the present invention allows for precise sensing of vibration employing an optical lateral resonator that may be readily positioned along a desired axis. 
   The present invention will be described with respect to an AC motor, however, it is to be appreciated that the present invention has applicability to many types of machines or vibrating structures whereby vibration analysis can be performed to determine the state (e.g., health) of the machines or structures. Other structures include buildings, bridges, automobiles, aircrafts, pumps, internal combustion engines, bearings, etc. Essentially, the aforementioned techniques may be applied to structures subject to vibrational forces—internally or externally generated as well as to lower frequency vibrational forces as may be sensed using any of a variety of seismometers. 
   By employing light modulating systems in a structure, or by employing separation distances using waveguide technology, or by readily positioning a precision sensor, or by using combinations of these methods, many components and/or sensors used in conventional systems may be eliminated or reduced via employment of the present invention. The present invention provides for a system and method for acquiring vibration data which is a more cost effective and reliable. 
   One aspect of the present invention relates to a system for sensing vibration of a machine. A light source directs a beam of light toward a light receiving system adapted to receive at least a portion of the beam of light. A light modulating system modulates the light beam received by the light receiving system so as to correspond to vibration of -the machine. A processing system operatively coupled to the light receiving system process data received from the light receiving system to facilitate determining vibration of the machine. 
   Another aspect of the present invention relates to a multiple axis vibration detection system. The system includes a light source for directing a beam of light and a light receiving system for receiving at least a portion of the beam of light. The system further includes a first light modulating system for modulating the light beam received by the light receiving system so as to correspond with vibration of the machine; and a second light modulating system for modulating the light beam received by the light receiving system so as to correspond with vibration of the machine, the second light modulating system being in series to the first light modulating system. A processing system operatively coupled to the light receiving system processes the data received from the light receiving system to facilitate determining vibration of the machine. 
   Another aspect of the present invention relates to a system for sensing vibration of a machine. The system includes a light source for directing a beam of light; and a light receiving system for receiving at least a portion of the beam of light. The system further includes a first waveguide for transmitting the beam of light, the first waveguide adapted to vibrate in response to vibration of the machine; and a second waveguide having at least a portion thereof located within a predetermined distance to at least a portion of the first waveguide such that evanescent coupling occurs between the waveguides whereby the second waveguide transmits the at least a portion of the beam of light to the receiving system. The intensity of the at least a portion of the beam of light varies as a function of the vibration of the machine. 
   Still yet another aspect of the present invention relates to a system for sensing vibration of a machine, comprising: first, second and third light sources for directing beams of light of different frequencies, respectively; a light receiving system for receiving at a least portion of the beams of light; a first waveguide for transmitting the first beam of light, the first waveguide adapted to vibrate in response to vibration of the machine; a second waveguide for transmitting the second beam of light, the second waveguide adapted to vibrate in response to vibration of the machine; a third waveguide for transmitting the third beam of light, the third waveguide adapted to vibrate in response to vibration of the machine; and a fourth waveguide having at least a portion thereof located within a predetermined distance to at least portions of the first, second and third waveguides, respectively, such that evanescent coupling occurs between the waveguides whereby the fourth waveguide transmits the at least portion of the beams of light to the receiving system; wherein the intensity of the respective at least portion of the beams of light vary as a function of the vibration of the machine. 
   Another aspect of the present invention relates to a system for sensing vibration of a machine. The system includes a light source for directing a beam of light; and a beam splitter for splitting the beam of light into at least a first beam and a second beam. The system further includes an optical lateral resonating system for receiving the second beam, the optical lateral resonator reflecting the second beam, the optical lateral resonating system deflecting in response to vibration such that a transmission path of the second beam varies in length as a function of deflection of the optical lateral resonating system; and a receiving system for receiving an interference beam, the interference beam including a combination of the first beam and reflected second beam. The system also includes a processing system which processes and analyzes the interference beam to facilitate determining vibration of the machine. 
   Still another aspect of the present invention relates to a system for sensing vibration of a machine, including: means for directing a beam of light; means for receiving at least a portion of the beam of light; means for modulating the light beam received by the means for receiving so as to correspond with vibration of the machine; and means for processing the data received from the means for receiving to facilitate determining vibration of the machine. 
   Yet another aspect of the present invention relates to a system for sensing vibration of a machine, including: means for directing a beam of light; means for receiving at least a portion of the beam of light; a first means for transmitting the beam of light, the first means adapted to vibrate in response to vibration of the machine; and a second means for transmitting light, having at least a portion thereof located within a predetermined distance to at least a portion of the first means such that evanescent coupling occurs between the first and second means whereby the second means transmits the at least a portion of the beam of light to the means for receiving; wherein the intensity of the at least a portion of the beam of light varies as a function of the vibration of the machine. 
   Another aspect of the present invention relates to a system for sensing vibration of a machine, including: means for directing a beam of light; means for splitting the beam of light into at least a first beam and a second beam; means for receiving the second beam, means for receiving the second beam reflecting the second beam, the means for receiving the second beam deflecting in response to vibration such that a transmission path of the second beam varies in length as a function of deflection of the means for receiving the second beam; means for receiving an interference beam, the interference beam including a combination of the first beam and reflected second beam; and means for processing and analyzing the interference beam to facilitate determining vibration of the machine. 
