DESCRIPTION OF THE PREFERRED EMBODIMENT

[0049] As generally described above, the device of the present invention has practical application in a number of situations. The device may be used to monitor the presence of a person, or animal, within a pre-defined space. The invention described may be used in hospitals or other medical facilities to monitor the occupancy of medical beds, chairs or other supportive structures whenever it may be useful to determine the status of occupancy of such structures. In addition to its use as a stand alone system in combination with such structures, it is possible that the sensing element capacitive array, through its inherently long service life, could be embedded in or under the surface materials of bed mattress covers and seating surfaces. In such fashion a medical facility would then only have to supply and interconnect the control/monitor module component. Equivalently, if appropriate, the entire monitoring system could become an integral component of an appropriate medical bed or chair on a permanent basis either by original manufacture or by retrofit.

[0050] Outside the hospital area, the present device may be used in nursing homes, intermediate and long-term care facilities, mental hospitals, and other similar institutions needing to track the presence of individuals. The invention is not limited to institutional use, but also has practical application as a single, stand alone device in addition to its potential for becoming a built-in device. Such applications could include in-home health care and presence monitoring for the increasing number of patients who choose to have medical care provided in their own homes.

[0051] Reference is made, therefore, to FIG. 1 for a description of a first embodiment of the current invention. FIG. 1 shows a schematic block diagram showing control/monitor module ( 10 ) for the invention interconnected through connections ( 12 ) and ( 13 ) to one embodiment of sensing element ( 14 ). Control/monitor module ( 10 ) is made up of several circuit components, including power supply ( 16 ). Power supply ( 16 ) may consist of an internal power source such as a battery, an external source with an appropriate feed to control/monitor module ( 10 ) or any other appropriate source of power known in the art.

[0052] Additional circuit components disclosed in FIG. 1 include driver/sensor circuit ( 18 ) which provides an appropriate driver current to capacitive array ( 26 ) contained within sensing element ( 14 ) and concurrently senses capacitive value changes produced within capacitive array ( 26 ) through dielectric shifts caused by the proximity or absence of the patient's body mass. Also disclosed in FIG. 1 is comparator/calibration logic circuit ( 20 ) which is preferably a microprocessor circuit containing embedded programming suitable to the applications described herein. Comparator/calibration logic circuit ( 20 ) interfaces with driver/sensor circuit ( 18 ) and alarm generation circuit ( 22 ) also contained within control/monitor module ( 10 ). In addition, comparator/calibration logic circuit ( 20 ) receives input data from system interconnection integrity circuit ( 24 ). Comparator/calibration logic circuit ( 20 ) continuously monitors the functions of driver/sensor circuit ( 18 ) both optimizing the appropriate driver current to capacitive array ( 26 ) embedded within sensing element ( 14 ) and equivalently continuously monitors and analyzes signal data from the driver/sensor circuit ( 18 ).

[0053] When the overall system is first activated comparator/calibration logic circuit ( 20 ) will determine, through the capacitive value readings it initially obtains, whether the overall system is correctly connected (through data derived from system interconnection integrity circuit ( 24 )) and, if such is the case, then whether a patient's body mass is already proximal to sensing element ( 14 ) or if the patient's body mass is absent. From the data derived from such capacitive value readings, comparator/calibration logic circuit ( 20 ) will set appropriate capacitive value calibration parameters which, when equaled or exceeded, would indicate the presence or absence of a patient's body mass from proximal contact with sensing element ( 14 ). Due to varying environmental conditions (humidity, the presence or absence of other grounded or nongrounded structures, body mass of the patient, etc.), that the capacitive elements ( 26 ) embedded within sensing element ( 14 ) may be subject to comparator/calibration logic circuit ( 20 ) may, as required, adjust the calibration of the capacitive value change parameters.

[0054] The principal signal characteristic utilized by comparator/calibration logic circuit ( 20 ) is not a direct analysis of capacitive change value derived from sensing element ( 14 ), but rather an analysis of the ratio comparing the inherent, resting “unoccupied” capacitance of sensing element ( 14 ) examined along side a capacitive value caused through a dielectric shift within sensing element ( 14 ) when a patient's body mass comes into contact with sensing element ( 14 ). It has been demonstrated through experimentation that a suitable ratio differential that provides accurate and reliable monitoring function by the invention, should be 3 to 1 or more.

[0055] The first embodiment of the invention utilizing sensing element ( 14 ), as shown in plan view in FIG. 1 , has experimentally produced an inherent, resting capacitance value of approximately 15 to 20 picofarads when the capacitive array conductive elements are each 2 inches wide by 30 inches long, separated by a dielectric interspace ( 28 ) of 2 inches. This overall array is embedded in polyester substrate matrix ( 30 ) of sensing element ( 14 ) whose overall dimensions are approximately 6 inches wide by 30 inches long. The proximity application of an adult human body mass to sensing element ( 14 ) as shown in FIG. 4 , has reliably produced capacitive value readings in excess of 250-300 picofarads or a ratio of 12 to 1 or more.

[0056] Existing materials utilized for capacitive array ( 26 ) manufacture may include copper film, aluminum film, silver/carbon conductive ink, etc. In a preferred embodiment sensing element ( 14 ) as shown in plan view in FIG. 1 and in cross-section in FIG. 2 , consists of 1 mil copper conductive film hermetically sandwiched between two 2.5 mil layers of inert polyester substrate ( 30 ).

[0057] Referencing FIG. 2 , the cross-sectional structure of sensing element ( 14 ) in general, and more specifically, the cross-section located at each connection point ( 13 ), is described in more detail. As indicated above, a metallic conductive film, 1 mil thick in the preferred embodiment, serves as capacitive array component ( 26 ). Capacitive array component ( 26 ) is hermetically sandwiched between two layers of inert polyester substrate ( 30 ). Connector ( 13 ) is a snap connection of the type that is typically used and referred to as an EKG connector. Attachment of snap connector ( 13 ) to conductive film ( 26 ) is made first by providing a circular window through polyester substrate ( 30 ) of a size sufficient to permit direct contact between the metallic components of snap connector ( 13 ) and the metallic conductive film, and then compressing the two-part components of snap connector ( 13 ) together so as to penetrate through conductive film ( 26 ) and compress a circular portion of conductive film ( 26 ) between the electrical contacting elements of snap connector ( 13 ). In order to provide further integrity to the connection, the electrical contacting elements of snap connector ( 13 ) may be soldered to the copper conductive film ( 26 ). Reinforcing layer ( 15 b ) is also configured with a window through which the electrically conductive components of snap connector ( 13 ) are allowed to protrude. The remaining portion of reinforcing layer ( 15 b ) adheres to the outer surfaces and edge of the sandwiched substrate/film/substrate layers as shown. This configuration provides not only an appropriate means for reinforcing the edge of sensing element ( 14 ) but also serves to seal the edge and the area around snap connection ( 13 ).

