Patent Publication Number: US-9423290-B2

Title: Abnormality diagnostic device for rolling bearing, wind turbine generation apparatus and abnormality diagnostic system

Description:
RELATED APPLICATIONS 
     This application is the U.S. National Phase under 35 U.S.C. §371 of International Application No. PCT/JP2010/073300, filed on Dec. 24, 2010, which in turn claims the benefit of Japanese Application Nos. 2010-000070 filed on Jan. 4, 2010, and 2010-281373filed on Dec. 17, 2010, the disclosures of which Applications are incorporated by reference herein. 
     TECHNICAL FIELD 
     The present invention relates to an abnormality diagnostic device for a rolling bearing, a wind turbine generation apparatus and an abnormality diagnostic system, and more particularly relates to an abnormality diagnostic technique for a rolling bearing provided for a main shaft, a gearbox, a generator, or the like of a wind turbine generation apparatus. 
     BACKGROUND ART 
     A wind turbine generation apparatus generates electric power by rotating a main shaft connected to a blade that receives wind force, accelerating rotation of the main shaft by a gearbox, and then rotating a rotor of a generator. Each of the main shaft and the rotation shafts of the gearbox and the generator is rotatably supported by a rolling bearing, and an abnormality diagnostic device that diagnoses an abnormality of such a bearing is known. 
     Japanese Patent Laying-Open No. 2006-105956 (Patent Literature 1) discloses an abnormality diagnostic device that diagnoses an abnormality of a rotating component such as a bearing device. This abnormality diagnostic device is an abnormality diagnostic device that diagnoses an abnormality of a double-row tapered rolling bearing incorporated into a rolling bearing device for a railroad vehicle that relatively rotates with respect to a bearing housing, and includes a drive motor for rotationally driving the double-row tapered rolling bearing and a vibration sensor attached to the bearing housing. At the time of inertial rotation of the double-row tapered rolling bearing within the range of predetermined rotational speeds during power off of the drive motor, an abnormality of the double-row tapered rolling bearing is diagnosed based on a detection signal from the vibration sensor. 
     According to this abnormality diagnostic device, an abnormality of a rotating component can be diagnosed without disassembling the device in which the rotating component is incorporated, and an erroneous diagnosis under the influence of electric disturbance noise produced by rotation driving means can be prevented to allow a reliable abnormality diagnosis to be performed (see Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Japanese Patent Laying-Open No. 2006-105956 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the abnormality diagnostic device disclosed in the above-mentioned Japanese Patent Laying-Open No. 2006-105956, an abnormality determination of the rotating component is made based on the result of frequency analysis of a vibration waveform measured by using the vibration sensor attached to the bearing housing. More specifically, in the rolling bearing, an occurrence cycle of abnormal vibrations produced by damage to the bearing varies depending on a damage occurring position. Therefore, the vibration waveform measured by using the vibration sensor is subjected to a frequency analysis to analyze its peak frequency, thereby identifying presence/absence of abnormality in the bearing and an abnormal portion. 
     However, with such a technique through the frequency analysis, in the case where, for example, a gearbox is provided as in the above-mentioned wind turbine generation apparatus, a correct abnormality diagnosis cannot be performed in some cases due to mixing of a meshing vibration frequency of gears of the gearbox and/or mixing of natural vibration frequencies of various peripheral components. 
     The present invention was therefore made to solve this problem, and has an object to provide an abnormality diagnostic device for a rolling bearing, a wind turbine generation apparatus and an abnormality diagnostic system that achieve a more correct abnormality diagnosis. 
     Solution to Problem 
     According to the present invention, an abnormality diagnostic device for a rolling bearing includes a vibration sensor for measuring a vibration waveform of the rolling bearing, and a processing unit for diagnosing an abnormality of the rolling bearing. The processing unit includes first and second operation units, an envelope processing unit and a diagnostic unit. The first operation unit calculates an effective value of the vibration waveform measured by using the vibration sensor. The envelope processing unit generates an envelope waveform of the vibration waveform by performing envelope processing on the vibration waveform measured by using the vibration sensor. The second operation unit calculates an effective value of an AC component of the envelope waveform generated by the envelope processing unit. The diagnostic unit diagnoses the abnormality of the rolling bearing based on the effective value of the vibration waveform calculated by the first operation unit and the effective value of the AC component of the envelope waveform calculated by the second operation unit. 
     Preferably, the abnormality diagnostic device for a rolling bearing further includes a rotation sensor for detecting a rotational speed of one of a shaft supported by the rolling bearing and the rolling bearing. The processing unit further includes a modified vibration degree calculation unit and a modified modulation degree calculation unit. The modified vibration degree calculation unit calculates a modified vibration degree obtained by normalizing, by the rotational speed, the effective value of the vibration waveform calculated by the first operation unit. The modified modulation degree calculation unit calculates a modified modulation degree obtained by normalizing, by the rotational speed, the effective value of the AC component of the envelope waveform calculated by the second operation unit. The diagnostic unit diagnoses the abnormality of the rolling bearing based on the modified vibration degree and the modified modulation degree. 
     Further preferably, the diagnostic unit diagnoses the abnormality of the rolling bearing based on transition of time changes in the modified vibration degree and the modified modulation degree. 
     Preferably, the processing unit further includes a frequency analysis unit. The frequency analysis unit performs a frequency analysis on at least one of the vibration waveform and the envelope waveform. The diagnostic unit further presumes an abnormal portion of the rolling bearing based on the result of analysis obtained by the frequency analysis unit. 
     Preferably, the vibration sensor includes an acceleration sensor. 
     Preferably, the abnormality diagnostic device for a rolling bearing further includes a displacement sensor for detecting a relative displacement between an inner ring and an outer ring of the rolling bearing. The diagnostic unit diagnoses the abnormality of the rolling bearing by further using a detected value of the displacement sensor. 
     Still preferably, the abnormality diagnostic device for a rolling bearing further includes an AE sensor for detecting an acoustic emission wave produced from the rolling bearing. The diagnostic unit diagnoses the abnormality of the rolling bearing by further using a detected value of the AE sensor. 
     Still preferably, the abnormality diagnostic device for a rolling bearing further includes a temperature sensor for measuring the temperature of the rolling bearing. The diagnostic unit diagnoses the abnormality of the rolling bearing by further using a measured value of the temperature sensor. 
     Still preferably, the abnormality diagnostic device for a rolling bearing further includes a sensor for measuring the amount of impurities contained in a lubricant of the rolling bearing. The diagnostic unit diagnoses the abnormality of the rolling bearing by further using a measured value of the sensor. 
     Preferably, the abnormality diagnostic device for a rolling bearing further includes a rotation sensor for detecting a rotational speed of one of a shaft supported by the rolling bearing and the rolling bearing. The envelope processing unit includes an absolute value detection unit and an envelope detection unit. The absolute value detection unit outputs an absolute value of the vibration waveform. The envelope detection unit generates the envelope waveform by performing attenuation processing with a predetermined time constant on an output signal from the absolute value detection unit. Herein, the time constant is set based on the rotational speed. 
