Abstract:
A method and apparatus are described for detecting obstacles in the “blind spot” of a motor vehicle&#39;s side mounted mirrors. Advantageously, the inventive apparatus is mounted on the vehicle as an attachment to the side mirror system or adjacent to it. The invention determines the presence of an obstacle in a sensing volume that encompasses the “blind spot”. The invention relies on the time-of-flight measurement of preferably short infrared pulses to locate obstacles. Multiple sensors are used to provide area coverage. If any sensor detects an obstacle within its predefined range limits then an indication is provided by a display unit at the side mirror location. The system can be used on both sides of the vehicle and each side operates independently.

Description:
This is a continuation of application Ser. No. 08/964,639 filed Nov. 5, 1997 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     Present day vehicular traffic in many areas can often be characterized as high density and high speed. Multilane highways afford the opportunity for passing on both sides of a vehicle, and aggressive drivers commonly weave their way through traffic, changing lanes many times in the process. Speed limits have been increased in many localities throughout the country. All this places demands on the driver to be aware of the surroundings and to be alert to changes which can happen quickly. It is also well known that side mounted mirrors have “blind spots” where overtaking vehicles may go undetected. 
     SUMMARY OF THE INVENTION 
     With the above considerations in mind, a system which could provide information to the driver prior to a lane change, on vehicles in the “blind spot” of the mirror system, would provide an additional measure of safety. Furthermore, if this system could be incorporated into or added onto the existing structure of the side mounted mirror and provide visual indication to the driver when the side mirror is viewed, then the device would require no additional driver actions beyond what is normally performed in a lane change. 
     The method and apparatus of the present invention detects the presence of objects within a sensing volume that encompasses the “blind spot” of the side mirrors provided on all vehicles. The “blind spot” of the side mirror system is a property of the vehicle body design, the mirror position and the viewing position of the vehicle operator. The sensing volume is defined as the volume covered by one or more sensing beams, each of which detects the presence of obstacles along its line of sight within a given distance and spatial location. The number of beams, directional orientation and beam width are arranged to provide indication of any obstacle above a minimum size corresponding to a motor vehicle or motorcycle, that may be present in the sensing volume, which itself covers the vehicle&#39;s “blind spot” to the rear and side of the vehicle. 
     Preferably, the invention is implemented in a system comprising a control unit and multiple transmitting and sensing units that working together (1) locate objects along the lines-of-sight of the respective sensing elements, (2) by time-of-flight or time interval analysis calculate the distance to the sensed object, and (3) provide indication of objects within a predefined sensing envelope or spatial location. 
     Advantageously, the system is implemented using pulsed infrared laser transmitters, photodiode receiver circuits including amplification and signal conditioning, a digital clock for elapsed time measurement, one or more digital signal processors or microprocessors for system control and algorithm realization, and a display module for indication of sensing volume status or presence of an obstacle. 
     The invention relies on the principle of the time-of-flight or elapsed time measurement of short infrared pulses to determine the distance, on a suitable algorithm to filter the result through a range gate corresponding to a selected range along the line of sight, and on multiple sensing beams to provide full target area coverage. 
     Additionally the system provides visual display at the location of the vehicle side mounted mirror permitting simultaneous viewing of the mirror image of the roadway and the indicator display of the present invention. 
     These and other objects, features and advantages of the invention will be more readily apparent from the following detailed description in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a functional block diagram of the preferred embodiment of the invention; 
     FIG. 2 is a flow chart illustrating the processing of information within the system; 
     FIG. 3 is a schematic depicting the area of coverage of a multiple rangefinder system; and 
     FIG. 4 is a schematic outline of the invention as appended to the side mirror structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 1, the system of the present invention comprises a main control unit  100  and at least one, and preferably several, rangefinder units  200 . Each rangefinder unit comprises a pulse transmitter,  10 , a pulse receiver  20 , a signal conditioner  30 , a clock  40 , a counter  50 , an averager  60  and a range gate discriminator  70 . 
