Abstract:
This present specification provides, amongst other things, an electro-optical monitoring system for obtaining a once-per-revolution signal based on the surface reflection of a rotating device that mandates non-contacting sensor input in potentially hostile environments. The system can use optical and electronic sections to illuminate and detect surface reflections from the rotating surface using existing mounting locations on the periphery of the machine to be measured. The electronic portion is configured to determine a unique mark as the once-per-revolution marker or allow an attending operator to assign a specific marker based on the observed reflected pattern. The optical portion consists of a light source, receiver, and optics that allow for focused and directed light paths.

Description:
PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 11/839,173 filed on Aug. 15, 2007, now U.S. Pat. No. 7,734,435, which claims priority from U.S. Provisional Patent Application 60/822,497, filed Aug. 15, 2006, the contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present specification relates generally to methods and systems for monitoring of vibration, motion and other aspects of moving devices, and more particularly relates to a monitoring system for gas turbine engines and other moving devices. 
     BACKGROUND 
     Systems and methods for measurement of vibration and motion of rotational devices are known. For example, many audio spectrum analyzers are available in the marketplace as well as modular approaches using analog-to-digital converter hardware. 
     The gas turbine engine is one rotational device that can benefit from this technology. Without positional information, many engine faults go unidentified or are identified incorrectly, until failure is imminent. Yet, due to extreme operating conditions, gas turbine engines are among the most difficult type of rotating machinery for engineering a synchronization solution. 
     The most common positioning solution for gas turbine engines is based on using a fixed reference point positioned on the shaft surface. However, this solution can be intrusive to normal turbine operation and can require shutdown conditions. Maintenance activities are then restricted only to those that can be performed when the unit is down (e.g. during a wash cycle). During shutdown conditions, dynamic testing is accomplished by applying a dab of reflective paint to mark a specific location on the shaft. A once-per-revolution signal is obtained by using a tachometer device connected to a borescope access port. Once the engine is started, however, the paint is reliable for only a short time as it loses its reflective characteristics soon after being subjected to the high temperatures and particulate matter passing through the engine. Use of the paint spot method also presents an operational limitation—the paint must typically be applied at least twenty-four hours prior to any subsequent testing. Typically, this prohibits normal turbine operation for thirty-six hours creating the potential for havoc for normal operations and severe financial losses. 
     In contrast to shutdown conditions, obtaining a clean once-per-revolution signal from the rotating shaft is the optimum method of gathering data of an operating gas turbine but poses significant engineering challenges. Some of these constraints include: (1) the probe cannot make contact with the shaft, (2) the shaft cannot be modified in any way, (3) nothing must be attached to the shaft, (4) the closest point to the shaft must be several inches away due to rotating compressor blades, (5) the shaft is fully enclosed in a pressurized section of the engine, where the nominal pressure can equal two-hundred pounds-per-square-inch (“PSI”), and (6) the shaft surface temperature can be approximately four-hundred degrees Fahrenheit. 
     Lacking accurate positional information during operation, many engine faults go unidentified until failure is imminent. While engine-monitoring technologies such as magnetic or radio frequency sensors can detect impending problems (e.g., engine vibration), they require special treatment or changes to the materials used in the machine construction. As a result, the fault remedy is global and not specific. Most often, the expeditious (but costly) remedy is replacement of the entire turbine, versus a time-consuming qualification of fault recognition, and subsequent repair of the causal condition. 
     SUMMARY 
     The present specification provides, amongst other things, a fiber-optic tachometer borescope and a focusing tip borescope. The borescope can be used for once-per-revolution phase-dependent turbine inspection and/or positionally aware tangential velocity and/or remote visual inspection. 
     The present specification provides, amongst other things, systems and methods for obtaining a fixed positional reference point on rotating surfaces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic representation of a system for monitoring for a moving surface. 
         FIG. 2  shows the optical portion of the system of  FIG. 1 . 
         FIG. 3  shows a partial perspective view of the electronics portion of the system of  FIG. 1 . 
         FIG. 4  shows a perspective view of the system of  FIG. 1 . 