     Further preferably, the time constant is set to be less than or equal to a half cycle of rotation of a rolling element in the rolling bearing. 
     Further preferably, the time constant is set to be more than or equal to 0.5 times the half cycle of the rolling element. 
     Still preferably, the time constant is set to be less than or equal to a passing cycle of a rolling element relative to a stationary ring of the rolling bearing. 
     Further preferably, the time constant is set to be more than or equal to 0.5 times the passing cycle of the rolling element. 
     Moreover, according to the present invention, a wind turbine generation apparatus includes a blade, a main shaft, a gearbox, a generator, a plurality of rolling bearings, and an abnormality diagnostic device. The blade receives wind force. The main shaft is connected to the blade. The gearbox accelerates rotation of the main shaft. The generator is connected to an output shaft of the gearbox. The plurality of rolling bearings are provided in the main shaft, the gearbox and the generator. The abnormality diagnostic device diagnoses an abnormality of at least one of the plurality of rolling bearings. The abnormality diagnostic device includes a vibration sensor for measuring a vibration waveform of a rolling bearing to be diagnosed, and a processing unit for diagnosing an abnormality of the rolling bearing to be diagnosed. The processing unit includes first and second operation units, an envelope processing unit and a diagnostic unit. The first operation unit calculates an effective value of the vibration waveform measured by using the vibration sensor. The envelope processing unit generates an envelope waveform of the vibration waveform by performing envelope processing on the vibration waveform measured by using the vibration sensor. The second operation unit calculates an effective value of an AC component of the envelope waveform generated by the envelope processing unit. The diagnostic unit diagnoses the abnormality of the rolling bearing based on the effective value of the vibration waveform calculated by the first operation unit and the effective value of the AC component of the envelope waveform calculated by the second operation unit. 
     Moreover, according to the present invention, an abnormality diagnostic system includes a wind turbine generation apparatus, an abnormality diagnostic device and a communications device. The abnormality diagnostic device is provided at a different position from the wind turbine generation apparatus. The communications device establishes communications between the wind turbine generation apparatus and the abnormality diagnostic device. The wind turbine generation apparatus includes a blade, a main shaft, a gearbox, a generator, a plurality of rolling bearings, a vibration sensor, and a data processing unit. The blade receives wind force. The main shaft is connected to the blade. The gearbox accelerates rotation of the main shaft. The generator is connected to an output shaft of the gearbox. The plurality of rolling bearings are provided in the main shaft, the gearbox and the generator. The vibration sensor measures a vibration waveform of at least one of the plurality of rolling bearings. The data processing unit performs primary processing on the vibration waveform measured by using the vibration sensor. The data processing unit includes first and second operation units and an envelope processing unit. The first operation unit calculates an effective value of the vibration waveform measured by using the vibration sensor. The envelope processing unit generates an envelope waveform of the vibration waveform by performing envelope processing on the vibration waveform measured by using the vibration sensor. The second operation unit calculates an effective value of an AC component of the envelope waveform generated by the envelope processing unit. The abnormality diagnostic device diagnoses an abnormality of a rolling bearing to be diagnosed based on the effective value of the vibration waveform and the effective value of the AC component of the envelope waveform received from the data processing unit of the wind turbine generation apparatus through the communications device. 
     Preferably, the abnormality diagnostic device and the communications device are provided separately from a system monitoring the amount of power generation of the wind turbine generation apparatus. 
     Preferably, the communications device includes wireless communications in part of a communications route. 
     Further preferably, the abnormality diagnostic device is connected to the Internet. The communications device includes a wireless communications unit and a communications server. The wireless communications unit is provided in the wind turbine generation apparatus. The communications server is connected to the Internet, and is configured to be capable of wirelessly communicating with the wireless communications unit. 
     Advantageous Effects of Invention 
     According to the present invention, since an abnormality of the rolling bearing is diagnosed based on the effective value of the vibration waveform measured by using the vibration sensor and the effective value of the AC component of the envelope waveform generated by performing envelope processing on the vibration waveform measured by using the vibration sensor, a more correct abnormality diagnosis can be achieved than in a conventional technique through a frequency analysis. In addition, unnecessary maintenance can be eliminated, so that the cost required for maintenance can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram schematically showing the structure of a wind turbine generation apparatus to which an abnormality diagnostic device for a rolling bearing according to a first embodiment of the present invention is applied. 
         FIG. 2  is a functional block diagram functionally showing the configuration of a data processing device shown in  FIG. 1 . 
         FIG. 3  is a diagram showing a vibration waveform of a bearing when no abnormality occurs in the bearing. 
         FIG. 4  is a diagram showing a vibration waveform of the bearing seen when surface roughness and/or poor lubrication occur in a raceway of the bearing. 
         FIG. 5  is a diagram showing a vibration waveform of the bearing in an initial stage when delamination occurs in the raceway of the bearing. 
         FIG. 6  is a diagram showing a vibration waveform of the bearing seen in a terminal stage of delamination abnormality. 
         FIG. 7  is a diagram showing time changes in an effective value of a vibration waveform of the bearing and an effective value of an AC component of an envelope waveform obtained when delamination occurs partly in the raceway of the bearing and delamination is then transferred all over the raceway. 
         FIG. 8  is a diagram showing time changes in an effective value of a vibration waveform of the bearing and an effective value of an AC component of an envelope waveform obtained when surface roughness and/or poor lubrication of the raceway of the bearing occur. 
         FIG. 9  is a functional block diagram functionally showing the configuration of a data processing device in a second embodiment. 
         FIG. 10  is a functional block diagram functionally showing the configuration of a data processing device in a third embodiment. 
         FIG. 11  is a functional block diagram functionally showing the configuration of a data processing device in a fourth embodiment. 
         FIG. 12  is a diagram schematically showing the overall structure of an abnormality diagnostic system according to a fifth embodiment. 
         FIG. 13  is a functional block diagram functionally showing the configuration of a data processing device included in a wind turbine generation apparatus shown in  FIG. 12 . 
         FIG. 14  is a functional block diagram of an envelope processing unit in a sixth embodiment. 
         FIG. 15  is a diagram showing changes in envelope waveform when a time constant in envelope processing is changed. 
         FIG. 16  is a diagram showing the relationship between a value obtained by dividing the modulation degree by the vibration degree and the time constant in envelope processing. 
         FIG. 17  is a diagram showing the relationship between the ratio of the modulation ratio of abnormal product (delamination) to the modulation ratio of normal product and the time constant in envelope processing. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention will be described in detail below with reference to the drawings. It is noted that, in the drawings, the same or corresponding portions have the same reference characters allotted, and description thereof will not be repeated. 