   To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of an integrated AC motor and optical sensing system in accordance with one particular aspect of the present invention; 
       FIG. 2   a  is a schematic block diagram of a light modulating system passing minimal light in accordance with the present invention; 
       FIGS. 2   b  and  2   c  are schematic block diagrams of a light modulating system passing maximum light in accordance with the present invention; 
       FIG. 2   d  is a schematic diagram of a detector output voltage at minimal light in accordance with the present invention; 
       FIG. 2   e  is a schematic diagram of a detector output voltage at maximum light in accordance with the present invention; 
       FIG. 2   f  is a schematic diagram of modulated detector output voltage in accordance with the present invention; 
       FIG. 2   g  is a schematic block diagram of a light modulating system passing maximum light in accordance with the present invention; 
       FIGS. 2   h  and  2   i  are schematic block diagrams of a light modulating system passing minimum light in accordance with the present invention; 
       FIG. 2   j  is a schematic diagram of a detector output voltage at maximum light in accordance with the present invention; 
       FIG. 2   k  is a schematic diagram of a detector output voltage at minimum light in accordance with the present invention; 
       FIG. 21  is a schematic diagram of modulated detector output voltage in accordance with the present invention; 
       FIG. 3   a  is a schematic diagram of a cantilevered obstruction modulator in accordance with the present invention; 
       FIG. 3   b  is a diagram of a detector front when no movement occurs in a cantilevered obstruction modulator in accordance with the present invention; 
       FIGS. 3   c  and  3   d  are diagrams of a detector front when movement occurs in a cantilevered obstruction modulator in accordance with the present invention; 
       FIG. 4   a  is a schematic diagram of a suspended portal modulator in accordance with the present invention; 
       FIG. 4   b  is a diagram of a detector front when no movement occurs in a suspended portal modulator in accordance with the present invention; 
       FIGS. 4   c  and  4   d  are diagrams of a detector front when movement occurs in a suspended portal modulator in accordance with the present invention; 
       FIG. 4   e  is a schematic diagram of a suspended portal modulator in a series configured system in accordance with the present invention; 
       FIG. 4   f  is a schematic diagram of a suspended portal modulator in a system with a light directing member in accordance with the present invention; 
       FIG. 4   g  is a schematic diagram of a suspended portal modulator cantilevered to a housing in accordance with the present invention; 
       FIG. 5  is a schematic block diagram of a signal processing system in accordance with the present invention; 
       FIG. 6   a  is a schematic block diagram of a waveguide system illustrating evanescent coupling in accordance with the present invention; 
       FIG. 6   b  is a schematic block diagram of a waveguide system illustrating minimal evanescent coupling in accordance with the present invention; 
       FIG. 7   a  is a schematic block diagram of a multi-axis waveguide system employing multiple light sources in accordance with the present invention; 
       FIG. 7   b  is a schematic block diagram of a band pass filter and system in accordance with the present invention; 
       FIG. 7   c  is a schematic block diagram of a multi-axis waveguide system employing a single light source in accordance with the present invention; 
       FIG. 8  is a schematic block diagram of an optical sensing system employing an optical lateral resonator in accordance with the present invention; 
       FIG. 9  is a flow diagram method for a light modulating system in accordance with the present invention; 
       FIG. 10  is a flow diagram method for an optical waveguide system in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. 
   Referring initially to  FIG. 1 , one specific environment in which the present invention may be employed is shown. Specifically, an optical sensing system  10  is shown which is coupled to a motor  28 . The motor  28  is depicted driving a load  32  through a shaft coupling  34 . The motor  28  is but one example of a vibrating structure whereby the optical sensing systems  10  of the present invention may be employed to gather vibration data. It is to be appreciated that the load  32  may be sensed for vibration although not shown in  FIG. 1 . 
   The optical sensing system  10  produces a signal which represents a modulated light signal. The light signal is modulated from vibrational movements of the motor  28 . The light signal may be modulated without placing light sources or optical detectors within the motor  28 . Thus, wiring expenses and maintenance costs may be minimized. Alternatively, the optical sensing system may be located internal to the motor  28  such as inside the motor end bracket adjacent to the motor bearing (often a source of critical motor vibration). Consequently, only a fiber optic cable is installed and no signal degradation will occur regardless of the degree of electrical noise inside the motor. Although a single optical sensing system  10  is shown, preferably multiple optical sensing systems  10  are employed to detect multiple axes of vibration The optical sensing system  10  may be placed in a plurality of directions necessary for proper diagnosis of the motor  28 . It is to be appreciated that a plurality of the optical sensing systems  10  may be employed depending on the need for more or less vibration data. It is further to be appreciated that the optical sensing system  10  could be located internally or externally on the motor  28 . In the preferred embodiment shown in  FIG. 1 , the optical sensing system  10  is located internal to the motor  28 . Finally, multiple optical sensing systems may be employed in a front end and rear end bracket (not shown) adjacent to the outer race (not shown) of the motor  28  bearings. 
   For example, a comprehensive vibration analysis of a motor may require five or more axis/locations for acceleration data. The axis/locations may include X and Y (orthogonal) radial directions at one end of the motor, X and Y (orthogonal) radical directions at the other end of the motor, an axial (parallel to the shaft) direction, and possible angular direction parallel to the mounting plane among others. 
