Abstract:
A method of assisting a driver in aligning a vehicle hitch with a trailer hitch and electronic trailer alignment system includes providing a stereoscopic-imaging system and positioning the imaging system at one of the vehicle hitch or the trailer hitch. The imaging system includes at least two image sensors. At least two different images of a surface at the other of the vehicle hitch or the trailer hitch are captured with the at least two image sensors. Position data is captured from the at least two different images of the surface at the other of the vehicle hitch or the trailer hitch. The position data defines a position of the other of the vehicle hitch or the trailer hitch with respect to the one of the vehicle hitch or the trailer hitch. Steering data that will cause the vehicle hitch to approach the position of the trailer hitch is determined.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from U.S. application Ser. No. 60/947,808, filed on Jul. 3, 2007, the disclosure of which is hereby incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to trailer locating devices and, more specifically, it relates to a trailer hitch alignment system for assisting a user to align a hitch of a vehicle with a trailer hitch. 
         [0003]    Users of trailers often have great difficulty in aligning their vehicle&#39;s hitch with the trailer hitch of a conventional trailer. A conventional trailer has a plurality of wheels rotatably supporting a frame and a trailer hitch for removably coupling with a vehicle that will be towing the conventional trailer. The user must align the hitch of the vehicle with the raised trailer hitch. This is extremely difficult since the hitch is usually out of viewing because of its location upon the vehicle&#39;s bumper. Generally, two persons are required to effectively and efficiently align the vehicle hitch with the trailer hitch. However, when the user is trying to align the hitches alone, the user must then slowly back up to the trailer hitch so as to prevent damage to the vehicle and trailer, stop the vehicle, exit the vehicle, view the position of the hitch relative to the trailer hitch to prevent damage to the trailer hitch and/or the vehicle, and then reenter the vehicle to repeat the process. This process is then generally repeated numerous times until the vehicle hitch and trailer hitch align. Hence, there is a need for a trailer hitch alignment system that allows a user to conveniently and precisely align a vehicle hitch with a trailer hitch without the user having to repeatedly exit the vehicle. 
         [0004]    The repeated exiting and entering the vehicle is undesirable to users. In addition, the constant exiting and entering of the vehicle is time consuming and potentially dangerous. Mother issue is the inevitable likelihood of vehicle or trailer damage during attempts for trailer hitch alignment. 
         [0005]    Devices presently in the art for trailer hitch alignment include systems utilizing cameras that are attached to the rear of the vehicle and display in the passenger compartment a view of the vehicle trailer hitch. Other devices include systems with mirrors mounted to provide a view of the vehicle&#39;s hitch. These systems are often expensive, inconvenient, and cumbersome to use. 
         [0006]    These and other objects, advantages and features of this invention will become apparent upon review of the following specification in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a side elevation view of an electronic trailer hitch alignment system according to an embodiment of the invention applied to a vehicle and trailer; 
           [0008]      FIG. 2  is a side elevation of a trailer hitch with a sensor applied thereto; 
           [0009]      FIG. 3  is a top plan view of the trailer hitch in  FIG. 2 ; 
           [0010]      FIGS. 4   a - 4   c  are perspective views of a vehicle hitch with a visible target applied to the vehicle hitch; 
           [0011]      FIGS. 5   a - 5   d  are perspective views of an alternative embodiment of a visible target; 
           [0012]      FIGS. 6   a - 6   c  are perspective views of another alternative embodiment of a visible target; 
           [0013]      FIG. 7  is a block diagram of a control system according to an embodiment of the invention; 
           [0014]      FIG. 8  is a diagram illustrating stereoscopic image processing; 
           [0015]      FIG. 9  is a flowchart of a method of assisting a driver in aligning a vehicle hitch with a trailer hitch; and 
           [0016]      FIG. 10  is a perspective view of a driver interface module. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]    Referring now specifically to the drawings, and the illustrative embodiments depicted therein, a trailer alignment system  10  is illustrated for use with aligning a trailer hitch  14  of a trailer  11  with a vehicle hitch  16  of a vehicle  12  ( FIG. 1 ). Trailer alignment system  10  includes a sensor  18  that is adapted to sense vehicle hitch  16 , if sensor  18  is positioned at the trailer hitch, and to sense the trailer hitch if sensor  18  is positioned at the vehicle hitch. In the illustrative embodiment, sensor  18  is illustrated as positioned at the trailer hitch. This is a configuration that is particularly adapted for use in the aftermarket. In the OEM market, sensor  18  may be conveniently incorporated into the vehicle  12  and used to sense the trailer hitch. 