     [First Embodiment] 
       FIG. 1  is a diagram schematically showing the structure of a wind turbine generation apparatus to which an abnormality diagnostic device for a rolling bearing according to a first embodiment of this invention is applied. Referring to  FIG. 1 , a wind turbine generation apparatus  10  includes a main shaft  20 , a blade  30 , a gearbox  40 , a generator  50 , a main shaft bearing (hereinafter simply referred to as a “bearing”)  60 , a vibration sensor  70 , and a data processing device  80 . Gearbox  40 , generator  50 , bearing  60 , vibration sensor  70 , and data processing device  80  are stored in a nacelle  90 , and nacelle  90  is supported by a tower  100 . 
     Main shaft  20  enters nacelle  90  to be connected to an input shaft of gearbox  40 , and is rotatably supported by bearing  60 . Main shaft  20  transmits rotating torque produced by blade  30  having received wind force, to the input shaft of gearbox  40 . Blade  30  is provided at the leading end of main shaft  20 , and converts wind force into rotating torque for transmission to main shaft  20 . 
     Bearing  60  is secured within nacelle  90 , and supports main shaft  20  rotatably. Bearing  60  is implemented by a rolling bearing, and, for example, implemented by a self-aligning rolling bearing, a tapered rolling bearing, a cylindrical rolling bearing, a ball bearing, or the like. It is noted that these bearings may be of either a single-row or double-row type. Vibration sensor  70  is secured to bearing  60 . Vibration sensor  70  detects vibrations of bearing  60 , and outputs a detected value to data processing device  80 . Vibration sensor  70  is implemented by, for example, an acceleration sensor in which a piezoelectric device is used. 
     Gearbox  40  is provided between main shaft  20  and generator  50 , and increases the rotational speed of main shaft  20  for output to generator  50 . As an example, gearbox  40  is implemented by a gearbox mechanism including a planetary gear, an intermediate shaft, a high speed shaft, and the like. It is noted that, although not particularly shown, a plurality of bearings rotatably supporting a plurality of shafts are also provided in this gearbox  40 . Generator  50  is connected to the output shaft of gearbox  40 , and generates power by means of rotating torque received from gearbox  40 . Generator  50  is implemented by an induction generator, for example. It is noted that a bearing rotatably supporting a rotor is also provided in this generator  50 . 
     Data processing device  80  is provided in nacelle  90 , and receives the detected value of vibrations of bearing  60  from vibration sensor  70 . Data processing device  80  then diagnoses abnormality of bearing  60  in accordance with a previously set program by a method which will be described later using a vibration waveform of bearing  60 . 
       FIG. 2  is a functional block diagram functionally showing the configuration of data processing device  80  shown in  FIG. 1 . Referring to  FIG. 2 , data processing device  80  includes high pass filters (hereinafter referred to as “HPF (High Pass Filter)”)  110  and  150 , effective value operation units  120  and  160 , an envelope processing unit  140 , a storage unit  180 , and a diagnostic unit  190 . 
     HPF  110  receives the detected value of vibrations of bearing  60  from vibration sensor  70 . For the received detection signal, HPF  110  passes a signal component higher than a predetermined frequency, and blocks a low frequency component. This HPF  110  is provided for removing a DC component included in the vibration waveform of bearing  60 . It is noted that, if the output from vibration sensor  70  does not include a DC component, HPF  110  may be omitted. 
     Effective value operation unit  120  receives, from HPF  110 , the vibration waveform of bearing  60  with a DC component removed therefrom. Effective value operation unit  120  then calculates an effective value (also referred to as a “RMS (Root Mean Square) value”) of the vibration waveform of bearing  60 , and outputs the calculated effective value of the vibration waveform to storage unit  180 . 
     Envelope processing unit  140  receives the detected value of vibrations of bearing  60  from vibration sensor  70 . Envelope processing unit  140  then performs envelope processing on the received detection signal, thereby generating an envelope waveform of the vibration waveform of bearing  60 . It is noted that various publicly-known techniques are applicable to the envelope processing operated in envelope processing unit  140 , and as an example, the vibration waveform of bearing  60  measured by using vibration sensor  70  is rectified into an absolute value and is passed through a low pass filter (LPF), thereby generating the envelope waveform of the vibration waveform of bearing  60 . 
     HPF  150  receives the envelope waveform of the vibration waveform of bearing  60  from envelope processing unit  140 . For the received envelope waveform, HPF  150  passes a signal component higher than a predetermined frequency, and blocks a low frequency component. This HPF  150  is provided for removing a DC component included in the envelope waveform and extracting an AC component of the envelope waveform. 
     Effective value operation unit  160  receives, from HPF  150 , the envelope waveform with a DC component removed therefrom, i.e., an AC component of the envelope waveform. Effective value operation unit  160  then calculates an effective value (RMS value) of the received AC component of the envelope waveform, and outputs the calculated effective value of the AC component of the envelope waveform to storage unit  180 . 
     Storage unit  180  synchronizes and momentarily stores the effective value of the vibration waveform of bearing  60  calculated by effective value operation unit  120  and the effective value of the AC component of the envelope waveform calculated by effective value operation unit  160 . This storage unit  180  is implemented by, for example, a readable and writable nonvolatile memory or the like. 
     Diagnostic unit  190  reads, from storage unit  180 , the effective value of the vibration waveform of bearing  60  and the effective value of the AC component of the envelope waveform momentarily stored in storage unit  180 , and diagnoses an abnormality of bearing  60  based on the read two effective values. In detail, diagnostic unit  190  diagnoses an abnormality of bearing  60  based on transition of time changes in the effective value of the vibration waveform of bearing  60  and the effective value of the AC component of the envelope waveform. 
     That is, the effective value of the vibration waveform of bearing  60  calculated by effective value operation unit  120  is an effective value of a raw vibration waveform not having been subjected to envelope processing, and therefore, for example, less increases in value in the case of impulse vibrations whose amplitude increases only when a rolling element passes over a position of delamination if delamination occurs partly in a raceway, but increases greatly in value in the case of continuous vibrations occurring at the time of surface roughness and/or poor lubrication of a contact area between the raceway and the rolling element. 
     On the other hand, the effective value of the AC component of the envelope waveform calculated by effective value operation unit  160  less increases in value in the case of continuous vibrations occurring at the time of surface roughness and/or poor lubrication of the raceway or does not increase depending on the case, but increases greatly in value in the case of impulse vibrations. Therefore, in this first embodiment, by using the effective value of the vibration waveform of bearing  60  and the effective value of the AC component of the envelope waveform, an abnormality that could not be detected only with either effective value can be detected, so that a more correct abnormality diagnosis can be achieved. 
       FIGS. 3 to 6  are diagrams each showing a vibration waveform of bearing  60  measured by using vibration sensor  70 . It is noted that the vibration waveforms when the rotational speed of main shaft  20  ( FIG. 1 ) is constant are shown in  FIGS. 3 to 6 . 
       FIG. 3  is a diagram showing the vibration waveform of bearing  60  when no abnormality occurs in bearing  60 . Referring to  FIG. 3 , the horizontal axis indicates the time, and the vertical axis indicates the vibration degree representing the magnitude of vibrations. 
