Showing papers on "Kinematics published in 2001"

Dynamic Measurements of Three-Dimensional Scapular Kinematics: A Validation Study

Abstract: The validation of two noninvasive methods for measuring the dynamic three-dimensional kinematics of the human scapula with a magnetic tracking device is presented. One method consists of simply fixing a sensor directly to the acromion and the other consists of mounting a sensor to an adjustable plastic jig that fits over the scapular spine and acromion. The concurrent validity of both methods was assessed separately by comparison with data collected simultaneously from an invasive approach in which pins were drilled directly into the scapula. The differences between bone and skin based measurements represents an estimation of skin motion artifact. The average motion pattern of each surface method was similar to that measured by the invasive technique, especially below 120 degrees of elevation. These results indicate that with careful consideration, both methods may offer reasonably accurate representations of scapular motion that may be used to study shoulder pathologies and help develop computational models.

Flexible Multibody Dynamics: A Finite Element Approach

Abstract: Preface. Introduction. Generalized Coordinates for Mechanism Analysis. Kinematics of Finite Motion. Parameterization of Spherical Motion. Rigid Body Dynamics. The Elastic Beam. System Constraints: Modelling of Joints. Substructuring Techniques. Static and Kinematic Analyses of Multibody Systems. Time Integration of Constrained Systems. Automatic Step Size Control. Energy Conserving Time Integration. References. Index.

Analysis of standing vertical jumps using a force platform

Abstract: A force platform analysis of vertical jumping provides an engaging demonstration of the kinematics and dynamics of one-dimensional motion. The height of the jump may be calculated (1) from the flight time of the jump, (2) by applying the impulse–momentum theorem to the force–time curve, and (3) by applying the work–energy theorem to the force-displacement curve.

High speed CNC system design. Part I: jerk limited trajectory generation and quintic spline interpolation

Abstract: Reference trajectory generation plays a key role in the computer control of machine tools. Generated trajectories must not only describe the desired tool path accurately, but must also have smooth kinematic profiles in order to maintain high tracking accuracy, and avoid exciting the natural modes of the mechanical structure or servo control system. Spline trajectory generation techniques have become widely adopted in machining aerospace parts, dies, and molds for this reason; they provide a more continuous feed motion compared to multiple linear or circular segments and result in shorter machining time, as well as better surface geometry. This paper presents a quintic spline trajectory generation algorithm that produces continuous position, velocity, and acceleration profiles. The spline interpolation is realized with a novel approach that eliminates feedrate fluctuations due to parametrization errors. Smooth accelerations and decelerations are obtained by imposing limits on the first and second time derivatives of feedrate, resulting in trapezoidal acceleration profiles along the toolpath. Finally, the reference trajectory generated with varying interpolation period is re-sampled at the servo loop closure period using fifth order polynomials, which enable the original kinematic profiles to be preserved. The proposed trajectory generation algorithm has been tested in machining a wing surface on a three axis milling machine, controlled with an in house developed open architecture CNC.

Learning inverse kinematics

Abstract: Real-time control of the end-effector of a humanoid robot in external coordinates requires computationally efficient solutions of the inverse kinematics problem. In this context, this paper investigates inverse kinematics learning for resolved motion rate control (RMRC) employing an optimization criterion to resolve kinematic redundancies. Our learning approach is based on the key observations that learning an inverse of a nonuniquely invertible function can be accomplished by augmenting the input representation to the inverse model and by using a spatially localized learning approach. We apply this strategy to inverse kinematics learning and demonstrate how a recently developed statistical learning algorithm, locally weighted projection regression, allows efficient learning of inverse kinematic mappings in an incremental fashion even when input spaces become rather high dimensional. Our results are illustrated with a 30-DOF humanoid robot.

Method and apparatus for transferring information between vehicles

Abstract: Sensor data is generated for areas around a vehicle. Any objects detected in the sensor data are identified and a kinematic state for the object determined. The kinematic states for the detected objects are compared with the kinematic state of the vehicle. If it is likely that a collision will occur between the detected objects and the local vehicle, a warning is automatically generated to notify the vehicle operator of the impending collision. The sensor data and kinematic state of the vehicle can be transmitted to other vehicles so that the other vehicles are also notified of possible collision conditions.