         [0018]    Trailer alignment system  10  may additionally include a driver interface module  20 , which is positioned in the driver&#39;s cab in order to provide visual and/or audible signals to the driver. Alternatively, trailer alignment system  10  may provide steering commands directly to the vehicle steering system in order to automate the trailer alignment process. Trailer alignment system  10  may additionally include a visual target  22  which is configured to be applied to the hitch  16 ,  18  that is opposite to the hitch  16 ,  18  to which the sensor  18  is applied ( FIGS. 4-6 ). In the illustrative embodiment, visual target  22  is configured to be temporarily applied to a structure, such a ball hitch  24 , for the alignment process and removed after the alignment process, but prior to the engaging of the respective hitches  16 ,  18 , as disclosed in commonly assigned United States Patent Application Publication No. US 2005/0285371 A1 published Dec. 29, 2005, by J. Edward Ramsey et al. entitled TRAILER ALIGNMENT DEVICE, the disclosure of which is hereby incorporated herein by reference. 
         [0019]    In the illustrative embodiment, sensor  18  is a camera system and, in particular, a stereoscopic-imaging system. As is known in the art, a stereoscopic-imaging system has two image sensors that are adapted to capturing at least two different images of a surface of an object at a distance. If stereoscopic-imaging system  18  is positioned at the trailer hitch, it captures an image of a surface at the vehicle hitch. If imaging system  18  is positioned at the vehicle hitch, it captures an image of a surface at the trailer hitch. In the illustrative embodiment, stereoscopic-imaging system  18  utilizes a commercially available digital stereo head of the type marketed by Videre Design Company. However, other stereoscopic-imaging techniques may be used. Stereoscopic-imaging system  18  additionally includes a control  26  having a computational unit, such as a processor  28  which processes digital images produced by two image sensors  30   a ,  30   b  that are at a fixed relationship to each other that allows the image sensors to capture stereoscopic images of the opposite hitch ( FIG. 7 ). Computational unit  28 , in the illustrative embodiment, is a digital signal processor of the type well known in the art that is available from various manufacturers, but may be a general purpose processor, an application specific integrated circuit, or the like. Computational unit  28  is provided with power, such as from a power source  32 , which may be a vehicle battery connection, an internal battery, or other known power source. Computational unit  28  may additionally be provided with peripheral devices, such as a random access memory  34 , a non-volatile memory  36 , both of which are used for storing various program code and parameters used by the processor, and an oscillator  38  to provide a clock for the computational unit. 
         [0020]    Computational unit  28  produces steering data at an output  40  that may be used to provide visual and/or audio information to a driver, such as using a video display  42  or speakers (not shown) that are part of driver interface module  20 . Where sensor  18  is positioned at the trailer hitch, a communication channel, such as a wireless communication channel including an RF transceiver  44  at sensor unit  18  and RF transceiver  46  at the driver interface module, may be utilized for communication. Other wireless communication, such as infrared, Bluetooth, or the like, may also be used. Alternatively, communication signals may be modulated over the vehicle-to-trailer wiring bundle. Where sensor  18  is at the vehicle hitch, it is possible to connect driver interface module  20  with sensor  18  by wireless communication, hardwired communication, fiber optics, or the like. 