   Operatively coupled to the optical sensing system  10  is a signal processing system  24  for receiving a vibration signal. The signal processing system  24  may compute, display, analyze, store, trend, and transmit vibration data to an operator or other intelligent system for analysis. In the preferred embodiment, the signal processing system  24  is local to the motor  28 . However, the signal processing system  24  maybe located remote to the motor  28 . When the signal processing system  24  is located remote from the motor  28 , it is beneficial to route the optical fibers that transmit optical signals in existing power trays adjacent to high power/high frequency cables. Unlike conventional electrical systems, there is no danger in corrupting the optical signals. In a remote system, the detector  60  may be located remote and integral to the signal processing system  24 . Preferably, the signal processing system  24  is coupled to a display  22  for viewing vibration data to diagnose and analyze the motor  28 . The signal processing system  24  may also be coupled to a remote system  23 . The remote system  23  may be used for gathering and processing vibration data from a plurality of signal processing systems and optical sensing systems associated with a plurality of vibrating machines, respectively. The remote system  23  may analyze the vibration to determine faults or impending faults of the motor  28  (bearings, loose mounting, out-of-balance, out-of-alignment) or the motor&#39;s operation. Note the remote system  23  and/or display  22  may be integral to the signal processing system  24 . Similarly, the signal processing system with or without the remote system or display may be integral with the optical sensing system  10  and located internal to the motor  28 . 
   Referring to  FIG. 2   a , an optical sensing s stem  40  is shown with a light source  50  projecting to a light modulating system  52 . The output of the light modulating system  52  is received by a detector  60 . The light source  50  which includes a power source (not shown), may be any suitable light source (e.g., lasers, LED&#39;s, bulbs, laser diodes, etc.) to produce light for carrying out the present invention. The detector  60  includes optically sensitive material which produces an electrical signal proportional to the amplitude and frequency of light received and may be a single detector, a linear detector, or an array. For example, if the detector  60  receives a large amount of light, the detector  60  will produce an electrical signal which is large in magnitude. Conversely, the detector  60  will produce an electrical signal with small magnitude when less light is received. Thus, the detector  60  produces an amplitude modulated electrical signal based on a variable amplitude optical signal. 
     FIG. 2   a , depicts a light modulating system (LMS)  52  without vibration. Since no vibration is occurring, the detector  60  receives a minimum light signal. Minimum light is graphically depicted as a dashed line from the LMS  52  to the detector  60 . As the LMS  52  moves because of vibration, shown as Y+ in  FIG. 2   b , and Y− in  FIG. 2   c , a greater amount of light reaches the detector  60  and an electrical signal proportional to the movement (e.g., larger magnitude signal) is produced by the detector  60 . A maximum light signal is depicted as a bold line from the LMS  52  to the detector  60  in  FIGS. 2   b  and  2   c . As the frequency of movement of the LMS  52  increases, the frequency of the electrical signal produced at the detector  60  will increase. Therefore, the LMS  52  will cause a signal to be produced at the detector  60  proportional to the magnitude and frequency of vibration. 
   Referring to  FIGS. 2   d  through  2   f , the voltage output from detector  60  may be observed with respect to time.  FIG. 2   d  illustrates a minimum voltage signal  60   d  produced when no movement of the LMS  52  occurs as in  FIG. 2   a .  FIG. 2   e  illustrates a maximum voltage signal  60   e  produced when movement of the LMS  52  occurs as in  FIGS. 2   b  and  2   c . It is noted that voltage  60   e  contains the fundamental frequency component of light source  50 .  FIG. 2   f  depicts the detector  60  voltage output  60   f  when the LMS  52  is subject to vibrational movement. As shown by voltage  60   f , the fundamental frequency of light source  50  is modulated by movement of the LMS  52 . 
   Referring now to  FIG. 2   g , another embodiment of a light modulating system  52   a  is shown which produces maximum light when no movement of the (LMS)  52   a  occurs. Conversely,  FIGS. 2   h  and  2   i  depict minimum light detected when movement of the LMS  52   a  occurs in the Y+ or Y− direction. 
   Referring to  FIGS. 2   j  through  21 , the voltage output from the detector  60  may be observed with respect to time.  FIG. 2   j  illustrates a maximum voltage signal  60   j  that is produced when no movement of the LMS  52   a  occurs as in  FIG. 2   g .  FIG. 2   k  illustrates a minimum voltage signal  60   k  that is produced when movement of the LMS  52   a  occurs as in  FIGS. 2   h  and  2   i . It is noted that voltage  60   j  contains the fundamental frequency component of light source  50 .  FIG. 21  depicts the detector  60  voltage output  601  when the LMS  52   a  is subject to vibrational movement. As shown by voltage  601 , the fundamental frequency of light source  50  is modulated by movement of the LMS  52   a.    
   Referring now to  FIG. 3   a , a preferred embodiment of a light modulating system (LMS)  52  is shown. LMS  53  has a housing  53   a  with a front opening  53   b  for receiving light from a light source  50  and an opposite opening  53   c  for passing light to a detector  60 . The light entering opening  53   b  is obstructed by an obstruction modulator  53   d  which is coupled to housing  53   a  by a cantilevered support arm  53   e . When no movement of LMS  53  occurs, the obstruction modulator  53   d  substantially prevents light from reaching a detector face  63 . The obstruction modulator  53   d  may be constructed of a plurality of light obstructing materials such as metal, wood, or plastic. It is to be appreciated that any material capable of preventing a substantial portion of light from reaching detector  60  when no movement of LMS  53  occurs, may be used as the obstruction modulator  53   d . It is also to be appreciated that obstruction modulator  53   d  may be a plurality of shapes such as circular, triangular, rectangular, ovular, etc. The preferred embodiment employs a circular shape. 
