TechTalks from event: Technical session talks from ICRA 2012

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Sampling-Based Motion Planning

  • A Scalable Method for Parallelizing Sampling-Based Motion Planning Algorithms Authors: Jacobs, Sam Ade; Burgos, Juan; Manavi, Kasra; Denny, Jory; Thomas, Shawna; Amato, Nancy
    This paper describes a scalable method for parallelizing sampling-based motion planning algorithms. It subdivides configuration space (C-space) into (possibly overlapping) regions and independently, in parallel, uses standard (sequential) sampling-based planners to construct roadmaps in each region. Next, in parallel, regional roadmaps in adjacent regions are connected to form a global roadmap. By subdividing the space and restricting the locality of connection attempts, we reduce the work and inter-processor communication associated with nearest neighbor calculation, a critical bottleneck for scalability in existing parallel motion planning methods. We show that our method is general enough to handle a variety of planning schemes, including the widely used Probabilistic Roadmap (PRM) and Rapidly-exploring Random Trees (RRT) algorithms.We compare our approach to two other existing parallel algorithms and demonstrate that our approach achieves better and more scalable performance. Our approach achieves almost linear scalability on a 2400 core LINUX cluster and on a 153,216 core Cray XE6 petascale machine.
  • LQR-RRT*: Optimal Sampling-Based Motion Planning with Automatically Derived Extension Heuristics Authors: Perez, Alejandro; Platt, Robert; Konidaris, George Dimitri; Kaelbling, Leslie; Lozano-Perez, Tomas
    The RRT* algorithm has recently been proposed as an optimal extension to the standard RRT algorithm [1]. However, like RRT, RRT* is difficult to apply in problems with complicated or underactuated dynamics because it requires the design of a two domain-specific extension heuristics: a distance metric and node extension method. We propose automatically deriving these two heuristics for RRT* by locally linearizing the domain dynamics and applying linear quadratic regulation (LQR). The resulting algorithm, LQR-RRT*, finds optimal plans in domains with complex or underactuated dynamics without requiring domain-specific design choices. We demonstrate its application in domains that are successively torquelimited, underactuated, and in belief space.
  • SR-RRT: Selective Retraction-Based RRT Planner Authors: Lee, Junghwan; Kwon, Osung; Zhang, Liangjun; Yoon, Sung-eui
    We present a novel retraction-based planner, selective retraction-based RRT, for efficiently handling a wide variety of environments that have different characteristics. We first present a bridge line-test that can identify regions around narrow passages, and then perform an optimizationbased retraction operation selectively only at those regions. We also propose a non-colliding line-test, a dual operator to the bridge line-test, as a culling method to avoid generating samples near wide-open free spaces and thus to generate more samples around narrow passages. These two tests are performed with a small computational overhead and are integrated with a retraction-based RRT. In order to demonstrate benefits of our method, we have tested our method with different benchmarks that have varying amounts of narrow passages. Our method achieves up to 21 times and 3.5 times performance improvements over a basic RRT and an optimizationbased retraction RRT, respectively. Furthermore, our method consistently improves the performances of other tested methods across all the tested benchmarks that have or do not have narrow passages.
  • Sampling-Based Motion Planning with Dynamic Intermediate State Objectives: Application to Throwing Authors: Zhang, Yajia; Luo, Jingru; Hauser, Kris
    Dynamic manipulations require attaining high velocities at specified configurations, all the while obeying geometric and dynamic constraints. This paper presents a motion planner that constructs a trajectory that passes at an intermediate state through a dynamic objective region, which is comprised of a certain lower dimensional submanifold in the configuration/velocity state space, and then returns to rest. Planning speed and reliability is greatly improved using optimizations based on the fact that ramp-up and ramp-down subproblems are coupled by the choice of intermediate state, and that very few (often less than 1%) intermediate states yield feasible solution trajectories. Simulation experiments demonstrate that our method quickly generates trajectories for a 6-DOF industrial manipulator throwing a small object.
  • Towards Small Asymptotically Near-Optimal Roadmaps Authors: Marble, James; Bekris, Kostas E.
    An exciting recent development is the definition of sampling-based motion planners which guarantee asymptotic optimality. Nevertheless, roadmaps with this property may grow too large and lead to longer query resolution times. If optimality requirements are relaxed, existing asymptotically near-optimal solutions produce sparser graphs by removing redundant edges. Even these alternatives, however, include all sampled configurations as nodes in the roadmap. This work proposes a method, which can reject redundant samples but does provide asymptotic coverage and connectivity guarantees, while keeping local path costs low. Not adding every sample can significantly reduce the size of the final roadmap. An additional advantage is that it is possible to define a reasonable stopping criterion for the approach inspired by previous methods. To achieve these objectives, the proposed method maintains a dense graph that is used for evaluating the performance of the roadmap with regards to local path costs. Experimental results show that the method indeed provides small roadmaps, allowing for shorter query resolution times. Furthermore, smoothing the final paths results in an even more advantageous comparison against alternatives with regards to path quality.
  • Proving Path Non-Existence Using Sampling and Alpha Shapes Authors: McCarthy, Zoe; Bretl, Timothy; Hutchinson, Seth
    In this paper, we address the problem determining the connectivity of a robot's free configuration space. Our method iteratively builds a constructive proof that two configurations lie in disjoint components of the free configuration space. Our algorithm first generates samples that correspond to configurations for which the robot is in collision with an obstacle. These samples are then weighted by their generalized penetration distance, and used to construct alpha shapes. The alpha shape defines a collection of simplices that are fully contained within the configuration space obstacle region. These simplices can be used to quickly solve connectivity queries, which in turn can be used to define termination conditions for sampling-based planners. Such planners, while typically either resolution complete or probabilistically complete, are not able to determine when a path does not exist, and therefore would otherwise rely on heuristics to determine when the search for a free path should be abandoned. An implementation of the algorithm is provided for the case of a 3D Euclidean configuration space, and a proof of correctness is provided.

