SIHVO, Tero (Liimattalantie 519, Äänekoski, FI-44150, FI)
UIMONEN, Tapio (Kivitie 15, Espoo, FI-02240, FI)
VIRKAJÄRVI, Mikko (Toivonpolku 2 C, Leppävesi, FI-41310, FI)
SIHVO, Tero (Liimattalantie 519, Äänekoski, FI-44150, FI)
UIMONEN, Tapio (Kivitie 15, Espoo, FI-02240, FI)
| Claims 1. A system for monitoring the condition of planetary gears by using at least vibration and/or temperature measurement and wireless data transfer, the system comprising: a base station (7) for wireless sensor devices, in connection with which is an induction antenna (8) radiating inside the gear housing for energy transfer, wireless data transfer means for the sensor devices (9), a processing unit for processing and storing measurement data, data transfer means for forwarding the measurement results, and mounted in connection with the rotating part of the planetary gear, for example a planet carrier (2), a wireless sensor device (9), which comprises means (11) for receiving energy transmitted by induction, means (13) for storing energy transferred by induction for the operation of the sensor device (9), measurement sensors (10, 15) for collecting condition monitoring data and for processing and storing measurement data from the processing unit, and wireless data transfer means (11, 12) for transmitting the measurement results to the base station (7), whereupon the said induction antenna (8) radiating inside the gear housing is fitted to generate an alternating-current magnetic field, and the energy- receiving means (11) of the sensor device receive energy from the alternating-current magnetic field when passing the induction antenna (8). 2. A system as claimed in claim 1, wherein there are means for synchronising the measurement with the rotating motion of the gears. 3. A system as claimed in claim 2, wherein the means for synchronising the measurement with the rotating motion of the gears include a means monitoring the signal generated by the charging antenna. 4. A system as claimed in claim 1, wherein the means for storing energy (13) comprise an accumulator or a capacitor. 5. A system as claimed in claim 1, wherein the planetary gears are the planetary gears of a wind power plant. 6. A system as claimed in claim 2, wherein the wireless measuring sensor means are provided with means for synchronising also with the periodic vibration produced by the gear wheels. 7. A system as claimed in claim 2, wherein the wireless measuring sensor means are connected to the bearing or shaft of the planetary wheel (3). 8. A system as claimed in claim 2, the sensor device of which has means for processing, storing or packing measurement data before transmitting it to the base station for further processing. 9. A system as claimed in claim 2, wherein the synchronising means comprise an angle sensor for the rotating motion of the gears, by means of the reading of which multiple synchronising pulses are generated during a cycle. 10. A system as claimed in either of the claims 1 or 2, which measures the torque transferred by the monitored planetary gears on the basis of the twist or deformation of the sun shaft or planet carrier. 11. A system as claimed in either of the claims 1 or 2, the base station of which is an intelligent condition management analysing and storage unit, which analyses measurement data locally. 12. A system as claimed in either of the claims 1 or 2 for monitoring the dition of the planetary wheel (3) of the planetary gears of a wind power plant. |
The invention relates to improving the condition monitoring of large plane- tary gears, especially of wind power plants, and to preventing serious defects.
Current wind power plants use planetary gears which typically transmit outputs of 3-8 MW. From the point of view of monitoring and maintenance, the gears are in very difficult conditions. In the high towers temperature variations are great, the devices themselves are highly inaccessible in the high towers, often also outside road networks which are under winter maintenance. Moreover, arranging a maintenance shutdown and transporting spare parts to and mounting them in the high tower is difficult.
A known wireless bearing condition monitoring device is described in the publication US2003030565 Al, where sensors and a wireless data transfer device are provided in the bearing body. Electric supply is provided by a generator operating by means of a permanent magnet fixed to a rotating part. This device is not practicable for monitoring the planetary gears of a wind power plant, because the permanent magnet accumulates metal particles from the oil in the planetary gears, which may then subsequently detach back into the oil and cause, for example, tooth damage. Should this solution be used for monitoring the planetary gears of a wind power plant, it would increase the risk of damage quite considerably. It is very difficult to arrange the circulation of oil in conjunction with the bearing of the planetary wheel so as to efficiently minimise the risk of tooth damage. Oil circulation passing the magnet cannot be guided directly to filtration. Electric power can be supplied or data transfer by wire can be arranged by means of slip-rings and brushes, but slip-rings are expensive, unreliable and difficult to retrofit. The aim of the invention is to provide reliable, maintenance-free and long- term condition monitoring in connection with the planetary gears of wind power plants.
