Patent Publication Number: US-2012035786-A1

Title: Weight Shifting System for Remote Vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part from U.S. patent application Ser. No. 12/853,277, filed Aug. 9, 2010, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     When a ground vehicle exceeds the limits of tire or track grip when turning a corner, the vehicle may understeer, oversteer, or roll over. Understeering occurs when the front of the vehicle loses grip first, and the vehicle turns less than desired. Oversteering occurs when the rear of the vehicle loses grip first, and the vehicle turns more than desired. Rollover occurs when turning forces cause the vehicle to lift off its inside wheels or tracks and flip over onto its side or top. 
     Conventional dynamic stability control systems address oversteering and understeering by, for example, comparing the vehicle&#39;s actual yaw rate with the commanded yaw rate and taking actions such as reducing throttle or applying brakes to regain control. 
     SUMMARY 
     The present teachings provide a system to shift a center of gravity of an unmanned ground vehicle, the system comprising a first guide attached to the vehicle substantially parallel to the forward direction of motion of the vehicle, a second guide attached to the vehicle substantially parallel to the forward direction of motion of the vehicle, a support guide movably attached to the first guide and to the second guide, extending between the first guide and the second guide, and configured to move along a lengthwise direction of the first guide and the second guide, a weight movably attached to the support guide and configured to move along a lengthwise direction of the support guide, wherein the lengthwise direction of the support guide is substantially perpendicular to the forward direction of motion of the vehicle, a first motor configured to move the support guide along the first guide and the second guide, a second motor configured to move the weight along the support guide, and a control interface coupled to the first motor and the second motor and configured to control the first motor and the second motor. 
     The present teachings also provide an unmanned ground vehicle comprising a central processing unit (CPU), a movement sensor coupled to the CPU and configured to sense a present turn angle of the vehicle and communicate the present turn angle to the CPU, a location sensor coupled to the CPU and configured to determine a present location of the vehicle and communicate the present location to the CPU, a speed sensor coupled to the CPU and configured to determine a present speed of the vehicle and communicate the present speed to the CPU, a wireless communication unit coupled to the CPU and configured to receive control information from a remote operation control unit and communicate the control information to the CPU, and a weight shifting system coupled to the CPU and configured to shift a center of gravity of the vehicle based on at least one of the present turn angle of the vehicle, the present location of the vehicle, the present speed of the vehicle, and the received control information. 
     The present teachings further provide a method to shift a center of gravity of an unmanned ground vehicle, the method comprising determining, by a movement sensor, a present turn angle of the vehicle, determining, by a processor, a desired turn angle of the vehicle according to a turn command, determining, by the processor, a difference between the present turn angle and the desired turn angle, and controlling, by the processor, a weight shifting system of the vehicle to relocate a weight movably attached to the weight shifting system based on the difference between the present turn angle and the desired turn angle. 
     The present teachings further provide a method to shift a center of gravity of an unmanned ground vehicle, the method comprising determining, by a location sensor, a present location of the vehicle, determining, by a speed sensor, a present speed of the vehicle, determining, by a movement sensor, a present turn angle of the vehicle, determining, by a processor, a planned turn angle of the vehicle at a planned location of the vehicle according to a planned path, and controlling, by the processor, a weight shifting system of the vehicle to relocate a weight movably attached to the weight shifting system based on at least one of the present location of the vehicle, the present speed of the vehicle, the present turn angle of the vehicle, and the planned turn angle of the vehicle at the planned location of the vehicle. 
     Additional objects and advantages of the present teachings will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present teachings. The objects and advantages of the present teachings will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of an exemplary embodiment of a weight shifting system in accordance with the present teachings. 
         FIG. 2  is a flowchart illustrating a process of operating an exemplary embodiment of a weight shifting system in accordance with the present teachings. 
         FIG. 3  is another flowchart illustrating a process of operating an exemplary embodiment of a weight shifting system in accordance with the present teachings. 
         FIG. 4  is a side perspective view of an exemplary embodiment of a weight shifting system in accordance with the present teachings, mounted on a remote vehicle. 
