Showing papers on "Kinematics published in 2007"

Methods and systems for robotic instrument tool tracking with adaptive fusion of kinematics information and image information

Abstract: In one embodiment of the invention, a method for a robotic system is disclosed to track one or more robotic instruments. The method includes generating kinematics information for the robotic instrument within a field of view of a camera; capturing image information in the field of view of the camera; and adaptively fusing the kinematics information and the image information together to determine pose information of the robotic instrument. Additionally disclosed is a robotic medical system with a tool tracking sub-system. The tool tracking sub-system receives raw kinematics information and video image information of the robotic instrument to generate corrected kinematics information for the robotic instrument by adaptively fusing the raw kinematics information and the video image information together.

Energy-minimizing kinematics in hovering insect flight

Abstract: We investigate aspects of hovering insect flight by finding the optimal wing kinematics which minimize power consumption while still providing enough lift to maintain a time-averaged constant altitude over one flapping period. In particular, we study the flight of three insects whose masses vary by approximately three orders of magnitude: fruitfly (Drosophila melanogaster), bumblebee (Bombus terrestris), and hawkmoth (Manduca sexta). Here, we model an insect wing as a rigid body with three rotational degrees of freedom. The aerodynamic forces are modelled via a quasi-steady model of a thin plate interacting with the surrounding fluid. The advantage of this model, as opposed to the more computationally costly method of direct numerical simulation via computational fluid dynamics, is that it allows us to perform optimization procedures and detailed sensitivity analyses which require many cost function evaluations. The optimal solutions are found via a hybrid optimization algorithm combining aspects of a genetic algorithm and a gradient-based optimizer. We find that the results of this optimization yield kinematics which are qualitatively and quantitatively similar to previously observed data. We also perform sensitivity analyses on parameters of the optimal kinematics to gain insight into the values of the observed optima. Additionally, we find that all of the optimal kinematics found here maintain the same leading edge throughout the stroke, as is the case for nearly all insect wing motions. We show that this type of stroke takes advantage of a passive wing rotation in which aerodynamic forces help to reverse the wing pitch, similar to the turning of a free-falling leaf.

SIMBICON: simple biped locomotion control

Abstract: Physics-based simulation and control of biped locomotion is difficult because bipeds are unstable, underactuated, high-dimensional dynamical systems. We develop a simple control strategy that can be used to generate a large variety of gaits and styles in real-time, including walking in all directions (forwards, backwards, sideways, turning), running, skipping, and hopping. Controllers can be authored using a small number of parameters, or their construction can be informed by motion capture data. The controllers are applied to 2D and 3D physically-simulated character models. Their robustness is demonstrated with respect to pushes in all directions, unexpected steps and slopes, and unexpected variations in kinematic and dynamic parameters. Direct transitions between controllers are demonstrated as well as parameterized control of changes in direction and speed. Feedback-error learning is applied to learn predictive torque models, which allows for the low-gain control that typifies many natural motions as well as producing smoother simulated motion.

Biomechatronic Design and Control of an Anthropomorphic Artificial Hand for Prosthetic and Robotic Applications

Abstract: This paper proposes a biomechatronic approach to the design of an anthropomorphic artificial hand able to mimic the natural motion of the human fingers. The hand is conceived to be applied to prosthetics as well as to humanoid and personal robotics; hence, anthropomorphism is a fundamental requirement to be addressed both in the physical aspect and in the functional behavior. In this paper, a biomechatronic approach is addressed to harmonize the mechanical design of the anthropomorphic artificial hand with the design of the hand control system. More in detail, this paper focuses on the control system of the hand and on the optimization of the hand design in order to obtain a human-like kinematics and dynamics. By evaluating the simulated hand performance, the mechanical design is iteratively refined. The mechanical structure and the ratio between number of actuators and number of degrees of freedom (DOFs) have been optimized in order to cope with the strict size and weight constraints that are typical of application of artificial hands to prosthetics and humanoid robotics. The proposed hand has a kinematic structure similar to the natural hand featuring three articulated fingers (thumb, index, and middle finger with 3 DOF for each finger and 1 DOF for the abduction/adduction of the thumb) driven by four dc motors. A special underactuated transmission has been designed that allows keeping the number of motors as low as possible while achieving a self-adaptive grasp, as a result of the passive compliance of the distal DOF of the fingers. A proper hand control scheme has been designed and implemented for the study and optimization of hand motor performance in order to achieve a human-like motor behavior. To this aim, available data on motion of the human fingers are collected from the neuroscience literature in order to derive a reference input for the control. Simulation trials and computer-aided design (CAD) mechanical tools are used to obtain a finger model including its dynamics. Also the closed-loop control system is simulated in order to study the effect of iterative mechanical redesign and to define the final set of mechanical parameters for the hand optimization. Results of the experimental tests carried out for validating the model of the robotic finger, and details on the process of integrated refinement and optimization of the mechanical structure and of the hand motor control scheme are extensively reported in the paper.