       FIG. 4  is a diagram showing the vibration waveform of bearing  60  seen when surface roughness and/or poor lubrication occur in the raceway of bearing  60 . Referring to  FIG. 4 , if surface roughness and/or poor lubrication of the raceway occur, vibrations increase, and the state where vibrations have increased occurs continuously. No remarkable peak occurs in the vibration waveform. Therefore, for such a vibration waveform, as compared with the effective value of the vibration waveform (output of effective value operation unit  120  ( FIG. 2 )) and the effective value of the AC component of the envelope waveform (output of effective value operation unit  160  ( FIG. 2 )) when no abnormality occurs in bearing  60 , the effective value of a raw vibration waveform not having been subjected to envelope processing increases and the effective value of the AC component of the envelope waveform less increases. 
       FIG. 5  is a diagram showing the vibration waveform of bearing  60  in an initial stage when delamination occurs in the raceway of bearing  60 . Referring to  FIG. 5 , the initial stage of delamination abnormality is a state where delamination occurs partly in the raceway, and since strong vibrations occur when the rolling element passes over the position of delamination, pulsed vibrations occur periodically in accordance with rotation of the shaft. While the rolling element is passing over positions other than the position of delamination, vibrations less increase. Therefore, for such a vibration waveform, the effective value of the AC component of the envelope waveform increases and the effective value of a raw vibration waveform not having been subjected to envelope processing less increases, as compared with the effective value of the vibration waveform and the effective value of the AC component of the envelope waveform when no abnormality occurs in bearing  60 . 
       FIG. 6  is a diagram showing the vibration waveform of bearing  60  seen in a terminal stage of delamination abnormality. Referring to  FIG. 6 , the terminal stage of delamination abnormality is a state where delamination is transferred all over the raceway, and vibrations increase as a whole, and a tendency to pulsed vibrations is weakened as compared to the initial stage of abnormality. Therefore, for such a vibration waveform, the effective value of a raw vibration waveform increases and the effective value of the AC component of the envelope waveform decreases, as compared with the effective value of the vibration waveform and the effective value of the AC component of the envelope waveform in the initial stage of delamination abnormality. 
       FIG. 7  is a diagram showing time changes in the effective value of the vibration waveform of bearing  60  and the effective value of the AC component of the envelope waveform when delamination occurs partly in the raceway of bearing  60  and is then transferred all over the raceway. It is noted that time changes in each effective value when the rotational speed of main shaft  20  is constant are shown in  FIG. 7  and  FIG. 8  which will be described later. 
     Referring to  FIG. 7 , a curve k 1  represents time changes in the effective value of the vibration waveform not having been subjected to envelope processing, and a curve k 2  represents time changes in the effective value of the AC component of the envelope waveform. At time t 1  before delamination occurs, the effective value (k 1 ) of the vibration waveform and the effective value (k 2 ) of the AC component of the envelope waveform are both small. It is noted that the vibration waveform at time t 1  will be a waveform as shown in above-mentioned  FIG. 3 . 
     When delamination occurs partly in the raceway of bearing  60 , the effective value (k 2 ) of the AC component of the envelope waveform increases greatly, and on the other hand, the effective value (k 1 ) of the vibration waveform not having been subjected to envelope processing less increases (around time t 2 ), as described with reference to  FIG. 5 . 
     Further, when delamination is then transferred thereafter all over the raceway, the effective value (k 1 ) of the vibration waveform not having been subjected to envelope processing increases greatly, and on the other hand, the effective value (k 2 ) of the AC component of the envelope waveform decreases (around time t 3 ), as described with reference to  FIG. 6 . 
       FIG. 8  is a diagram showing time changes in the effective value of the vibration waveform of bearing  60  and the effective value of the AC component of the envelope waveform when surface roughness and/or poor lubrication of the raceway of bearing  60  occur. Referring to  FIG. 8 , curve k 1  represents time changes in the effective value of the vibration waveform not having been subjected to envelope processing, and curve k 2  represents time changes in the effective value of the AC component of the envelope waveform, similarly to  FIG. 7 . 
     At time t 11  before surface roughness and/or poor lubrication of the raceway occur, the effective value (k 1 ) of the vibration waveform and the effective value (k 2 ) of the AC component of the envelope waveform are both small. It is noted that the vibration waveform at time t 11  will be a waveform as shown in above-mentioned  FIG. 3 . 
     When surface roughness and/or poor lubrication of the raceway of bearing  60  occur, the effective value (k 1 ) of the vibration waveform not having been subjected to envelope processing increases, and on the other hand, an increase in the effective value (k 2 ) of the AC component of the envelope waveform is not seen (around time t 12 ), as described with reference to  FIG. 4 . 
     In this way, an abnormality diagnosis of bearing  60  can be performed more correctly based on the transition of time changes in the effective value (k 1 ) of the raw vibration waveform not having been subjected to envelope processing and the effective value (k 2 ) of the AC component of the envelope waveform. 
     As described above, according to this first embodiment, since an abnormality of bearing  60  is diagnosed based on the effective value of the vibration waveform of bearing  60  measured by using vibration sensor  70  and the effective value of the AC component of the envelope waveform generated by performing envelope processing on the vibration waveform measured by using vibration sensor  70 , a more correct abnormality diagnosis can be achieved than in the conventional technique through a frequency analysis. In addition, unnecessary maintenance can be eliminated, so that the cost required for maintenance can be reduced. 
     [Second Embodiment] 
     When the rotational speed of main shaft  20  ( FIG. 1 ) changes, the magnitude of vibrations of bearing  60  changes. Generally, vibrations of bearing  60  increase as the rotational speed of main shaft  20  increases. Therefore, in this second embodiment, each of the effective value of the vibration waveform of bearing  60  and the effective value of the AC component of the envelope waveform is normalized by the rotational speed of main shaft  20 , and an abnormality diagnosis of bearing  60  is performed using each normalized effective value. 
     The overall structure of a wind turbine generation apparatus in this second embodiment is the same as the structure of the first embodiment shown in  FIG. 1 . 
       FIG. 9  is a functional block diagram functionally showing the configuration of a data processing device  80 A in the second embodiment. Referring to  FIG. 9 , data processing device  80 A further includes a modified vibration degree calculation unit  130 , a modified modulation degree calculation unit  170  and a speed function generation unit  200  in the configuration of data processing device  80  in the first embodiment shown in  FIG. 2 . 
     Speed function generation unit  200  receives a detected value of the rotational speed of main shaft  20  obtained by a rotation sensor  210  (not shown in  FIG. 1 ). It may be configured that rotation sensor  210  outputs a detected value of the rotational position of main shaft  20  and the rotational speed of main shaft  20  is calculated in speed function generation unit  200 . Speed function generation unit  200  generates a speed function A(N) for normalizing, by a rotational speed N of main shaft  20 , the effective value of the vibration waveform of bearing  60  calculated by effective value operation unit  120  and a speed function B(N) for normalizing, by rotational speed N of main shaft  20 , the effective value of the AC component of the envelope waveform calculated by effective value operation unit  160 . As an example, speed functions A(N) and B(N) are expressed by the following expressions:
 
