Lubrication sensor

Abstract

A lubrication fitting 30 and a grease gun 40 for applying a lubricant to the lubrication fitting of an aircraft assembly, the lubrication fitting has a passive radio frequency identification (RFID) co

Description

Field This invention relates to a system for lubricating components of an aircraft assembly using wireless communication, such as radio frequency identification, including RFID and near field communication (NFC) to monitor the application of lubrication across a component with multiple lubrication fittings. Background Components and subassemblies of aircraft, such as joints and moving parts, can be lubricated to avoid excessive wear and corrosion. This lubrication must be carried out at regular intervals to ensure that enough lubricant is present and to reduce the likelihood of contaminants building up and causing abrasion to the components. Presently, lubrication of aircraft landing gear components occurs manually by an engineer applying lubricant using a grease gun or pump via a lubrication fitting, such as a grease nipple. This requires the engineer to identify the lubrication fitting, often by identifying a brightly coloured component of the lubrication fitting. In order to confirm that the lubrication fitting has been serviced and that the correct level of lubricant has been introduced, the lubricant must be applied until excess lubricant is visually seen from a witness hole or extruded from the component being lubricated. This can be time consuming, especially for components which form part of a larger assembly with several lubrication fittings to service. It also requires a line of sight to the components being lubricated, which cannot always be achieved. Therefore, the present inventors have identified a need for a reliable way to improve the lubrication of aircraft components by reducing the likelihood of a lubrication fitting not being serviced to a sufficient level. Summary In accordance with a first aspect of the present invention, there is provided a system for monitoring an aircraft assembly, the system comprising: a plurality of lubrication fittings, each lubrication fitting comprising a passive radio frequency identification component; and a grease gun comprising a radio frequency identification reader and a processor, wherein the processor is configured to: transmit a first signal to cause the radio frequency identification reader to transmit a radio frequency, RF, signal to the passive radio frequency identification components in the lubrication fittings; receive a unique identifier from the passive radio frequency identification component in the lubrication fittings; and transmit a second signal comprising the unique identifier to a digital system. Therefore, the system provides a way to monitor the servicing status of all lubrication fittings on a component or subassembly of an aircraft assembly. This reduces the likelihood of a lubrication fitting not being serviced. The system also provides a more efficient means for confirming the service status of a lubrication fitting, rather than relying on manual inspection, in turn providing improved management of the lubrication process. This is achieved by enabling a digital system to identify lubrication fittings and digitally capture the servicing status of the lubrication fittings. Capturing a time stamp while the lubrication process occurs can provide a time limit for the next lubrication event. The grease gun may further comprise a hose or tube which is arranged to couple to each lubrication fitting and an antenna arranged to transmit the RF signal, wherein the antenna may be arranged at the distal end of the hose or tube. This is advantageous as it enables an RF system with a reduced range to be used in the system as the antenna is arranged on the component of the grease gun which will be closest to the lubrication fitting during engagement with a lubrication fitting. This reduces the likelihood that a passive radio frequency identification component of a lubrication fitting not engaged with the grease gun will be read by the radio frequency identification reader. Therefore, this reduces the likelihood of a false reading being transmitted to the digital system. The radio frequency identification reader may comprise the antenna. Therefore, the grease gun may comprise a hose or tube with the radio frequency identification reader of the grease gun arranged on the distal end of the hose or tube. The RF signal may have a frequency of about 125 kHz to 135 kHz. For example, the RF signal may have a frequency of 125 kHz and / or 134.3 kHz. Therefore, the system may be operating in the low frequency RFID range. Alternatively, the RF signal may have a frequency of about 3 MHz to 30 MHz. For example, the RF signal may have a frequency of 13.56 MHz. Therefore, the system may be operating in the high frequency RFID range, for example at the frequency of near field communication (NFC). These frequency ranges provides a suitable working range for data to be communicated between the passive radio frequency identification component and the radio frequency identification reader while reducing the likelihood of the radio frequency identification reader coupling to other passive radio frequency identification components which are not within the lubrication fitting being serviced. The low frequency RFID system is less sensitive to radio wave interference than higher frequency systems. The high frequency RFID system has a faster read speed than