Abstract:
An improved IR occupant position detection system that provides accurate and reliable classification and position information at a speed sufficient to timely inhibit or otherwise control deployment of occupant restraints. A two-dimensional array of IR emitters is selectively activated to periodically illuminate two or more of predetermined viewing planes in the vicinity of a passenger seating area, and the reflected IR energy is detected by a photo-sensitive receiver and analyzed to detect the presence of an occupant, to classify the occupant, and to identify and dynamically track the position of the occupant&#39;s head/torso relative to predefined zones of the passenger compartment. Modulating the intensity of the emitted IR beams with a known carrier frequency, band-pass filtering the received signal, and synchronously detecting the filtered signal distinguishes the reflected IR energy from other signals picked up by the IR receiver. Additionally, a two stage adaptive control mechanism compensates for the variation in intensity of the reflected energy with distance between the emitter and the occupant. The emitter is implemented with orthogonal anode and cathode power rails with individual IR LED elements placed at each anode-cathode intersection. Optical dispersion within the package is greatly reduced by an opaque cover layer that effectively forms a well for each LED element.

Description:
TECHNICAL FIELD 
     This invention relates to a motor vehicle control system, and more particularly to a system and method for detecting the position of an occupant of the vehicle. 
     BACKGROUND OF THE INVENTION 
     Vehicle occupant position detection systems are useful in connection with air bags and other pyrotechnically deployed restraints as a means of judging whether, and/or how forcefully, to deploy the restraint. Ideally, the system should be capable of classifying the type of occupant (i.e., large adult, small adult, child, etc.) and the position of the occupant relative to the point of deployment of the air bag. Various systems incorporating one or more infrared and/or acoustical ranging sensors have been proposed for this purpose; see, for example, the U.S. Pat. Nos. 5,330,226 and 5,785,347. In general, such systems emit one or more beams of infrared energy to define a corresponding number of viewing fields, and receive the reflected energy to detect the presence of an occupant within the viewing fields. However, the information obtained by such techniques is sometimes corrupted by other light sources (such as reflected sunlight, or pulsed incandescent light), and even under best conditions is typically insufficient to accurately classify the occupant type and position. For example, it may be desired to deploy an air bag even though the occupant&#39;s hand or arm is near the point of deployment, but undesirable to deploy if the occupant&#39;s head or torso is near the point of deployment. For this reason, other position sensors or weight sensors are typically used in combination with a ranging sensor to provide a more comprehensive understanding of occupant classification and position. Unfortunately, such systems tend to be quite costly, and are difficult to package in the automotive environment. Moreover, a relatively high speed of response is required so that deployment can be properly inhibited or allowed when the occupant position quickly changes, possibly in anticipation of an impending collision. Accordingly, what is needed is a low-cost system that can accurately and quickly recognize an occupant for purposes of classification and position. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improved infrared (IR) occupant recognition system that is low in cost, and provides accurate and reliable classification and position information at a speed sufficient to timely inhibit or otherwise control deployment of occupant restraints. A two-dimensional array of IR emitters is selectively activated to periodically illuminate two or more predetermined viewing planes in the vicinity of a passenger seating area, and the reflected IR energy is detected by a photo-sensitive receiver and analyzed to detect the presence of an occupant, to classify the occupant, and to determine the position of the occupant relative to predefined zones of the passenger compartment. 
     One aspect of the invention concerns a technique for reliably distinguishing the reflected IR energy from other signals picked up by the IR receiver. This involves modulating the intensity of the emitted IR beams with a known carrier frequency, band-pass filtering the received signal, and synchronously detecting the filtered signal. 
     Another aspect of the invention concerns a two stage adaptive control mechanism that compensates for the variation in intensity of the reflected energy. A first stage adaptively adjusts the gain of the receiver circuit, while a second stage adaptively adjusts the intensity of the emitted signal. 
     A further aspect of the invention concerns a novel mechanization of the two-dimensional emitter array which reduces manufacturing cost and package size, while retaining the flexibility of tailoring the dimensions of the array to suit a particular application. This is achieved through the use of orthogonal anode and cathode power rails with individual IR LED elements placed at each anode-cathode intersection. One of the anode and cathode terminals of each LED is mounted on its respective power rail, and the other is wire-bonded to its respective power rail. This eliminates interference between wire-bonds, reduces the number of driver circuits, and significantly shrinks the package size. Optical dispersion within the package is minimized by an opaque cover layer that effectively forms a deep cavity around each LED element. 