         FIG. 5  shows a partial view of the end of the optical portion of  FIG. 2 . 
         FIG. 6  shows a representation of an exemplary distribution of emitting and non-emitting of fiber optic strands in a cross section of the optical portion of  FIG. 2  through the lines VI-VI in  FIG. 5 . 
         FIG. 7  shows the surface of a spinning wheel embossed with metal stamped numerals in the upper half of  FIG. 7 , and an associated waveform. 
         FIG. 8  shows an example of three separate waveforms as detected by the system of  FIG. 1 . 
         FIG. 9  shows the waveforms of three separate speeds of the wheel of  FIG. 7 . 
         FIG. 10  shows a flow-chart depicting a method for monitoring a moving surface. 
         FIG. 11  shows a flow-chart depicting another method for monitoring a moving surface. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       FIGS. 1-4  show a system for monitoring a moving surface indicated generally at  50 , and which comprises an electronic portion  54  and an optical portion  58 . 
     Optical portion  58 , which is shown in greater detail in  FIG. 2 , comprises a Y-shaped fiber optic cable  62 . Cable  62  includes a V-section  66  and a collective section  70 . V-section  66  includes a source line  74  and a receiver line  78  which merge into collective section  70 . Source line  74  terminates with a source connector  82  while receiver line  78  terminates with a receiver connector  86 . Collective section  70  terminates with a tip portion  90 . Tip portion  90  (shown in both  FIG. 2  and in  FIG. 5 ) comprises a fiber-optic bundle  94  and a connector  98  disposed between bundle  94  and collective section  70 . Fiber-optic bundle  94  contains a plurality of fiber-optic strands. A portion of the fiber-optic strands within bundle  94  are emitting as they are connected to source-line  74 , and those emitting strands will thus emit light from an extreme tip  100  of bundle  94 . As will be discussed further below, the remaining portion of the fiber-optic strands within bundle  94  are non-emitting as they are connected to receiver-line  78 , and those non-emitting strands will thus receive light that is incident upon extreme tip  100 . In general, cable  70  uses multiple fibers, in the order of hundreds, to achieve flexibility allowing a small bend radius for cable  70  and in order to carry a concentrated light source. 
     Referring to  FIG. 2 , tip portion  90  is configured to be received into, and removably secured to, a bulkhead fitting  102  and an associated light focusing mechanism. Bulkhead fitting  102  is configured to be affixed to or integrated with a bulkhead, chassis, frame or the like that is fixed in relation to the rotating surface to be measured using system  50 , such that the extreme tip  100  of tip portion  90  is proximal to the rotating service. 
     A presently contemplated rotating surface is a gas turbine engine, but other moving surfaces are also contemplated. Indeed, the term “moving surfaces” is intended to be non-limiting to encompass, for example, rotating, reciprocating/oscillating, and linear movement. Indeed, other movement could include any patterns that repeat, whether truly periodic or not, can be monitored. For example, shafts or surfaces driven randomly by a stepper motor in robotics or automation can be monitored. 
     It should now be understood that bulkhead fitting  102  is optional and/or can be substituted for other types of mounts that are appropriate to the particular moving surface. However, in the present embodiment which includes bulkhead fitting  102 , bulkhead fitting  102  thus also includes a tube  108  complementary to fiber-optic bundle  94  in order to receive bundle  94  therein and a connector  106  complementary to connector  98  to permit removable attachment of tip portion  90  to bulkhead fitting  102 . Bulkhead fitting  102  also includes a set of exterior threads  109  on its distal tip. Threads  109  are for attaching a lens or other light focusing mechanism (not shown), and to allow adjustment thereof to focus emitted light onto the rotating surface. 
     Electronics portion  54 , which is shown in greater detail in  FIG. 3 , comprises a chassis  110  that encases electronics and supports a light source port  114  and a receiver port  118 . Light source port  114  includes a fitting that is complementary source connector  82  so that source-line  74  can be removably attached to light source port  114 . Likewise, receiver port  118  includes a fitting that is complementary to receiver connector  86  so that receiver-line  78  can be removably attached to receiver port  118 . Chassis  110  also supports a data port  122 , which in the present embodiment is a universal serial bus (USB) port, but in other embodiments can be based on any type of wired or wireless standard, including Ethernet, RS-485, Institute of Electronic and Electrical Engineers (IEEE) standard 802.11, Bluetooth. Data port  122  permits connection of electronics portion  54  to an external computing device either directly or through a network, so that programming changes can be made to electronics portion  54  and/or data collected on electronics portion  54  can be downloaded therefrom. 
