사람의 자연스러운 보행 동작 생성을 위한 물리 시뮬레이션 기반 휴머노이드 제어 방법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2014. 8. 이제희.휴머노이드를 제어하여 사람의 자연스러운 이동 동작을 만들어내는 것은 컴퓨터그래픽스 및 로봇공학 분야에서 중요한 문제로 생각되어 왔다. 하지만, 이는 사람의 이동에서 구동기가 부족한 (underactuated) 특성과 사람의 몸의 복잡한 구조를 모방하고 시뮬레이션해야 한다는 점 때문에 매우 어려운 문제로 알려져왔다. 본 학위논문은 물리 시뮬레이션 기반 휴머노이드가 외부의 변화에 안정적으로 대응하고 실제 사람처럼 자연스럽고 다양한 이동 동작을 만들어내도록 하는 제어 방법을 제안한다. 우리는 실제 사람으로부터 얻을 수 있는 관찰 가능하고 측정 가능한 데이터를 최대한으로 활용하여 문제의 어려움을 극복했다. 우리의 접근 방법은 모션 캡처 시스템으로부터 획득한 사람의 모션 데이터를 활용하며, 실제 사람의 측정 가능한 물리적, 생리학적 특성을 복원하여 사용하는 것이다. 우리는 토크로 구동되는 이족 보행 모델이 다양한 스타일로 걸을 수 있도록 제어하는 데이터 기반 알고리즘을 제안한다. 우리의 알고리즘은 모션 캡처 데이터에 내재된 이동 동작 자체의 강건성을 활용하여 실제 사람과 같은 사실적인 이동 제어를 구현한다. 구체적으로는, 참조 모션 데이터를 재현하는 자연스러운 보행 시뮬레이션을 위한 관절 토크를 계산하게 된다. 알고리즘에서 가장 핵심적인 아이디어는 간단한 추종 제어기만으로도 참조 모션을 재현할 수 있도록 참조 모션을 연속적으로 조절하는 것이다. 우리의 방법은 모션 블렌딩, 모션 와핑, 모션 그래프와 같은 기존에 존재하는 데이터 기반 기법들을 이족 보행 제어에 활용할 수 있게 한다. 우리는 보다 사실적인 이동 동작을 생성하기 위해 사람의 몸을 세부적으로 모델링한, 근육에 의해 관절이 구동되는 인체 모델을 제어하는 이동 제어 시스템을 제안한다. 시뮬레이션에 사용되는 휴머노이드는 실제 사람의 몸에서 측정된 수치들에 기반하고 있으며 최대 120개의 근육을 가진다. 우리의 알고리즘은 최적의 근육 활성화 정도를 계산하여 시뮬레이션을 수행하며, 참조 모션을 충실히 재현하거나 혹은 새로운 상황에 맞게 모션을 적응시키기 위해 주어진 참조 모션을 수정하는 방식으로 동작한다. 우리의 확장가능한 알고리즘은 다양한 종류의 근골격 인체 모델을 최적의 근육 조합을 사용하며 균형을 유지하도록 제어할 수 있다. 우리는 다양한 스타일로 걷기 및 달리기, 모델의 변화 (근육의 약화, 경직, 관절의 탈구), 환경의 변화 (외력), 목적의 변화 (통증의 감소, 효율성의 최대화)에 대한 대응, 방향 전환, 회전, 인터랙티브하게 방향을 바꾸며 걷기 등과 같은 보다 난이도 높은 동작들로 이루어진 예제를 통해 우리의 접근 방법이 효율적임을 보였다.Controlling artificial humanoids to generate realistic human locomotion has been considered as an important problem in computer graphics and robotics. However, it has been known to be very difficult because of the underactuated characteristics of the locomotion dynamics and the complex human body structure to be imitated and simulated. In this thesis, we presents controllers for physically simulated humanoids that exhibit a rich set of human-like and resilient simulated locomotion. Our approach exploits observable and measurable data of a human to effectively overcome difficulties of the problem. More specifically, our approach utilizes observed human motion data collected by motion capture systems and reconstructs measured physical and physiological properties of a human body. We propose a data-driven algorithm to control torque-actuated biped models to walk in a wide range of locomotion skills. Our algorithm uses human motion capture data and realizes an human-like locomotion control facilitated by inherent robustness of the locomotion motion. Concretely, it takes reference motion and generates a set of joint torques to generate human-like walking simulation. The idea is continuously modulating the reference motion such that even a simple tracking controller can reproduce the reference motion. A number of existing data-driven techniques such as motion blending, motion warping, and motion graph can facilitate the biped control with this framework. We present a locomotion control system that controls detailed models of a human body with the musculotendon actuating process to create more human-like simulated locomotion. The simulated humanoids are based on measured properties of a human body and contain maximum 120 muscles. Our algorithm computes the optimal coordination of muscle activations and actively modulates the reference motion to fathifully reproduce the reference motion or adapt the motion to meet new conditions. Our scalable algorithm can control various types of musculoskeletal humanoids while seeking harmonious coordination of many muscles and maintaining balance. We demonstrate the strength of our approach with examples that allow simulated humanoids to walk and run in various styles, adapt to change of models (e.g., muscle weakness, tightness, joint dislocation), environments (e.g., external pushes), goals (e.g., pain reduction and efficiency maximization), and perform more challenging locomotion tasks such as turn, spin, and walking while steering its direction interactively.Contents Abstract i Contents iii List of Figures v 1 Introduction 1 1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1 Computer Graphics Perspective . . . . . . . . . . . . . . . . . 3 1.1.2 Robotics Perspective . . . . . . . . . . . . . . . . . . . . . . . 5 1.1.3 Biomechanics Perspective . . . . . . . . . . . . . . . . . . . . 7 1.2 Aim of the Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.4 Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.5 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2 Previous Work 16 2.1 Biped Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.1.1 Controllers with Optimization . . . . . . . . . . . . . . . . . . 18 2.1.2 Controllers with Motion Capture Data . . . . . . . . . . . . . 20 2.2 Simulation of Musculoskeletal Humanoids . . . . . . . . . . . . . . . 21 2.2.1 Simulation of Specic Body Parts . . . . . . . . . . . . . . . . 21 2.2.2 Simulation of Full-Body Models . . . . . . . . . . . . . . . . . 22 2.2.3 Controllers for Musculoskeletal Humanoids . . . . . . . . . . . 23 3 Data-Driven Biped Control 24 3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.2 System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.3 Data-Driven Control . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 3.3.1 Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.3.2 Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . 37 3.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 4 Locomotion Control for Many-Muscle Humanoids 56 4.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 4.2 Humanoid Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.2.1 Muscle Force Generation . . . . . . . . . . . . . . . . . . . . . 61 4.2.2 Muscle Force Transfer . . . . . . . . . . . . . . . . . . . . . . 64 4.2.3 Equation of Motion . . . . . . . . . . . . . . . . . . . . . . . . 66 4.3 Muscle Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 4.3.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 4.3.2 Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 4.3.3 Quadratic Programming Formulation . . . . . . . . . . . . . . 70 4.4 Trajectory Optimization . . . . . . . . . . . . . . . . . . . . . . . . . 71 4.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 4.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 5 Conclusion 84 A Mathematical Definitions 88 A.1 Definitions of Transition Function . . . . . . . . . . . . . . . . . . . . 88 B Humanoid Models 89 B.1 Torque-Actuated Biped Models . . . . . . . . . . . . . . . . . . . . . 89 B.2 Many-Muscle Humanoid Models . . . . . . . . . . . . . . . . . . . . . 91 C Dynamics of Musculotendon Actuators 94 C.1 Contraction Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . 94 C.2 Initial Muscle States . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Glossary for Medical Terms 99 Bibliography 102 초록 113Docto