     A further aspect of the invention concerns a methodology for using the two-dimensional emitter array to recognize an occupant and quickly track any motion of the recognized occupant. This is achieved by identifying the emitter array positions corresponding to the torso of a recognized occupant, and scanning at least those positions at a rate much faster than the other positions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a diagram illustrating a portion of the passenger compartment of a motor vehicle equipped with an inflatable restraint and the IR occupant position and detection system of this invention. 
     FIG. 2 is a diagram illustrating the range determination technique used by the system of FIG.  1 . 
     FIG. 3 is a diagram of a two-dimensional IR LED emitter array used in the system of FIG.  1 . 
     FIG. 4 is a cross-sectional view of the emitter array of FIG. 3, taken along lines  4 — 4  of FIG.  3 . 
     FIG. 5 is a block diagram of the system of FIG. 1, including a programmed state-machine and microprocessor. 
     FIG. 6 is a diagram of the functions performed by the state machine of FIG.  5 . 
     FIGS. 7-11 and  14  are flow diagrams representative of computer program instructions performed by the microprocessor of FIG.  5 . FIG. 7 depicts a periodically executed background routine for setting up and enabling activation of a selected LED element. FIG. 8 depicts an interrupt driven routine for reading the received signal and computing occupant range. FIG. 9 depicts a portion of the flow diagram of FIG. 7 pertaining to adjustment of a programmable gain parameter; and FIG. 10 depicts a portion of the flow diagram of FIG. 7 pertaining to adjustment of an activation current for the selected LED element. FIG. 11 depicts a foreground routine for selectively enabling and disabling the inflatable restraint based on the occupant classification and range information; and FIG. 14 depicts a portion of the foreground routine of FIG. 11 pertaining to dynamic tracking of a recognized or classified occupant. 
     FIGS. 12 and 13 depict portions of the emitter array of FIGS. 3-4 in relation to the flow diagram of FIG.  14 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, and particularly to FIG. 1, the reference numeral  10  generally designates a vehicle occupant position detection system according to this invention. In the illustrated embodiment, the system  10  is mechanized as a single module, mounted in a ceiling console  12  between and above the driver and passenger seats  14 ,  16 . Obviously, other locations for the system  10  are also possible, but the illustrated location is generally preferred because it is least intrusive, easy to package and centrally located for flexibility in sensing one or more of several occupant positions, if desired. Of course, the vehicle may have a bench-style seat instead of the illustrated bucket seats  14 ,  16 ; in any event, the normal occupant positions on the seat(s) are defined by the placement of the seat belts (not shown). 
     In general, the system  10  is described herein in the context of an otherwise conventional supplemental inflatable restraint system, including an air bag  20  installed in the instrument panel  18  forward of the passenger seat  16 . The system  10  interacts with the restraint system by scanning the vicinity of the seat  16  where an occupant might be positioned, and producing a control signal to either inhibit or allow deployment of the air bag  20  in response to a crash event of sufficient severity, based on the occupant classification, and/or the position of a recognized occupant relative to the air bag  20 . The criteria concerning whether to enable or inhibit deployment are outside the scope of this invention, and are generally defined by the vehicle manufacturer or governmental regulation. It is generally agreed, however, that deployment of the air bag  20  should be disabled if the seat is unoccupied, or occupied by a front or rear facing infant seat, or by an out-of-position adult or small child, where the term out-of-position is defined by a predetermined proximity of the occupant&#39;s head or torso to the point of deployment of the air bag  20 . Accordingly, the objective of the system  10  is to classify or recognize the various types of occupants (or the absence of an occupant), and to detect if an occupant is out-of-position. 
