Showing papers on "Kinematics published in 1998"

Theory of sintering: from discrete to continuum

Abstract: Theoretical concepts of sintering were originally based upon ideas of the discrete nature of particulate media. However, the actual sintering kinetics of particulate bodies are determined not only by the properties of the particles themselves and the nature of their local interaction with each other, but also by macroscopic factors. Among them are externally applied forces, kinematic constraints (e.g. adhesion of the sample's end face and furnace surface), and inhomogeneity of properties in the volume under investigation (e.g. inhomogeneity of initial density distribution created during preliminary forming operations). Insufficient treatment of the questions enumerated above was one of the basic reasons hindering the use of sintering theory. A promising approach is connected with the use of continuum mechanics, which has been successfully applied to the analysis of compaction of porous bodies. This approach is based upon the theories of plastic and nonlinear-viscous deformation of porous bodies. Similar ideas have recently been embodied in a continuum theory of sintering. The main results of the application of this theory for the solution of certain technological problems of sintering are introduced including their thermo–mechanical aspects.

A point cluster method for in vivo motion analysis: applied to a study of knee kinematics.

Abstract: A new method for deriving limb segment motion from markers placed on the skin is described. The method provides a basis for determining the artifact associated with nonrigid body movement of points placed on the skin. The method is based on a cluster of points uniformly distributed on the limb segment. Each point is assigned an arbitrary mass. The center of mass and the inertia tensor of this cluster of points are calculated. The eigenvalues and eigenvectors of the inertia tensor are used to define a coordinate system in the cluster as well as to provide a basis for evaluating non-rigid body movement. The eigenvalues of the inertia tensor remain invariant if the segment is behaving as a rigid body, thereby providing a basis for determining variations for nonrigid body movement. The method was tested in a simulation model where systematic and random errors were introduced into a fixed cluster of points. The simulation demonstrated that the error due to nonrigid body movement could be substantially reduced. The method was also evaluated in a group of ten normal subjects during walking. The results for knee rotation and translation obtained from the point cluster method compared favorably to results previously obtained from normal subjects with intra-cortical pins placed into the femur and tibia. The resulting methodology described in this paper provides a unique approach to the measurement of in vivo motion using skin-based marker systems.

Inverse and forward numerical modeling of trishear fault‐propagation folds

Abstract: Fault-propagation folds commonly display footwall synclines as well as changes in stratigraphic thickness and dip on their forelimbs, features that cannot easily be explained by simple parallel kink fold kinematics. An alternative kinematic model, trishear, can explain these observations, as well as a variety of other features which have long intrigued structural geologists. Trishear has received little attention until recently, in part because it must be applied numerically rather than graphically. A new computer program has been developed to analyze trishear and hybrid trishear-fault-bend fold deformation. Trishear fold shape can vary considerably by changing the apical angle of the trishear zone and/or the propagation to slip ratio (P/S) during the evolution of the structure. Breakouts, anticlinal and synclinal ramps, and inversion structures can also be modeled, tracking the kinematics with growth strata. Strain within trishear zones can be used to predict fracture orientations throughout the structures as demonstrated by comparison with analog clay models. Also presented is a method for inverting data on real structures for a best fit trishear model by performing a grid search over a six-parameter space (ramp angle, trishear apical angle, displacement, P/S, and X and Y positions of the fault tip line). The inversion is performed by restoring a key bed to a planar orientation by least squares regression. Because trishear provides a bulk kinematic description of a deforming zone, it is complementary to, rather than competing with, other kinematic models.

Further passivity results for the attitude control problem

Abstract: In this paper we establish passivity for the system which describes the attitude motion of a rigid body in terms of minimal three-dimensional kinematic parameters. In particular, we show that linear asymptotically stabilizing controllers and control laws without angular velocity measurements follow naturally from these passivity properties. The results of this paper extend similar results for the case of the (nonminimal) Euler parameters.

Generalized 3-D tolerance analysis of mechanical assemblies with small kinematic adjustments

Abstract: The direct linearization method (DLM) for tolerance analysis of 3-D mechanical assemblies is presented. Vector assembly models are used, based on 3-D vector loops which represent the dimensional chains that produce tolerance stackup in an assembly. Tolerance analysis procedures are formulated for both open and closed loop assembly models. The method generalizes assembly variation models to include small kinematic adjustments between mating parts. Open vector loops describe critical assembly features. Closed vector loops describe kinematic constraints for an assembly. They result in a set of algebraic equations which are implicit functions of the resultant assembly dimensions. A general linearization procedure is outlined, by which the variation of assembly parameters may be estimated explicitly by matrix algebra. Solutions to an over-determined system or a system having more equations than unknowns are included. A detailed example is presented to demonstrate the procedures of applying the DLM to a 3-D mechanical assembly.

