Abstract:
A diagnostic method for a blind-zone sensing system including leading and trailing passive IR sensors periodically determines a separation distance between coverage areas of the leading and trailing sensors to diagnose sensor alignment. Signals produced by the leading and trailing sensors are sampled and stored over a defined interval of time for processing. A condition in which the sensor coverage areas abruptly encounter a stationary region of cooler temperature is detected when corresponding signal deflections are identified. The elapsed time between the identified signal deflections is measured and used along with an accurate measure of the vehicle speed to compute the separation distance between coverage areas of the leading and trailing sensors.

Description:
TECHNICAL FIELD  
       [0001]     The present invention relates to infrared (IR) blind-zone sensing systems, and more particularly to a method of detecting sensor alignment.  
       BACKGROUND OF THE INVENTION  
       [0002]     A potentially advantageous vehicular blind-zone detection system utilizes two or more passive IR sensors spaced along at least the driver side of the vehicle. The sensors are aimed at a lane adjacent the vehicle and respond to the temperature of objects (i.e., radiant energy or infrared radiation) in the respective coverage areas. As the vehicle is driven, the trailing sensor will respond to the same objects that the leading sensor responded to moments earlier; that is, the leading and trailing sensors will be responsive to the same stationary target area. The sensor outputs are therefore very similar when the adjacent lane is empty, but differ significantly when an object entering the blind-zone is registered by just one of the sensors—the trailing sensor, in the case of an over-taking vehicle. In operation, the sensor outputs can be monitored as the vehicle is being driven and used to produce a driver warning if lane changing is attempted or signaled when an object has been detected in the adjacent lane. Such a system is described, for example, in the Patent Publication No. 2002/0126002 A1, incorporated by reference herein.  
         [0003]     As described in the aforementioned patent publication, the sensors must be aligned very carefully to ensure that they respond to the same stationary target area such as the vehicle blind-zone. When the sensors are properly aligned, there is a known and fixed separation distance between the coverage areas of the leading and trailing sensors so that the time delay between outputs produced by the leading and trailing sensors may be accurately determined based on the known separation distance and the vehicle speed. Although the vehicle speed can be measured very accurately using wheel speeds for example, proper alignment of the passive IR sensors cannot be easily verified, and the alignment of a given sensor could change for a variety of reasons depending on how it is mounted and whether the vehicle sustains even minor damage from a collision, for example.  
       SUMMARY OF THE INVENTION  
       [0004]     The present invention is directed to an improved method of detecting and verifying proper alignment of leading and trailing passive IR sensors in a blind-zone sensing system by periodically determining a separation distance between coverage areas of the leading and trailing sensors. Signals produced by the leading and trailing sensors are sampled and stored over a defined interval of time for processing. The processing identifies sensor signal deflections that occur when the sensor coverage areas abruptly encounter a stationary region of cooler temperature such as a shadow from an overpass or bridge or a border between a grass median strip and asphalt pavement. When such a stationary region is detected, the elapsed time between the identified signal deflections is measured and used along with an accurate measure of the vehicle speed to compute the separation distance between coverage areas of the leading and trailing sensors. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a diagram of a vehicle equipped with a blind-zone sensing system including leading and trailing passive IR sensors and a microprocessor-based control unit;  
         [0006]      FIG. 2  is graphically depicts signals produced by the driver side leading and trailing sensors of  FIG. 1  as they respond to a stationary region of cooler temperature created by a shadow from an overpass; and  
         [0007]      FIG. 3  is a flow diagram representative of a software routine executed by the control unit of  FIG. 1  for carrying out the method of the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0008]     Referring to  FIG. 1 , the reference numeral  10  generally designates a motor vehicle equipped with a blind-zone sensing system of the kind generally described in the aforementioned Patent Publication No. 2002/0126002 A1. In the illustrated embodiment, the sensing system includes two passive IR sensors on each side of the vehicle  10 . The sensors  12  and  14  are respectively mounted in leading and trailing positions on the driver side, while the sensors  16  and  18  are respectively mounted in leading and trailing positions on the passenger side. The leading position sensors  12  and  16  maybe mounted in left and right outside rearview mirrors, for example, and the trailing position sensors  14  and  18  may be mounted in left and right side markers, or in a rear bumper, for example. The sensors  12 - 18  provide input signals to a microprocessor-based control unit  20 , which processes the signals to detect the presence of a moving object such as another vehicle in adjacent roadway lanes L 1  or L 2 . The control unit  20  also receives inputs from one or more wheel speed sensors  22 ,  24 ,  26 ,  28  and inputs  30  pertaining to parameters such as ambient light level and sensor temperature, and lane change indications such as turn signal actuation. The system also includes a warning actuator (A)  32  that is selectively activated by the control unit  20  to appropriately warn the driver of the presence of a moving object in an adjacent lane.  
