MONITORING SYSTEM FOR CONVEYANCE SYSTEM

Abstract

A monitoring system for a conveyance system includes a pressure sensor mounted on a conveyance apparatus; an accelerometer mounted on the conveyance apparatus; and a controller arranged to: acquire accelerometer data by sampling the accelerometer; store the accelerometer data in a buffer; acquire pressure sensor data by sampling the pressure sensor; determine from the pressure sensor data that a start or stop of the conveyance apparatus has occurred; and upon said determination, analyse the accelerometer data to determine a first position within the accelerometer data, wherein the first position is a position at which the start or stop of the conveyance apparatus occurred. Both pressure and acceleration readings are combined to determine a point in time at which motion started or stopped. The pressure sensor is used first to determine a robust indication that the motion state has changed (started or stopped).

Claims

1. A monitoring system for a conveyance system, comprising: a pressure sensor mounted on a conveyance apparatus; an accelerometer mounted on the conveyance apparatus; and a controller arranged to: acquire accelerometer data by sampling the accelerometer; store the accelerometer data in a buffer; acquire pressure sensor data by sampling the pressure sensor; determine from the pressure sensor data that a start or stop of the conveyance apparatus has occurred; and upon said determination, analyse the accelerometer data to determine a first position within the accelerometer data, wherein the first position is a position at which the start or stop of the conveyance apparatus occurred.

2. A monitoring system as claimed in claim 1, wherein the controller is arranged to determine that a start or stop of the conveyance apparatus has occurred based on detecting a change in the pressure data of at least a threshold amount within a predetermined period of time.

3. A monitoring system as claimed in claim 1, wherein the controller is arranged to analyse a recent time window of the accelerometer data.

4. A monitoring system as claimed in claim 1, wherein the controller is arranged to filter the accelerometer data with a low pass filter.

5. A monitoring system as claimed in claim 1, wherein the controller is arranged to analyse the accelerometer data to find a second position within the accelerometer data, the second position being a position at which the accelerometer data crosses a threshold value and wherein the controller is arranged to determine the first position based on the second position.

6. A monitoring system as claimed in claim 1, wherein the controller is arranged to analyse the accelerometer data to find a third position within the accelerometer data, the third position being a position at which the accelerometer data reaches a maximum or minimum value and wherein the controller is arranged to determine the first position based on the third position.

7. A monitoring system as claimed in claim 1, wherein the controller is arranged to associate a motion state of the conveyance apparatus with the accelerometer data, the motion state being an indication of whether the conveyance apparatus is in motion or stationary.

8. A monitoring system as claimed in claim 1, wherein the controller is arranged to segregate the accelerometer data into two or more groups based on the first position.

9. A monitoring system as claimed in claim 1, wherein the controller is arranged to process the accelerometer data to analyse the health of the conveyance system, wherein said processing is performed with a fixed time delay, and wherein the controller is arranged to change a type of health analysis when the first position in the accelerometer data corresponds to the fixed time delay.

10. A monitoring system as claimed in claim 9, wherein the conveyance system is an elevator system and wherein the controller is arranged to change the type of health analysis from elevator door analysis to elevator car analysis or from elevator car analysis to elevator door analysis.

11. A monitoring system as claimed in claim 1, wherein the conveyance system is an elevator system and the conveyance apparatus is an elevator car, wherein the elevator system implements an advanced door opening system and wherein when the controller determines a stop of the elevator car, the controller is arranged to determine the first position within the accelerometer data additionally based upon an advanced door opening adjustment.

12. A monitoring system as claimed in claim 1, wherein the monitoring system is powered by a battery or energy harvesting system.

13. A monitoring system as claimed in claim 1, wherein the monitoring system is independent from the conveyance system.

14. A monitoring system as claimed in claim 1, wherein a sampling rate of the accelerometer is greater than a sampling rate of the pressure sensor.

15. A method of monitoring a conveyance system, comprising: acquiring accelerometer data by sampling an accelerometer on a conveyance apparatus; storing the accelerometer data in a buffer; acquiring pressure sensor data by sampling a pressure sensor on the conveyance apparatus; determining from the pressure sensor data that a start or stop of the conveyance apparatus has occurred; and upon said determination, analysing the accelerometer data to determine a first position within the accelerometer data, wherein the first position is a position at which the start or stop of the conveyance apparatus occurred.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is a schematic illustration of an elevator system according to examples of the present disclosure;

[0032] FIG. 2 is a schematic illustration of a sensor system for the elevator system of FIG. 1, according to examples of the present disclosure;

[0033] FIG. 3 is a schematic illustration of the location of a sensor system for the elevator system of FIGS. 1 and 2, according to examples of the present disclosure;

[0034] FIG. 4 is a schematic illustration of a sensing unit according to examples of the present disclosure;

[0035] FIGS. 5a and 5b are flow charts showing operations carried out in a change of motion detection process according to examples of the present disclosure;

[0036] FIG. 6 is a flow chart showing operations carried out according to an initial motion detection process according to examples of the present disclosure;

[0037] FIG. 7 is a flow chart showing operations carried out according to an end of motion detection process according to examples of the present disclosure; and

[0038] FIGS. 8a-8d show a plot of acceleration data illustrating an acceleration profile of an elevator car, and ways in which acceleration data is stored to a buffer during the initial motion detection process according to examples of the present disclosure.