Autonomous Automobile Trajectory Tracking for Off-Road Driving: Controller Design, Experimental Validation and Racing

Abstract: This paper presents a nonlinear control law for an automobile to autonomously track a trajectory, provided in real-time, on rapidly varying, off-road terrain. Existing methods can suffer from a lack of global stability, a lack of tracking accuracy, or a dependence on smooth road surfaces, any one of which could lead to the loss of the vehicle in autonomous off-road driving. This work treats automobile trajectory tracking in a new manner, by considering the orientation of the front wheels - not the vehicle's body - with respect to the desired trajectory, enabling collocated control of the system. A steering control law is designed using the kinematic equations of motion, for which global asymptotic stability is proven. This control law is then augmented to handle the dynamics of pneumatic tires and of the servo-actuated steering wheel. To control vehicle speed, the brake and throttle are actuated by a switching proportional integral (PI) controller. The complete control system consumes a negligible fraction of a computer's resources. It was implemented on a Volkswagen Touareg, "Stanley", the Stanford Racing Team's entry in the DARPA Grand Challenge 2005, a 132 mi autonomous off-road race. Experimental results from Stanley demonstrate the ability of the controller to track trajectories between obstacles, over steep and wavy terrain, through deep mud puddles, and along cliff edges, with a typical root mean square (RMS) crosstrack error of under 0.1 m. In the DARPA National Qualification Event 2005, Stanley was the only vehicle out of 40 competitors to not hit an obstacle or miss a gate, and in the DARPA Grand Challenge 2005 Stanley had the fastest course completion time.

Adaptive Regulation of Amplitude Limited Robot Manipulators With Uncertain Kinematics and Dynamics

Abstract: Common assumptions in most of the previous robot controllers are that the robot kinematics and manipulator Jacobian are perfectly known and that the robot actuators are able to generate the necessary level of torque inputs. In this note, an amplitude-limited torque input controller is developed for revolute robot manipulators with uncertainty in the kinematic and dynamic models. The adaptive controller yields semiglobal asymptotic regulation of the task-space setpoint error. The advantages of the proposed controller include the ability to actively compensate for unknown parametric effects in the dynamic and kinematic model and the ability to ensure actuator constraints are not breached by calculating the maximum required torque a priori

Computational Motor Control: Redundancy and Invariance

Abstract: The nervous system controls the behavior of complex kinematically redundant biomechanical systems. How it computes appropriate commands to generate movements is unknown. Here we propose a model based on the assumption that the nervous system: 1) processes static (e.g., gravitational) and dynamic (e.g., inertial) forces separately; 2) calculates appropriate dynamic controls to master the dynamic forces and progress toward the goal according to principles of optimal feedback control; 3) uses the size of the dynamic commands (effort) as an optimality criterion; and 4) can specify movement duration from a given level of effort. The model was used to control kinematic chains with 2, 4, and 7 degrees of freedom [planar shoulder/elbow, three-dimensional (3D) shoulder/elbow, 3D shoulder/elbow/wrist] actuated by pairs of antagonist muscles. The muscles were modeled as second-order nonlinear filters and received the dynamics commands as inputs. Simulations showed that the model can quantitatively reproduce characteristic features of pointing and grasping movements in 3D space, i.e., trajectory, velocity profile, and final posture. Furthermore, it accounted for amplitude/duration scaling and kinematic invariance for distance and load. These results suggest that motor control could be explained in terms of a limited set of computational principles.