[0058] FIGS. 2 b and 2 c disclose yet another structural arrangement for sensing element ( 14 ) that under certain conditions would provide more optimal capacitive characteristics. In. FIG. 2 b, capacitive array elements ( 26 ) are divided into three components ( 26 a , 26 b , and 26 c ). These components are laid one on top of another so that they are concentrically arranged operating a very long interface edge for a relatively small linear geometry. The actual construction of sensor element ( 14 ) as described in FIGS. 2 b and 2 c is best seen in cross-section in FIG. 2 c taken along line B in FIG. 2 b . While the various array elements ( 26 a - 26 c ) are in fact vertically stacked, the resultant structure is such as to create a sequence of concentric, coplanar elements that function much in the same way as the above-referenced two-dimensional configurations. Interspaces ( 28 a and 28 b ) in this case would be layers of dielectric material such as, for example, the material utilized for polyester substrate ( 30 ). The primary requirement is that these layers be flexible and electrically insulative so as to create the electrical capacitive array described above.

[0059] Electrical connections for the embodiment shown in FIGS. 2 b and 2 c would be made as disclosed at connections ( 13 a , 13 b , and 13 c ). Capacitive elements ( 26 a and 26 c ) would, in this embodiment, function as a single electrical element of the capacitive array with element ( 26 b ) functioning as the opposite element. Connections ( 13 a ) through ( 13 c ) are made according to this arrangement.

[0060] Reference is again made to FIG. 1 for further details on the operation of the electronics of the present invention. As previously stated, when comparator/calibration logic circuit ( 20 ) achieves or exceeds a pre-defined high or low ratio limit set by its calibration circuitry in an ongoing manner, its logic circuit will determine whether control monitor module ( 10 ) enters a “resting”, “monitor”, or “alarm” state. Appropriate “hold” and “monitor activate override” commands to the logic circuit may be given by an external operator, such as a patient care giver through appropriate switches integral to the circuitry. Under its own command, the logic circuit will analyze the initial absence of a patient's body mass from sensing element ( 14 ) when first activated and will enter a resting or “hold” status. On proximity application of a patient's body mass to sensing element ( 14 ) logic circuit ( 20 ) will sense the increased capacitance value generated by driver/sensor circuit ( 18 ) and enter a “monitor” status mode. On removal of the patient's body mass from sensing element ( 14 ) and an equivalent appropriate ratio capacitance value decrease derived from driver/sensor circuit ( 18 ), logic circuit ( 20 ) will enter an “alarm” status mode. Should this “alarm” status exist for longer than a predetermined, operator programmed time delay, logic circuit ( 20 ) will instruct alarm generation circuit ( 22 ) to enter an “alarm” mode. The purpose of the operator programmed time delay, if required, is to prevent improper or false alarms being generated by the described device through the transient shifting by the patient of his or her body mass adjacent to sensing element ( 14 ). An “alarm” mode activation by control module ( 10 ) will trigger activity of nurse call relay circuit ( 32 ), which will in turn activate a medical facility's nurse call system ( 34 ) if so interfaced.

[0061] Should comparator/calibration logic circuit ( 20 ) ultimately require alarm generation circuit ( 22 ) to enter an alarm generation state caused by the absence of the patient's body mass from the sensing element, the alarm status so generated will be maintained, under normal circumstances, even though the patient reapplies his/her body mass to the sensing element following the generation of such an alarm. Such programming (which may be overridden by the caregiving operator) will dissuade the patient from frequently moving off and on the sensing element. Comparator/calibration logic circuit ( 20 ) may also be programmed to perform other functions as required (for instance, automatically shifting to a “monitor” mode from a “resting” or “hold” mode when the patient's body mass has been proximal to sensing element ( 14 ) for a defined period of time).

[0062] Driver/sensor circuit ( 18 ) is positioned in close attachment to sensing element ( 14 ) in order to reduce any extraneous electromagnetic field effects. Driver/sensor circuit ( 18 ) comprises circuitry appropriate for measuring the capacitance in capacitive array ( 26 ) and generating a variable frequency signal relative to the capacitance value. The variable frequency output thus encodes the capacitance value in a signal that is less susceptible to interference from extraneous fields. The signal can be provided through ordinary wire connections ( 12 ) in FIG. 1 back to control/monitor module ( 10 ).

[0063] Reference is now made to FIG. 3 for a detailed description of the structural nature of the system described schematically in FIG. 1 . Sensing element ( 14 ) is structurally much as described in FIG. 1 , being made of a flexible substrate ( 30 ) with embedded flexible capacitive array elements ( 26 ). Capacitive array ( 26 ) is separated by interspace ( 28 ). Substrate ( 30 ) effectively surrounds and encases capacitive array ( 26 ).

[0064] At each end of sensing element ( 14 ), as shown in FIG. 3 are reinforcing layers ( 15 a ) and ( 15 b ). These layers, as described generally above with respect to FIG. 2 , serve the dual purpose of reinforcing the attachment ends of sensing element ( 14 ) and sealing these ends at the same time. At a first end of sensing element ( 14 ), reinforcing layer ( 15 a ) covers the upper and lower surfaces of sensing element ( 14 ) and wraps around its edge much in the manner described in FIG. 2 with respect to reinforcing layer ( 15 b ). Hole or slot ( 11 a ) is punched through the entire structure (five layers) and is positioned to facilitate the attachment of a means for holding sensing element ( 14 ) to the patient's bed.

[0065] Likewise, reinforcing layer ( 15 b ) is positioned at an opposite end of sensing element ( 14 ) and wraps around the edge thereof in the manner described with regard to FIG. 2 . Hole or slot ( 11 b ) is punched through the layers of sensing mat ( 14 ) and provides a means for attaching this end of sensing element ( 14 ) to the patient's bed. In addition, hole or slot ( 11 b ) provides a strain-relief mechanism as described in more detail below.

[0066] Conductors ( 17 a ) and ( 17 b ) connect the array elements ( 26 ) to the electronics of the present invention through connection points ( 13 a ) and ( 13 b ). As described above, in the preferred embodiment, these connection points ( 13 a ) and ( 13 b ) constitute EKG-type snap connectors. These type of connectors provide a sufficiently rigid, yet removable electrical attachment. FIG. 3 a shows an alternative preferred embodiment and function of hole or slot ( 11 b ). To facilitate a strain-relief function on conductors ( 17 a ) and ( 17 b ), hole or slot ( 11 b ) is elongated and provides an aperture through which conductors ( 17 a ) and ( 17 b ) pass before connecting to connection points ( 13 a ) and ( 13 b ). In this manner, any strain on conductors ( 17 a ) and ( 17 b ) pulls at connection points ( 13 a ) and ( 13 b ) in a direction that is less likely to result in a disconnection.

