MOVEMENT DETECTION APPARATUS

Abstract: A sensor (10) for sensing respiratory movement of a person which consists of a resilient pad (18), a rigid base (14), a flexible top (16) and a transducer (26). The pad (18) has an aperture (20) and a longitudinal trough (22) on one of its faces (18a) to accommodate the transducer (26). The transducer (26) is a piezo device and has a pair of elongated rigid members (24) attached to it. The rigid members (24) are accommodated within the trough (22) so that each has an inner end (30) attached to the transducer (26). The rigid members (24) impose a mechanical force upon the transducer (26) to produce an electrical signal therefrom in response to movement of the flexible top (16). The signal is applied to a processing circuit (12), which issues an alarm upon the cessation of respiratory movements to the sensor (10). The processing circuit (12) includes means to discriminate between signals representing respiratory movements and signals representing heart beat and other high frequency noise.

Description: "MOVEMENT DETECTION APPARATUS" THIS INVENTION relates to a movement detection apparatus for detecting repetitive low frequency movements and a sensor device for sensing a mechanical force applied thereto. Moreover, the invention is particularly applic¬ able to sensing respiration of a person and to actuate an alarm means if respiration of a person ceases. There has been much publicity in recent times of the "cot death syndrome" which has stupefied medical experts for some time and has defied solution. Accordingly, much concern has been generated amongst parents of new bom babies as to whether their child is a likely candidate for "cot death syndrome". With the advent of recent medical search into this syndrome, it has been discovered that certain children are more prone to the syndrome than others. However, the level of present medical research has not advanced to ' the stage of providing an adequate solution to the problem, even if a child is known to be highly susceptible to the unfore¬ seen cessation of respiration. Accordingly, it is an object of one form of the present invention to provide a sensor device capable of sensing a mechanical force applied thereto. It is a preferred object of the above form of the present invention to provide a sensor device which is capable of sensing movement caused by respiration of a person and providing an electrical signal in response thereto. It is another object of the present invention in its other form to provide a movement detection apparatus which is capable of detecting repetitive low frequency movements . It is a preferred object of the other form of the invention to provide a movement detection apparatus which is capable of detecting movement caused by the respiration of a person and actuating an alarm means in the absence of said respiration movement. In one form, the invention resides in a sensor device for sensing a mechanical force applied thereto comprising: a resilient pad member having opposing side faces, an elongated rigid member disposed upon one face of said resilient member and a transducer disposed in contiguous relationship with one end of said rigid member; wherein said transducer is capable of generating an electrical signal in response to the imposition of a mechanical force to said sensor causing deflection of said rigid member relative to said resilient member. Preferably, the sensor is provided with a flexible member overlying said rigid member and said one face, the other end of said rigid member being hingedly connected to said flexible member. Preferably, the sensor device includes a rigid base member to overlie said other face. In another form, the invention resides in a movement detection apparatus for detecting repetitive low frequency movements comprising: a sensor device to sense movement and generate an electrical signal in response to said movement, a signal processing means to process said electrical signal and generate an actuating signal in response to detecting a predetermined condition relating to said electrical signal, said processing means having a selector means to select only those electrical signals which conform to prescribed parameters for further signal processing by said signal processing means, and an alarm means to produce a sensorially perceptible signal upon generation of said actuating signal; wherein said predetermined condition accords with the • frequency of generation of said selected electrical signals falling below a prescribed lower threshold frequency. Preferably, the selector means includes a filtering means to significantly attenuate electrical signals having a frequency of generation above a prescribed frequency. Preferably, _ the selector means includes a signal conditioning means to condition said selected signals to facilitate further signal processing by said processing means. Preferably, the selector means includes a discriminating means to discriminate between selected signals of different frequencies at a generally low frequency, and reject said selected signals which have a frequency above a prescribed upper