Minimally Invasive Interventions II

  • Configuration Comparison for Surgical Robotic Systems Using a Single Access Port and Continuum Mechanisms Authors: Zheng, Xidian; Xu, Kai
    Research on robot-assisted laparoscopic SPA (Single Port Access) surgery and N.O.T.E.S (Natural Orifice Translumenal Endoscopic Surgery) have thrived in the past a few years. A configuration similarity between these surgical robotic slaves is that two robotic arms are extended from the same access port (either a laparoscope or an endoscope) for surgical interventions. However, upon designing such a surgical robotic slave, the structure of the extended robotic arms has not been explored thoroughly based on evaluation of their distal dexterity. This paper presents a simulation-based comparison among three different structures which could be used to form these extended robotic arms. Results presented in this paper could serve as a design reference for surgical robotic slaves which use a single access port and continuum mechanisms.
  • Control of Untethered Magnetically Actuated Tools Using a Rotating Permanent Magnet in Any Position Authors: Mahoney, Arthur; Cowan, Daniel Lewis; Miller, Katie; Abbott, Jake
    It has been shown that when a magnetic dipole, such as a permanent magnet, is rotated around a fixed axis such that the dipole is perpendicular to the axis of rotation, the magnetic field vector at every point in space also rotates around a fixed axis. In this paper, we reformulate this phenomenon using linear algebraic techniques, which enables us to find the necessary dipole rotation axis to make the magnetic field at any desired point in space rotate about any desired axis. To date, untethered magnetically actuated tools (e.g., capsule endoscopes, rolling spheres, and helical-propeller microswimmers) controlled with a single rotating permanent magnet have been constrained to operate in positions where the rotating field behavior is simple and easy to visualize. We experimentally demonstrate that the results of this paper can be used to control a variety of untethered, rotating magnetic devices in any position even while the rotating permanent magnet follows trajectories independent of the devices themselves. This method constitutes a substantial step toward making a great deal of prior laboratory research regarding rotating magnetic microrobots and capsule endoscopes clinically feasible.
  • Integration and Preliminary Evaluation of an Insertable Robotic Effectors Platform for Single Port Access Surgery Authors: Bajo, Andrea; Goldman, Roger E.; Wang, Long; Fowler, Dennis; Simaan, Nabil
    In this paper, we present the integration and preliminary evaluation of a novel Insertable Robotic Effectors Platform (IREP) for Single Port Access Surgery (SPAS). The unique design of the IREP includes planar parallel mechanisms, continuum snake-like arms, wire-actuated wrists, and passive flexible components. While this design has advantages, it presents challenges in terms of modeling, control, and telemanipulation. The complete master-slave resolved-rates telemanipulation framework of the IREP along with its actuation compensation is presented. Experimental evaluation of the capabilities of this new surgical system include bi-manual exchange of rings, pick-and-place tasks, suture passing and knot tying. Results show that the IREP meets the minimal workspace and dexterity requirements specified for laparoscopic surgery, it allows for dual-arm operations such as tool exchange and knot tying in confined spaces. Although it was possible to tie a surgeon's knot with minimal training, suture passing was difficult due to the limited axial rotation of the distal wrists.
