Cable-driven parallel manipulators (CDPM) potentially offer many advantages over serial manipulators, including greater structural rigidity, greater accuracy, and higher payload-to-weight ratios. However, CDPMs possess limited moment resisting/exerting capabilities and relatively small orientation workspaces. Various methods have been contemplated for overcoming these limitations, each with its own advantages and disadvantages. The focus of this paper is on one such method: the addition of base mobility to the system. Such base mobility gives rise to kinematic redundancy, which needs to be resolved carefully in order to control the system. However, this redundancy can also be exploited in order to optimize some secondary criteria, e.g., maximizing the size and quality of the wrench-closure workspace with the addition of base mobility. In this work, the quality of the wrench-closure workspace is examined using a tension-factor index. Two planar mobile base configurations are investigated, and their results are compared with a traditional fixed-base system. In the rectangular configuration, each base is constrained to move along its own linear rail, with each rail forming right angles with the two adjacent rails. In the circular configuration, the bases are constrained to move along one circular rail. While a rectangular configuration enhances the size and quality of the orientation workspace in a particular rotational direction, the circular configuration allows for the platform to obtain any position and orientation within the boundary of the base circle. Furthermore, if the bases are configured in such a way that the cables are fully symmetric with respect to the platform, a maximum possible tension-factor of one is guaranteed. This fully symmetric configuration is shown to offer a variety of additional advantages: it eliminates the need to perform computationally expensive nonlinear optimization by providing a closed-form solution to the inverse kinematics problem, and it results in a convergence between kinematic singularities and wrench-closure singularities of the system. Finally, we discuss a particular limitation of this fully symmetric configuration: the inability of the cables to obtain an even tension distribution in a loaded configuration. For this reason, it may be useful to relax the fully symmetric cable requirement in order to yield reasonable tensions of equal magnitude.

Assisted motor therapies play a critical role in enhancing functional musculoskeletal recovery and neurological rehabilitation. Our long term goal is to assist and automate the performance of repetitive motor-therapy of the human lower limbs. Hence, in this paper, we examine the viability of a light-weight and reconfigurable hybrid (articulatedmultibody and cable) robotic system for assisting lowerextremity rehabilitation and analyze its performance. A hybrid cable-actuated articulated multibody system is formed when multiple cables are attached from a ground-frame to various locations on an articulated-linkage based orthosis. Our efforts initially focus on developing an analysis and simulation framework for the kinematics and dynamics of the cable-driven lower limb orthosis. A Monte Carlo approach is employed to select configuration parameters including cuff sizes, cuff locations, and the position of fixed winches. The desired motions for the rehabilitative exercises are prescribed based upon motion patterns from a normative subject cohort. We examine the viability of using two controllers -a joint-space feedback linearized PD controller and a task-space force-control strategy -to realize trajectory-and path-tracking of the desired motions within a simulation environment. In particular, we examine performance in terms of (i) coordinated control of the redundant system; (ii) reducing internal stresses within the lowerextremity joints; and (iii) continued satisfaction of the unilateral cable-tension constraints throughout the workspace. A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d Downloaded From: http://mechanismsrobotics.asmedigitalcollection.asme.org/ on 01/05/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use Alamdari 2 A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d Downloaded From: http://mechanismsrobotics.asmedigitalcollection.asme.org/ on 01/05/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use Journal of Mechanisms and Robotics.A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d Downloaded From: http://mechanismsrobotics.asmedigitalcollection.asme.org/ on 01/05/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use Journal of Mechanisms and Robotics.A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d Downloaded From: http://mechanismsrobotics.asmedigitalcollection.asme.org/ on 01/05/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use Journal of Mechanisms and Robotics.A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d Downloaded From: http://mechanismsrobotics.asmedigitalcollection.asme.org/ on 01/05/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use Journal of Mechanisms and Robotics.A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d Downloaded From: http://mechanismsrobotics.asmedigitalcollection.asme.org/ on 01/05/2016 Terms of Use: http://www.asme.org/about-asme/terms-of-use Alamdari 7 A c c e p t e d M a n u s c r i p t N o t C o p y e d i t e d Downloaded From: http://mech...

