Patent Publication Number: US-2023134924-A1

Title: Robotic system to control multiple robots to perform a task cooperatively

Description:
CROSS REFERENCE TO OTHER APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 63/274,461 entitled ROBOTIC SYSTEM TO CONTROL MULTIPLE ROBOTS TO PERFORM A TASK COOPERATIVELY filed Nov. 1, 2021, which is incorporated herein by reference for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     Robots have been provided to perform a variety of tasks, such as manipulating objects. For example, a robotic arm having an end effector may be used to pick and place items. Examples of commercial applications of such robots include sortation, kitting, palletization, depalletization, truck or container loading and unloading, etc. 
     In some contexts, the objects to be handled vary considerably in size, weight, packaging, and other attributes. Typically, a robotic arm is rated to handle up to a maximize size, weight, etc. of object. In some contexts, the conventional approach may require a robotic arm able to handle the largest, heaviest, and/or otherwise most difficult object that may be required to be handled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the invention are disclosed in the following detailed description and the accompanying drawings. 
         FIG.  1    is a block diagram illustrating an embodiment of a robotic system configured to control a plurality of robots to perform a task cooperatively. 
         FIGS.  2 A- 2 C  illustrate an example of a cooperative pick and place task performed in an embodiment of a robotic system as disclosed herein. 
         FIG.  3    is a block diagram illustrating an embodiment of a robotic control system. 
         FIG.  4    is a state diagram illustrating an embodiment of a robotic system configured to control a plurality of robots to perform a task cooperatively. 
         FIG.  5 A  is a flow diagram illustrating an embodiment of a process to cooperatively perform a task as a “leader” robot in an embodiment of a robotic system as disclosed herein. 
         FIG.  5 B  is a flow diagram illustrating an embodiment of a process to cooperatively perform a task as a “follower” robot in an embodiment of a robotic system as disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     The invention can be implemented in numerous ways, including as a process; an apparatus; a system; a composition of matter; a computer program product embodied on a computer readable storage medium; and/or a processor, such as a processor configured to execute instructions stored on and/or provided by a memory coupled to the processor. In this specification, these implementations, or any other form that the invention may take, may be referred to as techniques. In general, the order of the steps of disclosed processes may be altered within the scope of the invention. Unless stated otherwise, a component such as a processor or a memory described as being configured to perform a task may be implemented as a general component that is temporarily configured to perform the task at a given time or a specific component that is manufactured to perform the task. As used herein, the term ‘processor’ refers to one or more devices, circuits, and/or processing cores configured to process data, such as computer program instructions. 
     A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate the principles of the invention. The invention is described in connection with such embodiments, but the invention is not limited to any embodiment. The scope of the invention is limited only by the claims and the invention encompasses numerous alternatives, modifications and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for the purpose of example and the invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the invention is not unnecessarily obscured. 
     A robotic system is disclosed to control two or more robots, e.g., robotic arms each terminated with an end effector, such as a suction or gripper type end effector, to work cooperatively to perform a task, such as to grasp and move a package or other payload. In various embodiments, robots work independently to pick/place items the robots can grasp and move without using multiple robots. Payloads that are too large, heavy, awkwardly shaped, etc. to be moved by a single robot are moved by two or more robots working in cooperation as disclosed herein. 
     In various embodiments, multiple robots independently plan and execute motion trajectories for picking and grasping packages. A determination is made to use two or more robots to move a payload cooperatively. For example, an attribute of the payload may be known by the robotic control system, e.g., based on a classification of the payload using computer vision. For example, image data may be used to classify the payload by type, and a weight or other attribute of a payload of that type may be used to decide to use multiple robots to move the item. Or, a single robot may attempt to grasp the item, e.g., with a suction-based end effector, and may not be able to lift the item, or maintain a secure grip. In some embodiments, attributes and/or grasping strategies (e.g., single robot, multi-robot) are learned by the system over time, e.g., based on prior experience attempting to grasp and move a similar item and/or items of the same type. 
     In various embodiments, to use multiple robots to move an item, a single leader robot independently plans a package trajectory, e.g., in the leader robot frame, to move and place package, e.g., at a destination location. A planner, scheduler, or other application or module may signal the beginning of a collaborative place. One or more follower robots receive the signal, and in response each records a transformation from its follower end-effector position and orientation to the leader&#39;s end-effector positions and orientation. For example, for a two-robot pick/place of a rectangular box, a single follower may determine a transform to achieve and maintain a position and orientation that is opposite the leader&#39;s end effector at a distance corresponding to a dimension of the box across which the two robots will grasp the box cooperatively, e.g., by suction, each at a corresponding opposite side of the box. 
