TechTalks from event: Technical session talks from ICRA 2012

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Cable-Driven Mechanisms

  • Novel Equilibrium-Point Control of Agonist-Antagonist System with Pneumatic Artificial Muscles Authors: Ariga, Yohei; Uemura, Mitsunori; Hirai, Hiroaki; Miyazaki, Fumio
    This 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 Robot Authors: Gosselin, Clement; Ren, Ping
    This 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 Placements Authors: Mustafa, Shabbir Kurbanhusen; Agrawal, Sunil
    While 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 Issues Authors: Abdelaziz, Salih; Esteveny, Laure; Barbé, laurent; Renaud, Pierre; Bayle, Bernard; de Mathelin, Michel
    In 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 Study Authors: Ramadurai, Srikrishnan; Nia Kosari, Sina; King, H. Hawkeye; Chizeck, Howard; Hannaford, Blake
    Cable 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 Tendons Authors: Sawada, Daisuke; Ozawa, Ryuta
    This 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.

Parallel Robots

  • Simplified Static Analysis of Large-Dimension Parallel Cable-Driven Robots Authors: Gouttefarde, Marc; Collard, Jean-François; Riehl, Nicolas; Baradat, Cédric
    This paper introduces a new simplified static analysis of parallel robots driven by inextensible cables of non-negligible mass. It is based on a known hefty cable static modeling which seems to have been overlooked in previous works on parallel cable-driven robots. This cable modeling is obtained from a well-known sagging cable modeling, known as the catenary, by assuming that cable sag is relatively small. The use of the catenary has been shown to lead to a non-linear set of equations describing the kinetostatic behavior of parallel robots driven by cables of non-negligible mass. On the contrary, the proposed simplified static analysis yields a linear relationship between (components of) the forces in the cables and the external wrench applied to the robot mobile platform. As a consequence, by means of the simplified static analysis, useful wrench-based analysis and design techniques devised for parallel robots driven by massless cables can now be extended to cases in which cable mass is to be accounted for.
  • Design Optimization for Parallel Mechanism Using on Human Hip Joint Power Assisting Based on Manipulability Inclusive Principle Authors: Yu, Yong; LIANG, WenYuan
    This paper summarizes the design optimization of a parallel mechanism using on human hip joint power assisting. Manipulability Inclusive Principle (MIP) evaluation criterion for evaluating assisting mechanism's assisting feasibility and assisting effect is proposed. The design of parallel assisting mechanism and building kinematical Jacobian are discussed. Moreover, as an important part of this paper, in order to finding out a architecture, which can satisfy assisting feasibility and realize higher assisting efficiency, more assisting ability and better feature on assisting isotropy, design optimization MIP is shown in this paper.
  • The Kinematics of the Redundant $N-1$ Wire Driven Parallel Robot Authors: Merlet, Jean-Pierre
    We address the kinematics of the redundant N-1 wire-driven parallel robot, i.e. a robot with N > 3 wires connected at the same point on the platform. The redundancy allows one to increase the workspace size. But we show, both theoretically and experimentally that if the wires are not elastic, then the redundancy cannot be used to control the wire tensions. Indeed we show that whatever are the number of wires there will always be only at most 3 wires in tension, while the other N-3 wires will be slack. We then show that if the wires are elastic, then the platform positioning will be very sensitive to stiffness identification and wire lengths control. Hence classical redundant control schemes are difficult to use for such robot and alternate use of the geometry of redundant wires have to be considered.
  • Error Modeling and Accuracy Analysis of a Multi-Level Hybrid Support Robot Authors: Chai, Xiaoming; Tang, Xiaoqiang; Tang, Lewei; Lu, Qiujian
    As for the multi-level hybrid feed support robot in the Five-hundred-meter Aperture Spherical radio Telescope (FAST), the cabin's time-varying barycenter and structural deformation are main factors causing the terminal receivers’ pose error. In order to ensure tracking accuracy of astronomical observations, firstly the elasticity model of the cable-driven Stewart manipulator is deduced to analyze the terminal error caused by the gravity torque. Newton-Raphson method is adopted to acquire the terminal error range and propose compensation strategy. Then error model considering structural deformation is formulated and the terminal accuracy is analyzed with an improved set theory based method. Finally the sensitivity analysis is also carried out and accuracy synthesis is implemented. Error modeling and analysis method proposed for the support robot in this paper can also be used to other complex hybrid robots with either large dimension or heavy duty.
  • Point-To-Point Motion Planning of a Parallel 3-DOF Underactuated Cable-Suspended Robot Authors: Zoso, Nathaniel; Gosselin, Clement
    This paper presents a planar parallel three-degree-of-freedom underactuated cable-driven robot. The mechanism is first described and a dynamic model is derived. One of the advantages of the proposed mechanism is that it does not require any mechanical (e.g. pulleys) or electrical (e.g. actuators) hardware to be mounted on the end-effector. A trajectory planning approach is developed, which is based on the natural frequency of the pendulum-like free motion (unconstrained degree of freedom). Sine-like excitation functions are used and their frequency and phase delay are determined using simulation results. A prototype is then described and experimental results are provided together with a video clip of an example trajectory. The results confirm that the mechanism can be effectively used for point-to-point trajectories.

