A monitoring system comprising a self-powered sensor

Abstract

A system (100) for monitoring the operation of a machine (110), the system comprising a main control unit (140), at least one transceiver (130), and at least one sensor unit (120) arranged attached to the machine (110). The at least one transceiver (130) has a first data connection (131) to the control unit (140) and a first wireless connection to the sensor unit (120). The sensor unit (120) comprises an energy harvesting device (300), at least one sensor (122), and a processing unit (121). The processing unit (121) is arranged to obtain measurement data from the sensor (122) and to transmit measurement data to the at least one transceiver (130) over the first wireless connection. The transceiver (130) is arranged to receive measurement data over the first wireless connection and to transmit measurement data to the control unit (140) over the first data connection (131). The control unit (140) is arranged to monitor the operation of the machine (110) based on the measurement data and / or distribute measurement data to an external unit (150).

Description

[0001] TITLE

[0002] A MONITORING SYSTEM COMPRISING A SELF-POWERED SENSOR

[0003] TECHNICAL FIELD

[0004] The present disclosure relates to systems and methods for monitoring the operation of machines, particularly heavy-duty machinery used for example in mining.

[0005] BACKGROUND

[0006] In many industries it is desirable to monitor the operation of machinery in order to detect potential problems, plan maintenance, and avoid interruptions in the production process. Such monitoring, however, requires sensors to be placed on or in close contact with heavy machinery and may require the sensors to be placed in positions where it is difficult to connect cables for power supply and I or data transfer. A monitoring system for machinery must thus solve the problem of enabling sensors to be placed in the desired positions while still maintaining communication with other parts of the system and ensuring an adequate power supply.

[0007] AU2018295567 A1 discloses systems and methods for monitoring the operation of a vibrating screen.

[0008] Still, there is a need for improved systems for monitoring the operation of heavy machinery.

[0009] SUMMARY

[0010] It is an object of the present disclosure to provide improved means for monitoring the operation of heavy machinery. This object is at least in part obtained by a system for monitoring the operation of a machine. The system comprises a main control unit, at least one transceiver, and at least one sensor unit arranged attached to the machine. The at least one transceiver has a first data connection to the main control unit and a first wireless connection to the sensor unit. The sensor unit comprises an energy harvesting device, at least one sensor, and a processing unit. The processing unit is arranged to obtain measurement data from the sensor and to transmit measurement data to the at least one transceiver over the first wireless connection. The transceiver is arranged to receive measurement data over the first wireless connection and to transmit measurement data to the main control unit over the first data connection. The main control unit is arranged to monitor the operation of the machine based on the measurement data and I or distribute measurement data to one or more external units.

[0011] As the at least one sensor unit comprises an energy harvesting device it does not require power to be supplied via a power cable or battery. Since the transfer of measurement data from the sensor unit to the transceiver takes place over a wireless connection, this means that the sensor units are entirely wireless. This has the advantage of enabling more flexible placement of the sensor units. Additionally, the power supplied by energy harvesting devices is less limited than that which can be supplied by a battery, which enables transfer of more measurement data over the wireless connection.

[0012] Equipment such as sensor units and cables that are attached to heavy machinery are subject to vibrations. This leads to wear on cables and cable connectors, which subsequently need to be replaced. Using wireless sensor units thus reduces the need for maintenance of the monitoring system.

[0013] The transceiver can be arranged to transmit a first synchronization signal to at least one sensor unit.

[0014] According to an alternative, the at least one sensor is arranged to transmit a request for synchronization to the transceiver. The transceiver can be arranged to receive the request for synchronization and to capture a timestamp. The transceiver can subsequently transmit the captured timestamp to the sensor.

[0015] As an example, the transceiver may be arranged to transmit an acknowledgement message to the sensor on receipt of the request for synchronization. The acknowledgement message may comprise an ID number of the transceiver. The transceiver may subsequently obtain a time stamp and transmit it to the sensor. Optionally, a time delay is implemented between transmitting the acknowledgement message and obtaining the time stamp. This time delay can for example be 1 ms.

[0016] The transceiver and the at least one sensor unit can also be arranged to communicate over a second wireless connection. The transceiver may be arranged to transmit the first synchronization signal over the second wireless connection, and the sensor unit is then arranged to receive the first synchronization signal over the second wireless connection.

[0017] Advantageously, synchronizing the sensor units in the system makes it possible to compare measurement data acquired simultaneously from different sensor units. It also makes it possible to collect additional data simultaneously on all sensor units. Sending the synchronization signal over a second wireless connection ensures that it is not affected by issues with bandwidth or data transfer capacity that may occur for the first wireless connection, thus reducing a variability of a transfer time for the synchronization signal. According to some aspects, the second wireless connection is a sub-GHz radio connection.

[0018] Alternatively, the transceiver and the at least one sensor unit can be arranged to transmit and receive synchronization signals over the first wireless connection. Advantageously, both the transceiver and the processing unit comprised in the sensor unit can be arranged to process synchronization signals in a way that minimizes the variability of the transfer time. According to aspects, the first wireless connection may be a 2.4 GHz radio connection.

[0019] The system may comprise at least two transceivers, where one transceiver is arranged to transmit a second synchronization signal to at least one other transceiver.

[0020] Having one transceiver transmit a synchronization signal to one or more other transceivers means that the transceivers can be synchronized with each other. As the sensor units receive synchronization signals from the transceivers, this means that a sensor unit communicating with a first transceiver and a sensor unit communicating with a second transceiver can be synchronized with each other, which is an advantage.

[0021] The second synchronization signal may be transmitted over a second data connection. Having a second data connection for the synchronization signal can avoid bandwidth issues that may occur related to the first data connection. It also reduces the risk of irregularities and variation in the transfer time of the synchronization signal, which is an advantage.

[0022] According to aspects, at least one sensor comprised in the sensor unit can be any of an accelerometer, a gyro, a temperature sensor, and a humidity sensor. Using an accelerometer makes it possible to study the movement of the machine in detail, which is an advantage.

