Title of Invention: Whole body manipulation on a legged robot using dynamic balance Abstract: A robot system includes: an upper body section including one or more end-effectors; a lower body section including one or more legs; and an intermediate body section coupling the upper and lower body sections. An upper body control system operates at least one of the end-effectors. The intermediate body section experiences a first intermediate body linear force and/or moment based on an end-effector force acting on the at least one end-effector. A lower body control system operates the one or more legs. The one or more legs experience respective surface reaction forces. The intermediate body section experiences a second intermediate body linear force and/or moment based on the surface reaction forces. The lower body control system operates the one or more legs so that the second intermediate body linear force balances the first intermediate linear force and the second intermediate body moment balances the first intermediate body moment. Detailed Description: Part general_description_paragraphs: Part BACKGROUND: A robot may include a plurality of legs that are operable to balance the robot on a ground surface or to move the robot along the ground surface. The robot may also include one or more end-effectors that allow the robot to manipulate objects or support loads. Part SUMMARY: According to example implementations, a robot can operate its legs to dynamically balance itself on a surface while operating its end-effectors. When the legs contact a surface (e.g., ground surface), the legs apply forces to the surface and experience reaction forces from the surface. The robot can dynamically control the legs so that the reaction forces allow the robot to maintain a balance that supports the operation of the end-effectors. The dynamic balancing provided by the legs during operation of the end-effectors constitutes a whole body manipulation that more closely resembles actual motion by actual humans. According to an example implementation, a robot system includes a body. The body includes: an upper body section including one or more movable end-effectors; a lower body section including one or more legs configured to contact a surface; and an intermediate body section coupling the upper body section and the lower body section. The robot system also includes a control system implemented with one or more processors. The control system includes an upper body control system configured to operate at least one of the end-effectors. The at least one end-effector experiences an end-effector force based on the operation by the upper body control system. The intermediate body section experiences at least one of a first intermediate body linear force or a first intermediate body moment based on the end-effector force. The control system includes a lower body control system configured to operate the one or more legs in response to the operation of the at least one end-effector. The one or more legs experiences respective reaction forces from the surface based on the operation by the lower body control system. The intermediate body section experiences at least one of a second intermediate body linear force or a second intermediate body moment based on the reaction forces, The lower body control system operates the one or more legs so that the second intermediate body linear force balances the first intermediate linear force and the second intermediate body moment balances the first intermediate body moment. According to another example implementation, a robot system includes a body. The body includes: an upper body section including one or more movable end-effectors; a lower body section including one or more legs configured to contact a surface; and an intermediate body section coupling the upper body section and the lower body section. The robot system includes a control system implemented with one or more processors. The control system includes a lower body control system and an upper control system. A method for controlling a robot system includes operating, with the upper body control system, at least one of the end-effectors. The at least one end-effector experiences an end-effector force based on the operation by the upper body control system. The intermediate body section experiences at least one of a first intermediate body linear force or a first intermediate body moment based on the end-effector force. The method includes operating, with the lower body control system, the one or more legs in response to the operation of the at least one end-effector. The one or more legs experiences respective reaction forces from the surface based on the operation by the lower body control system. The intermediate body section experiences at least one of a second intermediate body linear force or a second intermediate body moment based on the reaction forces. According to yet another example implementation, a robot system includes a body. The body includes: an upper body section including one or more movable end-effectors; a lower body section including one or more legs configured to contact a surface; and an intermediate body section coupling the upper body section and the lower body section. The robot system includes a control system implemented with one or more processors. The control system includes an upper body control system configured to operate at least one of the end-effectors. The at least one end-effector experiences an end-effector force based on the operation by the upper body control system. The intermediate body section experiences at least one of a first intermediate body linear force or an first intermediate body moment based on the at least one end-effector force. The control system includes a lower body control system configured to operate the one or more legs based on the first intermediate body linear force or the first intermediate body moment. The one or more legs experiences respective reaction forces from the surface based on the operation by the lower body control system. The intermediate body section experiences at least one of a second intermediate body linear force or a second intermediate body moment based on the reaction forces. The lower body control system operates the one or more legs so that