TechTalks from event: Technical session talks from ICRA 2012

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Mechanism Design of Mobile Robots

  • Design and Analysis of Novel Friction Controlling Mechanism with Minimal Energy for In-Pipe Robot Applications Authors: Choi, Changrak; Youcef-Toumi, Kamal
    In-pipe robots require friction on the wheels to maintain traction. Ability to vary this friction is highly desirable but conventionally used linkage mechanism is not suitable for it. This paper presents a novel mechanism that generates controllable friction with minimal energy for in-pipe robots. Details of how the mechanism uses permanent magnets to achieve the objective are discussed. A simple but appropriate model of a permanent magnet is also presented for the analysis. The paper identifies the important design parameters, and more importantly establishes the relation between the design parameters and the system’s performance. In addition, a prototype of the mechanism was designed, fabricated and tested for validation. The experimental results agree well with the predicted behavior through simulation and demonstrate the effectiveness of the mechanism.
  • Developing a Gait Enhancing Mobile Shoe to Alter Over-Ground Walking Coordination Authors: Handzic, Ismet; Reed, Kyle Brandon
    This paper presents a Gait Enhancing Mobile Shoe (GEMS) that mimics the desirable kinematics of a split-belt treadmill except that it does so over ground. Split-belt treadmills, with two separate treads running at different speeds, have been found useful in the rehabilitation of persons with asymmetric walking patterns. Although in preliminary testing, beneficial after-effects have been recorded, various drawbacks include the stationary nature of the split-belt treadmill and the inability to keep a person on the split-belt treadmill for an extended period of time. For this reason, the after-effects for long-term gait training are still unknown. The mobile ability of the GEMS outlined in this paper enables it to be worn in different environments such as in one's own house and also enables it to be worn for a longer period of time since the GEMS is completely passive. Healthy subject testing has demonstrated that wearing this shoe for twenty minutes can alter the wearer's gait and will generate after-effects in a similar manner as a split-belt treadmill does.
  • Cycloid vs. Harmonic Drives for Use in High Ratio, Single Stage Robotic Transmissions Authors: Sensinger, Jonathon; Lipsey, James
    Harmonic and cycloid drives are both compact, high ratio transmissions appropriate for use in anthropomorphic robots, although cycloid drives are rarely used in the field. This paper describes the design parameters for cycloid drives and shows the results of six cycloid models designed to match corresponding harmonic drives. Cycloid drive models were compared with manufacturing data from corresponding harmonic drives with respect to maximum gear ratio, transmission thickness, efficiency, backlash/gear ratio ripple, and reflected inertia. Cycloid drive designs were found to be thinner, more efficient, and to have lower reflected inertia than corresponding harmonic drives. However, the cycloid designs had larger gear ratio ripple and substantial backlash, and they could not meet the maximum gear ratio provided by the corresponding harmonic drives in two out of six models for equal applied torques. Two cycloid drives were manufactured to confirm efficiency predictions and demonstrated moderate to high efficiency across a range of output torques. Cycloid drives should be considered for robotic and prosthetic applications where smaller thickness/higher efficiency requirements dominate over low backlash/gear ratio ripple considerations.
  • Robot Environment for Combat Vehicle Driving Simulation Authors: Kamnik, Roman
    The paper presents a driving simulator of a combat vehicle aimed for driver-vehicle interaction studies and design of a full-scale driving simulator. The simulator incorporates a real-time combat vehicle dynamics simulation module, a graphical presentation module, a robotic seat motion system, and a haptic steering system. The simulation module simulates dynamic motion and interaction with the environment of a combat vehicle in real-time. The graphical presentation module generates driving scenes that are displayed on a screen by a back projection. The robotic system generates seat motion cues by means of a three degree-of-freedom hydraulically driven mechanism. The force feedback steering system built on the basis of a torque controlled induction motor is an interface between the driver and the simulator. The developed driving simulator is validated through comparison of motion and force feedback responses with those measured with real vehicle when performing standard test manoeuvres. The results verify matching in simulated and real driving environments.