SLAM II

  • Efficient Data-Driven MCMC Sampling for Vision-Based 6D SLAM Authors: Min, Jihong; Kim, Jungho; Shin, Seunghak; Kweon, In So
    In this paper, we propose a Markov Chain Monte Carlo (MCMC) sampling method with the data-driven proposal distribution for six-degree-of-freedom (6-DoF) SLAM. Recently, visual odometry priors have been widely used as the process model in the SLAM formulation to improve the SLAM performance. However, modeling the uncertainties of incremental motions estimated by visual odometry is especially difficult under challenging conditions, such as erratic motion. For a particle-based model representation, it can represent the uncertainty of the camera motion well under erratic motion compared to the constant velocity model or a Gaussian noise model, but the manner of representing the proposal distribution and sampling the particles is extremely important, as we can maintain only a limited number of particles in the high-dimensional state space. Hence, we propose an effective sampling approach by exploiting MCMC sampling and the data-driven proposal distribution to propagate the particles. We demonstrate the performance of the proposed approach for 6-DoF SLAM using both synthetic and real datasets and compare the performance with those of other sampling methods.
  • Scan Segments Matching for Pairwise 3D Alignment Authors: Douillard, Bertrand; Quadros, Alastair James; Morton, Peter; Underwood, James Patrick; De Deuge, Mark; Hugosson, Simon; Hallström, Manfred; Bailey, Tim
    This paper presents a method for pairwise 3D alignment which solves data association by matching scan segments across scans. Generating accurate segment associations allows to run a modified version of the Iterative Closest Point (ICP) algorithm where the search for point-to-point correspondences is constrained to associated segments. The novelty of the proposed approach is in the segment matching process which takes into account the proximity of segments, their shape, and the consistency of their relative locations in each scan. Scan segmentation is here assumed to be given (recent studies provide various alternatives). The method is tested on seven sequences of Velodyne scans acquired in urban environments. Unlike various other standard versions of ICP, which fail to recover correct alignment when the displacement between scans increases, the proposed method is shown to be robust to displacements of several meters. In addition, it is shown to lead to savings in computational times which are potentially critical in real-time applications.
  • Planar Surface SLAM with 3D and 2D Sensors Authors: Trevor, Alexander J B; Rogers III, John G.; Christensen, Henrik Iskov
    We present an extension to our feature based mapping technique that allows for the use of planar surfaces such as walls, tables, counters, or other planar surfaces as landmarks in our mapper. These planar surfaces are measured both in 3D point clouds, as well as 2D laser scans. These sensing modalities compliment each other well, as they differ significantly in their measurable fields of view and maximum ranges. We present experiments to evaluate the contributions of each type of sensor.
  • Uncertainty Estimation for a 6-DoF Spectral Registration Method As Basis for Sonar-Based Underwater 3D SLAM Authors: Pfingsthorn, Max; Birk, Andreas; Buelow, Heiko
    An uncertainty estimation method for 6 degree of freedom (6-DoF) spectral registration is introduced here. The underlying 6-DoF registration method based on Phase Only Matched Filtering (POMF) is capable of dealing with very noisy sensor data. It is hence well suited for 3D underwater mapping, where relatively inaccurate sonar imaging devices have to be employed. An uncertainty estimation method is required to use this registration method in a Simultaneous Localization and Mapping (SLAM) framework. To our knowledge, the first such method for 6-DoF spectral registration is presented here. This new uncertainty estimation method treats the POMF results as probability mass functions (PMF). Due to the decoupling in the underlying method, yaw is computed by a one-dimensional POMF leading hence to a 1D PMF; roll and pitch are simultaneously computed and hence encoded in a 2D PMF. Furthermore, a 3D PMF is generated for the translation as it is determined by a 3D POMF. A normal distribution is fitted on each of the PMF to get the uncertainty estimate. The method is experimentally evaluated with simulated as well as real world sonar data. It is shown that it indeed can be used for SLAM, which significantly improves the map quality.
  • Interactive Acquisition of Residential Floor Plans Authors: Kim, Young Min; Dolson, Jennifer; Sokolsky, Michael; Koltun, Vladlen; Thrun, Sebastian
    We present a hand-held system for real-time, interactive acquisition of residential floor plans. The system integrates a commodity range camera, a micro-projector, and a button interface for user input and allows the user to freely move through a building to capture its important architectural elements. The system uses the Manhattan world assumption, which posits that wall layouts are rectilinear. This assumption allows generating floor plans in real time, enabling the operator to interactively guide the reconstruction process and to resolve structural ambiguities and errors during the acquisition. The interactive component aids users with no architectural training in acquiring wall layouts for their residences. We show a number of residential floor plans reconstructed with the system.
  • CFastSLAM: A New Jacobian Free Solution to SLAM Problem Authors: Song, Yu; Li, Qingling; Kang, Yifei
    While FastSLAM algorithm is a popular solution to SLAM problem, it suffers from two major drawbacks: one is particle set degeneracy due to lack of observation information in proposal distribution; the other is errors accumulation caused by inaccuracy linearization of the robot motion model and the observation model. To overcome the problems, we propose a new Jacobian free CFastSLAM algorithm. The main contribution of this work lies in the utilization of Cubature Kalman Filter (CKF), which calculate Gaussian Weight Integral based on Cubature Rule, to design an optimal proposal distribution of the particle filter and to estimate the environment feature landmarks. On the basis of Rao-Blackwellized particle filter, proposed algorithm is comprised by two main parts: in the first part, a Cubature Particle Filter (CPF) is derived to localize the robot; in the second part, a set of CKFs is used to estimate the environment landmarks. The performance of the CFastSLAM is investigated and compared with that of FastSLAM2.0 and UFastSLAM in simulations and experiments. Results verify that the CFastSLAM improves SLAM performance.