기구학적 및 동적 제한조건들을 고려한 모바일 매니퓰레이터의 작업 중심 전신 동작 생성 전략

학위논문(박사) -- 서울대학교대학원 : 융합과학기술대학원 융합과학부(지능형융합시스템전공), 2023. 2. 박재흥.모바일 매니퓰레이터는 모바일 로봇에 장착된 매니퓰레이터입니다. 모바일 매니퓰레이터는 고정형 매니퓰레이터에 비해 모바일 로봇의 이동성을 제공받기 때문에 다양하고 복잡한 작업을 수행할 수 있습니다. 그러나 두 개의 서로 다른 시스템을 결합함으로써 모바일 매니퓰레이터의 전신을 계획하고 제어할 때 여러 특징을 고려해야 합니다. 이러한 특징들은 여자유도, 두 시스템의 관성 차이 및 모바일 로봇의 비홀로노믹 제한 조건 등이 있습니다. 본 논문의 목적은 기구학적 및 동적 제한조건들을 고려하여 모바일 매니퓰레이터의 전신 동작 생성 전략을 제안하는 것입니다. 먼저, 모바일 매니퓰레이터가 초기 위치에서 문을 통과하여 목표 위치에 도달하기 위한 전신 경로를 계산하는 프레임워크를 제안합니다. 이 프레임워크는 로봇과 문에 의해 생기는 기구학적 제한조건을 고려합니다. 제안하는 프레임워크는 두 단계를 거쳐 전신의 경로를 얻습니다. 첫 번째 단계에서는 그래프 탐색 알고리즘을 이용하여 모바일 로봇의 자세 경로와 문의 각도 경로를 계산합니다. 특히, 그래프 탐색에서 area indicator라는 정수 변수를 상태의 구성 요소로서 정의하는데, 이는 문에 대한 모바일 로봇의 상대적 위치를 나타냅니다. 두 번째 단계에서는 모바일 로봇의 경로와 문의 각도를 통해 문의 손잡이 위치를 계산하고 역기구학을 활용하여 매니퓰레이터의 관절 위치를 계산합니다. 제안된 프레임워크의 효율성은 비홀로노믹 모바일 매니퓰레이터를 사용한 시뮬레이션 및 실제 실험을 통해 검증되었습니다. 둘 째, 최적화 방법을 기반으로한 전신 제어기를 제안합니다. 이 방법은 등식 및 부등식 제한조건 모두에 대해 가중 행렬을 반영한 계층적 최적화 문제의 해를 계산합니다. 이 방법은 모바일 매니퓰레이터 또는 휴머노이드와 같이 자유도가 많은 로봇의 여자유도를 해결하기 위해 개발되어 작업 우선 순위에 따라 가중치가 다른 관절 동작으로 여러 작업을 수행할 수 있습니다. 제안된 방법은 가중 행렬을 최적화 문제의 1차 최적 조건을 만족하도록 하며, Active-set 방법을 활용하여 등식 및 부등식 작업을 처리합니다. 또한, 대칭적인 영공간 사영 행렬을 사용하여 계산상 효율적입니다. 결과적으로, 제안된 제어기를 활용하는 로봇은 우선 순위에 따라 개별적인 관절 가중치를 반영하여 전신 움직임을 효과적으로 보여줍니다. 제안된 제어기의 효용성은 모바일 매니퓰레이터와 휴머노이드를 이용한 실험을 통해 검증하였습니다. 마지막으로, 모바일 매니퓰레이터의 동적 제한조건들 중 하나로서 자가 충돌 회피 알고리즘을 제안합니다. 제안된 방법은 매니퓰레이터와 모바일 로봇 간의 자가 충돌에 중점을 둡니다. 모바일 로봇의 버퍼 영역을 둘러싸는 3차원 곡면인 distance buffer border의 개념을 정의합니다. 버퍼 영역의 두께는 버퍼 거리입니다. 매니퓰레이터와 모바일 로봇 사이의 거리가 버퍼 거리보다 작은 경우, 즉 매니퓰레이터가 모바일 로봇의 버퍼 영역 내부에 있는 경우 제안된 전략은 매니퓰레이터를 버퍼 영역 밖으로 내보내기 위해 모바일 로봇의 움직임을 생성합니다. 따라서 매니퓰레이터는 미리 정의된 매니퓰레이터의 움직임을 수정하지 않고도 모바일 로봇과의 자가 충돌을 피할 수 있습니다. 모바일 로봇의 움직임은 가상의 힘을 가함으로써 생성됩니다. 특히, 힘의 방향은 차동 구동 이동 로봇의 비홀로노믹 제약 및 조작기의 도달 가능성을 고려하여 결정됩니다. 제안된 알고리즘은 7자유도 로봇팔을 가진 차동 구동 모바일 로봇에 적용하여 다양한 실험 시나리오에서 입증되었습니다.A mobile manipulator is a manipulator mounted on a mobile robot. Compared to a fixed-base manipulator, the mobile manipulator can perform various and complex tasks because the mobility is offered by the mobile robot. However, combining two different systems causes several features to be considered when generating the whole-body motion of the mobile manipulator. The features include redundancy, inertia difference, and non-holonomic constraint. The purpose of this thesis is to propose the whole-body motion generation strategy of the mobile manipulator for considering kinematic and dynamic constraints. First, a planning framework is proposed that computes a path for the whole-body configuration of the mobile manipulator to navigate from the initial position, traverse through the door, and arrive at the target position. The framework handles the kinematic constraint imposed by the closed-chain between the robot and door. The proposed framework obtains the path of the whole-body configuration in two steps. First, the path for the pose of the mobile robot and the path for the door angle are computed by using the graph search algorithm. In graph search, an integer variable called area indicator is introduced as an element of state, which indicates