A survey on human performance capture and animation

With the rapid development of computing technology, three-dimensional (3D) human body models and their dynamic motions are widely used in the digital entertainment industry. Human perfor- mance mainly involves human body shapes and motions. Key research problems include how to capture and analyze static geometric appearance and dynamic movement of human bodies, and how to simulate human body motions with physical e�ects. In this survey, according to main research directions of human body performance capture and animation, we summarize recent advances in key research topics, namely human body surface reconstruction, motion capture and synthesis, as well as physics-based motion sim- ulation, and further discuss future research problems and directions. We hope this will be helpful for readers to have a comprehensive understanding of human performance capture and animatio

Analysis and synthesis of bipedal humanoid movement : a physical simulation approach

textAdvances in graphics and robotics have increased the importance of tools for synthesizing humanoid movements to control animated characters and physical robots. There is also an increasing need for analyzing human movements for clinical diagnosis and rehabilitation. Existing tools can be expensive, inefficient, or difficult to use. Using simulated physics and motion capture to develop an interactive virtual reality environment, we capture natural human movements in response to controlled stimuli. This research then applies insights into the mathematics underlying physics simulation to adapt the physics solver to support many important tasks involved in analyzing and synthesizing humanoid movement. These tasks include fitting an articulated physical model to motion capture data, modifying the model pose to achieve a desired configuration (inverse kinematics), inferring internal torques consistent with changing pose data (inverse dynamics), and transferring a movement from one model to another model (retargeting). The result is a powerful and intuitive process for analyzing and synthesizing movement in a single unified framework.Computer Science

