Showing papers on "Kinematics published in 1997"

Modelling and Control of Robot Manipulators

Abstract: Introduction Kinematics Differential Kinematics and Statics Dynamics Trajectory Planning Motion Control Interaction Control Actuators and Sensors Control Architecture Appendices A. Linear Algebra B. Rigid Body Mechanics C. Feedback Control

Singularity-robust task-priority redundancy resolution for real-time kinematic control of robot manipulators

Abstract: Practical application of the task-priority redundancy resolution technique must deal with the occurrence of kinematic and algorithmic singularities. The aim of this paper is twofold. First, the application of existing singularity-robust methods to the case of kinematically redundant arms is studied. Then, a new task-priority redundancy resolution technique is developed that overcomes the effects of algorithmic singularities. Computational aspects of the solutions are also considered in view of real-time implementation of a kinematic control algorithm. The method is applied to a seven-degree-of-freedom manipulator in numerical case studies to demonstrate its effectiveness.

Speed/accuracy trade-offs in target-directed movements.

Abstract: This target article presents a critical survey of the scientific literature dealing with the speed/accuracy trade-offs in rapid-aimed movements. It highlights the numerous mathematical and theoretical interpretations that have been proposed in recent decades. Although the variety of points of view reflects the richness of the field and the high degree of interest that such basic phenomena attract in the understanding of human movements, it calls into question the ability of 'many models to explain the basic observations consistently reported in the field. This target article summarizes the kinematic theory of rapid human movements, proposed recently by R. Plamondon (1993b; 1993c; 1995a; 1995b), and analyzes its predictions in the context of speed/accuracy trade-offs. Data from human movement literature are reanalyzed and reinterpreted in the context of the new theory. It is shown that the various aspects of speed/accuracy trade- offs can be taken into account by considering the asymptotic behavior of a large number of coupled linear systems, from which a delta- lognormal law can be derived to describe the velocity profile of an end-effector driven by a neuromuscular synergy. This law not only describes velocity profiles almost perfectly, it also predicts the kinematic properties of simple rapid movements and provides a consistent framework for the analysis of different types of speed/accuracy trade-offs using a quadratic (or power) law that emerges from the model.

Control of a nonholomic mobile robot: Backstepping kinematics into dynamics

Abstract: A dynamical extension that makes possible the integration of a kinematic controller and a torque controller for nonholonomic mobile robots is presented. A combined kinematic/torque control law is developed using backstepping, and asymptotic stability is guaranteed by Lyapunov theory. Moreover, this control algorithm can be applied to the three basic nonholonomic navigation problems: tracking a reference trajectory, path following, and stabilization about a desired posture. The result is a general structure for controlling a mobile robot that can accommodate different control techniques, ranging from a conventional computed-torque controller, when all dynamics are known, to robust-adaptive controllers if this is not the case. A robust-adaptive controller based on neural networks (NNs) is proposed in this work. The NN controller can deal with unmodeled bounded disturbances and/or unstructured unmodeled dynamics in the vehicle. On-line NN weight tuning algorithms that do not require off-line learning yet guarantee small tracking errors and bounded control signals are utilized. © 1997 John Wiley & Sons, Inc.

Kinematic isotropy and the optimum design of parallel manipulators

Abstract: The differential kinematic equations (DKE) of parallel manip ulators usually involve two Jacobian matrices that, depending on the role they play in the kinetostatic transformation between the joint and Cartesian variables, are commonly referred to as the forward and the inverse Jacobians. In this article, we make use of the special structure of these Jacobians to define a set of conditions under which a parallel manipulator can be rendered isotropic. These conditions are general, and pro vide a systematic method for the optimum kinematic design of parallel manipulators, with or without introducing structural constraints. The application of the proposed conditions is illus trated in detail through a few examples, one of which pertains to the design of a 6-DOF isotropic parallel manipulator.

