WO2010007444A2

WO2010007444A2 - Wireless monitoring apparatus and method

Info

Publication number: WO2010007444A2
Application number: PCT/GB2009/050882
Authority: WO
Inventors: Greg Horler
Original assignee: Instrumentel Limited
Priority date: 2008-07-17
Filing date: 2009-07-17
Publication date: 2010-01-21
Also published as: GB2461815B; GB0813128D0; GB0912454D0; GB2461815A; WO2010007444A3

Abstract

A system for monitoring the relative movement between a first body and a second body, such as between a tool and a workpiece, the system comprising a plurality of tags, such as RFID tags, attached to the first body, a reader attached to the second body and arranged to produce a response that varies depending on the distance between the reader and the tag and a processor arranged to derive information regarding the relative movement between the first body and the second body from the response.

Description

WIRELESS MONITORING APPARATUS AND METHOD

The present invention relates to apparatus and a method for wirelessly monitoring the motion of moving articles.

There are countless industrial and engineering applications in which wireless monitoring of the movement of moving articles is desirable.

For example, in manufacturing industry the motion of tools in automated processes and the movement of conveyors must be monitored. In transportation, and in particular public transportation, the motion of a vehicle door must carefully be monitored to ensure safe operation and to allow for early detection of malfunction. Sliding doors are used in various different fields. A sliding door is usually mounted on, or suspended from, a track and is opened by sliding the door in a direction parallel to a plane in which the door lies. Sliding doors are often used where it is necessary or desirable for the door to be opened automatically as opposed to being opened by a human. This is because due to the linear motion of a sliding door it is often easier to automate a sliding door than a hinged door. Some examples of sliding doors include elevator doors, doors that open in response to the detection of the presence of a user, and train doors.

There are a number of different ways in which a sliding door may be driven. Examples include, but are not limited to, a pneumatic piston, a hydraulic piston and a rotational motor coupled to a rack and pinion. As with all automated systems, automatic sliding doors can sometimes fail. Such failures can cause a great deal of inconvenience. For example, if an automatically driven sliding train door fails then the passengers cannot use that particular door. This may result in passenger congestion. It is therefore desirable to be forewarned that an automated sliding door is likely to fail so that repair can be made before failure.

One way of doing this is to monitor the drive mechanism, such as the piston or motor, of the automated sliding door. When the drive mechanism starts to operate abnormally this may indicate that the automated sliding door is about to fail. However, access to the drive mechanism is not usually easy and it is therefore both expensive and time consuming to fit, and in particular to retrofit, such a monitoring system.

It is therefore desirable to provide a system and method for monitoring a sliding door that is simple, low in cost and effective, and one which lends itself easily to retrofitting. In accordance with an aspect of the invention there is provided a system for monitoring the relative movement between a first body and a second body, comprising: a tag attached to the first body; a reader attached to the second body and arranged to produce a response that varies depending on the distance between the reader and the tag; and a processor arranged to derive information regarding the relative movement between the first body and the second body from the response. A plurality of tags may be attached to the first body.

The or each tag may comprise a coil and the reader may be arranged to emit a radio frequency signal.

The or each tag may become inductively coupled to the reader.

The response may comprise the inductive load of the or each tag on the reader with respect to time.

The or each tag may further comprise a chip coupled to the coil and, in response to the radio frequency signal transmitted by the reader, the or each tag may transmit identification information which can be received by the reader.

In a preferred arrangement, the response comprises the detection or non-detection of the or each tag' s identification information with respect to time.

Preferably the processor is arranged to compare the or each response with a reference response.

The processor may be arranged to calculate the speed of relative movement from the or each response. The processor may be arranged to detect anomalies in the or each response.

At least one of the first and second bodies may comprise a door, or a tool, or conveyor means.