Humanoid Robots

For many years, the human being has been trying, in all ways, to recreate the complex mechanisms that form the human body. Such task is extremely complicated and the results are not totally satisfactory. However, with increasing technological advances based on theoretical and experimental researches, man gets, in a way, to copy or to imitate some systems of the human body. These researches not only intended to create humanoid robots, great part of them constituting autonomous systems, but also, in some way, to offer a higher knowledge of the systems that form the human body, objectifying possible applications in the technology of rehabilitation of human beings, gathering in a whole studies related not only to Robotics, but also to Biomechanics, Biomimmetics, Cybernetics, among other areas. This book presents a series of researches inspired by this ideal, carried through by various researchers worldwide, looking for to analyze and to discuss diverse subjects related to humanoid robots. The presented contributions explore aspects about robotic hands, learning, language, vision and locomotion

Biologically-inspired control framework for insect animation.

Insects are common in our world, such as ants, spiders, cockroaches etc. Virtual representations of them have wide applications in Virtual Reality (VR), video games and films. Compared with the large volume of works in biped animation, the problem of insect animation was less explored. Their small body parts, complex structures and high-speed movements challenge the standard techniques of motion synthesis. This thesis addressed the aforementioned challenge by presenting a framework to efficiently automate the modelling and authoring of insect locomotion. This framework is inspired by two key observations of real insects: fixed gait pattern and distributed neural system. At the top level, a Triangle Placement Engine (TPE) is modelled based on the double-tripod gait pattern of insects, and determines the location and orientation of insect foot contacts, given various user inputs. At the low level, a Central Pattern Generator (CPG) controller actuates individual joints by mimicking the distributed neural system of insects. A Controller Look-Up Table (CLUT) translates the high-level commands from the TPE into the low-level control parameters of the CPG. In addition, a novel strategy is introduced to determine when legs start to swing. During high-speed movements, the swing mode is triggered when the Centre of Mass (COM) steps outside the Supporting Triangle. However, this simplified mechanism is not sufficient to produce the gait variations when insects are moving at slow speed. The proposed strategy handles the case of slow speed by considering four independent factors, including the relative distance to the extreme poses, the stance period, the relative distance to the neighbouring legs, the load information etc. This strategy is able to avoid the issues of collisions between legs or over stretching of leg joints, which are produced by conventional methods. The framework developed in this thesis allows sufficient control and seamlessly fits into the existing pipeline of animation production. With this framework, animators can model the motion of a single insect in an intuitive way by specifying the walking path, terrains, speed etc. The success of this framework proves that the introduction of biological components could synthesise the insect animation in a naturalness and interactive fashion

Physics-based character locomotion control with large simulation time steps.

Physical simulated locomotion allows rich and varied interactions with environments and other characters. However, control is di cult due to factors such as a typical character's numerous degrees of freedom and small stability region, discontinuous ground contacts, and indirect control over the centre of mass. Previous academic work has made signi cant progress in addressing these problems, but typically uses simulation time steps much smaller than those suitable for games. This project deals with developing control strategies using larger time steps. After describing some introductory work showing the di culties of implementing a handcrafted controller with large physics time steps, three major areas of work are discussed. The rst area uses trajectory optimization to minimally alter reference motions to ensure physical validity, in order to improve simulated tracking. The approach builds on previous work which allows ground contacts to be modi ed as part of the optimization process, extending it to 3D problems. Incorporating contacts introduces di cult complementarity constraints, and an exact penalty method is shown here to improve solver robustness and performance compared to previous relaxation methods. Trajectory optimization is also used to modify reference motions to alter characteristics such as timing, stride length and heading direction, whilst maintaining physical validity, and to generate short transitions between existing motions. The second area uses a sampling-based approach, previously demonstrated with small time steps, to formulate open loop control policies which reproduce reference motions. As a prerequisite, the reproducibility of simulation output from a common game physics engine, PhysX, is examined and conditions leading to highly reproducible behaviour are determined. For large time steps, sampling is shown to be susceptible to physical inva- lidities in the reference motion but, using physically optimized motions, is successfully applied at 60 time steps per second. Finally, adaptations to an existing method using evolutionary algorithms to learn feedback policies are described. With large time steps, it is found to be necessary to use a dense feedback formulation and to introduce phase-dependence in order to obtain a successful controller, which is able to recover from impulses of several hundred Newtons applied for 0.1s. Additionally, it is shown that a recent machine learning approach based on support vector machines can identify whether disturbed character states will lead to failure, with high accuracy (99%) and with prediction times in the order of microseconds. Together, the trajectory optimization, open loop control, and feedback developments allow successful control for a walking motion at 60 time steps per second, with control and simulation time of 0.62ms per time step. This means that it could plausibly be used within the demanding performance constraints of games. Furthermore, the availability of rapid failure prediction for the controller will allow more high level control strategies to be explored in future

