Modelling and analysis of anthropomorphic cable-driven robots

Cable-driven parallel manipulators (CDPMs) have been studied in recent years due to their unique characteristics and advantages. In particular, CDPMs have been regarded as bio-inspired mechanisms that are structurally analogous to musculoskeletal systems. In this thesis, the study of anthropomorphic cable-driven robots is investigated. Multilink cable-driven manipulators (MCDMs) are a type of CDPM where cables actuate a multilink rigid body structure in parallel arrangement. The rigid links and cables of MCDMs are analogous to the bones and muscles of musculoskeletal systems, respectively. The use of MCDMs to study more complex biomechanical structures has been limited due to several reasons. Firstly, musculoskeletal systems are typically open-chain branched structures with complex cable routing and a large number of links. However, there currently exists no generalised model that allows arbitrary cable routing. Secondly, the analysis for MCDMs may require extensions from single link CDPMs to consider the different types of cable routing. Thirdly, the actuation characteristics between muscles and ideal cables are considerably different. These issues are investigated and addressed in this thesis and the contributions are presented in two parts. The first part deals with the modelling of MCDMs. One major challenge in the modelling of MCDMs is that the number of combinations in possible cable routing increases exponentially with the number of rigid bodies. Introducing the cable-routing matrix (CRM), it is shown that all possible cable routing can be encapsulated in a single representation. Using the CRM and a generalised representation for arbitrary joints, generalised kinematic and dynamic models for open-chain branched mechanisms are formulated. The proposed model allow both arbitrary cable routing and arbitrary rigid body structure. The effectiveness and robustness of the model is demoniii strated through two examples, a simple 2 link 4 degree-of-freedom (DoF) 6 cable manipulator and a complex human neck inspired 8 link 24 Dof 76 cable system. The more complex example serves to illustrate the potential in using the generalised MCDM model to study musculoskeletal structures. The second part of this thesis addresses the analysis of anthropomorphic CDPMs for both engineered and biomechanics applications. Using the generalised MCDM model, necessary conditions with respect to the CRM are derived for an MCDM to satisfy wrenchclosure. In the design of an MCDM, it is important that the cable routing results in a manipulator that is capable of producing wrench-closure. Finally, the workspace analysis of CDPMs allowing for state dependent force generators is investigated. Examples of state dependent force generators include artificial and physiological muscles. In particular, the static workspace of musculoskeletal systems is studied. The formulation is demonstrated through computationally generating the static workspace of a human shoulder. By validating the workspace against human benchmarks, it is shown that the inclusion of muscles is important to generate a physiologically accurate musculoskeletal workspace. Through this thesis, the fundamental components required in studying anthropomorphic cable-driven manipulators have been presented. The contributions of the thesis extend the boundaries of the current literature in both the robotics and biomechanics disciplines. In addition to enabling more complex engineered MCDM systems to be studied, the concept of studying biomechanical systems as MCDMs is proposed for the first time. The results of this work highlight the potential of using MCDMs to gain a better understanding of biomechanics.