Technical session talks from ICRA 2012
TechTalks from event: Technical session talks from ICRA 2012
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Novel Equilibrium-Point Control of Agonist-Antagonist System with Pneumatic Artificial MusclesThis paper presents a novel method for controlling a single-joint robot arm driven by two pneumatic artificial muscles (PAMs). We introduce the concepts of the agonist-antagonist muscle-pairs ratio (A-A ratio) and the agonist-antagonist muscle-pairs activity (A-A activity), and demonstrate that our concepts enable separate linear control of the equilibrium joint angle and joint stiffness. We also discuss our approach in comparison with the equilibrium-point (EP) hypothesis.
Dynamic Trajectory Planning of a Two-DOF Cable-Suspended Parallel RobotThis paper presents a trajectory planning approach for cable-suspended parallel mechanisms. A planar two-degree-of-freedom parallel mechanism is used for the analysis. Based on the dynamic model of the suspended robot, a set of algebraic inequalities is obtained that represents the constraints on the cable tensions. Parametric Cartesian trajectories are then defined and substituted into the constraints in order to obtain global conditions on the trajectory parameters which ensure that the trajectories are feasible. Special frequencies arise from the equations that are akin to natural frequencies of pendulum-type systems. An experimental validation is also presented using a two-dof prototype. The proposed trajectory planning approach can be used to plan dynamic trajectories that go beyond the static workspace of the mechanism, thereby opening novel applications and possibilities for cable-suspended robots.
Force-Closure of Spring-Loaded Cable-Driven Open Chains: Minimum Number of Cables Required & Influence of Spring PlacementsWhile cable-driven systems offer the advantages of being lightweight with low moving inertia, the unilateral driving property of cables generally require them to have a greater number of actuators than their rigid-linked counterparts. This paper investigates the use of springs in an attempt to reduce the number of cables required. Given an n-DOF spring-loaded cable-driven open chain, several important questions arise: (i) How can force-closure analysis be carried out for a given spring and cable routing configuration? (ii) Are n+1 cables still necessary to fully constrain the entire open chain? (iii) What is the influence of spring placement on force-closure and cable tension required? This paper will address these concerns by proposing a systematic approach based on reciprocal screw theory. The analysis shows that an n-DOF spring-loaded cable driven open chain still requires a minimum of n+1 cables to fully constrain it. From preliminary analysis, spring placement can have a positive effect on altering the cable tension required and increasing the feasible workspace.
Development of a MR-Compatible Cable-Driven Manipulator: Design and Technological IssuesIn this paper, we focus on the technology issues to be solved to develop a cable-driven robot compatible with Magnetic Resonance Imaging constraints. This study is based on the design of a new compact cable-driven manipulator with remote actuators, initially developed for prostate interventions. One of the originalities of the system is to use an instrumented structure to evaluate the cable tensions and lengths in order to perform an adequate control. The sensors assessment has been experimentally achieved and the necessity to introduce a new control strategy using the developed sensors has been demonstrated.
Application of Unscented Kalman Filter to a Cable Driven Surgical Robot: A Simulation StudyCable driven power transmissions are used in applications such as haptic devices, surgical robots etc. The use of flexible cable based power transmission often causes relative motion between the motor actuator and mechanism joint during operation due to the elasticity of the cable.State-space control methods can be used to improve performance, but may require state estimates. For nonlinear systems, the Unscented Kalman Filter (UKF) provides a computationally efficient way to obtain state estimates. The UKF is applied here to a simulation of a minimially invasive surgical robot, to study the state estimation for a cable driven system with non-linear dynamics. State estimates from the UKF are compared with the known states available from the simulation. These state estimates are also utilized by two different controllers interacting with the simulation to test the UKF performance under closed loop control. We tested the UKF performance with error perturbations in the system model's cable stiffness parameter.
Joint Control of Tendon-Driven Mechanisms with Branching TendonsThis paper proposes a joint control method for tendon-driven mechanisms (TDMs) with branching tendons that are connected to multiple tendons at a point, and which are often found in musculoskeletal systems. TDMs usually require the same number of tendons as actuators, which are one of the heaviest components in a robotics system. The utilization of branching tendons is useful for reducing the number of actuators needed for making lightweight robotic mechanisms, such as prosthetic hands. However, the under-actuation of the branching tendons makes it difficult to accurately control the joint motion of TDMs. Therefore, TDMs with branching tendons have been used only for simple adaptive grasping mechanisms. In this paper, we derive the tendon kinematics of TDMs with branching tendons and design a joint PD controller for the mechanisms. We demonstrate the stability of the control system using Lyapunov's direct method. We show that the bias force setting, which does not appear in conventional TDMs, is important in the realization of accurate control in TDMs with branching tendons. Simulations were performed to evaluate the proposed method.