Abstract:
An in-car video surveillance system for a law enforcement vehicle is automatically activated in response to a collision. The system is provided with an accelerometer having an axis of operation oriented to cause the accelerometer to be responsive to an impact, and an output signal is produced when the accelerometer senses a predetermined G force. A record command initiates operation of the video recorder of the system in response to the output signal to thereby record the incident responsible for the impact.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of a prior filed, co-pending application Ser. No. 60/513,488, filed Oct. 22, 2003, entitled ACCELEROMETER ACTIVATOR FOR IN-CAR VIDEO. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to a method and apparatus for automatically activating an in-car video surveillance system in response to a predetermined G force indicative of an incident that should be captured by the video system, such as a crash or collision that occurs in the course of a law enforcement operation.  
         [0003]     Vehicle mounted video cameras and accompanying recording equipment are widely used in law enforcement in order to make a video record of an incident or scene external to the law enforcement vehicle. For example, U.S. Pat. No. 4,949,186 to Peterson discloses a vehicle mounted system in which a video cassette recorder is housed in a vault located in the trunk of a patrol car. U.S. Pat. No. 5,677,979 to Squicciarini et al discloses a video surveillance system which integrates the outputs of a video camera, a radar unit, a wireless microphone and a remote control to produce a comprehensive video recording of an incident and accompanying data. More recently, digital video surveillance systems have been introduced which provide additional flexibility and advantages, including the ability to record on a hard drive shuttle or a DVD RAM disk. The newer systems utilizing digital media also include a history buffer that is recording at all times in order to ensure that activity occurring just prior to the activation of the system is recorded as well as post activation activity. The history buffer, being in continuous operation, ensures that the event that caused the officer to initiate operation of the recording system is included in the video record.  
         [0004]     Incidents in law enforcement occur, however, where the law enforcement officer may not be able to activate the video recorder. Although in most systems activation is automatic whenever the emergency lights or the siren of the vehicle are activated, crashes or collisions occurring suddenly and without warning may not give the officer time to respond, or the officer may be victim of the incident and unable to respond.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0005]     The aforementioned problem is addressed by providing automatic operation of an in-car video system in response to a crash or collision. An additional activator for the video system employs one or more accelerometers that, in response to a predetermined G force, deliver an output signal to the video system to instantly place the recorder in the record mode. Two accelerometers may be employed to provide response to forces acting generally in the front-to-rear direction of movement of the vehicle, and lateral forces on the vehicle from the side as would be experienced when a vehicle is struck from the side. An impact from any direction may be sensed to activate the recorder depending upon the orientation of the accelerometer or accelerometers.  
         [0006]     Other advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings, wherein is set forth by way of illustration and example, an embodiment of the present invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a block diagram of the activator and associated video recording system.  
         [0008]      FIG. 2  is an electrical schematic diagram of the circuitry of the activator.  
         [0009]      FIG. 3  is a plan view of a circuit board showing major components mounted and the orientation of the two accelerometers illustrated.  
     
    
     DETAILED DESCRIPTION  
       [0010]     Referring to  FIG. 1 , in an embodiment of the invention a voltage comparator  10  is responsive to the output of an X-axis accelerometer  12  and compares this output with a preset reference voltage from a potentiometer  14 , and delivers an output at  16  when the accelerometer output voltage exceeds the reference voltage. Similarly, a comparator  18  is responsive to a Y-axis accelerometer  20  and associated potentiometer  22  to deliver an output at  24  when the voltage from the accelerometer  20  exceeds the reference set by potentiometer  22 . A connector  26  receives the output from either comparator  10  or  18  and interfaces the circuitry with a video recording system  30  which includes a video camera  32  and accompanying audio sources, a controller  34 , a history buffer  36  for continuously receiving data from the camera  32 , and a recorder  38 . Typically, the camera  32  is directed forwardly through the windshield to view the scene in front of the vehicle, and may be accompanied by a second camera (not shown) pointed in a rearward direction to view the interior and occupants of the vehicle. The controller  34  is in a console (not shown) which may be mounted adjacent the rearview mirror for easy access by the driver of the vehicle. It will be appreciated that for simplicity, only those primary components of the system  30  concerned with the accelerometer activator are illustrated herein.  
         [0011]     The circuitry of the activator is shown in detail in  FIG. 2 . Each of the accelerometers  12  and  20  shown is a single monolithic IC containing a surface-micromachined sensor and signal conditioning circuitry to implement open loop acceleration measurement architecture. The IC illustrated is an Analog Devices ADXL190 and is capable of measuring both positive and negative forces up to 100Gs. The IC contains a switched-capacitor filter and all the circuitry necessary to drive the sensor and convert the capacitance change to a voltage output. The output is ratiometric to the supply voltage so tracking will occur if the supply voltage changes. The output voltage on lead  40  or lead  42  is a function of the acceleration or G force imposed and is calibrated to be 18 millivolts per G force. Although a particular IC is described and illustrated in the embodiment shown, other accelerometer configurations responsive to the G forces produced in a collision may be employed.  