low frequency systems. The lubrication fitting may comprise a washer and a greasing nipple and the passive RFID component may be arranged on the washer. This is advantageous as the washer can be easily removed and replaced and therefore the passive radio frequency identification component can be easily retrofitted to existing systems and added to new systems as they are manufactured. It also enables straightforward replacement of a passive radio frequency identification component if the component which holds the radio frequency identification tag degrades. The grease gun may further comprise a sensor arranged to measure a fluid parameter and the second signal may further comprise the fluid parameter. This is advantageous as it provides data indicative of the performance of the lubrication fitting and / or component / joint being lubricated. As the sensor data can be recorded against the unique identifier, performance of individual lubrication fittings can be determined. The sensor may be at least one of: a flow meter arranged to measure a flow rate of grease expelled by the grease gun; and a pressure sensor arranged to measure the pressure within the lubrication fitting. More specifically, the grease gun may further comprise a flow meter arranged to measure a flow rate of grease expelled by the grease gun and the second signal may further comprise the measured flow rate. Additionally or alternatively, the grease gun may further comprise a pressure sensor arranged to measure the pressure within the lubrication fitting and the second signal my further comprise the measured pressure. Therefore, the volume of lubricant added / released during one lubrication process may be measured. By collating the volume of lubricant added and / or the pressure required to push the lubricant into the lubrication fitting over a plurality of lubrication processes, the condition of the lubrication path can be determined. The condition of the lubrication path may be extrapolated in order to predict future failures. Another advantage of the system is that if the volume of lubricant detected is an insufficient volume, the system can alert an operator that the component has not been sufficiently serviced. The sensor may be arranged to detect when a sufficient volume of grease has been expelled by the gun. The grease gun may comprise a shut of valve which can automatically close when the sufficient volume has been detected. This may be implemented using an internal pump of the grease gun. This is advantageous as the system can automatically apply the required amount of lubricant upon engagement of the grease gun with the fitting. The processor may be arranged to receive operation instructions from the digital system, wherein the operational instructions comprise information on the type of lubricant to be used with the lubrication fitting the grease gun is engaged with. The digital system may determine which type of lubricant is to be used based on the unique identifier and / or detection of the lubricant previously applied to the lubrication fitting. This is advantageous as different components of aircraft may require different types of lubrication. Therefore, the system may be arranged to determine which type of lubricant is required for a specific fitting and automatically supply the correct lubricant. The aircraft assembly may be aircraft landing gear. As such, the lubrication fitting may be located on a component of the aircraft landing gear. In accordance with a second aspect of the present invention, there is provided a method for monitoring an aircraft assembly, the method comprising: engaging a grease gun with a lubrication fitting; transmitting a radio frequency, RF, signal from a radio frequency identifier reader arranged in the grease gun, wherein the RF signal is transmitted when the grease gun is engaged with the lubrication fitting; receiving, via the radio frequency identifier reader, a unique identifier from a passive radio frequency identifier component in the lubrication fitting; and transmitting the unique identifier to a digital system. Therefore, the method provides means to monitor the lubrication process of a component or subassembly. This is particularly useful when monitoring the maintenance of a subassembly with a plurality of lubrication fittings. The digital system may record the unique identifier. This is advantageous as it provides a method of storing historical maintenance events. The method may further comprise analysing the unique identifier to determine any previous instances of engagement of the grease gun with the lubrication fitting. This is advantageous as it provides a method that enables maintenance events to be tracked and accessed by an operator. The method may further comprise outputting a signal at the digital system, wherein the output signal indicates the time period between the most recent engagement of the grease gun with the lubrication fitting and the present time. Therefore, the method provides a way of alerting an operator to a due or an overdue lubrication maintenance event. The method may further comprise: receiving a fluid parameter from a sensor arranged in the grease gun when the grease gun is engaged with the lubrication fitting; transmitting the fluid parameter to the digital system; recording the fluid parameter at the digital system; analysing the fluid parameter to determine an operational property of the lubrication fitting. Therefore, the method allows an operator to measure and record the performance