Self-calibration of parallel mechanisms with a case study on Stewart platforms

Abstract: Self-calibration has the potential of: 1) removing the dependence on any external pose sensing information; 2) producing high accuracy measurement data over the entire workspace of the system with an extremely fast measurement rate; 3) being automated and completely noninvasive; 4) facilitating on-line accuracy compensation; and 5) being cost effective. A general framework is introduced in this paper for the self-calibration of parallel manipulators. The concept of creating forward and inverse measurement residuals by exploring conflicting information provided with redundant sensing is proposed. Some of these ideas have been widely used for robot calibration when robot end-effector poses are available. By this treatment, many existing kinematic parameter estimation techniques can be applied for the self-calibration of parallel mechanisms. It is illustrated through a case study, i.e. calibration of the Stewart platform, that with this framework the design of a suitable self-calibration system and the formulation of the relevant mathematical model become more systematic. A few principles important to the system self-calibration are also demonstrated through the case study. It is shown that by installing a number of redundant sensors on the Stewart platform, the system is able to perform self-calibration. The approach provides a tool for rapid and autonomous calibration of the parallel mechanism.

A modular system for robust positioning using feedback from stereo vision

Abstract: This paper introduces a modular framework for robot motion control using stereo vision. The approach is based on a small number of generic motion control operations referred to as primitive skills. Each primitive skill uses visual feedback to enforce a specific task-space kinematic constraint between a robot end-effector and a set of target features. By observing both the end-effector and target features, primitive skills are able to position with an accuracy that is independent of errors in hand-eye calibration. Furthermore, primitive skills are easily combined to form more complex kinematic constraints as required by different applications. These control laws have been integrated into a system that performs tracking and control on a single processor at real-time rates. Experiments with this system have shown that it is extremely accurate, and that it is insensitive to camera calibration error. The system has been applied to a number of example problems, showing that modular, high precision, vision-based motion control is easily achieved with off-the-shelf hardware.

The Process of Motion Capture: Dealing with the Data

Abstract: This paper presents a detailed description of the process of motion capture, whereby sensor information from a performer is transformed into an articulated, hierarchical rigid-body object. We describe the gathering of the data, the real-time construction of a virtual skeleton which a director can use for immediate feedback, and the offline processing which produces the articulated object. This offline process involves a robust statistical estimation of the size of the skeleton and an inverse kinematic optimization to produce the desired joint angle trajectories. Additionally, we discuss a variation on the inverse kinematic optimization which can be used when the standard approach does not yield satisfactory results for the special cases when joint angle consistency is desired between a group of motions. These procedures work well and have been used to produce motions for a number of commercial games.

Biomimetic robotic propulsion using polymeric artificial muscles

Abstract: Biomimetic fish-like propulsion using polyelectrolyte ion-exchange membrane metal composites as a propulsion fin for a robotic swimming structure, such as a boat swimming in water medium, was investigated. The membrane was chemically plated with platinum. The resulting membrane was cut in a strip to resemble fish-like caudal fin for propulsion. A small function generator circuit was designed and built to produce approximately /spl plusmn/2.0 V amplitude signal at desired frequency up to 50 Hz. The circuit board was mounted on a buoyant Styrofoam shaped like a boat or a tadpole. The fin was attached to the rear of the boat. By setting the signal frequency to the desired value and thereby setting the frequency of bending oscillation of the membrane, a proportional forward propulsion speed could be obtained. The speed was then measured using a high speed camera. Several theoretical hydrodynamic models were then presented to characterize speed-frequency of the forward motion using available theories on biological fish motion. The results were compared to experimental data which showed close agreement.

