Joint Angle Data Research Articles

The influence of gait speed on local dynamic stability of walking

The focus of this study was to examine the role of walking velocity in stability during normal gait. Local dynamic stability was quantified through the use of maximum finite-time Lyapunov exponents, λ Max. These quantify the rate of attenuation of kinematic variability of joint angle data recorded as subjects walked on a motorized treadmill at 20%, 40%, 60%, and 80% of the Froude velocity. A monotonic trend between λ Max and walking velocity was observed with smaller λ Max at slower walking velocities. Smaller λ Max indicates more stable walking dynamics. This trend was evident whether stride duration variability remained or was removed by time normalizing the data. This suggests that slower walking velocities lead to increases in stability. These results may reveal more detailed information on the behavior of the neuro-controller than variability-based analyses alone.

근골격계 부하 평가를 위한 2차원 자세 측정 시스템 개발

A two-dimensional posture measurement system was developed to evaluate the risks of work-related musculoskeletal disorders(MSDs) easily on various conditions of work. The posture measurement system is an essential tool to analyze the workload for preventing work-related musculoskeletal disorders. Although several posture measurement systems have been developed for workload assessment, some restrictions in industry still exist because of its difficulty on measuring work postures. In this study, an image recognition algorithm was developed based on a neural network method to measure work posture. Each joint angle of human body was automatically measured from the recognized images through the algorithm, and the measurement system makes it possible to evaluate the risks of work-related musculoskeletal disorders easily on various working conditions. The validation test on upper body postures was carried out to examine the accuracy of the measured joint angle data from the system, and the results showed good measuring performance for each joint angle. The differences between the joint angles measured directly and the angles measured by posture measurement software were not statistically significant. It is expected that the result help to properly estimate physical workload and can be used as a postural analysis system to evaluate the risk of work-related musculoskeletal disorders in industry.

Joint coordination during quiet stance: effects of vision

Stabilization of the center of mass (CM) is an important goal of the postural control system. Coordination of several joints along the human "pendulum" is required to achieve this goal. We studied the coordination among body segments with respect to horizontal CM stabilization during a quiet stance task and the effects of vision on CM stability. Subjects were asked to stand quietly on a narrow wooden block supporting only the mid-foot, with either open (EO) or closed (EC) eyes on separate trials. Instant equilibrium points (IEPs) in the center of pressure (CP) trajectory were determined when the horizontal component of the ground reaction force was zero and the CP data were decomposed into their rambling and trembling components. The joint angle, CM and CP data were divided into short cycles (time-normalized to 100 data points) or longer segments (time-normalized to 1000 data points) of equal length beginning and ending in an IEP. Motor abundance with respect to patterns of joint coordination was evaluated using the uncontrolled manifold (UCM) approach. Here, a UCM is a subspace spanning all joint combinations resulting in a given CM position. All combinations of joint angles that lie within this subspace are equivalent with respect to that CM position while joint angle combinations lying in a subspace orthogonal to the UCM lead to deviation from that CM position. UCM analysis was performed on data organized either across time within longer segments or at each point in time across multiple segments or across multiple cycles. Regardless of method of analysis, most of the variance in joint space was constrained to be within the UCM, preserving the mean CM position in both the EO and EC conditions. Joint configuration variance was significantly higher in the EC than in the EO condition although this increase occurred primarily within the UCM rather than in the orthogonal subspace that would have led to variation of the CM position. These results demonstrate the ability of the control system to selectively "channel" motor variability into directions in joint space that stabilize the CM position. This effect was enhanced when the task was made more challenging in the absence of vision. There was also a significant relationship between joint variance that led to a change in the CM position and, in particular, the rambling component of the CP path, lending some support to the idea that the CNS prescribes a certain stable trajectory of the CP during quiet stance that leads to a small controlled movement of the CM.

A stability theory of a manifold: concurrent realization of grasp and orientation control of an object by a pair of robot fingers

This paper is concerned with a stability theory of motion governed by Lagrange's equation for a pair of multi-degrees of freedom robot fingers with hemi-spherical finger ends grasping a rigid object under rolling contact constraints. When a pair of dual two d.o.f. fingers is used and motion of the overall fingers-object system is confined to a plane, it is shown that the total degree of freedom of the fingers-object system is redundant for realization of stable grasping though there arise four algebraic constraints. To resolve the redundancy problem without introducing any other extra and artificial performance index, a concept of stability of motion starting from a higher dimensional manifold to a lower-dimensional manifold, expressing a set of states of stable grasp with prescribed contact force, is introduced and thereby it is proved in a rigorous way that stable grasp in a dynamic sense is realized by a sensory feedback constructed by means of measurement data of finger joint angles and the rotational angle of the object. Further, it is shown that there exists an additional sensory feedback that realizes not only stable grasp but also orientation control of the object concurrently. Results of computer simulation based on Baumgarte's method are presented, which show the effectiveness of the proposed concept and analysis.