of the lubrication fitting. The sensor may be at least one of: a flow meter arranged to measure a flow rate of grease expelled by the grease gun; and a pressure sensor arranged to measure the pressure within the lubrication fitting. More specifically, the method may further comprise: receiving flow rate data from a flow meter arranged in the grease gun when the grease gun is engaged with the lubrication fitting; transmitting the flow rate data to the digital system; recording the flow rate data; and analysing the flow rate data to determine at least one of: the volume of grease applied to the lubrication fitting and any differences between the recorded flow rate data and any previously recorded flow rate data for the lubrication fitting. Additionally or alternatively, the method may further comprise: receiving pressure data from a pressure sensor arranged in the grease gun when the grease gun is engaged with the lubrication fitting; transmitting the pressure data to the digital system; recording the pressure data; and analysing the pressure data to determine at least one of: the pressure required to introduce grease into the lubrication fitting and any differences between the recorded pressure date and any previously recorded pressure data for the lubrication fitting. By recording pressure data and / or volumetric data, the method provides a means of monitoring the trend of the lubrication fitting performance. For example, the volume of injected lubricant may help assessing potential degradation of the lubrication channels that may be caused by accumulation of old lubricant leading to an increased risk of corrosion and reduced performance of the component / joint. The grease gun may engage with a single lubrication fitting at a time and may receive the unique identifier when the grease gun is engaged with the single lubrication fitting. The method may be for monitoring aircraft landing gear. As such, the lubrication fitting may be located on a component of the aircraft landing gear. In accordance with a third aspect of the present invention, there is provided a lubrication fitting for an aircraft assembly, the lubrication fitting comprising a passive radio frequency identification component arranged to transmit a unique identifier when engaged with a radio frequency identifier reader. The aircraft assembly may be aircraft landing gear. As such, the lubrication fitting may be located on a component of the aircraft landing gear. In accordance with a fourth aspect of the present invention, there is provided a grease gun for applying lubrication to a lubrication fitting of an aircraft assembly, the grease gun comprising a radio frequency identification reader arranged to transmit a radio frequency, RF, signal. The aircraft assembly may be aircraft landing gear. As such, the lubrication fitting may be located on a component of the aircraft landing gear. Brief Description of the Drawings By way of example only, certain embodiments of the invention will now be described by reference to the accompanying drawings, in which: Figure 1 is a schematic representation of an aircraft; Figure 2 is a schematic representation of a landing gear assembly; Figure 3 is a diagram of a system according to an embodiment of the invention; and Figure 4 is a flow chart of a method according to an embodiment of the invention. Detailed Description Figure 1 shows a diagram of an aircraft 10. The aircraft 10 includes subassemblies such as a nose landing gear 12, main landing gear 14 and engines 16. Other aircraft subassemblies will be apparent to the skilled person. A subassembly can be a group of interconnected parts which are arranged to be fitted to the aircraft as a unit. Referring now to Figure 2, an exemplary lubrication fitting 30 is shown on an aircraft subassembly, namely an aircraft landing gear assembly, shown generally at 14. The landing gear assembly 14 includes a foldable stay 18, a lock link 20 and a down lock spring assembly mounted to the stay 18 and arranged to urge the lock link 20 to assume a locked state. In addition, the landing gear assembly also includes a shock absorber, comprising a main fitting and a sliding tube, as well as a wheels and brake assembly. The lock link 20 is generally provided in conjunction with the stay 18 to maintain the stay in the locked condition, as shown in Figure 2. The lock link 20 generally includes a two-bar linkage that can be unfolded to assume a locked over centre condition to inhibit movement of the stay 18. The two arms of the lock link 20 can be coupled via a pivot pin 22 thereby allowing movement of an arm relative to the other. The lock link 20 must be broken to enable the stay 18 to be folded, thereby permitting the main fitting to be moved by the retraction actuator towards the stowed condition. Therefore, the lock link 20 is an example of a component which will require lubrication. Other components may include, but are not limited to, the stay, a torque link, the wheel assembly, or any other component which forms a joint or moving part. Figure 2 refers to an exemplary lubrication fitting 30 on an aircraft landing gear however, other examples of lubrication fittings may be arranged on alternative subassemblies and / or components, such as the engines 16. Figure 3 shows an exemplary arrangement of a system for monitoring aircraft landing gear. However, as described in relation for Figure 2, the system may be arranged for monitoring other aircraft sub-assemblies and / or components, such as the engines 