Comparison of Kinematic and Temporal Parameters between Different Pitch Velocity Groups

Abstract: This study investigated differences in kinematic and temporal parameters between two velocity groups of baseball pitchers. Data were collected from 127 healthy college and professional baseball pitchers. Those who threw faster than 1 SD above the sample mean (>38.0 m/s) were assigned to the high velocity group ( n = 29), and those who threw slower than 1 SD below the sample mean (<34.2 m/s) were assigned to the low velocity group (n = 23). Twelve kinematic parameters and 9 temporal parameters were measured and analyzed. The pattern of lead knee movement was also investigated. Maximum shoulder external rotation, forward trunk tilt at the instant of ball release, and lead knee extension angular velocity at the instant of ball release were significantly greater in the high velocity group. Maximum lead knee flexion angular velocity was significantly greater in the low velocity group. Seventy percent of the high velocity group showed knee extension during the approach to ball release, whereas the low velocity group showed a variety of knee movement patterns involving less knee extension and more knee flexion. The greater shoulder external rotation in the high velocity group produced an increased range of motion during the acceleration phase.

Modeling and IPC Control of Interactive Mechanical Systems - A Coordinate-Free Approach

Abstract: Rigid bodies and motions.- Kinematics of rigid mechanisms.- Dynamics of rigid mechanisms.- Intrinsically passive control.- A novel impedance crasping strategy.- IPC in telemanipulation.- Mathematical background.- Basics of bond graphs.

Modeling, Identification & Control of Robots

Abstract: Terminology and general definitions. Transformation matrix between vectors, frames and screws. Direct geometric model of serial robots. Inverse geometric model of serial robots. Direct kinematic model of serial robots. Inverse kinematic model of serial robots. Geometric and kinematic models of complex chain robots. Introduction to geometric and kinematic modelling of parallel robots. Dynamic modelling of serial robots. Dynamics of robots with complex structure. Geometric calibration of robots. Identification of the dynamic parameters. Trajectory control. Motion control. Compliant motion control. Appendices.

Portable system for analyzing human gait

Abstract: The invention is a portable gait analyzer comprising of at least one independent rear foot motion collection unit, at least one independent lower shank motion collection unit, plantar pressure collection unit, at least one processing and display unit, and a soft casing unit. A plurality of accelerometers, rate sensors, force sensor resistors, and pressure sensors provide for the acquisition of acceleration signals, angular velocity signals, foot force signals, and foot pressure signals to be processed. At least one central processing unit, a plurality of memory components, input/output components and ports, telemetry components, calibration components, liquid crystal displays components for the processing and outputting of three dimensional acceleration, angular velocity, tilt, and position. The rearfoot motion collection unit and lower shank motion collection unit interact with the processing and display unit to calculate rear foot kinematic data crucial to identify the motions of pronation and supination. The plantar pressure collection unit interacts with the processing and display unit to calculate plantar pressure data crucial to identify the center of pressure line and excessive and abnormal loads on the sole of the foot. These factors of rear-foot kinematics and plantar pressure lead to gait style identification.

Effects of dynamic office chairs on trunk kinematics, trunk extensor EMG and spinal shrinkage.

Abstract: Seated work has been shown to be a risk factor for low-back pain. This is attributed to the prolonged and monotonous low-level mechanical load imposed by a seated posture. To evaluate the potential health effects with respect to the low back of office chairs with a movable seat and back rest, trunk kinematics, erector spinae EMG, spinal shrinkage and local discomfort were assessed in 10 subjects performing simulated office work (word processing, computer-aided design and reading). Three chairs were used, one with a fixed seat and back rest and two dynamic chairs, one with a seat and back rest movable in a fixed ratio with respect to each other, and one with a freely movable seat and back rest. Spinal shrinkage measurements showed a larger stature gain when working on the two dynamic chairs as compared with working on the chair with fixed seat and back rest. Trunk kinematics and erector spinae EMG were strongly affected by the task performed but not by the chair type. The results imply that dynamic office chairs offer a potential advantage over fixed chairs, but the effects of the task on the indicators of trunk load investigated were more pronounced than the effects of the chair.