   It should also be appreciated that the cantilever support arm could be extended to the other (illuminated side) of the obstruction disk  53   d . Similarly other designs such as employing multiple support arms located circumferentially around the housing  53   a  may be employed. 
   By observing  FIGS. 3   b  through  3   d , the functions of LMS  53  may be illustrated.  FIG. 3   b  depicts detector face  63  when no movement of LMS  53  occurs. As depicted by a shaded region  63   b , light is obstructed by the obstruction modulator  53   d . The voltage output from detector  60  correlating to  FIG. 3   b  is shown in  FIG. 2   d . As movement occurs in the Y+ or Y− direction illustrated in  FIGS. 3   c  and  3   d , more light reaches detector front  63  correlating to the voltage shown in  FIG. 2   e . When vibrational movement of LMS  53  begins at a given frequency, a modulated voltage output from the detector  60  is shown in  FIG. 2   f . As will be described in more detail below, the voltage in  FIG. 2   f  is filtered to remove the light frequency component thereby leaving the vibration frequency component. It is to be appreciated that a plurality of directions may be detected, for example, movement in the X+ or X− direction. It is noted that axis vibration directions may be limited to a particular direction. For example, the cantilevered support arm  53   e may be stiffened horizontally or vertically to prevent vibration in the X or Y axis. 
   LMS  53  illustrates how costs may be reduced in an optical system. Light source  50  and detector  60  may be located externally to a structure thereby eliminating internal wiring and maintenance expenses. More importantly, the obstruction modulator  53   d  and housing  53   a  may be naturally occurring obstructions and openings in a machine or structure thereby eliminating additional sensing elements. 
   Turning to  FIG. 4   a , another embodiment of a low cost light modulating system (LMS)  54  is illustrated. LMS  54  has a housing  54   a  with a front opening  54   b  for receiving light from a light source  50  and an opposite opening  54   c  for passing light to a detector  60 . The light entering opening  54   b  is passed through a suspended portal modulator  54   d  having an opening  54   e  and secured to housing  54   a . When no movement of LMS  54  occurs, the suspended portal modulator  54   d  substantially allows light to reach a detector face  64 . The suspended portal modulator  54   d  may be constructed of a plurality of light obstructing material such as metal, wood, or plastic. It is to be appreciated that any material capable of preventing a substantial portion of light from reaching detector  60  when movement of LMS  54  occurs, may be used as the suspended portal modulator  54   d . It is also to be appreciated that opening  54   e  in the suspended portal modulator  54   d  may be a plurality of shapes such as circular, triangular, rectangular, ovular, etc. The preferred embodiment employs a circular shape. It is to be appreciated that a lens (not shown) may be inserted in the center of the portal modular  54   d.    
   By observing  FIGS. 4   b  through  4   d , the functions of LMS  54  may be illustrated.  FIG. 4   b  depicts the detector face  64  when no movement of LMS  54  occurs. As illustrated by non-shaded region  64   b , light is passed by the suspended portal modulator  54   d . The voltage output from detector  60  correlating to  FIG. 4   b  is shown in  FIG. 2   j . As movement occurs in the Y+ or Y− direction illustrated in  FIGS. 4   c  and  4   d , less light reaches detector face  64  correlating to the voltage shown in  FIG. 21   c . When vibrational movement of LMS  54  begins at a given frequency, a modulated voltage output from detector  60  is shown in  FIG. 21 . As will be described in more detail below, the voltage in  FIG. 21  is filtered to remove the light frequency component thereby leaving the vibration frequency component. It is to be appreciated that a plurality of directions may be detected, for example, movement in the X+ or X− direction. 
   LMS  54 , like LMS  53 , illustrates how costs may be reduced in an optical system. Light source  50  and detector  60  may be located externally to a structure thereby eliminating internal wiring and maintenance expenses. More importantly, the suspended portal modulator  54   d  and housing  54   a  may be naturally occurring obstructions and openings in a machine or structure thereby eliminating additional sensing elements. 
   Referring now to  FIG. 4   e , a low cost multiple axis and/or multi-location vibration detection system  54   h  is illustrated employing a single light source  50  and a detector  60 . In system  54   h , an LMS  54   f  and  54   g  are shown in a series configuration between the light source  50  and detector  60 . It is to be appreciated that a plurality of light modulating systems may be employed in a series configuration. If vibration were detected in either the LMS  54   f  or  54   g , a modulated light signal would be detected by the detector  60 . It is noted that LMS  54   f  and  54   g  may be along different lines of vibration and direction. For example, a single optical fiber may couple light from the light source  50  to a plurality of light modulating systems in different locations and directions. Several applications may benefit from low cost, series configured light modulating systems. The applications include smart material applications and motor applications whereby a plurality of light modulating systems are embedded in stator windings. 
   The system  54   h , described above, indicates vibration somewhere in the series configured system, however, location and direction information from a particular LMS  54   f  or  54   g  is lost because of the series configuration. Referring briefly to  FIG. 4   a , the suspended portals  54   d  of each light modulating system employed in series may be constructed such that each suspended portal  54   d  has a different mass. As a result, each LMS  54   f  or  54   g  in  FIG. 4   e , would have a different mechanical resonant frequency. Consequently, a composite frequency would be received by the detector  60 . As will be described in more detail below referring to multiple axis waveguide systems, filtering systems may be employed to extract a particular light modulating system frequency from the mechanical resonant frequency. 
