PATENT DOCUMENT

Publication Number: US-10247816-B1
Application Number: US-201615203731-A
Country: US
Kind Code: B1

Title: Apparatus and method to measure slip and velocity

Abstract:
Aspects of the present disclosure involve a method for determining a road vehicle velocity and slip angle. The current disclosure presents a technique for identifying a vehicle&#39;s velocity and slip angle, in the vehicle&#39;s coordinate frame. In one embodiment, two or more sensors are orthogonally located on the underside of the vehicle in order to obtain longitudinal and lateral velocity information for slip angle determination. In another embodiment, the two or more sensors can include an array of elements for beam steering and receiver beamforming. Spatial diversity is leveraged in identifying at least a slip angle and/or velocity of the vehicle. Doppler mapping is used as a means for slip angle determination and the clutter ridge of the Doppler map is embraced for identifying the slip angle.

Claims:
What is claimed is: 
     
       1. A method comprising:
 receiving a first plurality of electromagnetic waves from a first sensor; 
 determining a first frequency response from the first plurality of electromagnetic waves received from the first sensor, wherein the first frequency response is located within a first clutter ridge; 
 receiving a second plurality of electromagnetic waves from a second sensor; 
 determining a second frequency response from the second plurality of electromagnetic waves received from the second sensor, wherein the second frequency response is located within a second clutter ridge; 
 generating a first Doppler slope from the first frequency response and a second Doppler slope from the second frequency response; and 
 determining at least one of a slip angle and a velocity from the first Doppler slope and the second Doppler slope. 
 
     
     
       2. The method of  claim 1 , wherein the first sensor and the second sensor are orthogonally positioned relative to each other on an underside of a vehicle, with the first sensor receiving longitudinal velocity information in the first plurality of electromagnetic waves and the second sensor receiving lateral velocity information in the second plurality of electromagnetic waves. 
     
     
       3. The method of  claim 2 , wherein the first sensor is mounted on the underside of the vehicle, where the first sensor has a field of view that is approximately symmetrical about a center line, where the center line is approximately normal to a surface of a road. 
     
     
       4. The method of  claim 2 , wherein the first sensor is mounted on the underside of the vehicle, where the field of view of the first sensor is oblique to the surface of the road and the field of view of the first sensor remains in a near-field region. 
     
     
       5. The method of  claim 4 , wherein at least a first antenna in the array of antennas in the second sensor steers a second set of transmitted electromagnetic waves in a second desired direction toward the surface of the road and wherein at least a second antenna in the array of antennas in the second sensor creates a second receiving beamformer for receiving a second set of reflected electromagnetic waves from the second set of transmitted electromagnetic waves, and wherein the second set of reflected electromagnetic waves are the second plurality of electromagnetic waves. 
     
     
       6. The method of  claim 2 , wherein the longitudinal velocity information received by the first sensor, the lateral velocity information received by the second sensor, and measurement data from at least one of an Inertia Measurement Unit (IMU) and a global positioning system (GPS) is collectively used to extrapolate the velocity. 
     
     
       7. The method of  claim 1 , wherein the first sensor includes an array of antennas, where at least a first antenna in the array of antennas in the first sensor steers a first set of transmitted electromagnetic waves in a first desired direction toward the surface of the road and wherein at least a second antenna in the array of antennas in the first sensor creates a first receiving beamformer for receiving a first set of reflected electromagnetic waves from the first set of transmitted electromagnetic waves, and wherein the first set of reflected electromagnetic waves are the first plurality of electromagnetic waves. 
     
     
       8. The method of  claim 7 , wherein the first receiving beamformer is steered in a direction of the first set of reflected electromagnetic waves. 
     
     
       9. A system comprising:
 a first beamforming sensor, the first beamforming sensor configured to:
 transmit a first plurality of electromagnetic waves, the first plurality of electromagnetic waves transmitted in a direction of a road; 
 receive a reflected first plurality of electromagnetic waves; 
 
 a second beamforming sensor, the second beamforming sensor configured to:
 transmit a second plurality of electromagnetic waves, the second plurality of electromagnetic waves transmitted in the direction of the road; 
 receive a reflected second plurality of electromagnetic waves; 
 
 a hardware computing unit, the hardware computing unit configured to:
 receive the reflected first plurality of electromagnetic waves from the first beamforming sensor; 
 determine a first signal transform from the reflected first plurality of electromagnetic waves received from the first beamforming sensor, wherein the first signal transform is located within a first clutter ridge; 
 receive the reflected second plurality of electromagnetic waves from the second beamforming sensor; 
 determine a second signal transform from the reflected second plurality of electromagnetic waves received from the second beamforming sensor, wherein the second signal transform is located within a second clutter ridge; 
 generate a first Doppler slope from the first signal transform and a second Doppler slope from the second signal transform; and 
 determine at least one of a slip angle and a velocity from the first Doppler slope and the second Doppler slope. 
 
 
     
     
       10. The system of  claim 9 , wherein the first beamforming sensor and second beamforming sensor are orthogonally positioned relative to each other on an underside of a vehicle, with the first beamforming sensor receiving longitudinal velocity information in the first plurality of electromagnetic waves and the second beamforming sensor receiving lateral velocity information in the second plurality of electromagnetic waves. 
     
     
       11. The system of  claim 10 , wherein the velocity is a first function of the longitudinal velocity information and the lateral velocity information, and wherein the slip angle is a second function of the longitudinal velocity information and the lateral velocity information. 
     