     Control unit  100  sets the firing sequence of the individual units, stores data from the rangefinder units, provides system analysis and provides output for display of status in the display unit  300 . Illustratively, control unit  100  is a conventional microprocessor, microcontroller, or a digital signal processor. 
     Each individual rangefinder unit  200  measures the distance to objects in its sensing direction through the measurement of the elapsed time-of-flight of a short infrared pulse. Each transmitter  10  projects a narrow beam infrared pulse  12  and each receiver unit  20  detects reflected return pulses  14  from an obstacle  80  and provides initial amplification. Illustratively, each transmitter operates at a pulse repetition rate of 60 kHz, so that a single pulse is emitted every 16.7 μseconds. Return signals are amplified and gain adjusted in signal conditioner  30 , in order to provide a uniform return signal for further analysis. A digital clock  40  and a counter  50  are used to determine the time interval between the initiation of the transmitted pulse and the return of the reflected pulse. In particular, a signal from transmitter  10  causes counter  50  to begin counting clock pulses when an infrared pulse is emitted by the transmitter; and a signal from receiver  20  through signal conditioner  30  causes counter  50  to stop counting when the reflected pulse is received by receiver  20 . The count is then provided to the data averager  60 . The data averager  60  collects and stores the average of a predetermined number of successive readings, for example, ten. The average reading is provided to the range gate  70 , which tests the reading to determine if it falls within the preset sensing limits. If the output for any single one of the rangefinder units  200  represents a return signal from a distance which falls within the range gate window for that rangefinder, then the control unit  100  provides an indication in display unit  300  that an obstacle  80  is within the sensing volume. 
     Advantageously, each transmitter unit  10  is an infrared laser diode that produces a fast rise time pulse. The measurement of the distance to an obstacle using the elapsed time for a pulse to be transmitted to an obstacle, and returned to the receiver by reflection from the obstacle, is dependent, in part, on the temporal width of the pulse. Since the return pulse has been distorted due to reflection from the obstacle, there is a potential error in the measurement of the elapsed time interval of the order of the width of the pulse itself. To minimize this error, a short temporal pulse is desirable. Since light travels approximately one foot per nanosecond, a pulse width of 5 nanoseconds, for example, would correspond to a maximum distance error of 2.5 feet, since the distance traveled by the light pulse is twice the distance between the source and the obstacle. For this reason pulse width is of the order of five nanoseconds or smaller. A beam width of approximately 10 degrees is formed. Advantageously, the receiver  20  is a photodiode or avalanche photodiode, and the signal conditioner  30  provides a uniform response to reflected pulses that are received by the receiver. 
     Display unit  300  has visual displays preferably utilizing light emitting diodes (LEDs) which indicate power on, no obstacle present in the sensing volume, or obstacle present in the sensing volume. These conditions respectively are indicated by energized LEDs of yellow, green and red color, permitting instantaneous reading of sensing volume status. The LEDs can be continuously lit or blinking. 
     The time reading of the transit time of the reflected pulse constitutes the basic measured parameter of the system. The time measurement of each rangefinder is used as a measure of the distance to the obstacle that reflects the transmitted pulse. 
     A flowchart depicting the operation of the system is set forth in FIG.  2 . At step  400 , control unit  100  triggers the pulse transmitter  10  of each rangefinder unit so that each transmitter operates at a pulse repetition rate of 6.0×10 4  pulses per second, for a predetermined number of pulses, for example, ten. At step  410 , an average elapsed time-of-flight is determined by the system averager  60 . At step  420 , the range gate discriminator  70  is applied to the time-of-flight determination to ascertain whether the measurement falls within the limits of the sensing volume for the path of that rangefinder unit. At step  430  the main control unit reads the range gate discriminator and provides an update in step  440  to the display unit  300 . The main control unit  100  repeats the process for the next rangefinder unit  200 , and continuously provides update to the display unit  300 . Since the system will provide an indication of an obstacle within the sensing volume, the response of the individual rangefinder units are independently considered by the main control unit and it is only necessary for a single unit to register an obstacle such as an overtaking vehicle within its range gate for the main control unit to provide an indication of an obstacle present. 