     As indicated above, the information that can be gleaned from any given sensor type or location is generally inadequate to confidently classify an occupant and detect an out-of-position condition. However, the present invention overcomes the limitations of prior sensing systems through the use of a two-dimensional IR emitter  22  that is selectively activated to periodically illuminate multiple predetermined viewing planes in the vicinity of passenger seat  16 , as shown in FIG.  1 . Individual LEDs of the emitter  22  are selectively activated to produce an IR beam whose direction is determined by the position of the LED in the array and the optical parameters of a lens system incorporated within emitter  22 . As described in further detail below in respect to FIG. 3, the constituent LEDs are arranged in a rectangular grid three columns wide and ten rows in length. The emitter  22  is positioned in the console  12  so that the IR beams emitted by the LEDs in the first, second and third columns of the emitter  22  are respectively directed along first, second and third planes identified generally by the reference numerals  26 ,  28  and  30  in FIG.  1 . The plane  26  includes the normal orientation of an occupant&#39;s left leg and torso when normally seated, the plane  28  includes the normal orientation of the occupant&#39;s right leg and torso, and the plane  30  includes the interior edge of the passenger door  32 . In each plane, some of the beams are directed through an out-of-position (OOP) zone forward of the seat  16  and in proximity to the air bag  20 , some are directed onto the seat  16  or door  32 , and some are directed above the seat  16  and/or door  32 . The IR energy reflected by the occupant or seat  16  or door  32  is detected by a photo-sensitive receiver  24  disposed a predetermined distance B from the emitter  22 , and the range of the occupant from the emitter  22  is determined based on a pair of coordinate currents developed by the receiver  24 , as described in further detail below in reference to FIGS. 2 and 5. 
     As best seen in FIG. 2, the emitter  22  comprises an IR LED array  40  and a lens system comprising an aspheric element  42  for concentrating IR light emitted from the array  40 , and a symmetrical convex lens  44  for focusing the light on a target T, which in the illustrated embodiment, represents the passenger seat  16  or an occupant thereof. As indicated above, the array  40  comprises a two-dimensional arrangement of selectively activated IR LEDs, and is described in detail below in reference to FIGS. 3-4. The receiver  24  comprises a photo-sensitive device (PSD)  46  and a lens system comprising an IR filter  48 , an aspheric element  50  for imaging the received IR light, and a symmetrical convex lens  52  for focusing the imaged light on the PSD  46 . The PSD  46  is a conventional two-dimensional element, and provides a pair of coordinant currents, referred to herein as ix and iy, corresponding to the centroid of the IR light impinging on the active surface of the device. The range of the target T from the emitter/receiver pair is determined by the location of the received IR light relative to the emitted light. In the illustration of FIG. 2 where B is the distance between emitter  22  and receiver  24 , f is the focal length of the lens  52 , X is the location of the received light relative to the axis of the PSD  46 , the range or distance D of the target T is expressed as (f*B/x), where x can be determined by the ratio (ix−iy)/(ix+iy). As described below, an important aspect of this invention involves properly selecting an illumination pattern and properly analyzing the received range information. 
     FIGS. 3 and 4 depict a particularly advantageous mechanization of the emitter array  40 , in which individual IR LED elements L are arranged in a two-dimensional grid designated by “row” and “column” coordinate positions to form a three-by-ten array. Obviously, other array dimensions could be used as well. The horizontal “rows” are defined by the parallel cathode conductor segments C 1 -C 10 , while the vertical “columns” are defined by the parallel anode conductor segments A 1 -A 3 . For convenience, the portion of the array  40  between conductor segments C 2  and C 10  has been omitted from FIG. 3, as indicated. FIG. 4 depicts a cross-sectional view of the array through the center of cathode conductor segment C 1 , as indicated by the section lines  4 — 4  in FIG.  3 . The LED elements L are located at the intersections of the anode and cathode conductor segments A 1 -A 3  and C 1 -C 10 , and are designated by their “row, column” coordinate position. For example, the LED element in the upper left corner of the array  40  is designated as L 1 , 1  and the LED element in the opposite corner is designated as L 10 , 3 . 