     
       12. The system of  claim 10 , wherein the longitudinal velocity information received by the first beamforming sensor and the lateral velocity information received by the second beamforming sensor is combined with measurement data from at least one of an Inertia Measurement Unit (IMU) and a global positioning system (GPS). 
     
     
       13. The system of  claim 12 , wherein the GPS calibrates the first beamforming sensor and the second beamforming sensor. 
     
     
       14. The system of  claim 9 , wherein the first beamforming sensor is mounted on the underside of the vehicle, where the first beamforming sensor has a field of view that is approximately symmetrical about a first center line, where the first center line is approximately normal to a surface of the road. 
     
     
       15. The system of  claim 9 , wherein the first beamforming sensor is mounted on the underside of the vehicle, where the field of view of the first beamforming sensor is angled about a second center line, where the second center line is oblique to the surface of the road. 
     
     
       16. The system of  claim 15 , wherein the first beamforming sensor is steered in a direction of the reflected first plurality of electromagnetic waves and the second beamforming sensor is steered in a direction of the reflected second plurality of electromagnetic waves. 
     
     
       17. The system of  claim 9 , wherein the first signal transform is determined by taking a spatial transformation of the reflected first plurality of electromagnetic waves and the second signal transform is determined by taking the spatial transformation of the reflected second plurality of electromagnetic waves. 
     
     
       18. The system of  claim 17 , wherein the first signal transform provides the longitudinal velocity information and the second signal transform provides the lateral velocity information. 
     
     
       19. The system of  claim 9 , wherein the first beamforming sensor and second beamforming sensor include at least one of radar sensor and ultrasonic sensor. 
     
