GB2505896A - Room occupancy sensing - Google Patents

Abstract

Room occupancy is sensed by delivering a series of light pulses (22, fig. 1) via a plurality of waveguides (e.g. optical fibres) to one or more output nodes 60 located in each of a plurality of rooms 10. The scene in each room 10 reflects the light pulses (22), and the reflected light pulses (24) are detected. A difference between the detected waveform of a first light pulse reflected from the pulse emitted from an output node 60 and the detected waveform of a second reflected light pulse from the same output node is monitored. This monitoring step is performed for each of the output nodes 60. Movement is detected in a room 10 by detecting such a difference between detected waveforms, and the particular room in which movement has occurred is ascertained. There may be single or multiple light sources and the light pulses may be produced by a laser. A signal processor may be used to monitor the difference between the detected waveforms. The sensing apparatus may comprise one or more transducers for converting light signals into electric signals.

Description

Room Occupancy Sensing Apparatus and Mcthod

Background of the Invention

The present invention concerns a room occupancy sensing apparatus. More particularly, but not exclusively, this invention concerns a building comprising a plurality of rooms and a room occupancy sensing apparatus, and a corresponding method for sensing room occupancy.

In various applications thcrc is a dcsirc to bc able to dctcct which, if any, of a plurality of rooms are occupied. For example, such a function maybe of particular use in quickly assessing which of many rooms in a building are occupied in the case of an emcrgency, such as a fire, or in dctccting a burglar or othcr intmder or unauthoriscd pcrson. Room occupancy sensing systcms of thc prior art arc typically bascd on passive infrared sensors, which detect relatively large movements, and therefore occupancy, by mcans of monitoring a change in infra-rcd radiation from a moving hcat sourcc; howcvcr, such systems are not sufficiently sensitive for use in some applications: a relatively high background temperature in a room can adversely affect accuracy for example. For more scnsitivc applications, activc scnsor systcms may bc more appropriatc. Onc such activc sensor system uses radio frequency (RE) radiation and works by creating a field of radio 2 0 wave radiation with one or more RF emitters and detecting changes in that field via one or more RE detectors. Such changes are caused by movement, which suggests occupancy in the associated room. The wavelength and power of such RE radiation can be chosen to suit the application, and can be chosen such that movement can be detected through walls in a building. The sensitivity and range of motion detection in such RE-based systems can be difficult to get right, however: increasing sensitivity can have the effect that motion in an adjacent room is detected through a wall, leading to false positive detections being made (e.g. suggesting incorrectly that there is motion within a room based on detecting motion in an adjacent room through a partition wall), whereas reducing sensitivity to the level where false positives are reduced to a reasonable level can risk rcndcring thc motion dctcction systcm insufficicntly scnsitivc to dctcct room occupancy reliably.

US2O1O/0053330 (Hellickson et al) describes a LADAR based security sensor system that operates by comparing a 3D LADAR image of a scene with a 3D template of the scene. V/hen an intruder enters the scene the microprocessor detects a difference between the LADAR sensor output and the 3D template. Calibration of the system of US20 10/0053330 is required, which accounts for the fixed objects within the scene, so as to create the pre-determined spatial reference template against which the spatial image information is comparcd. If any objccts arc movcd (c.g., a chair \vhcn somconc movcs to a new location), the system needs to be recalibrated in order to avoid a false alarm.

US2O 10/0053330 is a relatively complicated spatial imaging system for monitoring a singlc sccnc, for cxamplc a singlc room. Monitoring of multiplc rooms would appear to rcquirc multiple systcms. Thc methodology of IJS2O1O/0053330 relics on capturing a spatial image of a room, namely a 3-D image comprising multiple pixels. The system of US2O1O/0053330 relics on thc dctcction of spatial information concerning thc sccnc being monitored; this results in a system that would be relatively complicated and expensive for a room occupancy sensing system.

Thc prcscnt invcntion sccks to mitigate thc above-mentioned problems.

Alternatively or additionally, the present invention seeks to provide an improved room 2 0 occupancy system, preferably one which provides improved sensitivity to small movements of or caused by, an occupant in the room.

Summary of the Invention

The present invention provides, according to a first aspect, a building comprising a plurality of rooms and a room occupancy sensing apparatus, the room occupancy sensing apparatus comprising: -at least one light source arranged to emit a series of light pulses, -a plurality of wavcguidcs, at Icast somc of thc wavcguidcs bcing arrangcd to deliver light from the light source to one or more output nodes located in each of the plurality of rooms, -at least one signal capture unit arranged to receive output signals resulting from light reflected by objects in the plurality ofrooms, and -a signal processor, wherein the apparatus is arranged so as to be able to distinguish between a light pulse rcflcctcd by an objcct in a room dclivcrcd to that room via any onc output nodc from a reflected light pulse originating from an output node in any different room (and preferably from any other output node), and thc apparatus is so arrangcd that, in usc, thc signal proccssor comparcs thc signal rcccivcd at thc signal capturc unit in rcsponsc to a first cmittcd light pulsc with thc signal received at the signal capture unit in response to a second emitted light pulse, whcrcby thc apparatus is ablc both to dctcct movcmcnt in a room and to asccrtain the particular room in which movement has occurred by virtue of(i) detecting a difference between signals received by the signal capture unit resulting from reflected light pulscs from such first and sccond cmittcd light pulscs and (ii) rclating said rcflcctcd light pulses to the room concerned (for example by relating said reflected light pulses to 2 0 the appropriate output node and therefore to the room associated with that output node).