 A ( N )= a×N   −0.5   (1)
 
 B ( N )= b×N   −0.5   (2)
 
     Herein, a and b are constants previously determined by an experiment or the like, which may be different values or the same value. 
     Modified vibration degree calculation unit  130  receives the effective value of the vibration waveform of bearing  60  from effective value operation unit  120 , and receives speed function A(N) from speed function generation unit  200 . Modified vibration degree calculation unit  130  then uses speed function A(N) to calculate a value (hereinafter referred to as a “modified vibration degree”) obtained by normalizing, by the rotational speed of main shaft  20 , the effective value of the vibration waveform calculated by effective value operation unit  120 . Specifically, a modified vibration degree Vr* is calculated by the following expression using an effective value Vr of the vibration waveform calculated by effective value operation unit  120  and speed function A(N). 
     
       
         
           
             
               
                 
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     Herein, Vra indicates the average value of Vr from time  0  to T. 
     Modified vibration degree calculation unit  130  then outputs modified vibration degree Vr* calculated by the expression (3) to storage unit  180 . 
     Modified modulation degree calculation unit  170  receives the effective value of the AC component of the envelope waveform from effective value operation unit  160 , and receives speed function B(N) from speed function generation unit  200 . Modified modulation degree calculation unit  170  then uses speed function B(N) to calculate a value (hereinafter referred to as a “modified modulation degree”) obtained by normalizing, by the rotational speed of main shaft  20 , the effective value of the AC component of the envelope waveform calculated by effective value operation unit  160 . Specifically, a modified modulation degree Ve* is calculated by the following expression using an effective value Ve of the AC component of the envelope waveform calculated by effective value operation unit  160  and speed function B(N). 
     
       
         
           
             
               
                 