     In various embodiments, at each time step in the place motion, the follower receives an update of the leader&#39;s end-effector position and orientation and uses the previously determined transform to recompute its goal position and orientation, e.g., to maintain the initial transformation from the leader. The follower uses operational-space control (e.g., computes and applies robotic arm joint motor torques necessary) to minimize the error between its current end-effector position and orientation and its recomputed goal position. 
     In some embodiments, once the follower robot has its end effector in the position and orientation opposite the leader robot and both (or all) robots have the package in their grasp, velocity control may be used to move the end effectors synchronously and maintain the position and orientation of the follower end effector relative to the leader. 
     In various embodiments, a force controller is used to maintain contact force and torque between the leader and follower robots. In some embodiments, the force controller is used to prevent translational and rotational slippages between robots and the picked object and guarantee the object pose between the robot leader and follower. 
     In some embodiments, to achieve precise placement, the object pose is controlled precisely. The object pose is estimated based on the leader and follower&#39;s end-effector poses as well as the contact forces and torques throughout the pick and place trajectories. 
       FIG.  1    is a block diagram illustrating an embodiment of a robotic system configured to control a plurality of robots to perform a task cooperatively. In the example shown, system and environment  100  includes a first robotic arm  102  equipped with a suction-type end effector  104  and a second robotic arm  106  equipped with a suction-type end effector  108 . In the state shown, robotic arm  102  and robotic arm  106  are positioned to perform cooperatively a pick and place task with respect to a large box  110 . A control computer  112  is configured to communicate wirelessly with one or more of the robotic arm  102 , robotic arm  106 , and one or more cameras or other sensors  114  in the workspace. Image data received from camera  114 , for example, may be used by the control computer  112  to generate a three-dimensional view of the workspace and to send commands and information to the robotic arm  102  and robotic arm  106 , as appropriate, to facilitate the cooperative pick and place task. 
       FIGS.  2 A- 2 C  illustrate an example of a cooperative pick and place task performed in an embodiment of a robotic system as disclosed herein. In the example shown, in  FIG.  2 A  robotic arm  202  with suction type end effector  204  and robotic arm  206  with suction type end effector  208  are positioned to begin to perform cooperatively a pick and place task with respect to large box  210 , similar to the starting state shown in  FIG.  1   . In various embodiments, robotic arm  202  may be the “leader” and robotic arm  206  the “follower” in a cooperative pick and place as disclosed herein. The “leader” may be selected by any suitable method, such as by assigning the “leader” role to the robot that initiated the cooperative task, by assigning the role randomly to one or the other of the participating robots, by an “election” or other selection method. 
     To initiate the operation, in various embodiments, as “leader” robotic arm  202  would move its end effector  204  to the position shown and would then grasp the box  210 , e.g., by moving the end effector  204  into a position in contact or nearly in contact with the side of box  210  and applying suction. A signal may be sent to the other robot (and/or a process to control the other robot) to indicate that the leader has completed its grasp. The follower, e.g., robotic arm  206  in this example, would then grasp the box  210 , e.g., at a side opposite from the side at which the leader (i.e., robotic arm  202 ) had grasped the box  210 . The follower would record a transform based on the position and orientation of the leader&#39;s end effector  204  and the relevant dimension of box  210 . For example, the vision system and/or other sensors may be used to measure the dimension, or to recognize the box  210  (e.g., specifically and/or by type) and to use the item and/or type information to determine the dimension, e.g., by look up. 
     As shown in  FIG.  2 B , once both robots ( 202 ,  206 ) have grasped box  210 . The leader, robotic arm  202  in this example, computes and moves the box along a trajectory determined by robotic arm  202  (and/or a control process associated therewith) independently of the follower robotic arm  206 . In various embodiments, the follower robot, robotic arm  206  in this example, receives (e.g., periodically, continuously, etc.) position and orientation information for the end effector  204  of leader robotic arm  202 . The follower robotic arm  206  (and/or a control process associated therewith) uses the position and orientation information of the leader robot ( 202 ,  204 ) and the previously-determined and recorded transform to compute a new target position and orientation for the follower&#39;s end effector  208 , and computes and applies torques to motors comprising robotic arm  206  as needed to minimize the error (difference) between the current position and orientation of the follower&#39;s end effector  208  and the (most recently updated) target. 
     Once the object (box  210 ) has been placed in the destination position, as shown in  FIG.  2 C  for example, the leader robot (robotic arm  202 ) releases its grasp and informs the follower that the pick and place task has been completed. In response, the follower (robotic arm  206 ) releases its grasp and both robots ( 202 ,  206 ) are free to perform other work, such as (returning to) independently picking and placing smaller/lighter objects and/or cooperatively performing a next pick and place task for another large or heavy object. 