Using a light source in this manner may allow the occupancy of a room to be ascertained whilst reducing significantly the risk of false positives from movement in a region outside of the room, because room layouts are often such that light is substantially prevented from transmifting from one room to another. Rooms are typically separated by partitions walls that do not transmit light. Even where rooms are separated by partitions that transmit some wavelengths of light, the light maybe selected to be of an operating wavelength that is not transmitted by the partition (for example, in the case of a glass partition, the wavelength may be an appropriate infrared wavelength). Also, using light as thc sourec of radiation may thcilitatc thc usc of fcwcr sourecs of radiation for thc system, as it is possible to use one source for many rooms, with appropriate optics and!or controls in place to allow the apparatus to distinguish bctwccn a reflected light pulse originating from one output node and a reflected light pulse originating from another output node.

The ability to detect a difference between signals received by the signal capture unit resulting from reflected light pulses from respective first and second emitted light pulses. such a difference for example being caused by movement or introduction of an object into the room, may be achieved by means of the apparatus comparing temporal differences between the respective pulses. For example, the shapes of the waveforms of thc reflected light pulses may diffcr as a result of at least some of thc light bcing reflected differently, as between the first and second pulse, and therefore travelling over paths of different lengths and therefore resulting in temporal differences in the waveforms of the reflected light signals. It is not essential for a room occupation system of thc typc provided by cmbodimcnts of thc present invcntion to have the ability to detect spatial image information concerning the scene in each room being monitored. Using temporal differences between the waveforms of pulses to detect a change in the scene being monitored (e.g. movement of an object in a room) provides a simple and elegant solution to detecting room occupation. For example, having a room occupancy sensing apparatus which operates by means of using the way in which the waveforms of reflected light pulses vary with time, does not require the use of a large array of image pixels, or the 2 0 detection or reconstruction of spatial image data.

It may be that the light is of an intensity and/or an operating wavelength selected to provide a signal-to-noise ratio sufficient to distinguish the pulses from ambient light sources. The apparatus may include a filter to aftenuate incoming light of wavelengths other than the operating wavelength.

The present invention has particular application in relation to detecting room occupancy, for example for ensuring fire-risk safety and/or intruder detection, in large buildings with many rooms (ten or more). The building may have more than five rooms, and may have more than ten rooms. Preferably, more than five rooms (and possibly more than ten rooms) are monitored with the room occupancy sensing apparatus. Preferably, substantially all rooms in the building that are designed for human occupation are associated with at Icast onc output nodc, and cach output nodc is only associatcd with onc room.

Optionally, the rooms in which one or more of the output nodes are located may include at least one communal area, for example an open plan area, corridor, kitchen or lavatory area.

As mentioned above, the apparatus is so arranged that, in use, the signal processor compares the signal received at the signal capture unit in response to a first emitted light pulse with the signal received at the signal capture unit in response to a second emitted light pulsc. It will of eoursc bc appreciatcd that thc words "first" and "sccond" arc used in this context as convenient labels to distinguish between the two emitted light pulses concemed. There may for example be other emitted light pulses that are received between the "first" and "second" light pulses. It is however preferred that the time between the first and second light pulses is less than 5 seconds, thus ensuring that the occupancy of a room is checked at least once every 5 seconds. Having a relatively short time between the first pulse and the second pulse effectively means that the occupancy or otherwise of a room is compared against a very recently generated reference (the first pulse for example being the reference for an unoccupied state of the room, against which the second pulse is effectively compared). Thus, movement of objects (for example, the position of a chair) within the room, when occupied, are accounted for, without any need 2 0 for recalibration of the apparatus, when the room becomes unoccupied again. The first pulse may be used as a reference pulse, and used for comparison with second, third, and successive pulses. Preferably, however, the apparatus uses a different pulse as the "first pulse" against which a subsequent pulse is effectively compared, at least once every minute.

At least a part of the signal processor may be formed as part of the signal capture unit. Alternatively, the signal processor maybe wholly separate from the signal capture unit.

The apparatus is preferably arranged to convert the reflected light pulses into digital signals for processing by the signal processor. There may therefore be transducers for converting the light signals into electric signals. The signal capture unit may be arranged to receive output signals resulting from light reflected by objects in the plurality of rooms by means of receiving the light directly. In such a case, the signal capture unit may itself include one or more light transducers. The light transducers may convert the light signal into an electric signal. Alternatively, or additionally, one or more light transducers may be provided separately from the signal capture unit, for example in each room having an output node. In such a case, the output signals received by the signal capture unit may include electric signals converted by the light transducers from light reflected in a room. There may be a transducer that is arranged to generate electric signals from light signals reflected by objects in each of a plurality of differcnt rooms. In such a case, the transducer may be arranged to receive a sequence of light waveforms, the successive light waveform each being associated with light reflections in a different room. One transducer can therefore be uscd to distinguish betwcen light reflections in onc room from those of another room. The or each transducer may be in the form of a photodiode.