threshold frequency. Preferably, the selector means includes a timing means to time the period between said selected signals and generate said actuating signal when said period exceeds the period corresponding to said lower threshold frequency. Preferably, the sensor device is of a form as defined in the preceding form of the invention. The invention will be better understood in the light of the following description of several embodiments there¬ of. The description is made with reference to the accompanying drawings wherein:- Figure 1 is a schematic circuit diagram of a movement detection apparatus as described in the second embodi¬ ment of the invention; Figure 2 is a cross-sectional view of the sensor device as described in the first embodiment of the invention, as taken along line A-A of figure 4; Figure 3 is an underview of an upper portion of the sensor device shown at figure 2; and Figure 4 is an upper perspective view of a resilient pad of the sensor device as shown in figures 2 and 3. The first embodiment is directed towards a sensor device for sensing a mechanical force applied thereto, resulting from movement caused by the respiration of a person, and for providing an electrical signal output in response thereto. The sensor device 10 generally comprises a rigid base member 14, a flexible member 16, a resilient pad member 18, a pair of elongated rigid members 24 and a transducer 26. The resilient pad 18 is provided with a pair of opposing side faces 18a, 18b which are respectively overlaid by the flexible member 16 and the rigid base member 14, such that the resilient pad member 18 and the rigid members 24 are sandwiched between the rigid base member 14 and the flexible member 16. The one face 18a of the resilient pad 18 is provided with a central aperture 20 extending through to the other face 18b, and a longitudinal trough 22. The two rigid members 24 are accommodated within the trough to substantially span the extent of the one face 18a. Each rigid member has one end 30 thereof extending in a cantilevered manner into the aperture 20, and the other opposing ends 31 are in hinged connection with the flexible member 16. The hinge connections are formed by fasteners 28, such as double sided adhesive tape or the like, and are generally located towards the peripheral edge of the flexible member 16 and pad. The fasteners 28 allow a limited amount of pivotal movement relative to the resilient pad 18 as a consequence of movement of the flexible member 16. The ends 30 of the rigid members are arranged in close proximity and are maintained in contiguous relationship with the transducer 26, which is disposed within the aperture 20. Moreover, each of the juxtaposed ends 30 are maintained in flexible contact with the flexible member 16 by a resilient spacer 32, such as double sided adhesive tape or the like. Furthermore, the transducer 26 is attached to the underside of each of the juxtaposed ends 30 of the rigid members 24 by a resilient fastener 36, which may also be double sided adhesive tape or the like. The transducer 26 is in the form of a piezo-electric crystal, which is capable of producing an electrical output signal in response to a mechanical force applied thereto. Accordingly, it is intended that in use, a downward force exerted on the flexible member 16 will cause it to bend, thereby causing deflection of the rigid members 24 relative to the resilient pad 18. This action will in turn cause the resilient spacer 32 and the ends 30 of the rigid members 24 to pivot relative to each other and thus impose a mechanical force upon the transducer 26. Consequently, the transducer 26 will produce an electrical signal in the form of an output potential proportional to the extent of the mechanical force applied to the transducer. In the present embodiment, it is envisaged that the mechanical force exerted upon the sensor device 10 will be an abdominal force corresponding to the respiratory pattern of a person laying upon a bed mattress overlying the sensor device 10. Although the present embodiment describes a trough 22 disposed along the length of the resilient pad 18 and arranged to accommodate the pair of rigid members 24, it should be appreciated that any number or shape of troughs 22 and rigid members 24 could be used. The electrical potential produced by the transducer 26 is normally interfaced by known means (not shown) to a movement detection apparatus, one form of which is described in the precedi-ng embodiment. The second embodiment is directed towards a movement detection apparatus for detecting repetitive low frequency movements of the kind associated with the respiration of a person, and for actuating an alarm in response to the cessation of respiration. ' The movement detection apparatus, generally consists of a sensor device 10, one form of which is described in the proceeding embodiment, a signal processing means 12 and an alarm means 90, as shown in figure 1. The sensor device 10, is provided with a sensor output 50 which provides a current path from the transducer of the sensor device to the signal processing means 12. The signal processing