Design analysis, fabrication and testing of a parallel-kinematic micropositioning XY stage

Abstract: This paper reports on a novel piezo-driven, parallel-kinematic, micropositioning XY stage. This monolithic design is comprised of parallelogram four-bar linkages, flexure hinges, and piezoelectric actuators. Kinematic and dynamic analysis shows that the mechanical structure of the stage has a large work space, high bandwidth and good linearity. The stage system was run in open-loop mode to measure the step response and frequency response. The results show that the resonation frequencies of the two vibration modes are 563 and 536 Hz and the damping ratios are 0.049 and 0.0228. Two fiber optic sensors were added to the system to build a closed-loop positioning system. Linear and circular contouring performance in closed-loop mode suggests high scanning performance for such parallel-kinematic stages. The positioning resolution of the stage, limited only by the feedback sensors used, is about 20 nm.

Finite-time stability of cascaded time-varying systems

Abstract: The uniform global finite-time stability is discussed for a cascaded time-varying system consisting of two uniformly finite-time stable subsystems. It is shown that a forward completeness condition is enough to ensure the uniform global finite-time stability of the system. For ease of reference, a particular result with a growth rate condition is also deduced. These stability results are applied to the tracking control problem of a non-holonomic wheeled mobile robot in kinematic model. Two tracking control laws are developed respectively for two different cases of the desired rotate velocity. Both control laws are continuous and can control the mobile robot to track the desired trajectory in finite time. Simulation results are provided to show the effectiveness of the method.

Kinematic analysis of a 3-PRS parallel manipulator

Abstract: Although the current 3-PRS parallel manipulators have different methods on the arrangement of actuators, they may be considered as the same kind of mechanism since they can be treated with the same kinematic algorithm. A 3-PRS parallel manipulator with adjustable layout angle of actuators has been proposed in this paper. The key issues of how the kinematic characteristics in terms of workspace and dexterity vary with differences in the arrangement of actuators are investigated in detail. The mobility of the manipulator is analyzed by resorting to reciprocal screw theory. Then the inverse, forward, and velocity kinematics problems are solved, which can be applied to a 3-PRS parallel manipulator regardless of the arrangement of actuators. The reachable workspace features and dexterity characteristics including kinematic manipulability and global dexterity index are derived by the changing of layout angle of actuators. Simulation results illustrate that different tasks should be taken into consideration when the layout angles of actuators of a 3-PRS parallel manipulator are designed.

A Fuzzy-Logic-Based Approach for Mobile Robot Path Tracking

Abstract: One important problem in autonomous robot navigation is the effective following of an unknown path traced in the environment in compliance with the kinematic limits of the vehicle, i.e., bounded linear and angular velocities and accelerations. In this case, the motion planning must be implemented in real-time and must be robust with respect to the geometric characteristics of the unknown path, namely curvature and sharpness. To achieve good tracking capability, this paper proposes a path following approach based on a fuzzy-logic set of rules which emulates the human driving behavior. The input to the fuzzy system is represented by approximate information concerning the next bend ahead the vehicle; the corresponding output is the cruise velocity that the vehicle needs to attain in order to safely drive on the path. To validate the proposed algorithm two completely different experiments have been run: in the first experiment, the vehicle has to perform a lane-following task acquiring lane information in real-time using an onboard camera; in the second, the motion of the vehicle is obtained assigning in real-time a given time law. The obtained results show the effectiveness of the proposed method

Constraint-based design of parallel kinematic XY flexure mechanisms

Abstract: This paper presents parallel kinematic XY flexure mechanism designs based on systematic constraint patterns that allow large ranges of motion without causing over-constraint or significant error motions. Key performance characteristics of XY mechanisms such as mobility, cross-axis coupling, parasitic errors, actuator isolation, drive stiffness, lost motion, and geometric sensitivity, are discussed. The standard double parallelogram flexure module is used as a constraint building-block and its nonlinear force-displacement characteristics are employed in analytically predicting the performance characteristics of two proposed XY flexure mechanism designs. Fundamental performance tradeoffs, including those resulting from the nonlinear load-stiffening and elastokinematic effects, in flexure mechanisms are highlighted. Comparisons between closed-form linear and nonlinear analyses are presented to emphasize the inadequacy of the former. It is shown that geometric symmetry in the constraint arrangement relaxes some of the design tradeoffs, resulting in improved performance. The nonlinear analytical predictions are validated by means of computational finite element analysis and experimental measurements.

