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Discrete Bimanual Manipulation for Wrench Balancing
KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.ORCID iD: 0000-0002-9171-8768
KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL. KTH.ORCID iD: 0000-0003-3252-715X
KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.ORCID iD: 0000-0003-2965-2953
KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, Perception and Learning, RPL.ORCID iD: 0000-0001-5129-342X
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Dual-arm robots can overcome grasping force and payload limitations of a single arm by jointly grasping an object.However, if the distribution of mass of the grasped object is not even, each arm will experience different wrenches that can exceed its payload limits.In this work, we consider the problem of balancing the wrenches experienced by  a dual-arm robot grasping a rigid tray.The distribution of wrenches among the robot arms changes due to objects being placed on the tray.We present an approach to reduce the wrench imbalance among arms through discrete bimanual manipulation.Our approach is based on sequential sliding motions of the grasp points on the surface of the object, to attain a more balanced configuration.%This is achieved in a discrete manner, one arm at a time, to minimize the potential for undesirable object motion during execution.We validate our modeling approach and system design through a set of robot experiments.

National Category
Robotics
Identifiers
URN: urn:nbn:se:kth:diva-263041OAI: oai:DiVA.org:kth-263041DiVA, id: diva2:1366107
Note

Under review for ICRA 2020. QC 20191029

Available from: 2019-10-28 Created: 2019-10-28 Last updated: 2019-10-29Bibliographically approved
In thesis
1. Dual-Arm Robotic Manipulation under Uncertainties and Task-Based Redundancy
Open this publication in new window or tab >>Dual-Arm Robotic Manipulation under Uncertainties and Task-Based Redundancy
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Robotic manipulators are mostly employed in industrial environments, where their tasks can be prescribed with little to no uncertainty. This is possible in scenarios where the deployment time of robot workcells is not prohibitive, such as in the automotive industry. In other contexts, however, the time cost of setting up a classical robotic automation workcell is often prohibitive. This is the case with cellphone manufacturing, for example, which is currently mostly executed by human workers. Robotic automation is nevertheless desirable in these human-centric environments, as a robot can automate the most tedious parts of an assembly. To deploy robots in these environments, however, requires an ability to deal with uncertainties and to robustly execute any given task. In this thesis, we discuss two topics related to autonomous robotic manipulation. First, we address parametric uncertainties in manipulation tasks, such as the location of contacts during the execution of an assembly. We propose and experimentally evaluate two methods that rely on force and torque measurements to produce estimates of task related uncertainties: a method for dexterous manipulation under uncertainties which relies on a compliant rotational degree of freedom at the robot's gripper grasp point and exploits contact  with an external surface, and a cooperative manipulation system which is able to identify the kinematics of a two degrees of freedom mechanism. Then, we consider redundancies in dual-arm robotic manipulation. Dual-armed robots offer a large degree of redundancy which can be exploited to ensure a more robust task execution. When executing an assembly task, for instance, robots can freely change the location of the assembly in their workspace without affecting the task execution. We discuss methods that explore these types of redundancies in relative motion tasks in the form of asymmetries in their execution. Finally, we approach the converse problem by presenting a system which is able to balance measured forces and torques at its end-effectors by leveraging relative motion between them, while grasping a rigid tray. This is achieved through discrete sliding of the grasp points, which constitutes a novel application of bimanual dexterous manipulation.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 40
Series
TRITA-EECS-AVL ; 2019:73
National Category
Robotics
Identifiers
urn:nbn:se:kth:diva-263043 (URN)978-91-7873-331-6 (ISBN)
Public defence
2019-11-22, Room F3, Lindstedtsvägen 26, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20191105

Available from: 2019-11-05 Created: 2019-10-28 Last updated: 2019-11-18Bibliographically approved
2. Vision-Based In-Hand Manipulation with Limited Dexterity
Open this publication in new window or tab >>Vision-Based In-Hand Manipulation with Limited Dexterity
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In-hand manipulation is an action that allows for changing the grasp on an object without the need for releasing it. This action is an important component in the manipulation process and helps solving many tasks. Human hands are dexterous instruments suitable for moving an object inside the hand. However, it is not common for robots to be equipped with dexterous hands due to many challenges in control and mechanical design. In fact, robots are frequently equipped with simple parallel grippers, robust but lacking dexterity. This thesis focuses on achieving in-hand manipulation with limited dexterity. The proposed solutions are based only on visual input, without the need for additional sensing capabilities in the robot's hand.