         [0021]    Visual target  22  provides an assist for capturing of an image of the hitch opposite the hitch bearing sensor  18  in order to assist in determining the position of the hitch opposite sensor  18 . As best seen by reference to  FIGS. 4   a - 4   c , visual target  22  includes a surface  44  having visual texture features  46  on the surface. In the illustrative embodiment, surface  44  wraps around a vertical axis of the target in a range of between approximately 180 degrees and 270 degrees for observation by sensor  18 . In the illustrative embodiment, visual texture features  46  are defined by a series of two or more spaced apart vertical stripes  48 . However, other visual texture features may be utilized. In the illustrative embodiment, vertical strips  48  converge at a top portion of visual target  22 . 
         [0022]    In an alternative embodiment illustrated in  FIGS. 5   a - 5   d , a visual target  122  includes a surface  144  defining texture features  146 , such as vertical stripes that terminate below the top of the visual target. Target  122  has a flat top in order to have stripes that parallel throughout their entire length. Visual target  122  further includes an interior clip  145  that is configured to flexibly engaging the ball hitch  24 . Clip  145  facilitates firm, but removable, retention of visual target  122  on the ball hitch. While clip  145  has an overall dome shape to directly engage the ball of the hitch, it could also be configured to engage other portions of the vehicle hitch, such as the neck of the ball hitch. In accordance with the principles set forth in commonly assigned United States Patent Application Publication No. US 2005/0285371 A1 published Dec. 29, 2005, by J. Edward Ramsey et al. entitled TRAILER ALIGNMENT DEVICE, the disclosure of which is hereby incorporated herein by reference, visual target  22 ,  122  may have an inner surface  50  having a domed portion in order to fit on ball hitch  24 . Because the visual target is coincident with the ball hitch, sensor  18  is able to identify the position of the ball hitch by identifying the position of visual target  22 ,  122 . However, visual target  22 ,  122  may be positioned elsewhere, such as on a vertical surface of vehicle  12  or trailer  11  with suitable compensation made for dimensional offset between the hitch feature, such as the ball hitch, the trailer hitch tongue, and the locations of the visual target and sensor. 
         [0023]    In another alternative embodiment, a visual target  222  includes one or more light sources  52  in order to illuminate surface  244 . By illuminating surface  244 , the visual contrast provided by visual texture features  246  becomes greater. This may be particularly useful, by way of example, where visual target  222  is adapted to be positioned on ball hitch  24 . As a visual imaging system, sensor  18  could, otherwise, be blinded by, for example, the vehicle&#39;s backup lights, which would be illuminated while the vehicle is backing up to position the trailer hitch and vehicle hitch together. By enhancing visual contrast, light source  52  allows the sensor to determine the position of visual target  222  even in the presence of the vehicle&#39;s illuminated backup lights, as well as other sources of visible noise, such as the lines of the vehicle, and the like. Light source  52  may be useful during daytime and nighttime conditions. Light source  52  may be a light-emitting diode (LED) source with a self-contained battery  53 . Alternatively, the light source may be powered from the vehicle&#39;s battery and may be configured to be energized when the vehicle&#39;s backup lights are energized. Visual target  222  may include a wire bundle (not shown) having a connector which connects with a conventional trailer connector on vehicle  12 . The connector on visual target  222  may be configured to plug into the conventional connector on the vehicle and provide for connection with the cable extending from the trailer  11 . This would allow the light source  52  to receive power from the vehicle without requiring separate wiring of the visual target to the vehicle. 
         [0024]    Other variations will be apparent to the skilled artisan. For example, rather than light source  52  being an internal light source, it could be an external light source directed onto visual texture features  246 . Alternatively, light source  52  could be a reflector to reflect the backup lights of the vehicle, or other light source, toward the visual texture features of surface  44 ,  144 ,  244 , or the like. Also, although visual target  22 ,  122 ,  222  is illustrated as a cylindrical shaped surface, it could be a flat surface or other three-dimensional shape. Also, it should be understood that visual texture features  46 ,  146 ,  246  may be applied directly to ball hitch  24 , to a surface of vehicle  12 , or to a surface of trailer  11 . 