[0067] In the preferred embodiment, driver/sensor circuit ( 18 ) is encased within a small enclosure immediately adjacent connection points ( 13 a ) and ( 13 b ). It is anticipated that in order to minimize external electromagnetic field influences, conductors ( 17 a ) and ( 17 b ), which are unshielded, would be relatively short. In the preferred embodiment, conductors ( 17 a ) and ( 17 b ) are approximately 3 inches in length. As indicated and described above, driver/sensor circuit ( 18 ) converts the capacitive values measured from sensing element ( 14 ) into a frequency output that is less susceptible to external electromagnetic field interference. This frequency signal is provided by way of connector ( 12 ) to control monitor module ( 10 ) as shown. In the preferred embodiment, connector ( 12 ) is a four-conductor telephone-type cable terminating in a removable plug insertable into an appropriate telephone-type jack in control monitor module ( 10 ).

[0068] In the preferred embodiment, control monitor module ( 10 ) comprises a box shell of dimensions approximately 4.50 inches high by 2.25 inches wide by 1.00 inches deep, surrounding the electronics described above. On the external surface of the module enclosure is provided guard ( 31 ) which serves the dual purpose of protecting and shielding control button ( 19 ) by way of cover panel ( 33 ) and acting as an attachment point for the module through strap slots ( 35 ). The attachment of monitor module ( 10 ) to the patient's bed is described in more detail below.

[0069] Control monitor module ( 10 ) includes, in the preferred embodiment, a piezoelectric acoustic sounder as is well known in the art for use with alarm systems and the like. Control monitor module ( 10 ) of the present invention, however, is structured so as to be capable of incorporating a piezoelectric device much larger than might normally be utilized in a modular enclosure of the size described above. This is possible because the resonance chamber for the piezoelectric sounder is incorporated into the wall structure of the control monitor module box. The cylindrical chamber normally associated with “off-the-shelf” sounders is eliminated and replaced with a chamber created by the front and back walls of the monitor module enclosure. This greatly reduces the amount of space required for a sounder with a high decibel output.

[0070] In addition, monitor module ( 10 ) retains a plurality of LED indicators as shown to provide the user (the care giver or nurse) with indications regarding the status of the system. According to the functions described above and below, monitor module ( 10 ) incorporates low battery indicator ( 21 ), check mat indicator ( 23 ), alarm indicator ( 25 ), monitor mode indicator ( 27 ) and hold mode indicator ( 29 ).

[0071] Monitor module ( 10 ) is connected by way of cable ( 37 ) to nurse call system connector ( 43 ). Connector ( 43 ) terminates in a standard phono jack ( 41 ) as is typically utilized in existing nurse call system connections. Connector ( 43 ) is intended to provide the electrical connection to nurse call system ( 34 ) shown above in FIG. 1 .

[0072] Control monitor module ( 10 ) in the preferred embodiment is powered by a 3 VDC power supply typically provided by two AA type alkaline or lithium batteries. The present invention may also operate off of an AC power source with an appropriate AC adaptor circuit. When operable through an AC adaptor, control monitor module ( 10 ) incorporates an automatic battery backup switch-over circuit to maintain operation of the device in the event of AC power interruption or failure. Such battery backup systems are well known in the art.

[0073] The low battery indicator ( 21 ) shown in FIG. 3 is connected to the electronics of the present invention so as to provide two stage indications of the internal power supply. Low battery indicator ( 21 ) is configured to begin blinking when the voltage of the internal power supply falls below 2.6 VDC. This would be indicative of a non-urgent need to replace the battery within the unit. A second stage low battery indication provided at LED ( 21 ) would occur when the power supply voltage falls below 2.48 VDC, indicating a more urgent need to replace the battery. In conjunction with the blinking low battery LED, an audible signal, as well as a closing (or opening as the case may be) of the nurse call connection would occur.

[0074] It should be noted that driver/sensor circuit ( 18 ) does not require a separate power supply to convert the capacitance values measured in sensing element ( 14 ) to a frequency shift values utilized by control monitor module ( 10 ).

[0075] Control monitor module ( 10 ) is designed to operate through manipulation of a single button to control its mode and status. The LED indicators described above are intended to provide a full system visual status identification and indication means for the user. There are two separate system integrity alarms that are incorporated into the electronics described above. The first involves a disconnected mat state that causes the check mat LED, the alarm, and the nurse call system to activate when the mat is not connected to the system. A second integrity alarm occurs when an internal electronic function failure occurs. When such an internal function failure occurs, all LEDs on control monitor module ( 10 ) are illuminated. In addition, the electronics of control monitor module ( 10 ) are configured so as to provide a means for indicating the presence of a battery when no LEDs are illuminated. Pushing control button ( 19 ) one time will also provide a single, short audible tone to indicate the presence of a battery within the system.

[0076] In general, control monitor module ( 10 ) is electronically configured to provide multiple alarm tones selectable by the user or installer. Five settings that include a “no audible alarm” state can be controlled and set by a standard DIP switch positioned within the enclosure. These DIP switch settings provide the user with the ability to select the delay time (the time between the sensing of an off-the-mat condition and the initiation of the alarm) and the duration and character of the alarm once it is activated. The electronics are configured so as to permit the selection of instantaneous alarm activation once an off-the-mat condition is detected, in which case, if the patient returns to the mat, the alarm is immediately silenced. Alternatively four or eight second delays between an off-the-mat condition and the alarm can be programmed. When such delays are utilized, it is preferable for the alarm to remain on even after the patient has returned to the mat. Utilization of the externally accessible time delay dip switch settings, as identified above, permit control monitor module ( 10 ) to conveniently and concurrently perform the dual roles of bed monitor or chair monitor as required.

[0077] In addition, the dip switches available to the user permit modification of a number of additional settings associated with the alarm and the type of system control monitor module ( 10 ) is utilized in conjunction with. The dip switches permit the selection of four different alarm tones for a particular control monitor module ( 10 ) so as to permit a care giver to distinguish between various patients within a single room or otherwise identify a particular patient by a particular type of alarm tone.

[0078] The dip switch settings also permit the user to time out the alarm tones for either a 30 second or two minute period of time. The switches also permit the user to select a completely silent alarm at the control monitor module while still utilizing and activating the existing nurse call system. Finally, the dip switches permit the system of the present invention to adapt to a normally open or a normally closed nurse call system, both of which are known in the art. These user accessible dip switch settings permit the system of the present invention, and in particular the control monitor module ( 10 ) of the system to be readily adaptable to any of a number of existing systems and environments within which the patient monitor is utilized.