The or each transducer is preferably able to convert a varying light signal (or waveform) into an electric signal (or waveform) having a resolution sufficient to enable detection of changes in light intensity of a duration of a nanosecond (more preferably, one-tenth of a nanosecond). The capture unit andior signal processor preferably utilise a sampling period of between 10 and 1,000 picoseconds. A higher sampling rate will provide greater resolution of detection and allow detection of smaller amounts of movement within a room. Light travels about 3mm in 10 picoseconds and about 30cm in a nanosecond (=1,000 picoseconds). Preferably, the apparatus is arranged to enable detection of changes in light intensity of a duration of 2 x 10b0 seconds (a sample rate of the order of 5GS' -i.e., 5 Giga-samples per second = 5 x l0 samples per second). In such a case, the transducer required to pmvide such resolution of measurement may be relatively expensive, in which case having one transducer serving many nodes is particularly advantageous.

Each room may comprise one or more input nodes for collecting light reflected in the room. Conveniently, at least some of the plurality of waveguides are arranged for delivering light reflected by objects in the plurality of rooms, via one or more input nodes in cach room, to thc signal capturc unit. At lca.st somc of thc plurality of wavcguidcs arc arranged both to deliver light from the light source to one or more output nodes and to deliver reflected light from one or more input nodes. Thus, the same waveguide may be used both to deliver light and to receive reflected light. At least one input node may also perform the ifinction of an output node. (As such references herein to an "output" node may, where the context so allows, equally apply to an "input" node and vice versa. Also, features described with reference to one of the three principal types of node, namely (a) an input node, (b) an output node, or (c) a node that performs both as an input node and an output nodc, may cqually apply to a nodc of a diffcrcnt onc ofthosc thrcc typcs.) There may be advantages in having more input nodes in a room than the number of output nodes in that room, for example in view of the way in which light may be reflected within thc layout of a ccrtain room. Each input nodc may bc arrangcd to collcct and/or dctcct light at a givcn rcgion, but may not bc configurcd to distinguish bctwccn thc intensity or wavelength of the light at different positions within that region. In effect, cach input nodc may bc in thc form of a singlc pixcl nodc. Whilst, thcrc may bc many nodes arranged in a room a majority of the nodes are preferably spaced apart from each other.

Thc nodcs may cach bc providcd with an appropriatc lcns suitcd to cnsurc that thc node covers the intended area of the room. A Fresnel lens may be used for example.

It is preferred to limit the number of output nodes. It is believed that a relatively small-sized room, having a floor area of about 5 square metres for example, can be monitored by means of a single output node. Preferably, there are a plurality of rooms in the building in each of which there are provided only one or two output nodes.

Preferably, there are a plurality of rooms in the building in which there is provided only one output node.

The light source may be a laser light source. The laser light source is preferably in the form of an Infra-Red laser unit.

Advantageously, one light source is arranged to deliver light to a multiplicity of output nodcs. Thus, a singlc laser sourcc with a sufficicntly high spccification to providc accuracy may serve many rooms thereby reducing the cost of the apparatus. The light sourcc is prcfcrably arranged to emit pulses each having a duration of between 0.1 and nanoseconds. The light source is preferably arranged to emit pulses each having a duration of less than 100 nanoseconds. The light source may be arranged to emit pulses each having a duration of more than 1 nanosecond. It is preferred however to have light pulses each having a duration of less than 1 nanosecond. Light can travel about 30cm in I nanosecond and can travel about óOm in 200 nanoseconds. The received waveform (or waveforms, for example if there are two or more input nodes) will typically have a duration that is longer than the emitted pulse. Some objects in the room maybe closer to thc output / input node(s) such that thc routc from an output nodc, via objcct (and reflection) and back to an input node is significantly shorter than other routes. If the room has a maximum dimension of say I Om then the difference in distance travelled by light along onc path and anothcr path could easily bc lOm or morc. The rcecivcd (reflcetcd) light pulses may thcrcforc havc a duration that is at least 30 nanoseconds, and possibly more than 100 nanoseconds.

Thc wavcguidcs arc conveniently in the form of fibre optic cable.

As mentioned above, the apparatus can distinguish between a light pulse reflected by an object in a room delivered to that room via any one output node and a reflected light pulse originating from any other output node. This may be achieved in any suitable way. In the described embodiments, where the width (duration) of the light pulses is relatively low, the timing ofthe pulse is used to determine which node the pulse has been reflected from. Preferably, the apparatus introduces a time delay between the light delivered to one room and the light delivered to the next room. When using a single light source with many rooms, this may be achieved by emitting a single pulse, splitting that pulse for delivering to multiple different output nodes, and ensuring that the path 2 5 length to each such output node differs sufficiently that the pulses are emitted from each output node with a delay between successive pulses at the time they are emitted. Thus, the reflected pulses are then advantageously separated from each other temporally, allowing the apparatus to determine the output node from which a reflected pulse originated. Conveniently, the wavcguides that deliver the light to the output nodcs differ in length sufficient to introduce such a time delay between the pulses by successive output nodcs. It will be appreciated that a waveguidc for delivering light from a light source to a distant room will necessarily have a minimum length that is longer than the minimum length required of a waveguide for delivering light to a room that is closer to the light source. As such, it may be convenient (but not necessary) to build in a longer time delay in relation to output nodes that are further away from the light source than the time delay in relation to output nodes that are closer to the light source. Alternatively, or additionally, different wavelengths of light could be used to distinguish between light sent to and reflected by certain rooms. Alternatively, or additionally, more light transduccrs could be providcd per room.