  • Constrained Filtering with Contact Detection Data for the Localization and Registration of Continuum Robots in Flexible Environments Authors: Tully, Stephen; Bajo, Andrea; Kantor, George; Choset, Howie; Simaan, Nabil
    This paper presents a novel filtering technique that uses contact detection data and environmental stiffness estimates to register and localize a robot with respect to an a priori 3D surface model. The algorithm leverages geometric constraints within a Kalman filter framework and relies on two distinct update procedures: 1) an equality constrained step for when the robot is forcefully contacting the environment, and 2) an inequality constrained step for when the robot lies in the freespace of the environment. This filtering procedure registers the robot by incrementally eliminating probabilistically infeasible state space regions until a high likelihood solution emerges. In addition to registration and localization, the algorithm can estimate the deformation of the surface model and can detect false positives with respect to contact estimation. This method is experimentally evaluated with an experiment involving a continuum robot interacting with a bench-top flexible structure. The presented algorithm produces an experimental error in registration (with respect to the end-effector position) of 1.1 mm, which is less than 0.8 percent of the robot length.
  • Real-Time Control Architecture of a Novel Single-Port Laparoscopy Bimanual Robot (SPRINT) Authors: Niccolini, Marta; Petroni, Gianluigi; Menciassi, Arianna; Dario, Paolo
    This paper presents a novel master-slave teleoperated robotic platform designed for Single Port Laparoscopy. The SPRINT (Single-Port lapaRoscopy bimaNual roboT) is composed of two high-dexterity 6 Degrees of Freedom (DOFs) robotic arms, a stereoscopic camera and a dedicated console for the robot control by the surgeon. Along with a short summary of the hardware features of the system, this paper describes the real-time control architecture of the SPRINT. Particular attention was given to the kinematic coupling between the master and the slave manipulators, as well as to the inverse kinematics algorithm. Tests performed to validate the performance of the robot in terms of accuracy are satisfactory, thus positioning the SPRINT as a candidate for the next generation of robots for Single Port Laparoscopy.
  • Remote Centre-Of-Motion Control Algorithms of 6-RRCRR Parallel Robot Assisted Surgery System (PRAMiSS) Authors: Moradi Dalvand, Mohsen; Shirinzadeh, Bijan
    In this paper a 6-RRCRR parallel robot assisted minimally invasive surgery/microsurgery system (PRAMiSS) is introduced. Remote centre-of-motion (RCM) control algorithms of PRAMiSS suitable for minimally invasive surgery and microsurgery are also presented. The programmable RCM approach is implemented in order to achieve manipulation under the constraint of moving through the fixed penetration point. Having minimised the displacements of the mobile platform of the parallel micropositioning robot, the algorithms also apply orientation constraint to the instrument and prevent the tool tip to orient due to the robot movements during the manipulation. Experimental results are provided to verify accuracy and effectiveness of the proposed RCM control algorithms for minimally invasive surgery.

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.