Showing papers by "Zexiang Li published in 1990"

Motion of two rigid bodies with rolling constraint

Abstract: The motion of two rigid bodies under rolling constraint is considered. In particular, the following two problems are addressed: (1) given the geometry of the rigid bodies, determine the existence of an admissible path between two contact configurations; and (2) assuming that an admissible path exists, find such a path. First, the configuration space of contact is defined, and the differential equations governing the rolling constraint are derived. Then, a generalized version of Frobenius's theorem, known as Chow's theorem, for determining the existence of motion is applied. Finally, an algorithm is proposed that generates a desired path with one of the objects being flat. Potential applications of this study include adjusting grasp configurations of a multifingered robot hand without slipping, contour following without dissipation or wear by the end-effector of a manipulator, and wheeled mobile robotics. >

Dynamics and optimal control of a legged robot in flight phase

Abstract: A discussion is presented of the control of legged-robot body orientation in flight using the internal motion of the leg. The angular momentum constraint (nonholonomic) is used to recast the problem into a nonholonomic motion planning problem. Chow's theorem is then applied to verify that the system is controllable, and the concept of holonomy is introduced for constructing an optimal path. Finally, linearization control is used in the internal motion space to realize the planned path. An additional degree of control to dynamically balance a legged robot that runs is provided with this strategy. >

An energy perturbation approach to limit cycle analysis in legged locomotion systems

Abstract: The energy-balance method, originally developed for systems whose behaviors are described by a single continuous differential equation, is extended to hopping systems, where the equations of motion are discontinuous from one phase to the other. Specifically, the perturbation and energy-balance methods were combined to study the existence and stability of the limit cycle behavior of a vertical hopper system. Estimated values of the limit cycles obtained using the proposed method are compared with the true (simulated) values for both the linear and the nonlinear models. The results confirm the validity of the proposed method. >

Issues in dextrous robot hands

Abstract: In this chapter, we study grasp planning and coordinated manipulation by a multifingered robot hand under various contact constraints. First, we formulate the hand kinematics and establish force/velocity transformation relations for a hand manipulation system. Then, we propose two quality measures for evaluating a grasp. These measures can be used to plan for good grasps. Finally, we derive a set of control laws for coordinated manipulation by a robot hand under either fixed points of contact or rolling contact. These control schemes all give decoupled error equations between the position loop and the internal grasp force loop.