means 12 has a selector means which essentially consists of a filtering means 52, a signal conditioning means 98, a discriminating means 68 and a timing means 74. The signal processing means is also provided with a fault detecting means 76 the opera¬ tion of which will be described in more detail later. The filtering means 52 receives the sensor output 50, and consists of a low pass filter having a cut off frequency set to substantially attenuate high frequency signals appearing above a prescribed frequency, e.g. 20Hz, which are to be disregarded by the signal processing means, but which may appear as electrical signals output by the transducer of the sensor device 10. For example, these high frequency signals may include stray mains frequency noise and other forms of interference. Accordingly, the filtering means 52 will allow electrical signals of frequencies in the order of the respiratory rate of a person to pass without or with little attenuation. For example, the filtering means would allow electrical signals having a frequency of up to about 20 Hertz to pass without attenuation. It should be noted, that the filtering means is required to receive electrical signals representing instantaneous respiratory movements of a person and not electrical signals representative of an average respiratory rate, as the former can be up to 10 time ' s the average rate of a persons respiratory movements. The filtering means 52 is provided with a filter output 54 which connects to the signal conditioning means 98. The signal conditioning means 98 essentially consists of an amplification means 56 and a pulse shaping circuit 64. The amplification means 56 is required to amplify the signals passed by the filtering means 52 to an acceptable level for signalling processing. The gain of the amplification means 56 can be adjusted by means of a potentiometer 58 connected thereto. In addition, the amplification means 56 operates to amplify relatively prominent signals, such as signals representing the respiratory movement of a person, to a much greater extent than comparatively weaker signals representing the heart beat of a person. The amplified signal is in turn input to the pulse shaping circuit 64 via the amplifier output 60. In addition, the amplified signal is connected to a visual indicator 62 such as an analogue voltage member or an incandescent lamp or the like. Thus, the visual indicator 62 provides a visual indication of the magnitude of an amplified signal which predominately indicates the presence of instantaneous respiratory move¬ ment of a person. By operating the potentiometer 58 in conjunction with the visual indicator 62, it is possible for a person to set the sensitiviy adjustment of the amplifying means 56 to an appropriate level to detect the respirations of a person. The pulse shaping circuit 64 incorporates a Schmitt trigger circuit, which is arranged to improve the shape of the amplified output signals received via the amplifier output 60, so as to produce a pulsed output signal having sharp edges. In addition the pulse shaping circuit 64 presents a threshold voltage level which must be attained by an incident signal thereto before an output pulse will be generated therefor. For example, any amplified signals input to the pulse shaping circuit via output line 60 having a magnitude falling between + or - one volt, will not be sufficient to cause the pulse shaping circuit to generate an output pulsed signal therefor. On the otherhand, incident amplified signals having a magnitude greater than + 1 volt and less than - 1 volt would be of sufficient magnitude to cause the pulse shaping circuit to generate an output pulse there¬ for. The aforementioned threshold voltage level is usually chosen with regard to the gain of the amplification means 56 and the magnitude of the electrical signal received from the sensor device 10. It is expected that, in use, the apparatus will be adjusted so that sensed breathing movement will produce an electrical signal at the sensor output 50, which would result in a pulsed output signal being produced by the pulse shaping circuit 64 representing respiratory movements, and in the absence of respiratory movement, no resultant signal would be input to the pulse shaping circuit having a magnitude exceeding the minimum threshold voltage level. However, in practice, the sensitivity of the device is sufficient to detect heart beat in addition to respiratory movements, which may not be desirable in certain cases. Accordingly, it is necessary to sometimes discriminate between signals representing respiratory movements and signals representing heart beat. Therefore, the pulse shaping circuit output 66 of the pulse shaping circuit 64 is subsequently connected to a discriminating means 68. The -discriminating means effectively discriminates between signals of slightly varying frequency, notwithstanding that these signals may be classified as low frequency signals in general. Essentially, the discriminating means is a timer intended- to time the period of an incident signal there¬ to, and reject signals having an instantaneous frequency