A dual neural network for kinematic control of redundant robot manipulators

Abstract: The inverse kinematics problem in robotics can be formulated as a time-varying quadratic optimization problem. A new recurrent neural network, called the dual network, is presented in this paper. The proposed neural network is composed of a single layer of neurons, and the number of neurons is equal to the dimensionality of the workspace. The proposed dual network is proven to be globally exponentially stable. The proposed dual network is also shown to be capable of asymptotic tracking for the motion control of kinematically redundant manipulators.

Relationship of Pelvis and Upper Torso Kinematics to Pitched Baseball Velocity

Abstract: Generating consistent maximum ball velocity is an important factor for a baseball pitcher’s success. While previous investigations have focused on the role of the upper and lower extremities, little attention has been given to the trunk. In this study it was hypothesized that variations in pelvis and upper torso kinematics within individual pitchers would be significantly associated with variations in pitched ball velocity. Nineteen elite baseball pitchers were analyzed using 3-D high-speed motion analysis. For inclusion in this study, each pitcher demonstrated a variation in ball velocity of at least 1.8 m/s (range: 1.8‐3.5 m/s) during his 10 fastball pitch trials. A mixed-model analysis was used to determine the relationship between 12 pelvis and upper torso kinematic variables and pitched ball velocity. Results indicated that five variables were associated with variations in ball velocity within individual pitchers: pelvis orientation at maximum external rotation of the throwing shoulder ( p = .026), pelvis orientation at ball release ( p = .044), upper torso orientation at maximum external rotation of the throwing shoulder ( p = .007), average pelvis velocity during arm cocking (p = .024), and average upper torso velocity during arm acceleration ( p = .035). As ball velocity increased, pitchers showed an increase in pelvis orientation and upper torso orientation at the instant of maximal external rotation of the throwing shoulder. In addition, average pelvis velocity during arm cocking and average upper torso velocity during arm acceleration increased as ball velocity increased. From a practical perspective, the athlete should be coached to strive for proper trunk rotation during arm cocking as well as strength and flexibility in order to generate angular velocity within the trunk for maximum ball velocity.

Kinematic controllability for decoupled trajectory planning in underactuated mechanical systems

Abstract: We introduce the notion of kinematic controllability for second-order underactuated mechanical systems. For systems satisfying this property, the problem of planning fast collision-free trajectories between zero velocity states can be decoupled into the computationally simpler problems of path planning for a kinematic system followed by time-optimal time scaling. While this approach is well known for fully actuated systems, until now there has been no way to apply it to underactuated dynamic systems. The results in this paper form the basis for efficient collision-free trajectory planning for a class of underactuated mechanical systems including manipulators and vehicles in space and underwater environments.

Three-Dimensional Dynamic Simulation of Total Knee Replacement Motion During a Step-Up Task

Abstract: A three-dimensional dynamic model of the tibiofemoral and patellofemoral articulations was developed to predict the motions of knee implants during a step-up activity. Patterns of muscle activity, initial joint angles and velocities, and kinematics of the hip and tinkle were measured experimentally and used as inputs to the simulation. Prosthetic knee kinematics were determined by integration of dynamic equations of motion subject to forces generated by muscles, ligaments, and contact at both the tibiofemoral and patellofemoral articulations. The modeling of contacts between implants did not rely upon explicit constraint equations; thus, changes in the number of contact points were allowed without modification to the model formulation. The simulation reproduced experimentally measured flexion-extension angle of the knee (within one standard deviation), but translations at the tibiofemoral articulations were larger during the simulated step-up task than those reported for patients with total knee replacements.

Smooth motion planning for car-like vehicles

Abstract: Presents a steering method for a car-like vehicle providing smooth paths subjected to curvature constraints. We show how to integrate this steering method in a global motion planning scheme taking obstacles into account. The main idea of the paper is to consider the car as a 4-D system from a kinematic point of view and as a 3-D system from a geometric point of view of collision checking. The resulting planned motions are guaranteed to be collision-free and C/sup 2/ between two cusp points.