In another aspect, the present invention provides a system for monitoring the position or motion of a moveable article, the system comprising: at least one electronic tag and a reading device arranged in use to detect the presence of the or each tag, wherein one of the reading device and the, or each, tag is arranged on a moveable article and the other of the reading device or the, or each, tag is arranged at a fixed location, such that when the article moves between open and closed configurations the reading device and the or each tag move relative to each other, and wherein the reading device and the or each tag are arranged in use to become wirelessly coupled when in sufficiently close proximity, the apparatus further comprising electronic processing means arranged to derive information about the motion or position of the article from signals wirelessly detected by the reading device.

Preferably a plurality of electronic tags is provided with known spaces, which may preferably be equal, therebetween. The invention also comprises a method of monitoring the position or motion of an article, the method comprising : providing one of a moveable article and a location fixed with respect to the article with an electronic tag and providing the other of the moveable article and the fixed location with an electronic reading device, wirelessly deriving signals in the reading device from the or each tag and processing the signals to derive information about the motion or position of the article.

The tags are preferably radio frequency identification (RFID) tags.

The article may comprise a door or tool or conveyor means.

The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figures l(a) and (b) schematically show an automatic sliding door system respectively in closed and open positions; Figure 2 schematically shows a sliding door system of the kind shown in Figures l(a) and 1 (b) having a monitoring system in accordance with the present invention comprising a reader and a plurality of tags;

Figure 3 schematically shows a block diagram of a reader for use in the system of Figure 2;

Figure 4 schematically shows a portion of a strip comprising a plurality of tags for use in the system of Figure 2; Figure 5 schematically shows one of the tags of Figure 4;

Figure 6 schematically illustrates an interaction of a tag and reader; Figure 7 schematically shows a plurality of tags on a strip passing a reader;

Figure 8 schematically shows the responses generated in the reader when a plurality of tags passes the reader;

Figure 9 schematically shows the responses generated by a reader when a sliding door opens and closes normally;

Figure 10 schematically shows the responses generated by a reader when a sliding door opens and closes abnormally; Figure 11 schematically shows a monitoring system mounted to a sliding train door; and

Figure 12 schematically shows a time series graph which shows an example of data obtained from the opening of a door. The general principles of the invention outlined above will now be illustrated with reference to specific examples, including the particular example of a sliding door.

With reference to Figure 1 an automatic sliding door system 100 comprises a door 102, a frame 104, defining an opening 105, and a drive mechanism 106. In the closed position the door 102 covers the opening 105 and a portion 103 of the door 102 resides within the frame 104. The drive mechanism 106 comprises an hydraulic piston 108. When the door 102 is to be opened a signal is sent to the drive mechanism. This causes the piston to be actuated and the door 102 slides horizontally into the frame 104 to reveal the opening 105.

When an automatic sliding door system 100 is operating normally, the door 102 opens and closes smoothly with little vibration. However, when an automatic sliding door system 100 is operating abnormally the door 102 may vibrate as it moves between open and closed configurations. If a sliding door system 100 begins to operate abnormally then this can be an indication that the door mechanism is about to fail. Therefore, by monitoring vibrations in the movement of a sliding door 102 it may be possible to anticipate when the door system 100 is about to fail. With this information the door system 100 can be repaired before failure actually occurs.

Referring now to Figure 2, an automatic sliding door system 100 is provided with a monitoring system 1 for monitoring the movement of the door. The monitoring system 1 comprises a reader 10 and a strip 30 comprising a plurality of radio frequency identification (RFID) tags 40. The reader 10 is mounted to the frame 104 and the strip 30 is mounted to the door 102. The reader 10 is mounted at the edge of the frame 104 in the region of the portion 103 of the door 102 that resides within the frame 104. The reader 10 is also aligned with the strip 30. The strip 30 extends across the width of the door 102, including the portion 103 of the door 102 that resides within the frame. The tags 40 are provided on the strip 30 and are horizontally spaced at known intervals. The tags 40 may be spaced equally.