[0023] The processing unit comprised in the sensor unit may be arranged to perform a processing operation on the measurement data. The processing operation may comprise any of low-pass filtering, down-sampling, and application of a machine learning algorithm. Processing the measurement data in the sensor node can serve several purposes. Simple processing operations such as low-pass filtering and down-sampling may serve to reduce the amount of data that has to be transmitted over the first wireless connection, which is an advantage as bandwidth is often limited. More advanced processing operations such as the calculation of statistical averages, determining a frequency of vibration, or the application of machine learning algorithms serve to extract features that can be used to directly detect problems in the operation of the machine. Quantities such as stroke length, stroke angle, and revolutions per minute (RPM) can also be determined.

[0024] The processing unit may be arranged to perform a coordinate transformation on the measurement data. This is particularly relevant if the sensor unit is mounted at an angle in relation to a coordinate system of the machine, or if different sensor units in the system are mounted at different orientations e.g. to optimize energy harvesting. The coordinate transformation then serves to bring all measurement data into a common coordinate system.

[0025] According to aspects, the processing unit comprises a data storage. The data storage comprises at least a first buffer and a second buffer, each buffer containing measurement data of a respective first and second data category. Measurement data of the first and second data category is transmitted to the transceiver according to a predetermined importance ranking.

[0026] The measurement data may comprise several data categories. The categories can correspond to data from different sensors, such as from a temperature sensor and an accelerometer, or to outputs from a processing operation performed on the measurement data. Being able to store data in buffers and transmit data to the transceivers in accordance with an importance ranking makes it possible to pass on the data considered most important first, which is an advantage.

[0027] The processing unit may be arranged to detect when a measurement value comprised in the measurement data exceeds a predetermined threshold. This makes it possible to quickly detect deviations from the expected behavior of the machine, which is an advantage.

[0028] The processing unit may also be arranged to, on detecting that the measurement value exceeds the predetermined threshold, record measurement data from a first time interval before the detection and from a second time interval after the detection, and to transmit the recorded measurement data to the transceiver. Recording additional data when unexpected behavior of the machine occurs makes it possible to perform a more detailed analysis of the unexpected behavior, which can make it possible to detect problems in the operation of the machine.

[0029] In addition to vibrations in the machine being monitored, it can be relevant to consider vibrations in structures surrounding the machine, e.g. if vibrations are transferred from the machine to its surroundings. Some of these structures may also be where the transceivers are mounted. Therefore, the transceiver may comprise a sensor arranged to detect vibrations.

[0030] At least one sensor unit may be arranged to monitor vibrations in a ball bearing and I or a gear in the machine. This enables early detection of defects such as cracks or unevenness in the ball bearings and I or gears, which is an advantage.

[0031] The main control unit may be arranged to transmit the processed measurement data to an external unit. An external unit can, for example, be a local or online server or a database. This makes it possible to e.g. store measurement data over time, perform additional analysis, and use the data to train machine learning models, which is an advantage.

[0032] There is also herein disclosed an energy harvesting device for harvesting vibrational energy. The device comprises a movable magnet, a leaf spring and a coil. The movable magnet is attached to a free end of the leaf spring, the leaf spring being arranged to perform an oscillatory movement in response to the energy harvesting device being exposed to vibrations. The coil is arranged such that the movable magnet passes above and I or below the coil during oscillatory movement of the leaf spring.

[0033] The device further comprises a first and a second stationary end magnet and a braking magnet attached to the movable magnet. Each end magnet is arranged near a respective first and second end point of the oscillatory movement of the leaf spring. The first and second end magnet are oriented so as to repel the braking magnet.

[0034] The energy harvesting device as described here has the advantage that as the first and second end magnets repel the braking magnet, the movement of the leaf spring slows down when approaching the end points of the oscillatory movement. This reduces the risk that the movable magnet will impact the walls of the energy harvesting device when the device is exposed to strong vibrations. Reducing the risk of impact is an advantage both because it reduces wear on the components and because it reduces the risk of negatively affecting other components that are powered by the energy harvesting device, for example an accelerometer.

[0035] The device may also comprise an electrically conductive member arranged near a middle point of the oscillatory movement of the leaf spring. When the movable magnet and the braking magnet pass by the conductive member, currents are induced in the conductive member. This contributes to slowing the movement of the leaf spring, further reducing the risk of the movable magnet impacting the walls.

[0036] The energy harvesting device may comprise a first and second elastic member arranged near the respective first and second end point of the oscillatory movement of the leaf spring. The elastic members should be arranged so that the movable magnet will hit the elastic members if its movement extends past the desired endpoints, rather than hitting the wall directly. The elastic member thus absorbs some of the impact, which is an advantage.

[0037] The energy harvesting device may comprise a conductive element arranged in contact with the first and second end magnets. This can enhance the effect of the two end magnets on the movable magnet, which is an advantage.

[0038] The movable magnet may comprise a plurality of individual magnetic bodies. The plurality of magnetic bodies can be arranged to improve energy harvesting efficiency, which is an advantage.

[0039] There is furthermore herein disclosed a sensor unit comprising at least one sensor, a processing unit, and an energy harvesting device as described above. Advantageously, such a sensor unit does not require a power cable or battery to function, making it possible to mount it in locations where a power cable would be inconvenient while simultaneously not being limited to the power that can be provided by a battery.

[0040] According to aspects, the sensor unit is arranged to communicate with a mobile device and to transmit measurement data to said mobile device. A mobile device such as a smartphone, tablet, or laptop computer can thus be used to check the operation of the sensor unit and to obtain data from it, for example when the system is being installed.

[0041] There is also herein disclosed a method for monitoring the operation of a machine using a system as previously described, the system comprising a main control unit, at least one transceiver, and at least one sensor unit. The method comprises obtaining, by the sensor unit, measurement data from a sensor comprised in the sensor unit and transmitting, by the sensor unit, the measurement data to the transceiver over a first wireless connection. The method also comprises transmitting, by the transceiver, the measurement data to the main control unit over a first data connection and monitoring, by the main control unit, the operation of the machine based on the measurement data and / or distributing, by the main control unit, measurement data to one or more external units.