       FIG.  3    is a block diagram illustrating an embodiment of a robotic control system. In various embodiments, the robotic control system  302  of  FIG.  3    includes or is included in the control computer  112  of  FIG.  1   . In various embodiments, one or more modules or subsystems comprising the robotic control system  302  of  FIG.  3    may be distributed across multiple computing nodes, such as computers and/or processors comprising one or more of control computer  112 , robotic arm  102 , and/or robotic arm  106  of  FIG.  1   . 
     In the example shown, robotic control system  302  includes a hierarchical planner, scheduler, and/or control module comprising a robot cooperation facilitation module  304  configured to facilitate cooperative performance of tasks by two or more robots, as disclosed herein, and robot-specific controllers  306  and  308 . For example, robot 1 controller  306  may be associated with robotic arm  102  of  FIG.  1    and/or robotic arm  202  of  FIGS.  2 A through  2 C , while robot 2 controller  308  may be associated with robotic arm  106  of  FIG.  1    and/or robotic arm  206  of  FIGS.  2 A through  2 C . 
     In various embodiments, the respective robots associated with robot 1 controller  306  and robot 2 controller  308 , respectively, each may operate independently, e.g., to pick and place objects the robot is able to handle singly. In various embodiments, cooperative tasks using two or more robots may be initiated and/or performed by one or more of communications sent between robot 1 controller  306  and robot 2 controller  308 ; bilateral communications between robot cooperation facilitation module  304 , on the one hand, and the respective robot 1 controller  306  and robot 2 controller  308 , on the other; and/or communications among all three (or more) entities. 
     In the example shown, robotic control system  302  further includes a computer vision subsystem  310  configured to receive image and depth data from one or more 3D cameras and/or other sensors, such as camera  114  of  FIG.  1   , and to use the received data to generate and/or update a three-dimensional view of the workspace. The output of the computer vision subsystem  310  may be provided to one or more of the robot cooperation facilitation module  304 , robot 1 controller  306 , and robot 2 controller  308 , to enable them to initiate and perform cooperatively a task to pick and place an item. For example, image data may be used to determine that a box or other object is too large and/or too heavy for a single robot to pick and place. The three-dimensional view of the workspace and objects within may also be used to determine respective grasp strategies and/or locations for each robot, to determine collision-free trajectories to move each robot&#39;s end effector to its corresponding pick location, and to determine a collision-free trajectory through which to cooperatively move the object to the destination location at which it is to be placed, for example. 
       FIG.  4    is a state diagram illustrating an embodiment of a robotic system configured to control a plurality of robots to perform a task cooperatively. In various embodiments, the state diagram  400  of  FIG.  4    may be implemented by and/or with respect to a robot configured to cooperatively perform an operation using two or more robots. In some embodiments, the state diagram  400  of  FIG.  4    may be implemented by control computer  112  of  FIG.  1    and/or one or more of robot cooperation facilitation module  304 , robot 1 controller  306 , and robot 2 controller  308  of  FIG.  3   . 
     In the example shown, in state  402  a robot works independently to perform tasks. For example, the robot may independently pick and place items, such as to fill a box or other receptacle in a kitting operation, place items on a conveyer belt or other conveyance in a sortation operation, stack items on a pallet, etc. Upon receiving an indication that help is needed to perform a task ( 404 ), such as an indication that an item that has been perceived and which needs to be picked and placed is too large to grasp and move with one robot, the robot and/or controller transitions to a state  406  in which cooperative performance of the task is initiated. For example, a communication may be sent to another robot (e.g., from robot 1 controller  306  to robot 2 controller  308  of  FIG.  3   ) or to a higher-level planner/scheduler (e.g., robot cooperation facilitation module  304  of  FIG.  3   ), or the higher-level planner/scheduler may recognize the need for cooperative performance of the task and may initiate the transition to state  406 . 
     In the example shown, the robot and/or controller may transition back to working independently in state  402 , via a “cancel help” transition  408 . For example, the robot/controller and/or a higher-level planner/scheduler may determine that the task has already been performed by and/or assigned to one or more other robots. 
     In some embodiments, in the “initiate cooperation” state  406 , the robot/controller that is initiating cooperative performance of the task communicates directly or indirectly with a helper robot, e.g., by requesting help. Another robot may be assigned to help and/or may agree to help. The robot may be assigned and/or agree to help at a future time or upon occurrence of a future condition, such as completion of a task the helper robot has already started and/or a task that has higher priority. For example, a task to clear other objects from around the large or heavy object, to facilitate the cooperative task, may have a higher priority and therefore may be completed first. Once the helper robot is ready to perform the cooperative task, the helper robot informs the task initiator, directly or indirectly (e.g., via a higher-level planner/scheduler, such as robot cooperation facilitation module  304  of  FIG.  3   ), that the helper robot is ready, prompting a transition  410  to “start cooperation” state  412 . The helper may transition directly from working independently, in state  402 , to “start cooperation” state  412 , via the “give help” transition  414  in the example shown. 