     In the illustrated embodiment, the cathode conductor segments C 1 -C 10  are formed on a substrate  60 , and the anode conductor segments A 1 -A 3  are then formed along with underlying segments  62  of insulation or dielectric material such that the segments  62  electrically isolate the anode and cathode segments at the intersections thereof. The anode terminal of each LED element L is mounted on the respective anode conductor segment A 1 -A 3  and cathode terminal is wire bonded to the underlying cathode conductor segment C 1 -C 10  in an area adjacent the anode conductor segment. A cover layer  64  formed atop the conductor segments A 1 -A 3 , C 1 -C 10 , insulator  62  and substrate  60  is windowed to define a cavity or window W (each being designated by its row, column coordinate position) around each of the LED elements L. As indicated in FIG. 4, the cover layer  64  is relatively thick compared to the conductor segments and LED elements L, thereby minimizing scattering of the IR light emitted by the LED elements L, and increasing the intensity of the focused light beams. In the illustrated embodiment, the substrate  60  is ceramic, and the conductor segments A 1 -A 3 , C 1 -C 10 , insulation segments  62  and cover layer  64  are formed using conventional thick film manufacturing processes, but obviously, a similar structure could be produced with different manufacturing processes. Other design variations are also possible; for example, the cathode conductor segments C 1 -C 10  could be formed atop the anode conductor segments A 1 -A 3 , if desired. 
     The above-described array configuration and obvious variations thereof are particularly advantageous for a number of reasons, including improved light emission (spot quality) and significantly reduced package size, compared to conventional arrays and devices. The improved spot quality of the emitted light is achieved by the cover layer  64 , as describe above. The use of a row-column selectable array significantly reduces the number of conductor terminals required for selective activation of individual LED elements, as well as the number of external driver circuits that interface with the array  40 . Moreover, the wire bonds are very short in length and do not interfere with each other. Further, the anode conductor segments A 1 -A 3  act as heatsinks for the LED elements, reducing the size and complexity of auxiliary heatsinks that may be required. These factors enable the construction of a multi-element array in flexible configurations, and with a very small size that can easily be packaged behind a minimum diameter lens, resulting in a two-dimensional emitter that is economical to produce, that reduces system cost, and that can be easily packaged in an automotive or other space restricted environment. 
     FIG. 5 is a block diagram of the vehicle occupant position decection system  10  of FIG.  1 . The system  10  comprises the emitter  22  and receiver  24 , a receiver circuit  70  for extracting occupant range related signals from the ix and iy outputs of the PSD  46 , a microprocessor (μP)  72  for receiving and analyzing the range signals, a transmitter circuit  74  for activating the IR LED array  40 , and a State Machine  76  for coordinating the operation of the transmitter and receiver circuits  74 ,  70 . In general, the microprocessor  72  selects a particular LED element (via Select line  78 ) and requests the State Machine  76  (via Request Line  80 ) to obtain the range signals for the selected LED. The State Machine responds by activating the selected LED element, controlling the receiver circuit  70  to synchronously detect and capture the received range signals, and signaling the microprocessor (via Acknowledgement line  82 ) that the range signals are available at its A/D input port  84 . 
     The selected LED element of array  40  is activated with a pulse of high frequency sinusoidal current to produce an intensity modulated IR light beam fitting into the pattern generally described above in reference to FIG.  1 . The frequency of the activation current is fixed by microprocessor  72  (via line  86 ) and its magnitude is controlled by the microprocessor  72  (via line  88 ) to compensate for variations in the reflected signal strength, as explained below. The decoder  90  receives the data on the microprocessor Select Line, and activates semiconductor switch elements in the anode and cathode driver circuits  92  and  94  corresponding to the column and row address of the selected LED element. The anode drive circuit couples the respective anode conductor segment A 1 -A 3  of array  40  to a Programmable Current Source  96 , which when enabled by State Machine  76  (via line  98 ), develops and outputs a sinusoidal drive current on line  100 , at the frequency and amplitude dictated by microprocessor  72  (via lines  86 ,  88 ). The cathode drive circuit  94  couples the respective cathode conductor segment C 1 -C 10  to the system common or ground. 
     When the IR light pulse thereby produced by the emitter  22  illuminates the passenger seat  16 , an occupant, or the door  32 , a reflected light pulse at the same frequency (intensity modulation) is returned to receiver  24 , which produces the coordinate currents ix and iy on lines  102  and  104 . Unfortunately, the components of the ix and iy signals corresponding solely to the reflected IR light pulse are buried in other signals (considered as noise to the system  10 ) arising from direct or reflected ambient light produced by sources both inside and outside the vehicle. However, the receiver circuit  70  is able to extract the ix and iy signal components corresponding to the reflected IR light pulse by converting ix and iy to voltage signals vx, vy with I/V conversion circuits  106 ,  108  and band-pass filtering the voltage signals vx, vy with the band-pass filter circuits  110 ,  112 . This is possible because the components of the ix and iy signals corresponding to the reflected IR light pulse have a characteristic frequency corresponding to the intensity modulation frequency of the emitted IR light pulse. Thus, the band pass filters  110 ,  112  pass only the desired components of the vx and vy signals, and reject all other components as noise. In practice, the LED elements may be activated at a frequency of 20 kHz-50 kHz, with the band pass filters  110 ,  112  tuned to distinguish signals of the emitted frequency from other light sources. The extracted vx and vy signals are then amplified, as also indicated at blocks  110  and  112 , to form the signals vx′ and vy′. 
