Inverse lagrangian dynamics for animating articulated models

This paper presents the application of inverse Lagrangian dynamics for the purpose of animating articulated models. The method orginates from mechanics and robotics and has been adapted to deal with branched kinematic chains and joints with multiple degrees of freedom. The method is then reformulated to calculate the ground reaction forces that apply to the body. The approach is direct and does not involve guesswork. The formulation has been implemented into a general animation system that is entirely interactive and supports the facility of simulating generic articulated models.     

Human body animation: a survey

A survey of human body animation is presented dealing with its geometrical representation, motion control techniques and rendering. A classification of human body animation systems is presented according to different criteria.The human body movement notations are described and the different existing geometric models of the body and the face are analised and compared.The body and face control motion techniques are presented and discussed, as well as human body motion in its environment. Finally, the different problems of human body rendering are presented.     

Hanging cloths and dangling rods: A unified approach to constraints in computer animation

A simple unified approach for dealing with constraints on real-valued parameters in computer simulations and computer animation is described. The main characteristics of the approach are its flexibility (it works for a variety of constraint-types and it can be implemented to handle both under- and over-constrained systems in a stable way) and its ease for distributed computation. The method is based on the idea of genetic algorithms. The mathematical merits of the method for one constraint-type are discussed in some detail and some examples of applications are given.     

An object-oriented architecture for a computer animation system

This paper describes the architecture, capabilities and implementation of The Clockworks, an object-oriented computer animation system encompassing a wide variety of modeling, image synthesis, animation, programming and simulation capabilities in a single integrated environment. The object-oriented features of The Clockworks are implemented in portable C under UNIX using a programming discipline. These features include objects with methods and instance variables, class hierarchies, inheritance, instantiation and message passing.     

Towards an integrated view of 3-D computer animation

To automate character animation and extend it to 3-D we need to create and manipulate three-dimensional models of articulated figures as well as the worlds they will inhabit.Abstraction andadaptive motion are key mechanisms for dealing with thedegrees of freedom problem, which refers to the sheer volume of control information necessary for coordinating the motion of an articulated figure when the number of links is large. A three level hierarchy of control modes for animation is proposed:guiding, animator-level, andtask-level systems. Guiding is best suited for specifiying fine details but unsuited for controlling complex motion. Animatorlevel programming is powerful but difficult. Task-level systems give us facile control over complex motions and tasks by trading off explicit control over the details of motion. The integration of the three control levels is discussed.     

An iterative approach to dynamic simulation of 3-D rigid-body motions for real-time interactive computer animation

A method is presented for approximating the motions of linked 3-dimensional rigid body systems that may be applied in the context of interactive motion specification for computer animation. The method is based on decoupling the ballistic (free) component of the motion of the points that constitute the solid, and the component due to the shape constraint of the solid. This allows for a conceptually simple and computationally efficient algorithm for motion specification.     

计算机动画技术发展研究

本文将国内外计算机动画发挥情况进行了对比,并介绍了目前计算机动画技术发挥在那的现状。     

Automatic differentiation of rigid body dynamics for optimal control and estimation

Abstract

Many algorithms for control, optimization and estimation in robotics depend on derivatives of the underlying system dynamics, e.g. to compute linearizations, sensitivities or gradient directions. However, we show that when dealing with rigid body dynamics, these derivatives are difficult to derive analytically and to implement efficiently. To overcome this issue, we extend the modelling tool ‘RobCoGen’ to be compatible with Automatic Differentiation. Additionally, we propose how to automatically obtain the derivatives and generate highly efficient source code. We highlight the flexibility and performance of the approach in two application examples. First, we show a trajectory optimization example for the quadrupedal robot HyQ, which employs auto-differentiation on the dynamics including a contact model. Second, we present a hardware experiment in which a six-DoF robotic arm avoids a randomly moving obstacle in a go-to task by fast, dynamic replanning.     

Rigid body constraints realized in massively-parallel molecular dynamics on graphics processing units

Molecular dynamics (MD) methods compute the trajectory of a system of point particles in response to a potential function by numerically integrating Newton?s equations of motion. Extending these basic methods with rigid body constraints enables composite particles with complex shapes such as anisotropic nanoparticles, grains, molecules, and rigid proteins to be modeled. Rigid body constraints are added to the GPU-accelerated MD package, HOOMD-blue, version 0.10.0. The software can now simulate systems of particles, rigid bodies, or mixed systems in microcanonical (NVE), canonical (NVT), and isothermal-isobaric (NPT) ensembles. It can also apply the FIRE energy minimization technique to these systems. In this paper, we detail the massively parallel scheme that implements these algorithms and discuss how our design is tuned for the maximum possible performance. Two different case studies are included to demonstrate the performance attained, patchy spheres and tethered nanorods. In typical cases, HOOMD-blue on a single GTX 480 executes 2.5–3.6 times faster than LAMMPS executing the same simulation on any number of CPU cores in parallel. Simulations with rigid bodies may now be run with larger systems and for longer time scales on a single workstation than was previously even possible on large clusters.     

Feedback stabilization of uniform rigid body rotation

This abstract discusses the stabilization of uniform rigid body rotation about an arbitrary axis by feedback control. The class of feedback control laws considered is linear and is shown to robustly stabilize rotation with respect to inertia uncertainty. The methodology developed in this paper is based on the energy-momentum method of stability analysis and fully exploits the underlying geometry. The methodology is illustrated with several examples.     

