Patent Publication Number: US-2023141353-A1

Title: Systems and methods for providing contact detection in an articulated arm

Description:
PRIORITY 
     The present application is a continuation of U.S. patent application Ser. No. 17/736,606, filed May 4, 2022, which is a continuation of U.S. patent application Ser. No. 17/123,862, filed Dec. 16, 2020, now issued as U.S. Pat. No. 11,370,122, on Jun. 28, 2022; which is a continuation of U.S. patent application Ser. No. 16/743,428, filed Jan. 15, 2020, now issued as U.S. Pat. No. 10,913,159, on Feb. 9, 2021; which is a continuation of U.S. patent application Ser. No. 16/545,627, filed Aug. 20, 2019, now issued as U.S. Pat. No. 10,875,185, on Dec. 29, 2020; which is a continuation of U.S. patent application Ser. No. 16/212,113, filed Dec. 6, 2018, now issued as U.S. Pat. No. 10,618,177, on Apr. 14, 2020; which is a continuation of U.S. patent application Ser. No. 15/242,255, filed Aug. 19, 2016, now issued as U.S. Pat. No. 10,343,284 on Jul. 9, 2019; which claims priority to U.S. Provisional Patent Application Ser. No. 62/210,235, filed Aug. 26, 2015, the disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The invention generally relates to robotic and other sortation systems, and relates in particular to articulated arm systems for use in sortation systems. 
     Systems and methods using mechanical compliance to improve robot performance during grasping and manipulation are known. Purpose-built compliant elements exist commercially that function as safety guards, such as, for example, position sensors sold by ABB Automation Technology Products AB of Sweden. These devices may include magnetic breakaway or spring elements that deflect when contact between the robot and the environment is made. Additionally, these designs can include rudimentary on/off sensing of a breakaway state, which is often used as a stop signal to the robot controller. 
     More modern robotic systems in industry and academia have incorporated flexible elements and deformation sensors in the joints of a robot arm (see for example, the Baxter Robot sold by Rethink Robotics, Inc. of Boston, Mass. and the DLR Lightweight Robot III developed by the Institute of Robotics and Mechanics at German Aerospace Center in Germany). Through the combined sensing of deformation at each joint, an approximation of the force at the end-effector may be deduced. Such an implementation is undesirable in certain applications however (for example, due to unnecessary added compliance that may degrade the positional accuracy of the end-effector, added mechanical complexity and cost, and decreased payload capabilities of the robotic system), with the added complication that any highly flexible end-effector on the robot arm causes the loads transmitted through to the joints to be fairly small and difficult to reliably measure. 
     Force sensors are also known to be used in robotic manipulation systems. A typical force sensor consists of a rigid plate instrumented with several micro-scale deformation sensors such as strain gauges. This plate is commonly placed between the robot end-effector and the robot arm, and used to sense forces and torques acting on the end-effector. These sensors tend to be expensive and difficult to calibrate accurately since they measure deflections or strain on very small scales. Furthermore, a force sensor mounted between the end-effector and robot arm suffers from the issue mentioned above for joint-sensors, namely that highly flexible elements on the end-effector will not create significant forces for detection at the force sensor. 
     There remains a need therefore for an improved sensing system for robotic and other sortation systems. 
     SUMMARY 
     In accordance with an embodiment, the invention provides a sensing manipulator of an articulated arm. The sensing manipulator includes a compliant section and a movement detection system provided along a first direction of the compliant section such that movement of the compliant section along both the first direction and at least one direction transverse to the first direction, are detectable by the movement detection system. 
     In accordance with another embodiment, the sensing manipulator includes a compliant section providing movement of the compliant section in at least two degrees of freedom, and a movement detection system providing output data regarding movement of the compliant section in the at least two degrees of freedom. 