Technology Overview:

The main purpose of gait analysis laboratories is to measure and study human gait walking patterns in order to better understand and treat gait abnormalities. Gait analysis involves the measurement of kinetics/kinematics of joint move- ment, muscular activity, stride characteristics, pedobarography, and energy consumption. Kinetic data are measured with a force platform that provides information about ground reaction forces and when combined with kinematic data, can yield joint forces and moments. Joint angle and limb segment motion data or kinematic data are obtained by motion analysis systems such as electrogoniometers or photographic systems. Electromyography is used to identify muscle tim- ing and relative muscle intensity. Stride characteristics are used to measure gait timing events. Pedobarography deals with plantar pressure under the foot and the efficiency of gait can be measured with oxygen consumption analysis. Gait analysis is useful for research on normal and abnormal walking patterns, gaining a better understanding of a subject's gait, and planning treatment strategy. Index W

Origins and violations of the 2/3 power law in rhythmic three-dimensional arm movements.

The 2/3 power law, the nonlinear relationship between tangential velocity and radius of curvature of the end-effector trajectory, is thought to be a fundamental constraint of the central nervous system in the formation of rhythmic endpoint trajectories. However, studies on the 2/3 power law have been confined largely to planar drawing patterns of relatively small size. With the hypothesis that this strategy overlooks nonlinear effects that are constitutive in movement generation, the present experiments tested the validity of the power law in elliptical patterns that were not confined to a planar surface and which were performed by the unconstrained 7-degrees of freedom (DOF) arm, with significant variations in pattern size and workspace orientation. Data were recorded from five human subjects where the seven joint angles and the endpoint trajectories were analyzed. Additionally, an anthropomorphic 7-DOF robot arm served as a "control subject" whose endpoint trajectories were generated on the basis of the human joint angle data, modeled as simple harmonic oscillations. Analyses of the endpoint trajectories demonstrate that the power law is systematically violated with increasing pattern size, in both exponent and the goodness of fit. The origins of these violations can be explained analytically based on smooth, rhythmic trajectory formation and the kinematic structure of the human arm. We conclude that, in unconstrained rhythmic movements, the power law seems to be a by-product of a movement system that favors smooth trajectories, and that it is unlikely to serve as a primary movement-generating principle. Our data rather suggest that subjects employed smooth oscillatory pattern generators in joint space to realize the required movement patterns.

A Method for Numerical Simulation of Single Limb Ground Contact Events: Application to Heel-Toe Running

The objective of this work was to develop a method to simulate single-limb ground contact events, which may be applied to study musculoskeletal injuries associated with such movements. To achieve this objective, a three-dimensional musculoskeletal model was developed consisting of the equations of motion for the musculoskeletal system, and models for the muscle force generation and ground contact elements. An optimization framework and a weighted least-squares objective function were presented that generated muscle stimulation patterns that optimally reproduced subject-specific movement data. Experimental data were collected from a single subject to provide initial conditions for the simulation and tracking data for the optimization. As an example application, a simulation of the stance phase of running was generated. The results showed that the average difference between the simulation and subject's ground reaction force and joint angle data was less than two inter-trial standard deviations. Further, there was good agreement between the model's muscle excitation patterns and experimentally collected electromyography data. These results give confidence in the model to examine musculoskeletal loading during a variety of landing movements and to study the effects of various factors associated with injury. Limitations were examined and areas of improvement for the model were presented.

Processing Motion Capture Data to Achieve Positional Accuracy

In animating an articulated entity with motion capture data, if the reconstruction is based on forward kinematics, there could be a large error in the end-effector position. The inaccuracy becomes conspicuous when the entity makes interactions with the environment or other entities. The frames at which the end-effector position needs to be accurate are designated as “keyframes” (e.g., the impact moment in a punch). We present an algorithm that processes the original joint angle data to produce a new motion in which the end-effector error is reduced to zero at keyframes. The new motion should not be too much different from the original motion. We formulated the problem as a constrained minimization problem so that the characteristics of the original joint angle data is optimally preserved during the enhancement steps. The algorithm was applied to several examples such as boxing, kicking, and catching motions. Experiments prove that our algorithm is a valuable tool to improve captured motion especially when the end-effector trajectory contains a special goal.

