Abstract:
A method and apparatus of recognizing the presence of a passenger in front of a door of a transit vehicle comprises directing an ultrasound transmitter/receiver at a volume of space adjacent the door, emitting an ultrasound pulse into the empty volume, recording and integrating intensity of the echoes and storing the integrated value as a standard value, repeatedly emitting an ultrasound pulse into the volume, and comparing the integrated values to the standard value.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an ultrasonic method and system for detecting passengers at a door of a transit vehicle without the need to define a plurality of dead zones. 
     2. Description of Related Art 
     Present ultrasonic detection methods used to detect and respond to the presence of passengers in the vicinity of a bus or other transit vehicle doorway are based on first detecting and memorizing a signature table for a “standard” environment, for example, with the doors closed and no passengers or objects in the vicinity other than permanent equipment. The table consists of echo response times that define the echoes from permanent equipment. These times are represented by a one bit digitalization of the echo signal in a memory or register position corresponding to echo return time. The amplitude of the echo is not considered. See, for example, Kuhn U.S. Pat. No. 5,148,410 entitled “Sonar Detector for Exiting Passengers.” When a passenger or object not previously in the vicinity of the door causes an echo response at a time not previously recorded, the passenger or object is considered detected. If, however, the echo from a passenger or object occurs at the same time (within established tolerances) as previously memorized, the response is ignored. There is no way to discriminate that response from a response due to permanent bus equipment. In effect, the memorized responses with their tolerances represent “dead zones.” 
     Repeatedly integrating the echoes following shifted multiple echo pluses to discriminate targets that are straight-on from off-axis targets has been suggested in Magori U.S. Pat. No. 4,634,947 entitled “Method for Evaluating Echo Signals of an Ultrasonic Sensor on a Robot Arm.” 
     SUMMARY OF THE INVENTION 
     Briefly, according to one embodiment of this invention, there is provided a method of recognizing the presence of a passenger in front of a door of a transit vehicle comprising the steps of directing an ultrasound transmitter/receiver at a volume of space adjacent the door and generally directed at the floor in front of the door, emitting an ultrasound pulse via the transmitter/receiver into the volume of space while the space is not occupied by a passenger, recording the ultrasound echoes from objects in the volume of space for a response period, integrating intensity of the echoes during at least a fixed portion of the response period and storing the integrated value as a standard value, repeatedly emitting an ultrasound pulse via the transmitter/receiver into the volume of space, recording the ultrasound echoes, integrating the intensity of the echoes during the fixed period, repeatedly comparing the integrated values to the standard value such that when the standard value differs by a fixed value, a passenger is deemed to have entered the volume of space adjacent the door such that the door may be opened if appropriate. In a preferred embodiment, multiple ultrasound transmitter/receivers are directed at the volume of space adjacent the door and generally directed at the floor and integrated echoes received at each transmitter/receiver are summed. 
     Briefly, according to another embodiment of this invention, there is provided a system for recognizing the presence of a passenger adjacent to a door of a transit vehicle comprising an ultrasound transmitter/receiver directed at a volume of space adjacent the door and generally directed at the floor near the door, a controller for triggering an ultrasound pulse via the transmitter/receiver into the volume of space while the space is not occupied by a passenger, recording the ultrasound echoes from objects in the volume of space for a response period, integrating the intensity of the echoes during at least a fixed portion of the response period and storing the integrated signals. The controller is programmed to repeatedly emit an ultrasound pulse via the transmitter/receiver into the volume of space adjacent the door, to record the ultrasound echoes, and to integrate the intensity of the echoes during the fixed period. The controller is further programmed to repeatedly compare the integrated values to a standard. According to a preferred embodiment, multiple ultrasound transmitter/receivers are directed at the volume of space adjacent the door generally directed at the floor and the integrated echoes of all transmitter/receivers are summed. 
     According to a preferred embodiment, the response period is insufficiently long for an echo to be received from the floor. 
     According to yet another embodiment, multiple, separate response periods are recorded and integrated to establish standard values for each response period. 
     According to yet another embodiment, multiple response periods, at least one sufficiently long enough to receive an echo from the floor and one insufficiently long to receive an echo from the floor, are recorded and integrated to establish standard values for each response period. 