A Unified Approach to Motion Control of Mobile Manipulators

Abstract: This paper presents a simple on-line approach for motion control of mobile manipulators comprising a manipulator arm mounted on a mobile base. The proposed approach is equally applicable to nonholonomic mobile robots such as rover-mounted manipulators and holonomic mobile robots such as tracked robots and compound manipulators. For wheeled mobile robots, the nonholonomic base constraints are incorporated directly into the task formulation as kinematic constraints. The configuration control approach is ex tended to exploit the redundancy introduced by the base mobility to perform a set of user-specified additional tasks during the end- effector motion while satisfying the nonholonomic base constraints (if applicable). This approach treats the base nonholonomy and the kinematic redundancy in a unified manner to formulate new task constraints. The computational efficiency of the proposed control scheme makes it particularly suitable for real-time implementation. Two simulation studies are presented to demons...

A Least-Squares Estimation Approach to Improving the Precision of Inverse Dynamics Computations

Abstract: A least-squares approach to computing inverse dynamics is proposed. The method utilizes equations of motion for a multi-segment body, incorporating terms for ground reaction forces and torques. The resulting system is overdetermined at each point in time, because kinematic and force measurements outnumber unknown torques, and may be solved using weighted least squares to yield estimates of the joint torques and joint angular accelerations that best match measured data. An error analysis makes it possible to predict error magnitudes for both conventional and least-squares methods. A modification of the method also makes it possible to reject constant biases such as those arising from misalignment of force plate and kinematic measurement reference frames. A benchmark case is presented, which demonstrates reductions in joint torque errors on the order of 30 percent compared to the conventional Newton-Euler method, for a wide range of noise levels on measured data. The advantages over the Newton-Euler method include making best use of all available measurements, ability to function when less than a full complement of ground reaction forces is measured, suppression of residual torques acting on the top-most body segment, and the rejection of constant biases in data.

Multi-Body Dynamics: Vehicles, Machines and Mechanisms

Abstract: Vectors and transformations kinematics and dynamics of particles and rigid bodies constraints formulation in multi-body systems multi-body dynamic analysis multi-body analysis - solution methodology engine dynamics power train dynamics optimal control of multi-body systems.

Singularity analysis for articulated object tracking

Abstract: We analyze the use of kinematic constraints for articulated object tracking. Conditions for the occurrence of singularities in 3-D models are presented and their effects on tracking are characterized We describe a novel 2-D Scaled Prismatic Model (SPM) for figure registration. In contrast to 3-D kinematic models, the SPM has fewer singularity problems and does not require detailed knowledge of the 3-D kinematics. We fully characterize the singularities in the SPM and illustrate tracking through singularities using synthetic and real examples with 3-D and 2-D models. Our results demonstrate the significant benefits of the SPM in tracking with a single source of video.

Calibration of stewart platforms and other parallel manipulators by minimizing inverse kinematic residuals

Abstract: This paper focuses on the accuracy enhancement of Stewart platforms through kinematic calibration The calibration problem is formulated in terms of a measurement residual, which is the discrepancy between the measured leg length and the computed leg length With this formulation, one is able to identify kinematic error parameters of the Stewart platform without the necessity of solving the forward kinematic problem; thus avoiding the numerical problems associated with any forward kinematic solution By this formulation, a concise differential error model with a well-structured identification Jacobian, which relates the pose measurement residual to the errors in the parameters of the platform, is derived Experimental studies confirmed the effectiveness of the method It is also shown in this paper that the proposed approach can be applied to other types of parallel manipulators, assuming that their inverse kinematic solution is simpler than its forward kinematic solution Because this condition is satisfied by almost all parallel manipulators, the method is very useful for kinematic calibration of such machines © 1998 John Wiley & Sons, Inc