DETAILED DESCRIPTION

[0039] FIG. 1 is a perspective view of an elevator system 101 including an elevator car 103, a counterweight 105, a tension member 107, a guide rail 109, a machine 111, a position reference system 113, and a controller 115. The elevator car 103 and counterweight 105 are connected to each other by the tension member 107. The tension member 107 may include or be configured as, for example, ropes, steel cables, and/or coated-steel belts. The counterweight 105 is configured to balance a load of the elevator car 103 and is configured to facilitate movement of the elevator car 103 concurrently and in an opposite direction with respect to the counterweight 105 within an elevator shaft 117 and along the guide rail 109.

[0040] The tension member 107 engages the machine 111, which is part of an overhead structure of the elevator system 101. The machine 111 is configured to control movement between the elevator car 103 and the counterweight 105. The position reference system 113 may be mounted on a fixed part at the top of the elevator shaft 117, such as on a support or guide rail, and may be configured to provide position signals related to a position of the elevator car 103 within the elevator shaft 117. In other embodiments, the position reference system 113 may be directly mounted to a moving component of the machine 111, or may be located in other positions and/or configurations as known in the art. The position reference system 113 can be any device or mechanism for monitoring a position of an elevator car and/or counter weight, as known in the art. For example, without limitation, the position reference system 113 can be an encoder, sensor, or other system and can include velocity sensing, absolute position sensing, etc., as will be appreciated by those of skill in the art.

[0041] The controller 115 is located, as shown, in a controller room 121 of the elevator shaft 117 and is configured to control the operation of the elevator system 101, and particularly the elevator car 103. For example, the controller 115 may provide drive signals to the machine 111 to control the acceleration, deceleration, leveling, stopping, etc. of the elevator car 103. The controller 115 may also be configured to receive position signals from the position reference system 113 or any other desired position reference device. When moving up or down within the elevator shaft 117 along guide rail 109, the elevator car 103 may stop at one or more landings 125 as controlled by the controller 115. Although shown in a controller room 121, those of skill in the art will appreciate that the controller 115 can be located and/or configured in other locations or positions within the elevator system 101. In one embodiment, the controller may be located remotely or in the cloud.

[0042] The machine 111 may include a motor or similar driving mechanism. In accordance with embodiments of the disclosure, the machine 111 is configured to include an electrically driven motor. The power supply for the motor may be any power source, including a power grid, which, in combination with other components, is supplied to the motor. The machine 111 may include a traction sheave that imparts force to tension member 107 to move the elevator car 103 within elevator shaft 117.

[0043] Although shown and described with a roping system including tension member 107, elevator systems that employ other methods and mechanisms of moving an elevator car within an elevator shaft may employ embodiments of the present disclosure. For example, embodiments may be employed in ropeless elevator systems using a linear motor or pinched wheel motors to impart motion to an elevator car. Embodiments may also be employed in ropeless elevator systems using a hydraulic lift to impart motion to an elevator car. FIG. 1 is merely a non-limiting example presented for illustrative and explanatory purposes.

[0044] In other embodiments, the system comprises a conveyance system that moves passengers between floors and/or along a single floor. Such conveyance systems may include escalators, people movers, etc. Accordingly, embodiments described herein are not limited to elevator systems, such as that shown in FIG. 1. In one example, embodiments disclosed herein may be applicable to conveyance systems such as an elevator system 101 and a conveyance apparatus of the conveyance system such as an elevator car 103 of the elevator system 101. In another example, embodiments disclosed herein may be applicable to conveyance systems such as an escalator system and a conveyance apparatus of the conveyance system such as a moving stair of the escalator system.

[0045] Referring now to FIG. 2, with continued referenced to FIG. 1, a view of a sensor system 200 including a sensing apparatus 210 is illustrated, according to an embodiment of the present disclosure. The sensing apparatus 210 is configured to detect sensor data 202 of the elevator car 103 and transmit the sensor data 202 to a remote device 280. Sensor data 202 may include but is not limited to pressure data 314, vibratory signatures (i.e., vibrations over a period of time) or accelerations 312 and derivatives or integrals of accelerations 312 of the elevator car 103, such as, for example, distance, velocity, jerk, jounce, snap . . . etc. Sensor data 202 may also include light, sound, humidity, and temperature, or any other desired data parameter. The pressure data 314 may include atmospheric air pressure within the elevator shaft 117. It should be appreciated that, although particular systems are separately defined in the schematic block diagrams, each or any of the systems may be otherwise combined or separated via hardware and/or software. For example, the sensing apparatus 210 may be a single sensor or may be multiple separate sensors that are interconnected.

[0046] In an embodiment, the sensing apparatus 210 is configured to transmit sensor data 202 that is raw and unprocessed to the controller 115 of the elevator system 101 for processing. In another embodiment, the sensing apparatus 210 is configured to process the sensor data 202 prior to transmitting the sensor data 202 to the controller 115 through a processing method, such as, for example, edge processing. In another embodiment, the sensing apparatus 210 is configured to transmit sensor data 202 that is raw and unprocessed to a remote system 280 for processing. In yet another embodiment, the sensing apparatus 210 is configured to process the sensor data 202 prior to transmitting the sensor data 202 to the remote device 280 through a processing method, such as, for example, edge processing.