Distributed Geodesic Control Laws for Flocking of Nonholonomic Agents

Abstract: We study the problem of flocking and velocity alignment in a group of kinematic nonholonomic agents in 2 and 3 dimensions. By analyzing the velocity vectors of agents on a circle (for planar motion) or sphere (for 3-D motion), we develop a geodesic control law that minimizes a misalignment potential and results in velocity alignment and flocking. The proposed control laws are distributed and will provably result in flocking when the underlying proximity graph which represents the neighborhood relation among agents is connected. We further show that flocking is possible even when the topology of the proximity graph changes over time, so long as a weaker notion of joint connectivity is preserved

Dynamic positioning and way-point tracking of underactuated AUVs in the presence of ocean currents

Abstract: This paper addresses the problem of dynamic positioning and way-point tracking of underactuated autonomous underwater vehicles (AUVs) in the presence of constant unknown ocean currents and parametric modelling uncertainty. A non-linear adaptive controller is proposed that steers an AUV along a sequence of way-points consisting of desired positions (x, y) in a inertial reference frame, followed by vehicle positioning at the final target point. The controller is first derived at the kinematic level assuming that the ocean current disturbance is known. An exponential observer for the current is then designed and convergence of the resulting closed-loop system trajectories is analysed. Finally, integrator backstepping and Lyapunov based techniques are used to extend the kinematic controller to the dynamic case and to deal with model parameter uncertainty. Simulation results with a dynamic model of an underactuated autonomous underwater shuttle for the transport of benthic labs are presented and discussed.

Chronic ankle instability and fatigue create proximal joint alterations during performance of the Star Excursion Balance Test.

Abstract: The combined effects of chronic ankle instability (CAI) and lower extremity fatigue on measures of neuromuscular control have not been well established. The purpose of this study was to investigate the influence of CAI on the performance of a dynamic postural control task, the Star Excursion Balance Test (SEBT), after fatiguing activities. Thirty subjects with (n = 14) or without (n = 16) unilateral CAI completed anterior, medial, and posterior reaching directions of the SEBT performed before and after a lunging fatigue protocol and an open chain ankle isokinetic fatigue protocol. Pre-post fatigue change scores were calculated for sagittal plane kinematics of the stance leg and the normalized reach distances (%MAXD). Using a regression model, group and kinematic data were used to explain between subject differences in %MAXD. For each reaching direction, a separate analysis was completed for the two fatigue conditions. When reaching anteriorly after the lunge fatigue condition, CAI and the changes in knee and hip flexion predicted approximately 49 % of the variance in %MAXD (R2 = .487; p = .001). When reaching medially under lunge fatigue, CAI predicted approximately 20 % of the variance in %MAXD (R2 = .198; p = .014). Isolated ankle fatigue did not cause significantly different responses between groups. For two of the reaching directions, CAI status significantly influenced the variances in %MAXD under the influence of lunge fatigue. Functional fatigue protocols

Use of virtual reality to improve upper-extremity control in children with cerebral palsy: a single-subject design.

Abstract: Background and Purpose: Virtual reality (VR) creates an exercise environment in which the intensity of practice and positive feedback can be systematically manipulated in various contexts. The purpose of this study was to investigate the training effects of a VR intervention on reaching behaviors in children with cerebral palsy (CP). Participants: Four children with spastic CP were recruited. Method: A single-subject design (A-B with follow-up) was used. All children were evaluated with 3 baseline, 4 intervention, and 2 follow-up measures. A 4-week individualized VR training program (2 hours per week) with 2 VR systems was applied to all children. The outcome measures included 4 kinematic parameters (movement time, path length, peak velocity, and number of movement units) for mail-delivery activities in 3 directions (neutral, outward, and inward) and the Fine Motor Domain of the Peabody Developmental Motor Scales–Second Edition (PDMS-2). Visual inspection and the 2-standard-deviation–band method were used to compare the outcome measures. Results: Three children who had normal cognition showed improvements in some aspects of reaching kinematics, and 2 children’s change scores on the PDMS-2 reached the minimal detectable change during the intervention. The improvements in kinematics were partially maintained during follow-up. Discussion and Conclusion: A 4-week individualized VR training program appeared to improve the quality of reaching in children with CP, especially in children with normal cognition and good cooperation. The training effects were retained in some children after the intervention.