   Referring to  FIG. 4   f , a system  54   i  is illustrated whereby the light source  50  and the detector  60  may be located in a similar proximity and position relative to the position of the LMS  54 . A light directing member  64   g , having an anti-reflective surface  64   h  and a reflective surface  64   i , passes light to the LMS  54 . As the light passes through and is modulated by the LMS  54 , a reflector  64   f  reflects the light back to the reflective surface  64   i  of the light directing member  64   g . The reflective surface  64   i  directs the light to the detector  60  whereby the modulated light is received. The light directing member  64   g may be of suitable material to allow light to pass when received in one direction and the light to reflect when received in the opposite direction as is commercially available. It is to be appreciated that the LMS  53  shown in  FIG. 3  may be employed for the LMS  54  in  FIG. 4   f.    
   Referring to briefly to  FIG. 4   g , another embodiment of a light modulating system  54  is shown. A suspended portal modulator  54   d ′ is coupled to a housing  54   a  via a cantilevered support arm  54   e ′. The suspended portal modulator  54   d ′ functions as in the system shown in  FIG. 4   a  and may be applied to the systems shown in  FIGS. 4   a  through  4   f . The cantilevered support arm  54   e ′ provides an alternative coupling to attach the suspended portal modulator  54   d ′ to the housing  54   a.    
   Referring now to  FIG. 5 , an optical sensing system  10  is shown operatively coupled to a signal processing system  24 . A processor  64  which controls the general operation of the signal processing system  24 , may be coupled to a display  22  and/or a remote system  23 . The display  22  is employed to provide vibration diagnostic and status information. The remote system  23  may be employed to capture vibration information from a plurality of signal processing systems  24 . 
   The processor  64  is tied to an analog to digital (A/D) converter  62 , which converts the analog signals provided by optical sensing system  10  to digital form. The processor  64  is programmed to control and operate various components within the signal processing system  24  in order to carry out the various functions described herein. The processor or CPU  64  can be any of a plurality of processors, such as the p24T, Pentium 50/75, Pentium 60/90, and Pentium 66/100, Pentium PRO and Pentium 2, and other similar and compatible processors. The manner in which the processor  64  can be programmed to carry out functions relating to the present invention will be readily apparent to those having ordinary skill in the art based on the description provided herein. 
   A memory  67  tied to the processor  64  is also included in the signal processing system  24  and serves to store program code executed by the processor  64  for carrying out operating functions of the signal processing system  24  as described herein. The memory  67  also serves as a storage medium for temporarily storing information such as historical vibration analysis data and the like. The memory  67  is adapted to store a complete set of information to be presented to the display  22  or transmitted to the remote system  23 . According to a preferred embodiment, the memory  67  has sufficient capacity to store multiple sets of information, and the processor  64  could include a program for alternating or cycling between various sets of display information. This feature enables the display  22  to show a variety of effects conducive for quickly conveying vibration and other diagnostic information to a user. The signal processing system  24  may also output a digital output of raw data and/or of vibration values. Additionally, the signal processing system  24  may output alarm notifications. Also, the signal processing system  24  and processor  64  may process sampled data from multiple sensing systems  10  employing standard techniques such as multi-channel input or multiplexing techniques. 
   The memory  67  includes read only memory (ROM) and random access memory (RAM). The ROM contains among other code the Basic Input-Output System (BIOS) which controls basic hardware operations of the signal processing system  24 . The RAM is the main memory into which the operating system and application programs are loaded. 
   Referring briefly to  FIGS. 2   f  and  2   l , modulated light frequency is depicted. The modulation frequency is the frequency of vibration. To retrieve the vibration frequency, a low pass filter (not shown in  FIG. 5 ) is employed to remove the light frequency. The preferred embodiment employs digital signal processing techniques that are well known in the art. In  FIG. 5 , the signal processing system employs a low pass filtering technique to retrieve the vibration frequency. The filtering techniques may include Z-transform or discrete transform digital filtering. Alternatively, the detector  60 , may incorporate a suitable low pass filter inherent in its operation. 
   Now referring to another embodiment depicted in  FIG. 6   a , a system  80  for obtaining optical vibration data is illustrated. In the preferred embodiment shown in  FIG. 6   a , a waveguide  82   a  and a waveguide  83   a  are employed to sense optical vibration data. As explained in more detail below, waveguides  82   a  and  83   a  couple vibration data over a separation distance (D)  88  and coupling length (L)  89 , in an evanescent coupling region  84 . The waveguide separation distance  88 , coupling length  89  of close waveguide proximity, and wavelength, λ are critical parameters affecting the coupling efficiency. Coupling efficiency determines the quantity of light transferred. As coupling efficiency increases, the quantity of light transferred increases. The system  80  does not require an external vibration sensor to modulate light in waveguide  82   a . More particularly, system  80  obtains optical vibration data directly from waveguide  82   a  by employing a variable separation distance  88  between the waveguides  82   a  and  83   a  thereby eliminating an external vibration sensor. 