[0079] The process of installing and activating the system shown in FIG. 3 is simple and straightforward. With the appropriate batteries installed and the connections between control monitor module ( 10 ) and driver sensor circuitry ( 18 ) in place, connections are made at ( 13 a ) and ( 13 b ) to sensing element ( 14 ). Three audible pulses are heard to indicate that the system has been switched on when this mat connection is made. Likewise, when this mat connection is removed, a single audible pulse indicates the system is off. Should control monitor module ( 10 ) be connected in like manner to a pressure sensitive switch array mat, two audible pulses are triggered. Control monitor module ( 10 ) then automatically continues to function in conjunction with the pressure sensitive mat with no external adjustment to its circuitry, in a manner identical to its function with the dielectric shift sensing mat of the present invention.

[0080] In the activation process, LED indicators on the front panel flash once to indicate their function and then the single LED hold indicator ( 29 ) activates. Once a patient is placed on the mat, the system will automatically enter a monitor mode after 15 seconds. Monitor mode may alternatively be immediately activated by pushing control button ( 19 ). The system may be switched back and forth between the hold and monitor mode by repeatedly pushing control button ( 19 ). It should be noted that the automatic activation of a monitor mode after 15 seconds, once a patient's body mass has been applied proximal to the sensing mat is different from earlier described and utilized circuits. In the present invention, the patient's body mass does not have to be removed from the sensing mat and subsequently returned to the sensing mat to reactivate the automatic monitor mode from the hold mode, once the hold mode has been manually activated. As long as the patient's body mass is consistently in contact with the sensing mat, the system will automatically enter the monitoring mode after 15 seconds with no necessity to remove the patient's body mass from the sensing mat and then reapply it.

[0081] It is anticipated that the system of the present invention can be installed with the elements shown in FIG. 3 or may be installed in conjunction with an existing nurse call activation system within the hospital. The switches within monitor control module ( 10 ) allow it to activate either a normally open or normally closed nurse call switch system.

[0082] Reference is now made to FIG. 4 for a detailed description of the placement of the apparatus of the present invention on the typical hospital bed. Bed ( 39 ) incorporates a plurality of side rails ( 38 ) that facilitate both the attachment and the use of the system of the present invention. Patient ( 40 ) is positioned on bed ( 39 ) as shown. As described above, the placement of sensing element ( 14 ) of the present invention is best made near the larger mass areas of patient ( 40 ). In FIG. 4 , sensing element ( 14 ) is positioned beneath the upper torso portion of patient ( 40 ). Sensing element ( 14 ) is placed beneath a mattress sheet or mattress cover (not shown) in an area beneath the upper torso of patient ( 40 ). Sensing element ( 14 ) is positioned on and held to the mattress of bed ( 39 ) through the use of elastic straps ( 9 a ) and ( 9 b ) as shown. In an alternative embodiment, a reverse side of sensing element ( 14 ) may be provided with adhesive material that allows the removable positioning of sensing element ( 14 ) on mattress ( 39 ) without permanent attachment to its surface. Various adhesives are well known in the art to permit such removable attachment of a flexible surface.

[0083] Positioned immediately adjacent to sensing element ( 14 ) is driver/sensor circuit ( 18 ). In the preferred embodiment both the enclosure and the circuitry associated with driver/sensor circuit ( 18 ) are sufficiently lightweight and flexible as to easily be suspended by connectors ( 17 a ) and ( 17 b ) along the side of mattress ( 39 ). It is anticipated that the mattress cover or mattress sheets (not shown) would partially cover driver/sensor circuit enclosure ( 18 ). Conductor ( 12 ) connects driver/sensor circuit ( 18 ) to control monitor module ( 10 ) which is more rigidly mounted at a position near the patient on the structural components of bed ( 39 ) or on the wall adjacent to the head of the patient's bed. Attachment to the wall is effected through the use of a wall mounted bracket that appropriately engages and retains strap slots ( 35 ).

[0084] Various mechanisms for the positioning and placement of control monitor module ( 10 ) are disclosed in FIG. 5 , FIG. 6 , and FIG. 7 . FIG. 5 discloses the manner in which control module ( 10 ) may be mounted on a patient's wheelchair through the use of mounting clip ( 70 ). The longer section ( 72 ) of wheelchair mounting clip ( 70 ) is slid over the flexible seat backing typically found on a patient's wheelchair, with the longer section ( 72 ) of wheelchair mounting clip ( 70 ) facing towards the front of the chair. Wheelchair mounting clip ( 70 ) is positioned in this manner close to one of the wheelchair handles. Control module ( 10 ) is then mounted on the shorter hook side ( 74 ) of wheelchair mounting clip ( 70 ) by inserting hook element ( 76 ) through lower strap slot ( 35 ) of control unit finger guard ( 31 ).

[0085] In the preferred embodiment, control monitor module ( 10 ) is attached to the wall adjacent to the patient's bed ( 39 ) by means of wall clip ( 80 ), shown in FIG. 6 , which in turn has been attached to the wall structure through the use of either screws, positioned through holes ( 88 ) in back plate ( 82 ), or through the use of double sided adhesive tape placed on the back of back plate ( 82 ). Front lip ( 86 ) of hook structure ( 84 ) protruding from clip ( 80 ) engages through top strap slot ( 35 ) of finger guard ( 31 ) to secure control monitor module ( 10 ) to the wall.

[0086] Yet a further, more secure, means for attaching control monitor module ( 10 ) to a wall adjacent the patient's bed is disclosed in FIG. 7 . Lockable wall clip ( 90 ) is attached to the wall surface in much the same manner as described above with respect to wall clip ( 80 ) shown in FIG. 6 . Lockable wall clip ( 90 ) is attached to the wall structure through the use of either screws, positioned through holes ( 98 ) in back plate ( 92 ), or through the use of double sided adhesive tape placed on the back of back plate ( 92 ). Protruding from back plate ( 92 ) of clip ( 90 ) is support plate ( 94 ) with extended edge ( 96 ) through which is positioned hole ( 99 ). Extended edge ( 96 ) of support plate ( 94 ) engages through top strap slot ( 35 ) of finger guard ( 31 ) to secure control monitor module ( 10 ). In this manner, hole ( 99 ) aligns with hole ( 97 ) positioned in cover panel ( 33 ) and permits the insertion of locking device ( 95 ) therethrough. Locking device ( 95 ) may be any of a number of well known devices designed to secure two objects through aligned holes. Small pad locks and plastic cable ties are typical examples.