     Once all participating robots are ready in the “start cooperation” state  412 , a “leader” is determined, if needed, and the leader transitions ( 416 ) to “do leader” state  418  while the follower(s) transition ( 420 ) to “do follower” state  422 . In the “do leader” state  418  and “do follower” state  422 , the leader and follower(s) cooperate as disclosed herein to cooperative perform the task, such as to pick and place a large or heavy object, as in the example illustrated in  FIG.  2 A through  2 C . Once the task has been completed, the leader and follower(s) transition ( 424 ,  426 ) back to the “work independently” state  402  and resume working independently. 
       FIG.  5 A  is a flow diagram illustrating an embodiment of a process to cooperatively perform a task as a “leader” robot in an embodiment of a robotic system as disclosed herein. In various embodiments, process  500  of  FIG.  5 A  may be implemented by a robot controller associated with a robot that is participating as the “leader” in cooperative performance of a task by two or more robots as disclosed herein. 
     In the example shown, at  502  an indication to begin a cooperative task (with one or more other robots) in the role of “leader” is received. For example, an indication to cooperatively perform a pick and place task may be received. At  504 , the leader determines a location at which to grasp the object and plans a trajectory to safely move its end effector into position to grasp the object and at  506  the leader moves its end effector along the trajectory to the grasp position. At  508 , the leader determines (independently of any other robot) a trajectory to move the object to an associated destination. For example, a model of the robot and its kinematics and image and/or other information about the workspace (e.g., configuration data, CAD files, etc.), one or more attributes of the object (e.g., dimensions, rigidity, etc.), and image/sensor data may be used to plan the trajectory. At  510 , an indication is received from the “follower” robot(s) with which the robot implement process  500  is to cooperate that the follower robot(s) is/are ready to begin cooperative performance of the task. In response, at  512  the “leader” robot moves its end effector (and the object in the joint grasp of the leader and follower(s)) to the destination along the trajectory determined by the leader. At  514 , upon placing the object at the destination the leader robot releases its grasp and informs the follower robot(s) that the task has been completed. In various embodiments, the leader then resumes operating independently. 
       FIG.  5 B  is a flow diagram illustrating an embodiment of a process to cooperatively perform a task as a “follower” robot in an embodiment of a robotic system as disclosed herein. In various embodiments, process  520  of  FIG.  5 B  may be implemented by a robot controller associated with a robot that is participating as the “follower” in cooperative performance of a task by two or more robots as disclosed herein. 
     In the example shown, at  522  an indication is received to begin performing a task cooperatively with one or more other robots in the “follower” role, as disclosed herein. At  524 , the follower determines a grasp point—e.g., one on an opposite side of the object from the side at which the “leader” has indicated it will grasp the object—and plans a trajectory to move into position to grasp the object at that point. At  526 , the follower moves its end effector to the determined grasp position and grasps the object, e.g., in response to receiving an indication that the leader has completed its grasp. At  528 , the leader&#39;s end effector position and orientation information are received, and the follower uses this information along with information about the object (e.g., the size of the object in the dimension that separates the leader&#39;s end effector and the follower&#39;s end effector) and computes a transform. In various embodiments, the transform comprises a matrix or other mathematical construct that can be applied to the position and orientation of the leader&#39;s end effector, typically expressed in the leader&#39;s frame of reference, to provide a corresponding position and orientation for the follower&#39;s end effector that would maintain the relative position and orientation of the follower&#39;s end effector with respect to the leader&#39;s end effector as the end effectors and the object grasped between them are moved through the workspace to the destination at which the object is to be placed. At  530 , the follower robot informs the leader that the follower is “ready”, e.g., the follower has grasped the objected, computed the transform, and is ready to maintain the position of its end effector relative to (e.g., opposite) the leader&#39;s end effector. 
     At  532 , as the leader robot begins to move along the trajectory determined independently by the leader, the follower uses the transform it computed and successively received position and orientation information for the leader&#39;s end effector, as it is moved through the workspace. For example, for each of at least a subset of the received positions and/or orientations of the leader&#39;s end effector, the follower computes a new goal position and/or orientation for its own end effector and applies torques to it motors as determined to be needed to minimize the error (e.g., difference) between the current position and/or orientation of its end effector and the current goal. 
     At  534 , the follower receives an indication (e.g., from the leader) that the cooperative task is “done”, in response to which the follower releases its grasp and the process  520  ends. 
     In various embodiments, techniques disclosed herein may be used to enable a robotic system to perform a wider variety of tasks with respect to a wider range of objects, e.g., by using two or more robots to perform a task cooperatively. 
     Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed embodiments are illustrative and not restrictive.