   Optical vibration data is coupled to a stationary waveguide  82   a  as light propagates the waveguide  83   a  which is subject to vibration. When the waveguide  82   a  is positioned suitably and substantially close to the waveguide  83   a , light from the waveguide  83   a  will evanescently couple or transfer to the waveguide  32   a  along the coupling length  89 . As distances between the waveguides  82   a  and  83   a  increase or decrease, evanescent coupling energy increases or decreases because coupling efficiency is critically dependent on the separation distance  88 . With greater coupling efficiency, more light will transfer from the waveguide  83   a  to the waveguide  82   a . In particular, system  80  functions as a directional coupler whereby the coupling efficiency is modulated by the lateral movement of the vibrating structure  85 . It is to be appreciated however, that evanescent coupling efficiency may decrease if the distance between the waveguides  82   a  and  83   a  continue to decrease. Conversely, as distances between the waveguides  82   a  and  83   a  increase, evanescent coupling decreases causing less light to transfer. When vibration causes the waveguide  83   a  to move smaller and larger distances relative to the stationary waveguide  82   a , more or less light will evanescently couple because distances between the waveguides  82   a  and  83   a  will vary at the amplitude and frequency of vibration. Thus, light intensity is modulated in the stationary waveguide  82   a  as vibration causes the distance to vary with respect to waveguide  83   a . It is to be appreciated that if the waveguides  82   a  and  83   a  were to vibrate with respect to the coupling length  89 , light intensity may also be modulated. 
   In the preferred embodiment, the waveguides  82   a  and  83   a  are positioned one half the distance between maximum coupling and minimum coupling determined at the detector  60 . For example, the waveguide  82   a  is positioned to a smaller distance toward the waveguide  83   a  until a maximum signal is detected at the detector  60 . Subsequently, moving in the opposite direction from maximum coupling, the waveguide  82   a  is positioned to a larger distance from the waveguide  83   a  until a minimum signal is detected at the detector  60 . Before vibration sensing begins, the waveguide  82   a  is positioned one half the distance between maximum and minimum coupling allowing full peak to peak detection of the vibration signal. 
   As illustrated in  FIG. 6   a , waveguide  82   a  is stationarily positioned relative to waveguide  83   a  which is secured to a vibrating structure  85 . Waveguide  83   a  is shown affixed to a stationary object  86 , however, it is noted that a plurality of suitable techniques may be employed to position waveguide  82   a  relative to waveguide  83   a . By positioning waveguides  82   a  and  83   a  in substantially close proximity, shown as D  88 , evanescent coupling occurs in region  84  which enables light from waveguide  83   a  to transfer to waveguide  82   a . As shown, a light source  50 , preferably a laser, projects light into a first end  83   b  of waveguide  83   a  which exits a second end  83   c . When waveguide  82   a  is positioned substantially close enough to waveguide  83   a , evanescent coupling occurs in region  84  whereby light will travel to the end  82   c  of waveguide  82   a . A detector  60  coupled to a second end  82   c  of waveguide  82   a  receives light evanescently coupled from region  84 . The detector  60  output voltage is illustrated in  FIG. 2   j  when maximum evanescent coupling occurs. Note that size and mass of the vibrating structure  85  may be substantially reduced as needed to provide higher frequency vibration sensing capability. 
   Referring to  FIG. 6   b , waveguides  82   a  and  83   a  are substantially separated, shown as D  88   a , whereby minimal evanescent coupling occurs and detector  60  receives minimal light. Thus, by varying the separation distance, light intensity is amplitude modulated at the detector  60 . The detector  60  output voltage is illustrated in  FIG. 2   k  when minimal evanescent coupling occurs and  FIG. 21  when vibration occurs. By positioning waveguide  82   a  in a fixed position relative to the variable position of waveguide  83   a , more or less light will be coupled when vibration causes waveguide  83   a  to move smaller and larger distances D  88  and D  88   a . It is noted that wires are not required to communicate the vibration data from waveguides  82   a  and  83   a . Therefore, lower maintenance and installation costs may be realized since wires are not required internally or externally on the machine or structure. It is further noted, that a plurality of waveguides as shown in  FIG. 6   a  may be positioned to sense vibration along a plurality of axis. 
   Now referring to  FIG. 7   a , a multidimensional vibration system  90  employing a single evanescent coupling region  96  is illustrated. System  90  is advantageous because multiple axis of vibration data may be obtained from a single location thereby reducing the amount of space required to employ multiple sensing systems. 
   System  90 , employs a waveguide  92  stationarily positioned relative to a waveguide  93 ,  94 , and  95  which sense a plurality of vibrational directions. It is to be appreciated that more or less waveguides may be employed than the preferred embodiment shown in  FIG. 7   a . A detector  60  is coupled to a second end  92   b  of waveguide  92 . Each waveguide  93 ,  94 , and  95  will couple more or less light to waveguide  92  in evanescent region  96  based on vibration of the respective waveguides as explained above in system  80  shown if  FIG. 6   a.    
   As shown in  FIG. 7   a , light sources  50   a ,  50   b , and  50   c  are coupled to a front end  93   a ,  94   a , and  95   a  of waveguides  93 ,  94 , and  95 . It is noted that each light source  50   a ,  50   b ,  50   c , uses a different wavelength of light. For example 600 nm, 580 nm, and 560 nm lasers, respectively. When coupling occurs in the evanescent region  96  with stationary waveguide  92 , multiple optical frequencies are produced at detector  60  because evanescent coupling occurs from waveguides  93 ,  94 , and  95 . Thus, the detector  60  will receive a composite amplitude modulated signal composed of various optical frequencies. Therefore, filter techniques well known in the art are applied at the detector  60  output in order to distinguish which axis frequency is received. For example, wavelength division multiplexing (WDM) networks may be readily employed in system  90 . 