     In an embodiment, the electronics within electronics portion  54  thus comprises any standard microcomputer configuration including one or more central processing units, volatile memory (e.g. random access memory), non-volatile memory (e.g. read only memory, FLASH memory), all interconnected by a bus to which ports  114 ,  118  and  122  will also connect. The microcomputer configuration renders electronics portion  54  functional to operate as a tachometer (or other monitoring system) in accordance with the teachings further described below. Those skilled in the art will now recognize that the electronics in electronics portion  54  can also be implemented using other hardware configurations, such as using field-programmable-gate arrays or the like. 
     In operation, optical portion  58  is connected to electronics portion  54  by attaching source connector  82  to source port  114  and receiver connector  86  to receiver port  118 . Bulkhead fitting  102  is disposed within the bore of a chassis of a gas turbine engine or other moving surface. Tip portion  90  is disposed within bulkhead fitting  102  and attached thereto by joining connector  98  to connector  106 , such that extreme tip  100  is proximal to the rotating surface. Power is then applied to electronics portion  54  and then light is driven through source line  74  and then emitted from extreme tip  100  and onto the rotating surface. The features of the rotating surface then reflect the emitted light back towards tip  100  into the non-emitting fiber-optic strands within tip  100 , and that light is then carried back through receiver line  78  and back into electronics portion  54 . 
     Those skilled in the art will now appreciate that the reflective features of the rotating surface will vary over the circumference of the surface. Accordingly, non-emitting fiber-optic strands within tip  100  will receive a time varying pattern of reflected light from the surface of the rotating surface that will substantially correspond to the reflective features of the rotating surface. Accordingly, time-varying periodic patterns of light will be collected through receiver line  78  and back into electronics portion  54 . 
       FIG. 6  shows a representation of an exemplary distribution of emitting and non-emitting of fiber optic strands in a cross section  145  of bundle  94 . Cross section  145  includes a plurality of emitting  147  and non-emitting fiber optic strands  149 . Emitting strands  145  are represented by a solid circle, while non-emitting strands  149  are represented by an empty circle. Cross section  145  includes in the order of hundreds of strands  147 ,  149 . In a present embodiment include about one-thousand strands  147 ,  149 . (For convenience and ease of explanation, only a representative few strands  147 ,  149  are actually shown in  FIG. 6 .) Approximately half of the strands in cross section  145  are emitting strands  147  that combine in source line  74 , while the remaining strands in cross section  145  are non-emitting strands  149  that combine in receiver line  78 . In a present embodiment, strands  147 ,  149  are dispersed in a substantially random pattern throughout cross section  145 . In a present embodiment, strands  147 ,  149  are also dispersed in a substantially evenly in relation to each other throughout cross section  145 . Such approximately sized distribution pattern of light can substantially fully illuminate the surface to be sensed. The individual strands  147 ,  149  can cooperate to create a visual “average” of the surface reflection for detection by the electronics portion  54 . It is to be understood, however, that such a visual “average” of reflection is not required and other measurement paradigms are contemplated as desired for a particular situation. 
     To provide a simplified example of a signal gathered from an exemplary rotating surface,  FIG. 7  represents the surface of a wheel  150  embossed with metal stamped numerals between the numbers one and fifteen. Wheel  150  is represented twice in FIG.  7 —once as a cylinder, and again as bar. The bar representation of wheel  150  represents a linear projection of the circumference of wheel  150 . The stamped numerals are distinct artifacts that are present on wheel  150  such that when wheel  150  is rotating, system  50  will detect those artifacts, as will be discussed in greater detail below. Wheel  150  also is shown with two physical artifacts  151 , which represent any kind of scuffing, abrasion, imperfections or any other type of marking that could appear on wheel  150 . Of note, while such markings can be specially applied for purposes of utilizing system  50 , such markings need not be specially applied. 