Design of Ball Wheel Mechanisms for Omnidirectional Vehicles With Full Mobility and Invariant Kinematics

Abstract: A new ball wheel design for fully mobile omnidirectional vehicles is presented. This ball wheel mechanism yields a unique vehicle design that is not only omnidirectional with no kinematic singularity but is configuration-invariant in kinematic behavior. Invariant kinematics greatly simplifies the control of smooth and precise vehicle motion. Multiple displacement sensors are easily incorporated into each ball wheel mechanism to enhance the accuracy of vehicle motion control. Two fundamental requirements of functioning ball wheel designs are established: one is the translational form closure requirement for holding a spherical tire, and the other is the non-overconstraint requirement to allow each ball to rotate in two directions. It is proved that a class of mechanisms in which a ball is held by rollers whose axes are fixed directly to the vehicle chassis cannot satisfy the fundamental requirements. A class of modified mechanisms are then analyzed and the necessary and sufficient conditions for the modified mechanisms the fundamental requirements are obtained. For this class of ball wheels (Class 1), conditions for configuration-invariant kinematics are found and two possible actuation schemes are discussed. Two prototype vehicles have been built: both have three Class 1 ball wheels but each uses a different actuation scheme. Performance data of the two prototypes are compared. Both achieve smooth motion and precise dead reckoning.

Head/neck kinematic response of human subjects in low-speed rear-end collisions

Abstract: Limited data exist which quantify the kinematic response of the human head and cervical spine in low-speed rear-end automobile collisions. The objectives of this study were to quantify human head/neck kinematics, and how they vary with vehicle speed change and gender during low-speed rear-end collisions. Forty-two human subjects (21 male, 21 female) were exposed to two rear-end vehicle-to-vehicle impacts (speed changes of 4 km/h and 8 km/h). Accelerations and displacements of the head and torso were measured using 6 degree-of-freedom accelerometry and sagittal high speed video respectively. Velocity was calculated by integrating the accelerometer data. Kinematic data of the head and C7-T1 joint axis in the global reference frame, and head kinematic data relative to the C7-T1 joint axis are presented. A statistical comparison between peak amplitude and time-to-peak amplitude for thirty-one common peaks in the kinematic response was performed. Peak amplitudes and time-to-peak amplitude varied significantly with collision severity for most response peaks, and varied significantly with gender for about one quarter of the response peaks. (A) For the covering abstract of the conference see IRRD E201172.

Method and apparatus for vehicle yaw rate estimation

Abstract: A method is provided for a vehicle yaw rate estimation using two accelerometers and a steer angle sensor. The new method combines two complimentary approaches to yaw rate estimation using accelerometers. A kinematic yaw rate estimate is weighted with a vehicle lateral acceleration at the center of gravity, and steering angle and vehicle forward speed are incorporated into a Kalman filter for estimating vehicle yaw rate based upon the kinematic yaw rate estimate, the lateral acceleration at the center of gravity, the vehicle steering angle, and the vehicle forward speed. The method incorporates use of either one or two accelerometers.

Complete, minimal and model-continuous kinematic models for robot calibration

Abstract: New general kinematic models for robot calibration are presented in this paper These models have the distinct advantage of satisfying the model-parameter identification requirements of completeness, minimality and model continuity for all combinations and configurations of revolute and prismatic joints A set of 17 model parametrizations are developed, including simple criteria for deciding which parametrizations are to be used in modelling a robot The parametrizations presented also result in an accurate representation of the physical robot and thus allow realistic integration of elastic deformation models Model continuity within each parametrization's application range is shown by means of differential geometry Also shown is how these models are be extracted from a non-complex “vector-chain” description of a robot

A new technique for measuring lumbar segmental motion in vivo. Method, accuracy, and preliminary results.

Abstract: Study design A direct method for three-dimensional in vivo spine kinematic studies was developed and used to measure segmental motion patterns in healthy subjects. Objectives To validate the new method, and to study the L3-L4 segmental motion patterns for complex dynamic movements. Summary of background data Conventional two-dimensional and three-dimensional radiographic methods have been used in the past to study spine kinematics. Few studies provided a direct approach to study segmental kinematics. No dynamic recordings of three-dimensional segmental motion patterns have been reported previously. Methods In 16 healthy men, Kirschner wires were inserted in the spinous processes of L3 and L4. Electromagnetic tracking sensors were attached to the pins. Motion data recorded during ranging exercises were used with biplanar radiographs to calculate L3-L4 segmental motion patterns. Errors resulting from pin deformation and the dynamic accuracy of the tracking system were investigated thoroughly. Results The average range of motion for flexion-extension was 16.9 degrees, for one side lateral bending 6.3 degrees and for one side axial rotation 1.1 degrees. Large intersubject variation was found in flexion-extension with values ranging from 7.1 to 29.9 degrees. Coupled motion patterns were found to be consistent among subjects in active lateral bending and inconsistent for active axial rotation. Conclusions This new method offers dynamic recording capabilities and a measurement error comparable with stereo radiographic methods. Repetitive ranging experiments are highly reproducible. The range of motion for axial rotation seems overestimated in previous cadaveric studies. Coupling patterns show large variations between individuals.