     In accordance with a further embodiment, the invention provides a method of sensing the position an orientation of an object held by a manipulator at an end effector of a robotic system. The method includes the steps of engaging the object in a working environment of the robotic system, perceiving an initial position of a movement detection system, lifting the object against gravity, and perceiving at least two of load, pitch, roll and yaw of the object with respect to the initial position of the movement detection system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following description may be further understood with reference to the accompanying drawings in which: 
         FIG.  1    shows an illustrative diagrammatic function block view of a robotic system including a sensing manipulator system in accordance with an embodiment of the present invention; 
         FIGS.  2 A and  2 B  show illustrative diagrammatic views of compliant interfaces for use in various embodiments of the present invention; 
         FIG.  3    shows an illustrative diagrammatic isometric view of a sensing manipulator in accordance with an embodiment of the present invention; 
         FIG.  4    shows an illustrative diagrammatic view of a sensing manipulator in accordance with another embodiment of the present invention; 
         FIGS.  5 A and  5 B  show illustrative diagrammatic views of an end effector in a system of an embodiment of the present invention engaging a relatively light object; 
         FIGS.  6 A and  6 B  show illustrative diagrammatic views of an end effector in a system of an embodiment of the present invention engaging a relatively heavy object; 
         FIGS.  7 A and  7 B  show illustrative diagrammatic views of an end effector in a system of an embodiment of the present invention engaging an object that presents an unbalanced load; 
         FIG.  8    shows an illustrative diagrammatic isometric view of a sensing manipulator in accordance with a further embodiment of the invention in an extended state (not engaging an object); 
         FIG.  9    shows an illustrative diagrammatic isometric view of the sensing manipulator of  FIG.  8    in an engaged state (engaging an object); 
         FIG.  10    shows an illustrative diagrammatic view of a sensing manipulator in accordance with a further embodiment of the invention that includes grippers; 
         FIG.  11    shows an illustrative diagrammatic view of a sensing manipulator in accordance with a further embodiment of the invention that includes sensing jaws; and 
         FIG.  12    shows an illustrative diagrammatic enlarged view of a portion of the sensing manipulator of  FIG.  11   . 
     
    
    
     The drawings are shown for illustrative purposes only. 
     DETAILED DESCRIPTION 
     The invention provides in accordance with an embodiment, a novel sensing manipulator that tracks the physical deformation of a robot end-effector as it makes contact with an environment, including an object within the environment. Many robot end-effector designs rely on flexible passively-compliant elements that deform to accommodate the environment. This compliance is used to improve the quality and reliability of contact during grasping and manipulation, and to reduce the impact loads applied to both the robot and objects during contact. 
     The novel sensing manipulator discussed herein in accordance with certain embodiments tracks these various modes of deformation, and provides this information for use in higher-level automation software to determine significant details about the state of end-effector contact with the environment. This mode of sensing eliminates the need for an additional complex mechanical element traditionally used to sense forces or add compliance to a robot system, while minimally altering the stiffness and inertia of the pre-existing hardware. Placing the sensor as close as possible to the contact site, in accordance with an embodiment, ensures it is able to obtain signals relevant to the manipulation task unaltered by the dynamics of transmission through the robot structure. 
     In accordance with certain embodiments, sensing manipulators of the present invention may have several primary features with many ancillary benefits, summarized here and discussed in more detail below. 
     The position deformation sensor design methodology provides A) a sensing strategy that can sense the deformation of a compliant element along multiple axes simultaneously, B) a sensing system that can be applied to a variety of pre-existing compliant elements and eliminates the need for new mechanical complexity along the serial chain of a robot arm, C) a sensor solution that minimally affects the stiffness or inertia of existing compliant elements, and D) a sensor that is placed near the end-effector contact surface to obtain data that is both highly sensitive and is unaltered by the dynamics of force transmission through the robot. 
     The novel software and algorithms of certain embodiments of the invention further provide A) software strategies that use the sensor information to detect the presence or absence of contact with the world, and B) software strategies that detect the amount of force and torque imparted on the end-effector due to the external load of the object and grasping configuration. 
     This general approach of deflection sensing and algorithms applied to process the resultant data, is illustrated via several examples as follows. The design and methodology may be understood initially by considering a simplified illustration of the deflection sensor design as shown in  FIG.  1   .  FIG.  1    shows a deformation sensor application diagram in accordance with an embodiment of the present invention, where the deformation sensor is positioned adjacent the environment such that the sensing of the deflection sensor of  FIG.  1    occurs at the point of contact with the environment. 
     In particular, the robotic system  10  includes a movement detection system  12  such as a deflection sensor that is provided with a compliant interface  14  such as a vacuum cup, for engaging an environment  16 . The movement detection system  12  and the compliant interface  14  are coupled to an end effector  18  attached to a robotic mass  20  of the robotic system. The compliant interface may be formed in a shape of a tubular or conical bellows using a flexible material as shown at  14  and  14   a  in  FIGS.  2 A and  2 B  respectively. Note that the compliant interface may move in not only a direction as shown at A, but may also move in second directions shown at B (as shown) and D (into and out of the page) that are transverse to the first direction, as well as directions as shown at C that are partially transverse to the first direction. Also note the compliant interface is not necessarily a part of the deflection sensor itself, but may, in certain embodiments, be a natural part of the manipulation system. 
