TechTalks from event: Technical session talks from ICRA 2012

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Trajectory Planning and Generation

  • Optimal Acceleration-Bounded Trajectory Planning in Dynamic Environments Along a Specified Path Authors: Johnson, Jeffrey; Hauser, Kris
    Vehicles that cross lanes of traffic encounter the problem of navigating around dynamic obstacles under actuation constraints. This paper presents an optimal, exact, polynomial-time planner for optimal bounded-acceleration trajectories along a fixed, given path with dynamic obstacles. The planner constructs reachable sets in the path-velocity-time (PVT) space by propagating reachable velocity sets between obstacle tangent points in the path-time (PT) space. The terminal velocities attainable by endpoint-constrained trajectories in the same homotopic class are proven to span a convex interval, so the planner merges contributions from individual homotopic classes to find the exact range of reachable velocities and times at the goal. A reachability analysis proves that running time is polynomial given reasonable assumptions, and empirical tests demonstrate that it scales well in practice and can handle hundreds of dynamic obstacles in a fraction of a second on a standard PC.
  • Robot Excitation Trajectories for Dynamic Parameter Estimation Using Optimized B-Splines Authors: Rackl, Wolfgang; Lampariello, Roberto; Hirzinger, Gerd
    In this paper we adressed the problem of finding exciting trajectories for the identification of manipulator link inertia parameters. This can be formulated as a constraint nonlinear optimization problem. The new approach in the presented method is the parameterization of the trajectories with optimized B-splines. Experiments are carried out on a 7 joint Light-Weight robot with torque sensoring in each joint. Thus, unmodeled joint friction and noisy motor current measurements must not be taken into account here. The estimated dynamic model is verified on a different validation trajectory. The results show a clearly improvement of the estimated dynamic model compared to a CAD-valued model.
  • On-Line Trajectory Generation: Nonconstant Motion Constraints Authors: Kroeger, Torsten
    A concept of on-line trajectory generation for robot motion control systems enabling instantaneous reactions to unforeseen sensor events was introduced in a former publication. This previously proposed class of algorithms requires constant kinematic motion constraints, and this paper extends the approach by the usage of time-variant motion constraints, such that low-level trajectory parameters can now abruptly be changed, and the system can react instantaneously within the same control cycle (typically one millisecond or less). This feature is important for instantaneous switchings between state spaces and reference frames at sensor-dependent instants of time, and for the usage of the algorithm as a control submodule in a hybrid switched robot motion control system. Real-world experimental results of two sample use-cases highlight the practical relevance of this extension.
  • Setpoint Scheduling for Autonomous Vehicle Controllers Authors: Au, Tsz-Chiu; Quinlan, Michael; Stone, Peter
    This paper considers the problem of controlling an autonomous vehicle to arrive at a specific position on a road at a given time and velocity. This ability is particularly useful for a recently introduced autonomous intersection management protocol, called AIM, which has been shown to lead to lower delays than traffic signals and stop signs. Specifically, we introduce a setpoint scheduling algorithm for generating setpoints for the PID controllers for the brake and throttle actuators of an autonomous vehicle. The algorithm constructs a feasible setpoint schedule such that the vehicle arrives at the position at the correct time and velocity. Our experimental results show that the algorithm outperforms a heuristic-based setpoint scheduler that does not provide any guarantee about the arrival time and velocity.
  • A Real-Time Motion Planner with Trajectory Optimization for Autonomous Vehicles Authors: Xu, Wenda; Wei, Junqing; Dolan, John M.; Zhao, Huijing; Zha, Hongbin
    In this paper, an efficient real-time autonomous driving motion planner with trajectory optimization is proposed. The planner first discretizes the plan space and searches for the best trajectory based on a set of cost functions. Then an iterative optimization is applied to both the path and speed of the resultant trajectory. The post-optimization is of low computational complexity and is able to converge to a higherquality solution within a few iterations. Compared with the planner without optimization, this framework can reduce the planning time by 52% and improve the trajectory quality. The proposed motion planner is implemented and tested both in simulation and on a real autonomous vehicle in three different scenarios. Experiments show that the planner outputs highquality trajectories and performs intelligent driving behaviors.
  • Improved Non-Linear Spline Fitting for Teaching Trajectories to Mobile Robots Authors: Sprunk, Christoph; Lau, Boris; Burgard, Wolfram
    In this paper, we present improved spline fitting techniques with the application of trajectory teaching for mobile robots. Given a recorded reference trajectory, we apply non-linear least-squares optimization to accurately approximate the trajectory using a parametric spline. The fitting process is carried out without fixed correspondences between data points and points along the spline, which improves the fit especially in sharp curves. By using a specific path model, our approach requires substantially fewer free parameters than standard approaches to achieve similar residual errors. Thus, the generated paths are ideal for subsequent optimization to reduce the time of travel or for the combination with autonomous planning to evade obstacles blocking the path. Our experiments on real-world data demonstrate the advantages of our method in comparison with standard approaches.