         FIG. 5A  illustrates a remote vehicle having a weight shifting system in accordance with the present teachings, the remote vehicle turning a corner without employing active weight shifting. 
         FIG. 5B  illustrates a remote vehicle having a weight shifting system in accordance with the present teachings, the remote vehicle turning a corner while employing active weight shifting. 
     
    
    
     DETAILED DESCRIPTION 
     The foregoing general description, the following detailed description, and the accompanying drawings, are exemplary and explanatory only and are not restrictive of the present invention, as claimed. The following detailed description and accompanying drawings teach the best mode of the invention. For the purpose of teaching inventive principles, some aspects of the best mode may be simplified or omitted where they would be known to those of ordinary skill in the art. 
     The appended claims specify the scope of the invention. Some aspects of the best mode may not fall within the scope of the invention as specified by the claims. Thus, those skilled in the art will appreciate variations from the best mode that fall within the scope of the invention. Those skilled in the art will also appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. 
       FIG. 1  illustrates an exemplary embodiment of a weight shifting system  100 , including certain aspects of the present teachings. Weight shifting system  100  includes a rectangular frame comprising guides  102  and  104  extending longitudinally between frame supports  106  and  108 . Weight shifting system  100  further includes a support guide  150  which extends laterally from guide  102  to guide  104 , perpendicular to guides  102  and  104 . Support guide  150  includes sliding couplers  110  and  112  that slide along guides  102  and  104 , respectively. 
     Weight shifting system  100  further includes toothed belts  118  and  120  running under and parallel to guides  102  and  104 , respectively, and attached to a circular drive gears  105  and  107 , respectively, at frame support  108 . Toothed belts  118  and  120  can be, for example, fixedly attached to sliding couplers  110  and  112 , respectively, so that circulating toothed belts  118  and  120  through the circular gears  105  and  107  can cause sliding couplers  110  and  112  to slide along guides  102  and  104 , respectively. 
     Weight shifting system  100  further includes a shaft element  122  attached to toothed belts  118  and  120  to circulate the toothed belts  118  and  120  (e.g., via gears on each side of the shaft that engage the teeth of the belts), and shaft motor  124  connected to shaft elements  122  for rotating shaft element  122 . When rotated, shaft element  122  rotates to circulate toothed belts  118  and  120  to move sliding couplers  110  and  112  along guide members  102  and  104 , respectively, and thus move support guide  150  along the frame. 
     Support guide  150  further includes slidable weight  152 , a toothed belt  154 , a pinion  153  attached to weight  152  and configured to move along toothed belt  154 , and a support motor  156  to drive (i.e., rotate) pinion  153 . Weight  152  may be any physical element providing enough weight to cause a shift in the center of gravity of the vehicle when relocated from one location of the weight shifting system to another. The physical element preferably comprises an element with a second purpose in the vehicle, such as a battery to power one or more components of the vehicle, a control unit for controlling one or more components of the vehicle, or a gas or other fluid tank. The physical element may also be a simple weight without a secondary purpose. 
     Weight  152  is preferably attached to support guide  150  such that it can slide along support guide  150  between sliding couplers  110  and  112 . Toothed belt  154  can be disposed along support guide  150 , and can be attached to sliding couplers  110  and  112 . Support motor  156  drives (i.e., rotates) pinion  153  to move the weight along the toothed belt  154  between coupler  110  to coupler  112 . 
     One skilled in the art will understand that an active weight shifting system in accordance with the present teachings need not employ a gear-based mechanism to move the weight to the sides and/or to the front and back of the remote vehicle, but rather can utilize other known drive mechanisms such as, for example, hydraulic drive mechanisms. The same type of mechanism need not be used for both side-to-side and front-to-back movement of the weight. 
     In operation, weight shifting system  100  can be implemented in a vehicle as an added feature to an existing vehicle or can be built into the vehicle. The weight shifting system preferable operates in a horizontal plane of the vehicle as shown in  FIG. 4 . When the vehicle needs to shift its center of gravity, for example to counteract oversteer or understeer or prevent rollover, the vehicle can control weight shifting system  100  to move weight element  152  to a desired location longitudinally and laterally along shifting system  100 &#39;s rectangular frame. 