[0047] The processing of the sensor data 202 may reveal data, such as, for example, a number of elevator door openings/closings, elevator door time, vibrations, vibratory signatures, a number of elevator rides, elevator ride performance, elevator flight time, probable car position (e.g. elevation, floor number), releveling events, rollbacks, elevator car 103 x, y acceleration at a position: (i.e., rail topology), elevator car 103 x, y vibration signatures at a position: (i.e., rail topology), door performance at a landing number, nudging event, vandalism events, emergency stops, etc.

[0048] The remote device 280 may be a computing device, such as, for example, a desktop, a cloud based computer, and/or a cloud based artificial intelligence (AI) computing system. The remote device 280 may also be a mobile computing device that is typically carried by a person, such as, for example a smartphone, PDA, smartwatch, tablet, laptop, etc. The remote device 280 may also be two separate devices that are synced together, such as, for example, a cellular phone and a desktop computer synced over an internet connection.

[0049] The remote device 280 may be an electronic controller including a processor 282 and an associated memory 284 comprising computer-executable instructions that, when executed by the processor 282, cause the processor 282 to perform various operations. The processor 282 may be, but is not limited to, a single-processor or multi-processor system of any of a wide array of possible architectures, including field programmable gate array (FPGA), central processing unit (CPU), application specific integrated circuits (ASIC), digital signal processor (DSP) or graphics processing unit (GPU) hardware arranged homogenously or heterogeneously. The memory 284 may be but is not limited to a random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic or any other computer readable medium.

[0050] The sensing apparatus 210 may be configured to transmit the sensor data 202 to the controller 115 or the remote device 280 via short-range wireless protocols 203 and/or long-range wireless protocols 204. Short-range wireless protocols 203 may include but are not limited to Bluetooth, Wi-Fi, HaLow (801.11ah), zWave, ZigBee, or Wireless M-Bus. Using short-range wireless protocols 203, the sensing apparatus 210 is configured to transmit the sensor data 202 directly to the controller 115 or to a local gateway device 240 and the local gateway device 240 is configured to transmit the sensor data 202 to the remote device 280 through a network 250 or to the controller 115. The network 250 may be a computing network, such as, for example, a cloud computing network, cellular network, or any other computing network known to one of skill in the art. Using long-range wireless protocols 204, the sensing apparatus 210 may be configured to transmit the sensor data 202 to the remote device 280 through a network 250. Long-range wireless protocols 204 may include but are not limited to cellular, satellite, LTE (NB-IoT, CAT M1), LoRa, Satellite, Ingenu, or SigFox.

[0051] The sensing apparatus 210 may be configured to detect sensor data 202 including acceleration in any number of directions. In an embodiment, the sensing apparatus may detect sensor data 202 including accelerations 312 along three axes, an X axis, a Y axis, and a Z axis, as show in in FIG. 2. The X axis may be perpendicular to the doors 104 of the elevator car 103, as shown in FIG. 2. The Y axis may be parallel to the doors 104 of the elevator car 103, as shown in FIG. 2. The Z axis may be aligned vertically parallel with the elevator shaft 117 and the pull of gravity, as shown in FIG. 2. The acceleration data 312 may reveal vibratory signatures generated along the X-axis, the Y-axis, and the Z-axis.

[0052] FIG. 3 shows a possible installation location of the sensing apparatus 210 within the elevator system 101. The sensing apparatus 210 may include a magnet (not show) to removably attach to the elevator car 103. In the illustrated embodiment shown in FIG. 3, the sensing apparatus 210 may be installed on the door hanger 104a and/or the door 104 of the elevator system 101. It is understood that the sensing apparatus 210 may also be installed in other locations other than the door hanger 104a and the door 104 of the elevator system 101. It is also understood that multiple sensing apparatus 210 are illustrated in FIG. 3 to show various locations of the sensing apparatus 210 and the embodiments disclosed herein may include one or more sensing apparatus 210. In another embodiment, the sensing apparatus 210 may be attached to a door header 104e of a door 104 of the elevator car 103. In another embodiment, the sensing apparatus 210 may be located on a door header 104e proximate a top portion 104f of the elevator car 103. In another embodiment, the sensing apparatus 210 is installed elsewhere on the elevator car 103, such as, for example, directly on the door 104.

[0053] As shown in FIG. 3, the sensing apparatus 201 may be located on the elevator car 103 in the selected areas 106, as shown in FIG. 3. The doors 104 are operably connected to the door header 104e through a door hanger 104a located proximate a top portion 104b of the door 104. The door hanger 104a includes guide wheels 104c that allow the door 104 to slide open and closed along a guide rail 104d on the door header 104e. Advantageously, the door hanger 104a is an easy to access area to attach the sensing apparatus 210 because the door hanger 104a is accessible when the elevator car 103 is at landing 125 and the elevator door 104 is open. Thus, installation of the sensing apparatus 210 is possible without taking special measures to take control over the elevator car 103. For example, the additional safety of an emergency door stop to hold the elevator door 104 open is not necessary as door 104 opening at landing 125 is a normal operation mode. The door hanger 104a also provides ample clearance for the sensing apparatus 210 during operation of the elevator car 103, such as, for example, door 104 opening and closing. Due to the mounting location of the sensing apparatus 210 on the door hanger 104a, the sensing apparatus 210 may detect open and close motions (i.e., acceleration) of the door 104 of the elevator car 103 and a door at the landing 125. Additionally mounting the sensing apparatus 210 on the hanger 104a allows for recording of a ride quality of the elevator car 103.