Nonholonomic motion planning for multiple mobile manipulators

Abstract: We address the problem of motion planning for nonholonomic cooperating mobile robots manipulating and transporting objects while holding them in a stable grasp. We present a general approach based on the calculus of variations that allows us to obtain optimal trajectories and actuator forces/torques for any manoeuvre in the presence of obstacles. In addition, geometric constraints such as joint limits, kinematic constraints such as nonholonomic velocity constraints and dynamic constraints can be easily incorporated into the planning scheme. The application of the method is illustrated by computing motion plans for several examples.

Tracking of persons in monocular image sequences

Abstract: We present an approach to extract quantitative geometric descriptions of the movements of persons by fitting the projection of a 3-dimensional human model to consecutive frames of an image sequence. The kinematics of the human model is given by a homogeneous transformation tree and its body parts are modeled by right-elliptical cones. The proposed approach can determine the values of a varying number of degrees of freedom (DOFs; body joints, position and orientation of the person relative to the camera) according to the application and the kind of image sequence. The determination of the DOFs is understood as an estimation problem which is solved by an iterated extended Kalman filter (IEKF). For this purpose, the human model is augmented by a simple motion model of constant velocity for all DOFs which is used in the prediction step of the IEKF. In the update step both region and edge information is used.

Visual Perception of Motor Anticipation in Cursive Handwriting: Influence of Spatial and Movement Information on the Prediction of Forthcoming Letters

Abstract: The execution of a graphemic sequence is constrained by spatial demands that result in fluctuations of letter shape and movement time. When producing two letters (ll, le, or ln) the movement time and the letter shape of the first letter depend on the execution constraints of the second one. The motor system thus anticipates the production of the forthcoming graphemic sequence during the production of the first letter. An experiment is reported the aim of which was to examine whether the visual system could exploit this anticipatory information to predict the identity of the letter following the l. Different ls belonging to ll, le, and ln were presented on a screen. Subjects had to predict to which couple of letters (ll, le, or ln) the presented l belonged to, by using information on the shape of the l and/or the movement that produced it. Results showed that the percentages of correct responses were higher in the conditions where the stimulus provided kinematic information than in the condition in which only spatial information was available. The ability to predict the forthcoming letter seems to be mediated by implicit knowledge on motor anticipation rules.

Development and experimentation of a fast 3-DOF camera-orienting device

Abstract: In this article, the mechanical design and the practical im plementation of a high-performance, three-degree-of-freedom, camera-orienting device is addressed. The agile eye, as it is referred to, is based on a spherical 3-DOF parallel mechanism, which leads to high-performance dynamics. The kinematics of such a mechanism is briefly recalled, and its mechanical prop erties are described. Then, experimental results obtained with the prototype are presented and commented upon. Because of its low-moving inertia and its inherent stiffness, the mechanism is capable of velocities larger than 1,000°ls and of accelera tions larger than 20,000°/s2.

Second-order kinematic control of robot manipulators with Jacobian damped least-squares inverse: theory and experiments

Abstract: This paper describes the application of a closed-loop inverse kinematics algorithm to kinematic control of a robot manipulator. The scheme is formulated at the second-order level, i.e., in terms of velocity and acceleration variables, so as to allow the use of joint space computed torque control. A damped least-squares inverse of the Jacobian is used to ensure feasible joint motion in the neighborhood of kinematic singularities. The theoretical analysis of algorithm convergence is performed on the basis of a Lyapunov argument. The results of experiments on a six-joint industrial robot with open control architecture are presented.