[0042] The method may also comprise processing the measurement data by a processing unit comprised in the sensor unit.

[0043] According to aspects, the method also comprises transmitting, by the transceiver, a first synchronization signal, and receiving, by the sensor unit, the first synchronization signal.

[0044] According to other aspects, the method comprises transmitting, by the sensor unit, a request for synchronization and receiving, by the transceiver, the request for synchronization. The method may further comprise capturing, by the transceiver, a timestamp and transmitting the timestamp to the sensor unit.

[0045] As an example, the method may comprise transmitting, by the transceiver, an acknowledgement message to the sensor on receipt of the request for synchronization. The acknowledgement message may comprise an ID number of the transceiver. The method may further comprise obtaining, by the transceiver, a time stamp and transmitting it to the sensor. Optionally, a time delay is implemented between transmitting the acknowledgement message and obtaining the time stamp. This time delay can for example be 1 ms.

[0046] There is also herein disclosed a computer program comprising program code means for performing the steps of the method described above, when said program is run on a control system comprising one or more control units. There is furthermore disclosed a computer readable medium carrying a computer program comprising program code means for performing the steps of methods described herein, when said program product is run on a control system comprising one or more control units.

[0047] The methods disclosed herein are associated with the same advantages as discussed above in connection to the different apparatuses. There is also disclosed herein computer programs, computer program products, and control units associated with the above-mentioned advantages. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a / an / the element, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

[0048] BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present disclosure will now be described in more detail with reference to the appended drawings, where:

[0050] Figure 1 schematically illustrates a monitoring system;

[0051] Figure 2 schematically illustrates a first and second transceiver;

[0052] Figures 3A-C schematically illustrate an energy harvesting device;

[0053] Figure 4 schematically illustrates a sensor unit;

[0054] Figure 5 schematically illustrates a control unit and / or processing unit;

[0055] Figure 6 illustrates a computer program product;

[0056] Figure 7 is a flow chart illustrating methods; and

[0057] Figure 8 is an illustration of an energy harvesting device.

[0058] DETAILED DESCRIPTION

[0059] Aspects of the present disclosure will now be described more fully with reference to the accompanying drawings. The different devices and methods disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein. Like numbers in the drawings refer to like elements throughout. The terminology used herein is for describing aspects of the disclosure only and is not intended to limit the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0060] The following description focuses on the use of the monitoring system of the invention to monitor equipment used in mining and ore processing, particularly vibrating screens. However, a person skilled in the art will realize that the systems and methods herein described can be applied also to other types of industrial equipment.

[0061] Vibrating screens are used to separate granulated materials, such as crushed ores, according to their size and density. A vibrating screen generally comprises at least one drive or motor that induces vibration, a screen medium arranged to separate particles, and a deck or frame on which the drive and screen medium are mounted. The screen medium is typically a mesh comprising a plurality of holes, where the size of the holes is selected in dependence of the size of the particles that the screen is intended to separate. The screen medium may be woven wire cloth, a punch plate, or be made from rubber or other polymer compounds. Many industrial screens comprise a plurality of screen media with different mesh sizes in order to be able to separate granulated materials into multiple grades.

[0062] Different types of vibrating screens are distinguished by factors such as how the vibration is generated and the direction of the vibration movement. The movement may for example be linear, circular, or elliptical. Vibrating screens can also be adapted to processing different types of materials, as well as to processing either dry or wet material. Generally, vibrating screens are known in the art.

[0063] Industrial processes involving heavy machinery such as vibrating screens necessarily have to be stopped if the machinery breaks down. This leads to costly interruptions in operation. Improved monitoring of the operation of such machines can make it possible to detect problems in advance and plan maintenance so that the risk of breakdowns and unplanned interruption is minimized. Additionally, information about the operation of the machinery can be used to improve performance.

[0064] Figure 1 shows a system 100 for monitoring the operation of a machine 110, the system comprising a main control unit 140, at least one transceiver 130, and at least one sensor unit 120 arranged attached to the machine 110. The at least one transceiver 130 has a first data connection 131 to the main control unit 140 and a first wireless connection to the sensor unit 120. The first data connection 131 may be a wired connection. Optionally, the connection may be a USB or Ethernet connection, or a data bus such as CAN. Ethernet or CAN is preferably used if the distance between the transceiver 130 and the main control unit 140 is more than 5 meters. The first wireless connection may for example be a Bluetooth connection.

[0065] According to one alternative, the main control unit 140 and transceiver 130 may be incorporated into one combined device, particularly if the system comprises only one transceiver 130. In this case, the first data connection 131 is also comprised in the combined device.

[0066] The sensor unit 120 comprises an energy harvesting device 300, at least one sensor 122, and a processing unit 121. The processing unit 121 is arranged to obtain measurement data from the sensor 122 and to transmit measurement data to the at least one transceiver 130 over the first wireless connection. The transceiver 130 is arranged to receive measurement data over the first wireless connection and to transmit measurement data to the main control unit 140 over the first data connection 131. The main control unit 140 is arranged to monitor the operation of the machine 110 based on the measurement data and I or to distribute measurement data to one or more external units 150.

[0067] The external unit 150 may be a local or online server or a cloud service, as will be discussed in more detail below. Furthermore, Figure 1 shows the main control unit 140 as connected to a power supply 160.

[0068] A transceiver 130 is herein taken to be a device which can send and receive wireless communications using electromagnetic waves, particularly in the radio frequency spectrum. The transceiver 130 in the present invention may be arranged to send and receive communications using any part of the radio-frequency spectrum, microwave radiation, infrared radiation, or visible light.