     
       20. A non-transitory computer-readable data storage medium comprising instructions that, when executed by at least one processor of a device, cause the device to perform operations comprising:
 obtaining a first set of electromagnetic waves from a first beamforming sensor; 
 performing a first spatial transformation of the first set of electromagnetic waves received from the first beamforming sensor; 
 determining a first dominant slope of a first Doppler map generated from the first spatial transformation; 
 obtaining a second set of electromagnetic waves from a second beamforming sensor; 
 performing a second spatial transformation of the second set of electromagnetic waves received from the second beamforming sensor; 
 determining a second dominant slope of a second Doppler map generated from the second spatial transformation; 
 trigonometrically computing at least one of a slip angle and a velocity using the first dominant slope and the second dominant slope determined.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to and claims priority under 35 U.S.C. § 119(e) from U.S. Patent Application No. 62/189,139, filed Jul. 6, 2015, titled “APPARATUS AND METHOD TO MEASURE SLIP AND VELOCITY,” the entire contents of each are incorporated herein by reference for all purposes. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to road vehicles, and more specifically to a method for determining a vehicle&#39;s road velocity and tire slip state. 
     BACKGROUND 
     Road vehicles use tires that are compliant air-filled structures that exert force on the road by continually deforming and slipping relative to the road. For road vehicle stability and traction, modern vehicle control systems often use an estimate of how the vehicle moves with respect to the road. Accurately estimating road-relative velocity vectors is of particular importance as velocity can be used for feedback control, position estimation, detection, and intelligent response to tire nonlinearities and sliding. However, because of the compliance of the tires, directional stiffness, the radius of the tire, among other things, can vary as well as various factors such as temperature, pressure, wear, and load from the car and road, can make conventional approaches to velocity estimation challenging. 
     In response, safety systems have been developed that can determine the road-relative velocity using wheel encoders, inertial sensors, and Global Navigation Satellite Systems (GNSS), among others. However, the current safety systems are often insufficient and can provide inaccurate road-relative velocity. For example, inertial sensors require the integration of noisy accelerometers which can experience drift, making velocity and slip determinations challenging. GNSS systems such as Global Positioning Systems (GPS) are often unreliable and subject to jammers, which similarly makes the use of GPS challenging for road relative velocity and other computations. 
     SUMMARY 
     Implementations described and claimed herein address the foregoing challenges by providing apparatuses and methods for facilitating slip angle and velocity measurements. In one embodiment a method includes receiving first set of electromagnetic waves from a first sensor to determine a first frequency response from the electromagnetic waves received. The first frequency response is located within a first clutter ridge. The method further includes receiving a second set of electromagnetic waves from a second sensor to determine a second frequency response. The second frequency response, like the first is also located within a second clutter ridge. Using the first and second frequency response, Doppler slopes are generated and used to determine a slip angle and a velocity. 
     In another embodiment, a system includes a first beamforming sensor configured to transmit a first set of electromagnetic waves in the direction of a road. The first beamforming sensor can also receive the reflected first set of electromagnetic waves. A second beamforming sensor is configured to transmit a second set of electromagnetic waves in the direction of the road and receive the reflected second set of electromagnetic waves. A hardware computing unit is configured to receive the reflected first plurality of electromagnetic waves from the first beamforming sensor and determine a first signal transform from the reflected first set of electromagnetic waves received from the first beamforming sensor. The first signal transform is located within a first clutter ridge. The hardware computing unit is further configured to receive the reflected second set of electromagnetic waves from the second beamforming sensor and determine a second signal transform from the reflected second set of electromagnetic waves received from the second beamforming sensor. The second signal transform is located within a second clutter ridge. The hardware computing unit generates a first Doppler slope from the first signal transform and a second Doppler slope from the second signal transform and determines a slip angle and a velocity. 
     In still another implementation a computer-readable data storage medium includes instructions that, when executed by at least one processor of a device, cause the device to perform operations including obtaining a first set of electromagnetic waves from a first beamforming sensor and perform a first spatial transformation of the first set of electromagnetic waves received from the first beamforming sensor. The device can also determine a first dominant slope of a first Doppler map generated from the first spatial transformation and receive a second set of electromagnetic waves from a second beamforming sensor. The device can further perform a second spatial transformation on the second set of electromagnetic waves received from the second beamforming sensor and determining a second dominant slope of a second Doppler map generated from the second spatial transformation. Using a trigonometric computation a slip angle using the first dominant slope and the second dominant slope is determined. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  illustrates a system architecture for a road vehicle. 
         FIG. 2  is a graph illustrating slip angle. 
         FIG. 3A  illustrates of a horizontal positioning of orthogonally oriented sensors on an underside of a vehicle, in one embodiment. 
         FIG. 3B  illustrates a non-horizontal positioning of orthogonally oriented sensors on an underside of a vehicle, in one embodiment. 
         FIG. 4  is a graph illustrating Doppler data, and particularly emphasizing a clutter ridge in such data that may be exploited to obtain slip and velocity information, in one embodiment. 
         FIG. 5  illustrates a set of linear sensor arrays that may be used in one of the orthogonally arranged sensors, in one embodiment. 
         FIG. 6  is a graph illustrating the Doppler of a moving road vehicle, in one embodiment. 
         FIG. 7  is a flowchart for a method to measure slip and velocity, in one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the present disclosure involve a set of sensors used for determining the velocity and slip angle of a vehicle. In one embodiment, one or more orthogonally arranged sensors are located in an under-vehicle space and positioned such that the road or other surface the vehicle travels on is in a field of view of the sensors. The orthogonally placed sensors may be mounted horizontally (parallel with the road) or positioned in a semi-horizontal manner and the information from the sensors used to compute the vehicle velocity, as well as discrete lateral and longitudinal components of velocity. The information from the sensors may also be used to compute the vehicle slip angle. The sensors may be antenna arrays or ultrasonic sensors in various possible embodiments. Further, in some arrangement, the sensors can create a beamformer which can exploit spatial diversity to enhance the velocity determination. 