The room occupancy sensing apparatus may be integrated with a system that detects operation of doors. For example, certain doors may require the use of an electronic key, swipe-card or the likc thcrcby allowing detcction of a human prcscncc at the door. Such integration could reducc thc numbcr of false positivcs by means of discounting detected occupancy in a room that has been deemed empty for reason of the entry door to that room not having been operated within a suitable time period (for example since the start of the day concerned). The room occupancy sensing apparatus may be integrated with other monitoring systems in the building.

There may be one or more thrther buildings having rooms that are also monitored by the same room occupancy sensing apparatus.

There is also provided, according to a second aspect, a room occupancy sensing apparatus for sensing the occupancy of two or more rooms in a building, the room occupancy sensing apparatus comprising (a) at least one light source arranged to emit a series of light pulses, (b) a plurality of waveguides, at least some of the waveguides being arranged to deliver light from the light source to a plurality of output nodes, which are each arranged for being located in a room, (c) at least one signal capture unit arranged to receive output signals, which in use (for example when the room occupancy sensing apparatus is installed and used in a building) result from light from the output nodes being reflected (for example by the scene within a room) and detected (for example via one or more input nodes), and (d) a signal processor. The apparatus is preferably arranged so as to be able to distinguish between a reflected light pulse resulting from light -10 -emitted by any one output node and a reflected light pulse resulting from light emitted by any other output node. The apparatus is preferably so arranged that, in use (for example when the room occupancy sensing apparatus is installed and used in a building), the signal processor compares the signal received at the signal capture unit in response to a first emitted light pulse with the signal received at the signal capture unit in response to a second emitted light pulse, whereby the apparatus is able in use both to detect movement in a room and to ascertain the particular room in which movement has occurred by virtue of 0) detecting a difference between signals received by the signal capture unit resulting from reflected light pulses from such first and second emitted light pulses and (ii) relating said reflected light pulses to the appropriate output node and therefore to the room associated with that output node. The room occupancy sensing apparatus of this second aspect of the invention may be provided as an installed system in a building, or may be providcd separately in order to convert a building comprising a plurality ofrooms into a building accotthng to the first aspect of the present invention. As such, features of the first aspect of the present invention may be incorporated into this second aspect of the invention.

According to a third aspect, the present invention also provides a kit of parts for converting a building comprising a plurality ofrooms into a building according to the first aspect of the present invention. The kit of parts may comprise at least one light source for emitting a series of light pulses. The kit of parts may comprise a plurality of waveguides. The kit of parts may comprise one or more output nodes. The kit of parts may comprise one or more input nodes. The kit of parts may comprise at least one signal capture unit. The kit of parts may comprise a signal processor. Features of the first aspect of the present invention may be incorporated into this third aspect of the invention.

The present invention also provides, according to a fourth aspect, a method of sensing room occupancy. The method may comprise using a room occupancy sensing apparatus according to the second aspect of the invention. The method may comprise a step of delivering a series of light pulses via a plurality of waveguides to one or more output nodes located in each of the plurality ofrooms. The scene in each room may then reflect the light pulses emitted by the output nodes. The method may comprise a step of -11 -detecting thc reflected light pulses. The method may comprisc a step of monitoring for a difference between the detected waveform of a first reflected light pulse reflected from the pulse emifted from an output node and the detected waveform of a second reflected light pulse from the same output node, and performing such a monitoring step in respect of each of the output nodes. Detecting movement in a room maybe achieved by means of detecting such a difference between detected waveforms. The particular room in which movement, and therefore occupancy, is detected may be ascertained, preferably by means of determining the output node with which the difference so detected is associated.

Thc method may comprisc using a signal processor (for exampic an electronic signal processor, computer or the like) to ascertain the difference if any between the detected waveforms.

It will of course bc apprcciatcd that features dcscribcd in relation to onc aspect of the prcscnt invention may be incorporatcd into othcr aspects ofthc present invcntion. For example, the method of the invention may incorporate any of the features described with refcrcncc to thc apparatus of thc invcntion and vice versa.

Description of the Drawings

Embodiments ofthe present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figures la and lb show an occupancy sensing system in accordance with a first embodiment of the present invention in an unoccupied room; Figures 2a and 2b show the occupancy sensing system of the first embodiment in an occupied room; Figure 3 shows the occupancy sensing system of the first embodiment in use in two adjacent rooms; Figures 4a to 4d show the steps of emitting and receiving light pulses as used in a second cmbodimcnt of thc invention; -12 -Figure 5 shows thc arrangement of the network of nodes provided for emitting and receiving light pulses in the second embodiment; and Figure 6 shows an occupancy sensing system in accordance with a third embodiment of the present invention.

Detailed Description

Figures Ia, lb. 2a, and 2b illustrate schematically the principle of operation of an occupancy sensing system in accordanec with a first embodiment of the present invention. Figures Ia and lb show the system working with an unoccupied room 10.

