United States Patent [191
`Pakett
`
`lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`5,325,096
`Jun. 28, 1994
`
`US005325096A
`[11] Patent Number:
`[45] Date of Patent:
`
`[54] SMART BLIND SPOT SENSOR
`[75]
`Inventor: Alan G. Pakett, San Diego, Calif.
`[73] Assignee: Vorad Safety Systems, Inc., San
`Diego, Calif.
`[21] Appl. No.: 111,826
`[22] Filed:
`
`Aug. 25, 1993
`
`Related U.S. Application Data
`[63] Continuation of Ser. No. 930,079, Aug. 14, 1992, aban(cid:173)
`doned.
`
`[51]
`Int. Cl.s .............................................. GOlS 13/93
`[52] u.s. Cl •... ~ ..................................... 342/70; 342!71
`[58] Field of Search .............................. 342/70, 71, 72
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,689,882 9/1972 Dessailly ........................... 342/71 X
`3,697,985 10/1972 Faris et al ............................. 342/72
`3,750,169 7/1973 Strenglein ............................. 342/21
`3,760,415 9/1973 Holmstrom et al ................... 342/59
`3,778,826 12/1973 Flannery et a!. ..................... 342/71
`3,859,660 1/1975 Augustine et al ................... 342/114
`3,898,652 8/1975 Rashid ................................... 342/59
`3,978,481 8/1976 Angwin eta!. ....................... 342/59
`4,072,945 2/1978 Katsumata eta!. ................... 342/70
`4,349,823 9/1982 Tagami et al.
`....................... 342/70
`4,845,506 7/1989 Shibata et al. ........................ 342/115
`4,920,520 4/1990 Gobel eta!. .......................... 367/99
`5,008,678 4/1991 Herman ............................... 342/158
`5,087,918 2/1992 May eta!. ............................. 342/85
`5,115,245 5/1992 Wen et al. ........................... 342/175
`
`5,181,038 1/1993 Asbury et al ......................... 342/70
`
`Primary Examiner-John B. Sotomayor
`Attorney, Agent, or Firm-Spensley Horn Jubas &
`Lubitz
`
`. ABSTRACI'
`[57]
`A radar system for sensing the presence of obstacles in
`a vehicle's "blind spots" and generating a signal to the
`vehicle operator indicative of the presence of such an
`obstacle. The system uses a common radar transceiver
`that transmits a radio frequency signal directed at a
`blind spot of the vehicle. The signal is reflected off any
`obstacles that are present in that blind spot region. A
`Doppler shift in the received reflected frequency gener(cid:173)
`ally indicates that an obstacle has moved into the blind
`spot. Doppler frequencies attributable to objects which
`are of no interest, such as stationary objects, are filtered
`out. Only obstacles that are traveling at approximately
`the same speed and direction as the vehicle are consid(cid:173)
`ered to be of interest, and will cause the blind spot
`sensor to generate an indication that an obstacle is pres(cid:173)
`ent in the blind spot. The indication is preferably an
`unobtrusive illuminated indicator which is affixed to
`one of the vehicle's mirrors. In addition to the illumi(cid:173)
`nated indicator affixed to a mirror, an obtrusive audible
`indicator is provided in the preferred embodiment of
`the present invention which creates an audible tone,
`whistle, or buzz when an obstacle is present and the
`vehicle's turn signal is active.
`
`5 Claims, 5 Drawing Sheets
`
`~35
`
`VOLTAGE
`REGULATOR
`
`PULSE
`GENERATOR
`
`33--.,_
`
`VIHUAL
`GROUND
`CllCUIT
`
`10MHz
`
`...__ __ _. TO GUNN DIODE
`
`,...
`DOPPLER
`FREOUENCYC>--~_,
`
`PRE-
`AMPLfiER , .