greater than a prescribed upper threshold frequency. The discriminating means 68 is provided- with an associated potentiometer 72 to allow adjustment of the said upper threshold frequency. In accordance with the above described arrangement, it is possible to reject signals representing the heart beat of a person and accept signals representing respiration since generally the heart rate of a person is significantly greater than there respiratory rate. For example the respiratory rate of a baby which may be subject to "cot death syndrome", could be anything from thirty to sixty respirations per minute whereas the heart rate of the same baby may be in the order of 120 to 160 beats per minute. Accordingly, by setting the potentiometer to reject input signals having a frequency of greater than approximately 80 cycles per minute, signals representing the heart breat may be rejected and signals representing the respiration rate may be accepted. The discriminating means 68 provides the additional feature of setting the pulse width of an output pulse signal applied thereto via line 66, to range from about 40 milliseconds to about 90 milliseconds. The selected signal accepted by the discriminating means 68 is output via the discriminating means output 70. The dis¬ criminating means output 70 is in turn connected to the timing means 74 and the fault detecting means 76. In addition, a visual indicator 77 such as a light emitting diode is connected to the discriminating means output 70 to provide a visual indication of the presence of selected signals appearing therat. The timing means- 74 is configured to receive the selected signal at its reset input so that it is repeatedly reset in response to the receipt of each selected signal, which is the form of pulse. The timing means 74 is arranged to time the period between succes¬ sive pulsed selected signals which have an instantaneous frequency corresponding to a lower threshold frequency as set via a potentiometer 80 associated with the timing means. However, if the period between successive pulses, input thereto, exceeds a period inversely proportional to the lower threshold frequency, the timing means 74 outputs an actuating signal via diode 84 at its timing output 78. As should the apparent, the lower threshold frequency may be adjusted by means of the potentiometer 80. In practice, the period inversely proportional to the lower threshold frequency, is in the order of 13 to 20 seconds and hence if this period is exceeded from the time a pulsed selected signal is input to the timing means before a succeeding pulse selected signal is received, the timing means 74 will generate an actuating signal at its timing output 78. Accordingly, such a condition generally arises when the respiration of a person has ceased for an abnormal period of time. The timing output 78, is in turn connected to the alarm means 90 via the alarm input line 88. The timing means 74 is arranged to produce an oscillating actuating signal in response to an excessive period between succes- sive selected signals, to cause the alarm means 90 to generate an oscillating tone. The alarm means 90 is connected via alarm output 92 to a loud speaker 94 which provides a sensorially perceptible signal in the form of an audible oscillating tone, in response to the application of an oscillating tone from the alarm means. The fault detecting means 76 is arranged to provide a dual function. Firstly it is intended to provide a back-up to the timing means 74, wherein an auxiliary timing means is provided which also times pulsed selected signals, output by the discriminating means at the discriminator outputs 70. However, the auxiliary timing means is arranged to generate a further actuating signal when the period between successive selected, signals exceeds a further period which is in fact longer than the period corresponding to the lower threshold frequency. In this manner, in the event of failure of the timing means 74, the auxiliary timing means should generate an actuating signal at a time when it is apparent that the timing means 74 is in fact faulty. For example, the auxiliary timing means may produce a further actuating signal after 30 seconds has elapsed from the appearance of the last selected signal output at the discriminator output 70. The second function of the fault detecting means 76, is to produce a further actuating signal in response to an instantaneous pulsed selected signal having a pulse width obviously in excess of the width prescribed by the discriminating means 68. For example, the pulse width of selected signals output by the discriminating means is in the range of 40 milliseconds to 90 milliseconds. Therefore, the fault detecting means can be arranged to generate a further actuating signal if a pulse duration in excess of about of 150 milliseconds is detected, which obviously indicates that the discriminating means is faulty. The further actuating signal produced by the fault detecting means 76 is generally different to the actuating signal. Preferably, the further actuating signal is a continuous signal which does not oscillate, so that the