     The extracted and amplified coordinate signal voltages vx′ and vy′ are then synchronously detected by the Peak Follower circuits  114 ,  116  and the Reset Circuit  118 , which is activated by State Machine  76 . The Peak Follower circuits  114 ,  116  generate output voltages xp and yp that track peak instantaneous voltage of the respective signals vx′ and vy′, and the State Machine  76  controls the operation of the Reset Circuit  118  (via line  120 ) so that the Peak Follower circuits  114 ,  116  are active only at the peak intensity points of the sinusoidal current waveform generated by the Programmable Current Source  96 . The timing information is available to the State Machine  76  because the sinusoidal current has a fixed frequency (and duty cycle) and is triggered on and off by the State Machine  76 . This provides further immunity from any noise component present in vx′ and vy′ signals. The peak signal outputs xp and yp are then amplified by Programmable Gain Amplifiers  122  and  124 , providing amplified input voltages to sample-and-hold (S/H) circuits  126 ,  128 . As explained below, the gains of blocks  122  and  124  are controlled by the microprocessor  72  (via lines  1   30  and  132 ) to compensate for variations due to the range of target T. The State Machine  76  triggers the S/H circuits  126 ,  128  (via lines  134  and  136 ) one or more times during each LED activation pulse, and the sampled signal values are provided as inputs to the respective Averaging circuits  138 ,  140 , which in turn provide inputs xsig, ysig to the microprocessor A/D port  84 . The Averaging circuits  138 ,  140  are required because the State Machine  76  triggers the S/H circuits  126 ,  128  two or more times in succession for improved accuracy, as described below in reference to FIG.  6 . In the illustrated embodiment, the microprocessor  72  determines the number of samples and signals the State Machine  76  accordingly via line  142 . 
     As indicated above, the microprocessor  72  controls both the amplitude of the LED activation current and the gain of the Programmable Gain Amplifiers  122 ,  124  to compensate for variations in the strength of the reflected signal. The adjustments are important because the PSD output signals ix and iy may vary in amplitude by several orders of magnitude depending on range. As explained below in reference to FIG. 9, the microprocessor  72  reads the averaged signals xsig, ysig applied to its A/D input port  84  and compares the signals to upper and lower thresholds UT 1  and LT 1  corresponding to a desired input signal range of A/D input port  84 . If a signal xsig or ysig exceeds the upper threshold UT 1 , the gain of the respective Programmable Gain Amplifier  122  or  124  is decremented. Similarly, if a signal xsig or ysig is below the lower threshold LT 1 , the gain of the respective Programmable Gain Amplifier  122  or  124  is incremented. This adjustment serves to keep the input signals xsig and ysig within the desired input signal range of the A/D input port  84 . Beyond the programmable gain adjustment, the microprocessor  72  also incrementally adjusts the amplitude of the LED activation current produced by Programmable Current Source  96 . As explained below in reference to FIG. 10, the activation current (beam current) is decremented to reduce the PSD output if either of the normalized range signals xnor, ynor exceeds an upper threshold UT 2 . Similarly, the beam current is incremented to increase the PSD output if xnor or ynor are below a lower threshold LT 2 . This serves to limit the dynamic range requirements of the receiver circuit  70 , significantly reducing the cost of its components. 