         [0012]      FIG. 3  shows the layout of the circuit board for the activator with X and Y axes shown in broken lines and associated with the respective accelerometer IC  12  and  20 . The Y axis represents the front to rear direction of movement of the vehicle, and the X axis extends from side to side perpendicular to the Y axis. It is not required that the Y axis be on the front to rear center line of the vehicle. The circuit board  44  may be housed with the other components of the video system with the Y axis extending in a generally front to rear direction. The orientation of the axes illustrated and described herein provides high sensitivity to the expected impact forces, but other orientations of the axes may be employed if desired.  
         [0013]     Adjustment and operation of the section of the circuitry responsive to X-axis G forces is set forth as follows, it being understood that the Y-axis accelerometer  20  operates in identical fashion. Referring to  FIG. 2 , leads  46  and  48  from connector  26  apply positive supply voltage (typically 5 VDC) and ground to the circuitry. Accordingly, terminals  50 ,  51 ,  52 ,  53 ,  54 ,  74  and  76  are at 5 volts positive (all supply connections are not shown for simplicity). An EMI filter  56  and a current limiting resistor  58  are connected in series from lead  46  to the supply terminals. Lead  48  is connected to circuit ground via EMI filter  60 . Filters  58  and  60  are both shielded and the shields are connected to the chassis ground of the vehicle as schematically illustrated.  
         [0014]     A filter capacitor  62  is connected from supply terminal  51  (pins  13  and  14  of IC  12 ) to ground. (The associated resistor to pin  8  is not used in this application.) The output is presented at pin  10  and is connected via lead  40  to the negative input of comparator  10  and test point  64 . A lead  66  connects the positive input of comparator  10  to potentiometer  14  and a test point  68  and thus presents a preset voltage to the positive input via the voltage divider comprising series resistor chain  70 ,  14  and  72 . Comparator  10  is an operational amplifier configured as a voltage comparator.  
         [0015]     The circuitry associated with Y-axis accelerometer  20  and comparator  18  is identical to that as described above for X-axis accelerometer  12  and comparator  10 . Positive supply voltage is at terminals  74  and  76 . Test points  78  and  80  are provided. The two comparators  10  and  18  have common output leads  16  and  24  connected via an EMI filter  82  to a lead  84  from connector  26 . In operation using the ADXL190 IC, potentiometer  14  is adjusted to a preset voltage of 2.68 volts at test point  68 . Potentiometer  22  is adjusted to a preset voltage of 2.698 volts at test point  80 . These voltage levels establish a setting for activation of the comparators  10  and  18  when the outputs from the respective accelerometers  12  and  20  exceed these voltage levels, which correspond to a G force of 10Gs. Examples of settings for higher G-force activation are:  
                                                   X AXIS   Y AXIS                           30 G = 3.04 V   30 G = 3.058 V           20 G = 2.86 V   20 G = 2.878 V                      
 
         [0016]     It is assumed for purposes of illustration that operation is desired at the 10G level, and that an impact equal to or exceeding 10Gs occurs along the X axis. When the output of accelerometer  12  exceeds the preset voltage level of 2.68 volts, comparator  10  is activated and provides a current sink to ground via a pull-up resistor  86  (such as 10,000 ohms) to EMI filter  82  and lead  84  to connector  26 . The controller electronics (controller  34 ,  FIG. 1 ) respond to this logic low to deliver a record command to the recorder  38  and transfer the data in the history buffer  36  to the recording medium. This initiates the record mode function to make a record of the incident in the same manner as occurs automatically in conventional systems when the siren or emergency lights are activated, or upon manual selection by the operator. The same action in the circuitry associated with accelerometer  20  occurs in response to a 10G force in the Y direction that could be caused, for example, by a frontal impact, resulting in a logic low on lead  84  to the connector  26  to which the controller  34  responds.  
         [0017]     For test purposes to simulate a G force of 40Gs, a test point  90 , common to pin  9  of both accelerometers is provided. When 5 volts is applied to test point  90  across resistor  88  (10,000 ohms, for example), the 40G force is simulated and both accelerometers will then produce a voltage at their output pins  10  (leads  40  and  42 ) of approximately 3.19 volts. This voltage can be measured at test points  64  and  78  to ensure each accelerometer is functioning.