     The deformation sensor may be applied to systems where the deformation is not tightly constrained but rather provides multi-axis sensing, meaning that deformation may occur linearly, rotationally, or along complex paths. The ability to allow for and sense this complex deformation is a key differentiator from prior art systems. Several technologies can be applied to provide sensors to the compliant interface. It is important that this sensing not restrict or impede the compliant motion, or add significant inertia or mass. Several sensors could be applied to measure the deformation including but not limited to; flex sensors (such as flex-sensitive resistors or capacitive sensors), magnetic field sensors (such as a compass or hall-effect sensors), or potentiometers. 
       FIG.  3    shows a sensing manipulator  30  in accordance with another embodiment of the invention wherein the sensing manipulator includes a movement detection system  32 . The movement detection system  32  includes a static 3-axis magnetic field sensor  34  that is aligned against a magnet  36  attached to the central part of the compliant cup  38  by a ring  50 . A vacuum is provided at an open end  46  of the complaint cup  38 . As the compliant cup  38  moves, so too does the ring  40 . As the ring  40  around the cup moves, so too does a bracket  42  as well as a magnet  46 , which movement is detected with respect to the magnet sensor  44  attached to the articulated arm  54  for sensing the axial flexure of the vacuum cup from which translations/roll/pitch of the cup may be determined. When the magnetic field sensor is employed, the system may determine not only movements in the elongated direction (x) of the deflection sensor with respect to the articulated arm, but also movements in directions (y and z) that are transverse to the elongated direction of the deflection sensor as well as directions that are partially transverse to the elongated direction of the deflection sensor. 
     With reference to  FIG.  4   , in accordance with a further embodiment, the system may include an articulated arm  80  to which is attached an end effector  82 , again, which may be a tubular or conical shaped bellows. The end effector  82  also includes a sensor  84  that includes an attachment band  86  on the bellows, as well as a bracket  88  attached to magnetic field sensor  90 , and a magnet  92  is mounted on the articulated arm  80 . As the bellows moves in any of three directions (e.g., toward and away from the articulated arm as shown diagrammatically at A, in directions transverse to the direction A as shown at B, and directions partially transverse to the direction A as shown at C. The magnetic field sensor  90  may communicate (e.g., wirelessly) with a controller  90 , which may also communicate with a flow monitor  94  to determine whether a high flow grasp of an object is sufficient for continued grasp and transport as discussed further below. In certain embodiment, for example, the system may return the object if the air flow is insufficient to carry the load, or may increase the air flow to safely maintain the load. 
       FIGS.  5 A and  5 B  show an object  160  being lifted from a surface  162  by the end effector  82  that includes the load detection device of  FIG.  5   . Upon engaging the object  160 , the system notes the position of the detection device. Once the object  160  is lifted ( FIG.  5 B ), the system notes the change in the sensor output. In this example, the load provided by the object  160  is relatively light.  FIGS.  6 A and  6 B , however, show the end effector lifting a heavy object. 
       FIGS.  6 A and  6 B  show an object  170  being lifted from a surface  172  by the end effector  82  that includes the load detection device of  FIG.  5   . Upon engaging the object  170 , the system notes the position of the detection device. Once the object  170  is lifted ( FIG.  6 B ), the system notes the change in the position of the detection device. As noted above, in this example, the object  170  is heavy, presenting a higher load. 
     The system may also detect whether a load is not sufficiently balanced.  FIGS.  7 A and  7 B  show an object  180  being lifted from a surface  182  by the end effector  82  that includes the load detection device of  FIG.  4   . Upon engaging the object  180 , the system notes the position of the detection device. Once the object  180  is lifted ( FIG.  7 B ), the system notes the change in the position of the detection device. In this example, the object  180  presents a non-balanced load. The compliant element may therefore, undergo substantial translational and angular deformation. 
     Various further platform applications include the following. The deformation sensor concept is designed to integrate with existing passive and active compliant components of a robot end-effector. In the above embodiments, suction cups are used as examples of compliant members. Many different compliant elements however, could be used based on the end-effector selected. In accordance with a further embodiment, the invention provides a movement detection system that includes force-sensitive resistors.  FIGS.  8  and  9   , for example, show a sensing manipulator  200  together with a vacuum cup  202  wherein the movement detection system includes an array (e.g., three) of detectors  204  for sensing the axial flexure of the vacuum cup from which translations/roll/pitch of the cup can be deduced. In particular, the force-sensitive resistors may include a conductive polymer that is printed on a surface, wherein the conductive polymer changes it&#39;s resistance in a predictable manner when a force is applied to the surface. The sensing manipulator  200  may be attached to a robotic arm via a mounting element  208  (which couples to a robotic arm mount that passes between two of the detectors  204 ). A vacuum may be provided at an open end  206  of the vacuum cup  202  for engaging an object  210  (as shown in  FIG.  9   ). 
