Patent Application
20200301420
The present invention generally relates to systems and methods for controlling the velocity and heading of a vehicle.
With regards to autonomous or semi-autonomous vehicles (highly autonomous), the control systems for these types of vehicles are commonly divided into two sub-modules. The first sub-module generally performs motion planning and the second sub-module generally performs vehicle dynamic control. The motion planning sub-module is responsible for generating a trajectory for the vehicle to maneuver in a complex environment. In order to efficiently generate the trajectory, the motion planning sub-module generally employs a simplified vehicle model. The simplified vehicle model may be a kinematic model.
The vehicle dynamic control sub-module is responsible for tracking the trajectory from the motion planning submodule taking into account the more complex vehicle dynamic behavior. This complex vehicle dynamic behavior may include non-linearity and model uncertainty, among other things. Due to the inconsistencies between a simplified vehicle model utilized by the motion planning submodule and dynamic assumptions, there can be challenges with having smooth and reliable performance.
For example, it is generally preferred by passengers of autonomous vehicles that the autonomous vehicle pilot itself in such a way that the motion of the vehicle is smooth and fluid. As such, the control of the steering and the speed of the vehicle must be such that any changes of the steering (heading) or the speed (velocity) of the vehicle are done naturally and fluidly.
A system and method for controlling the velocity and heading of a vehicle includes a processor, a steering controller in communication with the processor, and a speed controller in communication with the processor. The steering controller is arranged within the vehicle and is configured to control the steering angle of the vehicle. The speed controller is arranged within the vehicle and is configured to control the velocity of the vehicle. The processor is configured to receive an array of control commands, the array of control commands include steering angle positions and velocities of the vehicle for a present time and a preview time and generate a control request for instructing the steering controller and the speed controller based on the steering angle positions and velocities of the vehicle for both the present time and the preview time.
Further objects, features, and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification.
Referring to
Here, the vehicle 100 includes a processor 102. The processor 102 may be a single processor or may be multiple processors working in concert. Generally, the processor is arranged within the interior of the vehicle 100. The processor 102 may be separately connected to or may incorporate a memory device 103. Here, the memory device 103 is shown to be integrated within the processor 102, but it should be understood that the memory device 103 may be separate from the processor 102. The memory device 103 may be any type of memory device capable of storing digital information. As such, the memory device 103 may be a solid-state memory device, an optical memory device, a magnetic memory device, and the like. The memory device may include instructions 105 and/or other data, such as lookup tables. In the case of instructions, instructions may include executable code for executing any one of the methods disclosed in this specification.
The processor 102 may be connected to a number of different sensors for sensing different physical parameters of the vehicle. For example, the processor 102 may be in communication with the velocity sensor 104. The velocity sensor 104 may be a wheel speed sensor mounted and arranged within the vehicle 100 so as to be able to determine the wheel speed of at least one wheel 106 of the vehicle. Of course, it should be understood that the vehicle 100 may have multiple wheel speed sensors for each of the wheels.
Additionally, the vehicle 100 may include an accelerometer 108 also in communication with the processor 102. The accelerometer 108 is capable of determining the acceleration of the vehicle 100 and is mounted in the vehicle to accomplish this task. The accelerometer 108 may measure acceleration any one of a number of directions including lateral and/or transverse acceleration. The vehicle 100 may also include a steering wheel angle sensor 110 configured to determine the steering wheel angle of the vehicle 100.
The processor 102 may be connected to a number of different vehicle systems capable of controlling the vehicle 100. For example, the processor 102 may be in communication with a steering control system 112. The steering control system 112 may be connected to a steering system that essentially controls the steering of the vehicle 100 based on instructions from the processor 102.
The processor 102 may also be in communication with a throttle control system 114. The throttle control system 114 is configured to control the throttle position of the engine of the vehicle. As the throttle position of the engine of the vehicle changes, the vehicle can be instructed to change speeds.
The processor 102 may also be in communication with the brake control system 116 that is configured to control the brakes of the vehicle. The brakes of the vehicle allow the vehicle to slow down and/or remain in a stopped position. The brake control system 116 receives instructions from the processor 102 and is able to actuate the vehicle brakes so as to slow the vehicle 100 down or keep it in a stopped position. It should be understood that the throttle control system 114 in the brake control system 116 may be incorporated within a single control unit. This may be because the ability to control the brakes and/or throttle the vehicle are both related to controlling the velocity of the vehicle.