The system shown comprises a pulsed laser unit 20 which emits identical pulses 22 (labelled individually as pulse "a" and pulse "b") of laser light separated by a specified time, t. The pulses 22 emitted by the laser unit 20 are refleetcd by the physical surfaces in the scene within the sensor Field of View (FoV). The reflected pulses 24 are detected and stored by a capture unit 30 as digital waveforms. If no change (i.e. motion) occurs between the reflections oftwo sequential pulses, their reflected waveforms 24 will be identical, as shown in Figure la. Figures 2a and 2b show the system of Figures la and lb in operation when the room 10 is occupied by a moving person 40. As shown in Figures 2a and 2b, the motion that occurs in the sensor FoV during the time between the reflections of two sequential pulses ("a" and "b"), as a result of the person 40 entering the FoV, changes the physical layout of the scene between the first pulse and the second pulse. The laser pulses are therefore reflected differently, the second pulse for example being reflected so that at least part of the light travels along a path of different length, resulting in some light taking a different length of time before being detected (in 2 5 comparison to the first pulse). This results in temporal differences between the waveforms of the reflected pulses 24m, as shown in Figure 2a. The capture unit 30 detects that the shape of the waveform of the second pulse (pulse "b") of the two pulses 24m is different from the first, thereby detecting the motion in the room, and therefore detecting that the room is occupied. In this manner, the laser pulscs are effectively used for laser range-finding, rather than in a laser-imaging capacity. The system is a non- -13 -imaging system and instead uses temporal (time-based) characteristics of light pulses as the means of occupancy detection (for example, analysing and/or comparing waveforms in the time-domain).

The flnt embodiment is shown in further detail in Figure 3, which shows the occupancy sensing system installed in a building, which in this first embodiment is in the form of an office building having multiple rooms 10 any ofwhich could be occupied.

Two such rooms I Oa, I Ob are shown in Figure 3. The occupancy sensing system is arranged to detect which of many moms 10 are occupied, for example by one or more employees, at any given time. Such a function may be of particular use, for example in quickly assessing which of many rooms in a building are occupied in the case of an emergency, such as a fire. Tt may otherwise be difficult to determine whether one or more rooms have been successfully evacuated, particular if there are many rooms in the building, if there are rooms that are remotely located, and/or if access to any given room is restricted.

With reference to Figure 3, a single pulse laser unit 20 generates successive pulses of laser light, with a period of that are split by splitters 50 into multiple light paths (defined by fibre optic cable), each light path being associated with a respective pulse of light. The pulses are carried by fibre optic cable to multiple output nodes 60. An output node is fbnned at the end of the fibre optic cable in the room to be monitored and is associated with a suitable lens in order to provide an adequate field of view (although it would be possible for an output mode to be defined by the open end of the bare fibre, which would in any case pmvide a relatively wide field of view). The fin-out structure of the fibre optic cable network illustrated in fig. 3, particularly the arrangement of signal splitters 50 between the source 20 and each output node 60, allows each node 60 to output approximately the same pulse power, meaning that any required amplification of the pulse waveforms lbr analysis can be substantially unilbrm. Return reflections are carried back to the capture unit 30, which includes both a transducer, in the form of detector 32, and a control unit 34. The control unit 34 includes a computer processor.

The detector 32 receives and detects the reflected pulses and converts the received pulses -14 -into clcctrical digital wavcfbrms. Thc control unit controls the opcration of thc systcm and also processes the digital pulse waveforms.

The pulses 22 from each output node 60 are emitted at the point of the node at diflwnt times, separated by a delay At. The delay At between the time at which one pulse is emitted from one node and the time at which the same pulse is emitted from the next node is introduced by a delay loop 70 in the relevant fibre optic cable. This may be achieved in practice by using fibre optic cables of varying lengths as delay lines -the longer the cable, the longer the lime taken for a pulse to be emitted from the output node, rcflcctcd and rcccivcd by thc dctcctor. Thc lcngth of to fibrcs is thcrcforc incrcmcntcd cumulatively for each node by a length equivalent to the required interval.

Tn Figure 3 it will be seen that the route to the leftmost node in the Figure, has no dclay loops. Thc fibre optic cablc routc to thc ncxt nodc (sccond from thc lcft) has a dclay loop 70a that adds a dclay of At. Thc fibre optic cablc routc to thc ncxt pair of nodes (the two nodes on the right) includes a larger delay loop 70b that adds a delay of 2At to thc routcs to both nodes. Thc route to the node on the far right also includcs a further delay loop 70c that adds a delay of At Thus, during operation, a laser pulse is emitted by the source 20 and is then split into four laser pulses by the splitters 50, which arrivc at thc nodcs at timcs To (far lcit nodc), To+ At, To +2At, and To+ 3At, respectively. The reflected pulses travel back from the nodes 60 to the capture unit 30 along the same route as taken by the pulse from the laser source 20 to each such node 60.

Thesamenode6Oisusedbothasoutputandinputoflaserlightto andfromtheroom.

Thus a further delay is added so that the laser pulse that is delivered to each node 60 is reflected in the room and received back at the capture unit 30 at different times, separated by an interval of at least 2At.