     FIG. 3 illustrates the concept of the sensing volume, or distance and spatial location to the rear and side of a vehicle, that is covered with the system of this invention. In the preferred embodiment, the rangefinder unit  200  and the display unit  300  including a viewing window are mounted in an enclosure  600  that fits beneath the side mirror and can be incorporated into the mirror structure. The control unit  100  can also be mounted within the enclosure. A schematic outline drawing of enclosure  600  including viewing window  310  and side mirror  610 , indicated in dashed lines, is shown in FIG.  4 . 
     What is depicted in FIG. 3 is a four beam system, each beam being shown with an approximate 8 degree width. The lined area  500  corresponds to the sensing volume, with the range gate for each individual beam being defined as between the closest distance, D min , and the farthest distance, D max , from the rangefinder  200 , along the beam direction, that falls within the lined area. Since distance from the rangefinder unit is given by one-half the pulse transit time from projected to return pulses multiplied by the speed of light, D min  can be converted to a T min , according to the equation: 
     
       
           T   min =(2 ×D   min )/ c   
       
     
     where c is the speed of light and D min  is the desired minimum range, and T min  is the corresponding minimum transit time. 
     A similar equation can be written for the maximum transit time interval. 
     As can be seen from FIG. 3, each beam has a unique range gate corresponding to its traverse of the sensing volume. The range gate will be different for each rangefinder. For those that look sideways from the vehicle, a minimum range distance of 3 feet is suitable. Maximum range for a sideways looking rangefinder is adjustable to suit driver preference and is typically about the width of one traffic lane. For those that look backwards, it preferably will vary with the driver and driving conditions. However, it should be sufficient to have a maximum range of 100 feet. Since the speed of light is approximately 1 foot per nanosecond, these distances correspond to a time range of 6 ns to 200 ns. 
     Although FIG. 3 shows the system as employed on the driver&#39;s side of the vehicle, it is readily apparent that a similar system having an enclosure  620  and mirror can be deployed on the passenger side of the vehicle, as is also included within this invention. 
     With each beam operated at 60 kHz, and using as an example ten successive pulses to define an averaged reading, it can be seen that a four beam system can be updated in less than one millisecond. An overtaking vehicle, closing at a relative speed of 40 miles per hour as an example, reduces the distance at a rate of less than one inch per millisecond. The system is essentially updated instantaneously. 
     While FIG. 3 shows a four beam system it is readily apparent that the same system could be employed with a different number of beams, for example six beams instead of four. The number of beams to be employed depends on the beam width and desired area of coverage, and many variations are apparent. Due to the size of the obstacles being detected it is not necessary to have 100 percent area coverage, and the precise percent of coverage is a design parameter of the system. 
     In the preferred embodiment, the system determines the time-of-flight or elapsed time between a transmitted and reflected pulse and assesses the situation on that determination. As will be apparent, the relationship between time and distance and velocity makes it possible to use distance determinations to achieve the same result and such usage will be recognized as the equivalent of the use of time-of-flight. For example, time-of-flight information can be stored as a time measurement or converted to a distance measurement by using the speed of the pulses emitted by the transmitter  10 , i.e. the speed of light. And the measurement that is stored in the data averager  60  can be a running total or a running average. In either case the data is a measure of the location of the object that reflected the pulses. 
     As is also apparent, the 60 kHz frequency of the rangefinder can also be varied over a wide range of frequencies and the same result achieved. 
     As described, the rangefinders  200  are pulsed sequentially. As is also apparent, these rangefinder units can be operated continuously and sampled as required. 
     Other variations in the invention may be achieved by shifting more of the calculation and/or signal processing effort from the rangefinder  200  to the control unit  100 . For example, the function of the data averager  60  and range gate discriminator  70  might readily be transferred to the control unit  100 . Furthermore the operation of the system and the optics of the receiver units  20  may permit use of a single receiver unit  20  with multiple transmitter units  10 . It is also possible to locate the rangefinder units  200  within the tail light assembly with the display unit  300  located at the side mirror position. Other variations will be apparent to those skilled in the art.