Recognition of human gaits

Abstract: We pose the problem of recognizing different types of human gait in the space of dynamical systems where each gait is represented Established techniques are employed to track a kinematic model of a human body in motion, and the trajectories of the parameters are used to learn a representation of a dynamical system, which defines a gait. Various types of distance between models are then computed These computations are non trivial due to the fact that, even for the case of linear systems, the space of canonical realizations is not linear.

A constant feed and reduced angular acceleration interpolation algorithm for multi-axis machining

Abstract: Multi-axis tool paths are currently generated as a set of discrete data points consisting of a position vector, representing the tool tip, and an orientation unit vector, representing the tool axis. The CNC interpolator must convert these points into continuous machine tool axis motions. To achieve the highest quality parts, a constant feed and reduced angular acceleration must be maintained throughout the motion. This paper presents a new algorithm for off-line interpolation of the data points, followed by real-time axis command generation. The splines produced by the algorithm are C2 continuous, and independent of machine tool kinematics. Hence the motions produced will be the same on any five-axis machine tool, hexapod, or robotic arm. Three splines are computed: position, orientation, and reparameterization. The position spline is a near arc-length parameterized quintic polynomial spline. The paper introduces a near arc-length parameterized quintic spherical Bezier spline as the orientation spline. Coordinated motion is accomplished with an orientation reparameterization spline. The proposed algorithm is demonstrated using a practical example.

Stiffness estimation of a tripod-based parallel kinematic machine

Abstract: Presents a simple yet comprehensive approach that enables the stiffness of a tripod-based parallel kinematic machine to be quickly estimated. The approach arises from the basic idea for the determination of the equivalent stiffness of a group of serially connected linear springs and can be implemented in two steps. In the first step, the machine structure is decomposed into two substructures associated with the machine frame and parallel mechanism. The stiffness models of these two substructures are formulated by means of the virtual work principle. This is followed by the second step that enables the stiffness model of the machine structure as a whole to be achieved via linear superposition. The three-dimensional representations of the machine stiffness within the usable workspace are depicted and the contributions of different component rigidities to the machine stiffness are discussed. The results are compared with those obtained through experiments.

Mechanism Design: Enumeration of Kinematic Structures According to Function

Abstract: INTRODUCTION A Systematic Design Methodology Links and Joints Kinematic Chains, Mechanisms, and Machines Kinematics of Mechanisms Planar, Spherical, and Spatial Mechanisms Kinematic Inversions BASIC CONCEPT OF GRAPH THEORY Definitions Tree Planar Graph Spanning Trees and Fundamental Circuits Euler's Equation Topological Characteristics of Planar Graphs Matrix Representation of Graphs Contracted Graphs Dual Graphs STRUCTURAL REPRESENTATIONS OF MECHANISMS Functional Schematic Representation Structural Representation Graph Representation Matrix Representation STRUCTURAL ANALYSIS OF MECHANISMS Correspondence between Mechanisms and Graphs Degrees of Freedom Loop Mobility Criterion Lower and Upper Bounds on the Number of Joints on a Link Link Assortments Partition of Binary Link Chains Structural Isomorphism Permutation Group and Group of Automorphisms Identification of Structural Isomorphism Partially Locked Kinematic Chains ENUMERATION OF GRAPHS OF KINEMATIC CHAINS Enumeration of Contracted Graphs Enumeration of Conventional Graphs Atlas of Graphs of Kinematic Chains CLASSIFICATION OF MECHANISMS Planar Mechanisms Spherical Mechanisms Spatial Mechanisms EPICYCLIC GEAR TRAINS Structural Characteristics Buchsbaum-Freudenstein Method Genetic Graph Approach Parent Bar Linkage Method Mechanism Pseudo Isomorphisms Atlas of Epicyclic Gear Trains Kinematics of Epicyclic Gear Trains AUTOMOTIVE MECHANISMS Variable-Stroke Engine Mechanisms Constant-Velocity Shaft Couplings Automatic Transmission Mechanisms Canonical Graph Representation of EGMs Atlas of Epicyclic Gear Transmission Mechanisms ROBOTIC MECHANISMS Parallel Manipulators Robotic Wrist Mechanisms APPENDICES: A. Solving m Equations in n unknowns B. Atlas of Contracted Graphs C. Atlas of Graphs of Kinematic Chains D. Atlas of Planar Bar Linkages E. Atlas of Spatial One-dof Kinematic Chains F. Atlas of Epicyclic Gear Trains G. Atlas of Epicyclic Gear Transmission Mechanisms NOTE: Introduction at the beginning of Chapters 1,3-9 Summary at the end of Chapters 1-6,8-9