     The above-described functions of the State Machine  76  are illustrated in diagrammatic form in FIG.  6 . Referring to FIG. 6, the State Machine functionality is depicted by as comprising eight principle states designated by blocks  150 - 164 . In the quiescent or idle condition designated by block  150 , the State Machine is inactive, and waiting for an LED activation request from microprocessor  72  (via Request line  80 ). In response to an activation request, the State Machine progresses to block  152  and activates the Programmable Current Source  96  (via line  98 ) to pulse the LED element selected by the microprocessor  72 . Then in succession at blocks  154  and  156 , the Peak Follower circuits  114 ,  116  are enabled to track the peaks of the signals vx′, vy′ in synchronism with the peak values of the LED activation current, and the S/H circuits  126 ,  128  are signaled to latch the sampled input signals. If the microprocessor has requested only one sample, the State Machine  76  then proceeds to block  164 , and deactivates the selected LED element, disables the Peak Follower circuits  114 ,  116 , and issues an acknowledgement signal to microprocessor  72  (via line  82 ), indicating that the range signals xsig and ysig are available at the A/D port  84 . Alternatively, if the microprocessor  72  has requested the State Machine to obtain and average two samples, the State Machine advances to the block  158  where the S/H circuits  126 ,  128  are commanded to latch a second sample before advancing to block  164 . Or if the microprocessor  72  has requested the State Machine to obtain and average four samples, the State Machine additionally advances to the blocks  160  and  162  where the S/H circuits  126 ,  128  are commanded to latch third and fourth samples before advancing to block  164 . In any event, the Averaging circuits  138 ,  140  automatically average the samples and the microprocessor  72  only reads the value after receiving the State Machine&#39;s acknowledgement signal at block  164 . In practice, State Machine  76  may be implemented with a standard programmable logic array device, and significantly reduces the processing burden of the microprocessor  72 , which is primarily concerned with analyzing the range information to determine if air bag deployment should be enabled or disabled based on occupant classification and/or position. 
     The flow diagrams of FIGS. 7-10 represent computer program instructions executed by the microprocessor  72  in carrying out the functions attributed to microprocessor  72  in the above discussion of FIG.  5 . FIG. 7 is a routine executed periodically (that is, based on a timer interrupt) to set up and request activation of a selected LED element L. In response to the interrupt  170 , the blocks  172 - 178  are executed in sequence to determine the selected LED element from a table created by the foreground routine of FIGS. 11 and 14, to adjust the gains of Programmable Gain Amplifiers  122 ,  124 , to adjust the activation current of the selected LED, and to issue a request signal to State Machine  76  via Request line  80 . The block  174  is detailed in the flow diagram of FIG. 9, and the block  176  is detailed in the flow diagram of FIG.  10 . 
     FIG. 8 is a routine executed each time the State Machine signals via line  82  that the range signals are ready for access. In practice, the acknowledgement signal from State Machine  76  triggers an interrupt  180 , and in response, the microprocessor sequentially executes the blocks  182 - 188 , as indicated. This involves reading the inputs xsig, ysig adjusting their values for DC offsets, normalizing the adjusted values to account for the commanded amplitude of the activation current, and computing and storing the target range. As indicated above, the target range D is determined in accordance with the expression f*B/x, where x can be determined according to the expression (xnor−ynor)/(xnor+ynor), where xnor and ynor are the normalized range signals. 
     Referring to the flow diagram of FIG. 9, the programmable gain adjustment of block  174  in FIG. 7 involves comparing the input signals xsig and ysig to predetermined upper and lower thresholds UT 1  and LT 1 . If xsig is less than LT 1 , as determined at block  190 , the block  192  is executed to increment the gain of Programmable Gain Amplifier  122 . Similarly, if xsig is greater than UT 1 , as determined at block  194 , the block  196  is executed to decrement the gain of Programmable Gain Amplifier  122 . In a similar manner. the blocks  198 - 204  are then executed to increment the gain of Programmable Gain Amplifier  124  if ysig is less than LT 1 , and to decrement the gain of Programmable Gain Amplifier  124  if ysig is greater than UT 1 . 
     Referring to the flow diagram of FIG. 10, the LED activation current adjustment of block  176  of FIG. 7 involves comparing the normalized input signals xnor and ynor to predetermined upper and lower thresholds UT 2  and LT 2 . If xnor or ynor is greater than UT 2 , as determined at block  210 , the block  212  is executed to reduce or decrement the requested beam (LED activation) current. If xnor or ynor is less than LT 2 , as determined at block  214 , the block  216  is executed to increment the requested beam (LED activation) current. 