Modal System Design of Multirobot Systems by Interaction Mode Control

Abstract: Motion control technology in an open environment will be more important. Future motion systems should interact with other systems or environments. To adapt to complicated environments and do tasks, a realization of multi-degree-of-freedom motion is necessary for human cooperating motion. This paper proposes a unified control approach for multirobot systems by interaction mode control. The proposed interaction mode control considers only interactions between systems. The interactions are abstracted by using mode quarry matrices. Since the transformed modes are independent of each other, it is possible to design a controller in decoupled modal space. This paper also proposes a novel control index named "hybrid ratio." Hybrid ratio is defined as the influence of external acceleration input on the acceleration response of a system. Since it is possible to realize the assigned hybrid ratio in each mode according to the task, the motion command with hybrid ratio is represented as task code. Thus, the interaction mode control is able to be treated as task kinematics. The proposed interaction mode control is applied for grasping motion by multirobot systems. The numerical and experimental results show the viability of the proposed method

Rigorous 3D error analysis of kinematic scanning LIDAR systems

Abstract: Abstract To date, LIDAR sensors have been primarily airborne, and utilized as a fast and efficient means of collecting topographic information. As a result, in research studies and in most commercial work the accuracy of the LIDAR information is primarily obtained by examining the vertical component of LIDAR error only. However, more and more end users are using LIDAR intensity to produce planimetric feature maps, and there are also emerging ground based kinematic laser scanning systems which are mounted on a van or truck platform. For both of these uses, the traditional vertical only error analysis of the LIDAR system is inadequate when defining the overall expected accuracy of the end-product received from the system. Therefore, in order to quantify the overall 3D expected accuracy of LIDAR systems (both land and air based) a rigorous 1st order error analysis of the LIDAR georeferencing equations are undertaken. Typical error parameters are then placed into the error analysis to generate expected horizontal and vertical system accuracies for different LIDAR system configurations. Finally, the results obtained from the theoretical error analysis are independently verified using real world LIDAR data.

Differences in 3-Dimensional Shoulder Kinematics between Persons with Multidirectional Instability and Asymptomatic Controls

Abstract: BackgroundEvidence that persons with multidirectional instability (MDI) of the shoulder have abnormal shoulder kinematics is limited. A kinematic description of scapulothoracic and glenohumeral motion can assist both conservative and surgical rehabilitative programs.HypothesisPersons with MDI of the shoulder demonstrate increased anterior and inferior glenohumeral translation and decreased scapular upward rotation and increased scapular internal rotation compared with age-matched and gender-matched asymptomatic controls.Study DesignControlled laboratory study.MethodsSixty-two subjects were recruited from an outpatient orthopaedic clinic. Subjects with MDI were matched according to age, gender, and hand dominance to asymptomatic controls. An electromagnetic motion capture system evaluated the 3-dimensional position of the trunk, scapula, and humerus during frontal and scapular plane elevation. A repeated measures analysis of variance evaluated joint positions and glenohumeral translations during 4 phases o...

Revised distances of Northern HII regions

Abstract: Aims. Our aim is to determine the distance of outer Galaxy star-forming complexes in order to model the kinematic structure of our Galaxy.Methods. We searched for exciting star(s) of HII regions, with poor or unknown stellar distance, in the second and third galactic quadrants. We carried out spectroscopic and photometric (when necessary) observations in order to establish their spectral type and their U , B and V magnitudes. From these data, complemented with literature data, we determine the spectro-photometric distance of their associated complexes.Results. We (re)established the stellar distance of 23 star forming complexes. Reinvestigating the kinematics of the Perseus and Cygnus arms, we determined the velocity departures from circular rotation and we interpreted them as streaming motions in the spiral arms. Indeed, in addition to the Perseus arm where such departures were known for a long time, we added evidence for velocity deviations in the Cygnus arm. Most significant is that we found the opposite sign for these departures in the Perseus and Cygnus arms, which suggests that the co-rotation radius is located between these two arms at ~13 kpc from the galactic center.