Patent Application
20060095172
Vehicle navigation systems have long been touted as a mechanism for reducing accidents, controlling traffic flow, guiding drivers to desired destinations, and for generally enhancing the overall driving experience.
All vehicle navigation systems require some form of sensing mechanism to detect vehicle movement. For example, it has been suggested to embed sensors in roads to track the motion of vehicles traveling along the roads. Such an approach, however, will necessitate tearing up existing roads to embed the sensors, require frequent maintenance, and be generally very expensive. It has also been suggested to mount antennas at regular intervals along the sides of roads to monitor vehicle movement. Such an approach will require establishing a large network of antennas throughout the country, and also be quite costly.
In general, although various technologies exist to monitor vehicle movement for a vehicle navigation system, none have proven to be practical or reasonably affordable.
In accordance with the invention, an optical vehicle motion detection system is provided in which motion of a vehicle is determined by detecting positional change of the vehicle relative to a surface of a road along which the vehicle is traveling. An optical vehicle motion detection system according to the invention has at least one optical detector on a vehicle for detecting an image of a road surface and for generating image data corresponding to the detected image. An image processor processes image data corresponding to successive images of the road surface detected by the at least one optical detector as the vehicle travels along the road for determining positional change of the vehicle relative to the road surface and generates vehicle motion data. The optical vehicle motion detection system according to the invention can be incorporated in a vehicle navigation system to permit monitoring of the movement of the vehicle for accident prevention, traffic control and for other purposes.
Furthermore, the invention provides embodiments and other features and advantages in addition to or in lieu of those discussed above. Many of these features and advantages are apparent from the description below with reference to the following drawings.
Embodiments in accordance with the invention provide an optical vehicle motion detection system and a method for detecting motion of a vehicle.
In the exemplary embodiment illustrated in
As also shown in
As will be explained more fully hereinafter, optical vehicle motion detection system 100 is incorporated in a vehicle navigation system that includes a vehicle navigation system processor that receives the vehicle motion data generated by data processor 118 and generates data identifying the actual position of the vehicle. The actual position data is used by the vehicle navigation system to monitor movement of the vehicle.
Optical vehicle motion detection system 100 may be similar to an optical detection system used in an optical computer mouse to control the position of a cursor on a display screen of the computer. In particular, optical vehicle motion detection system 100 detects positional change of the vehicle by imaging the texture of a road surface similar to the manner in which an optical motion detection system of an optical mouse detects positional change of the mouse by imaging the texture of a mouse pad or the surface of a desk or the like.
A second image 214 of the road surface is then formed on photodetector 202 at time t2 after time t1 as shown in
It should be recognized that some road features detected by the optical detector may move somewhat as a result of the vehicle traveling over them. Such movable features may include, for example, cigarette butts, twigs, small pebbles and the like. Generally, it is believed that such features will tend to remain relatively stationary until picked up by turbulent air at the trailing edge of the vehicle after being detected by the optical detector; and thus will not significantly affect the accuracy of the vehicle motion determination. Also, inasmuch as vehicle motion is typically determined by averaging over thousands of images, the effects of such movable features will normally not be significant in any event.
An optical vehicle motion detection system according to exemplary embodiments in accordance with the invention should detect images of a road surface at frequent intervals, for example, about every 1-10 centimeters of travel, in order to permit vehicle motion to be accurately determined. At a maximum vehicle speed of 100 miles per hour, a sample rate of 4,469 kHz will result in an image being detected for every centimeter of vehicle travel. At more typical vehicle speeds, a reduced sample rate may be used and at slow vehicle speeds, for example, when parking a vehicle, the sample rate may be reduced even further. In general, the sample rate may be maintained at a constant value irrespective of vehicle speed, or may be adjusted as a function of the speed of the vehicle.
Although, as indicated above, optical vehicle motion detection system 100 may be similar to an optical detection system used in an optical computer mouse, an optical vehicle motion detection system presents many problems that are not encountered in the operation of an optical mouse. For example, in an optical vehicle motion detection system, it is important that the optical detector maintain visual contact with a road surface at all times in order to be able to accurately determine positional change of a vehicle relative to the road surface. The nature and condition of a road surface, however, can vary significantly and significant variations in the road surface can affect the ability of the optical detector to maintain visual contact with the road surface. For example, roads are constructed of concrete, asphalt, gravel and other materials, and the surface of a particular road may vary from place to place as a result of changes in the material of which the road is constructed. Also, even on a road constructed of a single material, the condition of the road surface can vary from place to place as a result of a new surface being applied to different portions of a road. As a vehicle transitions from one type of road surface to another, abrupt changes in the texture of the road surface may cause the optical detector to lose visual contact with the road surface.
Similarly, the condition of the road surface can vary as a result of dirt, snow, rain and the like which can also make it difficult for the optical detector to maintain proper visual contact with the road surface.
According to a further exemplary embodiment in accordance with the invention, loss of visual contact with a road surface by an optical detector can be obviated by providing an optical vehicle motion detection system that includes a plurality of optical detectors mounted at different locations on the vehicle.
By mounting a plurality of optical detectors at different locations on a vehicle, even if one optical detector loses visual contact with the road surface, it is likely that another of the plurality of optical detectors will maintain visual contact with the road surface and enable optical vehicle motion detection system 400 to continue to track positional change of the vehicle relative to the road surface.
As shown in
As a vehicle travels along a road, the vehicle chassis will tend to move up and down, changing the height of optical detectors mounted thereon relative to the road surface. Because the height changes are normally relatively slow as compared to the speed of the optical detectors, the optical detectors can usually track the height changes without losing visual contact with the road surface. A sudden and significant change in the height of an optical detector relative to the road surface, however, as a result of hitting a large bump, for example, may cause the optical detector to tilt and lose visual contact with the road surface. By providing a plurality of optical detector at different locations on the vehicle, however, it is probable that at least one of the plurality of optical detectors will maintain visual contact with the road surface permitting positional change of the vehicle to be tracked while optical detectors that lose visual contact with the road surface reacquire their position.
In general, when considering the effect of optical detectors losing visual contact with a road surface, general concepts relating to an observer that tracks the state of a system in the presence of disturbances and imprecise measurements are useful. A Kalman filter is a special case of a discrete time observer where gains are chosen to minimize the effects of mean square noise in the system and at a detector. In effect, the optical vehicle motion detection system of the present invention detects abrupt changes in the road surface and ignores measurements from optical detectors that require recalibration while accepting measurements from optical detectors that are properly tracking the road.
Variations in the height of an optical detector as a result of up and down movement of the vehicle as it travels along a road can also be accommodated by a lens system with a large depth of field or a lens system with variable focus.
In an optical vehicle motion detection system according to embodiments in accordance with the present invention, the optical detectors are spaced several inches above the surface of the road being imaged. As a result, the optical detectors are susceptible to receiving spurious light that can affect the ability of the detectors to properly track the road surface. This can particularly be a problem during daylight hours. The effects of spurious light can be reduced somewhat by positioning the plurality of optical detectors toward the center of the vehicle and away from the edges of the vehicle.
There is also some concern that the plurality of optical detectors can become dirty from road grime and the like. This problem can be obviated by recessing the optical detectors within a support tube, for example, by a couple of centimeters, and/or by providing a cowling or other protective structure to help divert dirt away from the optical detectors. If desired, a mechanism can also be provided to actively clean the optical detectors. For example, a dirt detector can be provided to monitor each optical detector and to activate a small sprayer or wiper when an optical detector becomes dirty. The dirt detectors can each include a projection system to project a known pattern, for example, a bar pattern, onto the road surface to be imaged by the optical detector. The detected image is compared with a stored version of the correct pattern to determine if the optical detector is dirty.
The optical vehicle motion detection system according to exemplary embodiments in accordance with the present invention can take many forms. For example, optical detectors of the system can include photodetectors comprising low resolution CCDs (charge coupled devices) or CMOS (complementary metal oxide semiconductor) image sensors. The light sources can be LEDs (light emitting diodes) or other suitable light sources. The light sources can provide a constant illumination or an intermittent illumination via a flash capability. The light sources can emit visible light or non-visible light, such as IR, and can also be selected to emit a preferred color, for example, by using a plurality of different LEDs, to improve the contrast or to reduce the effects of spurious light.
According to another exemplary embodiment in accordance with the invention, the optical detectors can each be a digital camera having a variable focus lens system with an autofocus capability as described above to assist in maintaining visual contact with the road surface as the vehicle travels along the road. A camera also provides an advantage of requiring very little light to illuminate the road surface, except, perhaps, at night. At night, an automatic flash feature can be provided to illuminate the road surface.
A camera provided with a variable focus lens system can also be provided to accommodate vehicles having different chassis heights. A simple image processing algorithm can be used to automatically adjust the focus to maximize image contrast. Alternatively, the focus can be fixed at the factory depending on the model of the vehicle on which the camera is to be mounted.
In general, optical detectors of an optical vehicle motion detection system according to exemplary embodiments in accordance with the invention must provide sufficient pixels to form sharp images of the road surface to permit positional change of the vehicle relative to the road surface to be accurately determined. The resolution must be sufficient to resolve relatively smooth road surfaces, for example, icy surfaces, but be small enough to process efficiently. In a camera, the relatively long focal length between the camera and the image increases the need for pixels, however, the need to image only a small patch of road surface decreases the pixel requirements. In general, for a patch of road surface 30 mm×30 mm, a resolution on the order of 1 mm2 is satisfactory.
Both autofocus cameras and computer mouse-type optical detectors are quite inexpensive and can be installed and replaced as frequently as necessary. The optical vehicle motion detection system of the present invention can be provided as original equipment on new vehicles or as add-ons to existing vehicles.
The optical vehicle motion detection system according to exemplary embodiments in accordance with the invention determines positional change of a vehicle relative to a road surface, and, accordingly, provides information regarding the relative position of a vehicle. In a vehicle navigation system, however, some mechanism is needed to establish the absolute position of the vehicle. A system such as GPS (Global Positioning System) can, for example, be used to establish a starting position for a vehicle, and the absolute vehicle position at any time can be determined from the GPS measurement. Alternatively, fiducials can be positioned at infrequent locations on or along a road to enable the optical vehicle motion detection system of the present invention to periodically acquire the absolute position of the vehicle. The fiducials can, for example, be provided on lines on the road that are detected when the vehicle travels over the lines. Alternatively, the fiducials can be provided on utility poles along the side of the road or in another manner.
By being able to determine the absolute position of a vehicle at any time, the optical vehicle motion detection system according to embodiments in accordance with the invention can be incorporated in a vehicle navigation system to monitor the position of the vehicle. The vehicle navigation system can be used to direct a driver to a desired location or to monitor the driver's driving ability, e.g., to detect erratic driving due to intoxication or drowsiness. The system can also be incorporated into a network to provide a real-time assessment of road and weather conditions.
An optical vehicle motion detection system according to exemplary embodiments in accordance with the invention can also be used maintain a record of vehicle travel. For example, sensor, motion and position data indicative of vehicle travel can be recorded in a vehicle “black box” data recorder and stored for use in accident investigations and for other purposes.
An optical vehicle motion detection system according to exemplary embodiments in accordance with the invention can be provided on different vehicles, and the optical navigation system can be used to improve traffic flow and reduce accidents by, for example, maintaining proper distances between vehicles.
While what has been described constitute exemplary embodiments in accordance with the invention, it should be recognized that embodiments in accordance with the invention can be varied in numerous ways without departing from the scope thereof. Because embodiments in accordance with the invention can be varied in numerous ways, it should be understood that the invention should be limited only insofar as is required by the scope of the following claims.