Extrinsic dexterity allows simple grippers to execute in-hand manipulation thanks to the exploitation of external supports. This thesis introduces new methods for solving in-hand manipulation using inertial forces, controlled friction and external pushes as additional supports to enhance the robot's manipulation capabilities. Pivoting is seen as a possible solution for simple grasp changes: two methods, which cope with inexact friction modeling, are reported, and pivoting is successfully integrated in an overall manipulation task. For large scale in-hand manipulation, the Dexterous Manipulation Graph is introduced as a novel representation of the object. This graph is a useful tool for planning how to change a certain grasp via in-hand manipulation. It can also be exploited to combine both in-hand manipulation and regrasping to augment the possibilities of adjusting the grasp. In addition, this method is extended to achieve in-hand manipulation even for objects with unknown shape. To execute the planned object motions within the gripper, dual-arm robots are exploited to enhance the poor dexterity of parallel grippers: the second arm is seen as an additional support that helps in pushing and holding the object to successfully adjust the grasp configuration.

This thesis presents examples of successful executions of tasks where in-hand manipulation is a fundamental step in the manipulation process, showing how the proposed methods are a viable solution for achieving in-hand manipulation with limited dexterity.

Abstract [sv]

In-hand manipulation gör det möjligt att ändra fattningen om ett objekt utan att behöva släppa det. Detta är en viktig komponent och gör det möjligt att lösa många uppgifter.Den mänskliga händen är ett flexibelt instrument som är lämpligt för att flytta föremål inuti handen. Det är dock inte vanligt att robotar är utrustade med lika flexibla händer på grund av utmaningar inom reglerteknik och design av mekaniska system. I själva verket är robotar ofta utrustade med enkla parallel gripper, som är robusta men saknar finmotorik. Denna avhandling fokuserar på att uppnå in-hand manipulation med begränsad finmotorik. De föreslagna lösningarna baseras endast på visuell perception, utan behov av ytterligare sensorer i robotens hand.

Extrinsic dexterity (extrinsisk finmotorik) gör att enkla robothänder kan utföra in-hand manipulation tack vare utnyttjandet av externa stöd. Denna avhandling introducerar nya metoder för att lösa in-hand manipulation med tröghetskrafter, kontrollerad friktion och yttre tryck som ytterligare stöd för att förbättra robotens manipuleringsförmåga. Pivoting ses som en möjlig lösning för enkla greppförändringar: två metoder som hanterar inexakt friktionsmodellering presenteras samt som gungning är framgångsrikt integrerats i en fullständig manipuleringsuppgift. För storskalig in-hand manipulation introduceras Dexterous Manipulation Graph som en ny representation av objektet. Denna graf är ett användbart verktyg för att planera ändring av grepp via in-hand manipulation. Det kan också utnyttjas för att kombinera både in-hand manipulation och regrasping för att öka möjligheterna att justera greppet. Dessutom utvidgas denna metod för att uppnå in-hand manipulation även för föremål med okänd form. För att utföra de planerade objektrörelserna i robothanden utnyttjas dubbelarmade robotar för att förbättra den dåliga färdigheten hos parallel gripper: den andra armen ses som ett ytterligare stöd som hjälper till att skjuta och hålla objektet för att framgångsrikt justera greppkonfigurationen.

Denna avhandling presenterar exempel på framgångsrika utföranden av uppgifter där manuell manipulation är ett grundläggande steg i manipuleringsprocessen och visar hur de föreslagna metoderna är en rimlig och effektiv lösning för att uppnå handmanipulation med begränsad finmotorik.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019
Series
TRITA-EECS-AVL ; 2019:74
National Category
Computer Vision and Robotics (Autonomous Systems)
Identifiers
urn:nbn:se:kth:diva-263051 (URN)978-91-7873-332-3 (ISBN)
Public defence
2019-11-25, Kollegiesalen, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20191105

Available from: 2019-11-05 Created: 2019-10-28 Last updated: 2019-11-05Bibliographically approved

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