where the robot is located relative to the door. Especially, the area indicator expresses a process of door traversal. In the second step, the configuration of the manipulator is computed by the inverse kinematics (IK) solver from the path of the mobile robot and door angle. The proposed framework has a distinct advantage over the existing methods that manually determine several parameters such as which direction to approach the door and the angle of the door required for passage. The effectiveness of the proposed framework was validated through experiments with a nonholonomic mobile manipulator. Second, a whole-body controller is presented based on the optimization method that can consider both equality and inequality constraints. The method computes the optimal solution of the weighted hierarchical optimization problem. The method is developed to resolve the redundancy of robots with a large number of Degrees of Freedom (DOFs), such as a mobile manipulator or a humanoid, so that they can execute multiple tasks with differently weighted joint motion for each task priority. The proposed method incorporates the weighting matrix into the first-order optimality condition of the optimization problem and leverages an active-set method to handle equality and inequality constraints. In addition, it is computationally efficient because the solution is calculated in a weighted joint space with symmetric null-space projection matrices for propagating recursively to a low priority task. Consequently, robots that utilize the proposed controller effectively show whole-body motions handling prioritized tasks with differently weighted joint spaces. The effectiveness of the proposed controller was validated through experiments with a nonholonomic mobile manipulator as well as a humanoid. Lastly, as one of dynamic constraints for the mobile manipulator, a reactive self-collision avoidance algorithm is developed. The proposed method mainly focuses on self-collision between a manipulator and the mobile robot. We introduce the concept of a distance buffer border (DBB), which is a 3D curved surface enclosing a buffer region of the mobile robot. The region has the thickness equal to buffer distance. When the distance between the manipulator and mobile robot is less than the buffer distance, i.e. the manipulator lies inside the buffer region of the mobile robot, the proposed strategy is to move the mobile robot away from the manipulator in order for the manipulator to be placed outside the border of the region, the DBB. The strategy is achieved by exerting force on the mobile robot. Therefore, the manipulator can avoid self-collision with the mobile robot without modifying the predefined motion of the manipulator in a world Cartesian coordinate frame. In particular, the direction of the force is determined by considering the non-holonomic constraint of the differentially driven mobile robot. Additionally, the reachability of the manipulator is considered to arrive at a configuration in which the manipulator can be more maneuverable. To realize the desired force and resulting torque, an