Dragomir N. Nenchev

Impact analysis and post-impact motion control issues of a free-floating Space robot subject to a force impulse

This article presents impact dynamic analysis of a free-floating space robot, subject to a force impulse at the hand. We study the joint and the base reactions in terms of finite velocity changes and clarify their role for the post-impact motion behavior of the robot. The analysis makes use of a joint-space orthogonal decomposition procedure involving the so called reaction null space. The article focuses on the specific case of a nonredundant arm and a reaction null space in terms of base angular motion. We further show that with proper post-impact control it is possible to transfer the whole angular momentum from the base toward the manipulator, and in the same time to reduce the joint velocity.

Impact analysis and post-impact motion control issues of a free-floating space robot contacting a tumbling object

This work is an extension of the authors previous result (1995), mainly to tackle the post-impact control problem. We focus on the specific case of a nonredundant arm and a reaction null space in terms of base angular motion. It is shown that with proper post-impact manipulator control it is possible to swiftly transfer the whole angular momentum from the base toward the manipulator, and in the same time to reduce the joint velocity.

Control of a tethered robot system using a spacecraft mounted manipulator

This paper describes a new type of space robot system consisting of a spacecraft and a robot attached through a tether to the spacecraft. We call this system a tethered robot system. Considering the utilization of the tethered robot system, we especially focus on the control of translational motion of the tethered robot from the spacecraft to the destination point. The main idea is that the tethered robot can receive its initial velocity in the direction of the destination point at the spacecraft. However, due to disturbances, the tethered robot may get off the desired trajectory. We consider trajectory adjustment using a spacecraft mounted manipulator. The tethered robot is attached through the tether to the end-point of the manipulator that applies tether tension. We clarify the characteristics of the tethered robot system and propose several control schemes for trajectory adjustment of the tethered robot, and examine these control schemes.

Real-time motion control in the neighborhood of singularities: a comparative study between the SC and the DLS methods

We compare the main features of the singularity-consistent (SC) method and the damped-least-squares (DLS) method. It is shown that both methods introduce a so-called algorithmic error in the vicinity of a singular point. The direction of this error is, however, different in each method. This is shown to play an important role for system stability.

Singularity consistency and the natural motion of robot manipulators

This paper presents a new formulation of the inverse kinematics and dynamics of robot manipulators. A robot manipulators motion is expressed as the motion of a point in Riemannian space. We show that the end-effector-motion constraint defines a specific metric over this space, in terms of pure kinematic motion. An inverse kinematic solution is obtained which guarantees the stability of the system in the neighborhood of kinematic singularities. Motion through singularities becomes also possible. Furthermore, we show that in the presence of forces, the metric has to be changed in an appropriate way. Then, taking advantage of full integrability of the equation of motion, we obtain another nonlinear solution of the inverse kinematics which gives rise to an internal potential energy.