[0069] The sensor unit 120 can be attached in different locations on the machine 110 depending on what parameters of the machine 110 need to be monitored. As an example, the sensor unit 120 may be attached at a corner of the machine 110, or at a drive axle. Preferably, a plurality of sensor units is used to collect data from multiple locations on the machine 110. According to some examples, two, four, six, or eight sensor units may be used. The sensor unit 120 is attached to the machine 110 using attachment means. A simple attachment means may be a bolt arranged to hold the sensor unit 120 in place. An attachment means may also be a bracket or a quick-release plate. Preferably, the attachment means comprise a magnetic mount.

[0070] According to some aspects, a mounting guide may be used. The mounting guide may comprise a rubber plate that is affixed to the machine 110, e.g. by means of a glue. The mounting guide indicates the correct position and orientation for mounting the sensor unit 120. This can be accomplished by having the mounting guide be of the same size and shape as the footprint of the sensor unit 120 and placing the mounting guide in the desired position and orientation of the sensor unit.

[0071] Optionally, the mounting guide may comprise a number of holes arranged to allow use of various mounting means. For example, if a magnetic mount is used, a hole in the mounting guide may be arranged to allow direct contact between the magnetic mount and the surface of the machine 110 through the mounting guide.

[0072] Advantageously, the mounting guide can remain affixed to the machine 110 if the sensor unit 120 is removed for repair or replacement. This facilitates the placement of a new sensor unit 120 in the same position. Optionally, the mounting guide may comprise an identification marker such as a serial number or QR code.

[0073] The energy harvesting device 300 is herein taken to be a device that harvests energy from its surroundings in order to power the sensor 122, processing unit 121 , and any other components comprised in the sensor unit 120. This means that the sensor unit does not require batteries or power cables. Note that the sensor unit 120 may still comprise an energy storage device such as a capacitor or rechargeable battery, but that said energy storage device is primarily used to store energy from the energy harvesting device. Energy harvesting devices will be discussed in more detail below.

[0074] In order for the sensor unit 120 to perform functions such as synchronization, measurements, data processing, and transfer of data to and from the transceiver 130, a sufficient amount of energy must be available. A sensor unit 120 can therefore be arranged so that synchronization, measurements etc. are only started once the energy harvesting device 300 provides a required level of energy output, or once the energy storage device is charged with a required amount of energy. The required amount of energy will depend on how demanding the functions to be performed are, e.g., how many sensors are in use and how much data processing is to be performed. The at least one sensor 122 comprised in the sensor unit 120 may comprise any of an accelerometer, a temperature sensor, a gyro, and a humidity sensor. The sensor unit may also comprise other sensors that generate outputs relevant to monitoring the operation of the machine 110. Preferably, the sensor unit 120 comprises two or more sensors of different types, such as an accelerometer and a temperature sensor.

[0075] Optionally, the sensor unit 120 may also comprise a sensor that measures an energy output from the energy harvester 300. If the sensor unit 120 comprises an energy storage device such as a rechargeable battery or a capacitor, it may comprise a sensor arranged to measure the output voltage of the energy storage device.

[0076] That the main control unit 140 is arranged to monitor the operation of the machine 110 based on the measurement data can for example mean that the main control unit 140 compares measurement data, such as vibration or temperature measurements, to a predetermined threshold. If the measurement data exceeds the threshold, the main control unit 140 may perform an operation such as sending an alert to a machine operator or in extreme cases triggering an emergency stop. According to aspects, the main control unit 140 may be arranged to apply a machine learning algorithm to the measurement data in order to detect deviations from the expected behavior of the machine 110.

[0077] The main control unit 140 is also arranged to distribute measurement data to one or more external units 150. The external unit may for example be a local server or PLC, a cloud server, a database, or a mobile device. The main control unit 140 may also transmit processed measurement data to more than one external unit, e.g. to both a PLC and a cloud server. In some cases, different external units may receive different types of data. The PLC could for example receive the results of a statistical analysis of the measurement data, referred to here as aggregate data, while the measurement data itself is sent to a cloud server for further analysis. Optionally, the results of such an analysis could be sent back to the PLC via the main control unit 140. Different types of data are discussed in more detail below.

[0078] The connection between the main control unit 140 and one or more external units may be a wired connection such as an ethernet or CAN connection, or it may be a wireless connection using Wi-Fi, 4G, or 5G. Optionally, the main control unit 140 may have a wired connection to a mobile device such as a smartphone, which in turn maintains a wireless connection with another external unit such as a server. According to some aspects, data can also be transmitted from an external unit to the main control unit 140. In particular, software updates may be transferred from an online server to the main control unit 140. In this case, the main control unit 140 will be arranged to transmit software updates targeting a transceiver 130 or a sensor unit 120 to the transceiver 130. If the target of the software update is one or more sensor units 120, the transceiver 130 will then transmit the software update to the one or more sensor units 120 using a FOTA (firmware over the air) method.

[0079] In order to take full advantage of the measurement data, it is preferable to ensure that each sample of measurement data is associated with a reliable timestamp. This requires synchronizing each sensor unit 120 and transceiver 130.

[0080] According to one example, the transceiver 130 is arranged to transmit a first synchronization signal to at least one sensor unit 120.

[0081] According to another example, the at least one sensor unit 120 is arranged to transmit a request for synchronization to the transceiver 130. The transceiver 130 is then arranged to receive the request for synchronization and to capture a timestamp. The transceiver can subsequently transmit the captured timestamp to the sensor unit 120.

[0082] As an example, the transceiver may be arranged to transmit an acknowledgement message to the sensor on receipt of the request for synchronization. The acknowledgement message may comprise an ID number of the transceiver. The transceiver may subsequently obtain a time stamp and transmit it to the sensor. Optionally, a time delay is implemented between transmitting the acknowledgement message and obtaining the time stamp. This time delay can for example be 1 ms.

[0083] The transceiver 130 and the sensor unit 120 can be arranged to communicate over a second wireless connection, where the transceiver 130 is arranged to transmit the first synchronization signal over the second wireless connection, and where the sensor unit 120 is arranged to receive the first synchronization signal over the second wireless connection.