the second intermediate body linear force balances the first intermediate linear force and the second intermediate body moment balances the first intermediate body moment. The upper body control system processes the lower body section as a virtual link coupled to the intermediate body section. The lower body control system is further configured to position the intermediate body section according to a first set of degrees of freedom based on the operation of the one or more legs. The upper body control system is further configured to position the intermediate body section according to a second set of degrees of freedom based on the operation of the at least one end-effector The upper body control system is constrained from positioning the intermediate body section according to the first set of degrees of freedom. According to a further example implementation, A robot system includes a body. The body includes: an upper body section; a lower body section including one or more legs configured to contact a surface; and an intermediate body section coupling the upper body section and the lower body section. The robot system includes a control system implemented with one or more processors. The control system includes an upper body control system configured to operate the upper body section. The upper body section experiences an upper body force in response to the operation by the upper body control system. The intermediate body section experiences at least one of a first intermediate body linear force or a first intermediate body moment based on the upper body force. The control system includes a lower body control system configured to operate the one or more legs. The one or more legs experiences respective reaction forces from the surface based on the operation by the lower body control system. The intermediate body section experiences at least one of a second intermediate body linear force or a second intermediate body moment based on the reaction forces. The lower body control system operates the one or more legs so that the second intermediate body linear force balances the first intermediate linear force and the second intermediate body moment balances the first intermediate body moment. These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description with reference where appropriate to the accompanying drawings. Further, it should be understood that the description provided in this summary section and elsewhere in this document is intended to illustrate the claimed subject matter by way of example and not by way of limitation. Part DETAILED DESCRIPTION: The following detailed description describes various features and functions of the disclosed systems and methods with reference to the accompanying figures. The illustrative system and method embodiments described herein are not meant to be limiting. It will be readily understood that certain aspects of the disclosed systems and methods can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein. I. Overview A robot may include a plurality of legs that are operable to balance the robot on a ground surface or to move the robot along the ground surface. The robot may also include one or more end-effectors that allow the robot to manipulate objects or support loads. According to one approach, the robot must first operate its legs to maintain position control and establish static balance before it can position the end-effectors to perform a task. For instance, the robot may initially operate the legs to form a static support polygon over which the center of mass of the robot is maintained during the positioning and operation of the end-effectors. According to this approach, the legs and the end-effectors are not simultaneously manipulated to act as a whole body. According to example implementations disclosed herein, however, a robot can operate its legs to dynamically balance itself on a surface while it operates end-effectors. When the legs contact a surface (e.g., ground surface), the legs apply forces to the surface and experience reaction forces from the surface. The robot can dynamically control the legs so that the reaction forces allow the robot to maintain a balance that supports the operation of the end-effectors. The dynamic balancing provided by the legs during operation of the end-effectors constitutes a whole body manipulation that may more closely resemble actual motion by actual humans. The legs can dynamically balance the robot even while the robot is moving according to a gait. For instance, the robot can walk or run along a ground surface, and due to dynamic balancing, the robot can simultaneously position the end-effector to grab an object without interrupting the gait. In example implementations, the robot includes a lower body section, an upper body section, and an intermediate body section. For a bipedal robot, the intermediate section may act as, or resemble, a pelvis. The lower body section includes the legs and the upper body section includes the end-effectors. In some cases, the end-effectors may be disposed on the ends of arms that can extend outwardly from the robot to position the end-effectors. The lower body section is coupled to the intermediate section from below, and the upper body section is coupled to the intermediate section from above. The robot includes a lower body control system and an upper body control system. The lower body control system controls the legs, and the upper body control system controls the end-effectors. The lower body control system and the upper body control system coordinate to achieve whole body manipulation and balance for the robot. In particular, the lower body control system controls the legs so that the reaction forces from the surface provide a dynamic balance that allows the upper body control system to perform tasks with the end-effectors. During its analysis, the upper body control system represents and processes the lower body section as a virtual link coupled to the intermediate body section. To position and operate the end-effectors, the upper body control system employs an inverse kinematics solver that accounts for the virtual link as well as the position and orientation of the intermediate body section. Inverse kinematics refers to the use of the kinematics equations