  • Frictional Step Climbing Analysis of Tumbling Locomotion Authors: Hemes, Brett; Papanikolopoulos, Nikos
    Tumbling robots provide the potential to produce increased mobility on smaller scales with respect to their size and/or complexity. In this paper we explore the frictional interactions between a tumbling robot and the terrain while climbing a single vertical step to illustrate the advantages of tumbling. We present a set of parametric configuration equations that express the relationships between the robot’s configuration parameters (morphology, geometry, mass, etc.), the environmental/task parameters (step geometry, available coefficients of friction, etc.), and the performance parameters (step height). The required body coefficient of friction is examined in detail for idealized tumbling and wheel-tail robots. We further illustrate the results of our analysis by experimentally determining optimal tumbling and wheel-tail configurations for a given step size and body (wheel) friction.
  • Hex-DMR: A Modular Robotic Test-Bed for Demonstrating Team Repair Authors: Ackerman, Martin Kendal; Chirikjian, Gregory
    This work presents a novel test-bed design for demonstrating techniques for team repair in modular robotic systems. The advantages of using modular and team repairable robots are discussed and theoretical constraints for creating a system capable of team repair are enumerated. These constraints are used to develop the Hex-DMR (Hexagonal Distributed Modular Robot) system which centers on a unique repair scheme based on modular components. The proposed system is demonstrated first with computer simulations, which outline the environment navigation scheme and team operation dynamics, and then with a physical prototype, with which a simple repair maneuver is shown.

Bipedal Robot Control

  • Switching Control Design for Accommodating Large Step-Down Disturbances in Bipedal Robot Walking Authors: Park, Hae Won; Sreenath, Koushil; Ramezani, Alireza; Grizzle, J.W
    This paper presents a feedback controller that allows MABEL, a kneed, planar bipedal robot, with 1 m-long legs, to accommodate an abrupt 20 cm decrease in ground height. The robot is provided information on neither where the step down occurs, nor by how much. After the robot has stepped off a raised platform, however, the height of the platform can be estimated from the lengths of the legs and the angles of the robot’s joints. A real-time control strategy is implemented that uses this on-line estimate of step-down height to switch from a baseline controller, that is designed for flat-ground walking, to a second controller, that is designed to attenuate torso oscillation resulting from the step-down disturbance. After one step, the baseline controller is re-applied. The control strategy is developed on a simplified model of the robot and then verified on a more realistic model before being evaluated experimentally. The paper concludes with experimental results showing MABEL (blindly) stepping off a 20 cm high platform.
  • Design and Experimental Implementation of a Compliant Hybrid Zero Dynamics Controller with Active Force Control for Running on MABEL Authors: Sreenath, Koushil; Park, Hae Won; Grizzle, J.W
    This paper presents a control design based on the method of virtual constraints and hybrid zero dynamics to achieve stable running on MABEL, a planar biped with compliance. In particular, a time-invariant feedback controller is designed such that the closed-loop system not only respects the natural compliance of the open-loop system, but also enables active force control within the compliant hybrid zero dynamics and results in exponentially stable running gaits. The compliant-hybrid-zero-dynamics-based controller with active force control is implemented experimentally and shown to realize stable running gaits on MABEL at an average speed of 1.95 m/s (4.4 mph) and a peak speed of 3.06 m/s (6.8 mph). The obtained gait has flight phases upto 39% of the gait, and an estimated ground clearance of 7.5-10 cm.
  • Walking Control Strategy for Biped Robots Based on Central Pattern Generator Authors: Liu, Chengju; Chen, Qijun
    This paper deals with the walking control of biped robots inspired by biological concept of central pattern generator (CPG). A control architecture is proposed with a trajectory generator and a motion engine. The trajectory generator consists of a CoG (center of gravity) trajectory generator and a foot trajectory modulator. The CoG generator generates adaptive CoG trajectories online and the foot trajectories can be modulated based on the generated CoG trajectories. A biped platform NAO is used to validate the proposed locomotion control system. The experimental results confirm the effectiveness of the proposed control architecture.