       FIG. 7  also shows a waveform  154  that corresponds to the detected reflective features of wheel  150 . Waveform  154  can be generated using system  50 . The reflected light from wheel  150  is represented on waveform  154  as arrows  158  indicating a relationship of ‘light’ and ‘dark’ characteristics of the stamped numerals and artifacts  151  (and other marking that are not expressly drawn but which are implied in waveform  154  for purposes of providing an example) on the surface of the spinning wheel  150 . A shorter arrow indicates a dark characteristic, while a longer arrow indicates a light characteristic. 
     To provide a more complex example of a signal gathered from an exemplary rotating surface,  FIG. 8  shows three separate waveforms  162 - 1 ,  162 - 2 ,  162 - 3  (Collectively, waveforms  162 , and generically waveform  162 . This nomenclature is used elsewhere herein.) as detected by system  50 . These waveforms represent three different speeds of a gas turbine engine. Waveform  162 - 1  represents a slow rotation, with only one complete rotation being shown in entire waveform  162 - 1 . Waveform  162 - 2  represents a faster rotation (in relation to waveform  162 - 1 ), with three complete rotations being shown in entire waveform  162 - 2 . Waveform  162 - 3  represents a faster rotation (in relation to waveform  162 - 2 ), with six complete rotations being shown in entire waveform  162 - 3 . The extreme negative-going excursion (or trough)  164  in each waveform  162  separate and distinct from the turbine blade reflections represents a unique mark that is present on shaft of the gas turbine, and can be used as the once-per-revolution marker. Of note is that the unique mark can be based on some inherent feature or artifact already present on the shaft of the gas turbine—and it need not be a specially-applied paint or other marker. 
       FIG. 9  shows waveforms  170  which respectively correspond to waveforms  162  of  FIG. 8 . The three separate speeds shown in  FIG. 8  are processed by electronic portion  54  creating pulses  174  that are the absolute positional dependent “once-per-revolution” signals created by the extreme negative going excursions  166  discussed in relation to  FIG. 8 . It should be understood that waveforms  170  and  162  are merely exemplary—individual revolutions can be associated with smoother and/or gentler changes in waveforms as well, and/or any other unique artifact associated with any given waveform shape. 
     Having provided an overview of system  50 , further discussion of various aspects and features of system  50  is provided below. As previously described, optical portion  58  is connected to electronics portion  54  by attaching source connector  82  to source port  114  and receiver connector  86  to receiver port  118 . Bulkhead fitting  102  is disposed within the bore of a chassis of a gas turbine engine or other rotating surface. Tip portion  90  is disposed within bulkhead fitting  102  and attached thereto by joining connector  98  to connector  106 , such that extreme tip  100  is proximal to the rotating surface. Power is then applied to electronics portion  54  and light is driven through source line  74  and then emitted from extreme tip  100  and onto the rotating surface. An optical focusing tip or other light focusing mechanism can be permanently applied to bulkhead fitting  102  within the chassis of the gas turbine engine. 
     System  50  is configured to transmit light onto the rotating surface via a light source as connected to a bulkhead fitting via a light focusing mechanism. The now-illuminated rotating surface then presents its reflection to a light sensitive device again via the light focusing mechanism. The light focusing mechanism is configurable to focus the reflected light from the rotating surface onto the receiving (i.e. non-emitting) ends of bundle  90 . 