     In addition to the one or more orthogonally placed sensors, an Inertia Measuring Unit (IMU) can be collectively used with the orthogonally placed sensors to independently extrapolate velocity before or while the orthogonal sensors are being used to determine velocity and slip angles and independently or in supplement may also be used for noise reduction. Additionally or alternatively, external positioning and velocity measurements such as those provided by a Global Positioning System (GPS) unit can also be collectively used with the sensors for error correction and location synchronization. Further, additional sensors (e.g., yaw, wheel speed, gyroscopic, ultrasonic sensors) may be placed on the underside of the vehicle to create a triad of sensors which can provide further information for the velocity measurement, relative to a two sensor system. The triad of sensors can be used to eliminate the effect of vehicle heave rate, roll rate, and pitch rate. 
     Various embodiments described herein, as well as combinations thereof, provide mechanisms for collecting data for measuring slip and velocity of a vehicle. In one specific example, the systems provide an estimate of slip and vehicle velocity using the information from the sensors placed on the underside of a road vehicle. The placement of the sensors on the under-side of the vehicle provide a reliable technique that can account for stability and traction issues that can arise as road vehicles encounter tire deformations and slippage, and might affect the accuracy of a conventional system. The systems set out herein provide a solution that improves velocity estimation in a wide variety of conditions as well as at and beyond vehicular handling limits where tire slip and the like are more pronounced. Knowledge of these handling limits can be of great benefit especially when encountering circumstances such as an icy surface, where the vehicle may slip and travel cannot necessarily be understood from tire rotation information and the like. In addition, the embodiments can also provide feedback signals which can assist with currently existing driver systems such as cruise control, anti-lock braking (ABS), electronic stability control (ESC), etc. Still further, systems discussed herein can also assist in the identification of objects and the determination of whether the object is static or mobile. Still even further, the embodiments provide a robust situational awareness for driving at the limits of vehicle handling. Other advantages exist which will become evident throughout the disclosure. 
       FIG. 1  is a block diagram illustrating an example of a computing device or computer system  100  of the vehicle which may be used in implementing the embodiments of the present disclosure. For example, the computing system  100  of  FIG. 1  may be a portion of a larger computing system located within the road vehicle. The computer system  100  includes one or more processors  102 , 106  and/or slip and velocity processing module  104 . Processors  102 , 106  and slip and velocity processing module  104  may include one or more internal levels of cache (not shown) and a bus controller  122  or bus interface unit for direct interaction with the processor bus  112 . Processor bus  112 , also known as the host bus or the front side bus, may be used to couple the processors  102 , 106  and slip and velocity processing module  104  with the computer system interface  114 . Computer system interface  114  may be connected to the processor bus  112  to interface other components of the computer system  100  with the processor bus  112 . For example, computer system interface  114  may include a memory controller  118  for interfacing a main memory  116  with the processor bus  112 . The main memory  116  may typically include one or more memory cards and a control circuit (not shown). Computer system interface  114  may also include an input/output (I/O) interface  120  to interface one or more I/O bridges  124  or I/O devices with the processor bus  112 . One or more I/O controllers and/or I/O devices may be connected with the I/O bus  126 , such as I/O controller  128  and I/O device  130 , as illustrated. 
     The I/O device  130  may also include an input device (not shown), such as an alphanumeric input device (e.g., an LCD display), including alphanumeric and other keys for communicating information and/or command selections to the processors  102 , 106 . Another type of user input device includes cursor control, such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to the processors  102 , 106  and for controlling cursor movement on the display device and other vehicular device. 
     Computer system  100  may include a dynamic storage device, referred to as main memory  116 , or a random access memory (RAM) or other computer-readable devices coupled to the processor bus  112  for storing information and instructions to be executed by the processors  102 , 106 . Main memory  116  also may be used for storing temporary variables or other intermediate information during execution of instructions by the processors  102 , 106  and other processing modules such as the slip and velocity processing module  104 . Computer system  100  may include a read only memory (ROM) and/or other static storage device coupled to the processor bus  112  for storing static information and instructions for the processors  102 , 106  and/or slip and velocity processing module  104 , and slip and velocity processing module  104 . The system set forth in  FIG. 1  is but one possible example of a computer system  100  that may be employed or be configured in accordance with aspects of the present disclosure. 
     According to one embodiment, the above techniques may be performed by computer system  100  in response to slip and velocity processing module  104  executing one or more sequences of one or more instructions contained in main memory  116 . These instructions may be read into main memory  116  from another machine-readable medium, such as a storage device. Execution of the sequences of instructions contained in main memory  116  may cause processors  102 , 106  and/or slip and velocity processing module  104  to perform the process steps described herein. In alternative embodiments, circuitry may be used in place of or in combination with the software instructions. Thus, embodiments of the present disclosure may include both hardware and software components. 
     The instructions executed by the slip and velocity processing module  104  can include determining a slip angle and corresponding velocity of the road vehicle. The slip and velocity of the road vehicle can be determined using the information collected by one or more sensors (e.g., lateral and longitudinal sensors  136 ,  138 ) placed on the road vehicle. The sensors  136 , 138  can also be used to detect road surface conditions. The sensors  136 , 138  may include a single antenna element or an array of antenna elements creating at least one focused antenna beam. In some instances, the sensors  136 , 138  can be used as a phased array to create a beamformer to enhance the velocity estimation. Additional processing components can also exist within the slip and velocity processing module  104 , including digital signal processing components common in heterodyne systems including, but not limited to, components capable of processing signal modulation, transformation, interleaving, puncturing, digital-to-analog conversion, frequency up/down conversion, and slope estimation. Additionally, the slip and velocity processing module  104  can also contain processors for receiving ultrasonic waves and using the information received from an ultrasonic sensor (not shown) to compute the slip and velocity of the vehicle. Further, the slip and velocity processing module  104  can communicate with at least the system I/O Interface  120  for reception of the ultrasonic and radar waves. 