     In accordance with certain embodiments of the present teachings, one or more processors (e.g., one or more of the vehicle&#39;s processors) can communicate with weight shifting system  100  to control shaft motor  124  to adjust the location of support guide  150  (and thus the location of weight  152 ) longitudinally along guides  102  and  104 , and support motor  156  to adjust the location of weight  152  laterally along support guide  150 . Relocation of weight  152  causes the center of gravity of the vehicle to shift to counteract oversteer, understeer, or a rollover tendency. 
     A weight shifting system consistent with the present teachings can be used as a driver assist behavior to support augmented teleoperation of remote vehicles, or it can be combined with autonomous behaviors to provide fully autonomous control of high speed vehicles that can perform aggressive maneuvers. For teleoperation, the driver would control the vehicle, and the weight shifting system may assist by shifting its weight element to maintain stability when driver commands would cause the vehicle to oversteer, understeer, or roll over. For autonomous operation, other behaviors (e.g. path planning, obstacle avoidance, pursuit/evasion) would determine the vehicle&#39;s path, and the weight shifting system may improve the vehicle&#39;s stability when following the selected path, by, for example, shifting the center of gravity in anticipation of an upcoming turn. 
     The weight shifting system may be integrated with the vehicle&#39;s Dynamic Stability Control (DSC) system, when such a system is available. When the vehicle understeers (turns at a lower rate than commanded) or oversteers (turns at a higher rate than commanded) a DSC system may react by reducing throttle or applying brakes selectively to individual wheels to control and minimize the slip angle (i.e., the angle between a wheel&#39;s orientation and its direction of travel). In an exemplary embodiment of the present teachings, the DSC system can control a weight shifting system of the present teachings to shift the center of gravity of the vehicle in response to a detected slip angle, thus giving the DSC an additional option for stability control. The shift of the center of gravity, alone or in combination with other corrective actions, may reduce the slip angle and improve the vehicle&#39;s maneuverability, particularly at higher speeds. 
     The embodiment of  FIG. 1  is intended to be exemplary, and it would be apparent to one skilled in the art that certain aspects of the present teachings may be implemented in a plurality of ways. For example, sliding couplers  110  and  112  and support guide  150  may move along guides  102  and  104  in a variety of ways, including a rack and pinion system in which a motor resides at one or both of the sliding couplers and drives a circular pinion to engage the teeth of a linear gear parallel to, or along guides  102  and  104 . Also, weight element  152  may move along support guide  150  in a variety of ways, including a motor attached to one of the couplers to drive a circular gear coupled to a toothed belt attached to weight  152 . Circulating the toothed belt would move weight  152  along support guide  150 . 
       FIG. 2  illustrates an exemplary process  200  for operating a weight shifting system such as the system  100  of  FIG. 1  in an unmanned ground vehicle, including certain aspects of the present teachings. At step  210 , the vehicle determines a present turn angle of the vehicle, which indicates the present direction of movement of the vehicle. The present turn angle may be determined by a processor based on environmental information received from an Inertial Measurement Unit (IMU) or other component capable of providing directional/movement information. At step  220 , the vehicle determines a desired turn angle of the vehicle, which indicates the desired direction of movement of the vehicle. The desired turn angle can be determined based on, for example, a command received from a remote control device, but the present teachings are not so limited. For example, the desired turn angle can alternatively be determined based on a planned path of the vehicle or on mapping information of the environment proximal to the vehicle (e.g., turn angle necessary to avoid an obstacle), without departing from the spirit of the present teachings. 
     At step  230 , the vehicle determines a difference between the present turn angle and the desired turn angle, and at step  240  the vehicle determines the present speed of the vehicle. The speed of the vehicle may be determined based on a global positioning system, a speedometer, or any other manner of measuring speed known in the art. At step  250 , the processor controls the weight shifting system to move a weight movably attached to the weight shifting system, the movement of the weight being based on, for example, the difference between the present turn angle and the desired turn angle and the present speed of the vehicle. 