     Additionally, electronics portion  54  can receive the reflected light (via cable  62 ) and be configured to provide a single averaged value of the averaged values already being received due to the dispersion of the emitting and non-emitting fiber optics within extreme tip  100 . This average of the average is used to quantify of the surface reflection. Electronics portion  54  is configured to convert the presented reflected light to an electronic signal that can be measured and recorded by a sampling mechanism also incorporated into electronics portion. The sampling mechanism within electronics portion  54  measures and records this electronic signal in accordance with timing instructions provided by its connection to the recognition process and timing mechanism. These measured and recorded points are called “sample points”. Over time, these sample points represent an electronic signature of the reflected image as viewed by the light focusing mechanism. The surface recognition feature records a high-speed electronic “fingerprint” of the rotating shaft surface. In an embodiment, up to 70,000 data points/second can be processed, which is suitable for a gas turbine engine. In other embodiments, hundreds-of-thousands of data points/second can be processed. In general, the number of data points/second that are processed can be chosen to correspond with the speed of the surface being monitored. The timing mechanism performs a series of comparisons of the electronic signal to determine a repeating pattern. When there is a sufficient correlation between previously recorded sample points and current sample points, this event is marked. When the recognition process finds a repeating event, it outputs a signal in coordination with the timing mechanism that marks the event marker position in time via the optional event marker. These signals are called “coded signals”. A signature representing one cycle of the surface with a known or derived position and/or velocity is used for comparison to subsequent data. As new data streams from the sampling mechanism to the processing device, the new data is compared to the signature; when the correlation is sufficient it is then determined to represent the appearance of a new cycle and an event marker may be issued. Signatures longer than one cycle can be created representing long-term trends; reflectivity, angle, etc. Other shorter signatures can be created representing short-term events such as peak power, transient events, scale, etc.—both for improvement of the cyclic recognition and general maintenance and monitoring. The foregoing and the other related functionalities of electronics portion  54 , can all be implemented as software and/or hardware and/or firmware and/or combinations thereof within electronics portion  54 . 
     Referring now to  FIG. 10 , a method for monitoring a rotating surface is depicted in the form of a flow-chart and indicated generally at  500 . Method  500  can be implemented as software and/or hardware and/or firmware and/or combinations thereof within electronics portion  54 . Method  500  further illustrates various features and aspects of system  50 , although method  500  (and variants thereof) can be used with variants of system  50 . Beginning at step  510 , a plurality of light signals are emitted in a random pattern onto a rotating (or other moving) surface. When performed using system  50 , electronics portion  54  will emit light through a plurality of emitting fiber optic strands  147  from light source port  114  and through cable  62  and out through distal tip  100 . Next, at step  515 , reflections from the rotating surface are collected at non-emitting fiber optic strands  149  at distal tip  100 , which are in turn carried back through cable  62  to electronics portion  54  via receiver port  118 . 
     Next, at step  520 , the light received at step  515  is combined into a at least one waveform. The waveform can have the appearance of any of waveforms  162  in  FIG. 7 . 
     Next, at step  525  sample points are derived from the waveform that is generated at step  520 . These sample points can be any or all of the troughs found in, for example, waveforms  162  of  FIG. 7 . Step  525  merely identifies these points. 
     Next, at step  530  a plurality of the sample points that are derived at step  525  are collected and analyzed. The analysis is configured to ascertain a repeating pattern within waveform  162 . Thus, at step  535 , a determination is made as to whether sufficient sample points have been collected to ascertain a repeating pattern. If “no”, method  500  cycles from step  535  back to step  530 . If “yes”, method  500  advances from step  535  to step  540 . 
     At step  540 , a timing period is derived based on the collected sample points, and a marker is defined therefrom at step  545 . At step  550  an output signal is generated based on the marker defined at step  545  and the timing period derived at step  540 . An example of an output signal that corresponds to signal  162 - 1  would include output signal  170 - 1  of  FIG. 9 . (Likewise, output signal  170 - 2  would correspond with signal  162 - 2  and output signal  170 - 3  would correspond without signal  162 - 3 ). 
     As one variation to method  500 , upon completion of step  550 , method  500  can return back to step  535 . Indeed, it is to be understood that method  500  is shown as a series of steps for ease of presentation and explanation, but that when implemented by persons skilled in the art, the steps of method  500  are deployed in an iterative, self-correcting manner so that as more sample points are derived at step  525 , an improved timing period can be derived at step  540  and more precise marker can be derived at step  545  so that a more meaningful output signal can be generated at step  550 . Indeed, such iterations can eventually reveal any variations or fluctuations in the surface that occur over a number of rotations or other period of time. 