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This paper examines the design, analysis and control of a novel hybrid articulated-cable parallel platform for upper limb rehabilitation in three dimensional space. The proposed lightweight, low-cost, modular reconfigurable parallel-architecture robotic device is comprised of five cables and a single linear actuator which connects a six degrees-of-freedom moving platform to a fixed base. This novel design provides an attractive architecture for implementation of a home-based rehabilitation device as an alternative to bulky and expensive serial robots. The manuscript first examines the kinematic analysis prior to developing the dynamic equations via the Newton-Euler formulation. Subsequently, different spatial motion trajectories are prescribed for rehabilitation of subjects with arm disabilities. A low-level trajectory tracking controller is developed to achieve the desired trajectory performance while ensuing that the unidirectional tensile forces in the cables are maintained. This is now evaluated via a simulation case-study and the development of a physical testbed is underway.

High mobility, maneuverability and obstacle-surmounting capabilities are highly desirable features for rough-terrain locomotion systems. In this paper, we explore the use of various candidate articulated leg-wheel subsystem designs (based on the four-bar mechanism) to enhance locomotion capabilities of land-based vehicles. Multiple leg-wheel design parameters, such as kinematic link lengths and static spring stiffnesses and preloads, influence the overall locomotion performance. Appropriate selection can not only enhance the robot climbing performance but also reduce the wheel slip as well as the overall energy consumption. In particular, we aim to: (i) achieve the greatest motion-ranges between wheel-axle and chassis; as well as to (ii) reduce the overall actuation requirements by spring assist. Hence, we explore the use of systematic kinetostatic design approaches coupled with optimization to determine the parameters for alternate leg-wheel subsystem designs. Further, we also examine enhancement of uneven-terrain locomotion by varying subsystem parameters during the terrain traversal via a semi-active leg-wheel subsystem. Extensive simulation is then employed to evaluate the capabilities of these alternate articulated leg-wheel designs to surmount a predetermined/sensed terrain traversal profile while reducing actuation requirements.

SUMMARYMaximum load carrying capacity (MLCC) of flexible robot manipulators is computed based on closed-loop approach. In open-loop approach, controller is not considered, so the end effector deviation from the predefined path is significant and the accuracy constraint restrains the maximum payload before actuators go into saturation mode. In order to improve the MLCC, a method based on closed-loop strategy is presented. Since in this case the accuracy is improved the actuators constraint is not a major concern and full power of actuators can be used. Since controller can play an important role in improving the maximum payload, a sliding mode based partial feedback linearization controller is designed. Furthermore, a fuzzy variable layer is used in sliding mode design to boost the performance of the controller. However, the control strategy required measurements of elastic variables velocity that are not conveniently measurable. So a nonlinear observer is designed to estimate these variables. Stability analysis of the proposed controller and state observer are performed on the basis of Lyapunov's direct method. In order to verify the effectiveness of the presented method, simulation is done for a two-link flexible manipulator. The obtained maximum payload in open-loop and closed-loop cases is compared and the superiority of the method is illustrated and the results are discussed.

Assisted motor therapies play a critical role in enhancing the functional musculoskeletal recovery and neurological rehabilitation. Our focus here is to assist the performance of repetitive motor-therapy of the human lower limbs — in both the sagittal and frontal planes. Hence, in this paper, we develop a lightweight, reconfigurable hybrid (articulated-multibody and cable) based robotic rehabilitative device as a surrogate for a human physiotherapists and analyze feasibility and performance. A hybrid cable-actuated articulated multibody system is formed when multiple cables are attached from a ground-frame to various locations on the lower limbs. The combined system now features multiple holonomic cable-loop-closure constraints acting on a tree-structured multibody system. Hence the paper initially focuses on developing the Newton-Euler dynamic equilibrium equations of the cable-driven lower limbs to develop a symbolic analysis framework. The desired motion for the proposed rehabilitative exercise are prescribed based upon normative subjects motion patterns. Trajectory-tracking within this system is realized by a position-based impedance controller in task-space and a feedback-linearized PD controllers in joint-space. Careful coordination of the multiple cable-motors are now necessary in order to achieve the co-robotic control of the overall system, avoiding development of internal stresses and ensuring continued satisfaction of the unilateral cable-tension constraints throughout the workspace. This is now evaluated via a simulation case-study and development of a physical testbed is underway.