Abstract:
Devices and methods for detecting the presence of and evaluating the approach to obstacles situated in the path of articles attached to the roof of a vehicle and alerting the driver of the vehicle when an impact or collision between the articles and the obstacles is likely to occur. An example device includes an ultrasonic transducer and circuitry to measure the distance to obstacles, an audible warning device, a microprocessor to perform such tasks as controlling the generation of ultrasonic pulses, measuring the echo delay, calculating the risk of collision, and signaling the warning device, and a housing which protects the components of the device and can be quickly and easily attached to and detached from the vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/434,881, filed Dec. 18, 2002, and which is hereby incorporated by reference in its entirety. 
     
    
     
       BACKGROUND INFORMATION  
         [0002]    Every year, a great number of drivers mount a bicycle, boat, or cargo container on a car top rack, and later drive into a garage or other low clearance area, causing an impact or collision that can damage thousands of dollars of equipment, accessories, rack components, and the roof of the vehicle itself. The devices and methods disclosed herein can be used to detect overhead obstacles as the vehicle approaches them, and can signal the driver to stop when the approach is fast enough or close enough to result in an impact or collision.  
         SUMMARY  
         [0003]    A device for and method of detecting the presence of and evaluating the approach to obstacles situated in the path of articles attached to the roof of a vehicle and alerting the driver of the vehicle when an impact or collision between the articles and the obstacles is likely to occur. An example device includes an ultrasonic transducer and circuitry to measure the distance to obstacles, an audible warning device, a microprocessor to perform such tasks as controlling the generation of ultrasonic pulses, measuring the echo delay, calculating the risk of collision, and signaling the warning device, and a housing which protects the components of the device and can be quickly and easily attached to and detached from the vehicle. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 is a diagram showing a vehicle fitted with an example device approaching a garage.  
         [0005]    [0005]FIG. 2 is a top view of an example device.  
         [0006]    [0006]FIG. 3 is a bottom view of an example device.  
         [0007]    [0007]FIG. 4 is a cutaway view of an example device.  
         [0008]    [0008]FIG. 5 is a view of an example remote warning component using a radio receiver.  
         [0009]    [0009]FIG. 6 is a an example block diagram of electronic components of an example device.  
         [0010]    [0010]FIG. 7 is an example of the ultrasonic transceiver circuit diagram.  
         [0011]    [0011]FIG. 8 is a flow diagram of an example main microprocessor program.  
         [0012]    [0012]FIG. 9 is a flow diagram of an example ping subroutine of the program depicted in FIG. 7.  
         [0013]    [0013]FIG. 10 is a flow diagram of an example risk calculation subroutine of the program depicted in FIG. 7.  
         [0014]    [0014]FIG. 11 is a flow diagram of an example test subroutine of the program depicted in FIG. 7.  
         [0015]    [0015]FIG. 12 is a diagram related to FIG. 1 showing the vehicle closer to the garage, and representing the point of echo fall-off.  
         [0016]    [0016]FIG. 13 is an example plot of echo delay vs. forward travel showing the echo fall-off condition. 
     
    
     DETAILED DESCRIPTION  
       [0017]    The devices and methods disclosed herein provide a new and practical way to prevent damage to articles carried on the roof of a vehicle. Examples of the devices and methods include electronic components for periodically measuring the distance between a point on the vehicle and an obstacle located in the path of travel of articles carried on the roof of the vehicle, an algorithm for evaluating the measurements to determine the risk of a collision between the articles and the obstacle, and a device for warning the driver of the vehicle to stop when the risk exceeds a predetermined value.  