of the robot to determine the parameters for components (e.g., joints) to allow an end-effector to reach a target position and perform a task. A motion plan specifies the movement of the robot so that the end-effector can reach a target position and perform a task. For instance, the inverse kinematics solver may use the velocity of the virtual link to determine a motion plan for the upper body section that achieves desired end-effector velocities in a static world frame. Inverse kinematics transforms the motion plan into actuator trajectories for components (e.g., joints) of the robot. To position the end-effectors, the upper body control system may reposition/reorient the intermediate body section. In general, the intermediate body section can be positioned and oriented according to any one or more of six degrees of freedom. To achieve dynamic balance, however, the lower body control system may need to reposition/reorient the intermediate body section according to one or more of these six degrees of freedom. As such, to maintain the dynamic balance, the upper body control system may be constrained from repositioning/reorienting the intermediate body section according to the degrees of freedom needed by the lower body control system to achieve the dynamic balance. In other words, the inverse kinematics solver for the upper body control system treats these particular degrees of freedom as constraints. These constraints free the lower body control system to balance dynamically. The loads supported by the end-effectors generate a resulting linear force and/or moment on the intermediate body section. The upper body control system can determine the resulting linear force and moment and communicate this information to the lower body control system. In response, the lower body control system can operate the legs so that the reaction forces can balance the linear force and/or moment at the intermediate body section. In general, a first force/moment is balanced by a second force/moment, when the second force/moment directionally opposes the first force/moment with at least substantially the same magnitude. Such balancing can also be employed when other loads are additionally or alternatively experienced by the upper body section. For instance, upper body section may experience dynamic forces, such as forces required to accelerate an arm, an end-effector, or a payload, during high-speed motions. Such dynamic forces also generate a resulting linear force and/or moment on the intermediate body section, which the lower body control can also balance with the reaction forces. Additionally, when the upper body control system wants to extend the end-effectors to a target position, the lower body control system can determine whether the current position of the legs allows the end-effectors to reach the target position with sufficient balance. If necessary, the legs can be operated to move the robot along the surface so that the end-effectors can reach the target position. II. Example Robotic Systems FIG. 1 illustrates an example configuration of a robotic system that may be used in connection with the implementations described herein. The robotic system 100 may be configured to operate autonomously, semi-autonomously, and/or using directions provided by user(s). The robotic system 100 may be implemented in various forms, such as a biped robot, quadruped robot, or some other arrangement. Furthermore, the robotic system 100 may also be referred to as a robot, robotic device, or mobile robot, among other designations. As shown in FIG. 1, the robotic system 100 may include processor(s) 102, data storage 104, and controller(s) 108, which together may be part of a control system 118. The robotic system 100 may also include sensor(s) 112, power source(s) 114, mechanical components 110, and electrical components 116. Nonetheless, the robotic system 100 is shown for illustrative purposes, and may include more or fewer components. The various components of robotic system 100 may be connected in any manner, including wired or wireless connections. Further, in some examples, components of the robotic system 100 may be distributed among multiple physical entities rather than a single physical entity. Other example illustrations of robotic system 100 may exist as well. Processor(s) 102 may operate as one or more general-purpose hardware processors or special purpose hardware processors (e.g., digital signal processors, application specific integrated circuits, etc.). The processor(s) 102 may be configured to execute computer-readable program instructions 106, and manipulate data 107, both of which are stored in the data storage 104. The processor(s) 102 may also directly or indirectly interact with other components of the robotic system 100, such as sensor(s) 112, power source(s) 114, mechanical components 110, and/or electrical components 116. The data storage 104 may be one or more types of hardware memory. For example, the data storage 104 may include or take the form of one or more computer-readable storage media that can be read or accessed by processor(s) 102. The one or more computer-readable storage media can include volatile and/or non-volatile storage components, such as optical, magnetic, organic, or another type of memory or storage, which can be integrated in whole or in part with processor(s) 102. In some implementations, the data storage 104 can be a single physical device. In other implementations, the data storage 104 can be implemented using two or more physical devices, which may communicate with one another via wired or wireless communication. As noted previously, the data storage 104 may include the computer-readable program instructions 106 and the data 107. The data 107 may be any type of data, such as configuration data, sensor data, and/or diagnostic data, among other possibilities. The controller 108 may include one or more electrical circuits, units of digital logic, computer chips, and/or microprocessors that are configured to (perhaps among other tasks), interface between any combination of the mechanical components 110, the sensor(s) 112, the power source(s) 114, the electrical components 116, the control system 118, and/or a user of the robotic system 100. In some implementations, the controller 