Figure 3 schematically shows the various elements of the reader 10. The reader 10 comprises a coil 12 (or any suitable antenna), a transmitting unit 14, a receiving unit 16, a processor 18 and a power source 20. The transmitting unit 14 and receiving unit 16 are connected to the processor 18 and the coil 12. Also connected to the processor 18 is a display 22, a memory 24, a transceiver 26 and an input device 28. The power source 20 powers all of the elements of the reader 10.

Figure 4 schematically shows a portion of the strip 30. The strip 30 comprises a substrate 32 upon which is mounted the plurality of tags 40 spaced at known intervals d which are attached to the substrate 32 by an adhesive. The side of the substrate 32 on which the tags 40 are not mounted is provided with a pressure sensitive adhesive so that the strip 30 may be attached to the door 102 by the application of pressure.

Figure 5 shows a close-up view of an individual RFID tag 40. The tag comprises a substrate 42 on which is mounted an antenna 44 and a chip 46 that are connected to each other. As will be readily apparent to one skilled in the art, there are many types of RFID tags commercially available that could be suitable for the purposes described herein.

Figure 6 shows three graphs. The first graph (a) shows the magnetic flux density (B) of a radio frequency signal 60 transmitted by the reader 10 as a function of the distance away from the reader. The second graph (b) shows the current (I) induced in the antenna 44 of the tag 40 due to the signal 60 as a function of the distance away from the reader. The third graph (c) shows the power (P) generated by the induced current (I) as a function of the distance away from the reader.

With reference to Figures 3-6, the reader 10 and a tag 40 interact as follows. The processor 18 and the transmitting unit 14 cooperate to provide a signal to the coil 12, which signal causes the coil 12 to emit a radio frequency (RF) signal 60. The signal 60 has a magnetic flux density B that is largest close to the coil 12. The magnetic flux density B of the signal 60 decreases with increasing distance x away from the coil 12. At a particular distance Xo away from the coil 12 the magnetic flux density B of the transmitted radio frequency signal becomes zero (or is negligible) .

If the tag 40 is sufficiently close to the coil that the magnetic flux density B of the signal 60 is greater than zero (i.e. x<Xo) , then the magnetic flux of the signal 60 will induce a current I in the antenna 44 of the tag 40. The effective range of the reader 10 can be defined as the distance over which the signal 60 can induce a (minimum) current I in the antenna 44 of the tag 40. The size of the induced current is a function of the proximity of the coil 12 and antenna 44.

Therefore, if the tag 40 is within range of the reader 10 (i.e. x< X₀) then the tag 40 and reader 10 become inductively coupled. The inductive coupling of the tag 40 and reader 10 can be detected by the processor 18 since the tag 40 inductively loads the coil 12 of the reader 10. In other words, the reader 10 is able to tell whether a tag 40 is within the range of the reader 10.

Accordingly, if the tag 40 is within range of the reader then an induced current I can be used by the tag 40 to power the chip 42. However, the chip requires a threshold current I_τ for operation. If the tag 40 is within range of the reader 10 (i.e. x< Xo) but the magnetic flux density B of the signal 60 induces too small a current I (i.e. K I_τ) in the antenna 44 of the tag 40 then the chip 44 will have insufficient power P to operate (i.e. below a threshold power P_T) . Therefore, the reader 10 has a second range, X_τ, which can be defined as the maximum distance away from the reader 10 that the magnetic flux density B of the signal 60 can induce a current I_τ in the antenna 44 of the tag 40 that is large enough to power the chip 44.