[0084] Alternatively, the transceiver 130 and the sensor unit 120 can be arranged to transmit and receive synchronization signals over the first wireless connection. The transceiver and the processing unit comprised in the sensor unit can be arranged to process synchronization signals so as to minimize the variability of the transfer time. According to aspects, the first wireless connection may be a 2.4 GHz radio connection. If more than one sensor unit 120 is comprised in the system 100, the transceiver 130 can advantageously be arranged to communicate over a second wireless connection with each sensor unit 120 and to send the first synchronization signal to each sensor unit 120. The second wireless connection may be a sub-GHz radio connection. Optionally, the second wireless connection uses the frequency band between 412 and 440 MHz. The second wireless connection may also be a Bluetooth Low Energy (BLE) connection, or a connection according to the radio standard IEEE 802.15.4.

[0085] The monitoring system 100 can comprise several transceivers 130. This is advantageous in particular when monitoring large machines and / or machines comprising a large quantity of metal. Such machines can scatter the electromagnetic waves used in the first and second wireless connections, which may lead to poor signal quality. In such cases, several transceivers can be placed around the machine 110 being monitored to ensure that all sensor units 120 have line of sight to at least one transceiver 130. Figure 1 shows two transceivers 130 mounted on either side of a machine 110. It is also possible to use more than two transceivers 130, for example if the machine 110 is larger or of a more complex shape.

[0086] If more than one transceiver 130 is used, it becomes necessary to synchronize the transceivers 130. Accordingly, if the system comprises at least two transceivers 130, one transceiver 130 is arranged to transmit a second synchronization signal to at least one other transceiver 130.

[0087] Figure 2 schematically illustrates one possible implementation of a pair of transceivers 130, each comprising a first transmit and receive antenna 210 for the first wireless connection and a second transmit and receive antenna 220 for the second wireless connection. The second synchronization signal is transmitted over a second data connection 230. The second data connection may be a USB, ethernet, or CAN data connection, or a simple conductor.

[0088] In a system 100 comprising at least two transceivers 130 and a plurality of sensor units 120, each transceiver 130 may send a first synchronization signal to a subset of the sensor units 120. For example, each sensor unit 120 may receive the synchronization signal from the transceiver 130 closest to it, or it may receive the synchronization signal that has the highest signal strength at the location of the sensor unit 120.

[0089] According to some aspects, the processing unit 121 comprised in the sensor unit 120 may be arranged to perform a processing operation on the measurement data. The processing operation may comprise any of low-pass filtering, down-sampling, statistical analysis such as the calculation of averages, and application of a machine learning algorithm.

[0090] Down-sampling and low-pass filtering of the measurement data in the sensor unit 120 has the advantage that less data needs to be sent over the first wireless connection to the transceiver 130. However, the processing operation may also comprise determining characteristics of the operation of the machine 110. This is discussed in further detail below.

[0091] The processed measurement data resulting from the processing operation can be divided into a number of categories depending on what sensors are used and the type of processing applied. According to one example, for a sensor unit 120 comprising at least an accelerometer, a temperature sensor, and a sensor for measuring the voltage level of the energy storage device, the processed measurement data may be divided into the categories of health data, temperature data, aggregated movement data, raw data, and event data.

[0092] Health data is here taken to mean data relating to the functioning of the sensor unit 120, such as the signal strength between the transceiver 130 and the sensor unit 120 and the voltage level of the energy storage device. Health data may be sampled at configurable time intervals. The time interval could for example be every 5 seconds.

[0093] Temperature data is the output of the temperature sensor. It may also be sampled at configurable time intervals. The time interval for the temperature data can be shorter or longer than for the health data. According to one example, the time interval for the temperature data may be 15 minutes.

[0094] Aggregated movement data is generated by performing a processing operation on the measurement data from the accelerometer. An accelerometer will typically measure acceleration along three spatial axes, which define a Cartesian coordinate system. It may be that an overall analysis of the movement of the machine 110 is preferably done in a coordinate system wherein one axis is oriented vertically, i.e. along the direction of the gravitational force, whereas the sensor unit 120 needs to be oriented in some other way for optimal operation. In such a case, the processing unit 121 may be arranged to perform a coordinate transformation on the measurement data. Generally, calculation of aggregated data is performed for each axis of measurement of the accelerometer, resulting in one set of data for each of the x, y, and z axes. Aggregated data may comprise any of a root mean square (RMS) acceleration, maximum acceleration, RMS velocity, maximum velocity, uniaxial stroke, in-plane stroke, and the frequency of the strongest vibrational component. The strongest vibrational component can be identified by applying a Fourier transform to the accelerometer measurement data, resulting in a frequency domain representation of the measurement data. This can for example be used to calculate a power spectrum.

[0095] Aggregated movement data is preferably timestamped using the synchronization signal received from the transceiver 130 as discussed above. This makes it possible to combine aggregated movement data obtained at the same point in time from different sensor units 120.

[0096] In addition to the aggregated movement data, raw data may be included. Raw data is herein taken to mean data representing the output of the sensor without the application of any statistical operation such as the calculation of an average value. Raw data may comprise all measurement data output by the accelerometer. Preferably, the raw data is sampled at a lower sampling rate compared to the sampling rate of the accelerometer. The sampling rate for the raw data can be selected in dependence of a bandwidth or data transfer capacity of the first wireless connection over which the data is to be transmitted. As an example, the sampling rate may be 832 Hz.

[0097] Preferably, raw data is recorded during a recording interval, with the recording interval being repeated at a repetition interval. As an example, if the recording interval is 3 s and the repetition interval is 60 s, 3 s of raw data will be recorded every 60 s. According to another example, the recording interval may be 1 s and the repetition interval 10 s. The recording interval and the repetition interval may be configured depending on factors such as the bandwidth of the first wireless connection.

[0098] Raw data recording should preferably be configured so that, in a system with multiple sensor units 120, raw data recording is performed simultaneously on all sensor units 120. This is possible when the sensor units are synchronized as previously described.

