Patent Publication Number: US-2018054569-A1

Title: Dual-focus camera for automated vehicles

Description:
TECHNICAL FIELD OF INVENTION 
     This disclosure generally relates to a dual-focus camera, and more particularly relates to equipping the camera with a negative-meniscus-lens configured to focus a portion of an image at a distance independent from the distance at which the remainder of the image is focused. 
     BACKGROUND OF INVENTION 
     It is known to install a camera behind a windshield of a vehicle to view an area proximate to, e.g. forward of, the vehicle to detect objects in or adjacent to the travel-path of the vehicle. It is also known to use camera technology to detect raindrops on a windshield for the purpose of controlling automated windshield wipers. However, since the focus-distance necessary to detect objects is much different than the focus-distance used to detect raindrops on the windshield are so different, the typical solution is to utilize two separate cameras. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment, a dual-focus camera suitable for use on an automated vehicle is provided. The camera includes an imager, a lens-assembly, and a negative-meniscus-lens (NML). The imager is used to detect an image of a field-of-view. The lens-assembly is used to direct the image from the field-of-view toward the imager. The lens-assembly is characterized as focused at a first-distance in the field-of view. The negative-meniscus-lens is interposed between the imager and the lens-assembly. The negative-meniscus-lens is configured to focus a portion of the image onto the imager. The portion is characterized as less than a whole of the image and focused at a second-distance in the field-of-view independent from the first-distance. 
     Further features and advantages will appear more clearly on a reading of the following detailed description of the preferred embodiment, which is given by way of non-limiting example only and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will now be described, by way of example with reference to the accompanying drawings, in which: 
         FIG. 1  is a vehicle equipped with a camera in accordance with one embodiment; 
         FIG. 2  is a side view of the camera of  FIG. 1  in accordance with one embodiment; 
         FIG. 3  is an image captured by the camera of  FIG. 2  in accordance with one embodiment; and 
         FIG. 4  is a side view of a negative-meniscus-lens usable in the camera of  FIG. 2  in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a non-limiting example of a dual-focus camera  20 , hereafter referred to as the camera  20 , which is installed behind a windshield  12  of an automated vehicle  10 , i.e. within the interior of the vehicle. In this example the camera  20  is oriented to observe or capture images from a field-of-view  14  forward of the automated vehicle  10 , however it is recognized that the camera  20  is suitable for uses elsewhere on the vehicle and directed to different fields-of-view. While the examples presented may be characterized as being generally directed to instances when the vehicle  10  is being operated in an automated-mode, i.e. a fully autonomous mode, where a human operator (not shown) of the vehicle  10  does little more than designate a destination, it is contemplated that the teachings presented herein are useful when the vehicle  10  is operated in a manual-mode. While in the manual-mode the degree or level of automation may be little more than providing steering assistance to a human operator who is generally in control of the steering, accelerator, and brakes of the vehicle  10 . That is, the camera  20  may only be used by a safety system of the vehicle  10  to assist the human operator as needed to, for example, keep the vehicle  10  centered in a travel-lane, maintain control of the vehicle  10 , and/or avoid interference and/or a collision with another vehicle. 
       FIG. 2  illustrates a non-limiting example of one possible embodiment of the camera  20  suitable for use on the automated vehicle  10 . The camera  20  includes an imager  22  used to detect an image  24  of the field-of-view  14 . The imager  22  may be any of many types of commercially available imagers such as an Aptina AR0132 1.3MP (1280×960) or an OmniVision OV7955 0.3MP (640×480) imaging device. 
     The camera  20  also includes a lens-assembly  26  used to direct the image  24  from the field-of-view  14  toward the imager  22 . The lens-assembly  26  may be any of many types of commercially available lens-assemblies known to be suitable for this application, having relatively few or numerous lens elements. In general, for the application suggested by  FIG. 1 , the lens-assembly  26  is selected to meet the requirements of the application, for example to have a viewing angle, i.e. the angle of the field-of-view  14 , suitable for detecting objects on or near the travel-path of the vehicle  10 . In particular, the lens-assembly  26  that is selected may be characterized as being focused at or on a first-distance  28  in the field-of view  14 . A suitable value for the first-distance  28  is thirty-five meters (35 m) from the lens-assembly  26 , which is illustrated to be interpreted as well past the left edge of the page showing  FIG. 3 . 