Image-Guided Interventions

  • Full state visual forceps tracking under a microscope using projective contour models Authors: Baek, Young Min; Tanaka, Shinichi; Harada, Kanako; Sugita, Naohiko; Morita, Akio; Sora, Shigeo; Mochizuki, Ryo; Mitsuishi, Mamoru
    Forceps tracking is an important element of high-level surgical assistance such as visual servoing and surgical motion analysis. In many computer vision algorithms, artificial markers are used to enable robust tracking; however, markerless tracking methods are more appropriate in surgical applications due to their sterilizability. This paper describes a robust, efficient tracking algorithm capable of estimating the full state parameters of a robotic surgical instrument on the basis of projective contour modeling using a 3-D CAD model of the forceps. Thus, the proposed method does not require any artificial markers. The likelihood of the contour model was measured using edge distance transformation to evaluate the similarity of the projected CAD model to the microscopic image, followed by particle filtering to estimate the full state of the forceps. Experimental results in simulated surgical environments indicate that the proposed method is robust and time-efficient, and fulfills real-time processing requirements.
  • MARVEL: A Wireless Miniature Anchored Robotic Videoscope for Expedited Laparoscopy Authors: Castro, Cristian; Smith, Sara; Alqassis, Adham; Ketterl, Thomas; Sun, Yu; Ross, Sharona; Rosemurgy, Alexander; Savage, Peter; Gitlin, Richard
    This paper describes the design and implementation of a Miniature Anchored Robotic Videoscope for Expedited Laparoscopy (MARVEL) camera module that features wireless communications and control. This device decreases the surgical-tool bottleneck experienced by surgeons in state-of-the art Laparoscopic Endoscopic Single-Site (LESS) procedures for minimally invasive abdominal surgery. The system includes: (1) a near-zero latency wireless communications link, (2) a pan/tilt camera platform, actuated by two tiny motors that gives surgeons a full field of view inside the abdominal cavity, (3) a small wireless camera, (4) a wireless luminosity control system, and (5) a wireless human-machine interface to control the device. An in-vivo experiment on a porcine subject was carried out to test the general performance of the system. The robotic design is a proof of concept, which creates a research platform for a broad range of experiments in a range of domains for faculty and students in the Colleges of Engineering and Medicine and at Tampa General Hospital. This research is the first step in developing semi-autonomous wirelessly controllable and observable communicating and networked laparoscopic devices to enable a paradigm shift in minimally invasive surgery.
  • Motion Planning for the Virtual Bronchoscopy Authors: Rosell, Jan; Pérez, Alexander; Cabras, Paolo; Rosell, Antoni
    Bronchoscopy is an interventional medical procedure employed to analyze the interior side of the human airways, clear possible obstructions and biopsy. Using a 3D reconstruction of the tracheobronchial tree, Virtual Bronchoscopy (VB) may help physicians in the exploration of peripheral lung lesions. We are developing a haptic-based navigation system for the VB that allows the navigation within the airways using a haptic device whose permitted motions mimics those done with the real bronchoscope. This paper describes the motion planning module of the system devoted to plan a path from the trachea to small peripheral pulmonary lesions, that takes into account the geometry and the kinematic constraints of the bronchoscope. The motion planner output is used to visually and haptically guide the navigation during the virtual exploration using the haptic device. Moreover, physicians can get useful information of whether the peripheral lesions can effectively be reached with a given bronchoscope or of which is the nearest point to the lesion that can be reached.