`
`SAMPLE
`AND
`HOLD
`
`CRCUIT -
`
`/__27
`
`Low·
`PASS
`FLTER
`
`:---
`
`0- SV
`WAVE
`GENERATOR
`
`-r--
`
`MEMORY
`REGISTER
`
`MALFI.INCTION
`DETECTOR
`
`IPR2016-00293 - Ex. 1002
`Toyota Motor Corp., Petitioner
`
`1
`
`

`
`~1
`
`GUNN
`DIODE
`
`COUPLER
`
`ANTENNA
`
`c::
`•
`rJ'1
`•
`
`TIMING
`CONTROL
`CIRCUIT
`
`FIG. 1
`
`MIXER
`
`SIGNAL
`PROCESSOR
`
`CPU
`
`INDICATOR
`CIRCUIT
`
`FROM
`STEERING SENSOR
`
`FROM
`TURN SIGNAL
`
`AUDIBLE
`TONE
`
`2
`
`

`
`c:: • 77.1
`
`•
`
`v-35
`
`VOLTAGE
`REGULATOR
`
`25
`
`PULSE
`GENERATOR
`
`33 ----._
`
`t
`
`VIRTUAL
`GROUND
`CIRCUIT
`
`V. GROUND
`
`10MHz
`
`.,__ __ --1_ TO GUNN DIODE
`
`FIG. 2
`
`/11
`
`DOPPLER .n
`~
`FREOUENCYL>~----~
`
`PRE-
`AMPLIFIER ~
`
`SAMPLE
`AND
`HOLD
`CIRCUIT
`
`LOW
`PASS
`ALTER
`
`r--
`
`0- sv
`WAVE
`GENERATOR
`
`MEMORY
`REGISTER
`
`MALFUNCTION
`DETECTOR
`
`3
`
`

`
`U.S. Patent
`
`June 28, 1994
`
`Sheet 3 of 5
`
`5,325,096
`
`START
`
`·
`
`STEP 302
`
`YES
`
`RESET THE
`MEMORY
`REGISTER FLAG
`
`STEP 303
`
`STEP 304
`
`DETERMINE HOW
`LONG TO GO
`15 FT.
`
`SET TIMER FOR
`TIME TO GO
`15 FT.
`
`NO
`
`YES
`
`STEP 306
`
`SET ONE SECOND
`FLAG TIMER:
`SET TWO SECOND
`FLAG TIMER
`
`TO
`FIG.3B
`
`STEP 307
`
`RESET FLAG IN
`MEMORY
`REGISTER
`
`NO
`
`NO
`
`YES
`
`STEP 319
`
`TURN RED INDICATOR
`OFF:
`TURN YELLOW INDICATOR
`ON
`
`· GO TO STEP 308 ·
`
`FIG. 3A
`
`4
`
`

`
`U.S. Patent
`
`June 28, 1994
`
`Sheet 4 of 5
`
`5,325,096
`
`STEP 309
`
`RESET MEMORY
`REGISTER FLAG
`
`GO TO STEP 303 ·
`
`STEP 313
`
`SET ONE SECOND
`>----.----.~ WARNING TIMER ;
`SET TWO SECOND
`WARNING TIMER
`
`STEP 314
`
`TURN OFF
`YELLOW
`INDICATOR;
`TURN ON REO
`INDICATOR
`
`BEEP
`
`YES
`
`NO
`
`STEP 316
`
`· GO TO STEP 308 ·
`
`YES
`
`GO TO STEP 303 ·
`
`FIG. 38
`
`5
`
`

`
`U.S. Patent
`
`June 28, 1994
`
`Sheet 5 of 5
`
`5,325,096
`
`.....:t
`•
`
`t..:) -u_
`
`("¥')
`C)
`
`-
`
`-C) -
`
`C)
`
`::;:
`
`en
`
`C) -
`
`I
`
`6
`
`

`
`1
`
`SMART BLIND SPOT SENSOR
`
`5,325,096
`
`2
`the frequency of a reflection of the transmitted signal to
`determine whether the reflected signal has been Dop(cid:173)
`pler shifted. A Doppler shift in the frequency generally
`indicates that an obstacle has moved into the blind spot.
`Analog filters and digital circuits are used to filter out
`Doppler frequencies attributable to objects which are of
`no interest, such as stationary objects (for example,
`parked cars, road signs, and road side trees). Only obsta(cid:173)
`cles that are traveling at approximately the same speed
`10 and direction as the vehicle are considered to be of
`interest. Therefore; it is only these obstacles that will
`cause the blind spot sensor to generate an indication that
`an obstacle is present in the blind spot.