[0054] FIG. 4 illustrates an example of a sensing apparatus 210 of FIGS. 2 and 3 in more detail. The sensing apparatus includes a controller 212, a plurality of sensors 217 in communication with the controller 212, a communication module 220 in communication with the controller 212, and a power source 222 electrically connected to the controller 212. The plurality of sensors 217 includes an inertial measurement unit (IMU) 218 and a pressure sensor 228. The IMU 218 comprises three accelerometers 229 and is configured to detect acceleration of the elevator car 103, and to generate the acceleration data 312. The pressure sensor 228 (which may be, for example a pressure altimeter or a barometric altimeter) is configured to detect an atmospheric air pressure within the elevator hoistway 117, and to generate the pressure data 314. Both the IMU 218 and the pressure sensor 228 are in communication with the controller 212 of the sensing apparatus 210. In some examples, the plurality of sensors 217 may also include additional sensors such as a light sensor, a microphone, a humidity sensor, and a temperature sensor.

[0055] The power source 222 of the sensing apparatus 210 is configured to store and supply electrical power to the sensing apparatus 210. The power source 222 may include an energy storage system, such as a battery or a capacitor, or other appropriate energy storage system known in the art.

[0056] The communication module 220 is configured to allow the controller 212 of the sensing apparatus 210 to communicate with the remote device 280 and/or controller 115 through at least one of short-range wireless protocols 203 and long-range wireless protocols 204 as described above.

[0057] The controller 212 of the sensing apparatus 210 includes a processor 214 and a memory 216 comprising computer-executable instructions that, when executed by the processor 214, cause the processor 214 to perform various operations such as processing of the sensor data 202 collected by the IMU 218 and the pressure sensor 228 to determine information about the motion of the elevator car 103. The sensing apparatus 210 also comprises a buffer 227, configured to store a pre-set number of data entries.

[0058] The system shown in FIGS. 2 and 3 may be used to monitor the elevator system 101. As described previously, sensor data 202 is measured in a raw, unprocessed form, and processing of the sensor data 202 may reveal data about the elevator system 101. For example, processing of acceleration data 312 may allow faults in the elevator system 101 to be identified. However, for the correct processing methods to be applied, it is necessary to know whether the acceleration data 312 being processed relates to an elevator car 103 that is stationary or an elevator car 103 that is in motion, as well as the direction of the motion of the elevator car 103. This is required to separate acceleration signals due to the motion of the elevator car 103 itself from acceleration signals due to, e.g. movement of the doors 104 of the elevator car 103.

[0059] In certain examples, to allow appropriate processing of the acceleration data 312, it is convenient to set a flag indicating a state of motion of the elevator car 103, and to process the acceleration data 312 in accordance with the flag. Accurate determination of the state of motion of the elevator car 103 is therefore useful.

[0060] The start and stop of elevator movement (i.e. a change of state between ‘in motion’ and ‘stationary’) provide good dividing points for separating the data relating to the door operation and the data relating to car movement. However, the start and stop can also be used in elevator systems employing “advanced door opening” technology, in which there is an overlap in time between the elevator car doors opening and the elevator car being in motion (i.e. the doors begin to open before the car comes to a complete stop). The start of elevator car motion is still generally a clear separator between the end of a door closing operation and the start of elevator car motion. The stop of elevator car motion can be used together with a known overlap window (e.g. a window of predetermined length) to separate pure door car motion from pure door motion. It will be appreciated that a similar overlap window could also be used at the start of elevator motion for other reasons, for example to take account of other sources of vibration such as an advanced brake lift operation which may overlap with the door motion and/or car motion.

[0061] Processes for monitoring motion of a conveyance apparatus (e.g. an elevator car) may be improved by using pressure data 314 to detect that a change in motion of the conveyance apparatus has occurred, and then analysing buffered acceleration data 312 only once a change in motion has been detected in order to determine more accurately when the change of motion of the conveyance apparatus occurred.

[0062] A process for monitoring the motion of a conveyance apparatus in a conveyance system in accordance with examples of the present disclosure will now be described with reference to FIG. 5a.

[0063] In the examples described herein, the conveyance system is an elevator system 101 and the conveyance apparatus is an elevator car 103. However it will be appreciated that the same process could equally be applied to a range of conveyance systems including escalator systems and moving walkways. The process illustrated in FIG. 5 may be performed by one or more of the sensing apparatus 210, the controller 115, and the remote device 280, using data from the sensing apparatus 210 as will be described in the following.