Novel Actuation Technologies

  • SheetBot: Two-Dimensional Sheet-Like Robot As a Tool for Constructing Universal Decentralized Control Systems Authors: Kano, Takeshi; Watanabe, Yuki; Ishiguro, Akio
    Autonomous decentralized control is a key concept for the realization of highly adaptive behavior. However, universal design of autonomous decentralized control that ensures rich adaptability is still lacking. In this study, we tackle this problem through the development of a two-dimensional sheet-like robot, SheetBot. The SheetBot is a suitable model system for the establishment of universal design principles for autonomous decentralized control, because it can bend reasonably to the circumstances encountered due to its large surface area, and also because its applications are widely expected. To realize highly adaptive locomotion with SheetBot, we are inspired by the decentralized control scheme of the scaffold-based locomotion of snakes. We extend this design scheme to a two-dimensional bodily structure on the basis of a continuum model. Simulation results show that SheetBot can locomote on various kinds of irregular terrain with minimal control inputs by implementing the proposed autonomous decentralized control scheme.
  • Deformable Robot Maneuvered by Magnetic Particles for Use in a Confined Environment Authors: Nokata, Makoto
    This paper presents an advanced locomotion method that produces non-slipping motion in digestive organs and the abdominal cavity. New movement principle of the robot, which has a soft and deformable body that can move through a confined space is proposed. The mechanism of a toy water snake is applied to this principle. Magnetic particles inside the water balloon are affected by the external magnetic field and exert an internal pressure. We construct an experimental model to verify the proposed principle, the sliding movement is measured using the model. Confirmatory experiments of movement are conducted in the two sheets that imitated internal organs.
  • Design of Dielectric Electroactive Polymers for a Compact and Scalable Variable Stiffness Device Authors: Dastoor, Sanjay; Cutkosky, Mark
    We present the design, analysis, and experimental validation of a variable stiffness device based on annular dielectric electroactive polymer (EAP) actuators. The device is based on a diaphragm geometry, which partially linearizes the viscoelastic response of acrylic dielectrics, providing voltage- controlled stiffness without high damping losses. Multiple diaphragms can be connected in a single device to increase stiffness or provide custom stiffness profiles. The geometry is analyzed to determine the relationship among force, displacement and voltage. A single-layer diaphragm was constructed and tested to validate the concept, demonstrating up to 10x change in stiffness.
  • Viscous Screw Pump for Highly Backdrivable Electro-Hydrostatic Actuator Authors: Kaminaga, Hiroshi; Tanaka, Hirokazu; Yasuda, Kazuki; Nakamura, Yoshihiko
    It is widely acknowledged that the actuator's intrinsic backdrivability is important in realizing a force sensitive behavior. It is desirable to realize such actuator with electric motor that is advantageous from power-to-weight ratio and controllability point of view. Electro-Hydrostatic Actuator is a type of hydraulic actuators that can realize high backdrivability by reducing transmission friction and by providing dynamics decoupling with an implicit serial damper. To farther enhance the backdrivability of a EHA, a pump with minimum static and Coulomb friction is necessary. In this paper, we introduce an EHA with viscous screw pump that minimizes static and Coulomb friction by eliminating the mechanical contact between pump components. Viscous screw pumps also have the advantage that there is no pulsation in pressure due to the continuity of the force transmission from the rotor to the fluid. The property of the actuator, including pulsation performance and impedance control performance were evaluated on a prototype of EHA with a viscous screw pump.
  • Development and Control of a Three DOF Planar Induction Motor Authors: Kumagai, Masaaki; Hollis, Ralph
    This paper reports a planar induction motor (PIM) that can output 70 N translational thrust and 9 Nm torque with a response time of 10 ms. The motor consists of three linear induction motor (LIM) armatures with vector control drivers and three optical mouse sensors. First, an idea to combine multiple linear induction elements is proposed. The power distribution to each element is derived from the position and orientation of that element. A discussion of the developed system and its measured characteristics follow. We implemented a PIM with position and orientation tracking control. Experiments were carried out using the system. First, response of individual LIM was measured, and we confirmed that it could output thrust up to 40 N in a response of 10 ms. It also showed linearity. Then, force/torque output of the integrated PIM was confirmed. Using the PIM and the position sensing system, the position feedback control was performed. The results were presented by graphs on the paper and by movie included in accompanying video. These experimental results highlights the potential of direct drive features of the PIM.
  • Controlling the Locomotion of a Separated Inner Robot from an Outer Robot Using Electropermanent Magnets Authors: Marchese, Andrew; Rus, Daniela; Asada, Harry
    This paper presents the design, modeling, and experimental verification of a novel, programmable connection mechanism for robots separated by a surface. The connector uses electropermanent magnets (EPMs) [1] to establish a continuum of clamping force between the robots, enabling the motion of one robot to slave the other during a variety of maneuvers. The authors design a novel, solid-state EPM arrangement capable of generating up to an estimated 890N of clamping force under environmental loading conditions. A relationship between geometric and environmental variables and connection assembly performance is first modeled and subsequently experimentally characterized. By implementing these connectors in a custom manufactured pair of assembly robots, the authors demonstrate the connection assembly and magnetizing hardware can be compactly fit within an autonomous robot application. We offer this mechanism as a repeatable, easily-automated alternative to robotic systems that depend on mechanic means to regulate clamping force [2].