     A machine readable medium includes any mechanism for storing or transmitting information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). Such media may take the form of, but is not limited to, non-volatile media and volatile media. Non-volatile media includes optical or magnetic disks. Volatile media includes dynamic memory, such as main memory  116 . Common forms of machine-readable medium may include, but are not limited to, magnetic storage medium; optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of mediums suitable for storing electronic instructions. 
       FIG. 1  illustrates one possible computing system architecture. The computer system  100 , however, is a simplified representation and can contain different arrangements of components, and may further include additional systems for performing additional processes. The computer system  100  can work jointly or independently of the additional systems that can exist within the road vehicle, as well as external devices, and/or networks. The components of the system  100  may communicate over any number of networks, including telecommunication networks and wireless networks. Further, it should be noted that the system  100  may include any number of additional or fewer components, including components used to communicate between the components shown. Also, the functionality of the components described below may be applied to two or more components of the system. For example, the sensors  136 , 138 , an Inertia Measurement Unit (IMU)  132 , and a GPS  134 , which can be initiated within the computer system  100 , or may be instantiated over many components of the computer system  100  applied to two or more components of the system. 
       FIG. 2  is an illustration of the underside of a vehicle  200  having four wheels  202   a - 202   d  and two orthogonally placed sensors  208 ,  212  (e.g., lateral and longitudinal sensors  136 , 138 ), where the vehicle  200  is moving with a longitudinal velocity  218  and a lateral velocity  220  corresponding to a slip angle  206 . As introduced above, longitudinal velocity  218 , lateral velocity  220  and vehicle slip angle  206  of a vehicle  200  are parameters that may be determined and used in systems involved with vehicle stability and traction, among other things. The relative motion between a tire and the road surface the tire is moving on is referred to as slip. In instances where a difference exists between the speeds, the tire&#39;s plane of rotation can exhibit a shift or tire slip angle  204  relative to the instantaneous velocity of the tire  224 . 
       FIG. 2  depicts the underside of a road vehicle  200  where the vehicle is exhibiting a slip angle  206 . Slip angle  206  is the angle of the vector sum (vehicle velocity)  221  of longitudinal velocity v x    218  and lateral velocity v y    220 . Therefore, slip angle  206  is computed from the lateral velocity  216  and the longitudinal velocity  218  components, which components may also be used to compute the vehicle velocity  221 . As such, longitudinal velocity  218  in combination with lateral velocity  220  can be used to determine slip angle  206  and the magnitude of the vehicle velocity  221 . 
     Additionally, each tire  202   a - 202   d  may exhibit a local slip angle  204 , referred to as “tire slip angle” that corresponds to the angle between the direction of the wheel  222  and the instantaneous velocity  224  between the point of contact of the tire and the road. The tire slip angle  204  can alter the handling qualities of a vehicle and can be used to ensure directional stability. The tire slip angle  204  can be used collectively with the slip angle  206  for better road vehicle  200  control. By identifying the slip angle  206  and controlling steering angle (not shown), vehicle sliding can be detected and managed, for example. Additionally, using the slip angle  206  and the yaw rate of the vehicle, for example, the tire slip angle  204  can be calculated and various other vehicle properties, including the limits of tire handling can be determined. 
     In one specific embodiment, the placement of two or more sensors  208  and  212  are used and presented to provide slip angle  206  and velocity measurements. The implementation can include these two or more sensors  208  and  212  that are orthogonally mounted on the underside of the vehicle  200  in order to obtain longitudinal and lateral velocity information such as longitudinal and lateral velocity vectors ( 218 ,  220 ) from which the velocity of the vehicle  221  and the slip angle  206  can be determined. The sensors  208 , 212  can be radio frequency (RF) sensors that can operate at gigahertz frequency. In one embodiment, GPS units  134  and IMUs  132  can be collectively used with the orthogonally placed sensors  208 , 212  to independently extrapolate velocity before or while the orthogonal sensors  208 , 212  are being used to determine vehicle velocity  221  and the slip angle  206 . In another embodiment, other sensors may be used, including, but not limited to optical, yaw, wheel speed, gyroscopic, ultrasonic and the like in conjunction with the orthogonal sensors  208 ,  212  to provide additional inputs for determining slip, vehicle velocity and other possible measurements. For example, wheel speed sensors can be used to determine the speed of the vehicle&#39;s tire rotation. This information can be merged with the information obtained from the two sensors (e.g.,  208  and  212 ) to obtain greater detail associated with the computation of the velocity estimate. Further, the sensors  208 ,  212  are not limited to being placed adjacent (proximate) to each other and can be placed at a distance from each other such that the field of view  226 ,  228  (e.g., the dimensions of visible ground area or visual field) of the surface under the vehicle  200  remains relative to the forward/rearward and side/side motion of the vehicle. 
     As indicated above, the sensors  208 , 212  can be orthogonally mounted and can be radar sensors. Radar sensors operate by emitting radio frequency waves toward an object, such as the road, and receiving the reflected radio frequency waves to determine the properties of the object. Similarly, sensors  208 , 212  can be radar sensors emitting radio waves toward the surface of the road and receiving the reflected radio frequency waves to determine the properties of the ground surface, such as ice on the road and potholes in the road, etc. In addition, the radar sensors may be multi-purposed such that in addition to being used for determining slip angle and vehicle velocity, the radar sensors may be used for the detection of other vehicles or objects. Orthogonal placement of sensors  208 ,  212  can include placement of the sensors  208 ,  212  in a perpendicular manner on the underside of the vehicle  200  such that a right (90°) angle exists between the sensors  208 , 212 . In some instances, the sensors  208 , 212  may not be orthogonally placed and instead placed angled from each other (e.g., at a 45° angle). In addition, these sensors  208 ,  212  can also be placed horizontally or partially horizontal among other configurations.  FIGS. 3A and 3B  provide two instances where sensor placement is varied on a vehicle  300 . For example,  FIGS. 3A and 3B  illustrate an exterior placement of one or more sensors  208 ,  212 . 
