SENSOR ARRANGEMENT FOR MONITORING PHYSICAL ACTIVITY

Abstract: A sensor arrangement for monitoring physical activity associated with a living being, comprising a flexible board (70) to which is fitted a transducer (80) for converting a distortion of the board into an electrical signal. The board comprises discontinuities (94) which enable parts of the board to distort somewhat independently of other parts of the board. The living being lies or sits on a cushion or mattress (30) under which is located the board. The signal from the transducer (80) is passed onto circuitry (50) which can detect the presence of the physical activity, which may be heartbeat, breathing or limb movement. The discontinuities can be plurality of slots formed in the board, a plurality of grooves formed in the board or a plurality of ribs formed in the board.

Description: SENSOR ARRANGEMENT FOR MONITORING PHYSICAL ACTIVITY The present invention relates to a sensor arrangement and monitor system for monitoring physical activity associated with a living being, without having to be fitted to the living being and without using fields or signals which might be perceived as harmful to a living being, in particular when the living being is a baby. Systems have been developed for home and hospital use to monitor the presence of a baby in a cot or a pram, for example by monitoring physical activity such as a heartbeat or breathing of the baby, which set off an alarm when the baby is removed by an unauthorised person. Further, medical staff monitor the patients under their care for any change relating to their well being. Monitoring the physical activity of a new born baby, particularly heartbeat and breathing, can alert staff immediately to medical problems, such as a potential cot death incident. For hospital use such systems must be capable of being applied to a number of cots simultaneously, for instance in a hospital ward where a number of cots would be present. Monitoring systems have been developed which use various types of sensors which are connected to the body of the living being. The sensors are then typically connected to a suitable form of processing facility. However, in such systems it is inconvenient to have to attach and detach the living being from the sensors when they are moved. Also, the attachment of sensors to a baby invariably requires the use of wires which may become entangled with the baby's limbs or around a baby's neck. GB 2.150,332 discloses a heartbeat monitor in which a sensor is fitted to the chest of a baby, for example by being secured in a pocket of a close fitting vest which pocket lies over the chest of the baby. The sensor comprises a microphone for picking up cardiac sounds and avoids the use of wires to connect the sensor to a processing facility by using a radio link. However, this system has the inconvenience of having to repeatedly fit the sensor to the baby. Equipment for monitoring a heartbeat has to be able to detect a signal having a very short pulse duration and if the sensor is not directly fitted to the living being will have to pick out the heartbeat signal of very small amplitude from a lot of background movement or noise including movement or noises made by the living being, such as breathing, vocal noises and limb movements as well as movement or noises emanating from the surroundings of the living being. GB 2,165.979 discloses a monitor apparatus which describes a system which monitors the breathing of a baby by sensing pressure changes in an air envelope on which the baby rests. The air envelope is designed to couple the signal of interest to a transducer which communicates with the air envelope. However, GB 2,165,979 does not disclose in detail how the air envelope is designed to discriminate between the signal of interest and other movement or noises occurring in the local environment. GB 2,192.460 discloses a sensor arrangement for monitoring respiration of a living being comprising a sounding board which is located underneath a mattress or cushion on which the living being rests and which transmits movement to a transducer which is fitted to the board. The signals from the transducer are processed to signal an alarm if respiration movement stops. However, this sensor arrangement is not arranged to be responsive to the much smaller movements associated with a heartbeat movement. Accordingly, the present invention provides a sensor arrangement for monitoring physical activity associated with a living being, comprising a flexible board which distorts in response to physical activity to which is fitted a transducer for converting a distortion of the board into an electrical signal, characterised in that the board comprises discontinuities. The discontinuities enable parts of the board to distort somewhat independently of other parts of the board and so allows the board to distort easily while being yet strong enough to support a mattress on which a living being rests and stiff enough to convey the signal. The more flexible the board is the more sensitive it is to J movement. The sensor arrangement according to the present invention is able to reliably pick up heartbeat movements from a living being through a mattress. The discontinuities may be in the form of a plurality of grooves or a plurality of slots. Good results are achieved if the discontinuities are linear and if at least some of the discontinuities terminate adjacent to the transducer. This makes the region in which the transducer is located flex more in response to movement. The flexible region close to the transducer causes the transducer to distort and generate an electrical signal. Preferably, the discontinuities extend radially from the transducer which has the effect of focussing movement of the board towards the transducer and of increasing the flexing of the board adjacent to the transducer. Alternatively, the discontinuities can comprise a plurality of ribs in a board made out of a more flexible material which without the ribs would not be able to support the mattress and living being. For the board to be able to distort optimally it should be spaced from the surface on which it rests. Therefore, preferably the board comprises at least one support member for spacing the board away from the surface on which the board rests. For best results at least one support member should act as a fulcrum for the transducer so that it is more responsive to distortions of the board. Preferably, the transducer is a piezo-electric device. The board can be made of plastic, preferably ABS plastic, metal, fibre board or hard board. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures in which: Figure 1 shows schematically an embodiment of a system for monitoring a heartbeat of a living being; and Figures 2a to 2e schematically illustrate embodiments of support boards on which a transducer is mounted. Referring to Figure 1, there is shown a schematic embodiment of a monitor system (10) for detecting physical activity, including heartbeat, associated with a baby. A cot (20) for a baby has underneath the mattress (30) a transducer arrangement (40). The transducer arrangement is exited by one or more physical activities associated with a baby, such as a heartbeat, breathing or limb movement, and produces a signal having components derived from or related to any such physical activities. The transducer arrangement (40) is coupled, via a suitable signal transmission medium to a cot unit (50). The cot unit (50) comprises circuitry for processing the signals received from the transducer arrangement (40) to distinguish between various forms of physical activity emanating from or associated with a baby in the cot (20). The cot unit can comprise an alarm or can be, directly or indirectly, connected to an alarm and can trigger the activation of an alarm (60) in the event that the signal from the transducer arrangement (40) indicates that at least a selectable one of a plurality of physical activities associated with the baby has changed or terminated. For example, the cot unit (50) may activate an alarm if a determination is made to the effect that the signal no longer contains a component indicative of heartbeat. Various thresholds can be set which monitor not only the presence of a particular component of the signal but also the level or rate of that component. The alarm (60) is typically located in a central location where it has a high probability of attracting the attention of a responsible adult during home use or nursing staff for hospital use. The alarm (60) may produce an audio output or a visual indication, for example, where it is undesirable to disturb other babies or patients in a hospital. In one embodiment, the transducer arrangement comprises a suitably flexible support board (70) (see Figures 2a to 2e) having a piezo-ceramic device (80) centrally disposed thereon which produces a voltage when stressed or flexed. The piezo-ceramic device (80) is in the form of a disc. Manufacturing the board from a suitable plastic can increase the sensitivity of the transducer arrangement as a whole to the physical activities of a baby. Preferably the support board is made from ABS plastic due to the low cost and ability to shape and work the plastic. Alternative embodiments can be realised in which the flexible board is manufactured from other plastics, metal, fibre board or hard board. Mechanical means are utilised which increase the sensitivity of the transducer arrangement to the movement of the mattress or baby by locating a fulcrum for the support board (70) directly below the piezo-electric element. The support board (70) is formed with a plurality of discontinuities, such as slots (90) (see Figures 2b to 2d). In a further embodiment (see Figure 2a) the support board (70) utilises an arrangement of U-shaped grooves (94) on at least one of either the top or bottom surfaces thereof. The discontinuities ensure that the board is flexible and so will readily distort in response to the physical activities of the baby while remaining strong enough to support the mattress (30) and a baby. Alternatively, the discontinuities can be a plurality of ribs (92) (see Figure 2e) which enable a more flexible board material to be used while the board is still strong enough to support a mattress and a baby. In a preferred embodiment (see in Figures 2b to 2d) the slots (90) are radially disposed with respect to a central portion of the support (70) board where the piezo device (80) is located. A further embodiment (Figure 2d) also comprises further slots (90) disposed around the periphery of the support board (70). In Figure 4d the support board (70) comprises a total of eight slots having at the ends thereof a hole which reduces the stresses conventionally associated with the slots. The support board (70) is generally rectangular although other shapes are also possible, for example square or circular Preferably the lower surface of the support board (70) is held in an elevated position above and not in contact with the bottom of the cot. This enables the support board to deform easily and so increases its sensitivity to physical activity. In the embodiments shown in Figures 2a to 2e, the degree by which the plastic support board (70) can flex is increased by using strategically placed feet (95) (shown in dotted lines) arranged to support the support board (70) such that movement thereof is not impeded by, for example, the bottom of the cot. The feet (95) are regularly disposed around the periphery of the support board (70) and one foot is centrally disposed so as to provide a fulcrum support for the piezo device. Therefore, as the baby moves, including breathing and heartbeat movements, the board flexes which, in turn, causes the piezo device to produce a signal indicative of such movement. The piezo device is situated at the position on the support board (70) which flexes the most and therefore stresses the piezo device the most. This position has been found to be typically the centre of the board, particularly if a fulcrum support is provided at the centre of the board. An alternative embodiment can be realised in which the feet are omitted. According to this alternative embodiment, the plastic support board is supported at its edges by the frame of the cot such that the board if free to flex and such movement is not impeded by the bottom surface, if any, of the cot. During deep sleep, the only physical activities which are present are the breathing and the heartbeat. Optionally, the support board (70) comprises a removable protective covering (not shown) to guard against damage, for