16. Therefore, the following description applies analogously to other sub-assemblies. The lubrication fitting 30 may be fitted to a component 36 to provide the component 36 with lubricant in a precise manner. The lubrication fitting 30 may be formed by a grease nipple 34 and a washer 32. The grease nipple 34 may have at least one channel which connects an opening to the location at which lubricant is required. The lubrication fitting 30 may instead be formed from any known grease fitting and a washer 32. In use, lubricant, such as a lubricating grease, is fed into the lubrication fitting 30 using a grease gun 40. The grease gun 40 typically comprises a source of lubricant and a means 42 to push the lubricant out of the grease gun 40 via a fixed tube or hose 44. A nozzle 46 may be arranged at the distal end of the fixed tube or hose 44. The nozzle 46 may compliment the lubrication fitting 30 so that a seal is formed when the nozzle is engaged with the lubrication fitting. Therefore, the grease gun 38 provides a means to direct and feed the lubricant into the component 36 at a high pressure via the lubrication fitting 30. The lubrication fitting comprises a passive radio frequency identifier component 38. As the radio frequency identifier component is passive, it does not require a power supply. The passive radio frequency identifier component 38 may be located on or within the washer 32 of a lubrication fitting 30. Alternatively, the passive RFID component 38 may be located on or within the grease nipple 34. The range of operation of the passive radio frequency identifier component may be less than 1 cm so that the component can only be read when a radio frequency identifier reader is within close proximity to the lubrication fitting in order to reduce the likelihood of the reader coupling to another component not being serviced. The passive radio frequency identifier component 38 may be integrated into lubrication fitting 30 during assembly or replacement of the fitting 30. The passive radio frequency identifier component 38 is associated with a unique identifier and the position of the passive radio frequency identifier component 38 can be recorded on a digital system. In the example in which the passive radio frequency identifier component 38 is located on the washer 32, the position of the radio frequency identifier tagged washer may be recorded during assembly or replacement, for example during the first lubrication at an original equipment manufacturer (OEM). The attachment of the passive radio frequency identifier component 38 may be repeated in case of replacement of the radio frequency equipped washer. The grease gun 40 comprises a radio frequency identifier reader 48 and a processor 52. The radio frequency identifier reader 48 is an active system meaning that it is powered and can therefore transmit a radio frequency (RF) signal. The processor is arranged to provide a first signal to cause the radio frequency identifier reader to transmit the RF signal. The RF signal may be transmitted via an antenna arranged in the nozzle 46 of the grease gun. Arranging the antenna within an extremity of the grease gun 40 increases the likelihood that the radio frequency identifier reader will only read a single passive radio frequency identifier tag at a time. The radio frequency identifier reader 48 may be arranged to transmit an RF signal continuously. Alternatively, the radio frequency identifier reader 48 may be arranged to transmit an RF signal when triggered by a user and / or when a sensor on the grease gun 40 detects that lubricant is being transferred to a lubrication fitting. When the radio frequency identifier reader 48 is within the working range of the radio frequency identifier system, the RF signal from the RFID reader 48 can couple to the passive radio frequency identifier component 38 of the lubrication fitting 30. Once coupled, information stored on the passive radio frequency identifier component 38 can be transferred to the radio frequency identifier reader 48. The passive radio frequency identifier component 38 stores the unique identifier which is transmitted to the radio frequency identifier reader 48 when the radio frequency identifier reader 48 and passive RFID component 38 are within the working distance. The unique identifier may be related to the lubrication fitting 30 so that each lubrication fitting 30 corresponds to a unique identifier. As such, when the nozzle of the grease gun is moved into working range with a specific lubrication fitting, the passive radio frequency identifier component of the lubrication fitting will be read by the radio frequency identifier reader in the grease gun nozzle and provide a return signal indicative of a unique identifier for the lubrication fitting. The unique identifier may be a serial number of a part of the lubrication fitting or a label given to the lubrication fitting by a user. The RF signal may have a frequency between 30 KHz and 500 KHz. The working distance / read distance of an RFID reader and passive RFID tag operating between 30 KHz and 500 KHz is typically 30 cm or less. The RF signal may have a main frequency of 125 kHz to 135 kHz. For example, the RF signal may be at a frequency of 125 kHz and / or 134.3 kHz Alternatively, the RF signal may have a frequency between 3 MHz and 30 MHz. The working distance / read distance of an RFID reader and passive RFID tag operating between 3 MHz and 30 MHz is typically 10 cm to 1 m. The RF signal may have a main frequency