[0099] Event data is recorded when a measurement value exceeds a threshold. According to one example, the processing unit 121 is arranged to detect when a measurement value comprised in the measurement data exceeds a threshold. The measurement value could be e.g. a temperature measurement or a measurement of movement speed or stroke length. Another type of measurement that can be used relates to the distribution of vibrational energy between different frequencies, which can be obtained from the power spectrum mentioned above by measuring the height of peaks in the power spectrum.

[0100] The processing unit 121 may be arranged to, on detecting that the measurement value exceeds the corresponding threshold, record measurement data from a predetermined first time interval before the detection and from a predetermined second time interval after the detection and to transmit the recorded measurement data to the transceiver 130. A measurement value exceeding the corresponding threshold is denoted an event, and the resulting measurement data is herein referred to as event data. The event data can be used for offline analysis of occasions where a predetermined threshold is exceeded, for example to aid in finding problems with the machine 110 or improving its efficiency.

[0101] According to some examples, event data may also be recorded at other times, such as at startup or shutdown of the machine 110.

[0102] The event data may be sampled at a similar rate as the recorded raw data mentioned above, e.g. 832 Hz, or at a different rate. The first and second time intervals can be configured depending on e.g. how much data is expected to be required for offline analysis of the event. According to one example, the first time interval is 5 seconds and the second time interval is 10 seconds.

[0103] The thresholds for each measurement value can be configured based on properties of the system, e.g., a temperature threshold can be chosen depending on the normal operating temperature of the system.

[0104] In order to record during the first time interval before an event, it is necessary to continuously store raw data corresponding to at least the first time interval. This can be accomplished using a data buffer implemented in the processing unit 121.

[0105] According to aspects, the processing unit 121 may be arranged to comprise one data buffer per data category, e.g., one for health data, one for temperature data, one for aggregated movement data, etc. The processing unit may furthermore be arranged to transmit the data to the transceiver according to an importance ranking of the different data categories. According to an example, health data may be considered more important than aggregated movement data according to the importance ranking. The health data would then be transmitted before the aggregated movement data. Among the data categories mentioned above, the importance ranking may be such that health data is considered most important, followed by event data, raw data, aggregated movement data, and temperature data.

[0106] Thus, with reference also to Figure 5, the processing unit 121 may comprise a data storage 430, the data storage comprising at least a first buffer and a second buffer, each buffer containing measurement data of a respective first and second data category, and wherein measurement data of the first and second data category is transmitted to the transceiver 130 according to an importance ranking.

[0107] At least one sensor unit 120 may be arranged to monitor vibrations in a ball bearing and / or a gear in the machine 110. In particular, a sensor unit 120 may be arranged to monitor vibrations in a ball bearing and I or gear forming part of a drive or motor comprised in the machine. Structures such as ball bearings and gears often produce vibrations at specific frequencies as a result of defects or breakage. These specific frequencies can be calculated in dependence of, among other things, the size of the bearings and / or gears. In a ball bearing, for example, a crack in an outer or inner race may result in a vibration with a frequency corresponding to how often a rolling element passes the crack. By monitoring vibrations at such frequencies using a sensor unit 120, potential problems can be discovered at an early stage.

[0108] In addition to the machine 110, buildings and other structures in the surroundings may also be exposed to vibrations especially if they are in physical contact with some part of the machine 110. To monitor such vibrations, a sensor arranged to detect vibrations may be included in the transceiver 130. The sensor may for example be an accelerometer.

[0109] With reference to Figure 6, as well as to Figures 1 and 3 A-D, there is also herein disclosed a method for monitoring the operation of a machine 110 using a system 100 according to any previous claim. The system comprises a main control unit 140, at least one transceiver 130, and at least one sensor unit 120 arranged attached to the machine 110. The method comprises obtaining S1 , by the sensor unit 120, measurement data from a sensor 122 comprised in the sensor unit, and transmitting S3, by the sensor unit 120, the measurement data to the transceiver 130 over a first wireless connection. The method also comprises transmitting S4, by the transceiver 130, the measurement data to the main control unit 140 over a first wired connection and monitoring S5, by the main control unit 140, the operation of the machine 110 based on the measurement data and / or distributing, by the main control unit 140, measurement data to one or more external units 150.

[0110] The method may also comprise processing S2, of the measurement data by a processing unit 121 comprised in the sensor unit 120.

[0111] The method may also comprise transmitting S5, by the transceiver, a first synchronization signal, and receiving S6, by the sensor unit, the first synchronization signal. The first synchronization signal may be transmitted over a second wireless connection, or over the first wireless connection.

[0112] According to an alternative, the method may comprise transmitting, by the sensor unit, a request for synchronization and receiving, by the transceiver, the request for synchronization. The method may further comprise capturing, by the transceiver, a timestamp and transmitting the timestamp to the sensor unit.

[0113] As an example, the method may comprise transmitting, by the transceiver, an acknowledgement message to the sensor on receipt of the request for synchronization. The acknowledgement message may comprise an ID number of the transceiver. The method may further comprise obtaining, by the transceiver, a time stamp and transmitting it to the sensor. Optionally, a time delay is implemented between transmitting the acknowledgement message and obtaining the time stamp. This time delay can for example be 1 ms.

[0114] Figure 5 schematically illustrates, in terms of a number of functional units, the components of a control unit 140 or processing unit 121 according to an embodiment of the discussions herein. Processing circuitry 410 is provided using any combination of one or more of a suitable central processing unit CPU, multiprocessor, microcontroller, digital signal processor DSP, etc., capable of executing software instructions stored in a computer program product, e.g. in the form of a storage medium 430. The processing circuitry 410 may further be provided as at least one application specific integrated circuit ASIC, or field programmable gate array FPGA.

[0115] Particularly, the processing circuitry 410 is configured to cause the control unit 140 or processing unit 121 to perform a set of operations, or steps, such as the methods discussed in connection to Figure 7. For example, the storage medium 430 may store the set of operations, and the processing circuitry 410 may be configured to retrieve the set of operations from the storage medium 430 to cause the control unit 140 / processing unit 121 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus, the processing circuitry 410 is thereby arranged to execute methods as herein disclosed.