The generation of handwriting with delta-lognormal synergies

Abstract: This paper presents a handwriting generation model that takes advantage of the asymptotic impulse response of neuromuscular networks to produce and control complex two-dimensional synergistic movements. A parametric definition of a ballistic stroke in the context of the kinematic theory of rapid human movements is given. Two types of parameters are used: command and system parameters. The first group provides a representation of the action plan while the second takes into account the temporal properties of the neuromuscular systems executing that plan. Handwriting is described as the time superimposition of basic discontinuous strokes that results in a continuous summation of delta-lognormal velocity vectors. The model leads to trajectory reconstruction, both in the spatial and in the kinematic domain. According to this new paradigm, the angular velocity does not have to be controlled independently and continuously; it naturally emerges from the vectorial summation process. Several psychophysical phenomena related to two-dimensional movements are explained and analyzed in the context of the model: the speed/accuracy trade-offs, spatial scaling, the isochrony principle, the two-thirds power law, effector independence, etc. The overall approach also shows how basic handwriting characteristics (dimension, slant, baseline, shape, etc.) are affected and controlled using an action plan made up of virtual targets fed into a neuromuscular synergy that is governed by a delta-lognormal law.

A comparative study of three methods for robot kinematics

Abstract: Three methods for the formulation of the kinematic equations of robots with rigid links are presented in this paper. The first and most common method in the robotics community is based on 4/spl times/4 homogeneous matrix transformation, the second one is based on Lie algebra, and the third one on screw theory expressed via dual quaternions algebra. These three methods are compared in this paper for their use in the kinematic analysis of robot arms. The basic theory and the transformation operators, upon which every method is based, are referenced. Three analytic algorithms are presented for the solution of the direct kinematic problem corresponding to each method, and the geometric significance of the transformation operators and parameters is explained. Finally, a comparative study on the computation and storage requirements for the three methods is worked out.

Evaluation of Performance Criteria for Simulation of Submaximal Steady-State Cycling Using a Forward Dynamic Model

Abstract: The objectives of this study were twofold. The first was to develop a forward dynamic model of cycling and an optimization framework to simulate pedaling during submaximal steady-state cycling conditions. The second was to use the model and framework to identify the kinetic, kinematic, and muscle timing quantities that should be included in a performance criterion to reproduce natural pedaling mechanics best during these pedaling conditions. To make this identification, kinetic and kinematic data were collected from 6 subjects who pedaled at 90 rpm and 225 W. Intersegmental joint moments were computed using an inverse dynamics technique and the muscle excitation onset and offset were taken from electromyographic (EMG) data collected previously (Neptune et al., 1997). Average cycles and their standard deviations for the various quantities were used to describe normal pedaling mechanics. The model of the bicycle-rider system was driven by 15 muscle actuators per leg. The optimization framework determined both the timing and magnitude of the muscle excitations to simulate pedaling at 90 rpm and 225 W. Using the model and optimization framework, seven performance criteria were evaluated. The criterion that included all of the kinematic and kinetic quantities combined with the EMG timing was the most successful in replicating the experimental data. The close agreement between the simulation results and the experimentally collected kinetic, kinematic, and EMG data gives confidence in the model to investigate individual muscle coordination during submaximal steady-state pedaling conditions from a theoretical perspective, which to date has only been performed experimentally.

Working modes and aspects in fully parallel manipulators

Abstract: The aim of this paper is to characterize the notion of aspects in the workspace and in the joint space for parallel manipulators. In opposite to the serial manipulators, the parallel manipulators can admit not only multiple inverse kinematic solutions, but also multiple direct kinematic solutions. Two Jacobian matrices appear in the kinematic relations between the joint-rate and the Cartesian-velocity vectors, which are called the "inverse kinematics" and the "direct kinematics" matrices. The study of these matrices allow one to define the parallel and the serial singularities respectively. The notion of working modes is introduced to separate inverse kinematic solutions. Thus we can find out the domains of the workspace and the joint space which exempt of singularity. An application of this study is the movability analysis in the workspace of the manipulator as well as the path-planning and control. This study is illustrated with a RR-RRR planar parallel manipulator.

Effects of incline on speed, acceleration, body posture and hindlimb kinematics in two species of lizard Callisaurus draconoides and Uma scoparia.

Abstract: We examined the effects of incline on locomotor performance and kinematics in two closely related species of iguanian lizards that co-occur in sandy desert habitats. Callisaurus draconoides differs from Uma scoparia of equal snout-vent length by being less massive and having greater limb and tail lengths. We analyzed high-speed video tapes of lizards sprinting from a standstill on a sand-covered racetrack which was level or inclined 30 degrees uphill. C. draconoides sprinted significantly faster than U. scoparia on both level and uphill sand surfaces, although U. scoparia is considered to be more specialized for sandy habitats. Initial accelerations (over the first 50 ms) did not differ significantly either between species or between inclines within species. Overall, the effects of incline were more pronounced for C. draconoides than for U. scoparia. For example, the incline caused a significant decrease in the maximum stride length of C. draconoides but not in that of U. scoparia. For C. draconoides, uphill stride durations were significantly shorter than on the level surface, and this partially compensated for the effects of shorter uphill stride lengths on velocity. C. draconoides ran bipedally more often than did U. scoparia on both the level and uphill surfaces.

