TechTalks from event: Technical session talks from ICRA 2012

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Biologically Inspired Robotics II

  • Approximating the Stance Map of the SLIP Runner Based on Perturbation Approach Authors: Yu, Haitao; Li, Mantian; Cai, Hegao
    The Spring-Loaded Inverted Pendulum (SLIP), or monopedal runner, is widely used to depict running and hopping in mammalian and human locomotion, which is also serving as a template for running robot design. This classic model describes quite a simple mechanical system. Nevertheless issue of seeking the accurate analytic solution revealing the characteristics of the motion during stance remains unsettled due to the nonintegrable terms contained in the system equations. Moreover, several existing analytic approximations by simply ignoring or linearizing the gravitational force can not reveal the entire dynamical behavior of nonlinear system as well as can be breakdown rapidly when applied to a non-symmetric motion case. In this paper, a novel method with perturbation technique is proposed to obtain analytic approximate solutions to the SLIP dynamics in stance phase with considering the effect of gravity. The perturbation solution achieves higher accuracy in predicting the apex trajectory and stance locomotion by comparing with typical existing analytical approximations. Particularly, our solution is validated for non-symmetric case in a large angle range. Additionally, the prediction for stance trajectory is also verified through numerical evaluation.
  • Analysis of Dynamics and Planar Motion Strategies of a Swimming Microorganism -- Giardia Lamblia Authors: Chen, Jun; Lenaghan, Scott; Zhang, Mingjun
    We studied the dynamics associated with planar swimming in the microorganism Giardia lamblia. Giardia parasitizes the small intestine of humans and other animals, and has evolved a robust attachment and swimming mechanism to survive this harsh environment, which provides potential bio-inspiration for microrobot design. In this paper, a 2D dynamic model of flagella-body-fluid interaction was developed to analyze the actuation of the flagellum, energy supply and dissipation, and thrust along the flagellum. We found that to achieve the observed flagella motion, the required actuation bending moment decreases in magnitude from the proximal to the distal end, and that energy only needs to be supplied to the proximal half portion of the flagellum. The supplied energy is dissipated to the fluid continuously along the flagellum, with almost linearly increasing magnitude towards the distal end. Consistently, thrust mainly comes from the posterior portion of the flagellum. We also analyzed the kinematics of the flagella. The characteristics of the forward and turning motion are revealed through simulation. These results may help the gait planning and actuation for energy efficient propulsion in swimming micro-robotic design.
  • Against the Flow: A Braitenberg Controller for a Fish Robot Authors: Salumae, Taavi; Rano, Inaki; Akanyeti, Otar; Kruusmaa, Maarja
    Underwater vehicles do not localise or navigate with respect to the flow, an ability needed for many underwater tasks. In this paper we implement rheotaxis behaviour in a fish robot, a behaviour common to many aquatic species. We use two pressure sensors on the head of the robot to identify the pressure differences on the left and right side and control the heading of the fish robot by turning a servo-motor actuated tail. The controller is inspired by the Braitenberg vehicle 2b, a simple biological model of tropotaxis, that has been used in many robotic applications. The experiments, conducted in a flow pipe with a uniform flow, show that the robot is able to orient itself, and keep the orientation, to the incoming current. Our results demonstrate that guidance of a fish robot relative to a flow can be implemented as a simple rheotaxis behaviour using two sensors and a Braitenberg 2b controller.
  • Simplified Motion Modeling for Snake Robots Authors: Enner, Florian; Rollinson, David; Choset, Howie
    We present a general method of estimating a snake robot’s motion over flat ground using only knowledge of the robot’s shape changes over time. Estimating world motion of snake robots is often difficult because of the complex way a robot’s cyclic shape changes (gaits) interact with the surrounding environment. By using the virtual chassis to separate the robot’s internal shape changes from its external motions through the world, we are able to construct a motion model based on the differential motion of the robot’s modules between time steps. In this way, we effectively treat the snake robot like a wheeled robot where the bottom-most modules propel the robot in much the way the bottom of the wheels would propel the chassis of a car. Experimental results using a 16-DOF snake robot are presented to demonstrate the effectiveness of this method for a variety of gaits that have been designed to traverse flat ground.