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     Herein, Vea indicates the average value of Ve from time  0  to T. Modified modulation degree calculation unit  170  outputs modified modulation degree Ve* calculated by the expression (4) to storage unit  180 . 
     Then, modified vibration degree Vr* and modified modulation degree Ve* stored momentarily in storage unit  180  are read by diagnostic unit  190 , and an abnormality diagnosis of bearing  60  is performed by diagnostic unit  190  based on transition of time changes in modified vibration degree Vr* and modified modulation degree Ve* having been read. 
     It is noted that, in the above description, rotation sensor  210  may be attached to main shaft  20 , or a rotation sensor-equipped bearing in which rotation sensor  210  is incorporated into bearing  60  may be used as bearing  60 . 
     As described above, according to this second embodiment, since an abnormality is diagnosed based on modified vibration degree Vr* obtained by normalizing the effective value of the vibration waveform of bearing  60  by the rotational speed and modified modulation degree Ve* obtained by normalizing the effective value of the AC component of the envelope waveform by the rotational speed, a disturbance due to variations in rotational speed is eliminated, so that a more correct abnormality diagnosis can be achieved. 
     [Third Embodiment] 
     In this third embodiment, to perform a further correct abnormality diagnosis, an abnormality diagnosis through a frequency analysis is used together with the above-described first or second embodiment. 
     The whole structure of a wind turbine generation apparatus in this third embodiment is the same as that of wind turbine generation apparatus  10  shown in  FIG. 1 . 
       FIG. 10  is a functional block diagram functionally showing the configuration of a data processing device  80 B in the third embodiment. Referring to  FIG. 10 , data processing device  80 B further includes frequency analysis units  220  and  230  in the configuration of data processing device  80 A shown in  FIG. 9 . 
     Frequency analysis unit  220  receives, from HPF  110 , the vibration waveform of bearing  60  with a DC component removed therefrom. Frequency analysis unit  220  then performs a frequency analysis on the received vibration waveform of bearing  60 , and outputs the result of frequency analysis to storage unit  180 . As an example, frequency analysis unit  220  performs fast Fourier transform (FFT) processing on the vibration waveform of bearing  60  received from HPF  110 , and outputs a peak frequency exceeding a previously set threshold value, to storage unit  180 . 
     Frequency analysis unit  230  receives, from HPF  150 , the AC component of the envelope waveform with a DC component removed therefrom. Frequency analysis unit  230  then performs a frequency analysis on the received AC component of the envelope waveform, and outputs the result of frequency analysis to storage unit  180 . As an example, frequency analysis unit  230  performs FFT processing on the AC component of the envelope waveform received from HPF  110 , and outputs a peak frequency exceeding a previously set threshold value, to storage unit  180 . 
     Diagnostic unit  190  then reads, from storage unit  180 , the result of frequency analyses by frequency analysis units  220  and  230  together with modified vibration degree Vr* and modified modulation degree Ve*, and uses the result of frequency analyses together with the transition of time changes in modified vibration degree Vr* and modified modulation degree Ve*, thereby performing a more reliable abnormality diagnosis. 
     For example, the result of frequency analyses by frequency analysis units  220  and  230  can be used for presuming an abnormality occurring portion when an abnormality is detected by the abnormality diagnosis based on modified vibration degree Vr* and modified modulation degree Ve*. That is, when damage occurs within the bearing, the peak of vibrations will occur at a specific frequency theoretically determined from the geometric configuration within the bearing and the rotational speed depending on a damaged portion (inner ring, outer ring, rolling element). Therefore, an abnormality occurring portion can be diagnosed more correctly by using the result of frequency analyses by frequency analysis units  220  and  230  together with the abnormality diagnosis based on modified vibration degree Vr* and modified modulation degree Ve* described above. 
     It is noted that, in the above description, frequency analysis units  220  and  230  shall be added in the second embodiment, however, frequency analysis units  220  and  230  may be added to data processing device  80  in the first embodiment shown in  FIG. 2 . 
     As described above, according to this third embodiment, since the abnormality diagnosis through the frequency analysis is used together, the reliability of abnormality diagnosis can be increased further, and an abnormality occurring portion can be diagnosed more correctly. 
     [Fourth Embodiment] 
     In the fourth embodiment, to further increase the reliability of abnormality diagnosis of bearing  60 , detected values of various sensors are used together. 
       FIG. 11  is a functional block diagram functionally showing the configuration of a data processing device  80 C in the fourth embodiment. Referring to  FIG. 11 , data processing device  80 C includes a diagnostic unit  190 A in place of diagnostic unit  190  in the configuration of data processing device  80 B shown in  FIG. 10 . 
     The wind turbine generation apparatus in this fourth embodiment is further provided with at least one of a displacement sensor  240 , an AE (Acoustic Emission) sensor  250 , a temperature sensor  260 , and a magnetic iron powder sensor  270 , in addition to vibration sensor  70  and rotation sensor  210 . Diagnostic unit  190 A receives a detected value from at least one of displacement sensor  240 , AE sensor  250 , temperature sensor  260 , and magnetic iron powder sensor  270  provided. Diagnostic unit  190 A also reads, from storage unit  180 , modified vibration degree Vr* and modified modulation degree Ve* as well as the result of frequency analyses by frequency analysis units  220  and  230 . 
     Then, diagnostic unit  190 A performs an abnormality diagnosis of bearing  60  by using the detected value received from at least one of displacement sensor  240 , AE sensor  250 , temperature sensor  260 , and magnetic iron powder sensor  270 , together with modified vibration degree Vr* and modified modulation degree Ve* as well as the result of frequency analyses by frequency analysis units  220  and  230 . 
     Displacement sensor  240  is attached to bearing  60 , and detects a relative displacement of the inner ring with respect to the outer ring of bearing  60  for output to diagnostic unit  190 A. It is difficult to detect an abnormality in overall abrasion of the rolling element surface with the above-described modified vibration degree Vr* and modified modulation degree Ve* as well as the frequency analysis technique through use of the detected value of vibration sensor  70 , however, abrasion inside the bearing can be detected by detecting the relative displacement of the inner ring with respect to the outer ring by displacement sensor  240 . When the detected value from displacement sensor  240  exceeds a previously set value, diagnostic unit  190 A determines that an abnormality has occurred in bearing  60 . It is noted that, since displacement sensor  240  detects the relative displacement between the outer ring and the inner ring, the accuracy of an unmeasured surface needs to be maintained at a high quality. 
     AE sensor  250  is attached to bearing  60 , and detects an acoustic emission wave (AE signal) produced from bearing  60  for output to diagnostic unit  190 A. This AE sensor  250  is superior in detection of internal crack of components constituting bearing  60 , and by using AE sensor  250  together, it will be possible to detect at an early stage a delamination abnormality that would be caused by an internal crack difficult to detect by vibration sensor  70 . When the number of times that the amplitude of the AE signal detected by AE sensor  250  exceeds a set value exceeds a threshold value or when the detected AE signal or a signal obtained by performing envelope processing on the AE signal exceeds a threshold value, diagnostic unit  190 A determines that an abnormality has occurred in bearing  60 . 
     Temperature sensor  260  is attached to bearing  60 , and detects the temperature of bearing  60  for output to diagnostic unit  190 A. Generally, a bearing generates heat due to poor lubrication, an excessively small clearance in the bearing or the like, and when experienced discoloration and/or softening adhesion of the rolling element surface to be brought into a burnt-out state, the bearing will be no longer able to rotate. Therefore, the temperature of bearing  60  is detected by temperature sensor  260 , so that an abnormality such as poor lubrication can be detected at an early stage. 
     When modified vibration degree Vr* and modified modulation degree Ve* exhibit behaviors as shown in  FIG. 8 , diagnostic unit  190 A further refers to the detected value from temperature sensor  260  to thereby diagnose an abnormality such as poor lubrication. It is noted that, when the detected value from temperature sensor  260  exceeds a previously set value, diagnostic unit  190 A may determine that an abnormality has occurred in bearing  60  based on that fact alone. 