`The indication that is communicated to the vehicle
`15 operator is preferably an unobtrusive illuminated indi(cid:173)
`cator which, in the preferred embodiment of the present
`invention, is affixed to or mounted near one of the vehi(cid:173)
`cle's side mirrors. Having the indicator affixed in this
`manner allows it to be seen by a normal, practiced mo(cid:173)
`tion of the driver's head. However, the operator is not
`distracted or disturbed by the frequent indications of
`obstacles which may occur under normal traffic condi(cid:173)
`tions, and which are of little or no interest to the opera(cid:173)
`tor unless a maneuver is planned which would cause the
`vehicle to come into contact with the obstacle. In addi(cid:173)
`tion to the illuminated indicator affixed to or mounted
`near a side mirror, an obtrusive audible indicator is
`provided in the preferred embodiment of the present
`invention which creates an audible tone, whistle, or
`buzz when an obstacle is present and the vehicle's turn
`signal is active.
`A malfunction detector is also included in the inven-
`tive blind spot sensor. The malfunction detector moni(cid:173)
`tors an output of a sample and hold circuit to ensure that
`an output voltage from the sample and hold circuit is
`within expected limits, thereby determining whether
`the system is functioning properly.
`The details of the preferred embodiments of the pres(cid:173)
`ent invention are set forth in the accompanying draw(cid:173)
`ings and the description below. Once the details of the
`invention are known, numerous additional innovations
`and changes will become obvious to one skilled in the
`art.
`
`This is a continuation of application Ser. No.
`07/930,079 flled on Aug. 14, 1992, now abandoned.
`
`5
`
`BACKGROUND OF THE INVENTION
`I. Field of the Invention
`This invention relates to automotive radar systems,
`and more particularly to a radar system for sensing the
`presence of obstacles in a vehicle's "blind spots".
`2. Description of Related Art
`A continuing problem that presents itself to operators
`of automotive vehicles is the difficulty in seeing obsta(cid:173)
`cles near the vehicle but in a location that is difficult to
`observe from the driver's seat. Such regions are com(cid:173)
`monly referred to as "blind spots". For example, the
`angles between 90° and 170° from the forward direction
`of a vehicle (i.e., to the right of the vehicle and slightly
`behind the operator thereof) is a common blind spot, 20
`particularly for large vehicles such as buses and trucks.
`This right-side blind spot is a source of numerous acci(cid:173)
`dents when a drive makes a right-hand turn or a right
`lane change and does not see another vehicle in the
`blind spot. Another common blind spot is the rear of a 25
`vehicle when backing up.
`The most common solution to the problem of blind
`spots has been to use mirrors to aid the operator of the
`vehicle in determining whether obstacles are present in
`a blind spot. Such mirrors have been made in a variety 30
`of shapes and mounted in various locations to provide
`the operator with the greatest ability to detect obstacles
`in particular blind spots. For example, it is common
`place today to see a concave mirror mounted to the
`right side of a vehicle aimed at the right-side blind spot. 35
`While mirrors provide the operator with some informa(cid:173)
`tion regarding the presence of obstacles in certain of a
`vehicle's blind spots, but they are less useful at night and
`under adverse weather conditions. Hence, a more com(cid:173)
`plete and satisfactory solution is still sought by many. 40
`A known alternative to the use of mirrors to detect
`obstacles in a vehicle's blind spot is to mount a camera
`on the vehicle to provide the operator with a visual
`image of obstacles in the vehicle's blind spot. However,
`this solution is complex and expensive, requiring a video 45
`camera and video monitor. Further, a video monitor
`can present a complex image that must be interpreted by
`a driver, and such monitors can be distracting. More(cid:173)
`over, like mirrors, such camera systems are less useful at
`night and under adverse weather conditions.
`Therefore, there is presently a need for a simple, and
`inexpensive solution to the problem of detecting haz(cid:173)
`ardous obstacles in the blind spots of a vehicle. Such a
`solution should also be useful at night and under adverse
`weather conditions. The present invention provides 55
`such a solution.