       FIG. 3  illustrates a process  300  for operating weight shifting system such as the system  100  of  FIG. 1  in an unmanned ground vehicle, including certain aspects of the present teachings. At step  310 , the vehicle determines a present location of the vehicle. The present location may be determined in a variety of ways, including via a global positioning system and/or via a planar laser-based Simultaneous Localization and Mapping (SLAM) system, or any other known system for determining a present location without departing from the spirit of the present teachings. 
     At step  320 , the vehicle determines the present speed of the vehicle. The speed of the vehicle may be determined based on a global positioning system, a speedometer, or any other manner of measuring speed known in the art. At step  330 , the vehicle determines a present turn angle of the vehicle. The present turn angle may be determined by a processor based on environmental information received from an Inertial Measurement Unit (IMU) or other component capable of providing directional/movement information. 
     At step  340 , the vehicle determines a planned turn angle of the vehicle at a planned location of the vehicle. The planned turn angle at the planned location may be based on path planning information received from a source external to the vehicle or on a path determined by the vehicle according to environmental conditions (e.g., obstacle avoidance). At step  350 , the vehicle controls a weight shifting system of the vehicle to relocate a weight movably attached to the weight shifting system based on at least one of the present location of the vehicle, the present speed of the vehicle, the present turn angle of the vehicle, and the planned turn angle of the vehicle at the planned location of the vehicle. 
     The exemplary embodiment illustrated in  FIG. 3  relates to using a planned path to anticipate an upcoming turn and relocate the weight shifting system&#39;s weight to a desired location before reaching the upcoming turn, as opposed to relocating the weight shifting system&#39;s weight in reaction to an oversteer/understeer situation (i.e., relocating the weight after detecting a slip angle). Thus, in addition to reducing a slip angle, the present embodiment may prevent a slip angle altogether. 
       FIG. 4  illustrates a vehicle  400 , which includes certain aspects of the present teachings. In particular, vehicle  400  illustrates an exemplary unmanned ground vehicle including an exemplary embodiment of a weight shifting system according to the present teachings. Vehicle  400  includes guides  402  and  404  and support guide  450  which extends from guide  402  to guide  404 , perpendicular to guides  402  and  404 . 
     Support guide  450  includes sliding couplers  410  and  412  for sliding support guide  450  along guides  402  and  404 . Support guide  450  further includes sliding weight element  452  movably attached to support guide  450  and is configured to slide along support guide  450  between sliding couplers  410  and  412 . Weight element  452  can, for example, comprise a battery for providing energy to one or more components of the vehicle. 
     Vehicle  400  can also include a Central Processing Unit (CPU) (not shown) for processing information such as control and environmental data, and environment sensors for providing environmental data, such as a Global Positioning System (GPS) for providing location data and speed data, an Inertia Measurement Unit (IMU) for providing turn/yaw rate data, and a Light Detection and Ranging (LIDAR) unit  470  for providing proximity data. Vehicle  400  may further include a planar laser-based Simultaneous Localization and Mapping (SLAM) system for environment mapping and path planning, and a stereo vision camera to capture environment information and provide a 3-Dimensional (3D) volumetric picture element (VOXEL)-based representation of the environment. 
     The environmental data can be used for path planning and vehicle control, including weight shifting control in accordance with various embodiments of the present teachings. The environmental data may also be used in combination with an Operation Control Unit (OCU) (not shown) remotely controlling the vehicle. The OCU may allow a user to manually control the vehicle  400 &#39;s speed and direction and provide visual feedback to the user by projecting in input from the vehicle&#39;s stereo vision camera. 
     An environment can be defined as a physical area that has a defined coordinate system for implementing a localization strategy and a path planning strategy. For example, an outdoor environment may be mapped according to a GPS-based coordinate system with a waypoint planning path strategy and GPS-based localization. An indoor environment (in which GPS may not be available) may be mapped according to a coordinate system defined using a planar laser-based SLAM strategy. Other embodiments may use, for example, a 3-Dimensional (3D) volumetric picture element (VOXEL)-based representation of an area based on stereo-vision information of the area, a 3D-based SLAM, or SLAM for a predetermined remote vehicle sensor. 