of 13.56 MHz. For components with several lubrication fittings in close proximity, an radio frequency identifier system with a smaller working distance is preferable so that the passive radio frequency identifier component is only coupled to when the nozzle of the grease gun is engaged with a lubrication fitting. This reduces the likelihood that a unique identifier for a lubrication fitting not yet serviced will be read by the radio frequency identifier reader. The processor 52 of the grease gun 40 is further arranged to provide a second signal to cause the unique identifier to be transmitted to a digital system 54. The digital system 54 may be a computing system, such as a mobile device or desktop electronic device. The digital system 54 may be external to the grease gun 40 or may be incorporated into the grease gun 40. The transmission of the unique identifier to the digital system 54 may occur via a wired or wireless communication link, for example via Bluetooth. The digital system 54 may comprise a processor and memory so that the unique identifiers can be received and recorded at the digital system 54. The digital system 54 may be connected to the Maintenance Information System of an aircraft operator. The digital system 54 may further comprise an output for providing a user with the unique identifier(s) received at the digital system 54. For example, the digital system 54 may comprise a display which is arranged to show a user the unique identifiers. This can be done by providing a user with a visual display of the component to be serviced and marking the displayed component at the location of lubrication fittings. The visual display may also be provided by augmented reality goggles worn by a user. For example, a visual interface may inform a user with information relating to the operation of the lubrication fitting 30, such as providing a time period in which the next lubrication servicing is required, a date marking the end of such time period (a "do not exceed" date), and / or lubrication fittings that have been already serviced in the current servicing period. Visual aids, such as a colour code, may be used to distinguish lubrication fittings. For example, a lubricated fitting during the current maintenance operation, a lubrication fitting serviced previously but that does not need immediate servicing, and / or lubrication fittings that need servicing during the present maintenance. As seen in figure 3, the digital system 54 may display an image of an aircraft landing gear with the location 56 of a lubrication fitting highlighted. Alternatively, the locations may be listed on the digital system 54. The grease gun 40 may further comprise at least one sensor 50a, 50b for detecting a property of the lubricant or lubrication fitting 30. For example, the grease gun 40 may comprise a fluid flow meter 50a to detect the volume of lubricant which has been fed into the lubrication fitting 30. Alternatively or additionally, the grease gun 40 may comprise a pressure sensor 50b to detect the pressure within the lubrication fitting 30. Pressure data from within the lubrication fitting 30 can provide information on the volume of lubricant within the component being lubricated as a higher pressure can be indicative of a volume of lubricant already present. The pressure sensor may be arranged within the nozzle 46 of the grease gun 40. The processor 52 may be further arranged to receive data from the sensor(s) 50a, 50b and may transmit this data to the digital system 54. The data from the sensor(s) 50a, 50b can be associated with the unique identifier received via the radio frequency identifier reader 48 so that the data is associated to a lubrication fitting 30. An exemplary method 60 for monitoring a component of aircraft landing gear is shown in Figure 4. However, as with Figures 2 and 3, the component may be any component of an aircraft and the method 60 may therefore apply analogously to such subassembly and / or component. At an initial step 62, the lubrication fitting 30 may be located. This can be carried out by a user visually inspecting the component or by a digital system providing a prompt to the user. At a next step 64, the grease gun 40 is engaged with the lubrication fitting 30, for example by a user bringing the nozzle of a grease gun into contact with a grease nipple. The grease gun nozzle can engage with the grease nipple to provide a sealed fluid connection between the grease gun and the lubrication channel of the grease nipple. At a next step 66, the radio frequency identifier reader 48 of the grease gun 40 transmits an RF signal to the passive radio frequency identifier component 38 of the lubrication fitting 30. Alternatively, the radio frequency identifier reader 48 may be arranged to continuously transmit an RF signal so that the RF signal is being transmitted on the approach of the grease gun 40 to the lubrication fitting 30. Once the RFID reader 48 and radio frequency identifier passive component 38 are within a working distance of the system, the reader and passive component are coupled. At a next step 68, once the radio frequency identifier reader 48 and the passive RFID component 38 are coupled, the radio frequency identifier passive component 38 transmits a unique identifier stored on the passive component to the reader. The unique identifier is transmitted via a processor 52 to a digital system 54. At step 70, the lubrication fitting 30 maintenance can be carried out. The maintenance can include adding lubricant