     The flow diagram of FIG. 11 represents an executive or foreground software routine executed by the microprocessor  72  for analyzing the range data as it is received in order to classify and track an occupant of passenger seat  16  for the purpose of deciding whether to enable or disable deployment of the air bag  20 . The block  220  designates a series of initialization instructions executed at the commencement of each period of vehicle operation for initializing various parameters and stored values to predetermined settings. Part of the initialization process, for example, may involve disabling deployment of the air bag  20  until classification can be resolved, and executing certain diagnostic or self-check routines. Also, various timer values and timer interrupt sequences are initialized, such as the timer interrupt discussed in reference to FIG. 7 for requesting occupant range data. Following initialization, the block  222  is executed to determine, based on the currently available occupant range data, whether the passenger seat  16  is occupied by a forward facing infant seat (FFIS), a rear facing infant seat (RFIS), a small child, or an adult, or if the seat is simply unoccupied. The software routines of block  222  contain a set of rules to which the range data of array  40  is applied for discriminating between the various occupant classifications. The rules are developed empirically by gathering libraries of data representative of different occupants, seating positions, clothing, etc., and using signal processing techniques to develop rules that identify range data characteristic of a particular occupant classification. Once the classification has been determined, and verified as explained below, the determination is “locked in” unless a major shift in range data occurs; for example, a change in occupants. 
     If the classification rules indicate that the passenger seat is unoccupied, the blocks  232  and  246  are executed to indicate an “empty seat” classification, and to perform secondary testing designed to either increase or decrease the confidence in the indicated classification. The tests of block  246  tend to be heuristic in nature, and may involve for example, monitoring for lack of movement in the scanned area. If the secondary testing tends to verify the indicated classification, as determined at block  248 , the classification is locked-in, and the block  250  is executed to disable deployment of the air bag  20 . Similarly, if the classification rules of block  222  indicate that the passenger seat is occupied by a forward facing infant seat, the blocks  230  and  240  are executed to indicate a “FFIS” classification, and to perform secondary testing designed to either increase or decrease the confidence in the indicated classification. In this case, the secondary testing may involve for example, monitoring for a limited movement in the central portion of the scanned area. If the secondary testing tends to verify the indicated classification, as determined at block  242 , the classification is locked-in, and the block  244  is executed to disable deployment of the air bag  20 . Similarly, if the classification rules of block  222  indicate that the passenger seat is occupied by a rear facing infant seat, the blocks  228  and  234  are executed to indicate a “RFIS” classification, and to perform secondary testing designed to either increase or decrease the confidence in the indicated classification. As with the FFIS, the secondary testing may involve for example, monitoring for a limited movement in the central portion of the scanned area. If the secondary testing tends to verify the indicated classification, as determined at block  236 , the classification is locked-in, and the block  238  is executed to disable deployment of the air bag  20 . 
     If the classification rules of block  222  indicate that the passenger seat is occupied by a small child, the blocks  226  and  254  are executed to indicate a “small child” condition, and to perform tracking and out-of-position (OOP) testing, as described below. Similarly, if the classification rules of block  222  indicate that the passenger seat is occupied by an adult, the blocks  224  and  252  are executed to indicate an “adult” condition, and to perform tracking and out-of-position (OOP) testing. The tracking and OOP testing are described below in reference to FIGS. 12-14 in a manner that is generic to both the adult and small child classifications. The primary difference is that the OOP thresholds are separately specified for each occupant classification. 
     In general, the tracking function involves identifying the head/torso portion of the imaged occupant based on range, forming a grouping of IR beam positions corresponding thereto, and updating the range of those beam positions at a very fast rate so that the position of the head/torso can be tracked relative to a predefined OOP threshold—i.e., a predefined distance from the point of deployment of the air bag  20 . In the illustrated embodiment, the grouping of IR beams comprises a “cone” of five contiguous emitter array positions most closely associated with the identified head/torso position, and a “halo” of four emitter array positions surrounding the “cone”. This concept is illustrated in FIGS. 12-13. FIG. 12 depicts the emitter array  40  as a series of contiguous squares identified by the row, column locations discussed above in respect to FIG.  3 . Thus, the beam position  1 / 1  corresponds to the LED L 1 , 1 , and so on, with the beam positions of row one (positions  1 / 1 ,  1 / 2  and  1 / 3 ) illuminating the viewing area closest to the air bag  20 . An example of a cone for an in-position occupant is shown by the shaded positions ( 5 / 2 ,  6 / 1 ,  6 / 2 ,  6 / 3  and  7 / 2 ), and the OOP threshold, for an adult for example, is represented by the broken line  256 , the recognized occupant being considered in-position (IP) if the “cone” beams are below the threshold (i.e., in row three and higher), and out-of-position (OOP) if at least one of the “cone” beams crosses the threshold. The “halo” positions for the example “cone” are the surrounding beam positions  5 / 1 ,  5 / 3 ,  7 / 1  and  7 / 3 . The halo positions are not used to enable or disable deployment, per se, but simply define a region surrounding and in proximity to the cone grouping for improved tracking. 