[0064] At block 500, the acceleration of the elevator car 103 is measured using the IMU 218 and acceleration data 312 is stored in the memory 216 of the sensing apparatus 210. The acceleration of the elevator car 103 is measured at a particular sampling frequency, for example 12 samples per second. In one example, any desired sampling frequency may be used. The acceleration data 312 stored in the memory 216 of the sensing apparatus 210 is saved, at least temporarily, in a buffer 227. The buffer 227 has size of at least n+1, i.e. it is configured to store at least n+1 data values, corresponding to the n+1 most recent acceleration measurements. Each acceleration measurement stored in the buffer 227 has an associated index between 0 and n, with the most recent entry in the buffer 227 having index 0, and the oldest entry in the buffer 227 having index n. As each new acceleration measurement is saved to the buffer 227, the index of each of the previous entries is increased by one, and the entry having index n is removed from the buffer 227. In this way, a series of the n+1 most recent acceleration measurements is temporarily stored in the buffer 227, and the series is updated with each new acceleration measurement saved to the buffer 227. The size of the buffer 227 may be chosen based on characteristics of the elevator system 101, for example based on an expected acceleration behaviour of the elevator car 103, and/or based on a desired update frequency of acceleration measurements from the IMU 218. By way of example, the buffer 227 may be implemented as a shift register or it may be implemented as a sliding window within a larger area of memory.

[0065] At block 502, a change of height of the elevator car 103 is determined using the pressure sensor 228 of the sensor apparatus 210. The pressure sensor 228 measures atmospheric air pressure in the vicinity of the elevator car 103 at a sample rate, for example 1 sample per second, and determines whether the height of the elevator car 103 has changed based on the measured pressure. The sample rate at which pressure measurements are taken may be significantly lower than that at which acceleration measurements are taken. A determination of a change in height of the elevator car 103 may be made, for example, by comparing the measured air pressure to a previously measured air pressure value saved in the memory 216 of the sensing apparatus 210, and calculating the difference. The difference in air pressure may be compared to a threshold, and if this threshold is exceeded it may be determined that the height of the elevator car 103 has changed, corresponding to a change in motion of the elevator car 103. This change of height over time does not need to be from adjacent pressure samples, but could span several samples. For example a change of 1.5 m in the space of 4 seconds may be considered to robustly identify that a change of motion has occurred. The process then continues to block 504.

[0066] In block 504, the acceleration measurements stored in the buffer 227 are analysed to determine a position (or index value, i) within the accelerometer data which corresponds to a change of motion (i.e. a start or stop) of the elevator car 103.

[0067] This analysis in step 504 may be achieved by determining a second position within the accelerometer data at which the acceleration crosses a threshold value. The threshold value may be chosen to be a value small enough to indicate that the elevator car 103 has just started moving, or is about to stop moving, but large enough to avoid being triggered by sensor noise. The analysis in step 504 may also involve determining a third position within the accelerometer data at which a maximum or minimum value of the accelerometer data is reached. This third position may be determined prior to determining the second position. In such cases a further constraint may be placed upon the determination of the second position, e.g. that the threshold value is crossed on a particular side of (i.e. before or after) the maximum or minimum. For example it may be desirable to determine the point at which the acceleration threshold is crossed before attaining a maximum value (and thereby excluding from processing any possible threshold crossing after the maximum value).

[0068] The processing of the accelerometer data depends on the type of change of motion that is being determined, e.g. whether the change of motion corresponds to a start or stop of the elevator car 103, and also depends on whether the elevator car 103 is (or was) travelling up or down in the hoistway 117.

[0069] As the accelerometer data which corresponds to the start and stop of the elevator car 103 is low frequency, a very steep, very low pass filter (i.e. one having a low cutoff frequency and a steep frequency transition) may first be applied to the acceleration measurements stored in the buffer 227. The filter ideally has minimum or linear phase delay. This filter removes high frequency contributions from noise and other vibrations, thereby simplifying the processing of the acceleration measurements stored in the buffer 227.

[0070] FIG. 5b is similar to FIG. 5a, but shows additional steps according to one example for additional analysis of the accelerometer data. After identifying the start or stop of the conveyance apparatus (e.g. elevator car 103) in step 504, the process calculates the difference between the identified start or stop (i.e. the first position) and the end of the buffer (representing the oldest data element). This difference (Δi) represents the number of new samples of accelerometer data that must be acquired before the first position (the start or stop) reaches the end of the buffer. When this happens, it is known that a fixed time (corresponding to the length of the buffer 227) has elapsed since the start or stop occurred. Older accelerometer data (i.e. older than the length of the buffer) can then be processed with certainty as to the motion state of the elevator car 103 at that time. Therefore, in step 508 the system waits for Δi more accelerometer samples so that the start or stop is at the end of the buffer 227 and in step 510 the system updates a motion status flag that indicates whether the conveyance apparatus is “in motion” or “stationary”.