  • Conical Sidewinding Authors: Gong, Chaohui; Hatton, Ross; Choset, Howie
    Sidewinding is an efficient translation gait used by snakes and snake robots over flat ground, and resembles a helical tread moving over a core cylindrical geometry. Most sidewinding research has focused on straight-line translation of the snake, and less on steering capabilities. Here, we offer a new, geometrically intuitive method for steering this gait: Tapering the core cylinder into a cone, such that one end moves faster than the other, changing the heading of the robot as it drives forward. We present several design tools for working with this cone, along with experimental results on a physical robot turning at different rates.
  • Altitude Feedback Control of a Flapping-Wing Microrobot Using an On-Board Biologically Inspired Optical Flow Sensor Authors: Duhamel, Pierre-Emile; Perez-Arancibia, Nestor O; Barrows, Geoffrey; Wood, Robert
    We present experimental results on the controlled vertical flight of a flapping-wing flying microrobot, in which for the first time an on-board sensing system is used for measuring the microrobot's altitude for feedback control. Both the control strategy and the sensing system are biologically inspired. The control strategy relies on amplitude modulation mediated by optical flow. The research presented here is a key step toward achieving the goal of complete autonomy for flying microrobots, since this demonstrates that strategies for controlling flapping-wing microrobots in vertical flight can rely on optical flow sensors.

Underactuated Robots

  • Trajectory Generation for Underactuated Control of a Suspended Mass Authors: Schultz, Jarvis; Murphey, Todd
    The underactuated system under consideration is a magnetically-suspended, differential drive robot with a winch system articulating a suspended mass. A dynamic model of the system is first constructed, and then a nonlinear, infinite-dimensional optimization algorithm is presented. The Lagrangian mechanics based system model uses the principles of kinematic reduction to produce a mixed kinematic-dynamic model that isolates the modeling of the system actuators from the modeling of the rest of the system. In this framework, the inputs become generalized velocities instead of generalized forces facilitating real-world implementation in an embedded system. The optimization algorithm automatically deals with the complexities introduced by the nonlinear dynamics and underactuation to synthesize dynamically feasible system trajectories for a wide array of trajectory generation problems. Applying this algorithm to the mixed kinematic-dynamic model, several example problems are solved and the results are tested experimentally. The experimental results agree quite well with the theoretical showing promise in extending the capabilities of the system to utilize more advanced feedback techniques and to handle more complex, three-dimensional problems.
  • Planning in High-Dimensional Shape Space for a Single-Wheeled Balancing Mobile Robot with Arms Authors: Nagarajan, Umashankar; Kim, Byungjun; Hollis, Ralph
    The ballbot with arms is an underactuated balancing mobile robot that moves on a single ball. Achieving desired motions in position space is a challenging task for such systems due to their unstable zero dynamics. This paper presents a novel approach that uses the dynamic constraint equations to plan shape trajectories, which when tracked will result in optimal tracking of desired position trajectories. The ballbot with arms has shape space of higher dimension than its position space and therefore, the procedure uses a user-defined weight matrix to choose between the infinite number of possible combinations of shape trajectories to achieve a particular desired trajectory in position space. Experimental results are shown on the real robot where different motions in position space are achieved by tracking motions of either the body lean angles, or the arm angles or combinations of both.
  • Integrated Planning and Control for Graceful Navigation of Shape-Accelerated Underactuated Balancing Mobile Robots Authors: Nagarajan, Umashankar; Kantor, George; Hollis, Ralph
    This paper presents controllers called motion policies that achieve fast, graceful motions in small, collision-free domains of the position space for balancing mobile robots like the ballbot. The motion policies are designed such that their valid compositions will produce overall graceful motions. An automatic instantiation procedure deploys motion policies on a 2D map of the environment to form a library and the validity of their composition is given by a gracefully prepares graph. Dijsktra's algorithm is used to plan in the space of these motion policies to achieve the desired navigation task. A hybrid controller is used to switch between the motion policies. The results of successful experimental testing of two navigation tasks, namely, point-point and surveillance motions on the ballbot platform are presented.