further actuating signal may be applied via the diode 86 to the alarm input 88 causing the alarm means 90 to produce a monotone signal, and so can be distinguished from an oscillating tone produced in response to an actuating signal from the timing means 74. The diodes 84 and 86 electrically isolate the outputs 78 and 82 of. the timing means 74 and the fault detecting means 76 respectively. Thus, the activity of either output 78 or 82 will not affect the activity of the other. The alarm means 90 receives a further input 95 from the pulse shaping circuit output 66. A potentiometer 96 is connected in series with the input 95 and operates as a volume control for the alarm means 90. The connection to the pulse shaping circuit output 66 is intended to give an audible indication of a persons respiratory pattern as generated at the output of the signal conditioning means 98. Accordingly, the volume control is provided to allow adjustment of the volume of the loud speaker 94. The operation of the movement detection apparatus will now be described. The sensor device 10 is preferably located under a bed mattress upon which a person is lying. As the person respires, his body will rise and fall. This motion should send pressure waves through the bed mattress and to the sensor device 10. The pressure waves impinging on the sensor device 10 cause a mechanical force to be applied to the piezo-electric crystal of the transducer 26 which consequently generates an output potential as described in the preceding embodiment and thus inputs an electrical signal via the sensor output 50 to the signal processing means 12. The electrical signal input via the sensor output 50 is then filtered by the filtering means 52 to remove relatively high frequency components that may appear as noice, interference or the like. The filtered signal output from the filtering means 52 is then amplified by the amplification means 56, in accordance with the setting of potentiometer 58. The adjustment of the potentiometer 58 is determined by watching the visual indicator 62 and adjusting the potentiometer 58 until the visual indicator 62 shows the presence of a signal corresponding to the respiratory pattern of the person laying upon the sensor device 10. It is intended that by this adjustment the signal at the amplifier output 60 predominantly comprises a signal corresponding to the instantaneous respiratory rate of the person. Subsequently, the pulse shaping circuit 64 shapes the amplified signal input thereto via the amplifier output 60, subject to exceeding the threshold voltage level as previously described. The resultant signal generated at the pulse shaping circuit output 66 is an oscillating signal representing in combination the instantaneous frequency of respira¬ tion of the person laying on the bed mattress above the sensor device 10, together with a signal representing the heart rate of the person. " The frequency of the resultant pulsed output signal is measured by the dis¬ criminating means 68 and the associated potentiometer 72 is adjusted to set an upper threshold frequency of approximately 0.8 Hz to 2.7Hz, above which signals shall be rejected and below which signals shall be accepted, and output the same as pulsed selected signals via output line 70. These selected signals are then applied to the timing means 74 to reset the same. If the period of a pulsed selected signal is too long, e.g. more than about 17 seconds, as determined by the potentiometer an actuating signal will be generated at the timer output 78. A time delay of about 17 seconds is generally allowed since it is reasonably common for babies to stop respira¬ tion for several seconds and then resume respiring again. The potentiometer 80 is adjusted to reduce the occurrence of false alarms, that may otherwise occur. The actuating signal is input to the alarm means 90 via input line 88 to effect operation of the loudspeaker 94, as described hereinabove. If the timing means 74 does not produce an actuating signal after a period of time greater than say 30 seconds, then the fault detecting means 76 will generate a further actuating signal. In addition, if the pulsed selected signal has a pulse width greater than approximately 150 ms, the fault detecting means 76 will generate a further actuating signal to actuate the alarm means 90 and operate the loudspeaker 94. This further actuating signal is generated in the preceding circumstances since it would be abnormal for a selected signal to have a pulse width of greather an about 150 ms, and therefore must indicate some form of malfunction. Thus, the fault detecting means 76 is intended to actuate the alarm means 90 in response to a detected malfunction. Modifications and variations such as would be apparent to a skilled addressee are deemed within the scope of the present invention. For example, the alarm means 90 could be arranged to activate a visual alarm to give a visual and/or audible indication of an alarm condition. It is intended that the apparatus of the present inven¬ tion be battery powered although it is understood that alternative supplies of power could be used.