avoidance task is constructed by converting them into the accelerations of the mobile robot and smoothly inserted with a top priority into the controller. The proposed algorithm was implemented on a differentially driven mobile robot with a 7-DOFs robotic arm and its performance was demonstrated in various experimental scenarios.1 INTRODUCTION 1 1.1 Motivation 1 1.2 Contributions of thesis 2 1.3 Overview of thesis 3 2 WHOLE-BODY MOTION PLANNER : APPLICATION TO NAVIGATION INCLUDING DOOR TRAVERSAL 5 2.1 Background & related works 7 2.2 Proposed framework 9 2.2.1 Computing path for mobile robot and door angle - S1 10 2.2.1.1 State 10 2.2.1.2 Action 13 2.2.1.3 Cost 15 2.2.1.4 Search 18 2.2.2 Computing path for arm configuration - S2 20 2.3 Results 21 2.3.1 Application to pull and push-type door 21 2.3.2 Experiment in cluttered environment 22 2.3.3 Experiment with different robot platform 23 2.3.4 Comparison with separate planning by existing works 24 2.3.5 Experiment with real robot 29 2.4 Conclusion 29 3 WHOLE-BODY CONTROLLER : WEIGHTED HIERARCHICAL QUADRATIC PROGRAMMING 31 3.1 Related works 32 3.2 Problem statement 34 3.2.1 Pseudo-inverse with weighted least-squares norm for each task 35 3.2.2 Problem statement 37 3.3 WHQP with equality constraints 37 3.4 WHQP with inequality constraints 45 3.5 Experimental results 48 3.5.1 Simulation experiment with nonholonomic mobile manipulator 48 3.5.1.1 Scenario description 48 3.5.1.2 Task and weighting matrix description 49 3.5.1.3 Results 51 3.5.2 Real experiment with nonholonomic mobile manipulator 53 3.5.2.1 Scenario description 53 3.5.2.2 Task and weighting matrix description 53 3.5.2.3 Results 54 3.5.3 Real experiment with humanoid 55 3.5.3.1 Scenario description 55 3.5.3.2 Task and weighting matrix description 55 3.5.3.3 Results 57 3.6 Discussions and implementation details 57 3.6.1 Computation cost 57 3.6.2 Composite weighting matrix in same hierarchy 59 3.6.3 Nullity of WHQP 59 3.7 Conclusion 59 4 WHOLE-BODY CONSTRAINT : SELF-COLLISION AVOIDANCE 61 4.1 Background & related Works 64 4.2 Distance buffer border and its score computation 65 4.2.1 Identification of potentially colliding link pairs 66 4.2.2 Distance buffer border 67 4.2.3 Evaluation of distance buffer border 69 4.2.3.1 Singularity of the differentially driven mobile robot 69 4.2.3.2 Reachability of the manipulator 72 4.2.3.3 Score of the DBB 74 4.3 Self-collision avoidance algorithm 75 4.3.1 Generation of the acceleration for the mobile robot 76 4.3.2 Generation of the repulsive acceleration for the other link pair 82 4.3.3 Construction of an acceleration-based task for self-collision avoidance 83 4.3.4 Insertion of the task in HQP-based controller 83 4.4 Experimental results 86 4.4.1 System overview 87 4.4.2 Experimental results 87 4.4.2.1 Self-collision avoidance while tracking the predefined trajectory 87 4.4.2.2 Self-collision avoidance while manually guiding the end-effector 89 4.4.2.3 Extension to obstacle avoidance when opening the refrigerator 91 4.4.3 Discussion 94 4.5 Conclusion 95 5 CONCLUSIONS 97 Abstract (In Korean) 113 Acknowlegement 116박