         [0018]    An overview of the operation of the example overhead obstacle detector and methods is shown in FIG. 1. Vehicle  1  carrying bicycle  2  on roof-top rack  3  approaches garage  4  or a similar overhead obstruction. Overhead obstacle detector device  5  is mounted on the forward portion of the roof of vehicle  1 , and generates periodic bursts of ultrasonic waves  6  along the path of angle θ, which is substantially in the direction of forward travel of vehicle  1 . When vehicle  1  moves sufficiently close to garage  4 , ultrasonic waves  6  are reflected by substantially vertical portions  8  and  9  of garage  4  and return to device  5 , where they are detected and amplified by an ultrasonic receiver circuit described later. A microprocessor in device  5  measures the elapsed time between transmission and reception of ultrasonic waves  6 , and the elapsed time represents the distance  10  between device  5  and reflecting surfaces  8  or  9 .  
         [0019]    If no echo is received from an obstacle in the path of ultrasonic waves  6 , such as when vehicle  1  is driving on the road and has not yet approached garage  4 , the microcontroller of device  5  is programmed to go into a low power idle mode for approximately one second before generating the next burst of ultrasonic waves  6 . Once an echo return signal from an obstacle is received, and is sufficiently strong to be detected by the receiver circuit, the microprocessor in device  5  begins sending bursts of pulses at a higher rate, for example every 250 ms, and begins calculating the risk of a collision between roof-top articles, represented by bicycle  2 , and obstacles, represented by garage  4 , using an evaluation technique described later. When the calculated risk exceeds a predetermined level, the microprocessor signals an audible and/or visual alarm contained in device  5 , warning the driver of the vehicle to stop immediately.  
         [0020]    [0020]FIG. 2 shows an example overhead obstacle detector  5  as it may appear when mounted on a vehicle. The measuring and evaluating components may instead be installed in the roof of the vehicle, and the warning component might instead be installed in the driver compartment. The visible features of the device can include housing  11 , ultrasonic transducer  12 , and magnetic base  13 . Magnetic base  13  is sufficiently powerful to hold the device on the roof of the vehicle under the conditions of road speed and wind speed encountered in typical highway driving. The magnetic base allows the driver to rapidly attach the device to the vehicle whenever articles are carried on the roof, and rapidly detach the device when removing the articles or leaving the vehicle unattended.  
         [0021]    In an alternate overhead obstacle detector, the magnetic base  13  is removed and replaced instead by one portion of a two piece quick-release clamping mechanism, the second portion of which may be clamped to some portion of the carrier or rack mounted on the roof of the vehicle. Thus the device may still be rapidly attached and detached from the vehicle by separating the two pieces of the quick-release mechanism. This device could be used on vehicles with a non-ferrous roof, and may also include the use of a remote warning device attached to a warning signal connector on housing  11 . To accommodate hearing-impaired drivers, an alternate example of the warning device includes a visual warning indicator connected to the external warning connection of the housing, and fixed to the vehicle windshield or mounted inside the driver compartment.  
         [0022]    Another example of the overhead obstacle detector is possible where the measuring, evaluating, and warning components are built permanently into the vehicle, and make use of the vehicle&#39;s battery for power.  
         [0023]    [0023]FIG. 3 is a bottom view of an overhead obstacle detector as it may appear when removed from the vehicle and turned over. Speaker  14  can provide the audible warning component of the example device, and has sufficient amplitude to be clearly heard by the driver through the roof of the vehicle and under normal driving conditions. Bottom cover  15  corresponds to magnetic base  13  described above, and may be constructed of magnetic material, or may contain an embedded magnet or magnets, or may be covered by an adhesive-backed magnetic sheet. Switch  16  can turn the device off and on when it is removed and replaced from the vehicle, and may be located in bottom cover  15  to protect it from inadvertent operation. In an alternate example of an overhead obstacle detector, switch  16  is a magnetic switch integrated into bottom cover  15  that is automatically closed when the device is attached to the vehicle roof, and automatically opened when the device is removed.  
