Abstract:
The disclosed invention uses two sensors to capture the heartbeat and environmental noises of an occupant of a vehicle or hospital bed. One of the sensors is placed on a seat or bed frame adjacent the occupant. A second sensor is placed remotely from the occupant, on a vehicle floor, or remote portion of the bed frame. A signal conditioning module is attached to the first and second sensors for detecting the heartbeat signal. Specialized software is used for processing the signal and decision making based upon the extracted heartbeat signal. The invention is capable of operating despite environmental noise and vibrations.

Description:
This application claims priority to U.S. Provisional Application Ser. No. 60/488,863, filed Jul. 18, 2003. 

   BACKGROUND OF THE INVENTION 
   The present invention relates to a heartbeat sensing system. More specifically to a heartbeat sensing system which is incorporated into a vehicle seat or hospital bed to monitor an occupant. 
   Heartbeat sensing systems are commonly used to monitor occupants of vehicles, beds, etc. The sensing systems can be used to detect the presence of an occupant. Often alarms are attached to the sensing systems to cause an alert in cases of heartbeat cessation, unusual heart rate activity, or occupant drowsiness. 
   Heartbeat sensing systems in vehicles are typically placed in an area that will be adjacent an occupant, for example, in a seat belt or seat. Vibration sensors are typically used to detect a heartbeat. In order for the heartbeat sensing system to be useful it must be able to detect the heartbeat separately from the environmental noise, such as the engine and/or road vibrations. 
   Heartbeat sensing systems in hospital beds may be attached to sheets or strips that are placed between the bed and the patient. While this type of monitoring system eliminates the need for wires directly on an occupant&#39;s body the monitoring system is susceptible to patient&#39;s movements. In addition, monitoring heartbeat during transportation of the patient can be difficult due to vibrations resulting from the transport vehicle that are picked up by the sensors obscuring the heartbeat. 
   Thus a heartbeat sensing system is needed that is unobtrusive to an occupant and which can filter out environmental noise is needed. 
   SUMMARY OF THE INVENTION 
   The disclosed invention uses two vibration or acceleration sensors to capture the heartbeat and environmental noises of an occupant of a vehicle seat or hospital bed. 
   One of the sensors is placed on a seat or bed frame adjacent the occupant. The first sensor will detect the heartbeat of an occupant, but the signal from the first sensor will also include environmental noise. The environmental noise could be vibrations from a running engine, vibrations from feedback from the road, vibrations created by movements of a patient, or movements of the bed, or the like. A second sensor is placed remotely from the occupant, on a vehicle floor, or remote portion of the bed frame. The signal from the second sensor will include the environmental noise, but will not significantly include the occupant heartbeat because it is placed in a location that will not significantly receive the heartbeat signal. 
   A signal conditioning module is attached to the first and second sensors for detecting and monitoring the heartbeat signal. The signal conditioning module includes a multi-level amplifier, a low pass filter, and a signal processing unit. Specialized software is used for processing the signal and decision making based upon the extracted heartbeat signal. The invention is capable of operating despite environmental noise and vibrations. 
   These and other features of the present invention will be best understood from the following specification and drawings, the following of which is a brief description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a first embodiment of the present invention showing a vehicle seat with the heartbeat sensing system; 
       FIG. 2  is a side view of a second embodiment of the present invention showing a hospital bed with the heartbeat sensing system; 
       FIG. 3  is a schematic showing the vibration signal mixing; 
       FIG. 4  is a heart beat spectrum showing before and after the environmental noise has been filtered; 
       FIG. 5  is an embodiment of a signal conditioning module; and 
       FIG. 6  is a flow chart of the operation of the heartbeat detection system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates a general view of a heartbeat sensing system  10  in a vehicle. A vehicle seat  12  is mounted on a vehicle floor  14 . A first sensor  16  is placed in the vehicle seat  12 . The first sensor  16  is preferably placed in a lower seat portion  18  on the seat frame  20 . A second sensor  22  is placed on the vehicle floor  14 . Seat support structure  24  supports the lower seat portion  18  on the vehicle floor  14 . Wiring  26  connects the first sensor  16  and second sensor  22  to a signal conditioning module  28 . The signal conditioning module  28  determines the heartbeat of the occupant in a manner described below and sends the heart rate to a response system  29 , which uses the heart rate as an input for determining a response. 
     FIG. 2  illustrates a general view the heartbeat sensing system  10  installed in a hospital bed  30 . The first sensor  16  is attached to a bed frame  32  near the likely position of the occupant&#39;s heart. The bed  30  may be a hospital bed, gurney, operating table, stretcher, or the like. A mattress or sheet  34  may be placed on the bed  30  between the occupant  36  and the first sensor  16 . The second sensor  22  may be mounted on the bed  30  in a position remote from the occupant&#39;s heartbeat. Both the first sensor  16  and second sensor  22  are connected to the signal conditioning module  28 , by means of wiring  26 . Bed support structure  35 , such as the frame and legs, separate the first sensor  16  and the second sensor  22 . The signal conditioning module  28  may be connected to a monitor  38  for monitoring the heartbeat. The signal conditioning module  28  and the monitor  38  may be mounted on the bed  30  such that wiring between the first sensor  16 , the second sensor  22 , the signal conditioning module  28 , and the monitor  38  is removed from sight. 
