Zhiyong Huang

Bio: Zhiyong Huang is an academic researcher. The author has contributed to research in topics: Animation. The author has an hindex of 1, co-authored 1 publications receiving 12 citations.

Motion control for human animation

Abstract: These Ecole polytechnique federale de Lausanne EPFL, n° 1601 (1997)Institut des systemes informatiques et multimediasLaboratoire de realite virtuelle Reference doi:10.5075/epfl-thesis-1601Print copy in library catalog Record created on 2005-03-16, modified on 2017-05-12

Interactive real-time articulated figure manipulation using multiple kinematic constraints.

Abstract: In this paper, we describe an interactive system for positioning articulated figures which uses a 3D direct manipulation technique to provide input to an inverse kinematics algorithm running in real time. The system allows the user to manipulate highly articulated figures, such as human figure models, by interactively dragging 3D "reach goals." The user may also define multiple "reach constraints" which are enforced during the manipulation. The 3D direct manipulation interface provides a good mechanism for control of the inverse kinematics algorithm and helps it to overcome problems with redundancies and singularities which occur with figures of many degrees of freedom. We use an adaptive technique for evaluating the constraints which allows us to ensure that only a certain user-controllable amount of time will be consumed by the inverse kinematics algorithm at each iteration of the manipulation process. This technique is also sensitive to the time it takes to redraw the screen, so it prevents the frame display rate of the direct manipulation from become too slow for interactive control.

Inverse kinematics techniques of the interactive posture control of articulated figures

Abstract: The context of this thesis is the interactive manipulation of complex articulated figures by means of geometric constraints (here called tasks), for the purpose of posture control and design. The goal is to determine a posture satisfying a set of prescribed tasks, usually expressed in the Cartesian space. This approach is known as Inverse Kinematics, and a number of analytic and numerical resolution methods have been developed for the control of robot manipulators. These methods have been applied to the computer animation of articulated figures, and to the control of human models for computer-aided ergonomic evaluations of products or workplaces. When dealing with figures that possess a large number of degrees of freedom, such as animal or human figures, their posture is usually controlled by several simultaneous tasks. There are tasks of different nature and function: they can control extremities such as the hands and the feet (for reaching or supporting purposes), as well as the center of mass, for balance control. They can also be used to avoid collisions with surrounding obstacles. The concurrent resolution of multiple tasks inevitably leads to conflicts that must be resolved with an appropriate strategy. A typical policy is to find a compromise solution that considers weights assigned to each task to indicate their relative importance. However, no task is precisely satisfied with this approach, and selecting appropriate weights is not always straightforward. In this thesis, we introduce a priority strategy for conflict resolution. With this policy, a task is not affected by other tasks of lower priority, and is satisfied as much as possible without affecting tasks of higher priority. The relative priority between two tasks is thus strictly enforced, which is appropriate for situations that cannot tolerate compromises. For example, keeping balance is more important than reaching an object with a hand, and avoiding inter-penetration of bodies is more important than any other task. Priorities are well-suited to express such hierarchical relationships. Based on a task-priority algorithm developed in robotics for simple manipulators, we introduce a framework that integrates the two conflict resolution strategies: first, the priorities assigned to the tasks are considered and, second, a weighting strategy solves the conflicts between tasks having same priority. We have improved the efficiency of the original algorithm by means of recursive relations, which is beneficial for interactive applications. Joint limits and joint couplings are also integrated in the framework to avoid unfeasible body postures. An interactive application, called BALANCE, has been developed to test the algorithm with a palette of task types: it allows us to illustrate the utility of task priorities for the manipulation of generic articulated figures, and of human models in particular. Besides simple geometric tasks, the application also proposes a task to keep the figure balanced under a set of static forces due to the interaction with its environment. It is shown that this task is easily integrated in the inverse kinematics framework, and that it is useful to generate postures in multiple supports with force exertions such as push and pull activities.

Keyframe interpolation with self-collision avoidance

Abstract: 3D-keyframe animation is a popular method for animating articulated figures. It allows artistic expressiveness by providing control to the animator. The drawback of this process is that it requires significant effort from the animator. Recently, work has focused on high level techniques such as adapting reference movements. However, whatever the way the animation is produced, the final process is an interpolation between keyframes. Our problem is that these interpolations do not deal with the avoidance of collisions between the limbs of an articulated figure, either an animator has to add new keyframes or the motion produced contains unrealistic positions. In this paper we present a new interpolation method producing self-collision free paths based on geometrical properties. Our method is a high level interpolation in which any classical interpolation method can be used. Experimental results using a human model show that the animator can reduce the level of detail needed for describing a movement and still get realistic results at interactive speeds.

Interactive human motion control using a closed-form of direct and inverse dynamics

Abstract: We propose the use of inverse dynamics in a closed form with direct dynamics for interactive motion control of a human skeleton. An efficient recursive algorithm based on Newton-Euler formulae is used to calculate the force and torque produced by a joint actuator in order to fulfill a desired motion. The resulting force and torque are then used in direct dynamics to make the final motion with external force and torque. The Armstrong-Green algorithm is used for direct dynamic simulation. To decrease the errors in numerical integration, we use the fourth order Runge-Kutta method instead of the Euler method. Inverse dynamic functions calculate the required force and torque at every small time interval in the process of direct dynamic simulation. In this way, it will correct errors at each time interval. The direct and inverse dynamic functions are integrated in the software, TRACK, with direct and inverse kinematics functions that provide a more powerful method for human animation

Realistic Collision Avoidance of Upper Limbs Based on Neuroscience Models

Abstract: When articulated figures interact in a 3D environment, collisions are highly likely and must often be avoided. We present a method automatically producing realistic collision-free animation of the upper arms. Based on the latest models of collision avoidance provided by neuroscience, our method allows realistic interpolation of keyframes at interactive speed. In order to validate our scheme we compared computer generated motions with motions performed by a sample of ten humans. These motions were defined by start and final postures and by an obstacle which had to be passed. In each case the generated positions are the same as those chosen by 30% of real humans, we therefore consider our method provides realistic motions. Moreover, the collision-free paths are automatically generated in a few seconds. Hence, our method can be very beneficial to animators by reducing the level of detail needed to define motions of articulated figures. It can also be used for the automatic generation of realistic animations for virtual reality applications.