         [0024]    [0024]FIG. 4 shows a cutaway view of overhead obstacle detector  5 , and illustrates the internal components. Ultrasonic transducer  17  may be attached to housing  18 , and could be sealed to prevent water from entering housing  18 . In this example, transducer  17  may be situated at angle  7  in FIG. 1 with respect to the longitudinal axis of housing  18 . In an alternate example of the overhead obstacle detector, the attachment method of transducer  17  may allow this angle to be adjusted by the driver when the nominal value of angle  7  is not suitable for typical operating conditions, such as when the vehicle has a roof plane that deviates substantially from horizontal. In another example of an overhead obstacle detector, adjustment of angle  7  could be accomplished with a mechanism for changing the angle of bottom cover  19  with respect to housing  18 , for example a wedge-shaped shim.  
         [0025]    In the example overhead obstacle detector, circuit board  20  contains the ultrasonic transmitter and receiver circuitry, microprocessor, and additional supporting electronic components. Transducer  17 , speaker  21 , external alarm connector  22 , external power connector  23 , and batteries  24  are connected to circuit board  20 .  
         [0026]    An alternate example of the warning component is shown in FIG. 5, and consists of a radio receiver  25 , microprocessor  26 , a warning speaker or buzzer  27 , and an accessory adapter plug  28 , or alternately a battery. This example of the warning component may be fitted inside the vehicle driver compartment, and receives signals from a low-power radio transmitter embedded on circuit board  20 . In this example, a signal could be transmitted from device  11  to warning component  29  when the alarm condition is met, and the warning speaker or buzzer  27  could be activated. The warning component may alternately include one or more LEDs or other visual status indicators  30  to signal the driver if the device  11  is not operating properly, for example when the battery is low, or the device  11  is not turned on, or the radio transmitter or receiver is not working. To provide status information about operating conditions, device  11  could transmit a periodic signal to warning component  29 , and microprocessor  26  could activate indicator or indicators  30  according to the presence or state of the periodic signal.  
         [0027]    In another example overhead obstacle detector, radio receiver  25  may be replaced with an infra-red optical receiver, and a remote infra-red optical transmitter may be attached to external alarm connector  22 .  
         [0028]    [0028]FIG. 6 is a block diagram showing an example of the circuit board, transducer, and speaker. Microcontroller  31  outputs a square wave signal on output line  32 , which is amplified by transmitter  33  and sent to the ultrasonic transducer  34 . Echo signals received by transducer  34 , which is used in this example for both transmitting and receiving, are detected and amplified by receiver  35 , which outputs a reference voltage and comparator signal on lines  36  and  37 , respectively. Alternate examples of the overhead obstacle detector may include a separate transmitting and receiving transducer. After sending the pulse signal on line  32 , microcontroller  31  starts an internal timer, waits for a time period corresponding to the ringing period of the transducer, and then monitors comparator line  37 . When the signal voltage on comparator line  37  exceeds the voltage on reference line  36 , the value of the internal timer is captured, and a risk evaluation calculation described below is initiated. When the risk exceeds a predetermined maximum value, the microcontroller outputs to speaker  38  a signal corresponding to a collision warning. In alternate examples of the overhead obstacle detector, the microcontroller periodically tests for low battery voltage and/or the presence of dirt or other contaminants on transducer  34  according to procedures described below, and outputs signals corresponding to these conditions on speaker  38 .  
         [0029]    The ultrasonic transceiver circuit of the example device is show in FIG. 7. The transmit pulse generated by the microcontroller is input on line  39 , and controls the gate of enhancement MOSFET  40 . This causes current to flow through the primary winding of transformer  41  and generates a high voltage signal driving ultrasonic transducer  42 . When an echo is received by transducer  42 , it generates a voltage on the input of operational amplifier  43 , which amplifies the signal and inputs it to operational amplifier  44 . Operational amplifier  44  outputs the comparator voltage which is sent to the microprocessor on line  45 . The reference voltage is output on line  46 . The detection sensitivity can be adjusted via resistor  47 . In an alternate example of the ultrasonic transceiver, the receiver circuit can be replaced by an integrated sonar ranging chip such as the Texas Instruments TL852.  
