The chapter presents modification of a dynamically equivalent manipulator (DEM) method, which enables dynamic modeling of space robots and manipulators, including free-floating maneuvers, via their suitable substitution by groundfixed manipulator models. DEM provides an attractive modeling and control design tool, since it enables conducting tests and experiments for space vehicles in earth laboratories. The modification of DEM method relies upon an introduction of quaternion-based modeling of manipulator attitude. Originally, DEM method was developed in Euler angles. The basic motivation for the presented DEM modification is to make dynamic and kinematic models more suitable for description of space robots and manipulator motions and their missions like debris removal, spacecraft servicing, space mining, and on-orbit docking and assemblies. It may also support control designs. The theoretical development is illustrated by an example of generation of spacecraft quaternion-based dynamics and simulation studies of its reorientation maneuvers.
Background The paper presents modeling of space manipulators whose structures are composed of rigid and flexible components. Due to their applications for variety of servicing missions, their dynamics and attitude are described using quaternions. Parameterization by the quaternions does not share Euler angles' drawbacks and is computationally more efficient. Another challenge is the motion equations derivation method. Methods Due to poor scalability of Lagrange method equations, authors decided to model the space robot as a set of links subjected to position constraints.The elastic effects are modeled with the assumed mode method successfully applied to a variety of ground manipulators with flexible links. The constrained dynamics approach and the assumed mode method are combined to derive a comprehensive space manipulator dynamics. Its dynamic model is readily scalable in terms of number of both rigid and flexible robotic arms and links. Conclusions The paper contributes to the development of effective quaternion-based constrained dynamics for space structures equipped with flexible links. The theory is illustrated by simulation studies of an example of a space manipulator attitude dynamics.
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