[0071] As an example of the processing of FIG. 5b, in the case where an elevator car 103 starts to move away from a stationary position, the processing of steps 500, 502 and 504 will begin with the motion status flag set to “stationary” and will identify an index i at which the start occurred. The system then acquires further accelerometer samples, loading them into one end of the buffer and moving all other data along the buffer (but making no change to the motion status flag) until the start has reached index n in the buffer. Only at this point is the motion status flag updated from “stationary” to “in motion”. Up until this point, data older than the buffer length is known to correspond to a stationary state as indicated by the motion status flag. The update of flag status indicates that this is no longer the case and therefore that data older than the buffer length can no longer be taken as purely “stationary” data. This allows simple processing of the accelerometer data using a fixed processing delay. While it is convenient to have the processing delay correspond to the length of the buffer 227 as described here, it will be appreciated that this need not be the case and that a longer or shorter fixed processing delay can be used so long as it is long enough to ensure that the start or stop reliably occurs before the fixed processing delay.

[0072] The processing of the accelerometer data after the fixed processing delay may be used to analyse the health of one or more components of the conveyance system. For example, if it is determined that, subsequent to an identified change of motion, the elevator car 103 is in motion, raw (i.e. unfiltered) acceleration data may be processed to determine the condition of the elevator car 103 and guiderails within the shaft 117. Similarly, if the elevator car 103 is determined to be stationary, it is likely that any measured acceleration will be caused by the doors 104 of the elevator car 103. As such, raw acceleration data obtained when the elevator car 103 is at rest may be processed to determine the condition of the elevator car doors 104. Such processed data may be transmitted to the remote device 280 using short-range wireless protocols 203 and/or long-range wireless protocols 204 to allow any faults with the elevator system 101 to be identified without requiring, for example, manual inspection of the elevator system 101. Such analysis may also be used by a condition based maintenance system to predict and schedule maintenance of the system 101.

[0073] Having described the general process for determining a change in motion of an elevator car 103 with reference to FIGS. 5a and 5b, two specific scenarios will be described with reference to FIGS. 6 to 8.

[0074] FIG. 6 shows a process for determining a start of motion of the elevator car 103 in accordance with the present disclosure. In block 600, it is determined that the elevator car 103 is stationary (i.e. the motion status flag indicates that the elevator car 103 is not in motion). In block 602, a change of pressure is determined by using the pressure sensor 228 of the sensor apparatus 210 as described previously. Based on the change of pressure, a change in height of the elevator car 103 is calculated. If the change of height in a given time period is greater than a threshold value (e.g. 1.5 metres within 4 seconds), the process continues to block 604, in which a direction of travel is determined, for example based on the sign of the change in height. Based on the direction of travel, the process continues to block 606a or block 606b if the direction of travel is upwards or downwards respectively. It will be appreciated that calculation of a change in height is not strictly required, and in some embodiments the measured change of pressure may be compared to a threshold in place of a change of height.

[0075] If it is determined that the change in height was in a vertically upward direction, the process continues to block 606a. In block 606a, a low pass filter is applied to the acceleration measurements stored in the buffer 227. The index of the maximum acceleration value i.sub.max, is then identified. To determine the index associated with the start of motion, the acceleration measurements stored in the buffer 227 with an index greater than the index i.sub.max¬of the maximum acceleration value (i.e. older measurements) are compared to a threshold upward acceleration value a.sub.1 (for example 10 mg) in order of increasing index value. The index i.sub.up of the first acceleration value lower than the threshold acceleration value a.sub.1 is then identified, and the index i.sub.up-1 is determined to be the index associated with the start of motion. The decrement by 1 in this example is to select the value at which the acceleration is above the threshold rather than the value that is below the threshold (lower index values represent newer measurements), but in other examples this decrement could be omitted. In block 608, if none of the acceleration values stored in the buffer 227 are determined to be below the threshold acceleration value a.sub.1, then it is likely that a start has not taken place, perhaps due to an error in the pressure readings or the like. If however, an index i.sub.up-1 is identified, then a determination is made that the elevator car 103 is in motion, and the position within the accelerometer data at which the upward motion started is identified in block 610 based on the identified index i.sub.up-1. As discussed above in relation to FIG. 5b, a motion status flag may then be set indicating that the elevator car 103 is in motion. In some examples, having identified the index i.sub.up−1 at which the motion of the elevator car 103 began, the system waits until the identified index i.sub.up−1 moves to the final position (n) of the buffer 227, and then changes the flag state from 0 to 1 (i.e. from “stationary” to “in motion”).

[0076] If however, it is determined in step 604 that the change in height was in a vertically downward direction, the process continues to block 606b. In block 606b, a low pass filter is applied to the acceleration measurements stored in the buffer 227. The index of the minimum acceleration value i.sub.min¬ is then identified. To determine the index associated with the start of motion, the acceleration measurements stored in the buffer 227 with an index greater than the index i.sub.min of the minimum acceleration value (i.e. older measurements) are compared to a threshold acceleration value in the downward direction a1 (e.g. −10 mg) in order of increasing index value. The index i.sub.down of the first acceleration value greater than the threshold acceleration value a.sub.1 is then identified, and the index i.sub.down−1 is determined to be the index associated with the start of motion. The decrement by 1 in this example is to select the value at which the acceleration is above the threshold rather than the value that is below the threshold (lower index values represent newer measurements), but in other examples this decrement could be omitted. In block 608, if none of the acceleration values are determined to be above the threshold acceleration value al, then it is likely that a start has not taken place, perhaps due to an error in the pressure readings or the like. If however, an index i.sub.down−1 is identified, then a determination is made that the elevator car 103 is in motion, and the position within the accelerometer data at which the motion started is identified in block 610 based on the identified index i.sub.down−1 and the length of the buffer n as described previously. A motion status flag may then be set indicating that the elevator car 103 is in motion. In some examples, having identified the index i.sub.down−1 at which the motion of the elevator car 103 began, the system waits until the identified index i.sub.down−1 moves to the final position (n) of the buffer 227, and then changes the flag state from 0 to 1 (i.e. from “stationary” to “in motion”).