     Another such alternative compliant element example is the use of a two-fingered robot gripper either at the wrist (as shown in  FIG.  10   ) or on the finger tips (as shown in  FIG.  11   ). Normally compliance is built in at the fingertips or directly behind the wrist of the gripper. A deflection sensor could easily be adapted to accommodate similar alternative designs. In particular,  FIG.  10    shows a sensing manipulator  220  in accordance with a further embodiment of the present invention that is attached to a robotic arm  222 . The sensing manipulator  220  includes a compliant section  224  and a sensing section  226  that includes a two finger gripper end effector  228 . As shown at D and E, the sensing section  226  may provide sensing of the position and orientation of the end effector  228  with respect to the robotic arm  222 , e.g., by magnetic or capacitive sensing. 
       FIG.  11    shows a sensing manipulator  230  that is attached to a robotic arm  232 . The sensing manipulator  230  includes a gripper  234  that includes two jaws  236 . On one or both jaws is provided a compliant element  238 , and on the compliant element  238  is provided a magnet  242 . With further reference to  FIG.  12    (which shows an enlarged view of a portion of one jaw  236 ) a corresponding magnetic sensor  240  is provided on the jaw. When the compliant element  238  is under a load (as shown by a force as shown at F), the sensor  242  will move with respect to the sensor  240 , providing position and orientation sensing data. 
     The stiffness and sensitivity of the compliant material are also important considerations. Note from  FIG.  1    that the location of sensing is along the preexisting compliant structure of the robot system. This allows a system using the deformation sensor to maintain its original stiffness and compliance properties, unlike prior art solutions. Also important to note is the target location for the deformation sensor in the system. The more distal the sensor is the closer it is to the interaction point, where non-linear complicating effects from the robot are less significant. 
     The software may involve high-level automation software that uses the data output from the deformation to make a series of important decisions as follows. 
     Contact State 
     The most straightforward application of the sensor is thresholding the deformation values from the sensor to detect when contact with the world has occurred. If any axis of deformation moves outside nominal levels, then robot motion can be stopped and appropriate gripping strategy motions may be executed (such as pushing more or less on the environment as needed). 
     Pre-Grasp Adjustment 
     When approaching an object for grasping, a robot arm will often first make contact with the object by pushing into it (either intentionally or unintentionally). Compliance is often used in robotic systems by allowing the end-effector to passively re-adjust to the environment by bending against the contact point. By using the deformation sensor to sense this angle of deflection, and then actively controlling the robot to re-adjust and compensate for the deflection by re-positioning itself, grasps can be made more reliable and centered on the object. 
     Force Sensing 
     Given a model of how the compliant element deflects under load, the deformation changes may be mapped to forces and torques on the end-effector. This may allow for a number of force-sensing strategies, such as force-guided insertions and grasps, and force-guided placement of objects on surfaces. 
     Post-Grasp Centerpoint Sensing and Adjustment 
     Similar to the above two points, after an object is grasped and lifted, gravitational effects will cause the robot end-effector to deflect under the load. Depending on the location of the grasp point with respect to the center-of-mass of the object, this may cause various deformations in the compliant element of the end-effector. Also, a poorly chosen grasp location on a heavy object can induce oscillations between the compliant components and object. The deformation sensor would be capable of sensing both these effects, and may be used to guide the robot to accept or reject grasps and give important information about the direction of the misalignment. 
     Human and Robot Safety 
     Due to centripetal effects the end-effector is often the most dangerous point on a moving robot arm. During motions where no environmental interaction is expected the deformation sensor can be monitored for changes and the robot stopped when unexpected events occur. The deformation has advantages over the more traditional joint-level or wrist-level safety guards on a robot, since it is designed into the low-inertia low-mass endpoint of the robot, and has the potential to respond before any damage has been done to the robot, environment, or human obstacles. 
     The deformation sensing strategy presented here provides a framework that allows sensitive high-resolution sensing of contact between a robot and its environment, while minimally altering the physical attributes of the robot&#39;s compliance. Given a model or properly tuned heuristics the sensor may be used to resolve important information for robot decision making to improve manipulation task performance. 
     Those skilled in the art will appreciate that numerous modifications and variations may be made to the above disclosed embodiments without departing from the spirit and scope of the present invention.