to the component, and / or monitoring the level of lubricant present. This step 70 can occur at any point in the method between the engagement 64 and a disengagement of the grease gun 40 with the lubrication fitting 30. Therefore, the maintenance step 70 can occur before, during, and / or after step 66 in which the radio frequency identifier reader 48 and the passive radio frequency identifier tag 38 couple. Similarly, the maintenance step 70 can occur before, during, and / or after step 68 in which the unique identifier is transmitted from the passive radio frequency identifier component 38 to the radio frequency identifier reader 48 and processor 52 of the grease gun 40. Whilst shown as separate steps, the coupling 66 of the radio frequency identifier reader and passive radio frequency identifier component and the transmission 68 of the unique identifier can occur in quick succession and therefore appear simultaneous. The method 60 may further comprise the unique identifier being stored on the digital system 54 or in a system accessible to the digital system. The unique identifier may be stored with a time stamp of the transmission or coupling of the radio frequency identifier system. The method 60 may further comprise an analysis of the unique identifier at the digital system 54. For example, previous occurrences of the detection of the transmitted unique identifier can be calculated to provide historical data on how regularly the radio frequency identifier reader and the passive radio frequency identifier component have coupled. This can provide an indication on the occurrence of maintenance on the lubrication fitting. Therefore, the digital system 54 can communicate with the grease gun 40 and collect information on the lubrication fitting and its operation. Specifically, the digital system 54 can receive information relating to the identification of the lubrication fitting, such as a washer unique identifier, only when the grease gun 40 is attached to or in close proximity to the lubrication fitting 30. The information transmitted from the grease gun 40 to the digital system 54 can provide the time and date of a lubrication and confirm whether lubricant has been introduced into the lubrication fitting and thus whether a level of service has been carried out. The method 60 may further comprise displaying a representation of the component or subassembly with the lubrication fittings highlighted. For example, as shown in Figure 3, an example landing gear assembly is shown with the location of a lubrication fitting highlighted. If the data regarding previous coupling events between the radio frequency identifier reader and passive radio frequency identifier tag are stored by the digital system 54, the display may further include an indication of when the previous coupling event occurred and / or an indication that a lubrication fitting requires maintenance either due to a fault detected or due to a period of time elapsing between lubrication fitting maintenance recorded via radio frequency identifier coupling events. As such, the content of the information being displayed to a user relates to the technical condition of the component which in turn enables the user to properly operate the component. Alternatively or additionally, the information displayed can relate to the maintenance event, such as the addition of lubricant to the component. Such maintenance event is related to the internal function of the component which can change dynamically between maintenance occurrences. Therefore, automatically detecting the need for maintenance via the digital system detecting an elapsed time period between maintenance events, allows the display to provide a prompt to the user to interact with the lubrication fitting of the component (by carrying out a lubrication service) to avoid technical malfunctions. The method 60 may further comprise displaying an indication of lubrication fittings which require maintenance so that a user can carry out the maintenance work on all lubrication fittings which require servicing in an efficient manner, whilst reducing the risk of a lubrication fitting being missed. Once a lubrication fitting has been maintained and thus the radio frequency identifier reader has coupled with that lubrication fitting's passive RFID component, the digital system 54 may display an indication that the lubrication fitting has been serviced. Optionally, the method 60 may further include providing an indication of which lubrication fitting to engage with next. The indication may be any suitable means of highlighting a lubrication fitting to a user, such as using a label or differentiating colours on a schematic drawing or image of the component or subassembly. Therefore, the digital system 54 assists the user in performing the maintenance of the component or subassembly by a guided human-machine interaction process. The method 60 may further comprise detecting a fluid parameter during engagement. The method 60 may further comprise analysing the detected fluid parameter to determine an operational property of the lubrication fitting. The operational property may be the expected remaining lifetime of the lubrication fitting, the volume of lubricant added to the fitting, an estimation of a blockage within a lubrication channel or component joint, or any other property relating to the technical operation of the lubrication fitting. The fluid parameter detected may be the flow rate of lubricant from the grease gun 40 to the lubrication