[0077] FIG. 7 shows a process for determining an end of motion of the elevator car 103 in accordance with the present disclosure. In block 800, it is determined that the elevator car 103 is moving (i.e. the motion status flag indicates that the elevator car 103 is in motion). In block 802, a change of pressure is determined by using the pressure sensor 228 of the sensor apparatus 210 as described previously. Based on the change of pressure, a change in height of the elevator car 103 is calculated. If the change of height in a given time is smaller than a threshold value (e.g. 1.5 metres within 4 seconds), the process continues to block 804. In block 804 the direction of travel is checked and used to determine the next step of the process. The direction of travel may be known from earlier processing, or may be determined based on, e.g. pressure or acceleration data prior to further steps being carried out.

[0078] If the known direction of travel is upwards the process continues to block 806a. However, if the known direction of travel is downwards, the process continues to block 806b. As noted previously, it will be appreciated that calculation of a change in height is not strictly required, and in some embodiments the measured change of pressure may be compared to a threshold in place of a change in height.

[0079] If the known direction of travel of the elevator car 103 is upwards, in block 806a, a low pass filter is applied to the acceleration measurements stored in the buffer 227. The index of the minimum acceleration value i.sub.min¬ is then identified. To determine the index associated with the end of motion, the acceleration measurements stored in the buffer 227 with an index lower than the index i.sub.min of the minimum acceleration value (i.e. newer measurements) are compared to a threshold downward acceleration value a.sub.1 (e.g. −10 mg) in order of decreasing index value. The index i*.sub.up of the first acceleration value greater than the threshold acceleration value a.sub.1 is then identified, and the index i*.sub.up+2 is determined to be the index associated with the end of motion. The increment by 2 in this example is to move the identified position a bit earlier in the measurement history in order to take account of an advanced door opening feature. The value of “2” can be varied according to a particular implementation and may be established through analysis and optimisation to find the best value. In other examples, e.g. where there is no advanced door opening, this increment may be omitted (or may be a decrement instead). In block 808, if none of the acceleration values are determined to be above the threshold acceleration value a.sub.1, then it is likely that something has gone wrong in the measurements or processing and so the system returns the motion state to zero (or “stationary”) immediately as this is the safest assumption. Thus, in this situation the process continues to block 810a, and a determination is effectively made that motion of the elevator car 103 ended exactly at index 0 (i.e. the most recent measurement corresponding to “now”). If however, an index i*.sub.up+2 is identified, then the process continues to block 810b. In block 810b a determination is made that the elevator car 103 is stationary, and the position within the accelerometer data at which the motion of the elevator car 103 ended is identified based on the identified index i*.sub.up+2. A motion status flag may then be set indicating that the elevator car 103 is stationary. In some examples, having identified the index i*.sub.up+2 at which the motion of the elevator car 103 stopped, the system waits until the identified index i*.sub.up+2 moves to the final position (n) of the buffer 227, and then changes the motion status flag from 1 to 0 (i.e. from “in motion” to “stationary”).

[0080] If the known direction of travel of the elevator car 103 is downwards, in block 806b, a low pass filter is applied to the acceleration measurements stored in the buffer 227. The index of the maximum acceleration value i.sub.max is then identified. To determine the index associated with the end of motion, the acceleration measurements stored in the buffer 227 with an index lower than the index i.sub.max of the maximum acceleration value (i.e. newer measurements) are compared to a threshold upward acceleration value a.sub.1 (e.g. 10 mg) in order of decreasing index value. The index i*.sub.down of the first acceleration value lower than the threshold acceleration value a.sub.1 is then identified, and the index i*.sub.down+2 is determined to be the index associated with the end of motion. The increment by 2 in this example is to move the identified position a bit earlier in the measurement history in order to take account of an advanced door opening feature. The value of “2” can be varied according to a particular implementation and may be established through analysis and optimisation to find the best value. In other examples, e.g. where there is no advanced door opening, this increment may be omitted (or may be a decrement instead). In block 808, if none of the acceleration values are determined to be below the threshold acceleration value a.sub.1, then it is likely that something has gone wrong in the measurements or processing and so the system returns the motion state to zero (or “stationary”) immediately as this is the safest assumption. Thus, in this situation, the process continues to block 810a, and a determination is effectively made that that motion of the elevator car 103 ended exactly at index 0 (i.e. the most recent measurement corresponding to “now”). If however, an index i*.sub.down+2 is identified, then the process continues to block 810b. In block 810b a determination is made that the elevator car 103 is stationary, and the position within the accelerometer data at which the motion of the elevator car 103 ended is identified based on the identified index i*.sub.down+2. A motion status flag may then be set indicating that the elevator car 103 is stationary. In some examples, having identified the index i*.sub.down+2 at which the motion of the elevator car 103 stopped, the system waits until the identified index i*.sub.down+2 moves to the final position (n) of the buffer 227, and then changes the motion status flag from 1 to 0 (i.e. from “in motion” to “stationary”).