     It is noted that temperature sensor  260  is implemented by, for example, a thermistor, a platinum resistor, a thermocouple, or the like. 
     Magnetic iron powder sensor  270  detects the amount of iron powder contained in a lubricant for bearing  60 , and outputs its detected value to diagnostic unit  190 A. Magnetic iron powder sensor  270  consists of, for example, an electrode with a magnet built therein and a rod-like electrode, and is provided on a circulation path of the lubricant in bearing  60 . Magnetic iron powder sensor  270  captures iron powder contained in the lubricant by the magnet, and outputs a signal when adhesion of iron powder causes an electric resistance between the electrodes to drop to a set value or below. That is, when the bearing is worn out, iron powder resulting from abrasion is mixed with the lubricant, and therefore, abrasion in bearing  60  can be detected by detecting the amount of iron powder contained in the lubricant in bearing  60  by magnetic iron powder sensor  270 . Upon receipt of the signal from magnetic iron powder sensor  270 , diagnostic unit  190 A determines that an abnormality has occurred in bearing  60 . 
     Although not particularly shown, an optical sensor that detects contamination of the lubricant in accordance with the light transmittance may be used in place of magnetic iron powder sensor  270 . For example, the optical sensor directs light of a light emitting element to a grease to detect the amount of bearing abrasion powder in the grease in accordance with changes in intensity of light arrived at the light receiving element. It is noted that the light transmittance is defined by the ratio between an output value of the light receiving element in the state where there is no foreign substance mixed in the grease and an output value of the light receiving element when ferrous oxide has been mixed, and when the transmittance exceeds a set value, diagnostic unit  190 A determines that an abnormality has occurred in bearing  60 . 
     It is noted that although displacement sensor  240 , AE sensor  250 , temperature sensor  260 , and magnetic iron powder sensor  270  are shown in  FIG. 11 , all of them are not necessarily be provided. The reliability of abnormality diagnosis can be increased by providing at least one of the sensors. 
     As described above, according to this fourth embodiment, since the detected values of various sensors are used together for an abnormality diagnosis, the reliability of abnormality diagnosis can be increased further. In particular, using displacement sensor  240  together allows abrasion inside the bearing to be diagnosed as well, and using AE sensor  250  together allows a delamination abnormality caused by an internal crack to be diagnosed at an early stage. Moreover, using temperature sensor  260  together allows an abnormality such as poor lubrication to be diagnosed at an early stage, and using magnetic iron powder sensor  270  or an optical sensor detecting contamination of the lubricant by the light transmittance allows an abrasion abnormality in bearing  60  to be diagnosed. 
     [Fifth Embodiment] 
     Since nacelle  90  ( FIG. 1 ) is placed at a high position, it is essentially desirable to place the abnormality diagnostic device described above distant from nacelle  90  in consideration of maintainability of the device itself. However, transmitting the vibration waveform itself of bearing  60  measured by using vibration sensor  70  to a remote place requires transmission means having a high transmission rate, which results in cost increase. Moreover, considering that nacelle  90  is placed at a high position as described above, it is desirable to use wireless communications for communications means from nacelle  90  to the outside. 
     Therefore, in this fifth embodiment, calculation of modified vibration degree Vr* and modified modulation degree Ve* as well as frequency analysis processing (in the case of using the frequency analysis together) are performed in the data processing device provided in nacelle  90 , and each piece of calculated data of modified vibration degree Vr*, modified modulation degree Ve* and the result of frequency analyses (peak frequencies) is transmitted wirelessly from nacelle  90  to the outside. The data transmitted wirelessly from nacelle  90  is received by a communications server connected to the Internet, and is transmitted to a diagnostic server through the Internet, so that an abnormality diagnosis of bearing  60  is performed. 
       FIG. 12  is a diagram schematically showing the overall structure of an abnormality diagnostic system according to the fifth embodiment. Referring to  FIG. 12 , the abnormality diagnostic system includes wind turbine generation apparatus  10 , a communications server  310 , Internet  320 , and a bearing state diagnostic server  330 . 
     The structure of wind turbine generation apparatus  10  is as described with reference to  FIG. 1 . It is noted that the data processing device of wind turbine generation apparatus  10  in this fifth embodiment is provided with a wireless communications unit in place of the diagnostic unit, as will be described later. Wind turbine generation apparatus  10  calculates modified vibration degree Vr*, modified modulation degree Ve* and the result of frequency analyses (in the case of using the frequency analysis together) described above using the detected value of vibration sensor  70  ( FIG. 1 ), and outputs the calculation results wirelessly to communications server  310 . 
     Communications server  310  is connected to Internet  320 . Communications server  310  receives the data transmitted wirelessly from wind turbine generation apparatus  10 , and outputs the received data to bearing state diagnostic server  330  through Internet  320 . Bearing state diagnostic server  330  is connected to Internet  320 . Bearing state diagnostic server  330  receives the data from communications server  310  through Internet  320 , and performs an abnormality diagnosis of bearing  60  ( FIG. 1 ) provided for wind turbine generation apparatus  10  based on modified vibration degree Vr* and modified modulation degree Ve* as well as the result of frequency analyses (in the case of using the frequency analysis together) calculated in wind turbine generation apparatus  10 . 
       FIG. 13  is a functional block diagram functionally showing the configuration of a data processing device  80 D included in wind turbine generation apparatus  10  shown in  FIG. 12 . Referring to  FIG. 13 , data processing device  80 D includes a wireless communications unit  280  in place of diagnostic unit  190  in the configuration of data processing device  80 B shown in  FIG. 10 . Wireless communications unit  280  reads, from storage unit  180 , modified vibration degree Vr* and modified modulation degree Ve* as well as the result of frequency analyses by frequency analysis units  220  and  230 , and transmits the read data to communications server  310  ( FIG. 12 ) wirelessly. 
     It is noted that the remaining configuration of data processing device  80 D is identical to that of data processing device  80 B shown in  FIG. 10 . 
     It is noted that, in the above description, wireless communications shall be made between nacelle  90  and communications server  310 , however, it is also possible to establish a wired connection between nacelle  90  and communications server  310 . Although wiring is required in this case, the need to provide a wireless communications device separately is eliminated, and more information can generally be transmitted through a wired connection, so that processing can be concentrated on a main substrate in nacelle  90 . 
     Moreover, it is desirable to configure the abnormality diagnostic device described above independently of an existing power generation monitoring system. With such a configuration, initial costs of the abnormality diagnostic system can be reduced without having to add changes to the existing system. 
     As described above, according to this fifth embodiment, an abnormality diagnosis of the bearing provided in wind turbine generation apparatus  10  is performed in bearing state diagnostic server  330  provided at a remote place, which can reduce maintenance work and cost. 
     Moreover, although nacelle  90  is placed at a high position, resulting in a severe work environment, signal output from nacelle  90  is made wirelessly by providing wireless communications unit  280  and communications server  310 , so that wiring work in nacelle  90  can be minimized, and wiring work in tower  100  that supports nacelle  90  is also unnecessary. 
     [Sixth Embodiment] 
     In this sixth embodiment, to perform an abnormality diagnosis of higher detection sensitivity, optimization of envelope processing in envelope processing unit  140  is accomplished in each of the above-described embodiments. 
       FIG. 14  is a functional block diagram of an envelope processing unit in this sixth embodiment. Referring to  FIG. 14 , an envelope processing unit  140 A includes an absolute value detection unit  410  and an envelope detection unit  420 . 
     Absolute value detection unit  410  receives a detected value of vibrations of bearing  60  from vibration sensor  70 , and outputs the absolute value of the received detection signal. Envelope detection unit  420  generates an envelope waveform of the vibration waveform of bearing  60  by performing attenuation processing with a predetermined time constant on the output signal from absolute value detection unit  410 . Specifically, envelope detection unit  420  generates the envelope waveform using the following expression. 
     