AO-Grasp: Articulated Object Grasp Generation

We introduce AO-Grasp, a grasp proposal method that generates stable and actionable 6 degree-of-freedom grasps for articulated objects. Our generated grasps enable robots to interact with articulated objects, such as opening and closing cabinets and appliances. Given a segmented partial point cloud of a single articulated object, AO-Grasp predicts the best grasp points on the object with a novel Actionable Grasp Point Predictor model and then finds corresponding grasp orientations for each point by leveraging a state-of-the-art rigid object grasping method. We train AO-Grasp on our new AO-Grasp Dataset, which contains 48K actionable parallel-jaw grasps on synthetic articulated objects. In simulation, AO-Grasp achieves higher grasp success rates than existing rigid object grasping and articulated object interaction baselines on both train and test categories. Additionally, we evaluate AO-Grasp on 120 realworld scenes of objects with varied geometries, articulation axes, and joint states, where AO-Grasp produces successful grasps on 67.5% of scenes, while the baseline only produces successful grasps on 33.3% of scenes.Comment: Project website: https://stanford-iprl-lab.github.io/ao-gras

Behavior-Tree-Based Person Search for Symbiotic Autonomous Mobile Robot Tasks

We consider the problem of people search by a mobile social robot in case of a situation that cannot be solved by the robot alone. Examples are physically opening a closed door or operating an elevator. Based on the Behavior Tree framework, we create a modular and easily extendable action sequence with the goal of finding a person to assist the robot. By decomposing the Behavior Tree as a Discrete Time Markov Chain, we obtain an estimate of the probability and rate of success of the options for action, especially where the robot should wait or search for people. In a real-world experiment, the presented method is compared with other common approaches in a total of 588 test runs over the course of one week, starting at two different locations in a university building. We show our method to be superior to other approaches in terms of success rate and duration until a finding person and returning to the start location.© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

An Incremental Navigation Localization Methodology for Application to Semi-Autonomous Mobile Robotic Platforms to Assist Individuals Having Severe Motor Disabilities.

In the present work, the author explores the issues surrounding the design and development of an intelligent wheelchair platform incorporating the semi-autonomous system paradigm, to meet the needs of individuals with severe motor disabilities. The author presents a discussion of the problems of navigation that must be solved before any system of this type can be instantiated, and enumerates the general design issues that must be addressed by the designers of systems of this type. This discussion includes reviews of various methodologies that have been proposed as solutions to the problems considered. Next, the author introduces a new navigation method, called Incremental Signature Recognition (ISR), for use by semi-autonomous systems in structured environments. This method is based on the recognition, recording, and tracking of environmental discontinuities: sensor reported anomalies in measured environmental parameters. The author then proposes a robust, redundant, dynamic, self-diagnosing sensing methodology for detecting and compensating for hidden failures of single sensors and sensor idiosyncrasies. This technique is optimized for the detection of spatial discontinuity anomalies. Finally, the author gives details of an effort to realize a prototype ISR based system, along with insights into the various implementation choices made

A quantitative investigation for deployment of mobile collaborative robots in high-value manufacturing

Component inspection is often the bottleneck in high-value manufacturing, driving industries like aerospace toward automated inspection technologies. Current systems often employ fixed arm robots, but they lack the flexibility in adapting to new components or orientations Advanced mobile robotic platforms with updated sensor technologies and algorithms have improved localization and path planning capabilities, making them ideal for bringing inspection processes directly to parts. However, mobile platforms introduce challenges in localization and maneuverability, leading to potential errors. Their positional uncertainty is higher than fixed systems due to the lack of a fixed calibrated location, posing challenges for position-sensitive inspection sensors. Therefore, it's essential to assess the positional accuracy and repeatability of mobile manipulator platforms. The KUKA KMR iiwa was chosen for its collaborative features, robust build, and scalability within the KUKA product range. The accuracy and repeatability of the mobile platform were evaluated through a series of tests to evaluate the performance of its integrated feature mapping, the effect of various speeds on positional accuracy, and the efficiency of the omnidirectional wheels for a range of translation orientations. Experimental evaluation revealed that enabling feature mapping substantially improves the KUKA KMR iiwa's performance, with accuracy gains and error reductions exceeding 90%. Repeatability errors were under 7 mm with mapping activated and around 2.5 mm in practical scenarios, demonstrating that mobile manipulators, incorporating both the manipulator and platform, can fulfil the precise requirements of industries with high precision needs. Providing a highly diverse alternative to traditional fixed-base industrial manipulators