`
`50
`
`SUMMARY OF THE INVENTION
`The present invention is a simple, compact, and inex(cid:173)
`pensive radar detection system configured to detect the 60
`presence of an obstacle in a vehicle's blind spots and
`generate a signal to the vehicle operator indicative of
`the presence of such an obstacle.
`The system uses a common radar transceiver that
`transmits a radio frequency (RF) signal directed at a 65
`blind spot of the vehicle. The signal is reflected off any
`obstacles that are present in that blind spot region. The
`frequency of the transmitted signal is compared with
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a simplified block diagram of the present
`invention.
`FIG. 2 is a detailed block diagram ofthe signal pro(cid:173)
`cessing section of the present invention.
`FIGS. 3a and 3b are flow charts of the procedure
`followed by the preferred embodiment of the present
`invention upon detection of an obstacle.
`FIG. 4 is a simplified schematic of the indicator cir(cid:173)
`cuit of the preferred embodiment of the present inven(cid:173)
`tion.
`Like reference numbers and designations in the vari(cid:173)
`ous drawings refer to like elements.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`Throughout this description, the preferred embodi(cid:173)
`ment and examples shown should be considered as ex(cid:173)
`emplars, rather than as limitations on the present inven(cid:173)
`tion.
`FIG. 1 is a block diagram of the preferred embodi(cid:173)
`ment of the present invention. The preferred embodi(cid:173)
`ment shown in FIG. 1 includes a radar transceiver
`which determines the presence or absence of a target.
`
`7
`
`

`
`5,325,096
`
`3
`However, in an alternative embodiment of the present
`invention, the transceiver may emit and receive electro(cid:173)
`magnetic signals to other frequencies, or signals other
`than electromagnetic radiation, such as ultrasonic radia(cid:173)
`tion. Such ultrasonic transceivers are well known in the S
`art and are used for detection of objects in the context of
`alarm systems, for example.
`In FIG. 1, a Gunn diode 1 generates an radio fre(cid:173)
`quency (RF) transmit signal based upon an input pro(cid:173)
`vided to the Gunn diode 1 from a timing control circuit 10
`3. The timing control Circuit 3 pulses for a duration of
`10 J.LS at a rate of 10 kHz (i.e., the timing control signal,
`and consequently the RF transmit signal output by the
`Gunn diode 1, has a 10% duty cycle). A 10% duty cycle
`was chosen to optimize the energy efficiency of the 15
`system. The RF transmit signal is coupled to an RF
`coupler circuit 5 which permits RF energy to be cou(cid:173)
`pled from the Gunn diode 1 to an antenna 7 and an RF
`mixer diode 9.
`The antenna 7 directs the RF transmit signal along a 20
`side of a vehicle upon which the radar system is
`mounted. In the illustrated embodiment of the present
`invention, a single antenna is used to transmit a single
`RF signal, and is mounted to provide the most effective
`coverage of a blind spot of a particular vehicle. How- 25
`ever, in an alternative embodiment of the present inven(cid:173)
`tion intended for use with large vehicles, such as busses,
`a plurality of antennas may be used to ensure that obsta(cid:173)
`cles which are present anywhere within the vehicle's
`blind spots are detected. The RF transmit signal is re- 30
`fleeted off obstacles in the path of the signal. The an(cid:173)
`tenna 7 receives a portion of the reflected signal. If an
`obstacle which reflects the transmit signal is in motion
`relative to the antenna 7, a Doppler frequency shift
`occurs between the transmitted signal and the received 35
`signal. Doppler shifting is a well-known phenomenon
`by which a signal which is reflected off an object which
`is approaching the source of the signal is compressed,
`thereby causing the frequency of the signal to be shifted
`upward. Likewise, the frequency of a signal that is re- 40
`fleeted off an object that is moving away from the
`source is shifted downward.