Condition monitoring is normally carried out through vibration measurements and by measuring, for example, the torque, temperature, etc. In connection with a planetary gear, the measurement must be wireless, because the planetary wheels move with the planet carrier. Wireless systems are available, but their maintenance requirement is intolerable for monitoring a wind power plant, because the batteries of wireless transmitters are not durable enough for this application. The temperatures of the gears may typically vary between -40 - +80 degrees. The maintenance of a device rotating with a planet carrier requires stopping the gears - and thus the entire power plant - and a maintenance call and maintenance is, therefore, very expensive. A further aim of the invention is to obtain long-term and accurate measurement data synchronised with the position of the gears, on the basis of which incipient damage to individual gear teeth can be detected before further damage occurs. Further aims are easy retrofitting and a low maintenance requirement.
The aims of the invention are achieved by means of the system according to claim 1.
The sensor arrangement of the system is described in the following by means of the accompanying Figure. Figure 1 shows the sensor arrangement of the planetary gears using sensors and a base station.
Figure 2 shows an embodiment of a wireless sensor device.
Figure 1 shows the sunwheel and planetary wheel, with carriers, of the planetary gear of a 2-step wind power plant. For the sake of clarity, ring gears and supporting structures have not been drawn in the Figure. A slow shaft 1 is connected to a planet carrier 2, the planetary wheels 3 are mounted in bearings on the planet carrier 2. The sunwheel 4 is the fast output shaft of the gears. For the sake of clarity, a stationary ring gear on the outer periphery of the planetary wheels has been omitted from the drawing and so have some of the bearings. In order to be able to identify minor damage to the gears in time, it must be possible to monitor the vibration of preferably individual planetary wheels and the operation of the bearing by measuring the temperature of the bearing and possibly oil pressure. The output shaft of the first phase is shaft 1.2, which functions as the input shaft of the following phase at the same time. Shaft 1.3 is the fast output shaft of the second phase of the gears. In the gears, the only stationary gear wheels are the ring gears that were omitted from the Figure. Of the bearings, the bearings of the planetary wheels rotate with the planet carriers, while the other bearings remain stationary.
Monitoring the condition of the planetary wheels of the gears of a wind power plant by measuring bearing vibration with a sensor requires wireless data transfer from the sensor or, for example, brushes and slip-rings for data transfer by wire. The most straightforward known prior art solution would be to use a battery-operated vibration sensor and wireless data transfer. The service life of a battery or accumulator is, however, insufficient with respect to the maintenance interval and severe environmental conditions also make predicting the service life of a battery difficult. The system according to the invention comprises a base station 7, to which are linked induction antennae 8. By means of the induction antennae 8 is created an alternating-current magnetic field for inductive power transfer along the path of the sensors 9 measuring the condition of the planetary wheel parts. The sensors 9 may be fixed on the planet carrier 2 in connection with the planetary wheel bearing or planetary wheel shaft. The sensors 9 comprise an antenna for receiving the energy of an alternating magnetic field and charging electronics for charging the energy into a capacitor or accumulator. The energy is received and charged only during a part of the cycle, when the sensor devices are in the vicinity of the induction antennae. Several induction antennae may be installed or there may be one or more receiving antennae in each sensor device. The capacitor is an advantageous energy reserve, because in practice the speed of rotation of the gear carrier of the planetary gears is at least several cycles per minute when the plant is in operation, whereupon charging also occurs several times per minute. The capacitor does not suffer from the frequent charging cycle and high-capacity capacitors with an expected reliable service life of over 10 years in the conditions of the application are available from several manufacturers. The means for storing energy may also be a modular super capacitor power source comprising charging and discharging electronics or a similar combination comprising an accumulator and a capacitor. The advantage of a combination device is, for example, a wider operating temperature range if a cold- resistant device is used in parallel with a device which loses its current- feeding capacity in the cold. For example, a lithium polymer accumulator and a super capacitor can be used in such a way that the accumulator normally remains almost fully charged in reserve and the capacitor stores the energy required during a normal cycle. In such a case, the accumulator can be used, for example, during a stoppage or, for instance, during software updating. The accumulator is thus not used very much and its charging state may be maintained optimal, keeping in mind the long service life. The base station 7 is an intelligent condition management analysing and storage unit which analyses measurement data locally. By analysing, storing samples and comparing local changes, the amount of data to be transferred, which is often a problem in extensive systems such as large wind farms, can be reduced.