The processor 102 may also be in communication with an autonomous vehicle control system 120 that provides instructions to the processor to relay these instructions to any which one of the vehicle control systems, such as the steering control system 112, throttle control system 114 and/or the braking control system 116. For example, the autonomous vehicle control system 120 may provide instructions to the processor 102 to accelerate the vehicle, slow down the vehicle, apply the brakes, and other commands. These commands may be arranged as an array of commands.
Referring to
From there, as the steering system 216 steers the vehicle, the hand wheel angle changes and is fed back into the steering angle controller 212. An automated controller 220 may also be utilized to automate the vehicle yaw rate determination.
Referring to
Here, a filtering and estimation module 304 receives a target speed 302. The filtering estimation module 304 determines a target speed 302 and a target acceleration 306 from the target speed 302. In addition, a filtering estimation module 304 determines the actual speed 308 that may be provided by the velocity sensor 104, which as stated previously, may be a wheel speed sensor.
Also shown is a switch 310 that determines if the throttle or brake should be controlled. This switch 310 may have the ability to control both the throttle and the brake at the same time. Here, the throttle controller 312 communicates to the throttle box 314 which then adjusts the throttle pedal position 316 of the vehicle 100. By adjusting the throttle position, the vehicle can be slowed down or sped up.
If the brake system is utilized, a brake look-up table 318 is utilized so as to determine how much force of the brake should be utilized based on the target speed 302, the target acceleration 306 and the actual speed 308. This look-up table provides the appropriate amount of brake pressure to the data speed brake box 320 which in turn adjusts the brake pedal position 322 of the vehicle 100. The brake lookup table may be stored within the memory device 103 of
Referring to
The preview time is a time period from the present time to approximately two seconds.
Thereafter, in step 406, the processor of 102 is configured to transmit the control request to the steering control system 112 and the throttle control system 114 and/or 116. Thereafter, the method then returns to step 402.
In addition to the steps shown in
Overall, as described above, the lateral and longitudinal control is based not only on current information but also preview information. An array of control commands generally includes instantaneous target commands and a look ahead for commands two seconds into the future. The control requests are modified based on the preview information to improve the control of the vehicle so that the vehicle operates in a smoother and more fluid-like manner.
The advantages to utilizing the system and method disclosed in this specification include providing an efficient computational method to smooth the trajectory from motion planning, emulating the naturalistic human driving behaviors, easy adaptation to different motion planning algorithms and vehicle dynamic control algorithms.
The array of control commands, stated previously, includes instantaneous target commands and a look ahead of approximately two seconds of future commands. These control commands could be expressed as:
u
array
={u
current
, u(ti)}, ti=tcurrent+Δt·i|i=1, . . . , previous horizon
this array commands may be transmitted through an Ethernet UDP (user datagram protocol) package. The control commands may be modified based on preview information to improve control smooth this. This may be expressed as:
u
array_f=filt(uarray)
u
preview
=w
preview
(1×n)
×u
array_f
(n×1)
u
control
=w
filter
(1×m
×{u
preview
, u
control(k)|k=−1, . . . , −m+1}
Referring to
In an alternative embodiment, dedicated hardware implementations, such as application specific integrated circuits, programmable logic arrays, and other hardware devices, can be constructed to implement one or more of the methods described herein. Applications that may include the apparatus and systems of various embodiments can broadly include a variety of electronic and computer systems. One or more embodiments described herein may implement functions using two or more specific interconnected hardware modules or devices with related control and data signals that can be communicated between and through the modules, or as portions of an application-specific integrated circuit. Accordingly, the present system encompasses software, firmware, and hardware implementations.
In accordance with various embodiments of the present disclosure, the methods described herein may be implemented by software programs executable by a computer system. Further, in an exemplary, non-limited embodiment, implementations can include distributed processing, component/object distributed processing, and parallel processing. Alternatively, virtual computer system processing can be constructed to implement one or more of the methods or functionality as described herein.
Further, the methods described herein may be embodied in a computer-readable medium. The term “computer-readable medium” includes a single medium or multiple media, such as a centralized or distributed database, and/or associated caches and servers that store one or more sets of instructions. The term “computer-readable medium” shall also include any medium that is capable of storing, encoding or carrying a set of instructions for execution by a processor or that cause a computer system to perform any one or more of the methods or operations disclosed herein.
As a person skilled in the art will readily appreciate, the above description is meant as an illustration of the principles of this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation, and change, without departing from the spirit of this invention, as defined in the following claims.