       FIG. 3A , illustrates a first configuration with one or more sensors  208 ,  212  orthogonally placed in a horizontal manner. Horizontal placement of the sensors refers to a positioning of the sensors in a manner such that the field of view of the sensors  208 ,  212  is approximately symmetrical about a center line  310 , where the center line  310  is approximately normal to the surface of the road  316 . For example, in  FIG. 3A , sensors  208 , and  212  are illustrated having horizontal placement such that the field of views  226 , 228  of the sensors  208 ,  212  are approximately symmetrical about the center line  310 , where the center line  310  is perpendicular to the surface of the road  316 . In some instances, the normal angle of projection (e.g., angle of the center line  310 ) is perpendicular to the surface of the road  316 , with the perspective of the sensors  208 , 212  positioned to view downward toward the surface of travel. As illustrated, an area  302  is representative of the field of view  226  of sensor  208 , whose placement permits the vehicle&#39;s longitudinal velocity vector to be measured. Similarly, sensor  212 , which is orthogonal to sensor  208 , which can also have a horizontal placement on the underside of the vehicle  300  can have a downward facing field of view  228  which is represented by area  304  and can be used to measure the vehicle&#39;s lateral velocity vector. Since the relative distance to the ground is quite near and the wavelength is not sufficiently short to reach far-field, the width of the beam projected by the sensors  208 , 212  may not be very narrow. Therefore, the wide beam projected by the sensors  208 ,  212  enables the computation of the velocity component using, for example, a polynomial fit on the frequency response of the Doppler shift. 
       FIG. 3B  illustrates a second configuration with one or more sensors  208 ,  212 . In this figure, the placement of the sensors  208 , 212  can deviate from a horizontal placement. Such a placement can include the placement of the sensors  208 , 212  such that one or both sensors are placed on the underside of the vehicle  300  at an angle that enables the sensors  208 , 212  to project the electromagnetic waves in a way so that the field of views  226 ,  228  remain in the near-field region of the sensors and the fields of view collects upcoming road surface information. For example, in  FIG. 3B , sensors  208 , and  212  are illustrated such that a center line  312  of the field of view  226 , 228  of the sensors  208 ,  212  is no longer perpendicular to the surface of the road  316 , but instead the field of view  226 , 228  of the sensors  208 ,  212  is angled about a center line  312  where the center line  312  is oblique to the surface of the road  316  and the field of view  226 , 228  of the sensors  208 , 212  remain in the near-field region. That is to say, the angle of projection  314  is tilted such that forthcoming road  316  surface characteristics and corresponding velocity components can be measured using the forward angled field of view. In some instances, the angle of projection  314  or angle of the center line  312  is obtuse to the surface of the road  316 , with the perspective of the sensor(s) positioned to view toward the front (F) of the vehicle. In other instances, the angle of projection  314  or angle of the center line  312  is acute to the surface of the road  316 . In addition and generally, with respect to the embodiments of  FIG. 3A or 3B , placement of the sensors  208 , 212  on the underside of the vehicle  300  can minimize the field of views  226 , 228  from being obstructed by external objects that can interfere with signal collection. 
     In one embodiment, the placement of the partially horizontally placed sensors  208 , 212  is such that the Doppler shift of the signals is measured by tracking the distance between points, within areas  306 , 308  which are representative of the field of views  226 ,  228  of sensors  208 , 212  respectively. By placing the sensor  208  in a partially horizontal position, a tighter peak (e.g., clutter ridge—described below) can be achieved on the frequency response providing a possibly more precise longitudinal (e.g., forward as shown in  FIG. 3B ) estimation. In contrast, the sensor  212  is arranged for lateral velocity and may be horizontally positioned. Therefore, the sensor  208  may be partially horizontal relative to the underside of the vehicle, so as to align the field of view projection in the direction of the forthcoming road surface with sensor  212  horizontal. As indicated, a partially horizontal placement of the sensor(s)  208  and/or  212  can provide velocity components relative to the road surface  316  to be encountered which can be used in the vehicle velocity  221  and slip angle  206  estimation. While the sensors are shown viewing the surface under the vehicle, it is also possible to place the sensors  308 , 312  on a side of the vehicle, extending from the roof, and in other positions where lateral and/or longitudinal velocity may be obtained with a view of the surface upon which the vehicle is traveling. 
     In addition to the one or more orthogonally placed sensors  208 , 212 , as previously indicated, additional components can be collectively used with the sensors  208 , 212  to enhance slip angle reading. For example, an Inertia Measurement Unit (IMU)  132  can be collectively used with the sensors  208 , 212  for noise reduction and to independently extrapolate velocity before or while the orthogonal sensors are being used to determine vehicle velocity  221  and slip angle  206 . The Inertia Measurement Unit  132  can aid in reducing noise of the estimate as well as in removing outliers that may occur from false returns as obstacles can temporarily appear under the road vehicle (e.g., an object blowing under the vehicle). As another example, a Global Positioning System (GPS) unit  134  can also be collectively used with the sensors  208 , 212  to improve sensor alignment and calibration. As an example, the data gathered by the GPS unit  134  can aid in error correction and location synchronization of the sensors  208 , 212 . In addition, or alternatively, the GPS data or data from another perception unit can be used to improve vehicular estimates such as altitude and position, as well as to determine whether objects (e.g., pot hole in the road, flying plastic bag that goes under the car, a tree branch) encountered are static or in motion. 
     An additional sensor may be placed on the underside of the vehicle  200 , or other locations, to form a triad of sensors. Information from the other sensor(s) may be used to compliment, error correct, or otherwise be used in conjunction with the orthogonal sensor information. The triad of sensors can be used to reduce the effect of vehicle heave rate, roll rate, and pitch rate, on the computation of slip and velocity among other advantages. The heave rate corresponds to the suspension&#39;s natural frequency in ride, while roll and pitch rate represent the rotation about a given axis (e.g., pitch is y-axis, roll is x-axis). The combination of sensors can also be created from the use of other sensors placed on the vehicle  300 . That is to say, any one or more of the sensors described above, and in conjunction with at least  FIG. 2 , can be included to provide an added degree of information that may be used in computing the velocity and/or slip angle measurement. For example, the sensors  208 , 212  may move, bounce, tilt, etc. in conjunction with vehicle heave, roll, and pitch rate. The use of a third or other sensor(s) tied to heave, roll, and pitch may provide information about such characteristics encountered by the vehicle, and the sensors  208 ,  212  mounted thereon, such that the effect (or effects) are corrected and/or accounted for during the velocity and slip angle measurements. 