         [0025]    Operation of sensor  18  may be understood by reference to  FIG. 8  in which a pair of image sensors  54 , which, in the illustrated embodiment, are CMOS low-noise high-sensitivity imagers that are packaged as a unit and are of the type commercially available and marketed by Videre Design Corporation. Processor  28  performs a disparity calculation based upon the baseline b, the focal length f of the imaging sensor and the offset O L  and O r  between image pixels and the focal points using the following equation:
       where D=bf/d,   where D is the distance to the target,   b is the baseline,   f is the focal length and   d is the difference between O L  and O r .       
 
         [0031]    The disparity value can then be used to find which pixels correspond in the two images. One of the two images is typically considered to be the reference image. Pixels in the reference image have higher x coordinates than their corresponding pixels in their other image. The x coordinates correspond to lateral left-to-right locations. The y coordinates, which correspond to vertical dimensions, are the same for both images. The x coordinates are related by x r  and x L  minus  16   d  where disparities are specified in units of 1/16 pixels. Disparity calculations and determination of which pixels correspond in the two images is known in the art and is disclosed in detail in a publication entitled “SRI Small Vision System,” User&#39;s Manual, Software Version 4.2, published in February 2006 by SRI International, the disclosure of which is hereby incorporated herein by reference. 
         [0032]    Computational unit  28  may be programmed with algorithms to carry out the object recognition illustrated in  FIG. 8 . A low-level image-processing algorithm  56  may provide some initial image processing on the output of image sensors  30   a  and  30   b . This may include, by way of example, providing image windows, such as area correlation windows, and the like, as described in the Small Vision System publication referred to above. Once the low-level image processing is carried out, a disparity calculation algorithm  58  may be provided to perform the disparity calculation illustrated in  FIG. 8  in order to determine the position of visual target  22 . A high-level algorithm may be provided at  60  in order to determine steering data for causing the vehicle hitch to become aligned with the trailer hitch, as will be described in more detail below. In the illustrated embodiment having a video display  42 , a video conversion algorithm  62  converts the steering data produced by algorithm  62  to a video format which is then transmitted by RF transceivers  44  and  46  to be displayed on video display  42 . 
         [0033]    Video produced by video conversion algorithm  42  may be of the type illustrated in  FIG. 10  in which driver interface module  20  is illustrated as having a video display  42  that produces at a minimum a first indicia  64  which represents the location of visual target  22  which may be positioned at ball hitch  44 . Second indicia  66  may be provided to represent the location of the other hitch, which, in the illustrative embodiment, is the trailer hitch. As vehicle  12  is moved towards the trailer, indicia  64  moves in the direction of indicia  66  as illustrated by the arrow in  FIG. 10 . Indicia  64  and indicia  66  provide a representation of the vehicle hitch and the trailer hitch as viewed from above. This provides a “birds-eye” view of the alignment process in order to be intuitive to the driver when attempting to move indicia  64  to be coincident with indicia  66  whereby the vehicle hitch will be aligned with the trailer hitch. In addition, driver interface module  20  may include driver feedback, such as one or more speakers or other feedback device, in order to produce a beep or other sound or indication when the indicia  64  lines up with indicia  66  to alert the driver to the aligned condition. The driver interface module may include various input devices, such as selector switches  68 , which may be mechanical switches, soft keys, or the like. Alternatively, the driver interface module may be equipped to respond to voice commands. Display  42  may be a liquid crystal display (LCD) screen, a light-emitting diode (LED) display screen, a cathode ray tube (CRT) display screen, a quartz display screen, a touch screen display screen, a plasma display screen, or the like. For example, display  42  may be a LED type display screen with a plurality of LEDs forming the display screen, such as 600 LEDs across by 1024 LEDs down. Moreover, magnification overlays may be added to enlarge the screen to ease viewing. While display  42  is illustrated as a dedicated unit, its function may be incorporated in a multi-function display incorporated into the dashboard of the vehicle. 