If the tag 40 is within the second range of the reader 10 (i.e. x<X_T) then the current I induced in the antenna 44 of the tag 40 is sufficient to power the chip 44 (i.e. I>I_T) . Upon powering the chip 44 the chip transmits a response back to the reader 10. The response is transmitted by the antenna 44 of the tag 40 as a radio frequency signal 70 modulated by an ID number that is specific to the tag 40. This signal 70 is detected by coil 12 and receiving unit 16 of the reader 10 and the ID number of the tag 40 is derived from the received signal 70 by the processor 18. The first range, within which the transmitted radio frequency signal can induce a current in the antenna 44 of the tag 40, and the second range, within which the transmitted radio frequency signal can induce a current in the antenna 44 of the tag 40 that is sufficient to power the chip 46, are in essence volumes that are characteristic of the specific tag 40 and specific reader 10. They are not usually spherical volumes because they depend on the orientation of the coil 12 of the reader 10 and the antenna 44 of the tag.

With reference to Figure 7, the operation of the monitoring system 1 (as schematically illustrated in Figure 2) will now be described in detail. As described above the reader 10 has a first range Rl and a second range R2. In Figure 7a the monitoring system 1 is in a resting position at time zero TO. As can be seen, one tag 40-1 is in the second range R2 of the reader 10 and two tags 40-1, 40-2 are in the first range Rl of the reader 10. This means that tag 40-1 transmits its ID to reader 10 and tags 40-1 and 40-2 load the reader 10. When the strip 30 moves horizontally to the left, as shown in Figure 7b, at time Tl tags 40-1 and 40-2 are in the second range R2 and tags 40-1, 40-2 and 40-3 are in the first range Rl. This means that tags 40-1 and 40-2 transmit their ID to reader 10 and tags 40-1, 40-2 and

40-3 load the reader 10. When the strip 30 moves further to the left, as shown in Figure 7c, at time T2 tags 40-2, and 40-3 are in the second range R2 and tags 40-1, 40-2, 40-3 and 40-4 are in the first range Rl. This means that tags 40-2 and 40-3 transmit their ID to reader 10 and tags 40-1, 40-2, 40-3 and 40-4 load the reader 10.

This can be expressed graphically as shown in Figure 8. Figure 8a shows when the reader 10 receives various tag ID numbers as a function of time. Figure 8b shows the load on the reader with respect to time.

As can be seen from Figure 8a, at time TO the ID of only tag 40-1 is detected, this is because at TO only tag 40-1 is within the second range R2. At time Tl, the ID of tags 40-1 and 40-2 are detected by the reader 10, this is because at time Tl tags 40-1 and 40-2 are within the second range R2. At time T2, the ID of tags 40-2 and 40- 3 are detected by the reader 10, this is because at time T2 tags 40-2 and 40-3 are within the second range R2.

As can be seen from Figure 8b, the load on the reader 10 increases with respect to time. This is because for the time period shown, the number of tags within the first range Rl increases with respect to time.

Referring now back to Figure 2, in which an automatic sliding door system 100 is shown having a monitoring system 1 mounted to it, when the sliding door 102 opens and closes the strip 30 having a plurality of tags 40 attached to it will pass through the reader.

Therefore, various tags 40 will enter the first range Rl and the second range R2 of the reader 10 and likewise various tags 40 will leave the first range Rl and second range R2 of the reader 10. As described above, the reader 10 is able to detect which tags 40 have entered and left the second range R2 of the reader 10 with respect to time. Further, the reader 10 can detect the load due to the tags 40 with respect to time.

Figure 9 shows a graphical representation of the responses the reader 10 generates when a sliding door 102 moves normally from a resting position to a fully open position and back to a resting position. Figure 9a shows when the reader 10 receives various tag ID numbers with respect to time. Figure 9b shows the load on the reader with respect to time. For ease and clarity of illustration, Figure 9 only illustrates the case in which four tags are present on the strip. In reality, many more tags may be present.