   In both the first and second embodiment the first sensor  16  receives vibrations from the heartbeat. However, vibrations from the environment may be received as well obscuring the heartbeat signal. The second sensor  22  is remote from the location of the occupant  36 . The second sensor  22  is preferably separated from the first sensor  16  by the support structure of the vehicle seat  12  or bed  30 . Because the second sensor  22  is remote from the occupant most of the vibrations received by the second sensor  22  will be from movement resulting from a vehicle running, or the rolling of the bed  30 , etc. 
     FIG. 3  shows a schematic of signal mixing that occurs. S 1 (t) represents the signal dominantly from the heart and S 2 (t) the signal from the vehicle floor  14  or the bed frame  32 . M 11 , M 12 , M 21  and M 22  are transfer functions from a first source  40  (the heart) to the first sensor  16 , first source  40  to the second sensor  22 , a second source  42  (the vehicle floor  14  or the bed frame  32 ) to the first sensor  16  and the second source  42  to the second sensor  22 . Using a digital signal adaptive filtering technique and the signals of the second sensor  22  as a reference, the environmental vibration signal can be suppressed from the vibration signal of first sensor  16 . 
     FIG. 4  is an example using adaptive filtering technique to extract the real heart beat signal, in which the first spectrum  44  is sampled by the first sensor  16  with an occupant  36  lying on a stationary bed  30 , or sitting in a non-running vehicle. The second spectrum  46  represents the signal from the first sensor  16  with occupant  36  lying on a moving bed  30 , or sitting in a running or moving vehicle. The third spectrum  48  is the result using adaptive filtering of reference signals sampled simultaneously by the first sensor  16  and the second sensor  22 . It can be seen the heart beat spectrum is recovered by this technique. 
   Some special concerns are paid to a signal conditioning module as shown in  FIG. 5 . This is because the analog signal, sampled by the first sensor  16  and the second sensor  22 , needs to go through a low-pass filter  50  before digitization for further adaptive filtering. However, a conventional physical filter cannot work correctly since the heartbeat signal is extremely small. Consequently, signal amplification is needed before filtering. On the other hand, gain cannot be set too high since the first sensor  16  is also subject to high levels of background vibration signals. The gain is designed such that the heartbeat signal is amplified at the point of first amplifier  52  just above the low threshold to allow for the working functionality of the low-pass filter. Signals pass to the low-pass filter with a cut-off frequency of 10 Hz, for example, after the first level amplification. Then the after-filtering signal is amplified by the second level amplifier  54  to the amplitude suitable for an A/D converter operation, performed by the signal processing unit  56 . An overload protection circuit is also integrated in the conditioning circuit. 
   The last portion of the signal conditioning module  56  is the signal processing unit  56  which completes the adaptive signal filtering based upon the transfer functions of  FIG. 3 .  FIG. 6  is a flowchart of the heartbeat detection system. Vibration signals from the seat  12  and floor  14  (or bed  30 ) are sampled through the sensors  16 ,  22 . Signal conditioning is performed as described above in step  70 . Blind source separation  72  and Principal Component Analysis and Independent Component Analysis  74  are then performed based upon the transfer functions ( FIG. 3 ). In step  76 , it is determined whether an occupant is present in the vehicle seat  12  (or bed  30 ) and the total number of occupants in the vehicle seats  12  (in the case of a vehicle seat  12 ). In step  78 , function activation occurs based upon the existence and/or the level of the occupant&#39;s heartbeat, such as activating an alarm  80 , climate control  82 , window control  84  and/or activating a transmitter  86  (such as calling for emergency assistance). 
   In vehicle seat  12  example of  FIG. 1 , for example, the function activation step  78  is the activation of the response system  29 , which may be an occupant presence detection system and/or a drowsiness detection system that alters the climate control system and/or generates an alarm based upon a determination that the alertness of the occupant has dropped below a predetermined threshold. One suitable drowsiness detection system is disclosed in U.S. application Ser. No. 10/348,037, filed Jan. 21, 2003, now U.S. Pat. No. 6,822,573, which is hereby incorporated by reference in its entirety. 
   The heartbeat detection system  10  may also be used to prevent solar heat or lack of oxygen accidents to children, disabled adult passengers or pets who may become trapped or are left waiting in a vehicle under extreme temperature conditions. The occupant heartbeat detection system  10  can be used to lower the windows in step  84 , trigger an alarm in step  80  or activate the appropriate the climate control system in step  82 . The occupant heartbeat detection system  10  may also be used during normal driving conditions to optimize climate control in the vehicle to provide the occupants with the desired comfort. In the case of a crash, the heartbeat data can be transmitted in step  86  to emergency service providers to provide them with information about the health conditions of the occupants. 
   Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.