Review of Attitude Representations Used for Aircraft Kinematics

Abstract: Adetailed survey ispresentedoftheliteratureonattituderepresentationdatingfromtheearlyworkofEulerand Hamilton to recent publications in e elds such as navigation and control. The scope is limited to the development of the aircraft kinematic transformation equations in terms of four different attitude representations, including the well-known Euler angles, the Euler-axis rotation parameters, the direction cosines, and the Euler ‐Rodrigues quaternion.Theemphasisisdirectedattheapplicationofthequaternionformulationtoaircraftkinematics.Results are presented that reinforce observations that the quaternion formulation, typically implemented to eliminate singularities associated with the Euler angle formulation, is far superior to the other commonly used formulations based on computational efe ciency alone. A development of quaternion constraints necessary to independently constrain roll, pitch, yaw, bank angle, elevation angle, and/or azimuth angle is presented. For verie cation of simulation codes, a general closed-form solution to the quaternion formulation, for the case of constant rotation, is also presented. Additionally, a discussion is provided of numerical integration methods and numerical errors for the quaternion formulation. This discussion is especially important for simulations that may still utilize a common error reduction scheme originally developed for analog computers.

Drift-free attitude estimation for accelerated rigid bodies

Abstract: We study the attitude estimation problem for an accelerated rigid body using gyros and accelerometers. The application in mind is that of a walking robot and particular attention is paid to the large and abrupt changes in accelerations that can be expected in such an environment. We propose a state estimation algorithm that fuses data from rate gyros and accelerometers to give long-term drift free attitude estimates. The algorithm does not use any local parameterization of the rigid body kinematics and can thus be used for a rigid body performing any kind of rotations. The algorithm is a combination of two non-standard, but in a sense linear, Kalman filters between which a trigger based switching takes place. The kinematics representation used makes it possible to construct a linear algorithm that can be shown to give convergent estimates for this nonlinear problem. The state estimator is evaluated in simulations demonstrating how the estimates are long term stable even in the presence of gyrodrift.

Dynamic modeling of musculoskeletal motion : a vectorized approach for biomechanical analysis in three dimensions

Abstract: Acknowledgments Foreword Part I: An Introduction to Musculotendon Modeling and Analysis 1 Overview of Dynamic Musculoskeletal Modeling 2 An Introduction to Modeling Muscle and Tendon Part II: Defining Skeletal Kinematics 3 Rigid Bodies and Reference Frames 4 Vector Based Kinematics 5 Models of the Skeletal System Part III: Dynamic Equations of Motion 6 Dynamic Equations of Motion 7 Control Appendices About the Author Index

On the Kinematic Error in Harmonic Drive Gears

Abstract: Harmonic drive gears are widely used in space applications, robotics, and precision positioning systems because of their attractive attributes including near-zero backlash, high speed reduction ratio, compact size, and small weight. On the other hand, they possess an inherent periodic positioning error known as kinematic error responsible for transmission performance degradation. No definite understanding of the mechanism of kinematic error as well as its characterization is available in the literature. In this paper, we report analytical and experimental results on kinematic error using a dedicated research Harmonic Drive Test Apparatus. We first show that the error referred to in the literature as kinematic error actually consists of a basic component, representing ‘‘pure’’ kinematic error, colored with a second component resulting from inherent torsional flexibility in the harmonic drive gear. The latter component explains the source of variability in published kinematic error profiles. The decomposition of the kinematic error into a basic component and a flexibility related component is demonstrated experimentally as well as analytically by matching a mathematical model to experimental data. We also characterize the dependence of the kinematic error on inertial load, gear assembly, and rotational speed. The results of this paper offer a new perspective in the understanding of the mechanism of kinematic error and will be valuable in the mechanical design of harmonic drive gears as well as in the dynamic modeling and precision control of harmonic drive systems. @DOI: 10.1115/1.1334379#

Reciprocal angular acceleration of the ankle and hip joints during quiet standing in humans.