As can been seen from Figure 9a, at time zero, when the door 102 is in its resting position, only tag 40-1 is within the second range R2 of the reader 10. As the door slides to the fully open position tag 40-1 moves out of the second range R2 of the reader 10, tags 40-2 and 40-3 move in and out of the second range R2 of the reader 10 and tag 40-4 moves into the second range R2 of the reader. When the door 102 is fully open only tag 40-4 is within the second range R2 of the reader 10. When the door 102 then slides to the fully closed (or resting) position tag 40-4 moves out of the second range R2 of the reader, tags 40-3 and 40-2 move in and out of the second range of the reader 10 and tag 40-1 moves into the second range R2 of the reader 10. The timings of when the various tags 40-1, 40-2, 40-3 and 40-4 move in and out of the second range of the reader 10 depend on the speed with which the door opens and closes. Therefore, the response of Figure 9a characterises the motion of the sliding door.

As can been seen from Figure 9b the load on the reader 10 increases and decreases as the door opens and then increases and decreases as the door closes. The variation of the load on the reader 10 with respect to time depends on the speed with which the door opens and closes. Therefore, the response of Figure 9b characterises the motion of the sliding door.

Figure 10 shows a graphical representation of the responses the reader 10 generates when a sliding door 102 moves abnormally from a resting position to a fully open position and back to a closed position. Figure 10a shows when the reader 10 receives various tag ID numbers with respect to time. Figure 10b shows the load on the reader with respect to time. As for Figure 9, Figure 10 only illustrates the case when four tags are present on the strip.

Using the responses generated by the reader 10, obtained by interrogating the tags 40 on the strips as a sliding door 102 opens and closes, it is possible to determine whether the automatic sliding door system 100 is operating normally, or within an acceptable tolerance of normal operation. There are a number of techniques that may be used to do this.

In one embodiment reference responses of a sliding door 102, opening and closing normally, are stored. These reference responses may be similar to those of

Figure 9. The reference responses are (1) the detection of various tag ID numbers as a function of time (Figure 9a), and (2) the load on the reader with respect to time (Figure 9b) . The reference responses are obtained from a particular sliding door 102 opening and closing normally. These responses are then stored in the memory 24 of the reader 10.

Every time the sliding door 102 opens and closes the reader 10 generates the responses caused by the tags 40 passing the reader 10. These new responses may be similar to those of Figure 10. The processor 18 of the reader then compares these new responses with those stored in the memory 24. If the new responses are different from the reference responses by an amount greater than a preset tolerance it can be determined that the sliding door system 100 is not operating normally and that failure may be about to occur. The reader 10 can then output a fault notification which may be acted upon

For example, if the reader compares the reference responses illustrated in Figure 9 (normal operation) with new responses illustrated in Figure 10 (abnormal operation) then the reader can determine that the door movement that generated the new responses of Figure 10 is abnormal . Specifically, the following faults can be deduced from a comparison of the reference response of Figure 9a and the new response of Figure 10a:

(1) In Figure 10a it can be seen that during opening tag 40-1 is within the second range R2 of the reader 10 for a longer period of time than in Figure 9a. This may indicate that the door is initially opening too slowly or that it is vibrating back and forth. (2) In Figure 10a it can be seen that during opening tag 40-2 is within the second range R2 of the reader 10 for a shorter period of time than in Figure 9a. This may indicate that the door is opening too fast for a period of time or is jumping forward.

(3) In Figure 10a it can be seen that during opening tag 40-3 is moving in and out of the second range R2 of the reader 10 twice. This may indicate that the door is vibrating or moving back and forth. (4) In Figure 10a it can be seen that when the door is ^Λopen' tag 40-4 moves in and out of the second range R2 of the reader 10. This may indicate that when then door is supposed to be fully open (and hence stationary) it is in fact moving back and forth. (5) In Figure 10a it can be seen that during closing tag 40-2 is within the second range R2 of the reader 10 for a longer period of time than in Figure 9a. This may indicate that the door is closing too slowly for a period of time or that it is vibrating back and forth. (6) In Figure 10a it can be seen that during closing tag 40-1 is within the second range R2 of the reader 10 for a shorter period of time than in Figure 9a. This may indicate that the door is closing too fast for a period of time or is jumping forward. Similar deductions can be made from a comparison of Figures 9b and 10b which illustrate the load on the reader 10.