  • Differentially Flat Design of a Closed-Chain Planar Under-Actuated 2 DOF System Authors: Zhang, Chengkun; Franch, Jaume; Agrawal, Sunil
    This paper investigates when a 2 degree-offreedom PRRRP closed-chain system with a single actuator is both strongly accessible and feedback linearizable. It is demonstrated that for certain choices of mass distribution and addition of springs, an under-actuated 2 DOF PRRRP system is static feedback linearizable, i.e., also differentially flat.
  • Design of Energy Efficient Walking Gaits for a Three-Link Planar Biped Walker with Two Unactuated Degrees of Freedom Authors: Ortiz Morales, Daniel; La Hera, Pedro
    We consider the example of a three-link planar biped walker with two passive links. The main objective is to design symmetric periodic gaits in flat ground, that can be exponentially stabilized by feedback control. To this end, we apply recent advances in nonlinear control, to propose a systematic procedure to the problems of gait synthesis and control design. The core of the method lays on a nontrivial coordinate transformation, in order to approach the problem in a state-dependent form. For gait synthesis, such procedure allows a reduction of the search space, with the feasibility of considering energetic performance for optimization. For control design, this allows to apply concepts of transverse linearization, to design a nonlinear feedback control law, which performance is studied by numerical simulations.
  • Biped Walking Stabilization Based on Gait Analysis Authors: Hashimoto, Kenji; Takezaki, Yuki; Motohashi, Hiromitsu; Lim, Hun-ok; Takanishi, Atsuo
    This paper describes a walking stabilization control based on gait analysis for a biped humanoid robot. We have developed a human-like foot mechanism mimicking the medial longitudinal arch to clarify the function of the foot arch structure. To evaluate the arch function through walking experiments using a robot, a walking stabilization control should also be designed based on gait analysis. Physiologists suggest the ankle, hip and stepping strategies, but these strategies are proposed by measuring human beings who are not "walking" but "standing" against force disturbances. Therefore, first we conducted gait analysis in this study, and we modeled human walking strategy enough to be implemented on humanoid robots. We obtained following two findings from gait analysis: i) a foot-landing point exists on the line joining the stance leg and the projected point of CoM on the ground, and ii) the distance between steps is modified to keep mechanical energy at the landing within a certain value. A walking stabilization control is designed based on the gait analysis. Verification of the proposed control is conducted through experiments with a human-sized humanoid robot WABIAN-2R. The experimental videos are supplemented.

Animation & Simulation

  • Conditions for Uniqueness in Simultaneous Impact with Application to Mechanical Design Authors: Seghete, Vlad; Murphey, Todd
    We present a collision resolution method based on momentum maps and show how it extends to handling multiple simultaneous collisions. Simultaneous collisions, which are common in robots that walk or climb, do not necessarily have unique outcomes, but we show that for special configurations—--e.g. when the surfaces of contact are orthogonal in the appropriate sense—--simultaneous impacts have unique outcomes, making them considerably easier to understand and simulate. This uniqueness helps us develop a measure of the unpredictability of the impact outcome based on the state at impact and is used for gait and mechanism design, such that a mechanism’s actions are more predictable and hence controllable. As a preliminary example, we explore the configuration space at impact for a model of the RHex running robot and find optimal configurations at which the unpredictability of the impact outcome is minimized.