The analysis of local measurement data also makes possible automatic responding to problems locally, for example, by stopping the apparatus automatically due to a detected incipient fault or lubrication failure. Fault signals may also be transmitted via a slow data link or even by text message.
Figure 2 shows the possible structure of a wireless sensor device 9. The receiving antenna is a coil 11. Below the antenna is a charging and radio electronic circuit board 12. The charging electronics charges the energy reserves, for example capacitors 13, when the sensor device 9 passes the induction antenna 8. The Figure shows, for example, the circuit board of MEMS acceleration sensors in the space between the capacitors 13. There may be several acceleration sensors measuring diverging vibrations. Instead of an MEMS sensor may also be used, for example, a piezoelectric sensor. The sensor housing may be connected to the object of measurement, for example, by means of a male screw 15. There may also be a connection, for example, to a strain-gauge for measuring torque or deformations.
The sensor device preferably has its own non-volatile memory in which measurement results can be stored before transmitting them via the base station. The non-volatile memory may be, for example, static CMOS memory, the operating voltage of which is secured by its own capacitor or, for large amounts of data, storing can be done in a flash memory, for example on an SD card. The sensor preferably has data processing capacity for processing the measurement data, in order that the amount of data to be transmitted can be reduced, if necessary, and the sensor itself may identify changes. In this way, the same base station may serve several antennae alternately, and high data transfer capacity is not required. In practice, for example, the characteristic values of vibration can be measured or the vibration measurements for each cycle can be compared with older measurement results and the data to be transmitted can be packed by means of these. Since vibration measurement is generally done over a wide bandwidth and with relatively high resolution, the amount of unprocessed measurement data produced per planet gear carrier is so high that it is advantageous to arrange data preprocessing in the system, in connection with the measuring sensor 9 itself. A simple pre-processing method is, for example, storing a sample of one or more cycles and transmitting it later when the data line allows. Locally, the sensor device or support station may also compare stored samples and send out fault signals on changes or transfer sample data only when a detectable change has taken place in it, which means that the need for data transfer decreases decisively.
The measuring sensor devices 9 can be synchronised with the rotating motion of the parts of the gears by using induction antennae for the synchronisation. Resolution can be improved by using, for example, two successive transmitter antennae 8, the signals of which are in an opposite phase. The output received by the receiving antenna 11 is then lost for a short moment halfway between the antennae as the signals transmitted by the antennae cancel one another out. The space between the transmitter antennae 8 is, for example, slightly narrower than the receiving coil 11, in which case there is a narrow area between the induction antennae, where the fields of the transmitting antennae cancel one another out sharply and shortly. The synchronisation may also be carried out with light, or even acceleration sensors, by measuring the direction of acceleration caused by earth gravity. In addition may be used an external position or angle sensor and the synchronisa- tion signal produced by it can be transmitted for use by the sensor devices wirelessly. The synchronisation of the measuring sensors may further be used for specifying condition monitoring measurement, because by means of synchronisation, even vibrations caused by single gear teeth and bearing angles can be distinguished. In this way, for example, tooth damage in the gear ring, sun- wheel and planetary gear wheel can be distinguished from one another, different bearing fault types can similarly be distinguished and the speed of rotation of a faulty bearing can be identified also when the same sensor monitors the vibration of several bearings rotating at different speeds. The synchronisation data from the measuring sensors is preferably utilised further also for scheduling data communication. For example, measurement data from each sensor can be transmitted immediately after passing the charging antenna, which is an easy way of avoiding the simultaneous transmission of information transfer from the same planetary rim.