108 may be a purpose-built embedded device for performing specific operations with one or more subsystems of the robotic device 100. The control system 118 may monitor and physically change the operating conditions of the robotic system 100. In doing so, the control system 118 may serve as a link between portions of the robotic system 100, such as between mechanical components 110 and/or electrical components 116. In some instances, the control system 118 may serve as an interface between the robotic system 100 and another computing device. Further, the control system 118 may serve as an interface between the robotic system 100 and a user. The instance, the control system 118 may include various components for communicating with the robotic system 100, including a joystick, buttons, and/or ports, etc. The example interfaces and communications noted above may be implemented via a wired or wireless connection, or both. The control system 118 may perform other operations for the robotic system 100 as well. During operation, the control system 118 may communicate with other systems of the robotic system 100 via wired or wireless connections, and may further be configured to communicate with one or more users of the robot. As one possible illustration, the control system 118 may receive an input (e.g., from a user or from another robot) indicating an instruction to perform a particular gait in a particular direction, and at a particular speed. A gait is a pattern of movement of the limbs of an animal, robot, or other mechanical structure. Based on this input, the control system 118 may perform operations to cause the robotic device 100 to move according to the requested gait. As another illustration, a control system may receive an input indicating an instruction to move to a particular geographical location. In response, the control system 118 (perhaps with the assistance of other components or systems) may determine a direction, speed, and/or gait based on the environment through which the robotic system 100 is moving en route to the geographical location. Operations of the control system 118 may be carried out by the processor(s) 102. Alternatively, these operations may be carried out by the controller 108, or a combination of the processor(s) 102 and the controller 108. In some implementations, the control system 118 may partially or wholly reside on a device other than the robotic system 100, and therefore may at least in part control the robotic system 100 remotely. Mechanical components 110 represent hardware of the robotic system 100 that may enable the robotic system 100 to perform physical operations. As a few examples, the robotic system 100 may include physical members such as leg(s), arm(s), and/or wheel(s). The physical members or other parts of robotic system 100 may further include actuators arranged to move the physical members in relation to one another. The robotic system 100 may also include one or more structured bodies for housing the control system 118 and/or other components, and may further include other types of mechanical components. The particular mechanical components 110 used in a given robot may vary based on the design of the robot, and may also be based on the operations and/or tasks the robot may be configured to perform. In some examples, the mechanical components 110 may include one or more removable components. The robotic system 100 may be configured to add and/or remove such removable components, which may involve assistance from a user and/or another robot. For example, the robotic system 100 may be configured with removable arms, hands, feet, and/or legs, so that these appendages can be replaced or changed as needed or desired. In some implementations, the robotic system 100 may include one or more removable and/or replaceable battery units or sensors. Other types of removable components may be included within some implementations. The robotic system 100 may include sensor(s) 112 arranged to sense aspects of the robotic system 100. The sensor(s) 112 may include one or more force sensors, torque sensors, velocity sensors, acceleration sensors, position sensors, proximity sensors, motion sensors, location sensors, load sensors, temperature sensors, touch sensors, depth sensors, ultrasonic range sensors, infrared sensors, object sensors, and/or cameras, among other possibilities. Within some examples, the robotic system 100 may be configured to receive sensor data from sensors that are physically separated from the robot (e.g., sensors that are positioned on other robots or located within the environment in which the robot is operating). The sensor(s) 112 may provide sensor data to the processor(s) 102 (perhaps by way of data 107) to allow for interaction of the robotic system 100 with its environment, as well as monitoring of the operation of the robotic system 100. The sensor data may be used in evaluation of various factors for activation, movement, and deactivation of mechanical components 110 and electrical components 116 by control system 118. For example, the sensor(s) 112 may capture data corresponding to the terrain of the environment or location of nearby objects, which may assist with environment recognition and navigation. In an example configuration, sensor(s) 112 may include RADAR (e.g., for long-range object detection, distance determination, and/or speed determination), LIDAR (e.g., for short-range object detection, distance determination, and/or speed determination), SONAR (e.g., for underwater object detection, distance determination, and/or speed determination), VICON® (e.g., for motion capture), one or more cameras (e.g., stereoscopic cameras for 3D vision), a global positioning system (GPS) transceiver, and/or other sensors for capturing information of the environment in which the robotic system 100 is operating. The sensor(s) 112 may monitor the environment in real time, and detect obstacles, elements of the terrain, weather conditions, temperature, and/or other aspects of the environment. Further, the robotic system 100 may include sensor(s) 112 configured to receive information indicative of the state of the robotic system 100, including sensor(s) 112 that may monitor the state of the various components of the robotic system 100. The