  • Dynamics Simulation for the Training of Teleoperated Retrieval of Spent Nuclear Fuel Authors: Cornella, Jordi; Zerbato, Davide; Giona, Luca; Fiorini, Paolo; Sequeira, Vitor
    This paper addresses the problem of training of operators for telemanipulation tasks. In particular it describes the development of a physics based virtual environment that allows a user to train in the control of an innovative robotic tools designed for the retrieval of spent nuclear fuels. The robotic device is designed to adapt to very different environments, at the cost of an increased complexity in its control. The virtual environment provides realistic simulation of robot dynamics. The two most challenging tasks related to robot control have been identified and implemented in the simulation, leading to an effective tool for the training. The developed application is described in details and the outcome of one simulated intervention is proposed and analyzed in terms of user interaction and realism.
  • Putting the Fish in the Fish Tank: Immersive VR for Animal Behavior Experiments Authors: Butail, Sachit; Paley, Derek; Chicoli, Amanda
    We describe a virtual-reality framework for investigating startle-response behavior in fish. Using real-time three-dimensional tracking, we generate looming stimuli at a specific location on a computer screen, such that the shape and size of the looming stimuli change according to the fish's perspective and location in the tank. We demonstrate the effectiveness of the setup through experiments on Giant danio and compute the success rate in eliciting a response. We also estimate visual startle sensitivity by presenting the stimulus from different directions around the fish head. The aim of this work is to provide the basis for quantifying escape behavior in fish schools.
  • Design and Implementation of Dynamic Simulators for the Testing of Inertial Sensors Authors: allotta, benedetto; Becciolini, Lorenzo; Costanzi, Riccardo; Giardi, Francesca; Ridolfi, Alessandro; Vettori, Gregorio
    Many dynamic simulators have been developed in the last thirty years for different types of vehicles. Flight simulators and drive simulators are very well known examples. This paper describes the design and implementation of a dynamic simulator for the testing of inertial sensors devoted to vehicle navigation through a Hardware-In-The-Loop test rig composed of an industrial robot and a commercially available Inertial Measurement Unit (IMU). The authors are developing an innovative localization algorithm for railway vehicles which integrates inertial sensors with tachometers. The opportunity to set up a testing simulator capable of replicating in a realistic fashion the dynamic effects of the vehicle motion on inertial sensors allows to avoid expensive on board acquisitions and to speed up algorithm tuning. The real-time control architecture featured by the available industrial robot allows to precisely specify and execute motion trajectories with tight path and time law constraints required by the application at hand.
  • Automatic Data Driven Vegetation Modeling for Lidar Simulation Authors: Deschaud, Jean-Emmanuel; Prasser, David; Dias, M. Freddie; Browning, Brett; Rander, Peter
    Traditional lidar simulations render surface models to generate simulated range data. For objects with well-defined surfaces, this approach works well, and traditional 3D scene reconstruction algorithms can be employed to automatically generate the surface models. This approach breaks down, though, for many trees, tall grasses, and other objects with fine-scale geometry: surface models do not easily represent the geometry, and automated reconstruction from real data is difficult. In this paper, we introduce a new stochastic volumetric model that better captures the complexities of real lidar data of vegetation and is far better suited for automatic modeling of scenes from field collected lidar data. We also introduce several methods for automatic modeling and for simulating lidar data utilizing the new model. To measure the performance of the stochastic simulation we use histogram comparison metrics to quantify the differences between data produced by the real and simulated lidar. We evaluate our approach on a range of real world datasets and show improved fidelity for simulating geo-specific outdoor, vegetation scenes.
  • Simulation of Tactile Sensors Using Soft Contacts for Robot Grasping Applications Authors: Moisio, Sami; Leon, Beatriz; Korkealaakso, Pasi; Morales, Antonio
    In the context of robot grasping and manipulation, realistic simulation requires accurate modeling of contacts between bodies and, in a practical level, accurate simulation of touch sensors. This paper addresses the problem of simulating a tactile sensor considering soft contacts and full friction description. The developed model consists of a surface contact patch described by a mesh of contact elements. For each element, a full friction description is built considering stick-slip phenomena. The model is then implemented and used to perform typical tasks related to tactile sensors. The performance of the simulated sensor is then compared to a real one. It is also demonstrated how it can be integrated on the simulation of a complete robot grasping system.