   As illustrated in  FIG. 7   b , a composite waveform  97  is received by the signal processing system  24  and applied to a band pass filter  99 . It is to be appreciated, that hardware bandpass filtering techniques may be employed to extract the 600 nm, 580 nm, and  560 nm light frequencies  99   a ,  99   b , and  99   c , for example. However, the preferred embodiment employs well known digital filtering techniques. The band pass filtering  99  is implemented by the signal processing system  24  shown in  FIG. 5 . After the axis frequencies  99   a ,  99   b , and  99   c  are extracted, low pass filtering as described above is employed to extract vibration frequencies from the axis frequencies. 
   Alternatively, optical wavelength filtering (not shown) may be employed in the detector  60 . For example, electro-optic material such as Lithium Niobate (LiNbO 3 ) may be employed which changes the index of refraction as a function of applied voltage. As the applied voltage is changed to the detector  60  by the signal processing system  24 , the particular optical frequency of interest would be included in the detector  60  output whereas other optical frequencies would be excluded. 
   As shown in  FIG. 7   c , a system  100  is illustrated which employs a single light source  50 . System lOO provides a technique to reduce the number of light sources  50  illustrated in  FIG. 7   a . System  100  produces multiple optical frequencies in waveguide  92  by employing resonant mechanical couplings  93   c .,  94   c , and  95   c , to couple waveguides  93 ,  94 , and  95  to a vibrating structure (not shown). 
   The resonant mechanical couplings  93   c ,  94   c , and  95   c  have different mechanical resonant frequencies of vibration. Therefore, when waveguide  93  for example, is coupled via resonant mechanical coupling  93   c , the frequency of vibration of waveguide  93 , is combined with the frequency of the resonant mechanical coupling  93   c . Since each resonant mechanical coupling  93   c ,  94   c , and  95   c , employs a different resonant frequency, a composite frequency  97  as shown in  FIG. 7   b  is produced by the detector  60 . The preferred embodiment employs electronically activated resonating structures for couplings  93   c ,  94   c , and  95   c , with dissimilar frequency constants. Alternatively, mechanical springs may be employed with each  93   c ,  94   c , and  95   c  having different spring constants. It is to be appreciated that other resonant mechanical couplings may be employed. As discussed previously, digital bandpass filtering techniques may be applied to extract the desired axis frequencies by band pass filtering at the resonant mechanical frequencies. As discussed previously, well known low pass filtering techniques may be applied to extract axis vibration frequencies from the resonant mechanical frequencies. 
   Another embodiment for an optical sensing system is illustrated in  FIG. 8 . An optical lateral resonator  120  optically coupled to an interferometer system  110  is employed to detect precise vibrations. Interferometric techniques are employed to detect precise distances on the order of the wavelength of light or smaller. For example, if an 800 nm laser were used, distance movements on the order of 80 nm may be detected. By combining the interferometer system  110  with an optical lateral resonator  120 , precise vibrations of a machine or structure may be detected to aid in diagnosis and analysis of mechanical failures. 
   Turning now to  FIG. 8 , a schematic diagram of an interferometric system  110  is shown coupled to an optical lateral resonator  120 . The interferometric system  110  is employed to determine vibrational movements on the surface of the optical lateral resonator  120 . The optical lateral resonator  120  has a mirrored surface  122  for reflecting light to the interferometric system  110 . The mirrored surface  122  is a flexible medium which can deflect in a plurality of directions based on vibrations of the optical lateral resonator  120 . When the mirrored surface  122  deflects, the optical path in this transmission path is changed in length in accordance with the vibration or lateral displacement of the reflective structure. 
   One specific aspect of the present invention employs a Michelson-type interferometer  110 . In this kind of interferometer, a light beam  152  from a coherent light source  142  is split into two beams, one of which can be referred to as a reference light beam  154  and the other as a measuring light beam  156 . A semireflective mirror  160  is disposed in the beam path  152  at an angle of  45  degrees and is used as the beam splitter. A cube formed by cementing two prisms together may also be used as the beam splitter  160 , where the cemented surface being also disposed in the beam path at a 45° angle. 
   When the beam  152  from the light source  142  (e.g., laser) reaches the beam splitter  160 , the beam is split into the reference beam  154  and the measuring beam  156 . The reference beam  154  is reflected toward mirror  162  where it is reflected back toward the detector  170  going through the beam splitter  160 . The measuring beam passes through the beam splitter  160  and moves toward focus lens  164 . The focus lens  164  focuses the measuring beam  156  at the mirrored surface  122  of the optical lateral resonator  120 . It is to be appreciated that the lens  164  will not usually be needed. The measuring beam  156  is reflected off the mirrored surface  122  and travels back toward the beam splitter  160 . The reflected reference beam  154  and reflected measuring beam  156  are combined by the beam splitter  160  to form an interference beam  168  which is directed toward optical detector  170 . 
   Depending on the phasing of the two beams  154 ,  156  with respect to one another, the interference beam  162  can assume an amplitude between the sum of the individual amplitudes of the two beams  154 ,  156  (constructive interference) and zero (destructive interference). When the two beams  154 ,  156  are 180° out of phase (i.e., zero—destructive interference), a completely dark fringe results. When the two beams  154 ,  156  are in phase, a bright fringe results. The light being preferably of laser form is a standing wave pattern. Accordingly, each dark fringe that results as the interference beam  154  is cycled through detector  170  corresponds to a change in the length of the optical distance to the mirrored surface  122  of ½λ (i.e., ½ the wavelength of the light source  142 ). As the mirrored surface  122  deflects because of vibration, the optical distance to the mirrored surface  122  increases or decreases causing changes in the fringe intensity. Thus, by monitoring periodic changes in the fringe, vibration data may be extracted. 