For any given specific response only one, more than one, or none of (I)- (6) may be deduced. As will be apparent to one skilled in the art other faults may be deduced from the responses.

As described above, if a potential fault is detected then a fault notification may be conveyed to an operator. This may be done in one of a number of possible ways. The transceiver 26 may send a notification to an operator terminal. The transceiver 26 may be a Wi-Fi transceiver and may be arranged to transmit the signal to a computer terminal. Alternatively, the display 22 of the reader 10 may visually indicate that the door is not operating normally. This may be in the form of one or more LEDs. In one embodiment the display 22 is only operational when an operator sends a signal to the reader 10, for example, by using the input device 28 of the reader. As will be readily apparent to one skilled in the art there are a number of ways of obtaining the fault notification from the reader.

The monitoring system 1, as described herein, is particularly beneficial because it is inexpensive and simple to install as a retrofit if necessary. This is because the strip 30 can be simply adhered to the surface of the door without requiring access to internal parts. Further, the reader 10 may be mounted both simply and easily.

In another embodiment the reader 10 may only use a single type of response to determine if the sliding door is operating normally. In other words, it may use either (1) the detection of various tag ID numbers as a function of time (Figure 10a), or (2) the load on the reader with respect to time (Figure 10b) . Either type of response may be compared with a reference response (Figure 9a or 9b) to determine whether the door is functioning normally. This is done in a similar way to the technique described above.

It is not essential that the reader 10, or other device, compares new responses with reference responses. For example, by simply analysing Figure 10a it can be ascertained that the door is not operating correctly since during opening tag 40-3 moves in and out of the second range R2 of the reader 10 twice. Without comparison with a reference this indicates that the door may be vibrating excessively.

In a further embodiment, if the spacings of the tags 40 on the strip 30 are known, then the speed and also if necessary the acceleration/deceleration with which the sliding door opens and closes can be calculated. This can be compared with a reference speed in order to determine if the door is operating normally. It is not essential that the tags 40 have a chip 46. The tags 40 may simply comprise an antenna 44, or coil. In this embodiment the reader 10 would only determine response (2) which is a measure of the load on the reader (Figure 9b and 10b) . It has been described that the reader 10 determines whether the sliding door 102 is opening and closing normally, however, this need not necessarily be the case. The reader 10 may transmit the data obtained by interrogating the tags 40 to a computer via the transceiver 26 or a hard-wired connection. The computer may then determine whether or not the door is operating normally using techniques similar to those described above or more sophisticated processing.

Although it has been described that graphical comparisons of the responses are used to determine whether the sliding door 102 is operating properly, this need not necessarily be the case. The reader 10, or external device, may compare data obtained by interrogating the tags 40 of the strip 30 as the door 102 opens and closes with a reference set of data. As will be readily apparent to one skilled in the art there are a number of ways in which the data obtained by the reader 10 interrogating the tags 40 may be used to determine if the door 102 is opening and closing normally. The tag 40 may also include a sensor (not shown) in addition to the chip 46. This sensor may measure parameters such as temperature, vibration, acceleration, velocity or any other physical parameter. When the chip 46 is powered by the signal 60 of the reader 10 then the chip 46 may transmit a response 70 to the reader 10 that includes the physical parameter measured by the sensor. The reader 10, or an external device, may then use this data to help ascertain whether or not the door 102 is operating normally. However, the measured physical parameter may be used for other purposes.