`The reflections of the RF transmit signal which are
`received by the antenna 7 are coupled to the RF coupler
`circuit 5, which in turn couples the received reflections 45
`to the RF mixer diode 9. The mixer diode 9 generates an
`output which has a frequency equal to the difference
`between the frequency of the RF transmit signal and the
`received reflections of the RF transmit signal. In the
`preferred embodiment of the present invention a Dop- SO
`pier detection module, such as part no. DR02980 mar(cid:173)
`keted by Alpha Industries, includes the RF antenna 7,
`the RF coupler circuit 5, the Gunn diode 1, and the
`mixer diode 9 in a single housing.
`The output of the mixer diode 9 is coupled to a signal 55
`processing section 11. The signal processing section 11
`amplifies, time demultiplexes, and filters the output of
`the mixer diode 9. The signal processing section 11 is
`coupled to a central processing unit (CPU) 31 that de(cid:173)
`termines whether the output of the signal processing 60
`section 11 represents an obstacle of interest in the blind
`spot. The CPU 31 is coupled to an indicator circuit 41
`which presents warnings to the vehicle operator.
`FIG. 2 shows a detailed diagram block of the signal
`processing section 11 of the preferred embodiment of 65
`the present invention. An adjustable preamplifier (pre(cid:173)
`amp) 21 receives the output from the mixer diode 9. The
`preamp 21 has a very low frequency response of ap-
`
`4
`proximately ! Hz, thereby permitting very low frequen(cid:173)
`cies to be amplified. By adjusting the gain of the preamp
`21, the sensitivity of the system is set to permit only
`those obstacles which are'in the immediate presence of
`the vehicle to be detected. Since the signal strength of
`the reflection drops by the square of the distance (i.e.,
`P= l!d2), proper adjustment of the preamp 21 is very
`effective in limiting the range of the blind spot sensor.
`For example, experimentation has shown that a motor(cid:173)
`cycle will be detected in the lane adjacent to a vehicle
`equipped with the· present invention at a distance of
`approximately 3 feet, while an automobile of average
`size will not be detected as being present if there is an
`empty lane between the automobile and the radar(cid:173)
`equipped vehicle.
`In an alternative embodiment of the present inven(cid:173)
`tion, the distance to an obstacle can be detected and
`obstacles that are beyond a specified range can be disre(cid:173)
`garded. Thus, obstacles that are outside the blind spot
`(i.e., two lanes from the vehicle) but which are highly
`reflective will not cause the blind spot sensor to falsely
`indicate the presence of an obstacle in the blind spot. In
`one such alternative embodiment, a continuous wave
`(CW) frequency-modulated (FM) ramped modulation
`signal is applied to the input of the Gunn diode 9, caus(cid:173)
`ing the Gunn diode 9 to change frequency in a linearly
`proportional relationship to time for a first period. After
`the first period, the CW FM ramped modulation signal
`causes the Gunn diode 9 to change frequency in an
`inverse linearly proportional relationship to time for a
`second period, which may be equal to the first period.
`Because there is a time delay between the transmis(cid:173)
`sion of a signal and the receipt of the reflection of that
`signal off an obstacle, the delay being proportional to
`the distance from the transceiver to the obstacle, the
`frequency of the received reflection differs from the
`transmit frequency by an amount that is proportional to
`the time required for the signal to travel to the obstacle
`and return. Therefore, the frequency is also propor(cid:173)
`tional to the distance between the antenna 7 and the
`obstacle. Because the CW FM ramped modulation sig(cid:173)
`nal causes the frequency of the transmit signal to rise for
`a period of time and then to fall for a period of time, the
`frequency shift caused by the Doppler phenomenon can
`be distinguished from the frequency shift caused by the
`range of the obstacle. CW FM ramping modulation
`range detection schemes, such as described here, are
`well known in the art.
`In another such alternative embodiment of the pres(cid:173)
`ent invention, the receiver circuitry is gated off a speci(cid:173)
`fied amount of time after the beginning of a transmission
`pulse. If the specified amount of time is equal to the
`amount of time required for the transmit signal to reach
`the outer limits of the range of interest, only those ob(cid:173)
`stacles that are within the range of interest are detected.