The length of the pulses is chosen to be sufficiently short (relative to the delay At) and the separation between successive pulses emitted by the laser source 20 is chosen to be sufficiently long (longer than the lime between the instant at which thepulse is emitted and last reflected pulse is received at the capture unit) to ensure that the pulses received at thc capture unit, originating from diffcrcnt nodes, do not ovcrlap or intcrfcrc with cach other and can be readily distinguished by the capture unit. Thus, for a system having n -15 -nodcs, a singlc pulsc cmittcd by thc lascr sourcc is split into n pulscs and cmittcd by thc n nodes. The capture unit receives a sequence of n reflected pulses resulting from that single pulse emifted by the laser source, before the laser source emits the next pulse (consider also the explanation provided below with reference to Figure 4a to 4d of the second embodiment).

The reflected pulses are captured, digitised, stored and processed by the capture unit. The node from which the reflected pulse is received is identified by means of the time at which the pulse is received. The digital waveforms from successive reflected pulses from thc same nodc arc comparcd by thc computer proccssor of thc control unit 34 (in the capture unit 30). In this embodiment, a Binary Two's Complement method is used to compare the pulse waveforms. This is equivalent to inverting one of the waveforms and adding thc two resulting waveforms in analoguc space. Regardlcss of thcir shape, if thc waveforms are identical, a null output \vill occur. Ho\vcver, if the two waveforms differ due to motion occurring during the time between the pulse reflections, a non-zcro output will bc apparent, indicating occupancy. Thc room in which occupancy has been detected can be determined by relating the input/output node from which the reflected pulse was received to the room it is associated with.

In thc prcscnt embodimcnt, thc timc t1, is about one second, equating to a pulse repetition rate (at the laser source) of about 1Hz. A faster rate could be used, but 1 Hz allows for detection of motion of typical speed in the workplace. The rate may be calibrated according to the type of application/installation. The present embodiment is used in relation to rooms having a height of 5m, where the nodes are ceiling mounted.

The average pulse from each node travels a lOm return journey from the node, via reflection in the room and back to the node. The light travels at 3 x i08 ms1. A lOm journey by the light thus takes about 33 nanoseconds. The width of the pulse emitted from the laser source is about I nanosecond (i.e. about 30cm). The width of the pulse will spread as a result of different reflections in the room and as a result of dispersion and other pulse-spreading effects as the light travels along the fibre optic cable. The capture unit thercforc opcratcs using a pulsc sampling interval of about 100 nanoscconds, resulting in 100 nanoseconds worth of data being stored per pulse per node. Each 100 -16 -nanoseconds worth of data includes 1,000 data points, requiring a sampling frequency of 1OGSs1 The resolution of movement that can be detected with such a system is thus of the order of 3cm. Given that each pulse requires of the order of 100 nanoseconds of sampling at the capture unit, the system of this embodiment (operating at a pulse repetition rate ofis) coulduse as many as 106 (andpossiblyup to almost 10'-i.e. I second cycle time divided by tOO nanoseconds pulse sampling interval time) pulse output nodes without any overlap in successive pulses.

The system of the first embodiment can be readily scaled up by adding more splitters and delay loops. By way of illustration, Figurcs 4a to 4d and 5 illustrate a second embodiment of the invention installed in a building for monitoring a larger number of nodes. Figures 4ato 4d show the steps of emitting andreceivingpulses. In this embodiment, there is onc nodc pcr room. Initially (Figurc 4a) thc lascr sourcc cmits a single pulse, which by means of thc delay loops, gcncratcs succcssivc pulses at thc respective output nodes. The successive pulses are separated by a time delay ofAt.

Figure 4a shows thc first thrcc pulscs and thc last (nth) pulse only. Each pulsc is emitted from an end ofthe fibre oplic cable which is positioned and configured in each room to provide an adequate field of view. The pulse is then reflected in the room, apart of the reflection being dctcctcd via thc samc cnd ofthc fibrc optic cable (so that the output node in each room also performs the function ofthe input node). Consequently (with reference to Figure 4b) as the reflected pulses 24 fravel back via the fibre optic cable network, extra delays are introduced so that the received pulses are separated by time 2At. The reflected pulses 24 each have a modified waveform (compared to the emitted pulses) that depends in part on the physical layout of the room and the way in which the emitted pulse is reflected in the room and back to the input1output node. Each respective reflected pulse 24 may therefore have a shape that is particular to the layout and shape of the room and its contents (of field of view) at a given time. The reflected pulses 24 will therefore almost certainly have different waveform shapes.

After a time t the next pulse is emitted by the laser source (as shown schematically in Figure 4c). In this ease, there has bccn a movement in room number 3 and no movement in any of the other rooms. As such this latter reflected waveform 24m -17 - (sec Figure 4d) from the third node has a different shape from the immediately preceding reflected waveform 24i (see Figure 4b) from the third node. The capture unit compares successive reflected pulses from each node for changes sufficiently large to signify movement in the room. Thus, in this example, the capture unit detects a change in the shape of the third node's reflected pulses and deems the associated room to be occupied.

