Research On A Three-fingered End-effector For Orbital Payload Replacement And Operation Control

With the development of space technology and robotics,robot is playing a more and more important role in space activities.Manipulator is one of the most common space robots.Adopting manipulator to conduct orbital payload replacement is the basic task in on-orbit servicing.The key part is the manipulator end-effector,in which many problems have not been solved.This thesis investigates the task analysis,prototype design and control of an end-effector for orbital payload replacement.A three-fingered end-effector is developed with the characteristics of large misalignment tolerance,small volume and mass,mechani cal and electronic interface supply.An operation controller is proposed with limited sensor information.The experiments are carried out to validate the effectiveness of the proposed design method and controller.A three-fingered end-effector has been developed.After analyzing basic geometrical constraint models,an end-effector geometrical constraint guideline is promoted,which ensures the characteristic of large misalignment tolerance.A grapple chain based on an approximate straight path linkage is pr oposed,which can generate desired fingertip trajectory within a limited dimension.The linkage has the characteristics of small volume,light mass and high stability.In addition,the mechanical implementation of the guideline is conducted.A highly integ rated and mechatronic prototype is developed.Model simulations validate the misalignment tolerance and the effectiveness of the geometrical constraint guideline.To solve the problem of grasping with large misalignment,this thesis investigates into the cooperative grasping method of the manipulator and end-effector system.The grasping process is divided into pose estimation,pose correction and dynamic grasping.Firstly,the target pose estimation is conducted based on the contact force information.The calculating process meets the requirements of on-line computation and stability.Then,Artificial Potential Field(APF)is built with the pose estimation result.The trajectory for linear pose correction is modified with virtual impedance control,which co ntributes to pose correction without collision.Besides,the grasping speed is adjusted with the pose misalignment.A fuzzy logical controller is designed for establishing the relationship between misalignment and speed,which contributes to smooth and fas t grasping.Simulations validate the effectiveness of the cooperative grasping method.To solve the problem of electrical interface assembly,the thesis investigates into the compliant assembly method.The electrical interface for assembly has the characteristics of small clearance and weak resistibility to impact.The control strategy of applying force in assembly direction and keeping compliant in other directions is presented firstly,which leads to the control scheme based on hybrid impedance control.An adaptive controller is proposed for improving force tracking performance in assembly.In addition,an event-based strategy switch is conducted for adjusting parameters in the hybrid impedance control,which results in a smooth transition from unconstrained to constrained space.Simulations validate the effectiveness of the proposed controller in electrical interface assembly.To validate the design and control of the end-effector,two experimental setups of planar free floating environment and the manipulator end-effector system are constructed.The experiments of operation in free floating environment,cooperative grasping,electrical interface assembly and end-effector operation are conducted.The following can be concluded from the results: the misalignment tolerance meets the requirement and the constraint of relative motion increases gradually;the cooperative grasping method can guarantee the steady grasping with large misalignment;the compliant assembly method can guarantee the stable electr ical connection between the end-effector and payload;the proposed end-effector can fulfill the operation task steadily,which meets the requirement of orbital payload replacement.