     In yet another embodiment, at preset multiple positions of the door as it is being opened and/or closed, the controller triggers an ultrasound pulse into the volume of space and records ultrasound echo signals for a short fixed response period, integrates the intensity of the echo signals, and stores the integrated echo signals as standards for an unobstructed doorway. The controller is further programmed for during door opening and/or closing to trigger an ultrasound pulse at the preset positions, record the echo signals during the short fixed response period, integrate the intensity of the signals and compare the integrated signals to the standard for each door position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates the placement of ultrasound sensors relative to a transit doorway according to one embodiment of this invention; 
         FIG. 2  is a diagram of a circuit for practice of one embodiment of this invention; 
         FIG. 3A  is a flow diagram illustrating the programming of the microcontroller according to one embodiment of this invention during the setup mode; and 
         FIG. 3B  is a flow diagram illustrating the programming of the microcontroller according to one embodiment of this invention during the monitoring mode. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to one embodiment of this invention, the entire echo signal is recorded and digitized for a given period of time. Multi-bit digitalization of the echo signal may be stored in multiple memory locations corresponding to echo return times. The entries in each location are summed or integrated. At the time of setup when no passenger or object is in the vicinity of the doorway, the sum total of the echo signal is stored as a standard or reference. This summing or integration takes into account amplitude as well as time. Since most real world targets cause multiple reflections instead of a single echo pulse at a single time after the output pulse, taking full account of amplitude verses time allows increased likelihood of detection. Appropriate algorithms may be used to repeat the setup to accommodate slow, environmentally-caused changes in the standard or reference. Such changes might be brought about by changes in temperature or humidity. Rapid changes would be considered indicative of a passenger. 
     Referring to  FIG. 1 , the inside face of a doorway is illustrated. The door has two sections  10 ,  12  that swing by reason of the well-known actuating assembly illustrated as a box  14 . The doors may be any of swing doors, bifold doors, slide-glide doors or parallelogram plug doors, for example. The door is illustrated with protruding handles  24 ,  26  for purposes of illustrating permanent objects that will reflect an ultrasound pulse. Mounted under the actuator assembly are three spaced ultrasound transmitter/receivers  16 ,  18 ,  20  directed downwardly toward the floor  22 . Ultrasound pulses emitted from the transmitter/receivers are directed in overlapping cones illustrated by lines on  FIG. 1 . 
     Referring now to  FIG. 2 , the three ultrasound transmitter/receivers (sensors)  16 ,  18  and  20  are connected to an electronic control unit  30 . The electronic control unit comprises a microcontroller  32 , three analog-to-digital converters  34 ,  35 ,  36 , a power supply  39  for the electric control unit  30  and for the transmitter/receivers. 
     The electric control unit  30  triggers ultrasound pulses via sensor control  38  and the transmitter/receivers  16 ,  18 ,  20  and then permits the transmitter/receivers to listen for echoes for a preset response period which may be established insufficiently long for an echo to be received from the floor. The received echoes are returned via the analog-to-digital converters  34 ,  35 ,  36  and the microcontroller  32  integrates the intensity of the echoes during at least a fixed portion of the response period and stores the integrated signal. 
     The microcontroller  32  is programmed to repeatedly trigger the transmitter/receivers to emit an ultrasound pulse into the volume of space adjacent the door. The controller is further programmed to repeatedly compare the integrated values to a standard. 
     Referring to  FIG. 3A , the microprocessor is programmed to operate in the setup mode to emit a trigger pulse or a plurality of trigger pulses at  40 , to receive echo signals caused from each pulse during a period of time which may be established insufficient to receive an echo from the floor at  42 , to integrate the echo signals at  44 , and store the integrated results as a standard at  46 . During the setup, it is necessary to adjust the length of time following a pulse that echoes will be received. This may be accomplished by measuring the distance from the transmitter/receiver to the floor and dividing by the speed of sound. As the speed of sound can vary slightly with ambient conditions, the time period should be somewhat longer or shorter than calculated from the measurement. This may be a first step  48  in the setup mode. According to a preferred embodiment, the setup is run for both the door closed condition and the door open condition enabling the determination of a passenger waiting to exit as well as whether a passenger has cleared the doorway. 
     Referring to  FIG. 3B , the microprocessor is programmed to operate in the monitoring mode to emit a trigger pulse or a plurality of trigger pulses at  50 , to receive echo signals caused from each pulse during a period of time insufficient to receive an echo from the floor at  52 , to integrate the echo signals at  54 , and compare the integrated results to a standard at  56 . If the integrated result is sufficiently close to the stored standard, control returns to emitting a new trigger pulse at  50 . If the integrated result is not sufficiently close to the stored standard, a signal indicative of a passenger present at the door is output at  58 . 
     Of course, the microprocessor may be programmed with additional tasks such as keeping track of whether the door is open or shut and for how long a period of time based upon additional inputs. 
     Having thus described our invention in the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.