     In the illustrated embodiment, the system  10  is mounted in an overhead console as described in reference to FIG. 1, and the center beam position (i.e., in column two of the array) of the row having the shortest range from system  10  is used to form the center of the cone. For example, if it has been determined that an adult or small child is occupying the passenger seat  16 , and a comparison of the range data obtained from a complete scan of the viewing area as illustrated in FIG. 1 reveals that the minimum range corresponds to the LED beam position  6 / 1 , the microprocessor  72  selects the center beam position in row six (i.e., position  6 / 2 ) as the center of the cone, and constructs the remainder of the cone and halo as shown in FIG.  12 . This is shown more clearly in FIG. 13, where the cone is seen as comprising the center beam position (CRB) and the contiguous positions C 1 , C 2 , C 3  and C 4 , and the halo comprises the surrounding positions H 1 , H 2 , H 3  and H 4 . 
     FIG. 14 depicts the tracking and OOP block  252  of FIG. 11 in more detail. Initially, blocks  260 - 264  are executed to identify the minimum range position of the array  40 , to determine the center row position associated with the identified minimum range position, and to build a cone/halo table based on that center row position. This will be recognized as the process described above in reference to FIGS. 12-13. The cone/halo table is simply a table that lists the emitter array positions (beam positions) that form the cone and the halo of the IR beam grouping centered on the head/torso of the recognized adult or small child passenger. Once the table has been created, the block  266  is executed to update a “beam request table” that indicates the relative priority of the various beam positions, with beam positions having a higher priority being scanned more frequently that beam positions of lower priority. In the illustrated embodiment, there are three different priorities: low, medium and high. The cone positions identified at block  264  are stored in the high priority list of the beam request table, and are scanned more frequently than any of the other beam positions. The halo positions identified at block  264  are stored in the medium priority list of the beam request table, and are scanned more frequently than non-cone and non-halo positions, but less frequently than the cone positions. When the interrupt service routine block  172  of FIG. 7 is executed in response to the timer interrupt, the microprocessor  72  reads the beam request table, and decides which LED element to activate accordingly. By way of example, the microprocessor  72  can scan the halo positions several times as often as the normal priority positions, and the cone positions several times as often as the halo positions. Scanning the cone and halo beam positions at a high rate improves the ability of the system  10  to dynamically track a moving head/torso since the head/torso is identified by range, and most critical range information is updated at a very fast rate. 
     The block  268  is then executed to verify that the IR grouping is tracking the occupant&#39;s head/torso, as opposed to a hand or newspaper, for example. This is achieved by determining the difference in range between adjacent cone positions, and distinguishes an occupant&#39;s head/torso from an outstretched arm, for example. If the head/torso is verified, the blocks  270 - 274  are executed to enable or disable deployment of the air bag  20  based on a comparison of the IR beam grouping relative to the OOP threshold. If any cone position of the IR beam grouping has crossed the OOP threshold, block  272  disables deployment, and if no cones have crossed the OOP threshold, block  274  enables deployment. If a head/torso is not verified, deployment of the air bag  20  is enabled. In a preferred embodiment, the block  270  also keeps track of the rate of change in position of the IR beam grouping so that movement of a cone into the OOP zone can be anticipated prior to actual crossing of the OOP threshold. 
     In summary, the present invention provides a reliable, easily packaged, and cost efficient occupant recognition and position detection system for motor vehicle applications. As pointed out above, the illustrated embodiment is intended to be exemplary in nature, and it is expected that various modifications will occur to those skilled in the art. As such, it will also be understood, that systems incorporating such modifications may fall within the scope of this invention, which is defined by the appended claims.