sensor(s) 112 may measure activity of systems of the robotic system 100 and receive information based on the operation of the various features of the robotic system 100, such the operation of extendable legs, arms, or other mechanical and/or electrical features of the robotic system 100. The data provided by the sensor(s) 112 may enable the control system 118 to determine errors in operation as well as monitor overall operation of components of the robotic system 100. As an example, the robotic system 100 may use force sensors to measure load on various components of the robotic system 100. In some implementations, the robotic system 100 may include one or more force sensors on an arm or a leg to measure the load on the actuators that move one or more members of the arm or leg. As another example, the robotic system 100 may use one or more position sensors to sense the position of the actuators of the robotic system. For instance, such position sensors may sense states of extension, retraction, or rotation of the actuators on arms or legs. As another example, the sensor(s) 112 may include one or more velocity and/or acceleration sensors. For instance, the sensor(s) 112 may include an inertial measurement unit (IMU). The IMU may sense velocity and acceleration in the world frame, with respect to the gravity vector. The velocity and acceleration sensed by the IMU may then be translated to that of the robotic system 100 based on the location of the IMU in the robotic system 100 and the kinematics of the robotic system 100. The robotic system 100 may include other types of sensors not explicated discussed herein. Additionally or alternatively, the robotic system may use particular sensors for purposes not enumerated herein. The robotic system 100 may also include one or more power source(s) 114 configured to supply power to various components of the robotic system 100. Among other possible power systems, the robotic system 100 may include a hydraulic system, electrical system, batteries, and/or other types of power systems. As an example illustration, the robotic system 100 may include one or more batteries configured to provide charge to components of the robotic system 100. Some of the mechanical components 110 and/or electrical components 116 may each connect to a different power source, may be powered by the same power source, or be powered by multiple power sources. Any type of power source may be used to power the robotic system 100, such as electrical power or a gasoline engine. Additionally or alternatively, the robotic system 100 may include a hydraulic system configured to provide power to the mechanical components 110 using fluid power. Components of the robotic system 100 may operate based on hydraulic fluid being transmitted throughout the hydraulic system to various hydraulic motors and hydraulic cylinders, for example. The hydraulic system may transfer hydraulic power by way of pressurized hydraulic fluid through tubes, flexible hoses, or other links between components of the robotic system 100. The power source(s) 114 may charge using various types of charging, such as wired connections to an outside power source, wireless charging, combustion, or other examples. The electrical components 116 may include various mechanisms capable of processing, transferring, and/or providing electrical charge or electric signals. Among possible examples, the electrical components 116 may include electrical wires, circuitry, and/or wireless communication transmitters and receivers to enable operations of the robotic system 100. The electrical components 116 may interwork with the mechanical components 110 to enable the robotic system 100 to perform various operations. The electrical components 116 may be configured to provide power from the power source(s) 114 to the various mechanical components 110, for example. Further, the robotic system 100 may include electric motors. Other examples of electrical components 116 may exist as well. Although not shown in FIG. 1, the robotic system 100 may include a body, which may connect to or house appendages and components of the robotic system. As such, the structure of the body may vary within examples and may further depend on particular operations that a given robot may have been designed to perform. For example, a robot developed to carry heavy loads may have a wide body that enables placement of the load. Similarly, a robot designed to reach high speeds may have a narrow, small body that does not have substantial weight. Further, the body and/or the other components may be developed using various types of materials, such as metals or plastics. Within other examples, a robot may have a body with a different structure or made of various types of materials. The body and/or the other components may include or carry the sensor(s) 112. These sensors may be positioned in various locations on the robotic device 100, such as on the body and/or on one or more of the appendages, among other examples. On its body, the robotic device 100 may carry a load, such as a type of cargo that is to be transported. The load may also represent external batteries or other types of power sources (e.g., solar panels) that the robotic device 100 may utilize. Carrying the load represents one example use for which the robotic device 100 may be configured, but the robotic device 100 may be configured to perform other operations as well. As noted above, the robotic system 100 may include various types of legs, arms, wheels, and so on. In general, the robotic system 100 may be configured with zero or more legs. An implementation of the robotic system with zero legs may include wheels, treads, or some other form of locomotion. An implementation of the robotic system with two legs may be referred to as a biped, and an implementation with four legs may be referred as a quadruped. Implementations with six or eight legs are also possible. For purposes of illustration, biped and quadruped implementations of the robotic system 100 are described below. FIG. 2 illustrates a quadruped robot 200, according to an example implementation. Among other possible features, the robot 200 may be configured to perform some of the operations described herein. The robot 200 includes a control system, and legs 