         [0030]    [0030]FIG. 8 is a flow diagram of an example of the main program of the microprocessor. Upon startup at  48 , such as when the device is switched on or power is connected, the microcontroller can immediately execute the ping subroutine  49 , which is described in detail below. Ping subroutine  49  returns a value representing the time delay D between sending and receiving the burst of ultrasonic pulses, and hence the distance to the closest object which returns an echo loud enough to trigger the comparator as described above. If there are no detectable echoes within a predetermined time out period, the ping subroutine returns 0. If a time value is returned, the program proceeds to step  50 , which tests for the presence of a stored time value from the previous ping. If a previous time value exists, the program proceeds to the calculation subroutine  51 , which is described below. The current and previous time values are used by calculation subroutine  51  to calculate the value of the risk parameter. Next, the program compares the risk parameter returned by the calculation subroutine to a predetermined maximum value. If the risk is greater than the predetermined maximum, the collision alarm routine  52  is called to signal the alarm device and thus warn the driver of a collision. The program then proceeds to  53 , where the stored time value is replaced by the current time value. Next, the program waits for an interval representing the desired sample rate between successful pings of approximately 250 ms. If the ping subroutine  49  times out instead of returning a value, the program proceeds to block  54 , where the stored time value is cleared. The program then proceeds to  55 , where the microprocessor is put to sleep for a period of approximately one second. The processor then wakes up and proceeds again to the ping subroutine  49 . In an alternate example, the program may proceed from block  54  to the test subroutine  56 , which optionally tests the battery voltage, and/or the condition of the ultrasonic transducer, as described later.  
         [0031]    The flow diagram of the ping subroutine is shown in FIG. 9. The program first starts the pulse interval timer in block  58 , which begins generating the square wave output for the ultrasonic transmitter as described above. The interrupt routine for the pulse timer increments a counter after each cycle, which is checked in block  59 , and when a predetermined number of pulses have been sent, the program proceeds to block  60  and turns off the pulse timer. Next, the comparator capture timer is started in block  61 , and the program loops through blocks  62  and  63  waiting for the capture timer to expire, or a value to be captured, whichever comes first. The ping subroutine then ends, and returns either the captured timer value, or zero if the timer expired. The expiration time for the capture timer is at least the echo delay time required for echoes at the maximum range of the ultrasonic detection circuit from a large acoustically reflective surface.  
         [0032]    [0032]FIG. 10 is a flow diagram of an example of the calculation subroutine, corresponding to the evaluation components of the overhead obstacle detector. The critical condition for signaling the alarm is determined by the control program using the current value of the pulse echo delay returned by the ping routine of FIG. 9 to represent the distance between the obstacle detector and an obstacle, and the current value along with the stored previous value to calculate the relative speed between the detector and the obstacle. To facilitate parameterisation of the distance and speed components, and to provide a single parameter representing the risk of collision, the system may be modeled as a virtual spring and damper connected between the vehicle and the obstacle, where the virtual spring is compressed as the vehicle approaches the obstacle. The risk parameter could thus be the total virtual force F exerted by the spring and damper:  
       F   =     kx   +     δ             x          t                                 
 
         [0033]    The virtual spring rate k and damping coefficient δ are determined empirically to provide a reasonable degree of advance warning, and to prevent undesirable false alarms, such as when approaching a slowing vehicle in traffic or stopping behind a truck or in front of a large acoustically reflective surface. The virtual spring compression x can be calculated by subtracting the current echo delay from a value representing the echo delay at the maximum range of the ultrasonic detection circuit. The velocity can be calculated using the difference between the current and previous echo delay values, divided by the elapsed time period between those two values, which in an alternate example of the program may be varied according to the current value of the delay time. Thus the virtual force F is:  
       F   =       k        (       x   max     -   x     )       +     δ        (       x   -     x     t   -   1         P     )                               
 
         [0034]    where F is the virtual force, k is the virtual spring constant, x max  is the maximum distance, x is the current distance, δ is the virtual damping coefficient, x t-1  is the previous sample distance, and P is the time between the current and previous samples. The alarm condition is met when: 
         
       F&gt;F 
       max 
     
         [0035]    where F max  may be determined empirically along with k and δ to correspond to the closest approach distance and highest approach speed that are acceptable under most actual circumstances.  