[0087] An alternative method of positioning control monitor ( 10 ) adjacent to a patient's bed ( 39 ) is by attaching it to bed railing ( 38 ) by means of flexible attachment strap ( 7 ). Attachment strap ( 7 ) slips through strap slots ( 35 ) (shown in FIG. 3 ) and attaches control monitor module ( 10 ) to the bed in a position serviceable by care giver personnel. It is anticipated that the care giver would be the individual responsible for activating and monitoring the function of the system of the present invention so control monitor module ( 10 ) is positioned on the outside of bed rail ( 38 ). Finally, as described above, connector ( 37 ), which may be an electrical cord of any reasonable length, connects the system of the present invention to existing nurse call system connections. In the preferred embodiment, connecting cord ( 37 ) is completely detachable from control monitor module ( 10 ) through the use of any suitable, easy to use electrical connector (such as a modular U.S. style telephone connector) this enables connecting cord ( 37 ) to be completely removed from control monitor module ( 10 ) when such monitor module may be utilized as a mobile monitor—for instance on a patient's wheelchair—and where no connection is required between control monitor module ( 10 ) and a nurse call system connection.

[0088] It is anticipated that the flexible structure of the sensing element of the present invention permits large variations in the placement for association with a particular patient. The adaptability of the electronics of the system further permits use of a single sensing element structure in a number of applications with variations in the patient body mass that is brought in proximity to the sensing element.

[0089] In addition to being installed in environments where patient monitoring systems have not been in use, the structures of the present invention lend themselves to be retrofit into existing patient monitor systems previously based upon alternate sensing mechanisms. In many cases, existing electronics are already in place that provide the link between the patient monitor and the nurse's call system.

OPTIONAL SYSTEM COMPONENTS

[0090] One objective of the present invention is versatility of use in conjunction with a number of different nurse call systems installed within a number of different health care environments. FIGS. 8 through 15 provide various additional optional elements to the patient monitoring system that have specific advantages under certain conditions and patient environments. The objective of versatility is achieved through the consistent use of 4 and 6 wire modular phone jack connectors and the use of “pass-through” electronics that permit the devices to be “daisy chained” together into the system.

[0091] FIG. 8 is a plan view of an auxiliary alarm module ( 100 ) of the present patient monitoring system. Alarm module ( 100 ) incorporates means for providing specialized alarms in the vicinity of the patient as conditions might require. Module ( 100 ) provides (in addition to the alarm in the control monitor module ( 10 ) and the standard nurse call system alarm) a selectable extra loud tone or a voice announcement alarm. Module ( 100 ) is connected to the nurse call system output of control monitor module ( 10 ) of the present invention by way of 6 wire modular cord ( 102 ) and modular phone jack ( 104 ). Connection to the existing nurse call system is maintained through 6 pin modular output connector ( 106 ) in a manner described in more detail below.

[0092] Utilizing well known electronic circuits, module ( 100 ) provides the ability to switch between an extra loud tone and a voice announcement by way of switch ( 110 ). Both audible alarms are produced through speaker ( 108 ) positioned centrally in module ( 100 ). In either case the volume of the audible alarm selected may be incrementally varied between high and low levels through the use of volume switch ( 112 ). The extra loud tone generated as an alarm in module ( 100 ) is electronically established through well known tone generating circuits triggered by an alarm state as described in more detail below. The voice announcement alarm is likewise triggered by an alarm state as relayed by control monitor module ( 10 ) and provides a digitally recorded voice message appropriate for the particular patient's situation. Commands such as “please return to bed” may be digitally recorded to be played back upon the occurrence of an alarm event. To facilitate the recording of such customized commands, module ( 100 ) provides a play button switch ( 114 ), a record button switch ( 116 ), and a microphone ( 118 ). The electronic circuits for providing these functions are well known in the art and may typically be found in hand held digital voice memo recorders and telephone answering machines and the like.

[0093] Reference is now made to FIG. 9 for a general description of the various electronic circuit components that are incorporated into auxiliary alarm module ( 100 ). As indicated above, control monitor module ( 10 ) provides, by way of its output to the nurse call system, a switched indication of an alarm state. This is received into module ( 100 ) through 6 pin input connector ( 104 ). Depending on the position of mode select switch ( 110 ), the alarm condition trigger is provided either to loud tone circuit ( 120 ) or voice announce circuit ( 122 ). Whichever circuit is activated, the audible alarm is generated through the speaker ( 108 ) of module ( 100 ). In conjunction with generating the audible alarm, both loud tone circuit ( 120 ) and voice announce circuit ( 122 ) activate output relay ( 124 ) which duplicates the on-off state of the alarm condition provided by control monitor module ( 10 ). This on-off alarm condition state is output from module ( 100 ) through 6 pin output connector ( 106 ) where the system is again connected to the existing nurse call system as described above with the primary embodiment.

[0094] In addition to being installed in environments where patient monitoring systems have not been in use, the structures of the present invention lend themselves to be retrofit into existing patient monitor systems previously based upon alternate sensing mechanisms. In many cases, existing electronics are already in place that provide the link between the patient monitor and the nurse's call system. FIG. 10 describes just such a situation and indicates how the structures of the present invention can be retrofit to take advantage of the existing electronics in place and still provide the benefits of the improvements found in the present invention.

[0095] In place of control module ( 10 ) in the above described embodiment of the invention, interconnect adaptor module ( 50 ) connects with driver/sensor circuit ( 18 ). The structures of sensing element ( 14 ) and its capacitive array ( 26 ) with interspace ( 28 ) positioned within substrate ( 30 ) are basically as described above. Within interconnect adaptor module ( 50 ) is input data logic circuit ( 52 ) which in turn is connected with relay circuit ( 54 ). Both are provided with power from power supply circuit ( 16 ). Power supply circuit ( 16 ) also supplies power through interconnection ( 12 ) to driver sensor circuit ( 18 ).

[0096] Interconnect adaptor module ( 50 ) is connected to an existing switch-based monitor/control unit ( 60 ) through logic circuit ( 62 ) contained therein. Connection ( 64 ) therefore typically carries an on/off condition between interconnect adaptor module ( 50 ) and existing switch based monitor/control unit ( 60 ). Logic circuit ( 62 ) of switch based monitor/control unit ( 60 ) typically generates an electrical signal into connections ( 64 ) which, if the system were using a mechanical switch sensor would determine the opening or closing of contacts within that sensor. The driver current produced by logic circuit ( 62 ) might typically be 6-10 volts at 2-3 microamps. Should the contacts of a mechanical switch sensor be closed, thereby completing the driver circuit, logic circuit ( 62 ) of the switch based monitor\control unit ( 60 ) would signal and indicate a monitoring status mode within monitor/control unit ( 60 ). Should the switch sensor contacts open in such an arrangement, then by sensing an open circuit status, logic circuit ( 62 ) would in turn generate an appropriate status signal which would activate alarm circuit ( 66 ) and relay circuit ( 68 ) to effectively generate an alarm condition from monitor/control unit ( 60 ). This alarm status condition may or may not be interconnected with the medical facility's nearest call system as desired.