204A, 204B, 204C, 204D connected to a body 208. Each leg may include a respective foot 206A, 206B, 206C, 206D that may contact a surface (e.g., a ground surface). Further, the robot 200 is illustrated with sensor(s) 210, and may be capable of carrying a load on the body 208. Within other examples, the robot 200 may include more or fewer components, and thus may include components not shown in FIG. 2. The robot 200 may be a physical representation of the robotic system 100 shown in FIG. 1, or may be based on other configurations. Thus, the robot 200 may include one or more of mechanical components 110, sensor(s) 112, power source(s) 114, electrical components 116, and/or control system 118, among other possible components or systems. The configuration, position, and/or structure of the legs 204A-204D may vary in example implementations. The legs 204A-204D enable the robot 200 to move relative to its environment, and may be configured to operate in multiple degrees of freedom to enable different techniques of travel. In particular, the legs 204A-204D may enable the robot 200 to travel at various speeds according to the mechanics set forth within different gaits. The robot 200 may use one or more gaits to travel within an environment, which may involve selecting a gait based on speed, terrain, the need to maneuver, and/or energy efficiency. Further, different types of robots may use different gaits due to variations in design. Although some gaits may have specific names (e.g., walk, trot, run, bound, gallop, etc.), the distinctions between gaits may overlap. The gaits may be classified based on footfall patterns—the locations on a surface for the placement the feet 206A-206D. Similarly, gaits may also be classified based on ambulatory mechanics. The body 208 of the robot 200 connects to the legs 204A-204D and may house various components of the robot 200. For example, the body 208 may include or carry sensor(s) 210. These sensors may be any of the sensors discussed in the context of sensor(s) 112, such as a camera, LIDAR, or an infrared sensor. Further, the locations of sensor(s) 210 are not limited to those illustrated in FIG. 2. Thus, sensor(s) 210 may be positioned in various locations on the robot 200, such as on the body 208 and/or on one or more of the legs 204A-204D, among other examples. FIG. 3 illustrates a biped robot 300 according to another example implementation. Similar to robot 200, the robot 300 may correspond to the robotic system 100 shown in FIG. 1, and may be configured to perform some of the implementations described herein. Thus, like the robot 200, the robot 300 may include one or more of mechanical components 110, sensor(s) 112, power source(s) 114, electrical components 116, and/or control system 118. For example, the robot 300 may include legs 304 and 306 connected to a body 308. Each leg may consist of one or more members connected by joints and configured to operate with various degrees of freedom with respect to one another. Each leg may also include a respective foot 310 and 312, which may contact a surface (e.g., the ground surface). Like the robot 200, the legs 304 and 306 may enable the robot 300 to travel at various speeds according to the mechanics set forth within gaits. The robot 300, however, may utilize different gaits from that of the robot 200, due at least in part to the differences between biped and quadruped capabilities. The robot 300 may also include arms 318 and 320. These arms may facilitate object manipulation, load carrying, and/or balancing for the robot 300. Like legs 304 and 306, each arm may consist of one or more members connected by joints and configured to operate with various degrees of freedom with respect to one another. Each arm may also include a respective hand 322 and 324. The robot 300 may use hands 322 and 324 for gripping, turning, pulling, and/or pushing objects. The hands 322 and 324 may include various types of appendages or attachments, such as fingers, grippers, welding tools, cutting tools, and so on. The robot 300 may also include sensor(s) 314, corresponding to sensor(s) 112, and configured to provide sensor data to its control system. In some cases, the locations of these sensors may be chosen in order to suggest an anthropomorphic structure of the robot 300. Thus, as illustrated in FIG. 3, the robot 300 may contain vision sensors (e.g., cameras, infrared sensors, object sensors, range sensors, etc.) within its head 316. III. Example Robot Employing Dynamic Balance For Whole Body Manipulation FIG. 4A illustrates an example biped robot 400 that includes a body 408 defined by a lower body section 408a, an upper body section 408b, and an intermediate body section 408c. The lower body section 408a and the upper body section 408b are coupled to the intermediate body section 408c. The lower body section 408a includes two legs 404 and 406 that generally extend downward to a surface (e.g., ground surface) from the intermediate body section 408c. Like the legs 304 and 306 of the robot 300, each leg 404, 406 may include one or more members connected by joints and configured to operate with various degrees of freedom with respect to one another. As shown in FIG. 4A, for instance, the leg 404 includes at least members 404a1-a2 and joints 404b1-b2, and the leg 406 includes at least members 406a1-a2 and joints 406b1-b2. Each leg 404, 406 may also include a respective foot 410, 412 to establish direct contact with the surface. The legs 404, 406 can stably support the robot 400 on the surface. Additionally, the legs 404, 406 enable the robot 400 to move at various speeds according to the mechanics for different gaits. As shown in FIG. 4A, for instance, the legs 404, 406 are operable to move the robot 400 according to at least forward/backward translation along a y-axis and/or left/right lateral translation along a x-axis. The upper body section 408b includes end-effectors 422, 424 disposed on the ends of respective arms 418, 420. The arms 418, 420 may extend outwardly from the upper body section 408b to position the respective end-effectors 422, 424. Like the arms 318, 320 of the robot 300, each arm 418, 420 may include one or more members connected by joints and configured to operate with various degrees of freedom with respect to one