     Alternatively, a second set of ultrasonic sensors and corresponding hardware/software can be placed on the underside of the vehicle  200  or in a position with a sufficient view of the travel surface. This second set of sensors can also be orthogonally placed with a horizontal or partially horizontal orientation and used for slip angle  206  and velocity measurements as described herein. In some instances, the ultrasonic sensors can work independently of the radar sensors transmitting the radio frequency waves. In other instances, the radar sensors may work independently of the ultrasonic sensors for velocity estimation. Still, in other instances, both the ultrasonic sensors and the radar sensors can work mutually to enhance velocity estimation. 
     An obstacle that is often encountered in computing velocity and slip on a road vehicle is an accumulation of power over an area. This accumulation of power, known as a clutter ridge, can lead to a large area of interference or a large peak on the Doppler map and thus create the inability to identify a vehicle/target located within the contours of a Doppler map.  FIG. 4  is a graph illustrating Doppler data. As it is well understood in the art, incoming reflected signals can be organized into a Doppler map  400  as illustrated in  FIG. 4 . Note that the Doppler map  400  is not limited to factors illustrated on the map and can include a range of time over velocity, wavelength, frequency, etc. 
     The Doppler map  400  is a mapping of the incoming signal strength power as it is aggregated over a range of frequencies. Often times, the Doppler map  400  includes a main lobe known as a clutter ridge  402  which represents a peak running across a narrow range of Doppler values that extend the range of a radar scan. The presence of this running peak (e.g., clutter ridge  402 ) can generally be noisy and interference bound. Consequently, it is difficult to identify the velocity of a road vehicle within this range. Therefore, in conventional radar systems, it is preferable to identify solutions outside the clutter ridge  402 . In some conventional instances, a means for suppressing the clutter ridge  402  has been adopted. In the embodiment discussed herein, however, the clutter ridge  402  is embraced and used to determine the road vehicle velocity. 
       FIG. 5  illustrates a specific example of the orthogonal sensors  208  and/or  212  operable in the clutter ridge with the use of beamforming. In this example, sensor  208  can be a combination of linear sensor/antenna arrays  502 ,  504 A- 504 B configured to function as both a transmitter and a receiver. The transmitting portion can be performed by an array of transmitting sensors  506  and the receiving portion can be performed by an array of receiving sensors  508 . As transmitting sensors  506 , the sensors  506  emit electromagnetic waves toward the ground at radio frequencies. In one embodiment, millimeterwave frequencies can be used as a preferred transmission frequency. An advantage to using millimeterwave is the ability to minimize the distance to far-field, as wavelength is proportional to frequency. Sample millimeterwave frequencies used for transmitting the electromagnetic waves can include, but are not limited to, the 24 GHz ISM K-band, and 77 GHz, 79 GHz in the W-band. In some instances, the kilohertz to megahertz frequency range may be targeted when ultrasonic sensors are used. 
     Another advantage to the use of millimeterwave is the ability to decrease antenna size. Antenna apertures are a function of frequency, as such; higher frequencies decrease antenna size permitting an array of antennas on a smaller area. The use of an array of antennas therefore increases the overall collective aperture of the sensor, providing a higher system gain and thus a smaller angular beam width. Thus, the collective use of an array  502 ,  504 A- 504 B enables beamforming for both a focused transmission of radio frequency waves to the ground/road  316  and a focused reception of the reflected radio frequency waves. 
     As indicated, sensor  208  can also function as a receiving medium (e.g., receiving sensors  508 ) for the transmitted radio waves emitted by transmitting sensors  506 . The receiving sensors  508  can also consist of numerous and/or an array of antennas  504 A- 504 B designed to receive the emitted electromagnetic waves from the transmitting sensors  506  as the electromagnetic waves reflect from the ground/road  316 . 
     In other words, sensor  208  can create a monostatic radar. The monostatic radar is a radar unit with both the transmitter and the receiver collocated. The monostatic radar uses the arrays at the transmit and receive sensors  506 ,  508  to create a beamformer. The transmitting sensor  506  can transmit a series of focused radio waves illuminating the ground, which get reflected and detected/received by the receiving sensor  508 . The receiving portion of sensor  508  can create a phased array which can act as a receive beamformer. Transmitting sensor  506  can transmit the radio waves as a continuous waveform and can additionally modulate the signal for interference mitigation. 
     Because the sensor  208  can include numerous antennas  502 ,  504 A, and  504 B, the spatial domain can be exploited. The spatial domain provides an added degree of freedom for determining at least velocity and elevation using a spatial transform. Fourier Transforms may be used for suppressing interference created by objects on the road and locating the vehicle and the vehicle velocity within the clutter ridge. As an example, transmitting sensor  506  can illuminate a portion of the road beneath the vehicle and the multiple received channels from the beamforming receiving sensor  508  can receive the transmitted signal, take its spatial transform in the longitudinal dimension of the vehicle, and determine the Doppler shift versus the angle. The dominant slope of the resulting Doppler map can then be used to understand the vehicular velocity. Similarly, the lateral velocity can be obtained using a second sensor (e.g., sensor  212 ) oriented orthogonally. Thus, vehicle velocity and/or slip angle can be completing a trigonometry computation, for example. Vehicle velocity estimation using beamforming sensors can include both radar and ultrasonic sensors. 
       FIG. 6  is a graph illustrating the Doppler of a moving road vehicle. As described above, and in conjunction with  FIG. 4 , Doppler mapping generally includes a clutter ridge. The clutter ridge is an area of high peak values that extends for the range of the radar scan. In the present embodiment, the high peak range will be exploited by identifying a region  604  within the Doppler function  602 , which is indicative of the velocity of the road vehicle. As an example, region  604  can include the range of frequencies in which the road vehicle can be operating at. Therefore, a stationary road vehicle can ideally stand at a  0  velocity  606 , a forward moving vehicle can lay on the forward slanting slope  608  of the Doppler function  602  going on a positive frequency (f(+)) direction, and a backward moving vehicle can lay on the declining slope  610  of the Doppler function  602  going in a negative frequency (f−) direction. Similarly, the lateral velocity can also be measured using a Doppler function with corresponding frequency components using a second orthogonal sensor (e.g., sensor  212 ). Therefore, the sensors  208 , 212 , through spatial transformation, can be used to identify a line of a certain slope that maps to the desired velocity by finding the dominant return. 