[0097] The principle effect of the described interconnect adaptor module ( 50 ) is to replace, in an electrically transparent manner, the contact points of a mechanical switch sensor with those of an appropriate relay circuit (most preferably of a solid state design) which will effectively imitate the mechanical switch sensor from the viewpoint of monitor/control unit ( 60 ). A capacitance shift value produced by sensing element ( 14 ), which might typically be 20 picofarads in a resting, unoccupied state, to 200 picofarads or more in an active occupied state is converted by driver/sensor circuit ( 18 ) to an equivalent frequency drop generated by an appropriate oscillator circuit imbedded in driver/sensor circuit ( 18 ). This oscillator driven frequency drop may typically be 100 kilocycles in a resting unoccupied state to 20 kilocycles in an active occupied state. This frequency shift signal is carried through conductive elements ( 12 ) from driver/sensor circuit ( 18 ) to input data logic circuit ( 52 ) within interconnect adaptor module ( 50 ). By analyzing this input frequency shift, the input data logic circuit ( 52 ) may determine the active/occupied status or equivalent inactive/unoccupied status of capacitive sensing element ( 14 ). This data is fed into relay circuit ( 54 ), also contained within interconnect adaptor module ( 50 , which will open or close its secondary conducting elements interfacing directly to logic circuit ( 62 ) of monitor control unit ( 60 ). In this manner, the alternative manufacturer's monitor control unit ( 60 ) may, through interconnect adaptor module ( 50 ) and driver/sensor circuit ( 18 ) directly interface, and equivalently and appropriately respond to status signals generated by the capacitive sensing elements of the present invention.

[0098] Those skilled in the art will also recognize that appropriate adaptor circuit modules could be incorporated in line with the patient monitoring system of the present invention in order to allow the use of switch based sensor mats in conjunction with the control monitor module ( 10 ) based system of the first preferred embodiment. Such a switch to capacitance adaptor circuit would receive the on/off input from a pressure sensing mat (for example) by sampling the open or closed status of the switching circuit at a preset sampling weight (for example, four samples per second). Appropriate, well known, circuit elements would respond to the on/off condition of the pressure sensing mat by generating a capacitance value at an output connection in one of two capacitance ranges. In the preferred embodiment, for example, a switch off condition in the pressure sensing mat could originate a 10 to 20 picofarad capacitance value at the connector output. Likewise, a switch on condition in the pressure sensing mat would generate a 750 to 1000 picofarad capacitance value. These capacitance values would be seen by the driver/sensor circuit of the present system and would be appropriately interpreted into a frequency signal for the control monitor module.

[0099] In similar fashion, appropriate circuits, well known in the art, could be inserted between other manufacturer's capacitance based sensing mats in order to bring the capacitance ranges for alarm conditions into line with the system of the present invention. As an example, an input capacitance value of 10 to 20 picofarads could translate directly to the same output capacitance range while an input capacitance range of 200 to 400 picofarads (would be translated to an output capacitance range of 750 to 1000 picofarads in order to match with the parameters of the system of the present invention).

[0100] FIG. 11 a and FIG. 11 b provide an optional mechanism for sensing the presence or absence of a patient within a predefined space such as a hospital bed, a wheel chair, or a hospital room toilet facility. The device disclosed comprises the use of a reflective energy beam such as is described in U.S. Pat. No. 5,471,198 entitled Device for Monitoring the Presence of a Person Using a Reflective Energy Beam, the disclosure of which is incorporated herein by reference. In the preferred embodiment an infrared (IR) sensor system is employed. Active IR sensing module ( 130 ) is designed to replace the capacitive sensor mat ( 14 ) described above. Otherwise the system components required for patient monitoring are the same as described above. Module ( 130 ) is connected to control monitor module ( 10 ) sensor input by way of modular cord ( 135 ) with terminal modular connectors ( 136 ) and ( 134 ). Modular connector ( 134 ) is plugged into modular jack ( 133 ) positioned on sensor module ( 130 ).

[0101] IR sensor module ( 130 ) incorporates bidirectional IR transmitters ( 132 a )/( 132 b ) and sensors ( 134 a )/( 134 b ) switchable by means of directional slide switch ( 136 ). In this manner the most appropriate orientation and attachment of module ( 130 ) can be achieved. In either case, electromagnetic waves are generated by IR transmitters ( 132 a )/( 132 b ), reflect off of objects (the patient) within the field of view, and are detected by IR sensors ( 134 a )/( 134 b ). In the preferred embodiment a selectable alarm delay time is provided to avoid false alarms for ordinary patient movement. This alarm delay selectability is provided by way of three position slide switch ( 138 ). Module ( 130 ) additionally provides an on indicator ( 140 ) and a low battery indicator ( 142 ). A sense indicator ( 144 ) is illuminated when an occupant is detected within the field of view.

[0102] FIG. 11 b describes the basic functional circuit elements provided in sensor module ( 130 ) to achieve the operation as discussed above. Control logic circuit ( 150 ), which in the preferred embodiment is a digital processor controls pulsed waveform generator ( 146 ) which in turn controls IR source ( 132 ) which generates the interrogating energy beam. The reflected beam is received back at IR sensor ( 134 ) whose output passes through a window comparator circuit ( 148 ) tuned to identify appropriate variations in the reflected signal indicative of an alarm or a no-alarm condition. When an alarm condition is detected due to the movement of a patient from the field of view for a selectable period of time (0 seconds, 4 seconds, or 8 seconds) control logic circuit ( 150 ) activates output relay ( 152 ) which provides the preferred on-off alarm condition described above in conjunction with the first preferred embodiments of the present invention. The sensor module ( 130 ) retains its own internal power source ( 154 ) as indicated and is powered on when this power source (battery) is installed. The sensor module ( 130 ) described is operable in three modes once powered. A first, passive, “hold” mode represents a standby condition prior to the sensing of an occupant in the field of view for the sensor. A second, “sense” mode represents the condition where an occupant has been sensed within the field of view and the sense indicator ( 144 ) is illuminated. The third, “alarm” mode occurs when the occupant leaves the field of view for at least a selectable period of time (the alarm delay). Under “alarm” conditions, an internal relay ( 152 ) is closed for ten seconds (an alarm condition that is output to the control monitor module) before returning to the “hold” mode.