Proceedings of the NASA Conference on Space Telerobotics, volume 2

These proceedings contain papers presented at the NASA Conference on Space Telerobotics held in Pasadena, January 31 to February 2, 1989. The theme of the Conference was man-machine collaboration in space. The Conference provided a forum for researchers and engineers to exchange ideas on the research and development required for application of telerobotics technology to the space systems planned for the 1990s and beyond. The Conference: (1) provided a view of current NASA telerobotic research and development; (2) stimulated technical exchange on man-machine systems, manipulator control, machine sensing, machine intelligence, concurrent computation, and system architectures; and (3) identified important unsolved problems of current interest which can be dealt with by future research

Path planning for robotic truss assembly

A new Potential Fields approach to the robotic path planning problem is proposed and implemented. Our approach, which is based on one originally proposed by Munger, computes an incremental joint vector based upon attraction to a goal and repulsion from obstacles. By repetitively adding and computing these 'steps', it is hoped (but not guaranteed) that the robot will reach its goal. An attractive force exerted by the goal is found by solving for the the minimum norm solution to the linear Jacobian equation. A repulsive force between obstacles and the robot's links is used to avoid collisions. Its magnitude is inversely proportional to the distance. Together, these forces make the goal the global minimum potential point, but local minima can stop the robot from ever reaching that point. Our approach improves on a basic, potential field paradigm developed by Munger by using an active, adaptive field - what we will call a 'flexible' potential field. Active fields are stronger when objects move towards one another and weaker when they move apart. An adaptive field's strength is individually tailored to be just strong enough to avoid any collision. In addition to the local planner, a global planning algorithm helps the planner to avoid local field minima by providing subgoals. These subgoals are based on the obstacles which caused the local planner to fail. A best-first search algorithm A* is used for graph search

Robot Control and Programming: Class notes.

The term robot is quite complex because it can mean different things to different people. Mostly, it recalls us images of science fiction robots, such as the famous C3PO and R2D2 of Star Wars Trilogy. However, we have to focus on other types, and wait a little for the progress of the technology. If we focus on the real robots, we can find different types. However, the vast majority are classified into the industrial robot category. Industrial robots are recognised easily since their shape usually reminds the human arm. The term industrial shows the fact that those robots work in factories as components of larger manufacturing systems and processes. This book are focused on the lectures that Emilio Sánchez delivers in the frame of Robot Control and Programing subject in TECNUN, where the reader can find and introduction to the basic problems and control and programming techniques of industrial robots. Despite the fact the book is based on classnotes, the author prepared them very carefully to give to them the appearance of a real book. The book starts with a discussion about what is and what isn't a robot, classification and a very brief note about robotics history. The course will cover the different and basic programming and control strategies. Another issue discussed will be the morphology classification. The most important section is the kinematics model. This problem can be solved by means of Denavit-Hartenberg method and homogeneous transformations among coordinate systems. The last chapters are devoted to position control strategies and path planning. Finally the author encourages the reader to open and read this book since he really thinks that Robotics is a very large and interesting field, involving many different disciplines: mechanical design, sensors, actuation (pneumatic, hydraulic, electrical...), control, programming... For this reason, the term mechatronics is also used to express the link between the mechanics and electronics

Mobile Robots Navigation

Mobile robots navigation includes different interrelated activities: (i) perception, as obtaining and interpreting sensory information; (ii) exploration, as the strategy that guides the robot to select the next direction to go; (iii) mapping, involving the construction of a spatial representation by using the sensory information perceived; (iv) localization, as the strategy to estimate the robot position within the spatial map; (v) path planning, as the strategy to find a path towards a goal location being optimal or not; and (vi) path execution, where motor actions are determined and adapted to environmental changes. The book addresses those activities by integrating results from the research work of several authors all over the world. Research cases are documented in 32 chapters organized within 7 categories next described