Modelling, analysis and control of multi-link cable-driven manipulators

Cable-driven parallel robots (CDPRs) form a class of robotic manipulator in which the actuation is transmitted through cables. Due to the unique characteristics and advantages of cable transmission, CDPRs have become increasingly studied in recent years. In this thesis, the study of operational space motion generation of CDPRs is investigated. The operational space corresponds to the space in which a task to be executed by an end effector is defined. The generation of operational space motions on CDPRs allows the specification of tasks to be intuitive to human users, in addition to enabling the application of CDPRs to tasks exploiting their human-like configurations. The study of CDPR operational space motion generation has been limited due to several reasons. Firstly, cable transmission results in both redundant and constrained actuation. This means that it is possible for a motion to be either infeasible or for there to be an infinite number of different actuation profiles which can produce the same desired motion. Secondly, in the case of multi-link CDPRs (MCDRs) the generalised coordinates differ from that of the end effector. This means that there may be infinite different joint space motions which achieve the same operational space behaviour. The study of MCDR operational space motion generation therefore must consider both a means of ensuring that a feasible solution exists and a means of selecting a particular joint space solution from the possibly infinite set. Finally, in the implementation and evaluation of different CDPR motion generation schemes there is currently no software which can consider all possible CDPR models and hardware interfaces. These issues are investigated within this thesis and presented as two separate parts. The first part develops a generalised framework for the operational space motion generation of CDPRs. To understand the requirements of CDPR motion generation, this v part firstly considers quantifications of CDPR motion generation capability, in which new metrics are proposed to indicate the capability of a CDPR to produce additional acceleration and to identify the magnitude of cable force necessary to produce an arbitrary joint space wrench. An expansive search tree inspired formulation is then presented with which to solve MCDR operational space motion planning problems while ensuring solution feasibility. The effectiveness and robustness of this method is demonstrated through a set of different operational space motion tracking problems solved on two different MCDRs. The second part of the thesis addresses the development of a generalised CDPR simulation and hardware interfacing software tool. The cable-robot analysis and simulation platform for research (CASPR) is presented and shown to provide a modular and extendible software framework in which new CDPRs can be easily added through simple XML specifications. The proposed framework is open source and allows for common kinematic and dynamic CDPR problems to be solved using a range of different algorithms. To allow for implementation onto different hardware platforms, the integration of CASPR with the Robotics Operating System (ROS) is also presented. The application and flexibility of CASPR is shown through example simulations and hardware based experiments conducted on single and multi link CDPRs.