       FIG. 7  is a flowchart for a method for measuring slip and velocity of a road vehicle. The process generally begins with one or more sensors located on the underside of the road vehicle. The sensors can be orthogonally placed, which can help in obtaining both longitudinal and lateral information. One or more of the sensors can be placed horizontally (e.g., facing downward) relative to the ground. Alternatively, the one or more of the sensors can be placed at least partially horizontal. Also, one or more sensor sets can be placed on the underside of the vehicle such that two velocity estimations can simultaneously occur. For example, an RF/radar sensor set can be used for velocity and independently or simultaneously, a set of orthogonal ultrasonic sensors are also used for velocity calculation. 
     Additionally, the one or more sensors can include an array of antennas which can be used to focus the beam of the transmitted signals downward, illuminating the ground. Each row within the transmitting sensor array can independently represent a channel, in order to introduce spatial diversity and beamforming. Alternatively, a single sensor with a transmitting portion can be used for ground illumination, presenting a wider beam used for RF signal transmission. The method for velocity estimation, therefore, begins with the operation of transmitting radio waves in step  702 . A road vehicle in motion will have a lateral and longitudinal component as described above and in conjunction with  FIG. 2 , which can be computed based at least in part from the transmitted radio waves. 
     The operation then continues to step  704 , where the transmitted signals are received by a second portion of the sensor as the waves are reflected from the ground. The ground reflection provides a frequency response that can be used for determining the Doppler slope in step  706 . In instances where a single sensor exists at the transmit end, a polynomial fit can be used to identify the slope of the Doppler curve. In other instances where an array is used for transmitting the radio waves at step  702 , a receiving beamformer is used in steering the array for signal reception and a spatial transform is solved to determine the velocity and even location of the vehicle. When a receiving beamformer is used, each of the antenna elements can be treated independently and thus reception of the incoming waves can be analyzed with greater accuracy. In addition, the transmitting sensor can steer the beam in the desired direction while using the clutter ridge with high peak data for slip detection. A similar operation can also run simultaneously on an orthogonally placed sensor which is collecting lateral information using a similar method. That is to say, an orthogonal sensor can include one sensor or an array of sensors can use a transmitting portion to reflect waves on the ground, while a second portion collects the reflected waves to determine a Doppler curve that will be used to determine lateral velocity. 
     In addition, during the operation of step  704 , environmental characteristics can be obtained from other sensors. These sensors can be located throughout the vehicle, and can be used for sensor triangulation and/or for merging with other systems, such as GPS units and IMU units. As described above, the additional sensors and/or the GPS, IMU can be used to provide additional measurements that can be combined with the orthogonal sensors to provide additional measurements that may be used for slip angle and velocity estimations. 
     A frequency response, also known as a Doppler map is generated using the information obtained and the Doppler slope is determined in step  706 . A clutter ridge, which is a peak region running across a narrow range of Doppler values that extend the range of a radar scan is present in the Doppler map. This peak is embraced such that the frequency response used to determine the Doppler slope is located within the clutter ridge. The Doppler slope can be determined using polynomial fitting, signal processing, and/or spatial transformations as described above. 
     Once the Doppler slope has been determined in step  706 , the operation can proceed to step  708 , where the vehicle velocity and slip angle can be determined. As indicated above and in conjunction with  FIG. 2 , slip angle  206  is the angle of the vector sum of longitudinal velocity v x  and lateral velocity v y . Longitudinal velocity can be computed from the longitudinal received signals obtained at the receiving sensor (e.g., for sensor  208 , receiving sensors  504 ). The lateral velocity can be computed from the received signals obtained at the lateral receiving sensor (which can be orthogonally located to the sensor used in conjunction with the longitudinal velocity). The measured signals will have frequency responses that depend on the respective longitudinal and lateral velocities of the vehicle. The frequency response, located within the clutter ridge, can then be used to obtain the Doppler slope for each sensor as indicated in step  706  above. The longitudinal and lateral velocities, obtained from the Doppler slopes, can then be used to compute the slip angle. Hence, the slip angle can be computed from estimates of lateral and longitudinal velocity. Similarly, the magnitude of the vehicle velocity can be computed from the estimates of lateral and longitudinal velocity. The computed vehicle velocity and/or slip angle may be provided to at least the computing system of  FIG. 1 , and then used in road vehicle stability and control functions. 
     In the present disclosure, the methods disclosed may be implemented as sets of instructions or software readable by a device. Further, it is understood that the specific order or hierarchy of steps in the methods disclosed are instances of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the method can be rearranged while remaining within the disclosed subject matter. The accompanying method claims present elements of the various steps in a sample order, and are not necessarily meant to be limited to the specific order or hierarchy presented. 
     The described disclosure may be provided as a computer program product, or software, that may include a non-transitory machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to the present disclosure. A machine-readable medium includes any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The machine-readable medium may include, but is not limited to, magnetic storage medium, optical storage medium; magneto-optical storage medium, read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of medium suitable for storing electronic instructions. 
     While the present disclosure has been described with reference to various implementations, it will be understood that these implementations are illustrative and that the scope of the disclosure is not limited to them. Many variations, modifications, additions, and improvements are possible. More generally, implementations in accordance with the present disclosure have been described in the context of particular implementations. Functionality may be separated or combined in blocks differently in various embodiments of the disclosure or described with different terminology. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow.

Metadata:
Filing Date: 20160706
Publication Date: 20190402
Grant Date: 20190402
Priority Date: 20150706
Inventors: HOFFMANN, GABRIEL M.
GADDA, CHRISTOPHER D.
STRONKS, David A.
AL-DAHLE, AHMAD
ROGERS, GREGORY E.
Assignee: APPLE INC
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Family ID: 65898385