example, by bodily or other fluids. The piezo-ceramic device (80) is connected to the cot unit (50) using a co-axial cable (100). Co-axial cable is preferred as it is less susceptible to mains interference than most cables. However, as an alternative, suitable screened twisted pair may be utilised. The cot unit is suitably programmed to determine whether or not it is necessary to sound the alarm. The presence or absence of the signals relating to heartbeat, breathing or limb movement can be utilised for monitoring the health of the baby or simply for monitoring whether or not the baby is present in the cot. For example, the alarm may be sounded as soon as a determination has been made that the breathing/limb movement and/or heartbeat signals are not present. A microprocessor or alternative electrical circuitry can be provided within the cot unit (50). However, other embodiments can be realised in which the processing is performed remotely by, for example, a computer. With further reference to Figure 1, in this embodiment which is suitable for monitoring a number of cots in a hospital ward, each cot unit (50) is connected via communication link (102) to a computer or a system controller (107). Also, a relay output unit (110) is provided under the control of the cot unit (50) and/or the system controller (107) to perform various functions, such as to lock the doors to a maternity ward to prevent a baby being stolen, send a signal to a pager informing the holder of the pager of the problem, or to sound an alarm. The system controller (107) receives and displays status information associated with a plurality of cots, each having its own transducer arrangement (40) and associated cot unit (50). The cot units (50) and the system controller (107) can operate an alarm independently. If the system controller ( 107) does not receive an appropriate response after interrogating a cot unit (50) via the communication link (102) it will go into alarm immediately. Likewise each cot unit (50) detects or monitors interrogation by the system controller (107) and will sound an alarm if it fails to be interrogated regularly. This will highlight hardware failure and guard against leads being cut. The cot unit can be arranged so that it can be deactivated by a security system such as a magnetic swipe card device (1 12) or a security key-pad device by an authorised adult that wishes to remove a baby from a cot without setting off an alarm. In the version of the monitor for domestic use it is useful for the cot unit to include an audio-microphone to detect audible sounds made by the baby. The cot unit can then also incorporate a radio transmitter which transmits a radio signal carrying the audible sounds plus any alarm signal to a remote radio receiving unit which incorporates a loud speaker. The receiving unit is mobile and can be carried by and located in the neighbourhood of an adult responsible for the baby. Therefore, if the baby cries, the crying noise will be transmitted by the receiving unit and the responsible adult can act appropriately. Further, if the heartbeat, breathing and/or limb movement activity of the baby ceases an audible alarm signal will be emitted by the receiving unit to alert the responsible adult to the danger. Although, the above embodiments have been described in relation to babies, it will be appreciated that the present invention can equally be applied to other living mammals such as adults, small children and even animals. For example, in a hospital for patients suffering from senile dementia or similar illnesses, the monitor system could be used to warn nursing staff when such patients get out of bed during the night. In this case, it may be necessary to use two transducer arrangements spaced apart under the mattress in order to reliably detect the presence of an adult patient.

Claims: CLAIMS 1. A sensor arrangement for monitoring physical activity associated with a living being, comprising a flexible board which distorts in response to physical activity and to which is fitted a transducer for converting distortion of the board into an electrical signal, characterised in that the board comprises discontinuities which enable parts of the board to distort somewhat independently of other parts of the board. 2. A sensor arrangement according to claim 1 characterised in that the discontinuities comprise a plurality of slots formed in the board. 3. A sensor arrangement according to claim 2 characterised in that the discontinuities comprise a plurality of grooves formed in the board. 4. A sensor arrangement according to any one of the preceding claims characterised in that the discontinuities are linear. 5. A sensor arrangement according to any one of the preceding claims characterised in that at least some of the discontinuities terminate adjacent to the transducer. 6. A sensor arrangement according to any one of the preceding claims characterised in that at least some of the discontinuities extend radially from the transducer. 7. A sensor arrangement according to claim 1 characterised in that the discontinuities comprise a plurality of ribs formed in the board. 8. A sensor arrangement according to any one of the preceding claims characterised in that the board comprises at least one support member for spacing the board away from a surface on which the board rests. 9. A sensor arrangement according to claim 8 characterised in that at least one support member forms a fulcrum for the transducer. 10. A sensor arrangement according to any one of the preceding claims characterised in that the transducer comprises a piezo-electric device. 11. A monitor system for monitoring physical activity associated with a living being characterised in that it comprises a sensor arrangement according to any one of claims 1 to 10.

Inventors: GIBBON PAUL WILLIAM, ROSS KEITH ALEXANDER, RUSSELL BRIAN ERIC, SMITH DEREK TRAVERS, GIBBON, PAUL, WILLIAM, ROSS, KEITH, ALEXANDER, RUSSELL, BRIAN, ERIC, SMITH, DEREK, TRAVERS
Applicants: GIBBON PAUL WILLIAM, MOVEMENT CONTROL SYSTEMS LIMIT, ROSS KEITH ALEXANDER, RUSSELL BRIAN ERIC, SMITH DEREK TRAVERS, GIBBON, PAUL, WILLIAM, MOVEMENT CONTROL SYSTEMS LIMITED, ROSS, KEITH, ALEXANDER, RUSSELL, BRIAN, ERIC, SMITH, DEREK, TRAVERS
Application year: 1997
Main classification: A61B5
IPC codes: A61B5, G01P13