         [0009]     The sensors  12 - 18  are mounted on vehicle  10  so that leading and trailing position sensors on each side of the vehicle are focused on respective stationary target areas alongside the vehicle  10 . In a typical implementation, the sensors  12 ,  14  on the left or driver side of vehicle  10  will be aligned to focus on the center of a roadway lane L 1  to the left-rear of vehicle  10 , and the sensors  16 ,  18  on the right or passenger side of vehicle  10  will be aligned to focus on the center of a roadway lane L 2  to the right-rear of vehicle  10 . The ellipses  34 ,  36 ,  38  and  40  designate the respective coverage areas of the sensors  12 ,  14 ,  16  and  18 . Referring to the driver side of vehicle  10 , the sensors  12  and  14  will be accurately aligned when the coverage areas  34  and  36  both lie on the center of lane L 1  and are spaced by a longitudinal separation distance S. In operation of the blind-zone sensing system, this separation distance S can be used in conjunction with the vehicle speed VS (the average of the sensed wheel speeds, for example) to compute the time delay TD between detection of an object by the leading sensor  12  and the trailing sensor  14 . The same is true of the right or passenger side sensors  16  and  18 . As described in the aforementioned Patent Publication No. 2002/0126002 A1, the computed time delay TD can be applied to the signal produced by the leading sensor  12  or  16  so that the difference between the trailing and delayed leading signals on a given side of the vehicle  10  can be used to detect the presence of a moving object such as a passing vehicle.  
         [0010]     When the sensors  12 - 18  are properly aligned, the above-described system effectively defects moving objects such as other vehicles in adjacent lanes, and can be used to activate the warning actuator  32  at least when the driver of vehicle  10  indicates an intention to change lanes inappropriately. However, proper alignment of the IR sensors  12 - 18  cannot be easily verified, particularly because they are passive devices, and the alignment of a given sensor  12 - 18  could change for a variety of reasons depending on how it is mounted and whether the vehicle  10  is damaged in a collision, for example. If one or more of the sensors  12 - 18  are misaligned, the coverage area separation distance S changes from the predetermined setting, which introduces errors into the computation of delay time TD and corresponding object detection errors.  
         [0011]     The method of the present invention overcomes the above-described problem by processing the signals produced by the sensors  12 - 18  during normal operation of the vehicle  10  to actually detect the coverage area separation distance S on both driver and passenger sides. In general, this is accomplished by identifying sensor signal deflections indicative of the passage of the coverage areas  34  and  36  (or  38  and  40 ) through a region of cooler temperature caused by a stationary object such as an overpass (or its shadow) or a border between a grass median strip and asphalt pavement. When such a stationary region is detected, the sensor signal deflections produced by the respective leading and trailing sensors are identified, and the time difference ΔT between the identified deflections is measured. This measured time difference ΔT is multiplied by the vehicle speed VS to compute the coverage area separation distance S. If the computed separation distance S is within a window of acceptability, it is recorded and used for moving object detection as described above; otherwise, the controller  20  can issue a diagnostic warning via actuator  32 , signaling the driver that sensor re-alignment is needed.  
         [0012]     The solid and dashed traces  42  and  44  of  FIG. 2  respectively depict successive samples of the signals produced by the leading and trailing sensors  12  and  14  when the corresponding coverage areas  34  and  36  pass through a stationary region of cooler temperature caused by a shadow from an overpass. The negative going signal deflections, with the signal  42  of the leading sensor  12  deflecting before the signal  44  of the trailing sensor  14 , positively identify such a stationary region. The control unit  20  buffers successive samples of the sensor signals, and can easily identify the maximum negative-going deflections in each signal and determine the time difference ΔT based the number of samples separating the two deflections.  
         [0013]     Referring to  FIG. 3 , the flow diagram blocks  50 - 66  represent a software routine periodically executed by the control unit  20  according to this invention. The blocks  50  and  52  sample the various input signals mentioned above in respect to  FIG. 1  and buffer the IR sensor signals. The block  54  carries out a routine for detecting the presence of moving objects in the stationary sensing areas as described above and for issuing a driver warning when appropriate. The block  56  monitors the buffered leading and trailing sensor signals for a given side of the vehicle  10  to identify negative-going signal deflections indicative of a stationary region of cooler temperature as described above in respect to  FIG. 2 . Block  58  determines if block  56  has identified the crossing of such a region. If not, the remainder of the routine is skipped; if so, the blocks  60 - 66  are executed to determine the coverage zone separation distance S and to issue a driver warning if appropriate. Block  60  determines the time difference ΔT between the identified signal deflections, and block  62  calculates and stores the corresponding coverage zone separation distance S according to the product of the time difference ΔT and the current vehicle speed VS. The block  64  determines if the calculated separation distance S is within a range or window of acceptable values—i.e., if the deviation of the separation distance S from a predetermined separation distance is less than a reference value. If so, the remainder of the routine is skipped, and successive executions of the moving object detection routine (block  54 ) are carried out using the newly stored separation distance S. If the calculated separation distance S is outside the range of acceptable values, the block  66  is executed to issue a diagnostic warning via actuator  32 , signaling the driver that re-alignment of the IR sensors  12 - 18  is needed.  
         [0014]     In summary, the method of the present invention advantageously addresses a practical concern associated with IR-based blind-zone sensing systems. The method confirms and periodically verifies proper sensor alignment, and adaptively adjusts the coverage zone separation distance S when it falls within an acceptable range for improved detection of moving objects. While the present invention has been described with respect to the illustrated embodiment, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the number of IR sensors may be different than depicted, the vehicle speed may be determined in a different way, and so forth. Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.