       FIG. 11  shows another variation of method  500 , shown as method  500   a . Steps  510   a  through  530   a  are substantially the same as step  500  through  530 . At step  535   a , new data is correlated to a previously-collected signature pattern. The previously-collected signature pattern can be a signature pattern associated with the rotating surface associated with step  510   a , and the previously-collected signature pattern can be obtained by performing steps substantially equivalent to steps  510   a - 530   a  on a separate process prior to the actual performance of method  500   a . At step  545   a  the marker associated with the previously-collected signature pattern is defined and/or updated and/or refined as the case may require. At step  555   a  output is generated. After step  555   a  the method returns to step  530   a . The output that is generated at step  555   a  can be a waveform or in any other suitable format. Note that it can be desired to perform steps  530   a - 545   a  according to a desired criteria (e.g. a number of cycles so that the results of those cycles can be averaged) prior to actually performing step  550   a.    
     The functionality of method  500 , and the other related functionalities of electronics portion  54 , can all be implemented as software and/or hardware and/or firmware and/or combinations thereof within electronics portion  54 . 
     While the foregoing presents certain specific embodiments, variations, combinations and/or subsets of those embodiments are contemplated. For example, system  50  can be altered to employ a camera in place of tip portion  90 . As another example, embodiments herein refer to a bundle  94  of fibre optic strands in cable  62 . However, in other embodiments, cable  62  can be implemented with a single fiber as an emitter and another an a collector. In a single-fiber solution it can be desired to use a brighter source, such as a laser or a pulsed light emitting diode (“LED”) to compensate for reduced reflection. Alternatively, fibre can be omitted altogether and other types of emitters or collectors can be used. In addition, cable  62  can be eliminated altogether by a configuration that implements the emitting and receiving function of electronics portion  54  within a device that is resident all within the same form-factor as tip  94  in and of itself. As a still further example variation, hybrids of the above are contemplated whereby a source is housed completely within tip  94 , but a receiver line (such as line  78 ) is connected to a modified version of electronics portion  54  that does not include a source or a source port  114 . In these variations, it can be desired to provide additional cooling capabilities, particularly where the entire system is incorporated into tip  94  and located proximal to the moving surface. As a still further variation, a lasing device can be used in place of an emitting lamp within electronics portion  54 . Those skilled in the art will now recognize that method  500  and method  500   a  and variations of each can be implemented on other systems, other than system  50 . 
     There are various novel features of the present specification. For example, the use of the tip portion  90  and the signal processing electronics within electronics portion  54 . The tip portion  90  allows system  50  to be used in many different applications. The electronics of electronics portion  58  also process an electronic representation of the observed surface reflection inherent to the surface of the rotating object to obtain the desired output. 
     The electronic portion  58  is configured to amplify and filter the waveform obtained at receiver port  118  into yet another waveform that also represents the passing rotating surface. In Mode 1 operation the repeating pattern can have a distinguishing unique “marker” that deviates from the normal signal level. This unique mark can be directly related to a known physical location on the rotating surface and thereby becomes a known reference point that the surface recognition technology can utilize without operator intervention. In Mode 2 the pattern repeats by there is no unique distinguishing marker evident in the waveform. In this Mode an operator will observe the waveform and either create a physical reference point or assign a physical reference point that electronics portion  58  will then retain. 
     In both Mode 1 and Mode 2 the Electronic Portion produces a Transistor-Transistor Logic (“TTL”) level output pulse in accordance with the processed data that has produced a reference point as seen in  FIG. 9  as derived from the waveforms  162  shown in  FIG. 8 . It should also be understood that other types of output signals are contemplated, other than the type of signal shown in  FIG. 9 . 
     While system  50  addresses the positioning problem associated with gas turbine engines, this technology also applies to other less restrictive applications. Such uses include: commercial power systems; the aircraft industry; industrial infrastructure machinery such as pumps, compressors and motors; gas turbine power system engines, which includes stationary engines such as commercial and military power systems, co-generation plants, and emergency standby generators; gas and steam turbine powered marine propulsion systems; and mobile turbines. These are other possible applications and are not intended to be an exhaustive list of all potential applications.