     As previously mentioned, camera based technology is used by various vehicle safety systems to detect objects proximate to a vehicle, and by automated wiper systems to detect raindrops on the windshield  12  of the vehicle. Prior solutions for image detection at such disparate ranges (e.g. 35 m for object detection and 25 mm for raindrop detection) required two cameras. However, the camera  20  described herein is able to do both tasks because the camera  20  is equipped with a negative-meniscus-lens  30 , hereafter referred to as the NML  30 , which is interposed between the imager  22  and the lens-assembly  26 . The NML  30  is generally configured to focus a portion  32  of the image onto the imager  22 , where the portion  32  is characterized as less than a whole of the image  24 . Furthermore, the portion  32  is characterized as focused at a second-distance  34  in the field-of-view  14  independent from the first-distance  28 . For example, the second-distance  34  may be twenty-five millimeters (25 mm) so raindrops on the windshield  12  while the first-distance  28  may be thirty-five meters, as previous suggested. As used herein, the term negative-meniscus-lens is used to indicate any type of an optical-element design or a lens-element that could be interposed between the lens-assembly  26  and the imager  22  that could effectively change the focus-distance of the lens-assembly  26  from the first-distance  28  to the second-distance  34 . 
       FIG. 3  illustrates a non-limiting example of the image  24  received or detected by the imager  22  that is produced by the combination of the lens-assembly  26  and the NML  30 . The dashed line that segregates the portion  32  from a remainder  38  of the image  24  is not actually present in what is received by the imager  22 , but is provided here to help distinguish the portion  32  from the remainder  38 . Note that the raindrops  36  in the portion  32  are in-focus, while relatively distance objects such as buildings and other vehicles in the portion  32  are out-of-focus. In contrast, relatively distance objects such as buildings and other vehicles in the remainder  38  are in-focus while any raindrops in the remainder  38  are so out-of-focus as to be undetectable. 
     In one embodiment, the NML  30  is configured to have a fixed focal-length, i.e. is not adjustable. It is recognized in view of the image  24  that having a fixed focal-length may make it difficult to detect, identify, and/or classify distant objects within the portion  32 . However, it is contemplated that distance objects in the remainder  38  may be readily detected, identified, and/or classified, and that objects moving through the remainder  38  toward the portion  32  may be detected by safety system more quickly than would be the case if the portion  32  occupied the entire image as is the case when a camera is only used for raindrop detection, i.e. when all of the field-of-view  14  is focused at the second-distance  34 . 
     Preferably, the NML  30  is configured to have an adjustable focal-length. It is further preferable that the adjustable focal-length is characterized by a range of adjustability, and the range is selected such that the second-distance  34  can be adjusted to be equal the first-distance  28 . The technology used to provide for the adjustable focal-length is preferably fast enough so that the variable focus-distance in the portion  32  provided by the NML  30  allows the focus-distance of the portion  32  to be quickly switched between the first-distance and the second-distance so both object detection and raindrop detection can be performed by a single instance of the camera  20 . 
       FIG. 4  illustrates a non-limiting example of how a variable-version 40 of the NML  30  can be provided. The variable-version 40 uses an electro-wetting lens set packaged between 2 glass layers. As will be recognized by those in the art, a voltage is applied to a conducting fluid ( 2  sections) and induces a change in the shape of the conducting fluid relative to the insulating fluid. Varying the voltage creates changes in the shapes of the lens, including the shape needed to provide the variable-version 40 of the NML  30 . Two separate conducting fluid compartments are used to create the inner and outer NML curvatures. The conducting and insulating fluids have different indices of refraction and allow the combination to create various lens refractive characteristics. The glass layers containing the lens set uses a transparent conductive film layer (e.g. ITO or Indium Tin Oxide) to facilitate the voltage drop across the conductive fluid allowing for the shape change. The typical response is thirty milliseconds with a maximum voltage requirement of 60V rms. 
     In order to optimize the detection of the raindrops  36  in the portion  32  and distant objects in the remainder  38 , it may be advantageous if the camera  20  includes a filter  42  configured so light that passes through the NML  30  is filtered different from light that does not pass through the negative-meniscus-lens. By way of example and not limitation, it may be preferable if the filter  42  for light from the portion that passes through NML  30  is characterized as a near-infrared (NIR) filter as most rain sensing uses active NIR LEDs whose light is directed at the windshield  12 , and a reflected signal from the windshield  12  is sensed, where the LED NIR wavelength spectrum is about 800-1000 nm. The outer area of the filter  42  where light for the remainder  38  passes could be either a visible color or visible monochrome filter depending upon the outer field camera function. It is also recognized that using an outer field visible color filter camera allows better discrimination for some object characteristics, e.g.—traffic lighting, lane marking colors. 
     Accordingly, a dual-focus camera (the camera  20 ) is provided. The camera  20  provides for raindrop detection and object detection using a single camera. 
     While this invention has been described in terms of the preferred embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.