  • On the Lyapunov Stability of Quasistatic Planar Biped Robots Authors: Varkonyi, Peter L.; Gontier, David; Burdick, Joel
    We investigate the local motion of a planar rigid body with unilateral constraints in the neighborhood of a two-contact frictional equilibrium configuration on a slope. A new sufficient condition of Lyapunov stability is developed in the presence of arbitrary external forces. Additionally, we construct an example, which is stable against perturbations by infinitesimal forces, but does not possess Lyapunov stability against infinitesimal displacements or impulses. The great difference between previous stability criteria and ours leads to further questions about the nature of the exact stability condition.
  • Humanoid Robot Safe Fall Using Aldebaran NAO Authors: Yun, Seung-kook; Goswami, Ambarish
    Although the fall of a humanoid robot is rare in controlled environments, it cannot be avoided in the real world where the robot may physically interact with the environment. Our earlier work introduced the strategy of direction changing fall, in which the robot attempts to reduce the chance of human injury by changing its default fall direction in realtime and falling in a safer direction. The current paper reports further theoretical developments culminating in a successful hardware implementation of this fall strategy conducted on the Aldebaran NAO robot[3]. This includes new algorithms for humanoid kinematics and Jacobians involving coupled joints and a complete estimation of the body frame attitude using an additional inertial measurement unit. Simulations and experiments are smoothly handled by our platform independent humanoid control software called Locomote. We report experiment scenarios where we demonstrate the effectiveness of the proposed strategies in changing the fall direction.
  • Control Design to Achieve Dynamic Walking on a Bipedal Robot with Compliance Authors: Lim, Bokman; Lee, Minhyung; Kim, Joohyung; Lee, Jusuk; Park, Jaeho; Seo, Keehong; Roh, Kyungshik
    We propose a control framework for dynamic bipedal locomotion with compliant joints. A novel 3D dynamic walking is achieved by utilizing natural dynamics of the system. It is done by 1) driving robot joints directly with the posture-based state machine and 2) controlling tendon-driven compliant actuators. To enlarge gait's basin attraction for stable walking, we also adaptively plan step-to-step motion and compensate stance/swing motion. Final joint input is described by a superposition of state machine control torques and compensation torques of balancers. Various walking styles are easily generated by composing straight and turning gait-primitives and such walking is effectively able to adapt on various environments. Our proposed method is applied to a torque controlled robot platform, Roboray. Experimental results show that gaits are able to traverse inclined and rough terrains with bounded variations, and the result gaits are human-like comparing the conventional knee bent walkers.

Navigation and Visual Sensing

  • Navigation among Visually Connected Sets of Partially Distinguishable Landmarks Authors: Erickson, Lawrence H; LaValle, Steven M
    A robot navigates in a polygonal region populated by a set of partially distinguishable landmarks. The robot's motion primitives consist of actions of the form ``drive toward a landmark of class x''. To effectively navigate, the robot must always be able to see a landmark. Also, if the robot sees two landmarks of the same class, its motion primitives become ambiguous. Finally, if the robot wishes to navigate from landmark s_0 to landmark s_{goal} with a simple graph search algorithm, then there must be a sequence of landmarks [s_0,s_1,s_2,...,s_k=s_{goal}], in which landmark s_i is visible from s_{i-1}. Given these three conditions, how many landmark classes are required for navigation in a given polygon P? We call this minimum number of landmark classes the connected landmark class number, denoted chi_{CL}(P). We study this problem for the monotone polygons, an important family of polygons that are frequently generated as intermediate steps in other decomposition algorithms. We demonstrate that for all odd k, there exists a monotone polygon M_k with (3/4)(k^2+2k+1) vertices such that chi_{CL}(P) geq k. We also demonstrate that for any n-vertex monotone polygon P, chi_{CL}(P) leq n/3+12.
  • Natural Landmark Extraction in Cluttered Forested Environments Authors: Song, Meng; Sun, Fengchi; Iagnemma, Karl
    In this paper, a new systematical method for extracting tree trunk landmarks from 3D point clouds of cluttered forested environments is proposed. This purely geometric method is established on scene understanding and automatic analysis of trees. The pipeline of our method includes three steps. First, the raw point clouds are segmented by utilizing the circular shape of trees, and segments are grouped into tree sections based on the principle of spatial proximity. Second, circles and axes are extracted from tree sections which are subject to loss of shape information. Third, by clustering and integrating the tree sections resulted from various space inconsistencies, straight tree trunk landmarks are finally formed for future localization. The experimental results from real forested environments are presented.