Referring now to Figure 11, in one embodiment the monitoring system 1 is installed to monitor the opening and closing of a sliding train door 102. When the train door opens it initially moves horizontally in a direction perpendicular to a plane within which the door lies and then moves horizontally in a direction parallel to a plane within which the door lies. When the door moves in the perpendicular direction, the tags 40 move away from the reader 10. The responses that the reader 10 generates show this movement providing that at least one tag 40 is within range of the reader 10 when the door is in its resting position. For example, if one tag is within the first range Rl of the reader then when the door moves in the perpendicular direction then the load on the reader 10 will decrease as the tag moves away from the reader 10. It is therefore possible for the reader 10 to determine if the door is moving normally in the perpendicular direction as well as normally in the parallel direction. This can be done by a technique similar to the techniques described above for determining if the door is moving normally in the parallel direction. Whilst the description has described embodiments only in which a monitoring system 1 is used to monitor the movement of a sliding door 102, it should be apparent to a skilled reader that the monitoring system 1 could be used to monitor the movement of other objects. The monitoring system 1 requires only that a tag 40 moves relative to a reader 1 with which the tag can become coupled, such as inductively coupled. Other applications of the monitoring system 1 could include the movement of a conveyor belt or the movement of articles along a production or manufacturing line.

Another useful application of the present invention is in the field of automated machinery such as CNC machinery where a tool is used to work a workpiece. The motion of the tool in relation to the workpiece can be closely monitored for example by configuring a strip of tags to move with the tool and detecting movement of the tool using a reader mounted in fixed relation to a workpiece .

In order to minimise the collection of unnecessary data from the objects under consideration (such as a door or tool) it is desirable to trigger the start and stop of the data collection process. A trigger signal could be derived from an external signal, such as is generated when an operation is commenced, for example a button is depressed to commence movement of the door/tool. However the present invention enables the derivation of a trigger which is independent of secondary signals.

In the example of doors, these are usually in a steady state, i.e. open or closed. Notification of the open or closed state is provided by the presence (reading) of a know tag ID. The system has previously determined the ID of the tags in the open and closed position respectively, and in order to determine whether the door is in the open or closed position the system polls the tags. However this data does not require storage, as it provides no information regarding door travel/performance.

Data collection should commence as soon as the door has been requested to change state. In normal use this trigger could be provided by a user depressing a button to either open or close the door. While such external signals could be used to start data collection, many applications do not allow access to such signals. In such cases, the beginning of a data capture event can be notified by a change in state, detected from the polling of the system. Examples of two methods are described below:

Binary Trigger Here the change in ID state is considered to be the trigger. This could comprise the change from one ID value to another, or alternatively the change from the presence of a known ID value to the absence of that ID value. Analogue Trigger

In this example the trigger is associated with a specific loading level of the reader by the tag. Once the reader becomes loaded to a predetermined threshold level, this is taken to be indicative of the beginning of a data capture event. This approach is useful for certain tags, such as EAS tags, which do not provide an ID.

In use, either or both trigger mechanisms can be deployed, subject to the application. For example in the case of a door monitoring application a door open action could require the door to pop out before sliding open. Here the analogue approach could be used to detect the "popping out" of the door, with the binary trigger being used to determine when the door reaches the end of its travel . Furthermore, whilst the detection of the presence of a particular tag is handled in an analogue fashion in the examples given above, the skilled person will realise that this could equally be managed in the digital domain. Figure 12 is a time series graph which shows an example of data obtained from the opening of a door.

Referring to Figure 12, in this embodiment system performance relies on the fact that the reader continually polls for tags at a predetermined sample rate

T. The table below presents data obtained by the reader during the time period covered by Figure 12:

Each polling event produces a numbered sample, and the result is either that an identified tag has been detected or that no tag has been detected (i.e. a "null") .

The period T defines the resolution of the system performance i.e. T must be matched to the speed of movement of the door in this example, or e.g. tool bit in another example, in order to achieve a specific resolution in terms of displacement.