Claims: THE CLAIMS defining the invention are as follows:- 1. A sensor device for sensing a mechanical force applied thereto comprising: a resilient pad member having opposing side faces, an elongated rigid member disposed upon one face of said resilient member and a transducer disposed in contiguous relationship with one end of said rigid member; wherein said transducer is capable of generating an electrical signal in response to the imposition of a mechanical force to said sensor causing deflection of said rigid member relative to said resilient member. 2. A sensor device as claimed at claim 1, wherein the sensor is provided with a flexible member overlying said rigid member and said one face, the other end of said rigid member being hingedly connected to said flexible member. 3. A sensor device as claimed at claim 1 or 2, wherein the sensor device is provided with a plurality of rigid members to substantially span the extent of said one face. 4. A sensor device as claimed at any of the preceding claims, wherein the sensor device includes a rigid base member to overlie said other face. 5. A sensor device as claimed at claims 2 and 4, wherein the resilient pad member and the elongated rigid member are sandwiched between said rigid base member and said flexible member. 6. A sensor device as claimed at any of the preceding claims, as dependent upon claim 3, wherein the resilient pad member has an aperture in which the transducer is located, said transducer being attached to the under¬ sides of the respective said one ends of the elongated rigid members by a resilient fastener. 7. A sensor device as claimed at any of the preceding claims, wherein the resilient pad member has a trough located in said one face to accommodate said elongated rigid member. 8. A sensor device substantially as described herein. 9. A sensor device substantially as described herein with reference to the accompanying drawings. 10. A movement detection apparatus for detecting repetitive low frequency movements comprising; a sensor device to sense movement and generate an electrical signal in response to said movement, a signal processing means to process said electrical signal and generate an actuating signal in response to detecting a predetermined condition relating to said electrical signal, processing means having a selector means to select only those electrical signals which conform to prescribed parameters for further signal processing by said signal processing means, and an alarm means to produce a sensorially perceptible signal upon generation of said actuating signal; wherein said predetermined condition accords with the frequency of generation of said selected electrical signals falling below a prescribed lower threshold frequency. 11. A movement detection apparatus as claimed at claim 10, wherein said selector means includes a filtering means to significantly attenuate electrical signals having a frequency of generation above a prescribed frequency. 12. A movement detection apparatus as claimed at claim 10 or 11, wherein said selector means includes a signal conditioning means to condition said selected signals to facilitate further signal processing by said processing means. 13. A movement detection apparatus as claimed at claim 12, wherein the signal processing means includes a fault detecting means to generate a further actuating signal if the instantaneous duration of a conditioned selected signal exceeds said period corresponding to said lower threshold frequency. 14. A movement detection apparatus as claimed at any of claims 10 to 13, wherein said selector means includes a discriminating means to discriminate between selected signals of different frequencies at a generally low frequency, and reject said selected signals which have a frequency above a prescribed upper threshold frequency. 15. A movement detection apparatus as claimed at any of claims 10 to 14, wherein said selector means includes a timing means to time the period between said selected signals and generate said actuating signal when said period exceeds the period corresponding to said lower threshold frequency. 16. A movement detection apparatus as claimed at claim 15, wherein said signal processing means includes an auxiliary timing means to time the period between said selected signals and generate a further actuating signal when said period exceeds a further period, said further period being longer than said period corresponding to said lower threshold frequency. 17. A movement detection apparatus as claimed at any of claims 10 to 16, wherein the sensor device is as claimed at any of claims 1 to 9. 18. A movement detection apparatus substantially as herein described. 19. A movement detection apparatus substantially as herein described with reference to the accompanying drawings.

Inventors: BENKENDORF RITA, BENKENDORF RUDIGER, BENKENDORF, RITA, BENKENDORF, RUDIGER
Applicants: BENKENDORF RITA, BENKENDORF RUDIGER, BENKENDORF, RITA, BENKENDORF, RUDIGER
Application year: 1985
Main classification: G01P13
IPC codes: A61B5, G01P13