Figure 5 shows how the fibre optic cable network can be expanded to allow for many output/input nodes for each laser source / capture unit. Figure 5 shows a network for 8 nodes. The network has 3 levels, LI, L2, L3 which in Figure 5 are labelled such that thc lcvcl closcst to thc nodcs is labcllcd Li). At cach lcvcl, thc numbcr of pulses is doubled by means of optical splitter units dividing each pulse received by that unit into two pulses. Delay loops are then inserted to provide different delay times for each rcspcctivc pulsc as outputtcd at a nodc. Thc dclay loops could of coursc bc inscrtcd diffcrcntly, but for an cfficicnt usc of optical cablc, longcr dclay loops arc inscrtcd closcr to the source. Thus, in Figure 5, at the topmost level, L3, the single pulse from the laser light sourcc 20 is split into two pulscs, onc passing down a lcft-hand branch to which no delay is added and one down a right-hand branch to which a delay of 4At is added. The two pulses then pass to the next level at which each pulse is split into two pulses, one having no dclay addcd and onc having a dclay of 2At addcd. Thc proccss is rcpcatcd again at the lowest level, Li, with the split pulses having either no delay or a delay of At added. As a result, the pulses arriving at the nodes 60 have successive delays (from lefi to right) of 0, At, 2At, 3At... 7At. If more than 8 nodes are required another level is added above level L3 in a similar paftern. Thus, for n nodes, there needs to be I levels, where us equal to (log n) / (log 2), rounded up. The delay to be inserted at the tih level will be equal to 2' (2 to the power of/-l) At. It will also be appreciated that 2n At will ideally be relatively low compared to tm,, so that all reflected pulses generated by a first pulse emitted from the laser source are received before the reflected pulses generated by the next pulse emitted from the laser source start to arrive.

The physical length of the delay loops introduced into the fibre optic cable nctwork should bc dctcrmincd taking into account thc lcngth and rcfractivc mdcx ofthc fibre optic cable from the laser source to the nodes. Thus, the physical separation of -18 -rooms, and diffcring distanccs of thc rooms from thc location of the laser sourec may introduce part of the delay required for each node. For this reason, it may be more efficient and convenient if the nodes that are closest to the laser source are connected by fibre optic cables having less in the way of cable added to introduce delay loops, whereas the nodes that are fUrther away have the longer delays.

It will be seen that the scalable system illustrated by the first and second embodiments enable occupancy sensing of large areas at relatively low cost, because the system design proposed consists of a smaller number of lasers than there are sensing areas (e.g. a single pulsed laser) and a nctwork of pulse output nodes connected by optical fibres. These are emitted from the laser unit and will travel along the optical fibres to be emitted by each pulse output node. The pulses are reflected and received by a smaller number of detectors than sensing areas, (e.g. a single dcteetor and capture unit).

Thc numbcr of units required to provide full covcrage of thc area or areas of interest will depend on the Field ofview (FoV) of each pulse output unit. Sensor FoY may be adjusted to the required width using optical lenses on each pulse unit. Maximum coverage using the minimum number of laser nodes and computers may be achieved by increasing sensor FoV. Conversely, using a greater number of laser nodes with a narrow FoV may enable the system to be uscd as a high-resolution motion location and therefore tracking system.

Figure 6 illustrates schematically an occupancy sensing system in accordance with a third embodiment of the present invention, showing part of the system only in relation to a single room. The system has many independently operable pulsed laser units 120 each of which emits identical pulses of laser light, in turn. The light pulses are split by splitters 150 and outputted from output nodes 160. Some laser units supply more output nodes than others. The path length between the laser unit and the output node is set by the length of the path of the one or more waveguides, which may include one or more delay loops, between the laser unit and the output node. The laser units are controlled by a central control unit such that pulses of laser light are emitted in sequence from the output nodes, the start of the pulse emitted from one output node to the next being predetermined by the control unit and the path length between the laser unit and the -19 -output node, and being a prc-set parameter of the system. There is a delay between triggering the laser unit and the laser unit emitting a light pulse, but this delay can be assumed to be approximately the same for all laser pulses, and therefore does not need to be accounted for. Return reflections are carried back to a capture unit 130 via input nodes 165 and associated waveguides, and optionally combiners 155. In Figure 6, only one node 180 is illustrated as acting as both an input node and an output node. The return reflected waveforms are analysed in a similar manner as that described with reference to the first embodiment. Some nodes are shared and thus in this embodiment it may not be possible for the apparatus to detect (or "know") the exact path taken by light that is received at the capture unit 130. However, the apparatus is able to distinguish between light received from a node or nodes in one room from light received from nodes in other rooms. The system of the present embodiment is also, like the other illustrated embodiments, able to cope with a situation in which, inadvertently, a detector in a room can see stray radiation from a light source (output node), other than the one to which it is matched. Consider, for example, a scene which contains a computer monitor with a glossy screen. A first output node may illuminate part of the scene which contains the monitor, and whilst a first input node may receive most of the signal, some stray radiation may accidcntly be reflected off the glossy screen into anothcr input node, which is in the same room. Despite this, the embodiment still functions correctly, since the same amount 2 0 of stray radiation would be found as between successive pulses (assuming no other changes in the scene): it is successive pulses that are compared, and so the system is, in effect, constantly recalibrating itself.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

The apparatus may be arranged so as to account for changes in background radiation. If a person in a room turns a light on or off in a room, or otherwise changes the lighting, there may be changes in the shape or magnitude of the waveform of light detected by the room occupancy sensing apparatus. However, in the case where the -20 -apparatus is a room occupancy scnsing apparatus and not a motion dctcction system such changes would correctly indicate occupancy of the room. Changes in background light conditions in a room not caused by a person occupying the room may be discounted by the room occupancy sensing apparatus. For example, all lighting in the building may be controlled by a system that integrates with the room occupancy sensing apparatus. In such a case, energy savings may be made by means of the system turning off lights in rooms that are deemed empty. The apparatus may be able to discount changes in outside lighting conditions, if such conditions affect the light conditions in the room, by methods that will bc readily apparcnt to thc skillcd pcrson.