       
         
           
             
               
                 
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     Herein, n indicates the number of a numerical value obtained by discretizing a continuous signal over time, E[n] indicates the n-th signal after envelope processing, Max (a, b) indicates a function of returning a larger one of a and b, |S[n]| indicates the n-th discretization signal of the output from absolute value detection unit  410 , |S[n−1]| indicates the (n−1)th discretization signal, Δt indicates the discretization cycle, and τ indicates the time constant. This expression (5) is intended to attenuate the output by time constant τ from a peak value when a signal is input, and to attenuate the output from a new peak value when a signal exceeding the output is input. According to this expression (5), the envelope waveform can be generated by simple processing, and a signal with a large peak produced instantaneously by a delamination abnormality or the like can be left reliably. 
     Further, herein, envelope detection unit  420  sets time constant τ based on rotational speed N of main shaft  20  or bearing  60 . If time constant τ that determines the envelope waveform has an excessively large value, the characteristics of an input signal (vibration waveform) will be removed, which is not preferable. On the other hand, if time constant τ is excessively small, a signal equivalent to an input signal (vibration waveform) will be output, which will not result in the envelope waveform. Therefore, it is necessary to set time constant τ at a suitable value. 
       FIG. 15  is a diagram showing changes in envelope waveform when time constant τ in envelope processing is changed. It is noted that this waveforms is of a signal having only an AC component with a DC component removed therefrom. Referring to  FIG. 15 , envelope waveforms obtained when time constant τ is set at τ 1 , τ 2  and τ 3  (τ 1 &lt;τ 2 &lt;τ 3 ) for the same input signal (vibration waveform) are shown here. The horizontal axis indicates the time. It can be seen from  FIG. 15  that as time constant τ is increased, the attenuation speed of envelope waveform decreases. 
       FIG. 16  is a diagram showing the relationship between a value obtained by dividing the effective value of the AC component of the envelope waveform (hereinafter also referred to as a “modulation degree”) by the effective value of the vibration waveform (hereinafter also referred to as a “vibration degree”) and the time constant in envelope processing. Referring to  FIG. 16 , the vertical axis indicates the modulation degree/the vibration degree (hereinafter also referred to as a “modulation ratio”). The horizontal axis indicates the dimensionless time constant (τ/τ 0 ) obtained by dividing time constant τ by a passing cycle τ 0  of a rolling element relative to a stationary ring (e.g., the outer ring) of bearing  60 . It is noted that τ 0  corresponds to the cycle of pulsed vibrations in the vibration waveform shown in  FIG. 5 , for example. 
     A curve k 11  represents the modulation ratio of normal product in which no abnormality occurs in bearing  60 , and a curve k 12  represents the modulation ratio of abnormal product in which delamination occurs in the stationary ring of bearing  60 . The occurrence cycle of pulsed vibrations when delamination occurs in the stationary ring will be the passing cycle of the rolling element relative to the stationary ring, namely, the time constant on the horizontal axis will be τ 0 . In this way, when delamination occurs, the modulation degree increases and the vibration degree less increases as described with reference to  FIG. 5 , so that the modulation ratio increases. To increase the sensitivity to detect delamination, a larger ratio of the modulation ratio of abnormal product to the modulation ratio of normal product is preferable. 
       FIG. 17  is a diagram showing the relationship between the ratio of the modulation ratio of abnormal product (delamination) to the modulation ratio of normal product and the time constant in envelope processing. Referring to  FIG. 17 , the horizontal axis indicates the dimensionless time constant. The ratio of the modulation ratio of abnormal product to the modulation ratio of normal product increases as the dimensionless time constant increases from 0, and decreases monotonously when the dimensionless time constant exceeds 0.5. 
     This result is considered as follows. That is, since the vibration waveform of normal product is a waveform in which equivalent vibrations continue in a short cycle as shown in  FIG. 3 , the modulation degree less changes even when the time constant in envelope processing is changed. Therefore, for a normal product, the modulation ratio less changes even when the time constant is changed (see curve k 11  in  FIG. 16 ). 
     On the other hand, for an abnormal product (delamination), the modulation ratio increases as the dimensionless time constant increases from 0, and decreases monotonously when the dimensionless time constant exceeds 0.5, as shown in  FIG. 16 . This is because, although the effective value of the AC component of the envelope waveform (modulation degree) increases as the time constant increases from 0 as presumed also from changes in envelope waveform associated with changes in time constant τ shown in  FIG. 15 , attenuation of the envelope waveform slows down when the dimensionless time constant exceeds 0.5, so that the effective value of the AC component of the envelope waveform (modulation degree) decreases. 
     It is noted that, when the dimensionless time constant is more than or equal to 1, information on the input signal (vibration waveform) will be impaired greatly. That is, since the envelope waveform has a low frequency, the waveform quality can be maintained even if the discretization cycle is made longer. The envelope waveform allows reduction in storage capacity, which is suitable for storing data. However, when the time constant is excessively large, the characteristics of an original vibration waveform can no longer be presumed from the envelope waveform. Therefore, the dimensionless time constant is preferably set at a value of more than or equal to 0.5 and less than or equal to 1. That is, time constant τ is preferably set to be more than or equal to 0.5 times passing cycle τ 0  of the rolling element relative to the stationary ring of bearing  60  and less than or equal to passing cycle τ 0 . 
     Referring again to  FIG. 14 , envelope detection unit  420  sets time constant τ based on rotational speed N of main shaft  20  or bearing  60 . That is, passing cycle τ 0  can be calculated based on rotational speed N of main shaft  20  or bearing  60  and specifications of bearing  60 . Therefore, envelope detection unit  420  calculates passing cycle τ 0  based on rotational speed N and the specifications of bearing  60 , and sets time constant τ in a range of more than or equal to 0.5 times calculated passing cycle τ 0  and less than or equal to 1 (e.g., a value of 0.5 times τ 0 ). It is noted that rotational speed N can be detected by rotation sensor  210  shown in  FIG. 9  or the like. 
     It is noted that, in the above description, time constant τ shall be set based on passing cycle τ 0  of the rolling element relative to the stationary ring since it is often in the stationary ring that delamination first occurs in bearing  60 . When delamination is more likely to occur in the rolling element than in the stationary ring, time constant may be set based on the half cycle of rotation of the rolling element. That is, envelope detection unit  420  calculates the half cycle of rotation of the rolling element based on rotational speed N and the specifications of bearing  60 , and time constant τ may be set in a range of more than or equal to 0.5 times the half cycle and less than or equal to 1 (e.g., a value of 0.5 times the half cycle of rotation). It is noted that the reason why the half cycle of rotation of the rolling element is used as a basis is because the rolling element contacts the raceway twice each time the rolling element rotates once. 
     As described above, according to this sixth embodiment, in which time constant in envelope processing is set based on rotational speed N of main shaft  20  or bearing  60 , an abnormality diagnosis with a high detection sensitivity can be achieved even when rotational speed N changes. 
     It is noted that, referring to  FIG. 1  again, vibration sensor  70  shall be attached to bearing  60  so that an abnormality diagnosis of bearing  60  shall be performed in each of the above-described embodiments, however, in addition to or in place of bearing  60 , vibration sensors can be provided for the bearings provided in gearbox  40  and generator  50 , so that an abnormality diagnosis of the bearings provided in gearbox  40  and generator  50  can be performed with a technique similar to that of each of the above-described embodiments. 
     It is noted that, in the above description, data processing devices  80  and  80 A to  80 C correspond to an example of “a processing unit” in the present invention, and effective value operation units  120  and  160  correspond to an example of “a first operation unit” and “a second operation unit” in the present invention, respectively. Moreover, data processing device  80 D corresponds to an example of “a data processing unit” in the present invention, and bearing state diagnostic server  330  corresponds to an example of “a bearing abnormality diagnostic device” in the present invention. 
     It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the claims not by the description above, and is intended to include any modification within the meaning and scope equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
       10  wind turbine generation apparatus;  20  main shaft;  30  blade;  40  gearbox;  50  generator;  60  bearing;  70  vibration sensor;  80 ,  80 A to  80 D data processing device;  90  nacelle;  100  tower;  110 ,  150  HPF;  120 ,  160  effective value operation unit;  130  modified vibration degree calculation unit;  140 ,  140 A envelope processing unit;  170  modified modulation degree calculation unit;  180  storage unit;  190 ,  190 A diagnostic unit;  200  speed function generation unit;  210  rotation sensor;  220 ,  230  frequency analysis unit;  240  displacement sensor;  250  AE sensor;  260  temperature sensor;  270  magnetic iron powder sensor;  280  wireless communications unit;  310  communications server;  320  Internet;  330  bearing state diagnostic server;  410  absolute value detection unit;  420  envelope detection unit.