`In the preferred embodiment of the present invention,
`the output of the preamp 21 is coupled to a sample and
`hold circuit 23. The sample and hold circuit 23 samples
`the output of the preamp 21 at a rate and for a duration
`equal to the rate and duration at which the transmit
`signal is pulsed by the Gunn diode 1 (i.e., for 10 J.LS at a
`rate of 10kHz in the preferred embodiment). The sam(cid:173)
`pling is synchronized to the transmission of the transmit
`signal by applying the same synchronization signal from
`a pulse generator circuit 25 to both the Gunn diode 1
`and the sample and hold circuit 23. The synchronization
`signal causes the Gunn diode 1 to generate the transmit
`signal when the synchronization signal is at a relatively
`
`8
`
`

`
`5,325,096
`
`5
`high voltage level, and also gates the sample and hold
`circuit 23 to sample the output of the preamp 21 during
`the same period. Each time the sample and hold circuit
`23 samples the output of the preamp 21, a voltage level
`is recorded. Thus, the output of the sample and hold 5
`circuit 23 is a series of voltage levels which increment
`or decrement every 100 /LS· The voltage levels represent
`the phase difference (i.e., Doppler shift) between the
`transmit signal and the received signal applied to the
`mixer diode 9 during each sample period.
`The output of the sample and hold circuit 23 is cou(cid:173)
`pled to a low pass filter 27. The low pass filter 27 of the
`preferred embodiment of the present invention has a 3
`dB cutoff frequency of about 100 Hz. The low pass
`fllter 27 serves three purposes: 1) to smooth the signal 15
`output by the sample and hold circuit 23 by removing
`high-frequency components of the output waveform; 2)
`to reduce noise, thus improving sensitivity without
`increasing RF power; and 3) to eliminate signals which
`represent objects moving rapidly relative to the vehicle, 20
`including stationary objects. Since the purpose of the
`present invention is to determine whether an obstacle
`which would otherwise go undetected by the operator
`is present in a blind spot of the vehicle, those obstacles
`which move rapidly through the blind spot are not of 25
`interest. It is assumed that obstacles that are moving
`rapidly through one of the vehicle's blind spots will be
`seen before entering the blind spot, or will pass through
`the blind spot before the operator causes the vehicle to
`perform a maneuver which would present a danger due 30
`to the presence of that obstacle.
`The low pass filter 27 is coupled to a square wave
`generator 29 which generates a square wave signal that
`alternates between 0 volts and 5 volts. The frequency of
`the signal output by the square wave generator 29 is 35
`determined by the frequency of the input to the square
`wave generator 29 from the low pass filter 27. A square
`wave transition is output by the square wave generator
`29 whenever an obstacle has been detected.
`In the preferred embodiment of the present invention, 40
`the square wave generator 29 is a comparator circuit
`with hysteresis. The hysteresis provides noise immu(cid:173)
`nity, prevents the comparator from oscillating, and
`limits range detection to a defined distance. Thus, when
`the input to the square wave generator 29 rises to cross 45
`a first relatively high threshold, the output of the square
`wave generator 29 transitions to a 5 volt level. When
`the input to the square wave generator 29 falls below a
`second relatively low threshold, the output of the
`square wave generator 29 transitions to a 0 volt level. 50
`The creation of a square wave output provides noise
`immunity and allows the output to be further processed
`by the CPU 31.
`Because some of the circuitry used in the present
`invention operates more efficiently when power is sup- 55
`plied from a bipolar power supply (i.e., both positive
`and negative voltages), a virtual ground circuit 33 is
`included in the illustrated embodiment of the present
`invention. The virtual ground circuit 33 works in con(cid:173)
`junction with a voltage regulator 35 to supply the 60
`power requirements of the illustrated embodiment of
`the present invention. Most automotive vehicles today
`include a 12 volt battery which powers the starter
`motor and the electrical system when the engine of the
`vehicle is not operating, and a voltage generator or 65
`alternator which recharges the battery and supplies
`current to the vehicle electrical system when the engine
`is operating. The voltage regulator 35 of the present
`
`6
`invention receives power from the 12 volt vehicle
`power source and generates a stable 5 volt output. The
`5 volt output of the voltage regulator 35 is applied to
`those components of the present invention which oper(cid:173)
`ate from a positive 5 volt source, and to the virtual
`ground circuit 33. The virtual ground circuit 33 creates
`a 2.5 volt output which acts as a virtual ground refer(cid:173)
`ence for those components within the present invention
`that require both positive and negative supply voltages.