[0081] In this way, the processes described in FIGS. 6 and 7 can be used to accurately determine the time (or data index) at which a change in motion of the elevator car 103 occurred, and set a flag based on the motion of the elevator car 103 without requiring constant processing of accelerometer data. As processing of acceleration data is only carried out when the pressure sensor 228 identifies a change of position of the elevator car, these processes allow significant resource (e.g. power) conservation, and allow accurate determination of changes in car motion to be made.

[0082] FIG. 8a shows an example of the low pass filtered acceleration values a(t) stored in a buffer 227 of length 10, and used in the determination of the start of motion in a vertically upward direction as described above in relation to FIG. 6. It should be understood that the example shown in FIG. 8 is purely illustrative, and that the acceleration values and buffer length shown are not necessarily representative of those expected to be used in practice. For example, in practice the buffer may be longer or may have a significantly finer time resolution than illustrated. In the example shown in FIG. 8a, the maximum acceleration value stored in the buffer 227, represented by peak 701, can be seen to have an index i.sub.max=5. The threshold acceleration value a.sub.1 is shown by dashed line 703. The first acceleration value with size smaller than the threshold acceleration value a.sub.1 can therefore be seen to have index i.sub.up=7. The start of upward motion is then determined to have occurred at index i.sub.up−1=6. Based on this determination, a motion status flag can be set indicating that buffer values having index greater than i.sub.up−1 are associated with a stationary elevator car (and hence are likely to be related to motion of, e.g. the elevator car doors 104), while buffer values having index less than or equal to i.sub.up−1 are associated with motion of the elevator car 103 itself. This segregation of data is illustrated in FIG. 8b which shows a first group 705 of data points (older than i.sub.up−1) identified as belonging to door motion (stationary elevator car 103) and a second group 706 of data points (i.sub.up−1 and newer) identified as belonging to a moving elevator car 103.

[0083] FIGS. 8c and 8d show two ways in which a motion status flag indicating the state of motion of the elevator car 103 may be set after a change in motion of the elevator car 103 has been determined, and the associated index value (i.sub.up−1) has been identified.

[0084] FIG. 8c illustrates a first method for setting a flag 708 indicating the state of motion of the elevator car 103. In the method illustrated by FIG. 8c, each accelerometer data value has an associated flag value 708 indicating whether the elevator car 103 was in motion (flag 708 is set to 1) or stationary (flag 708 is set to 0) at the time of that acceleration value. Such data could be stored and processed in bulk at a later time while retaining accurate knowledge of which data points correspond to which motion state.

[0085] FIG. 8d illustrates a second method of setting a flag indicating the state of motion of the elevator car 103, in which a flag 710 is set once a change of motion of the elevator car 103 has been identified as having occurred a fixed time ago (therefore allowing delayed processing with a fixed time delay). FIG. 8d shows a series of five successive snapshots in time of the accelerometer data, each snapshot having acquired a new data sample relative to the snapshot above. In the first (uppermost) set of values shown in FIG. 8d, the buffer 227 can be seen to contain 10 values, corresponding to the 10 most recent acceleration values shown in FIG. 8a. The end of the buffer 227 (indicated by dashed line 709) is also shown in FIG. 8d, in addition to older values 707 which are no longer stored within the buffer 227. In the uppermost line of FIG. 8d the older values 707 correspond to a time when the elevator car 103 was known to be stationary, and hence at this time, the flag 710 is set to 0. As each new value is saved to the buffer 227 (in position 0 at the right hand end), the other acceleration measurements are shifted left (index increased by one), and the oldest value within the buffer 227 (having index value i=9 in this example) is removed from the buffer 227. In the example shown in FIG. 8d, the index value associated with a change of motion (i.sub.up−1) is initially identified at position 6 of the buffer 227. When this value passes beyond the final entry in the buffer 227 (i.e. has an index entry greater than n), the flag 710 is changed from 0 to 1 to indicate that the elevator car 103 was in motion at a fixed time in the past, the fixed time corresponding to the length of the buffer 227. In FIG. 8d this happens in the final (fifth) line when the value “15” from original index 6 (in the first line) has shifted left of the dashed line 709. The flag 710 then remains set at 1 until it is determined that the elevator car 103 is stationary again, i.e. until an end of motion of the elevator car 103 is identified as was described above in relation to FIG. 7. As can be seen from FIG. 8d, this processing can be done in real time with only a single bit flag 710 and without having to store the flag in association with the data. The motion status for the older data 707 is known with accuracy and therefore this data 707 can be processing with a time delay equal to the length of the buffer 227 and using the flag 710 to indicate changes in the motion state associated with that data 707. The flag 710 will reliably indicate the motion state of the elevator car 103 associated with the most recent of the older data points 707.

[0086] It will be appreciated by those skilled in the art that the disclosure has been illustrated by describing one or more specific examples thereof, but is not limited to these examples; many variations and modifications are possible, within the scope of the accompanying claims.