Abstract: Human quiet standing is often modeled as a single inverted pendulum rotating around the ankle joint, under the assumption that movement around the hip joint is quite small. However, several recent studies have shown that movement around the hip joint can play a significant role in the efficient maintenance of the center of body mass (COM) above the support area. The aim of this study was to investigate how coordination between the hip and ankle joints is controlled during human quiet standing. Subjects stood quietly for 30 s with their eyes either opened (EO) or closed (EC), and we measured subtle angular displacements around the ankle (θ a ) and hip (θ h ) joints using three highly sensitive CCD laser displacement sensors. Reliable data were obtained for both angular displacement and angular velocity (the first derivative of the angular displacement). Further, measurement error was not predominant, even among the angular acceleration data, which were obtained by taking the second derivative of the angular displacement. The angular displacement, velocity, and acceleration of the hip were found to be significantly greater (P<0.001) than those of the ankle, confirming that hip-joint motion cannot be ignored, even during quiet standing. We also found that a consistent reciprocal relationship exists between the angular accelerations of the hip and ankle joints, namely positive or negative angular acceleration of ankle joint is compensated for by oppositely directed angular acceleration of the hip joint. Principal component analysis revealed that this relationship can be expressed as: $$\ddot \theta _h = \gamma \ddot \theta _a $$ with γ=–3.15±1.24 and γ=–3.12±1.46 (mean ±SD) for EO and EC, respectively, where ' $$\ddot \theta $$ ' is the angular acceleration. There was no significant difference in the values of γ for EO and EC, and these values were in agreement with the theoretical value calculated assuming the acceleration of COM was zero. On the other hand, such a consistent relationship was never observed for angular displacement itself. These results suggest that the angular motions around the hip and ankle joints are not to keep the COM at a constant position, but rather to minimize acceleration of the COM.

Biomechanical analysis of movement strategies in human forward trunk bending. I. Modeling.

Abstract: Two behavioral goals are achieved simultaneously during forward trunk bending in humans: the bending movement per se and equilibrium maintenance. The objective of the present study was to understand how the two goals are achieved by using a biomechanical model of this task. Since keeping the center of pressure inside the support area is a crucial condition for equilibrium maintenance during the movement, we decided to model an extreme case, called "optimal bending", in which the movement is performed without any center of pressure displacement at all, as if standing on an extremely narrow support. The "optimal bending" is used as a reference in the analysis of experimental data in a companion paper. The study is based on a three-joint (ankle, knee, and hip) model of the human body and is performed in terms of "eigenmovements", i.e., the movements along eigenvectors of the motion equation. They are termed "ankle", "hip", and "knee" eigenmovements according to the dominant joint that provides the largest contribution to the corresponding eigenmovement. The advantage of the eigenmovement approach is the presentation of the coupled system of dynamic equations in the form of three independent motion equations. Each of these equations is equivalent to the motion equation for an inverted pendulum. Optimal bending is constructed as a superposition of two (hip and ankle) eigenmovements. The hip eigenmovement contributes the most to the movement kinematics, whereas the contributions of both eigenmovements into the movement dynamics are comparable. The ankle eigenmovement moves the center of gravity forward and compensates for the backward center of gravity shift that is provoked by trunk bending as a result of dynamic interactions between body segments. An important characteristic of the optimal bending is the timing of the onset of each eigenmovement: the ankle eigenmovement onset precedes that of the hip eigenmovement. Without an earlier onset of the ankle eigenmovement, forward bending on the extremely narrow support results in falling backward. This modeling approach suggests that during trunk bending, two motion units--the hip and ankle eigenmovements--are responsible for the movement and for equilibrium maintenance, respectively.