`10 Thus, the 5 volt output of the voltage regulator 35 is 2.5
`volts positive with respect to the virtual ground refer(cid:173)
`ence, and earth ground (0 volts) is 2.5 volts negative
`with respect to the virtual ground reference. Such vir-
`tual ground circuits are well known in the art.
`A malfunction detector circuit 39 is coupled to both
`the sample and hold circuit 23 and the square wave
`generator 29. The malfunction detector circuit 39 gen(cid:173)
`erates an output that indicates whether the present in(cid:173)
`vention is operating properly. When the present inven(cid:173)
`tion is operating properly, a direct current (DC) offset is
`present at the analog output of the sample and hold
`circuit 23. The DC offset is stripped from the analog
`output by capacitively coupling the analog output from
`the sample and hold circuit 23 to the low pass filter 27.
`However, the DC portion of the output of the sample
`and hold circuit 23 is present in the output that is cou-
`pled to the malfunction detector 39. In the preferred
`embodiment of the present invention, if the DC offset is
`not above a specified voltage, the malfunction detector
`39 generates and sends a gate control signal to the
`square wave generator 29 which decouples the square
`wave generator 29 from output circuitry of the signal
`processing section 11. A voltage divider circuit coupled
`to the signal processing section 11 output causes the
`output of the signal processing section 11 to be 2.5 volts.
`Since, under normal conditions, the square wave gener-
`ator 29 outputs only 0 volts or 5 volts, the presence of
`a 2.5 volt output from the square wave generator 29
`indicates a problem.
`The output of the square wave generator 29 is cou(cid:173)
`pled to a dual edge-triggered memory register (flip(cid:173)
`flop) 37, which is used to establish a "persistence per(cid:173)
`iod", as described below. A "persistence period" is
`defined in the preferred embodiment as the amount of
`time that it takes the vehicle upon which the radar
`system in mounted to travel 15 feet. When an obstacle is
`first detected, as determined by a transition at the out(cid:173)
`put of the square wave generator 29, the CPU 31 waits
`the persistence period before responding to additional
`transitions. During the persistence period, no warnings
`are sent to the driver indicators. After the end of the
`persistence period, a warning is sent after each such
`transition if the transition occurs either within one sec(cid:173)
`ond after the end of the last persistence period or two
`seconds after a prior warning was sent. Otherwise, a
`new persistence period cycle begins.
`If it is determined that an obstacle persists in the blind
`spot, a indication is presented to the operator of the
`vehicle. In the preferred embodiment of the present
`invention, three types of indications are used. If the
`vehicle's turn signal becomes active (as detected by a
`position sensor coupled to an input of the CPU 31), and
`an obstacle is detected in the blind spot, an audible
`alarm sounds (e.g., emits an audible tone, whistle, or
`buzz) and a red visual indicator illuminates. If the turn
`signal is not active and an obstacle is detected in the
`blind spot, the audible alarm is not activated, but the red
`visual indicator illuminates. If no obstacle is detected, a
`
`9
`
`

`
`5,325,096
`
`7
`yellow visual indicator illuminates and the red indicator
`is inactive (illumination of the yellow indicator signifies
`that the blind spot sensor and circuit are active.)
`In an alternative embodiment of the present inven(cid:173)
`tion, sensors to detect the steering wheel position and(cid:173)
`/ or the position of the turn signal are used to provide an
`indication that the operator is attempting to turn or
`change lanes. Other sensors may also be used to aid in
`the determination as to when the operator is attempting
`to cause the vehicle to enter a blind spot region. The
`system can be configured, if desired, to detect turning
`indicated by the position of the turn signal and/or by
`sensing the position and movement of the steering
`wheel, and to activate the audible alarm only if a turn is
`indicated in the direction of a blind spot in which an
`obstacle is present.