another. As shown in FIG. 4A, for instance, the arm 418 includes at least members 418a1-a2 and joints 418b1-b2, and the arm 420 includes at least members 420a1-a2 and joints 420b1-b2. The end-effectors 422, 424 may be employed to perform a task by manipulating objects, acting on loads, etc. For instance, the robot 400 may use the end-effector 422, 424 for gripping, turning, carrying, pulling, and/or pushing objects. As shown, the end-effectors 422, 424 may be hand-like structures with movable fingers. Alternatively, the end-effectors 422, 424 may include other types of appendages or attachments, such as grippers, welding tools, cutting tools, and the like. As shown in FIG. 4A, the intermediate body section 408c acts as, or resembles, a pelvis for the bipedal configuration of the robot 400. The intermediate body section 408c is supported by the lower body section 408a below, and correspondingly, the intermediate body section 408c supports the upper body section 408b above. As described further below, the intermediate body section 408c may be positioned and/or oriented to allow for desired positioning and operation of the legs 404, 406 and the end-effectors 422, 424. The robot 400 may include aspects of the robotic system 100 described above. In particular, sensors similar to the sensors 112 may provide information regarding the position and movement of a component of the robot 400 relative to other components and/or the external environment. As shown in FIG. 4A, for instance, the robot 400 may include sensors 414 (e.g., cameras, infrared sensors, object sensors, range sensors, etc.) within a head 416. Furthermore, as shown in FIG. 5, the robot 400 may include a control system 417 with a lower body control system 417a, an upper body control system 417b, and a master control system 417c, each of which may include aspects of the control system 118 described above. The lower body control system 417a can operate aspects of the lower body section 408a. The upper body control system 417b can operate aspects of the upper body section 408b. The master controller 417c can control other aspects of the robot 400. The master controller 417c may also coordinate the actions of the lower body control system 417a and the upper body control system 417b. Each of the control systems 417a-c may receive sensor data from the sensors to operate respective aspects of the robot 400. Although the control systems 417a-c are shown as separate elements in FIG. 5, aspects of the control systems 417a-c may be implemented with common hardware and/or software. To achieve the desired positions for the feet 410, 412 and/or the desired forces with the legs 404, 406, the lower body control system 417a may employ an inverse kinematics solver 419a to determine the corresponding positions of the joints and the orientations of the members of the respective legs 404, 406. Meanwhile, to achieve desired positions for the end-effectors 422, 424, the upper body control system 417a may employ an inverse kinematics solver 419b to determine the corresponding positions of the joints and the orientations of the members of the respective arms 418, 420. In general, inverse kinematics refers to the use of the kinematics equations of the robot 400 to determine the parameters for components, such as the joints of a leg 404, 406 or an arm 418, 420, to allow the respective foot 410, 412 or end-effector 422, 424 to reach a target position. A motion plan specifies the movement of the robot so that the foot 410, 412 or the end-effector 422, 424 can reach a target position. The inverse kinematics solver 419a, 419b transforms the motion plan into actuator trajectories for components (e.g., the joints) of the robot 400. The lower body control system 417a can operate the legs 404, 406 to balance the robot 400 dynamically on the surface, while the upper body control system 417b operates the arms 418, 420 and the end-effectors 422, 424 to perform a task. As shown in FIG. 4A, when the foot 410 is in contact with the surface, the leg 404 experiences a reaction force Fr1 in response to the force applied by the leg 404. Similarly, when the foot 412 is in contact with the surface, the leg 406 experiences a reaction force Fr2 in response to the force applied by the leg 406. Each reaction force Fr1, Fr2 may include components along one or more of the x-, y-, and z-axes. The lower body control system 417a can dynamically control the legs 404, 406 so that the reaction forces Fr1, Fr2 allow the robot 400 to maintain a balance that supports the operation of the arms 418, 420 and the end-effectors 422, 424. In response to any moments experienced by the robot 400, the reaction forces Fr1, Fr2 may also produce opposing moments Mr1, Mr2, respectively, (not shown) to balance the robot 400. The dynamic balancing provided by the legs 404, 406 during operation of the end-effectors 422, 424 constitutes a whole body manipulation that more closely resembles actual motion by actual humans. A. Example Balancing with the Lower Body Referring to FIG. 4B, the robot 400 is supported on the surface solely by the leg 404. The weight of the robot 400, i.e., a gravitational force Fgr, is applied via the foot 410 in the negative z-direction to the surface. The gravitational force Fgr effectively acts at the center of mass (COM) of the body 408 in the negative z-direction. A component of the reaction force Fr1 is applied in the positive z-direction at the foot 410 with a magnitude equal to the gravitational force Fgr. Thus, the gravitational force Fgr is balanced by the z-component of the reaction force Fr1. If, however, the center of mass of the robot 400 is not aligned with the foot 410 along the x-axis and/or y-axis, the gravitational force Fgr may produce a moment Mgr at the foot 410. The moment Mgr may include components about the x-axis and/or y-axis. The reaction force Fr1 includes a frictional force between the foot 410 and the surface, where the frictional force acts on the foot 410 in the x- and/or y-directions. The frictional force provides a torque that opposes the moment Mgr produced by the gravitational force Fgr. If the moment Mgr does not exceed the maximum torque that can be provided by the frictional force, the robot 400 can maintain a balance. On the other hand, if the moment