A kinematic theory of rapid human movements: Part III. Kinetic outcomes.

Abstract: This paper describes the kinematic and kinetic properties of simple rapid movements using a single and unique framework based on a delta-lognormal law (Plamondon 1993a,b, 1995a,b). Predictions concerning isotonic measurements are made using the properties of acceleration profiles, as described by the first time derivative of the delta-lognormal law. Predictions dealing with isometric measurements are directly analyzed using the delta-lognormal law, after demonstrating the experimental equivalence between isometric forces and virtual velocity profiles. The theory is also used to make statistical predictions about the variability of numerous kinematic and kinetic variables. The overall approach can be viewed as if, at some level of representation, the central nervous system were planning, executing and evaluating simple rapid movements in terms of momentum and energy instead of forces. The unifying perspective provided by the theory constitutes a powerful tool with which to study and analyze movements under numerous experimental conditions, using a single analytical law.

Force Control of Robotics Systems

Abstract: Force Information and its Use in Robotic Systems Use of Force Information: Objectives and Problems Force Measurement Use of Force Information in Control PART I. FORCE SENSORS Conceptual Designs of Force Sensors Fundamentals of Sensor Design Gripper Sensors Wrist Sensors Other Types of Force Sensor Basic Theory and Design Computation of Force Sensors Main Characteristics of Force Sensors Design Computations for Sensor Modular Elements Six-Component Sensors with a Bending Elastic Element Sensors with a Compressive-Tensile and Shear Elastic Element PART II. MATHEMATICAL MODELS AND CONTROL Research Robotic System Manipulator Design and Kinematics Control System End-Effectors and Sensors Control of Manipulator Contact With an Object Mathematical Model for One-Degree-of-Freedom Manipulator Motion Problem Statement for Keeping Contact with an Object Linear Control Switching Control Contact Transition Control Influence of Delay in Feedback Loop on the Stability of Contact Influence of Transmission Compliance on the Stability of Contact Influence of Manipulator Frame Compliance on the Stability of Contact Keeping Contact with a Moving Object Two-Degree-of-Freedom Manipulator Motion in Contact With an Object Mathematical Model for Two-Degree-of-Freedom Manipulator Motion Control Problem Statement Following a Linear Contour Following a Circular Contour Experiments in Contour Following Rotating a Steering Wheel Planar Two-Link Manipulator Control of Constraint Motion General Mathematical Model for a Manipulator With a Force Sensor Discussion on Equations of Motion. Simplified Model Control of Manipulator Motion Along Constraints Articulated Manipulator Motion in Contact with an Object Motion Along a Screw Constraint Opening a Hatch Lid Discrete-Time Manipulator Control Design Problems of Keeping Contact With a Stationary and Moving Object The Simplest Discrete-Time Model for One-Degree-of-Freedom Manipulator Motion Discrete-Time Model for Manipulator with Compliance in Gear Train Manipulator Model with a Compliant Base Discrete Control of Contact Transition Maintaining Contact Force with a Moving Object Control of Manipulator with Structural Compliance for a Moving Contact Point Experiments in Maintaining Contact Force for a Moving Contact Point PART III. APPLICATIONS Manipulator Control in Surface Machining Requirements for Grinding Tasks Grinding of a Stationary Part Grinding of a Part in the Manipulator Arm Experiments in Grinding Assembly Operations Inserting a Peg into a Hole Manipulator Control in a Peg-Hole Insertion Threaded Joint Assembly Manipulator Control in Threaded Joint Assembly Searching for Parts and Grasping Part Pickup Tasks One-by-One Pickup of Parts Using Electromagnetic Gripper Part Pickup Using Force Sensing Fingers References Index