[0103] FIGS. 12 and 13 disclose a further optional, in-line component of the patient monitoring system of the present invention designed to provide a record of alarm events and care giver response times. Elapsed time module ( 160 ), like auxiliary alarm module ( 100 ) described above, may be inserted into the system in-line between the control monitor module and the existing nurse call system. Elapsed time module ( 160 ) comprises modular cord ( 162 ) terminating in modular phone jack ( 164 ) for connection to control monitor module ( 10 ), or to a device such as auxiliary alarm module ( 100 ) which is connected to control monitor module ( 10 ).

[0104] Externally, module ( 160 ) is a simple device that is positioned in-line in the system, having output modular connector ( 166 ) for further connection of the existing nurse call system. On front panel ( 168 ) of module ( 160 ) is positioned IR window ( 170 ) which is transparent to IR transmitter ( 172 ) and IR sensor ( 174 ). This transmitter/sensor pair carries out data communication between module ( 160 ) and an external, IR communication capable, programmable processor. The function of elapsed time module ( 160 ) is understood from the schematic block diagram shown in FIG. 13 . Module ( 160 ) includes control logic circuit ( 175 ), which in the preferred embodiment is a digital microprocessor. Control logic circuit ( 175 ) receives the on-off alarm status of the overall system as communicated by control monitor module ( 10 ) through 6 pin input connector ( 164 ). Control logic circuit ( 175 ) functions in association with clock ( 176 ) as an event recorder by storing in memory ( 178 ) an array of event data comprising alarm state and time every time the alarm condition switches state. Thus, when an alarm condition is triggered control logic circuit ( 175 ) stores the date/time of the event and waits for the next change in alarm status, which will most likely be the deactivation of the alarm by the responding care giver. In this manner a record of patient movement and care giver response is maintained.

[0105] In the preferred embodiment, module ( 160 ) is provided with memory sufficient to maintain a record of 100 events. IR input/output ( 180 ) is provided to communicate or download this data from module ( 160 ) to a data processing device for reporting and analysis. In addition, the clock parameters may be set and reset through this same IR communication link. The circuitry and protocols by which this communication may be carried out are well known in the art and are now commonly used in conjunction with various data processing and data storage devices. As indicated above, elapsed time module ( 160 ) is an in-line device that duplicates the input alarm on-off state at an output relay ( 182 ) that provides this alarm state through 6 pin output connector ( 166 ) to the existing nurse call system ( 34 ).

[0106] FIGS. 14 and 15 describe yet another optional component operable in conjunction with the system of the present invention. Wireless remote alarm module ( 190 ) comprises two primary elements; wireless transmitter ( 192 ) and wireless receiver ( 194 ). Wireless module ( 190 ) is designed to function in the absence of an existing nurse call system, a condition that might be found for example within a residential home environment. In addition (or in place of) the alarm provided by the control monitor module ( 10 ) or the auxiliary alarm module ( 100 ), wireless module ( 190 ) provides a remote alarm activated by the sensor systems described above. The combination of wireless transmitter ( 192 ) and wireless receiver ( 194 ) is frequently utilized in the art as a wireless doorbell system or the like. Such radio frequency transmitters and receivers are capable of operating over short distances and provide a convenient means for signaling events within a residential dwelling. Transmitter ( 192 ) is connected to the system of the present invention in place of the existing nurse call system through modular cord ( 198 ) terminating in modular phone jack ( 202 ). One manner of operating transmitter ( 192 ) is by pushing button switch ( 196 ) in the manner typical for such signaling systems. A second manner of activating transmitter ( 192 ) is by using the on-off alarm state provided by the control monitor module ( 10 ) which is connected in parallel with switch ( 196 ) within transmitter ( 192 ). In either case, transmitter ( 192 ) generates a radio frequency signal that is readily detectable by wireless receiver ( 194 ). Receiver ( 194 ) is a self-powered RF tuned receiver that incorporates an alarm (or signal) relay which generates an alarm tone though speaker ( 200 ). System on and low battery indicators ( 204 ) and ( 206 ) are provided. In this manner, the remote alarm will be activated if either the patient signals the care giver by pressing button switch ( 196 ) on transmitter ( 192 ) or the control monitor module ( 10 ), in response to a condition from a sensor device, indicates an alarm on state in the system. A typical arrangement according to this function is shown in FIG. 15 wherein sensor mat ( 14 ), connected through driver sensor circuit ( 18 ) provides the patient occupancy state to control monitor module ( 10 ), which in turn relays this state to RF transmitter ( 192 ). Transmitter ( 192 ) operates as described above to send a signal to receiver ( 194 ) to alert the remote care giver of the alarm condition.

[0107] Reference is now made to FIG. 16 , FIG. 17 a , and FIG. 17 b for a description of an alternative mechanism for attaching conductors to the capacitance sensing mat of the present invention. FIG. 16 shows one end of sensing element ( 14 ) with connection points ( 212 ) and ( 214 ) appropriately positioned on capacitive array components ( 26 ). In the alternative embodiment described herein, connection points ( 212 ) and ( 214 ) are apertures cut into sensing element ( 14 ) for attachment of snap-on connector ( 210 ). Conductor ( 216 ) provides the electrical connection from snap-on connector ( 210 ) to the balance of the electronics of the system of the present invention. Connection points ( 212 ) and ( 214 ) each comprise holes or apertures through the layers of sensing element ( 14 ) as well as a concentric window through the upper layer of insulation on sensing element ( 14 ) through to the conductive components ( 26 ).

[0108] Reference is now made to FIG. 17 a for a detailed description of the structure of snap-on connector ( 210 ) as used in FIG. 16 above. Snap-on connector ( 210 ) is comprised of female snap component ( 222 ) and male snap component ( 220 ). Each of these snap components are positioned on flexible support structure ( 218 ). Support structure ( 218 ) is folded as indicated to permit female snap component ( 222 ) to mate with male snap component ( 220 ). The detailed structures of the snap components and their assembly is also disclosed in FIG. 17 a as is well known in the art.

[0109] FIG. 17 b shows in cross-sectional view the attachment of snap component ( 210 ) to sensing element ( 14 ) to provide electrical connection thereto. Sensing element ( 14 ) is shown in its multi-layer configuration comprising substrate layers ( 28 ) and conductive layer ( 26 ). Flexible support structure ( 218 ) retains and appropriately positions male snap component ( 220 ) below sensing element ( 14 ) and female snap component ( 222 ) coaxially above sensing element ( 14 ). In this manner snapping the components together creates pressure against conductive layer ( 26 ) through the window aperture described above in the upper substrate layer ( 28 ). Electrical connections provided by way of wire conductor ( 216 ) as described above.