     Other aspects of the present teachings described with respect to weight shifting system  100  of  FIG. 1  are not shown for simplicity or are not visible in  FIG. 4 , and their description is therefore omitted. Furthermore, particular elements of vehicle  400  illustrated in  FIG. 4  (e.g., wheel  460 ) will not be described for the purposes of simplicity. 
     In operation, vehicle  400  captures and analyses environment data from, for example, a GPS system (e.g., vehicle location and speed), a IMU (e.g., actual turn rate/yaw rate), and/or a LIDAR unit  470  (e.g., mapping of the proximate environment and/or an obstacle detection/obstacle avoidance behavior). The CPU processes the environment data, as well as any control data (e.g., desired speed and direction based on either manual control through an OCU or a planned path) to determine if a shift of the vehicle&#39;s center of gravity is required. If a shift is required, the vehicle CPU can control the weight shifting system to move a weight  452  to a desired location along the vehicle. Relocation of weight  452  causes the center of gravity of the vehicle to shift to reduce/minimize oversteering, understeering, and/or a vehicle&#39;s rollover tendency. 
     For example, and not as a limitation, when vehicle  400  operates under a planned path, the GPS can provide the current location and speed of the vehicle  400  in real-time to a CPU. A LIDAR sensor can provide a real-time map of the environment proximal to the vehicle  400  (e.g., nearby objects or obstacles) to the CPU. The CPU can then control the vehicle&#39;s speed and direction according to the planned path and the real-time map. When the CPU determines that a desired turn may cause the vehicle to understeer, oversteer, or rollover, the CPU determines where the weight of the weight shifting system should be located to achieve a desired shift of the center of gravity and controls the weight shifting system to relocate the weight to the determined location. This weight shift may be performed independently or in combination with other actions, such as controlling the speed of one or more of the vehicle&#39;s wheels. After the vehicle completes the turn, the CPU may return the weight to its previous location or to a predetermined location. 
     As a further example, and not as a limitation, when a vehicle such as vehicle  400  of  FIG. 4  operates under user control (i.e., the user controls the direction and/or speed of the vehicle), the GPS system may provide the current location of the vehicle  400  and its current speed to the CPU. The LIDAR may provide a map of the environment and be utilized to avoid collisions, with the CPU controlling the vehicle according to the user&#39;s commands. When the user requests the vehicle to turn, the CPU determines whether a shift of the center of gravity is needed and/or would aid in stabilizing the vehicle through the requested turn. If the CPU determines that a shift is necessary or desirable, the CPU can then determine where the weight of the weight shifting system should be relocated to achieve a desired shift of the center of gravity, and control the weight shifting system to relocate the weight to the determined location. This weight shift may be performed independently or in combination with other actions, such as controlling the speed of one or more of the vehicle&#39;s wheels. After the vehicle completes the turn, the CPU may return the weight to its previous location or to a predetermined location. 
       FIGS. 5A and 5B  illustrate exemplary operations of vehicle  400  according to certain aspects of the present teachings.  FIG. 5A  depicts vehicle  400  taking a sharp turn at high speed with weight  452  being located near the front of the vehicle  400  and near the center of support guide  450 . With this arrangement of the weight  452 , vehicle  400  oversteers and spins out of control. In contrast,  FIG. 5B  depicts vehicle  400  taking the same sharp turn at high speed, but with weight  452  located near the back and towards the left side of vehicle  400 . This rear and left location of weight  452  prevents oversteering during the sharp turn as shown. 
     Some or all of the actions performed by the exemplary embodiments described herein can be performed under the control of a computer system executing computer-readable codes either in a computer-readable recording medium or in communication signals transmitted through a transmission medium. The computer-readable recording medium is any data storage device that can store data for a non-fleeting period of time such that the data can thereafter be read by a computer system. Examples of the computer-readable recording medium include, but are not limited to, read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, and optical data storage devices. The computer-readable recording medium can also be distributed over network-coupled computer systems so that the computer-readable code is stored and executed in a distributed fashion. The communication signals transmitted through a transmission medium may include, for example, signals which modulate carrier waves transmitted through wired or wireless transmission paths. 
     The above description and associated figures teach the best mode of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the teachings disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit invention being indicated by the following claims.