[0116] The storage medium 430 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory, memory card or even remotely mounted memory.

[0117] The control unit 140 1 processing unit 121 may further comprise an interface 420 for communications with at least one external device. As such the interface 420 may comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number ports for wireline or wireless communication.

[0118] The processing circuitry 410 controls the general operation of the control unit 140 / processing unit 121 e.g. by sending data and control signals to the interface 420 and the storage medium 430, by receiving data and reports from the interface 420, and by retrieving data and instructions from the storage medium 430. Other components, as well as the related functionality, of the control node are omitted in order not to obscure the concepts presented herein.

[0119] Figure 6 schematically illustrates a computer program product 500, comprising a set of operations 510 executable by a control unit 140 I processing unit 121. The set of operations 510 may be loaded into the storage medium 530 in the control unit 140 / processing unit 121 . The set of operations may correspond to the methods discussed above in connection to Figure 7 or to the different operations by the monitoring system discussed above.

[0120] In the example of Figure 6, the computer program product 500 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu- Ray disc. The computer program product could also be embodied as a memory, such as a random-access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program is here schematically shown as a track on the depicted optical disk, the computer program can be stored in any way which is suitable for the computer program product. Figures 3A - C schematically illustrate an energy harvesting device 300 for harvesting vibrational energy. The device 300, also illustrated in Figure 8, comprises a movable magnet 310, a leaf spring 311 and an electrically conductive coil 320. The movable magnet 310 is attached to a free end of the leaf spring 311 and the leaf spring 311 is arranged to perform an oscillatory movement in response to the energy harvesting device 300 being exposed to vibrations. The electrically conductive coil 320 is arranged such that the movable magnet 310 passes above and I or below the coil 320 during oscillatory movement of the leaf spring 311 , which results in a current being induced in the electrically conductive coil. The device thereby transforms the mechanical energy of the vibrations into electrical energy.

[0121] The term electrically conductive is herein taken to mean that it has an electric conductivity similar to that of a metal, or an electric conductivity above 100 (Qm)-1.

[0122] According to one example, the movable magnet 310 is oriented with its magnetization direction perpendicular to the plane of oscillation of the leaf spring 311. This direction is indicated as the z direction in Figure 3B. Figure 3B also shows an alternative in which the movable magnet comprises at least two separate magnetic bodies mounted such that one passes above the coil 320 and one below the coil 320.

[0123] The device also comprises a first and a second stationary end magnet 330 and a braking magnet 340. Each end magnet is arranged near a respective first and second end point of the oscillatory movement of the leaf spring 311 , while the braking magnet 340 is attached to the movable magnet 310. The end points of the oscillatory movement are schematically illustrated as points a and b in Figure 3C. The middle point is indicated as point c.

[0124] The first and second end magnets 330 are oriented so as to repel the braking magnet 340. This can for example be accomplished by orienting the first and second end magnet and the braking magnet perpendicular to the plane of oscillation of the leaf spring 311 and placing the braking magnet so that it passes above or below the end magnets. If the end magnets 330 are then placed so that the south poles face downwards and the braking magnet 340 is placed so that it south pole faces upwards, the end magnets 330 will repel the braking magnet 340 as it approaches.

[0125] The end magnets 330 and braking magnet 340 serve to reduce a speed of the movable magnet 310 as it approaches the end points a, b. This in turn reduces the risk that the movable magnet strikes the walls of the energy harvesting device 300 when exposed to strong vibrations. If the end magnet would strike the walls, this may negatively affect processes such as accelerator measurements that are powered by the energy harvesting device 300.

[0126] The energy harvesting device may also comprise an electrically conductive member 350 arranged near the midpoint c of the oscillatory movement. As the movable magnet 310 and the braking magnet 340 pass by the conductive member, currents are induced into the conductive member 350, which leads to that the movable magnet 310 and braking magnet 340 lose kinetic energy. This further contributes to slowing down the oscillatory movement and reduce the risk of impacting the walls of the device. The conductive member comprises a material with an electrical conductivity similar to that of a metal. It may for example be a metal plate such as a copper plate, or a coil of metal wire.

[0127] The energy harvesting device may also comprise a first and second elastic member 331 , the first and second elastic members 331 being arranged near the respective first and second end point of the oscillatory movement of the leaf spring 311. In particular, the elastic members are arranged so that the movable magnet 310 will hit the elastic members 331 rather than the wall of the energy harvesting device if it moves past the end points a, b of the oscillatory motion. Thus, the elastic members will absorb some of the kinetic energy of the movable magnet 310. The elastic members may for example be made of rubber.

[0128] The energy harvesting device may also comprise a conductive element 332 arranged in contact with the first and second end magnets 330. The conductive element preferably comprises a metallic material such as steel.

[0129] According to aspects, the movable magnet 310 comprises a plurality of individual magnetic bodies.

[0130] There is also herein disclosed a sensor unit 120 comprising at least one sensor 122, a processing unit 121 , and an energy harvesting device 300 as described above. Figure 4 schematically illustrates such a sensor unit 120 where the sensor 122 and the processing unit 121 are mounted on a printed circuit board, PCB, 125. The sensor unit is suitable for use in a monitoring system 100 as described above and can comprise all components and fulfill all functions previously discussed in relation to the sensor unit 120 comprised in the system 100.

[0131] Optionally, the sensor unit may comprise one or more external light emitting diodes, LEDs, 124. The external LEDs may be arranged to indicate whether the energy harvesting device is producing enough energy for the sensor unit 120 to perform functions such as measurements, data processing, and sending I receiving data. If the sensor unit 120 comprises an energy storage device such as a capacitor, as discussed above, an external LED may also be used to indicate an amount of energy stored in the energy storage device.