   By counting changes in the number of dark fringes over time, the increase and reduction in the length of the optical distance to the mirrored surface  122  over time (i.e., vibration) can be determined with great precision since the reference beam  154  is typically of high frequency. For instance, if the reference beam is from a laser diode having an emission wavelength of 800 nm, one dark fringe represents a reduction in length to the mirrored surface  122  of 400 nm. It is also possible to more precisely determine the change in reference beam length by interpreting intensity values between dark fringes and maximally bright fringes. Therefore, minute and precise vibrational movements may be detected. 
   The electric signal output by the detector  170  is an analog signal which is input to an analog-to-digital (A/D) converter  126  which digitizes the analog signal for ease of processing. The digital signal output by the A/D converter  126  is input via line  128  to a pulse counter  130 . Each dark fringe appears as a zero (“0”) or low signal in digital form. Each dark fringe that results as the interference beam  168  is cycled through the detector  170  corresponds to a reduction in the length of the mirrored surface  122  of ½λ (i.e., ½ the wavelength of the reference beam  154 ). The pulse counter  130  monitors for fringes and counts each fringe that cycles therethrough. The controller then determines the change in the number of counts over time to determine the vibration data. It will be appreciated that any suitable method for determining the number of fringes may be employed to carry out the present invention and falls within the scope of the claims. It is further to be appreciated that other interferometric techniques such as Mach-Zehnder may be employed to carry out the present invention. 
   It is important to note that all the above mentioned embodiments shown in  FIGS. 3   a ,  4   a ,  6   a ,  7   a , and  8  may be implemented with micro-electro-mechanical-systems (MEMS), or micro-opto-electro-mechanical systems (MOEMS). Waveguides, for example, may be fabricated directly in silicon by employing a small amount of doping to change the index of refraction of adjacent material respective to the waveguide material. 
   Now referring to  FIG. 9 , a method for determining vibration employing the obstruction modulator depicted in  FIG. 3  is illustrated in a flow diagram. In step  200 , general initializations are performed such as resetting variables, pointers, and registers. The variables include vibration data determined at previous points in time. Proceeding to step  210 , the method energizes light source  50  and proceeds to step  220 . At step  220 , the method projects light on to the obstruction modulator  53   d  and proceeds to step  230  whereby the detector  60  is positioned such that minimal signal output is detected when minimal vibration occurs. The method then proceeds to step  240 . 
   At step  240 , a vibration sample period begins. In the preferred embodiment, a sample period of about 1 ms is chosen. It is to be appreciated that many other sample periods maybe chosen such as 0.1 ms, 10 ms, 50 ms, etc. The method proceeds to step  250   a  and a vibration sample begins whereby a modulated optical signal is produced by the obstruction modulator  53   d . Proceeding to step  260 , the method converts the modulated optical signal to an electrical signal employing the detector  60 . Then, signal processing, as shown in  FIG. 5 , filters the vibration signal from the optical signal and the method proceeds to step  270 . At step  270 , the method determines whether the sample period has ended. If the sample period has not ended, the method proceeds back to step  250   a  whereby more vibration samples are acquired. If the sample period has ended, the method proceeds to step  280 . At step  280 , the method determines vibration magnitude by computing the largest amplitude of the vibration signal over the sample period. The frequency of vibration is determined by computing changes in amplitude over the sampled period. After determining vibration amplitude and frequency, the method proceeds to step  290  whereby the vibration data is output to the display  22  and/or stored for later analysis. After outputting the vibration data to the display  22 , the method returns to step  240  whereby a new sample period begins. 
   Finally, referring to  FIG. 10 , a similar method for determining vibration employing the variable separation waveguides depicted in  FIG. 7   a  is illustrated in a flow diagram. In step  200 , general initializations are performed such as resetting variables, pointers, and registers. The variables include vibration data determined at previous points in time. Proceeding to step  210 , the method energizes light source  50  and proceeds to step  220 . At step  220 , the method projects light on to waveguide  83   a  and proceeds to step  230  whereby waveguide  82   a  is positioned such that evanescent coupling occurs and an optical signal is received at the detector  60 . The positioning of waveguide  82   a  should be centrally located between maximum and minimum signal at detector  60  when minimal vibration occurs. The method then proceeds to step  240 . 
   At step  240 , a vibration sample period begins. In the preferred embodiment, a sample period of about 1 ms is chosen. It is to be appreciated that many other sample periods may be chosen such as 0.1 ms, 10 ms, 50 ms, etc. The method proceeds to step  250   b  and a vibration sample begins whereby a modulated optical signal is produced by the waveguides  82   a  and  83   a . Proceeding to step  260 , the method converts the modulated optical signal to an electrical signal employing the detector  60 . Then, signal processing, as shown in  FIG. 5 , filters the vibration signal from the optical signal and the method proceeds to step  270 . At step  270 , the method determines whether the sample period has ended. If the sample period has not ended, the method proceeds back to step  250   b  whereby more vibration samples are acquired. If the sample period has ended, the method proceeds to step  280 . At step  280 , the method determines vibration magnitude by computing the largest amplitude of the vibration signal over the sample period. The frequency of vibration is determined by computing changes in amplitude over the sampled period. After determining vibration amplitude and frequency, the method proceeds to step  290  whereby the vibration data is output to the display  22  and/or stored for later analysis. After outputting the vibration data to the display  22 , the method returns to step  240  whereby a new sample period begins. 
   What has been described above are preferred embodiments of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims.