Patent Description:
More recently, automated vehicle features have become possible to allow for autonomous or semi-autonomous vehicle control. For example, cruise control systems may incorporate light detection and ranging (LiDAR) for detecting an object or another vehicle in the pathway of a vehicle. Depending on the approach speed, the cruise control setting may be automatically adjusted to reduce the speed of the vehicle based on detecting another vehicle in the pathway of the vehicle.

<CIT> discloses a movable calibration fixture mounted separately from a vehicle, said fixture having a front panel that is non-transparent to radiation emitted from a range-finding sensor. <CIT> and <CIT> disclose calibration targets that are positioned separate from a vehicle. <CIT> discloses a device for calibrating at least one image sensor system connected to a motor vehicle by using at least one calibration object, wherein the calibration object is situated on the inside of an engine hood of the vehicle. <CIT> discloses a moveable body which allows detection of an axial deviation of an axis of a surroundings detector such as a camera or a radar using a marker.

While LiDAR sensors are useful there are challenges associated with their use. For example, it is necessary to ensure proper calibration and positioning of the sensor over time.

An illustrative example object detection system as set out in claim <NUM> includes a LiDAR sensor installed on a vehicle having a field of view. The LiDAR sensor is configured to emit radiation and to detect at least some of the radiation reflected by an object within the field of view. A panel is installed on the vehicle in the field of view, wherein the panel is a windshield of the vehicle that is transparent to the radiation emitted by the LiDAR sensor. The panel is configured to be set in a fixed position relative to a vehicle coordinate system. A plurality of reflective alignment markers are situated on the panel in the field of view. The reflective alignment markers reflect radiation emitted by the LiDAR sensor back toward the LiDAR sensor. A processor is configured to determine an alignment of the LiDAR sensor with the vehicle coordinate system based on an indication from the LiDAR sensor regarding radiation reflected by the reflective alignment markers and detected by the LiDAR sensor.

Various features and advantages of at least one disclosed example embodiment will become apparent to those skilled in the art from the following detailed description.

Embodiments of this invention provide the ability to monitor the alignment of an object detection sensor with a vehicle coordinate system, which serves as a frame of reference. Reflective alignment markers in the field of view of the sensor allow the sensor to provide an indication of an alignment of the sensor field of view with the vehicle coordinate system.

<FIG> schematically illustrate an object detection system <NUM> associated with a vehicle <NUM>. In some example embodiments, the object detection system <NUM> is used to provide driver-assist features while, in other embodiments, the object detection system <NUM> is used for autonomous vehicle operation.

The object detection system <NUM> includes a sensor <NUM> that has a field of view <NUM> for detecting objects in a vicinity or pathway of the vehicle <NUM>. The sensor is a LiDAR sensor. The radiation emitted by such a sensor comprises light. Other sensor configurations that include other types of radiation are used in some example embodiments. The sensor <NUM> is situated near a panel <NUM>, which in <FIG> is a windshield of the vehicle <NUM>. The panel <NUM> remains in a fixed position relative to a vehicle coordinate system <NUM>. The panel <NUM> is transparent to radiation emitted by the sensor <NUM> as schematically shown at <NUM> in <FIG>. When such radiation reflects off an object <NUM>, the system <NUM> is capable of providing information regarding such an object including, for example, its position relative to the vehicle <NUM>.

A plurality of reflective alignment markers <NUM> are situated on the panel <NUM> in fixed positions that remain constant relative to the panel <NUM> and the vehicle coordinate system <NUM>. When the sensor <NUM> is set in a desired position and orientation relative to the panel <NUM>, the reflective alignment markers <NUM> are within the field of view <NUM> of the sensor <NUM>. The reflective alignment markers <NUM> reflect at least some of the radiation emitted by the sensor <NUM> as schematically shown at <NUM>. Such reflected radiation is detected by the sensor <NUM> and provides an indication of the orientation of the sensor <NUM> and its field of view <NUM> with respect to the vehicle coordinate system <NUM>. A processor <NUM> is configured to determine an alignment of the sensor <NUM> with the vehicle coordinate system <NUM> based on an indication from the sensor <NUM> regarding the radiation <NUM> reflected by the reflective alignment markers <NUM> as such radiation <NUM> is detected by the sensor <NUM>.

The panel <NUM> comprises a first material that is essentially transparent to the radiation emitted by the sensor <NUM>.

According to the invention , the reflective alignment markers are established by a surface treatment on corresponding portions of the panel <NUM>, such as etching or through micro-optical surface shaping to create a reflective grating or pattern on the panel <NUM>. The gratings or patterns are shaped to enhance focusing the reflected radiation toward the sensor <NUM> due to the relatively short distance between the panel <NUM> and the sensor <NUM>.

Since the reflective alignment markers <NUM> remain in a fixed position on the panel <NUM> and the panel <NUM> remains in a fixed position with respect to the vehicle coordinate system <NUM>, the reflective alignment markers <NUM> provide a reference to allow the processor <NUM> to determine whether the sensor <NUM> is properly aligned with the vehicle coordinate system <NUM>. For example, over time a sensor position may change as a result of vibration or impact. The processor <NUM> is capable of determining when such misalignment has occurred and provides an output indicating a need for sensor pose compensation, sensor service or including an alert or alarm regarding the sensor misalignment condition. In example embodiments, sensor pose compensation is accomplished through software, using an actuator or both.

<FIG> schematically illustrates an example arrangement of reflective alignment markers <NUM>. In this example, given the orientation of the windshield panel <NUM> relative to the sensor <NUM> and the shape of the windshield panel <NUM>, the alignment markers <NUM> are in a generally trapezoidal configuration. A first one of the alignment markers 32A is situated as a horizontal line segment and is parallel to a second alignment marker 32B. A third alignment marker 32C is situated generally vertical and at an oblique angle relative to the alignment markers 32A and 32B. A fourth alignment marker 32D is generally vertical and situated at an oblique angle relative to the alignment markers 32A and 32B.

Although the actual, physical orientation of the alignment markers <NUM> shown in <FIG> is not truly rectangular, the field of vision <NUM> of the sensor <NUM> is and the relative positions between the sensor <NUM> and the windshield panel <NUM> result in the sensor <NUM> detecting the reflective alignment markers <NUM> in a way that results in a rectangular output schematically shown at <NUM> in <FIG> from the sensor <NUM>. The field of view <NUM>, in this example, is effectively framed by the reflective alignment markers 32A-32D with any objects <NUM> within the field of view <NUM> situated within that frame. The reflective alignment markers, in this example, border the periphery of the field of view <NUM> when the sensor <NUM> is properly aligned with the vehicle coordinate system <NUM>.

The sensor <NUM> provides an indication of the positions of the reflective alignment markers <NUM> within the field of view <NUM> in a manner that is recognizable by the processor <NUM> for making a determination regarding the alignment of the sensor <NUM> with the vehicle coordinate system <NUM>. In some embodiments, the indication regarding the radiation reflected at <NUM> from the reflective alignment markers <NUM> is a first, predetermined indication, such as bordering the field of view <NUM>, when the sensor <NUM> is properly aligned with the vehicle coordinate system <NUM>. A second, different indication from the sensor <NUM> is the result of any misalignment between the sensor <NUM> and the vehicle coordinate system <NUM>. The processor <NUM>, in such embodiments, is programmed or configured to compare the indication from the sensor <NUM> regarding the radiation <NUM> reflected by the reflective alignment markers <NUM> to the first indication and to recognize any difference from that as an indication that there is some misalignment.

While the example of <FIG> includes linear segment reflective alignment markers, other embodiments include different configurations. <FIG> illustrates an example sensor output when the alignment markers <NUM> include relatively small rectangular segments situated near corners of the field of view <NUM>. In this example, the field of view <NUM> is generally rectangular. In the example of <FIG>, only three reflective alignment markers 32A, 32B, and 32C are provided. Having at least two of those alignment markers aligned with each other along a generally horizontal line and two of the reflective alignment markers situated relative to each other in alignment along a generally vertical line allows for the processor <NUM> to make a determination regarding the alignment of the sensor <NUM> in two dimensions.

Given this description, those skilled in the art will realize that a variety of arrangements of reflective alignment markers <NUM> are possible and they will be able to select an appropriate arrangement and configuration of such alignment markers to meet their particular needs. The contour and position of the panel <NUM> relative to the sensor <NUM> and its field of view may dictate particular requirements for positioning the reflective alignment markers <NUM> to provide desired results for a particular sensor arrangement.

With the reflective alignment markers <NUM>, the processor <NUM> is able to use information from the sensor <NUM> for detecting a variety of potential misalignment conditions. <FIG> schematically shows a situation in which the field of view <NUM> is tilted relative to the frame established by the alignment markers <NUM>. Under such conditions, instead of the alignments markers <NUM> establishing a frame around the border of the field of view <NUM>, only portions of the alignment markers appear in the image information from the sensor <NUM> and those portions are not properly aligned with the borders of the field of view <NUM>. As schematically shown in <FIG>, portions of the reflective alignment markers <NUM> are outside the field of view <NUM> and do not appear in the sensor output <NUM>' shown in <FIG>.

Another example condition in which the sensor <NUM> is misaligned with the vehicle coordinate system <NUM> is schematically represented in <FIG>. In this example, the sensor <NUM> has been shifted to the right (according to the illustration) compared to a proper installation position of the sensor <NUM>. Alternatively, the sensor may have been rotated about a vertical axis slightly to the right (again, according to the illustration). In this example, the sensor output <NUM>' does not include all of the reflective alignment markers <NUM>. For example, the reflective alignment marker <NUM> that should border the left side of the field of view <NUM> is not within the field of view <NUM>. Additionally, the reflective alignment marker <NUM> that should border the right side of the field of view <NUM> appears inward inside the field of view to the left of the right border of the field of view <NUM>.

Another misalignment situation that can be determined using an embodiment of this invention is schematically shown in <FIG>. In this condition, the sensor <NUM> has been tilted relative to the panel <NUM> such that the frame or border provided by the radiation reflected by the reflective alignment markers <NUM> appears shorter than the field of view <NUM>. The indication of the alignment marker that should be bordering the bottom edge of the field of view <NUM> appears to be shifted upward making the frame height less than the height of the field of view <NUM>.

The processor <NUM> is programmed to recognize any of the misalignment conditions shown in <FIG> along with other potential misalignment conditions.

The reflective alignment markers <NUM>, in some example embodiments, include a concave reflecting surface that focuses the radiation <NUM> reflected by the alignment markers <NUM> back toward the sensor <NUM>. Providing a focusing surface enhances the ability of the sensor <NUM> to properly detect the reflected radiation at <NUM>, which might otherwise introduce some challenges because the alignment markers <NUM> are relatively close to the sensor <NUM>.

The way in which the sensor <NUM> provides an indication of the position of the alignment markers <NUM> relative to the field of view <NUM> may vary depending on the particular embodiment. In some embodiments, the intensity of the reflected radiation is greater when reflected by the reflective alignment markers <NUM> compared to that reflected by objects <NUM> at a further distance from the sensor <NUM>. Other examples include using a time of flight or time difference information between emitted radiation pulses and the detected reflected radiation. The much closer position of the alignment markers <NUM> results in a much shorter time of flight or time difference compared to that associated with objects further from the sensor <NUM>. The processor <NUM> is programmed or otherwise configured to recognize the indication from the sensor <NUM> to determine the position of the reflective alignment markers <NUM> relative to the field of view <NUM>.

Claim 1:
An object detection system (<NUM>), comprising:
a LiDAR sensor (<NUM>) installed on a vehicle (<NUM>) having a field of view (<NUM>), the LiDAR sensor (<NUM>) being configured to emit radiation (<NUM>) and to detect at least some of the radiation (<NUM>) reflected by an object within the field of view (<NUM>);
a panel (<NUM>) installed on the vehicle (<NUM>) in the field of view (<NUM>), the panel (<NUM>) being a windshield of the vehicle (<NUM>) that is transparent to the radiation (<NUM>) emitted by the LiDAR sensor (<NUM>), the panel (<NUM>) being in a fixed position relative to a vehicle coordinate system (<NUM>);
a plurality of reflective alignment markers (<NUM>) situated on the panel (<NUM>) in the field of view (<NUM>), the reflective alignment markers (<NUM>) reflecting radiation (<NUM>) emitted by the LiDAR sensor (<NUM>) back toward the LiDAR sensor (<NUM>); and
a processor (<NUM>) that is configured to determine an alignment of the LiDAR sensor (<NUM>) with the vehicle coordinate system (<NUM>) based on an indication from the LiDAR sensor (<NUM>) regarding radiation (<NUM>) reflected by the reflective alignment markers (<NUM>) and detected by the LiDAR sensor (<NUM>),
wherein the reflective alignment markers are reflective gratings or patterns on the panel established by etching or micro-optical surface shaping corresponding portions of the panel.