The number of detected samples or nulls is in direct proportion to the speed at which the tag or space moves past the reader. Therefore if x, the path length through the reader field or the distance between tags (nulls) is known, then the velocity v of the tag (or space) can be determined by using the number of polls or nulls n and the period T, using Equation 1. v = x/nT ms-1 Equation 1 Any change in door performance can then be identified by comparing the number of polls associated with the presence or absence of each tag or the profile of tags and nulls, with a previously determined reference profile. Observations which can be made include the following: a: The reader is continually sampling, but not continually transmitting data. b: Extraneous data is being generated that would benefit from processing and management. c: If required the useful data can be processed in a variety of ways, using the reader electronics, to extract information and reduce transmission bandwidth

The turning points, tag to null and null to tag can be identified by the reader and used to trigger processing events.

The sampled data can be processed to extract pertinent information from the sampled data and reduce the transmission bandwidth respectively. Using the trigger approach described above allows for the discarding of samples which are not considered to be data. Comparison with a reference profile can be used as a "go/no-go" function, i.e. determining simply that there is normal performance or that there is an abnormality, which result can be represented by a single message bit.

Ultimately the system provides the flexibility to process data in a multitude of ways so as to manage information content and reduce bandwidth.

Whilst the examples described herein use RFID type tags it will be clear to the skilled person that other types of tag can be used without departing from the scope of the invention as defined in the claims. For example magnetic tags could be detected using a reader which is sensitive to a magnetic field. Alternatively optical reading of machine-readable codes, such as barcodes, could be employed.

Claims

1. A system for monitoring the relative movement between a first body and a second body, the system comprising: a tag attached to the first body; a reader attached to the second body and arranged to produce a response that varies depending on the distance between the reader and the tag; and a processor arranged to derive information regarding the relative movement between the first body and the second body from the response.

2. A system according to Claim 1 wherein a plurality of tags is attached to the first body.

3. A system according to Claim 1 or Claim 2 wherein the or each tag comprises a coil and the reader is arranged to emit a radio frequency signal.

4. A system according to any of Claims 1 to 3 wherein the or each tag is arranged to become inductively coupled to the reader.

5. A system according to Claim 4 wherein the response comprises the inductive load of the or each tag on the reader with respect to time.

6. A system according to any of Claims 1 to 5 wherein the or each tag further comprises a chip coupled to a coil and, in response to a radio frequency signal transmitted by the reader, the or each tag may transmit identification information which can be received by the reader .

7. A system according to Claim 6 wherein the response comprises the detection or non-detection of the or each tag's identification information with respect to time.

8. A system according to any of Claims 1 to 7 wherein the processor is arranged to compare the or each response with a reference response.

9. A system according to any of Claims 1 to 8 wherein the processor is arranged to calculate the speed of relative movement from the or each response.

10. A system according to any of Claims 1 to 9 wherein at least one of the first and second bodies comprises a door, or a tool, or conveyor means.

11. A system for monitoring the position or motion of a moveable article, the system comprising: at least one electronic tag and a reading device arranged in use to detect the presence of the or each tag, wherein one of the reading device and the, or each, tag is arranged on a moveable article and the other of the reading device or the, or each, tag is arranged at a fixed location, such that when the article moves between open and closed configurations the reading device and the or each tag move relative to each other, and wherein the reading device and the or each tag are arranged in use to become wirelessly coupled when in sufficiently close proximity, the apparatus further comprising electronic processing means arranged to derive information about the motion or position of the article from signals wirelessly detected by the reading device.

12. A system according to Claim 11 wherein a plurality of electronic tags is provided with known spaces therebetween.

13. A method of monitoring the position or motion of an article, the method comprising: providing one of a moveable article and a location fixed with respect to the article with an electronic tag and providing the other of the moveable article and the fixed location with an electronic reading device, wirelessly deriving signals in the reading device from the or each tag and processing the signals to derive information about the motion or position of the article.

14. A method according to Claim 13 wherein the tags are radio frequency identification (RFID) tags.

15. A method according to Claim 13 or Claim 14 wherein the article comprises a door or tool or conveyor means.