[0110] Reference is now made to FIGS. 18 and 19 for a further alternative embodiment of the sensor structure of the present invention. FIG. 18 discloses in perspective view the implementation of the capacitive sensing elements of the present invention on the underside of a typical bed mattress cover. In this manner the sensing element component of the present invention is semi-permanently established on the patient's bed in a manner that eliminates the need to replace sensing elements after use. In the embodiment described herein, bed ( 39 ) is covered with mattress cover ( 240 ) having a generally planar top surface ( 242 ) surrounded by orthogonal wall components ( 244 ). As is typical in the art, an elastic band ( 246 ) is placed on the periphery of wall components ( 244 ) in order to secure the mattress cover to the surface of bed ( 39 ).

[0111] The capacitive sensing array in this embodiment comprises a pair of bands ( 248 a ) and ( 248 b ) made up of principal conductive ink deposited on an underside of mattress cover ( 240 ) as shown. Various durable conductive materials may be utilized for the deposited capacitive sensing array elements. Appropriate snap connectors ( 250 ) are positioned at terminal ends of each conductive band ( 248 a ) and ( 248 b ) as in a manner similar to that described above in conjunction with the disposable sensing element. In this manner electrical connections can be made to the under mattress cover sensing element at the side of the bed where wall panels ( 244 ) of mattress cover ( 240 ) extend down.

[0112] In FIG. 19 a more complete view of the printed conductive ink sensing elements ( 248 a ) and ( 248 b ) are shown. In this view the underside of top panel ( 242 ) of mattress cover ( 240 ) is shown flattened out. Side wall panels ( 244 ) are shown on either side bearing the terminal ends of conductive bands ( 248 a ) and ( 248 b ). Positioned at these terminal ends just inside of elastic band ( 246 ) are connectors ( 250 ) positioned as described above. The balance of the components of the present invention may be utilized in conjunction with the under mattress cover sensing element of this alternative embodiment.

[0113] Reference is now made to FIG. 21 for a brief description of an alternative embodiment of the mattress cover construction of the present invention. FIG. 21 shows a typical mattress cover for a hospital bed or the like in an inverted view showing the underside of the mattress cover that would normally be in contact with the mattress. In this view, mattress cover ( 300 ) comprises top panel ( 302 ) surrounded by side walls ( 304 ) shown in a construction well known in the art. Perimeter edge ( 306 ) may comprise an attachment or closure means such as a zipper or elastic band intended to secure the mattress cover either to a matching panel positioned below the mattress on the bed or simply to surround the mattress in a manner well known in the art.

[0114] In this embodiment the conductive sensor elements ( 308 ) each comprise a layer of silver oxide conductive ink ( 310 a ) and ( 310 b ) which adhere to the underside of top panel ( 302 ) of the mattress cover. Covering each of the layers of silver oxide ink ( 310 a ) and ( 310 b ) are carbon graphite impregnated rubber protective elements ( 312 a ) and ( 312 b ). These rubber protective elements ( 312 a ) and ( 312 b ) extend beyond the layers of conductive ink ( 310 a ) and ( 310 b ) and effectively seal a major portion of the conductive elements to the mattress cover.

[0115] Exposed on each end of each conductive element is an amount of silver oxide ink conductive material wherein snap connectors ( 314 ) are placed through the mattress cover as described in more detail below. Four of these snap connectors ( 314 ) are positioned as indicated in FIG. 21 .

[0116] FIG. 22 a discloses in cross sectional detail the layering of the sensor elements described above. Specifically, the top panel ( 302 ) of the mattress cover ( 300 ) is layered first with two silver oxide ink conductive elements ( 310 a ) and ( 310 b ) and then secondly is layered with carbon graphite impregnated rubber protective elements ( 312 a ) and ( 312 b ). In this manner the conductive sensor elements necessary for operation of the present invention are appropriately positioned and retained on the bed beneath the patient. The appropriate distance between the sensor elements is therefore maintained regardless of any movement of the patient on the mattress.

[0117] FIG. 22 b shows in cross sectional detail the structure of the end connector for each of the sensor elements. In this view mattress cover ( 300 ) is shown to comprise top panel( 302 ) and side wall ( 304 ). Side wall ( 304 ) retains the attachment mechanism ( 306 ) which in the preferred embodiment is an attachment zipper or elastic material. Silver oxide ink conductive element ( 310 a ) is shown adhered to the underside of top panel ( 302 ) and carbon graphite impregnated rubber protecting element ( 312 a ) is shown over conductive element ( 310 a ). A portion of conductive element ( 310 a ) is left exposed so that snap connector ( 314 ) may be attached there through to be exposed on the upper surface of top panel ( 302 ). This provides ready access for the caregiver to attach the remaining components of the present invention to the sensor element shown and described herein.

[0118] The fabric of the mattress cover described above may be any of a variety of different mattress cover materials already used in the industry. Typically, these mattress covers for hospital applications and the like consist of low friction nylon woven material as an outside surface bounded to a butyl rubber layer or urethane layer backing providing an inside surface. Adherence of the conductive materials described above to any of these standard mattress cover fabrics can be achieved by methods well known in the art.

[0119] The primary conductive elements of the present invention shown in this embodiment of the mattress cover comprise high density silver oxide ink of high electrical conductivity. This silver oxide ink is bonded to the backing of the mattress cover, typically in four inch wide bands separated by one-half inch. The protective rubber secondary element comprises a graphite impregnated rubber material that serves to provide abrasion protection to the primary conductive element. Foam core mattresses, for example, can have a significantly abrasive upper surface that might otherwise degrade or destroy the conductive sensor element. In addition, the protective rubber secondary element provides a stabilizing and supporting surface for the primary conductive element. Further, the graphite impregnated rubber provides a back-up secondary electrical conductivity material should any part of the primary conductive element fracture through use. It is therefore the combination of the two layers that serve as the complete electrical sensor element of the present invention.

[0120] The snap connectors shown in this alternative embodiment of the mattress cover structure are as described above with the previous embodiments. The snap connectors herein pass through the primary conductive element and the mattress cover to an access point on the outside surface of the mattress cover.

[0121] To permit the interconnection of capacitive sensing elements (such as those described above) with patient occupancy monitoring electronic controls that may already be present on a medical bed (such as those manufactured by Hill-Rom and others), an interface connector is needed and is described in FIG. 20 . Interface connector ( 260 ) consists of an appropriate female electronic connector ( 262 ), namely a Molex Part #03-06-2043, connected to an appropriate length of four conductor modular telephone cord ( 264 ). The fou