The control of multi-muscle systems: human jaw and hyoid movements

Abstract: A model is presented of sagittal plane jaw and hyoid motion based on the λ model of motor control. The model, which is implemented as a computer simulation, includes central neural control signals, position- and velocity-dependent reflexes, reflex delays, and muscle properties such as the dependence of force on muscle length and velocity The model has seven muscles (or muscle groups) attached to the jaw and hyoid as well as separate jaw and hyoid bone dynamics. According to the model, movements result from changes in neurophysiological control variables which shift the equilibrium state of the motor system. One such control variable is an independent change in the membrane potential of α-motoneurons (MNs): this variable establishes a thresh-old muscle length (λ) at which MN recruitment begins. Motor functions may be specified by various combinations of λs. One combination of λs is associated with the level of coactivation of muscles. Others are associated with motions in specific degrees of freedom. Using the model, we study the mapping between control variables specified at the level of degrees of freedom and control variables corresponding to individual muscles. We demonstrate that commands can be defined involving linear combinations of λ change which produce essentially independent movements in each of the four kinematic degrees of freedom represented in the model (jaw orientation, jaw position, vertical and horizontal hyoid position) These linear combinations are represented by vectors in λ space which may be scaled in magnitude. The vector directions are constant over the jaw/hyoid workspace and result in essentially the same motion from any workspace position. The demonstration that it is not necessary to adjust control signals to produce the same movements in different parts of the workspace supports the idea that the nervous system need not take explicit account of musculo-skeletal geometry in planning movements.

Knee joint motion: description and measurement.

Abstract: Knee joint motion has been described in various ways in the literature. These are explained and commented on. Two methods for describing knee joint motion with 6 degrees of freedom (DOF)--Euler angle and the helical axis of motion--are discussed. Techniques to measure joint motion which can either approximate the motion to less than 6 DOF or fully measure the spatial motion are identified. These include electrical linkage methods, radiographic and video techniques, fluoroscopic techniques and electromagnetic devices. In those cases where the full spatial motion is measured, the data are available to describe the motion in simpler terms (or with less DOF) than three rotations with three translations. This is necessary for clinical application and to facilitate communication between the clinician and the engineer.

New concepts for linear beam theory with arbitrary geometry and loading

Abstract: A new approach is introduced for the analysis and calculation of straight prismatic beams of piecewise constant cross-section under arbitrary loads. This theory can be called “exact” because it determines exact static and kinematic generalized quantities. Moreover, contrary to classical theories, it is not limited to high-aspect ratio (i.e. relatively slender) beams.

Two degree-of-freedom spherical orienting device

Abstract: The invention provides a simple rugged two degree-of-freedom spherical orienting device applicable to point payloads such as cameras, mirrors, lasers, antennas and the like. A spherical five-bar mechanism with payload support is actuated by two rotary actuators fixed in position to a base. Advantages of the device include: the preserving of image horizon for cameras (in contrast to three degree-of-freedom devices); the ability to position the payload at the geometric center of rotation thereby reducing inertia; high stiffness enabling orientation of large loads and use of high angular velocities and accelerations; simplification of inverse kinematic computation; relatively large outward workspace (approximating a hemisphere) and large internal free space for payload orienting.

Advances in Robot Kinematics: Analysis and Control

Abstract: From the Publisher: The book provides a state-of-the-art and recent advances in the area of kinematics of robots and mechanisms. The book consists of about fifty outstanding contributions dedicated to various aspects of kinematic modelling and control, emphasising in particular the kinematics performances of robots and mechanisms, workspace and trajectory analysis, numerical and symbolic computational methods and algorithms, analysis, simulation and optimisation. The book is of interest to researchers, graduate students, and engineers specialising in the kinematics of robots and mechanisms. The book should also be of interest to those engaged in work relating to kinematic chains, mechatronics, mechanism design, biomechanics and intelligent systems.

An anthropomorphic biped robot: dynamic concepts and technological design

Abstract: The authors of this study are a part of a joint project, involving four French laboratories, whose goal is the design and construction of a mechanical biped robot with anthropomorphic characteristics. In the first section of this paper, we will examine mechanical architectures of some representatives of state-of-the art biped robots by focusing on their kinematic arrangement. It is widely known that the existence of natural gaits is closely linked to the intrinsic dynamic characteristics of the mechanical structure of the biped robot. In order to further develop this idea, two studies will be presented in the second section: the first is relative to the lateral instability of the system while the second deals with the existence of passive pendular gaits during the swing phase of walking in the sagittal plane. In the last section, in correlation with the observations made, we will gain insight into main characteristics of the mechanical architecture that we have designed for the BIP project: 15 active degrees of freedom (DOF), joints actuated by special transmission system, anthropometric mass distribution.