Mgr exceeds the maximum torque, the foot 410 may slip and the moment Mgr may cause the robot 400 to lose balance. With the foot 410 in a given position on the surface, the lower body control system 417a can control the positions and orientations of the members 404a1-a2 and joints 404b1-b2 to control the effect of the reaction forces Fr1 on the leg 404 and to achieve a balance the body 408. For instance, if the lower body control system 417a determines that the robot 400 as shown in FIG. 4B cannot maintain balance due to the moment Mgr, the lower body control system 417a can control the members 404a1-a2 and the joints 404b1-b2 of the leg 404 to reposition the center of mass of the robot 400 into closer alignment with the foot 410 along the x-axis and/or y-axis. This can reduce the moment Mgr and allow the frictional force from the reaction force Fr1 to balance the robot 400 as described above. As shown in FIG. 4B, when the lower body control system 417a repositions the center of mass, the intermediate body section 408c may correspondingly move in the x- and y-directions from a position (xi, yi, zi) to a new position (xi′, yi′, zi). Although the center of mass in FIG. 4B may appear to coincide with the intermediate body section 408c, it is understood that the center of mass may be located at other positions relative to the robot 400. Although not shown in FIG. 4B, the leg 406 may be manipulated in a manner similar to the leg 404. In general, with the feet 410, 412 in given positions on the surface, the lower body control system 417a can reposition and/or reorient the members and joints of the legs 404, 406 to control how the reaction forces Fr1 and Fr2 affect the body 408. Specifically, the lower body control system 417a can control the legs so that the reaction forces Fg1 and Fg2 balance the body 408. Indeed, both feet 410, 412 can simultaneously contact the surface and the legs 404, 406 may experience reaction forces Fr1 and Fr2. The gravitational force Fgr can be balanced by the sum of the z-components of the reaction forces Fr1 and Fr2. In addition, the lower body control system 417a may control the members and joints of both legs 404, 406 to change the position of the center of mass and allow opposing moments Mr1, Mr2 from the reaction forces Fr1, Fr2 (e.g., frictional forces) to balance the moment Mgr from the gravitational force Fgr. B. Dynamic Balancing with the Lower Body to Support Operation of End-Effectors As described above, the upper body control system 417b can operate each end-effector 422, 424 to perform a respective task. To perform different tasks, the upper body control system 417b can move the end-effectors 422, 424 with the arms 418, 420 to different positions in order to reach and move objects, act on loads, etc. As shown in FIG. 4A, for instance, the end effector 424 is initially positioned at coordinates (xe2, ye2, ze2). In FIG. 4C, the upper body control system 417b repositions the end effector 424 to (xe2′, ye2′, ze2′) to perform a task. To reposition, the upper body control system 417b operates the members 420a1-a2 and joints 420b1-b2 of the arm 420 to extend the end-effector 424 to the target position (xe2′, ye2′, ze2′). Depending on the mass associated with the arms 418, 420, the position of the center of mass of the robot 400 may change when the arms 418, 420 and corresponding end-effectors 422, 424 are repositioned. The change in the position of the center of mass changes the effect of the gravitational force Fgr on the body 408. In particular, the moment Mgr produced by the gravitational force Fgr also changes. To maintain the balance of the robot 400, the members and joints of the legs 404, 406 may need to be repositioned and/or reoriented to achieve reaction forces Fr1, Fr2 that balance the new moment Mg. When performing a task, each end-effector 422, 424 may also experience a respective external end-effector force Fe1, Fe2, as shown in FIG. 4A. For instance, if each end-effector 422, 424 is tasked with carrying a respective object, the respective end-effector force Fe1, Fe2 may include the weight of the respective object acting in the negative z-direction. In another instance, if the end-effectors 422, 424 are tasked with pushing a large object along the surface, the end-effector forces Fe1 and Fe2 may include the opposing frictional forces between the large object and the surface. Although both end-effector forces Fe1 and Fe2 are shown in FIG. 4A, the end-effectors 410, 412 do not necessarily experience the end-effector forces Fe1 and Fe2 simultaneously. The robot 400 may thus experience the external forces Fe1 and Fe2 in addition to the gravitational force Fgr. In addition, the robot 400 may experience moments Me1, Me2 produced by the end-effector forces Fe1, Fe2, respectively As such, the lower body control system 417a can also account for the effects of the external end-effector forces Fe1 and Fe2 as well as the gravitational force Fgr to balance the robot 400 on the surface. In particular, the lower body control system 417a can control the members and joints of the legs 404, 406 to allow the reaction forces Fr1, Fr2 to balance the sum of the forces Fe1, Fe2, Fgr as well as the sum of moments produced by forces Fe1, Fe2, Fgr. For instance, if each end-effector 422, 424 is carrying an object, the end-effector forces Fe1, Fe2 include the weight of each object acting in the negative z-direction. In addition to the gravitational force Fgr, the legs 404, 406 apply the weight of each object to the surface via the feet 410, 412. The reaction forces Fr1, Fr2 correspondingly apply a force in the positive z-direction to balance the forces applied by the legs 404, 406. Moreover, in addition to the moment Mgr produced by the gravitational force Fgr, the forces Fe1, Fe2 also produce moments Me1, Me2. The reaction forces Fr1, Fr2 correspondingly produce moments Mr1, Mr2 that oppose the moments Me1, Me2. The lower body control system 417a can operate the members and joints of the legs
{'bibliographic_information': "{'country': 'US', 'doc-number': '15377559', 'kind': 'B2', 'date': '20161213', 'extension': '295', 'invention_title': 'Whole body manipulation on a legged robot using dynamic balance'}", 'source_file': './grant/2019/ipg190716.xml', 'source_data': 'USPTO-Grant'}