1997 Volvo Award winner in biomechanical studies. Kinematic behavior of the porcine lumbar spine: a chronic lesion model.

Abstract: Study design Experimental models of intervertebral disc and facet joint degeneration were created in vivo in the porcine lumbar spine for studying spinal kinematics, using a dynamic technique. Objectives To quantify the changes in spinal kinematics and the stabilizing capacity of the lumbar musculature caused by chronic lesions in the intervertebral disc and facet joints. Summary of background data Segmental kinematics are detrimentally altered by acute injury to passive structures of the motion segment. However, stimulation of the surrounding musculature adds stability to the motion segment. The in vivo kinematics of a degenerated lumbar motion segment and the stabilizing function of the surrounding musculature have not been quantified dynamically. Methods Forty-four pigs were used in six chronic lesions models: sham, disc anulus, disc nucleus, facet capsule, facet joint slit, and facet joint wedge. Three months after injury, an instrumented linkage was used to measure continuously the sagittal kinematics of the L3-L4 motion segment during flexion-extension, with and without stimulation of the lumbar paraspinal musculature. Flexion-extension end point and maximum ranges of motion, and hysteresis were analyzed. Results Significant alterations in the kinematics caused by chronic lesions were observed, particularly when using the maximum range of motion and when comparing changes in axial translation. Muscular stimulation reduced the hysteresis in the sham, facet capsule, and disc nucleus groups; however, increased hysteresis was observed in the remaining lesion groups. Conclusions The kinematic behavior of motion segments with chronic lesions was established. The maximum range of motion, which must be measured using a dynamic technique, was a more sensitive parameter for identifying changes in segmental kinematics caused by chronic lesions than was the end range of motion. The lumbar musculature was less efficient overall in stabilizing the motion segment, possibly because of altered mechanisms in the neuromuscular feedback system.

An examination of the degrees of freedom of human jaw motion in speech and mastication

Abstract: The kinematics of human jaw movements were assessed in terms of the three orientation angles and three positions that characterize the motion of the jaw as a rigid body. The analysis focused on the identification of the jaw's independent movement dimensions, and was based on an examination of jaw motion paths that were plotted in various combinations of linear and angular coordinate frames. Overall, both behaviors were characterized by independent motion in four degrees of freedom. In general, when jaw movements were plotted to show orientation in the sagittal plane as a function of horizontal position, relatively straight paths were observed. In speech, the slopes and intercepts of these paths varied depending on the phonetic material. The vertical position of the jaw was observed to shift up or down so as to displace the overall form of the sagittal plane motion path of the jaw. Yaw movements were small but independent of pitch, and vertical and horizontal position. In mastication, the slope and intercept of the relationship between pitch and horizontal position were affected by the type of food and its size. However, the range of variation was less than that observed in speech. When vertical jaw position was plotted as a function of horizontal position, the basic form of the path of the jaw was maintained but could be shifted vertically. In general, larger bolus diameters were associated with lower jaw positions throughout the movement. The timing of pitch and yaw motion differed. The most common pattern involved changes in pitch angle during jaw opening followed by a phase predominated by lateral motion (yaw). Thus, in both behaviors there was evidence of independent motion in pitch, yaw, horizontal position, and vertical position. This is consistent with the idea that motions in these degrees of freedom are independently controlled.

Interpolation synthesis for articulated figure motion

Abstract: Realistic real time articulated figure motion is achieved by reprocessing a stored database of motions. Motions are created to exact specification by interpolation from a set of example motions, effectively forming a parameterized motion model. A pre-processing step involving iterative calculations is used to allow efficient direct computations at run time. An inverse kinematics capability is shown that is based on interpolation. This method preserves the underlying qualities of the data, such as dynamical realism of motion capture, while generating a continuous range of required motions. Relevant applications include networked virtual reality and interactive entertainment.