There may be more than one output node per room. The circuit and fibre optic cables for detecting and analysing reflections in the rooms may be separate from the circuit for causing pulscs of light to bc cmittcd in each room. Whilst having identical laser pulscs (cmittcd from diffcrcnt output nodcs) is desirablc, this is not cssential. Morc than one laser could be provided. The laser light is split in two at each level of signal splitting. Thc lascr light could howcvcr bc split into morc scparatc pulses at cach level of signal splitting.

The pulse sample interval and rates could be changed to improve resolution or to rcducc resolution, but perhaps rcducc thc cost of thc componcnts rcquircd for thc systcm.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims (15)

1. -21 -Claims 1. A building comprising a plurality of rooms and a room occupancy sensing apparatus, the room occupancy sensing apparatus comprising: -at least one light source arranged to emit a series of light pulses, -a plurality of waveguides, at least some of the waveguides being arranged to deliver light from the light source to one or more output nodes located in each of the plurality of rooms, -at least one signal capture unit arranged to receive output signals resulting from light reflected by objects in the plurality ofrooms, and -a signal processor, wherein the apparatus is arranged so as to be able to distinguish between a light pulse reflected by an object in a room delivered to that room via any one output node from a reflected light pulse originating from any output node associated with any different room, the apparatus is so arranged that, in use, the signal processor compares the signal received at the signal capture unit in response to a first emitted light pulse with the signal received at the signal capture unit in response to a second emitted light pulse, whereby the apparatus is able both to detect movement in a room and to ascertain the particular room in which movement has occurred by virtue of(i) detecting a difference between signals received by the signal capture unit resulting from reflected light pulses from such first and second emitted light pulses and (ii) relating said reflected light pulses to the room concerned.
2. 2. A building according to claim I, wherein said at least one signal capture unit is arranged to receive light signals reflected by objects in the rooms.
3. 3. A building according to claim I or claim 2, wherein the room occupancy sensing apparatus comprises one or more transducers for converting light signals reflected by objects in the rooms into electric signals.

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4. 4. A building according to claim 3, wherein at least one ofthe transducers is arranged to convert light signals from each of a plurality of different rooms into electric signals.
5. 5. A building according to claim 3 or claim 4, wherein at least one of the one or more transducers forms a part of the capture unit.
6. 6. A building according to any of claims 3 to 5, whcrcin cach ofthc onc of thc onc or more transducers is able to convert a varying light signal into an electric signal having a resolution sufficient to enable detection of changes in light intensity of a duration of a nanosccond.
7. 7 A building according to any preceding claim, wherein at least some of the plurality of wavcguidcs arc arrangcd for dclivcring light rcflcctcd by objccts in thc plurality of rooms, via one or more input nodes in each room, to the signal capture unit.
8. 8. A building according to claim 7, whcrcin at lcast somc of thc plurality of waveguides are arranged both to deliver light from the light source to one or more output nodes and to deliver reflected light from one or more input nodes.
9. 9. A building according to claim 7 or claim 8, wherein at least one input node also performs the function of an output node.
10. 10. A building according to any preceding claim, wherein there are a plurality of rooms in which there is only one or two output nodes.
11. II. A building according to any preceding claim, wherein the one light source is arrangcd to dclivcr light to a multiplicity of output nodcs.

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12. 12. A building according to any prcccding claim, whcrcin the light source is a laser light source arranged to emitpulses having a duration of between 0.1 and 100 nanoseconds.
13. 13. A kit of parts comprising: -at least one light source for emitting a series of light pulses, -a plurality of waveguides, -one or more input and/or output nodes, -at least one signal capture unit, and -a signal processor, wherein the kit of parts is so arranged as to be suitable for converting a building comprising a plurality of rooms into a building according to any preceding claims.
14. 14. A method of sensing room occupancy, wherein the method comprises the following steps: -delivering a series of light pulses via a plurality of waveguides to one or more output nodes located in each of the plurality ofrooms, -the scene in each room reflecting the light pulses emifted by the output nodes, -detecting the reflected light pulses, -monitoring for a difference between the detected waveform of a first reflected light pulse reflected from the pulse emitted from an output node and the detected waveform of a second reflected light pulse from the same output node, and performing such a monitoring step in respect of each of the output nodes, -detecting movement in a room by means of detecting such a difference between detected waveforms and ascertaining the room concerned.
15. 15. A method according to claim 14, wherein the step of monitoring for a difference between the detected waveforms is performed by means of a signal processor.