`FIG. 3 is a flow chart of the procedure followed by
`the preferred embodiment of the present invention for
`determining whether to warn the vehicle's operator of
`the presence of an obstacle in a monitored blind spot. 20
`When a transition from 0 volts to 5 volts or from 5 volts
`to 0 volts occurs, a flag within the register 37 is set. In
`the illustrated embodiment of the present invention, the
`CPU 31 polls the register 37 at regular intervals to
`determine whether the register 37 has been set (STEP 25
`301). (In an alternative embodiment of the present in(cid:173)
`vention, the CPU 31 is interrupted when the flag within
`the register 37 is set.) Once the CPU 31 detects that the
`flag within the register 37 has been set, the CPU 31
`resets the flag (STEP 302) and ceases polling the regis- 30
`ter 37. The CPU 31 is coupled to a speedometer which
`measures the ground speed of the vehicle. The CPU 31
`uses the vehicle speed to calculate how long it will take
`the vehicle to travel 15 feet (i.e., the persistence period)
`(STEP 303), and sets a timer to "time-out" at the end of 35
`the calculated amount of time (STEP 304). Once the
`timer times out (STEP 305), the CPU 31 sets a one
`second and a two second flag timer (STEP 306), and
`resets the flag in register 37 to ensure that any new
`transitions that may have occurred during the persis- 40
`tence period are cleared (STEP 307).
`In an alternative embodiment of the present inven(cid:173)
`tion, one timer is used to indicate the amount of time
`elapsed after the flag in the register 37 is reset. Thus, the
`same timer which was used to determine when the 45
`persistence period has elapsed is reset and can be read at
`any time to determine the amount of time elapsed since
`the flag in the register 37 was reset.
`The timers of the preferred embodiment of the pres(cid:173)
`ent invention are integrated into the CPU 31. However, 50
`one or more of the timers may be implemented in exter(cid:173)
`nal circuitry.
`In the illustrated embodiment of the invention, the
`CPU 31 once again begins polling the flag within the
`register _37 after the persistence timer has timed out 55
`(STEP 308). By suspending the polling of the register
`37 for the persistence period, and resetting the register
`37 at the end thereof, the system effectively ignores
`transitions at the output of the square wave generator 29
`caused by reflections of the RF transmit signal off sta- 60
`tionary obstacles, such as parked cars and road signs,
`which are present in the blind spot for less than the
`persistence period.
`The CPU 31 checks whether a warning is presently
`being displayed (i.e., in the preferred embodiment of the 65
`present invention, whether the red indicator is illumi(cid:173)
`nated) (STEP 317) while waiting for the flag in the
`register 37 to be set. If a warning is presently being
`
`8
`displayed, the CPU 31 determines how long it has been
`since the warning was last activated. If the warning has
`been on display for more than one second without being
`reactivated (STEP 318), the CPU 31 causes the warning
`5 to cease being displayed (STEP 319). The CPU 31 also
`determines whether an audible alarm has been sounding
`for more .than one second without being reactivated
`(STEP 320), and causes the audible alarm to cease if
`reactivation of the alarm has not occurred in the last
`10 one second (STEP 321).
`If the CPU 31 determines that the flag in the register
`37 is set (STEP 308), the CPU 31 resets the flag (STEP
`309) and checks how long it has been since the persis(cid:173)
`tence timer timed-out (STEP 310). If more than two
`15 seconds have passed since the persistence timer timed(cid:173)
`out, the process returns to STEP 303 and suspends the
`polling of the register 37 once again. Thus, if an obstacle
`reflects the RF transmit signal back to the antenna 7,
`causing the output of the square wave generator 29 to
`transition, but no further reflections are detected for
`over two seconds, the system behaves as if the next
`transition of the square wave generator 29 is unrelated
`to the last transition, i.e., polling is suspended to ensure
`that the obstacle that caused the transition persists for
`more than the time required to travel 15 feet.
`However, if the transition has occurred within two
`seconds of the time-out of the persistence timer (i.e., the
`two-second persistence timer has not timed-out), then
`the CPU 31 checks whether one second has elapsed
`between the end of the persisten