로봇 시스템의 설계 및 동작 동시 최적화

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 기계공학부, 2020. 8. 박종우.A robot design has the potential for numerous combinations of the components such as the actuators, links, joints, etc. Therefore, a process of finding a good design is a challenging problem even for the robot experts. To overcome this difficulty, we present an optimization framework for the morphological shape of a robot, considering its motion. Both the design and motion parameters can be simultaneously optimized for specific tasks by our methodology. In the space where the design and motion parameters are combined, our framework seeks the steepest direction that reduces the objective function on the constraint manifold. To overcome the flaws of the previous studies, we utilize the recently discovered recursive differential dynamics, which informs of the analytic relationship between the variation of joint torques and design parameters, thus our framework brings faster and more accurate optimization results. We validate our optimization framework through two numerical experiments: the 2-R planar manipulator with a given end-effector trajectory and the quadruped robot with a locomotion task.로봇 디자인에는 액츄에이터, 링크, 관절 등과 같은 구성요소의 수많은 조합 가능성이 존재한다. 따라서, 좋은 로봇 디자인을 찾는 과정은 전문가에게도 어려운 문제이다. 위 문제점을 극복하기 위해 로봇의 동작을 고려하여 형태를 최적화하는 방법론을 제시한다. 제시된 방법론을 통해 특정 작업을 위한 로봇 형태 및 동작의 동시 최적화가 가능하다. 위 방법론은 형태 및 동작 변수가 결합된 공간 상에서 목적함수를 가장 많이 감소시키는 구속조건 매니폴드 상에서의 방향을 찾아 최적화를 진행한다. 이전 연구들의 결점을 극복하기 위해 우리는 최근 개발된 반복 미분 동역학(recursive differential dynamics) 알고리즘을 사용한다. 이 알고리즘을 통해 관절 토크 변화와 형태 변화 사이의 해석적 관계를 계산할 수 있다. 따라서, 제시된 방법론을 사용하면 더욱 빠르고 정확한 최적화 결과를 도출할 수 있다. 총 두 가지 수치적 실험을 통해 위 최적화 방법론을 검증하였다: 엔드이펙터가 주어진 궤적을 추종하는 2축 평면 매니퓰레이터, 4족로봇의 보행작업.1 Introduction 1 1.1 Design Optimization of Robotic Devices 1 1.2 Limitations of Previous Works 4 1.3 Main Contributions of This Thesis 5 2 Preliminaries 7 2.1 Lie Group Theory 7 2.1.1 SO(3) and SE(3) 8 2.1.2 Twists and Wrenches 10 2.1.3 Adjoint Mappings 10 2.2 Rigid Body Dynamics 11 2.2.1 Dynamics of a Single Rigid Body 11 2.2.2 Dynamics of Open Chains 12 2.2.3 Dynamics of Floating Bodies 14 2.3 Recursive Differential Dynamics 15 3 Simultaneous Design and Motion Optimization 18 3.1 Problem Definition 18 3.2 Optimization Parameters 20 3.2.1 Design Parameters 20 3.2.2 Motion Parameters 23 3.2.3 Constraints 24 3.2.4 Inertial Changes 26 3.3 Optimization Algorithm Description 27 4 Numerical Experiments31 4.1 2-R Planar Manipulator 31 4.1.1Experimental Settings 31 4.1.2Optimization Results 33 4.2 Quadruped Robot 36 4.2.1Experimental Settings 37 4.2.2Optimization Results 39 5 Conclusion 44 A Appendix 46 A.1 Local parametrization of the design 46 A.2 Design rule for the link 48 A.3 Derivative of the constraints 51 A.3.1 End-effector trajectory 51 A.3.2 Equations of motion of the base for quadruped robots 52 A.4 Laikago Specification 53 Bibliography 55 국문초록 60Maste

Computational Synthesis of Wearable Robot Mechanisms: Application to Hip-Joint Mechanisms

Since wearable linkage mechanisms could control the moment transmission from actuator(s) to wearers, they can help ensure that even low-cost wearable systems provide advanced functionality tailored to users' needs. For example, if a hip mechanism transforms an input torque into a spatially-varying moment, a wearer can get effective assistance both in the sagittal and frontal planes during walking, even with an affordable single-actuator system. However, due to the combinatorial nature of the linkage mechanism design space, the topologies of such nonlinear-moment-generating mechanisms are challenging to determine, even with significant computational resources and numerical data. Furthermore, on-premise production development and interactive design are nearly impossible in conventional synthesis approaches. Here, we propose an innovative autonomous computational approach for synthesizing such wearable robot mechanisms, eliminating the need for exhaustive searches or numerous data sets. Our method transforms the synthesis problem into a gradient-based optimization problem with sophisticated objective and constraint functions while ensuring the desired degree of freedom, range of motion, and force transmission characteristics. To generate arbitrary mechanism topologies and dimensions, we employed a unified ground model. By applying the proposed method for the design of hip joint mechanisms, the topologies and dimensions of non-series-type hip joint mechanisms were obtained. Biomechanical simulations validated its multi-moment assistance capability, and its wearability was verified via prototype fabrication. The proposed design strategy can open a new way to design various wearable robot mechanisms, such as shoulders, knees, and ankles.Comment: 28 pages, 7 figures, Supplementary Material

Mechanism and Behaviour Co-optimisation of High Performance Mobile Robots

Mobile robots do not display the level of physical performance one would expect, given the specifications of their hardware. This research is based on the idea that their poor performance is at least partly due to their design, and proposes an optimisation approach for the design of high-performance mobile robots. The aim is to facilitate the design process, and produce versatile and robust robots that can exploit the maximum potential of today's technology. This can be achieved by a systematic optimisation study that is based on careful modelling of the robot's dynamics and its limitations, and takes into consideration the performance requirements that the robot is designed to meet. The approach is divided into two parts: (1) an optimisation framework, and (2) an optimisation methodology. In the framework, designs that can perform a large set of tasks are sought, by simultaneously optimising the design and the behaviours to perform them. The optimisation methodology consists of several stages, where various techniques are used for determining the design's most important parameters, and for maximising the chances of finding the best possible design based on the designer's evaluation criteria. The effectiveness of the optimisation approach is proved via a specific case-study of a high-performance balancing and hopping monopedal robot. The outcome is a robot design and a set of optimal behaviours that can meet several performance requirements of conflicting nature, by pushing the hardware to its limits in a safe way. The findings of this research demonstrate the importance of using realistic models, and taking into consideration the tasks that the robot is meant to perform in the design process