fitting 30 during engagement. For example, a flow rate meter 50a may be arranged on the grease gun 40 to provide the flow rate of lubricant and / or the time period in which lubricant was flowing as it passes along a component of the grease gun, such as the fixed tube / hose 44. The processor 52 of the grease gun 40 may receive the data from the flow rate meter 50a and calculate an estimated volume of lubricant inserted into the fitting 30. The estimated volume of lubricant may be transmitted to the digital system 54. Alternatively, the data may be transferred to the digital system 54 and analysed at the digital system to calculate the volume of lubricant. The digital system 54 may inform a user when an adequate volume of lubricant has been added, for example, via the output of the digital system 54 and / or the digital system 54 may record the volume of lubricant added to a component. The estimated volume may also be associated with the unique identifier such that the digital system can analyse and record volumes and maintenance events for each lubrication fitting. This provides information on the performance of the component being lubricated. For example, if higher than average volumes of lubricant are being introduced to the component at shorter intervals, the digital system 54 could flag this as an anomaly within the overall system to indicate to a user further maintenance is required for normal operation. Furthermore, a slower flow rate than average / expected may indicate that the lubrication fitting is partially blocked. Additionally, if a user can visually see lubricant being extruded from the component before an expected volume of lubricant has been added, the user may infer that there is an obstruction of lubrication channels within a joint. The method 60 may further comprise detecting the pressure required to move lubricant from the grease gun 40 to the lubrication fitting 30 during engagement. For example, a pressure sensor 50b may be arranged at the nozzle 46 of the grease gun 40. The processor 52 of the grease gun or the digital system 54 may receive the pressure data and determine whether the pressure required to move lubricant is within an expected or average range. The digital system 54 may inform the user when an abnormal pressure has been detected, for example, via the output of the digital system 54. The digital system 54 may store the pressure data. The pressure data may also be associated with the unique identifier such that the digital system can analyse and record the pressure and maintenance events for each lubrication fitting. This provides information on the performance of the component being lubricated. For example, if the pressure sensor detects an abnormally high pressure or a pressure outside an accepted range, this could indicate that the lubrication fitting is blocked or has enough lubricant already present. The method 60 may further comprise monitoring fluid parameters, such as flow rate and pressure over a plurality of maintenance operations. The data gathered on the fluid parameters may be transmitted and stored in the digital system 54. In turn, the evolution of the fluid parameters can be monitored over several maintenance cycles which enables the assessment of the condition of the component or joint. In turn, this can be used to carry out predictive maintenance. Monitoring of fluid parameters can be event based, i.e., based on the quantity of lubricant introduced to the component and / or based on the pressure detected at the nozzle / lubrication fitting. Alternatively, the monitoring may be trend based, i.e., tracking the evolution of a mean value with any exceedance over a threshold triggers an alert. Alternatively, the monitoring may be slope based, i.e., the variation of a parameter may be tracked so that an acceleration in degradation triggers an alert. The method may further include issuing a recommendation based on the degradation determined from tracking fluid parameters, for example, recommending a reduced lubrication interval. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be capable of designing many alternative embodiments without departing from the scope of the invention as defined by the appended claims. In the claims, any reference signs placed in parenthesis shall not be construed as limiting the claims. The word "comprising" can mean "including" or "consisting of" and therefore does not exclude the presence of elements or steps other than those listed in any claim or the specification as a whole. The word "coupled" can mean "attached" or "connected". The singular reference of an element does not exclude the plural reference of such elements and vice-versa. In an apparatus claim 5 enumerating several parts, several of these parts may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A system for monitoring an aircraft assembly, the system comprising:a plurality of lubrication fittings, each lubrication fitting comprising a passive radio frequency identification component; anda grease gun comprising a radio frequency identifier reader and a processor, wherein the processor is configured to:transmit a first signal to cause the radio frequency identifier reader to transmit a radio frequency, RF, signal to the passive radio frequency identifier components in the lubrication fittings;receive a unique identifier from the passive radio frequency identifier component in the lubrication fittings; andtransmit a second signal comprising the unique identifier to a digital system.