         [0036]    Returning to FIG. 10, program blocks  64 ,  65 , and  66  correspond to an alternate example of the evaluation method, and will be described later. The example calculation subroutine begins at block  67 , calculating the velocity of the approach by dividing the difference between the current and last delay times by the sample period. The last delay time is represented in the diagram as REG, the current time by D, the sample period by P, and the velocity by V. In block  68  the program then calculates the virtual force parameter, represented in the diagram by F, using a representation of the force equation above where k represents the spring constant k, D max  the value of x max , and d the damping coefficient δ. The subroutine then exits and returns the virtual force value to the main program.  
         [0037]    As discussed previously, some examples of the overhead obstacle detector may test the battery condition and/or transducer contamination. FIG. 11 shows the flow diagram for the test program code. Blocks  69  and  70  increment a counter to determine if it is time to run the battery test, and if so, block  71  is executed and uses the comparator or optionally an additional circuit on the circuit board to test the battery voltage. If the voltage is below a predetermined minimum, the alarm is signaled and the counter is reset in blocks  72  and  73 . The test for transducer contamination begins at block  74  incrementing the test counter, and if it is time to run the test executes block  75 , which sends a burst of pulses to the transducer. In block  76 , a timer is set up to isolate a time window in which to activate the comparator and corresponding to the period in which a clean transducer is still ringing. The comparator is used to measure the transducer voltage during this window, and if the transducer has been damped by dirt or other contaminants, the ringing amplitude will not be sufficient to trip the comparator, and the dirty transducer alarm is sent to the alarm device in block  77 . If the transducer is clean, the comparator will be set, and the alarm is not signaled. After clearing the alarm counter in block  78 , the subroutine returns.  
         [0038]    [0038]FIG. 12, which is closely related to FIG. 1, shows vehicle  79  closely approaching garage  80 , and depicts a condition referred to herein as echo fall-off. In this condition, vehicle  79  has advanced far enough toward or into garage  80  that the ultrasonic beam path  81  is no longer reflected by garage surface  82 , and echo signals are now reflected by objects on garage ceiling  83 , such as beams or garage door equipment, or reflected by back wall  84  of the garage. In an alternate example of the main and calculating routines of the microcontroller program logic, and in case the control logic of the device has not already signaled an alarm, the sudden increase in echo delay time as the echo signal falls off of surface  82  may be treated by the control logic as an indication that an echo fall-off has occurred, and the difference between the echo delay before and after the fall-off condition may be subtracted from subsequent echo delays. Looking at FIG. 10, program block  64  detects the echo fall-off, using the predetermined value MAXJUMP, and executes the offset adjusting block  65 . Block  64  tests for both echo fall-off and the inverse of echo fall-off, which occurs as the vehicle is backing away from the garage. In this way, a reasonably accurate representation of the position of the vehicle is maintained as long as the device is operating continuously during approach and backing maneuvers. The offset value may then subtracted from the current echo time value in block  66 , and the subsequent calculation of the virtual force continues with block  66 . In addition, the main program block in FIG. 8 contains an additional block  57 , to clear the offset value when the vehicle leaves the approach area and the ping subroutine begins timing out.  
         [0039]    [0039]FIG. 13 is a plot of data obtained with a prototype device as echo fall-off occurs. The horizontal axis represents the forward position of the vehicle as it approaches a garage, and the vertical axis is the echo delay measurement. The jump in echo delay time between points  85  and  86  represents a first echo fall-off condition, and the jump between points  87  and  88  show a second echo fall-off. The alternate example of the control logic described above effectively joins point  85  with point  86 , and point  87  with point  88 , to form a continuous curve. Thus the risk evaluation method can continue to function progressively as the vehicle moves into the garage.  
         [0040]    Having described the components of and examples of the device and methods of this disclosure, it should now be understood that many additional enhancements and modifications can be made to the device or methods which are still within the scope and intent of the disclosure.