[0132] The sensor unit 120 may also be arranged to communicate with a mobile device and to transmit measurement data to said mobile device. The mobile device may for example be a smartphone, tablet, or laptop computer. The communication may take place over a wireless connection such as a Bluetooth connection. The data sent to the mobile device may comprise any of the data categories previously discussed, e.g. health data, temperature data, aggregate movement data, event data, or raw data. Advantageously, the ability to connect the sensor unit 120 to a mobile device may be used during installation of a system 100 in order to verify that the sensor unit 120 is functioning correctly.

Claims

CLAIMS1. A system (100) for monitoring the operation of a machine (110), the system comprising a main control unit (140), at least one transceiver (130), and at least one sensor unit (120) arranged attached to the machine (110), the at least one transceiver (130) having a first data connection (131) to the main control unit (140) and a first wireless connection to the sensor unit (120), the sensor unit (120) comprising an energy harvesting device (300), at least one sensor (122), and a processing unit (121), the processing unit (121) being arranged to obtain measurement data from the sensor (122) and to transmit measurement data to the at least one transceiver (130) over the first wireless connection, the transceiver (130) being arranged to receive measurement data over the first wireless connection and to transmit measurement data to the main control unit (140) over the first data connection (131), and the main control unit (140) being arranged to monitor the operation of the machine (110) based on the measurement data and I or to distribute measurement data to one or more external units (150).

2. The system according to claim 1 , wherein the transceiver (130) is arranged to transmit a first synchronization signal to the at least one sensor unit (120).

3. The system according to claim 2, wherein the transceiver (130) and the at least one sensor unit (120) are arranged to communicate over a second wireless connection, and the first synchronization signal is transmitted over the second wireless connection.

4. The system according to any previous claim, wherein the system comprises at least two transceivers (130), where one transceiver (130) is arranged to transmit a second synchronization signal to at least one other transceiver (130).

5. The system according to claim 4, wherein the second synchronization signal is transmitted over a second data connection (230).

6. The system according to any previous claim, wherein at least one sensor (122) comprised in the sensor unit (120) comprises any of an accelerometer, a temperature sensor, and a humidity sensor.

7. The system according to any previous claim, wherein the processing unit (121) comprised in the sensor unit (120) is arranged to perform a processing operation onthe measurement data, the processing operation comprising any of low-pass filtering, down-sampling, and application of a machine learning algorithm.

8. The system according to any previous claim, wherein the processing unit (121) is arranged to perform a coordinate transformation on the measurement data.

9. The system according to any previous claim, wherein the processing unit (121) comprises a data storage (430), the data storage comprising at least a first buffer and a second buffer, each buffer containing measurement data of a respective first and second data category, and wherein measurement data of the first and second data category is transmitted to the transceiver (130) according to a predetermined importance ranking.

10. The system according to any previous claim, wherein the processing unit (121) is arranged to detect when a measurement value comprised in the measurement data exceeds a predetermined threshold.

11. The system according to claim 10, wherein the processing unit (121) is arranged to, on detecting that the measurement value exceeds the predetermined threshold, record measurement data from a first time interval before the detection and from a second time interval after the detection, and to transmit the recorded measurement data to the transceiver (130).

12. The system according to any previous claim, wherein the transceiver (130) comprises a sensor arranged to detect vibrations.

13. The system according to any previous claim, wherein at least one sensor unit (120) is arranged to monitor vibrations in a ball bearing and / or a gear in the machine (110).

14. A method for monitoring the operation of a machine (110) using a system (100) according to any previous claim, the system comprising a main control unit (140), at least one transceiver (130), and at least one sensor unit (120) arranged attached to the machine (110), the method comprising: obtaining (S1), by the sensor unit (120), measurement data from a sensor (122) comprised in the sensor unit, transmitting (S3), by the sensor unit (120), the measurement data to the transceiver (130) over a first wireless connection,transmitting (S4), by the transceiver (130), the measurement data to the main control unit (140) over a first data connection, monitoring (S5), by the main control unit (140), the operation of the machine (110) based on the measurement data and or distributing, by the main control unit (140), measurement data to one or more external units (150).

15. The method according to claim 14, where the method also comprises processing (S2), of the measurement data by a processing unit (121) comprised in the sensor unit (120).

16. The method according to claim 14 or 15, the method also comprising transmitting (S6), by the transceiver, a first synchronization signal, and receiving (S7), by the sensor unit, the first synchronization signal.

17. A computer program comprising program code means (510) for performing the steps of any of claims 14 to 16, when said program is run on a control system comprising one or more control units.

18. A computer readable medium (500) carrying a computer program comprising program code means (510) for performing the steps of any of claims 14 to 16, when said program product is run on a control system comprising one or more control units.

19. An energy harvesting device (300) for harvesting vibrational energy, the device (300) comprising a movable magnet (310), a leaf spring (311) and an electrically conductive coil (320), the movable magnet (310) being attached to a free end of the leaf spring (311), the leaf spring (311) being arranged to perform an oscillatory movement in response to the energy harvesting device (300) being exposed to vibrations, where the electrically conductive coil (320) is arranged such that the movable magnet (320) passes above and I or below the coil (320) during oscillatory movement of the leaf spring (311), the device further comprising a first and a second stationary end magnet (330), each end magnet being arranged near a respective first (a) and second (b) end point of the oscillatory movement of the leaf spring (311), and a braking magnet (340) attached to the movable magnet (310), wherein the first and second end magnet (330) are oriented so as to repel the braking magnet (340).

20. The energy harvesting device according to claim 19, comprising a first and second elastic member (331), the first and second elastic members (331) being arranged nearthe respective first (a) and second (b) end point of the oscillatory movement of the leaf spring (311).

21. The energy harvesting device according to claim 19 or 20, comprising a conductive element (332) arranged in contact with the first and second end magnets (330).

22. The energy harvesting device according to any of claims 19 to 21 , wherein the movable magnet (310) comprises a plurality of individual magnetic bodies.

23. A sensor unit (120) comprising at least one sensor (122), a processing unit (121), and an energy harvesting device (300) according to any of claims 19 to 22.

24. A sensor unit (120) according to claim 23, wherein the sensor unit (120) is arranged to communicate with a mobile device and to transmit measurement data to said mobile device.

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