2. The system according to claim 1, wherein the grease gun further comprises a hose or tube which is arranged to couple to each lubrication fitting and an antenna arranged to transmit the RF signal, wherein the antenna is arranged at the distal end of the hose or tube.

3. The system according to any preceding claim, wherein the RF signal has a frequency of about 125 kHz to 135 kHz or about 3 MHz to 30 MHz.

4. The system according to any preceding claim, wherein the lubrication fitting comprises a washer and a greasing nipple and the passive radio frequency identifier component is arranged on the washer.

5. The system according to any preceding claim, wherein the grease gun further comprises a sensor arranged to measure a fluid parameter and wherein the second signal further comprises the fluid parameter.

6. The system according to claim 5, wherein the sensor is at least one of:a flow meter arranged to measure a flow rate of grease expelled by the grease gun;anda pressure sensor arranged to measure the pressure within the lubrication fitting.

7. A method for monitoring an aircraft assembly, the method comprising:engaging a grease gun with a lubrication fitting;transmitting a radio frequency, RF, signal from a radio frequency identifier, RFID, reader arranged in the grease gun, wherein the RF signal is transmitted when the grease gun is engaged with the lubrication fitting;receiving, via the radio frequency identifier reader, a unique identifier from a passive radio frequency identifier component in the lubrication fitting; and transmitting the unique identifier to a digital system.

8. The method according to claim 7, wherein the digital system records the unique identifier.

9. The method according to claim 8, further comprising analysing the unique identifier to determine any previous instances of engagement of the grease gun with the lubrication fitting.

10. The method according to any of 8 to 9, further comprising outputting a signal at the digital system, wherein the output signal indicates the time period between the most recent engagement of the grease gun with the lubrication fitting and the present time.

11. The method according to any of claims 8 to 10, further comprising:receiving a fluid parameter from a sensor arranged in the grease gun when the grease gun is engaged with the lubrication fitting;transmitting the fluid parameter to the digital system;recording the fluid parameter at the digital system;analysing the fluid parameter to determine an operational property of the lubrication fitting.

12. The method according to claim 11, wherein the sensor is at least one of:a flow meter arranged to measure a flow rate of grease expelled by the grease gun;anda pressure sensor arranged to measure the pressure within the lubrication fitting.

13. The method according to any of claims 7 to 12 wherein the grease gun engages with a single lubrication fitting at a time and receives the unique identifier when the grease gun is engaged with the single lubrication fitting.

14. A lubrication fitting for an aircraft assembly, the lubrication fitting comprising a passive radio frequency identification component arranged to transmit a unique identifier when engaged with an radio frequency identifier reader.

15. A grease gun for applying lubrication to a lubrication fitting of an aircraft assembly, the grease gun comprising a radio frequency identification reader arranged to transmit a radio frequency, RF, signal.

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