  • Rapid Vanishing Point Estimation for General Road Detection Authors: Miksik, Ondrej
    This paper deals with fast vanishing point estimation for autonomous robot navigation. Preceding approaches showed suitable results and vanishing point estimation was used in many robotics tasks, especially in the detection of ill-structured roads. The main drawback of such approaches is the computational complexity - the possibilities of hardware accelerations are mentioned in many papers, however, we believe, that the biggest benefit of a vanishing point estimation algorithm is for primarily tele-operated robots in the case of signal loss, etc., that cannot use specialized hardware just for this feature. In this paper, we investigate possibilities of an efficient implementation by the expansion of Gabor wavelets into a linear combination of Haar-like box functions to perform fast filtering via integral image trick and discuss the utilization of superpixels in the voting scheme to provide a significant speed-up (more than 40 times), while we loose only 3-5% in precision.
  • A New Tentacles-Based Technique for Avoiding Obstacles During Visual Navigation Authors: Cherubini, Andrea; Spindler, Fabien; Chaumette, Francois
    In this paper, we design and validate a new tentacle-based approach, for avoiding obstacles during appearance-based navigation with a wheeled mobile robot. In the past, we have developed a framework for safe visual navigation. The robot follows a path represented as a set of key images, and during obstacle circumnavigation, the on-board camera is actuated to maintain scene visibility. In those works, the model used for obstacle avoidance was obtained using a potential vector field. Here, a more sophisticated and efficient method, that exploits the robot kinematic model, and predicts collision at look-ahead distances, is designed and integrated in that framework. Outdoor experiments comparing the two models show that the new approach presents many advantages. Higher speeds and precision can be attained, very cluttered scenarios involving large obstacles can be successfully dealt with, and the control inputs are smoother.
  • Maintaining visibility constraints during tele-echography with ultrasound visual servoing Authors: LI, Tao; Kermorgant, Olivier; Krupa, Alexandre
    This paper presents a multi-task control method to maintain the visibility of an anatomic element of interest while the doctor tele-operates a 2D ultrasound probe held by a medical robot. The prior task consists in automatically maintaining several visual constraints that guarantee an intersection between the ultrasound image plane and the anatomic object of interest and the second task allows the medical expert to manually apply probe motion through tele-operation. Unlike classical visual servoing technique which continually regulate the current visual features to desired values, our control approach gradually activates the regulation of one or several ultrasound visual features that go close to fixed limits in such a way to keep them in a safe domain. The main advantage of this approach is to give to the clinician the control of all the degrees of freedom of the probe to examine the patient while automatically preserving the visibility of the element of interest if required. Both simulations and experiments performed on an abdominal phantom demonstrate the efficiency of the visibility assistance task.
  • Simple and Robust Visual Servo Control of Robot Arms Using an On-Line Trajectory Generator Authors: Kroeger, Torsten; Padial, Jose
    Common visual servoing methods use image features to define a signal error in the feedback loops of robot motion controllers. This paper suggests a new visual servo control scheme that uses an on-line trajectory generator as an intermediate layer between image processing algorithms and robot motion controllers. The motion generation algorithm is capable of computing an entire trajectory from an arbitrary initial state of motion within one servo control cycle (typically one millisecond or less). This algorithm is fed with desired pose and velocity signals that are generated by an image processing algorithm. The advantages of this new architecture are: (a) jerk-limited and continuous motions are guaranteed independently of image processing signals, (b) kinematic motion constraints as well as physical and/or artificial workspace limits can be directly considered, and (c) the system can instantaneously and safely react to sensor failures (e.g., if cameras are covered or image processing fails). Real-world experimental results using a seven-joint robot arm are presented to underline the relevance for the field of robust sensor-guided robot motion control.