Developing agile motor skills on virtual and real humanoids

Demonstrating strength and agility on virtual and real humanoids has been an important goal in computer graphics and robotics. However, developing physics- based controllers for various agile motor skills requires a tremendous amount of prior knowledge and manual labor due to complex mechanisms of the motor skills. The focus of the dissertation is to develop a set of computational tools to expedite the design process of physics-based controllers that can execute a variety of agile motor skills on virtual and real humanoids. Instead of designing directly controllers real humanoids, this dissertation takes an approach that develops appropriate theories and models in virtual simulation and systematically transfers the solutions to hardware systems. The algorithms and frameworks in this dissertation span various topics from spe- cific physics-based controllers to general learning frameworks. We first present an online algorithm for controlling falling and landing motions of virtual characters. The proposed algorithm is effective and efficient enough to generate falling motions for a wide range of arbitrary initial conditions in real-time. Next, we present a robust falling strategy for real humanoids that can manage a wide range of perturbations by planning the optimal contact sequences. We then introduce an iterative learning framework to easily design various agile motions, which is inspired by human learn- ing techniques. The proposed framework is followed by novel algorithms to efficiently optimize control parameters for the target tasks, especially when they have many constraints or parameterized goals. Finally, we introduce an iterative approach for exporting simulation-optimized control policies to hardware of robots to reduce the number of hardware experiments, that accompany expensive costs and labors.Ph.D

Implementation of a robot platform to study bipedal walking

On this project, a modi cation of an open source, 3D printed robot, was implemented, with the purpose to create a more a ordable bipedal platform proper for studying Bipedal Walking algorithms. The original robot is a part of an open-source platform, called Poppy, that is formed from an interdisciplinary community of beginners and experts. One of the robots of this platform, is the Poppy Humanoid. The rigid parts of the Poppy Humanoid (as well as the rest of the Poppy platform robots) are 3D printed, a key factor of lowering the cost of a robot. The actuators used though, are expensive commercial DC-motors that increase the total cost of the robot drastically. This high cost of the actuators of Poppy, led this project to modify cheaper actuators while maintaining the same performance of their predecessors. Taking apart the components of the cheaper actuator, only the motor, the gears and the case that host them were kept, and a new design was made to control the motor and to meet the requirements set from the commercial motors. This new design of the actuator include a 12-bit resolution magnetic encoder to read the position of the shaft of the motor, a driver to run the motor, and also an embedded Arduino micro-controller. This feature of an Arduino as part of the actuator, gives the advantage over the commercial motor, as the user has the freedom to upload his own codes and to implement his own motor controllers. The result is a fully programmable actuator hosted on the same motor case. The size of this actuator though, is di erent from the commercial one. In order to mount the new actuators to the platform, Joan Guasch designed proper 3D printed parts. Apart of these parts, Joan also modi ed the leg design, in order to add another joint on the ankle (roll) as this Degree of Freedom (DoF) is important for Bipedal Walking algorithms and was missing from the original Poppy Humanoid leg design. The modi ed robot, is called Poppy-UPC and is a 12 DoF biped platform. For the communication between the motors and the main computer unit, a serial communication protocol was implemented based to the RS-485 standard. Multiple receivers (motors and sensors) can be connected to such a network in a linear, multi-drop con guration. The main computer unit of Poppy-UPC is an Odroid-C1 board. Essentially, this board is a Quad-core Linux computer fully compatible to run ROS. Odroid is acting as the master of the network and is gathering all the informations of the connected nodes, in order to publish them in ROS-topics. That way, the Poppy-UPC is connected to the ROS environment and ROS packages can be used for any further implementation with this platform. Finally, following the open-source spirit of the Poppy platform, all the codes and information are available at https://github.com/dimitris-zervas