The measuring sensor devices 9 may comprise a pressure sensor for measuring oil pressure, vibration sensors or microphones for vibration measurement; active vibration measurement in connection with an ultrasound transmitter may also be used. The sensor devices may further comprise a ther- mometer for measuring oil or bearing temperature, a strain gauge, for example, for torsion or force measurement. The torque transferred by the planetary gears may be measured by measuring the twist of the sun shaft or planet carrier by means of strain gauges 10. The strain gauges 10 may be connected to the vibration measuring sensor devices 9.
The torque is preferably measured from the rotating part. The body of the two-phase planetary gears of a typical wind power plant is subjected to other supporting forces in addition to the torque and thus deformations in the body represent the torque of the gears poorly. Measuring the forces exerted on the ring gear requires flexibility of their fastening or installation of a sensor between the body and the ring gears. It may be advantageous to carry out measurements also with piezoelectronic or Emfi film sensors in addition to or instead of the conventional strain gauge sensors. They do not give an absolute stretch value or torque value, but are extremely sensitive for measuring changes and thus, by means of them it may be possible to detect, for exam- pie, even weak vibrations.
The measuring sensor devices preferably include a microprocessor which is able to pack and analyse the measurement results, for example, calculate the frequency response and correlation with respect to the phase of rotation. In this way, the amount of data to be transferred can be reduced or data from several sensors can be transmitted alternately at the same RF frequency, for example, in such a way that data from each sensor is collected at regular intervals as samples. Since typical wind power plant planetary gears have two phases, each of which includes three planetary wheels, typical planetary gears would require six monitoring measuring sensor devices.
Since the amount of data produced in vibration measurement is relatively high, the data must be collected and possibly processed before transmission. A simple way of arranging the transmission turns of the sensors is, for example, that having passed the charging antenna, the sensor transmits the collected data on request. In this way, the sensor data from the phase of each planetary gear can be collected alternately by means of a very simple protocol by requesting data alternately from the sensors of different phases or by requesting data samples from individual sensors. One measuring sensor device may measure one or more sensors. For example, a sensor device in a planet carrier may comprise a sensor per each planet carrier bearing, or each bearing may have its own measuring sensor device. The base station preferably has sufficient memory for storing the sensor data and sufficient computing capacity for carrying out analysis algorithms. The data may be transferred further to be analysed elsewhere. The data may be filed, for example, for the needs of product development, whereby for example the measurement result history of damaged gears can be examined afterwards. On the other hand, the data pre-processing carried out in the sen- sor devices may reduce the amount of data to be transferred, in which case wireless data transfer from several sensors is easier to carry out. For example, in active ultrasound measurement, the amount of data per sensor is so high that continuous wireless data collection from several sensors is difficult due to the high data transfer capacity requirement.
It is also possible to carry out a part of the analyses in the sensor device 9 and a part in the base station 7. For example, the sensor device may collect periodic data with respect to the cycle of the gear wheel, synchronised with the phase of the cycle, and process this statistically in accordance with the rotation cycles of one or more gear wheels. In that case, the average vibration measurement of several cycles, for example, a hundred cycles, and the divergence relating to it and other statistical functions can be calculated by sample. This does not necessarily require very high memory or data processing capacity of the sensor or base station, but reduces the amount of data to be transferred to a fraction, hardly lessening the usefulness of the information in connection with further analysis. Calculating the average of several measurement results reduces the effect of random external disturbances on measurement, or by comparing repeated measurements with the average, a rare phenomenon may be found through perceiving a measurement period deviating from the other measurements. The deviating measurement periods can then be transmitted for further examination.
The synchronisation of the sample points before summing the average may require, for example, using the measurement data itself for aligning the samples from the cycles or a different method for measuring the angle of rotation may be used. The speed of rotation of a wind power plant varies and thus mere induction antenna passing data once during a cycle is usually insufficient for synchronisation. One possibility is to use a fixed angle sensor by means of which several pulses are generated during a cycle at constant angle intervals and the pulses thus obtained are transmitted wirelessly to the sensor devices. The angle sensor may transmit, for example, 16 or 256 pulses during a cycle. The sensor device may then either mark the measurement data with the points of time of the synchronisation pulses for further processing or synchronise the measurements before the further processing of the measurement data.
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