Planning rigid body motions using elastic curves

This paper tackles the problem of computing smooth, optimal trajectories on the Euclidean group of motions SE(3). The problem is formulated as an optimal control problem where the cost function to be minimized is equal to the integral of the classical curvature squared. This problem is analogous to the elastic problem from differential geometry and thus the resulting rigid body motions will trace elastic curves. An application of the Maximum Principle to this optimal control problem shifts the emphasis to the language of symplectic geometry and to the associated Hamiltonian formalism. This results in a system of first order differential equations that yield coordinate free necessary conditions for optimality for these curves. From these necessary conditions we identify an integrable case and these particular set of curves are solved analytically. These analytic solutions provide interpolating curves between an initial given position and orientation and a desired position and orientation that would be useful in motion planning for systems such as robotic manipulators and autonomous-oriented vehicles.     

A model for the three-dimensional reconstruction and animation of the human heart

This paper presents a strategy for the production of a computer-generated film showing the complete motion of a human heart. The model for construction and animation is discussed. The heart is decomposed into different parts; each part is considered as a subactor of the heart which is viewed as the main actor. The left ventricle simulation is emphasized, because it is based on medical measures. The atrium simulation is based on beta-spline surfaces and blood volume considerations.     

Comments on the stabilizability of the angular velocity of a rigid body

This paper discusses the stabilizability by smooth feedback of the angular velocity of a rigid body. First we show how to asymptotically stabilize the system with a single control. Then it is shown that a single control aligned with a principal axis cannot asymptotically stabilize the system. Finally we present some new results on stabilization by means of scalar feedback control.     

Interactive computer simulation and animation for improving student learning of particle kinetics

Computer simulation and animation (CSA) has been receiving growing attention and wide application in engineering education in recent years. A new interactive CSA module was developed in the present study to improve student learning of particle kinetics in an undergraduate engineering dynamics course. The unique feature of this CSA module is that it integrates computer visualization with mathematical modeling, so students can directly connect engineering dynamics phenomena to underlying mathematics. A quasi‐experimental pretest–post‐test research design including a comparison group (n = 65) and an intervention group (n = 77) was implemented to assess to what extent the developed CSA module improved student learning. The results show that this new CSA module increased students' class‐average conceptual and procedural learning gains by 29% and 37% respectively. The difference in learning gains between the two groups is statistically significant (Z = ?4.526, p = 0.000) based on a nonparametric statistical Mann–Whitney U test. It is found that the improvement of students' conceptual understanding and the improvement of their procedural skills are asymmetrical in this CSA learning environment. The CSA module can serve as an excellent tool to supplement traditional lectures, but cannot fully replace human teachers or tutors in teaching.     

Sequential-goal constraints for computer animation

The dynamic constraints technique has been proposed for building geometrical models composed of rigid bodies, which are made to act naturally, according to Newtonian laws, by specifying constraints on their states. In computer animation, the dynamic constraints technique alleviates the work-load of animators who formerly had to plan animated sequences in detail by intuition alone. Nevertheless, for some real-world applications, it is desirable to have a mechanism that makes physically-based elements move according to a given scenario by providing some control states. The control states can be represented by transient constraints that are to be met and then released immediately. In this paper, a technique called the sequential-goal constraints technique is proposed to provide such a mechanism. With the sequential-goal constraints technique, it is easy to specify transient constraints according to a given scenario and derive proper forces and torques to drive an element to meet each transient constraint exactly at a specified time so that the whole motion of the element is continuous and integral.     

Realistic modeling and animation of human body based on scanned data

In this paper we propose a novel method for building animation model of real human body from surface scanned data. The human model is represented by a triangular mesh and described as a layered geometric model. The model consists of two layers: the control skeleton generating body animation from motion capture data, and the simplified surface model providing an efficient representation of the skin surface shape. The skeleton is generated automatically from surface scanned data using the feature extraction, and then a point-to-line mapping is used to map the surface model onto the underlying skeleton. The resulting model enables real-time and smooth animation by manipulation of the skeleton while maintaining the surface detail. Compared with earlier approach, the principal advantages of our approach are the automated generation of body control skeletons from the scanned data for real-time animation, and the automatic mapping and animation of the captured human surface shape. The human model constructed in this work can be used for applications of ergonomic design,garment CAD, real-time simulating humans in virtual reality environment and so on.     

Dimensionality reduction for computer facial animation

This paper describes the usage of dimensionality reduction techniques for computer facial animation. Techniques such as Principal Components Analysis (PCA), Expectation-Maximization (EM) algorithm for PCA, Multidimensional Scaling (MDS), and Locally Linear Embedding (LLE) are compared for the purpose of facial animation of different emotions. The experimental results on our facial animation data demonstrate the usefulness of dimensionality reduction techniques for both space and time reduction. In particular, the EMPCA algorithm performed especially well in our dataset, with negligible error of only 1-2%.     

A framework for interactive responsive animation

The availability of high‐performance 3D workstations has increased the range of application for interactive real‐time animation. In these applications the user can directly interact with the objects in the animation and direct the evolution of their motion, rather than simply watching a pre‐computed animation sequence. Interactive real‐time animation has fast‐growing applications in virtual reality, scientific visualization, medical training and distant learning. Traditional approaches to computer animation have been based on the animator having complete control over all aspects of the motion. In interactive animation the user can interact with any of the objects, which changes the current motion path or behaviour in real time. The objects in the animation must be capable of reacting to the user's actions and not simply replay a canned motion sequence. This paper presents a framework for interactive animation that allows the animator to specify the reactions of objects to events generated by other objects and the user. This framework is based on the concept of relations that describe how an object reacts to the influence of a dynamic environment. Each relation specifies one motion primitive triggered by either its enabling condition or the state of the environment. A collection of the relations is structured through several hierarchical layers to produce responsive behaviours and their variations. This framework is illustrated by several room‐based dancing examples that are modelled by relations. Copyright © 2000 John Wiley & Sons, Ltd.