Singularity Avoidance Strategies For Satellite Mounted Manipulators Using Attitude Control

摘要

Control concepts for satellite mounted manipulators (SMM) are examined. The primary focus is on base actuated concepts, which eliminate singularity problems associated with free floating SMMs. A new form of the equations of motion for an n-link SMM is developed using a quasi coordinate form of Lagrange's Equation. Alternative free floating SMM designs are presented which eliminate dynamic singularities, but still experience difficulties due to the unactuated base. A new generic SMM controller is developed as a framework for various control concepts with and without base actuation. Momentum constrained Jacobians are shown to produce better SMM tracking than fixed base Jacobians, even when base motion feedback is incorporated into the controller. A variation of the generic controller, termed the Reduced Base Torque Controller (RBTC), is introduced and shown to reduce attitude control costs significantly while retaining the advantages of base control. The RBTC uses a task priority technique, assigning the first priority to end effector control and secondary priority to maintaining a zero angular momentum state. Finally, the SMM dynamic model and generic controller are modified to include a cluster of control moment gyroscopes (CMG), and the effects of using the cluster for base attitude control in the SMM system are considered. A controller variation is developed which avoids singularities of both the CMG cluster and the manipulator system. A variety of planar and spatial simulations are used to validate the performance of the controllers. The results indicate that the base attitude control concept is the most viable SMM control concept in terms of tracking performance and singularity avoidance.