         [0034]    A process  70  carried out by digital signal processor  28  to produce steering data begins at  72  with system initialization ( FIG. 9 ). Once the system is initialized, control  26  will attempt to acquire an image of visual target  22  at  74  and will obtain a left image  76  with one of the image sensors  54  and a right image  78  with the other image sensor  54 . The processor will then perform a depth calculation at  80  in order to determine a distance to the visual target in the form of a depth image  82 . The processor will also produce three-dimensional coordinates of the visual target by detecting the target at  84  and carrying out three-dimensional coordinate calculations at  86  utilizing the formula previous set forth. 
         [0035]    Once the coordinates of the position of visual target  22  have been obtained at  86 , a projection of the anticipated path of vehicle trailer hitch is made at  88  and displayed with video display  42  at  90 . Current path projection algorithms are known in the art. An example includes the backup system utilized with the commercially availably Lexus LS 460 vehicle marketed by Toyota. The processor also determines an ideal path at  90 , which would be an optimal path to direct the vehicle hitch toward the trailer hitch, and provide steering data at  92 . The steering data may be advised to the driver, such as audible commands (“turn left,” “turn right”) or by the display of a path with video display  42 . Examples of ideal path calculations are known in the art and are within the knowledge of the skilled artisan. 
         [0036]    The use of stereoscopic imaging allows the trailer alignment system to provide data to the driver and/or the vehicle to guide the vehicle hitch toward the trailer hitch at a greater distance than is known with prior systems and to do so in a more accurate manner. Also, it may do so in an intuitive manner that assists the driver in moving the vehicle, which is typically in reverse gear, to cause the vehicle hitch to become aligned with the trailer hitch. This is accomplished in a manner that may be incorporated into the vehicle for OEM applications or may be marketed as an aftermarket application. The use of a visual target having visual texture features facilitates object recognition to enhance the ability of the system to calculate the location of the target position opposite the sensor or detection unit. 
         [0037]    The use of a visual target, which may be in the form of a cap to fit over the ball hitch of the vehicle hitch, provides a device that may be applied to the vehicle when in use and removed for connection of the hitches thereby allowing the visual target to be stored away from the elements when not in use. Also, the ability in certain embodiments to internally illuminate the visual target facilitates the ability to distinguish the visual target in the presence of, for example, vehicle backup lights which will be illuminated during the trailer alignment process, as well as other sources of visible noise, such as the lines of the vehicle, and the like. 
         [0038]    The trailer alignment system disclosed herein may include a display that is user friendly and relates the positioning between the vehicle hitch and the trailer hitch coupler as the vehicle moves towards the trailer. The driver interface module may be mounted inside the vehicle or held by the driver. An RF transceiver may be incorporated into the display and the sensor unit to transmit data wirelessly from the sensor unit and display the data on the video display. The display may show the positioning in a “birds-eye” view with each trailer hitch being depicted as either a dot or a circle. However, other embodiments may include other shapes. On the display, the trailer hitches will be oriented in a vertical relationship with the trailer coupler icon located at the bottom of the display in a stationary position and the vehicle hitch icon located at the top of the display. The top indicia will move in a vertical direction downwardly as the vehicle moves closer to the trailer. This alignment will be displayed by the incorrect path that the vehicle hitch indicia, or icon, takes on the display as it nears the trailer hitch icon. Once the dot is positioned inside the circle, the representation demonstrates that the ball hitch is located under the trailer hitch coupler such that the coupler can be lowered onto the ball hitch once a visual target is removed from the ball hitch. Upon alignment, an audible or visual acknowledgement of alignment may be generated by driver interface module  20 . 
         [0039]    Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention which is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law including the doctrine of equivalents.