Proprioceptive control of multijoint movement: unimanual circle drawing.

The present experiments addressed whether proprioception is used by the central nervous system (CNS) to control the spatial and temporal characteristics of unimanual circle drawing. Circle drawing is a multijoint movement, in which the muscles crossing the elbow and the shoulder are sequentially activated. The spatial and temporal characteristics of circle drawing depend on the precise coordination of these sequential activation patterns, and proprioception is ideally suited to support this coordination. Blindfolded human subjects produced a counterclockwise circular drawing motion (diameter = 16 cm) with the dominant arm at a repetition rate of 1/s. In some trials, 60-70 Hz vibration was applied to the tendons of the biceps brachii and/or the anterior deltoid. Spatial parameters measured from hand-movement data included the x- and y-axis diameters, circularity, and drift of the hand in the workspace. Vibration of either the biceps brachii or the anterior deltoid caused subjects to draw circles with decreased diameter, with changes in circularity, and with a systematic drift of the hand. These distortions to circle drawing by tendon vibration demonstrate that the CNS uses proprioceptive information to accomplish the spatial characteristics of this motor task. Simultaneous vibration of both muscles produced a drift that exceeded the individual vibration effects, which suggests that the CNS combined proprioceptive information related to elbow and shoulder rotation to control the movement of the hand. The temporal characteristics of circle drawing were quantified from joint angle data. While vibration did not significantly influence the relative phase between elbow and shoulder rotation, the variability of the phase relationship increased significantly, which suggests that proprioception contributes to phase stabilization. During circle drawing, elbow flexion-extension movements were produced with limited activation of the biceps. Nevertheless, biceps vibration distorted the circle metrics, suggesting that a muscle's significance as a sensory transducer is independent of its activity level.

Segmentation of endpoint trajectories does not imply segmented control.

While it is generally assumed that complex movements consist of a sequence of simpler units, the quest to define these units of action, or movement primitives, remains an open question. In this context, two hypotheses of movement segmentation of endpoint trajectories in three-dimensional human drawing movements are reexamined: (1) the stroke-based segmentation hypothesis based on the results that the proportionality coefficient of the two-thirds power law changes discontinuously with each new "stroke," and (2) the segmentation hypothesis inferred from the observation of piecewise planar endpoint trajectories of three-dimensional drawing movements. In two experiments human subjects performed a set of elliptical and figure eight patterns of different sizes and orientations using their whole arm in three dimensions. The kinematic characteristics of the endpoint trajectories and the seven joint angles of the arm were analyzed. While the endpoint trajectories produced similar segmentation features to those reported in the literature, analyses of the joint angles show no obvious segmentation but rather continuous oscillatory patterns. By approximating the joint angle data of human subjects with sinusoidal trajectories, and by implementing this model on a 7-degree-of-freedom (DOF) anthropomorphic robot arm, it is shown that such a continuous movement strategy can produce exactly the same features as observed by the above segmentation hypotheses. The origin of this apparent segmentation of endpoint trajectories is traced back to the nonlinear transformations of the forward kinematics of human arms. The presented results demonstrate that principles of discrete movement generation may not be reconciled with those of rhythmic movement as easily as has been previously suggested, while the generalization of nonlinear pattern generators to arm movements can offer an interesting alternative to approach the question of units of action.

Kinematic Description of Self-Organized Leg Motion Transition in Human Locomotion Learning

Leg motion learning while walking backward with eyes closed on a treadmill was studied to gain information on self-organization in locomotion learning. Eight adults walked on a treadmill at a belt speed of 50 m/min for five minutes,, four times. The angles of the hip, knee, and ankle joints were calculated to describe lower limb motion transition with learning progress. The attractor of a dynamical system creating joint flexion and extension was reconstructed from time-series joint angle data by the method of Takens (1981). Main findings were that: 1) the joint motion transition pattern with learning progress differs for the three leg joints; 2) with learning progress, ankle joint motion converged from complex to a certain clear pattern and, as a result, the chaotic property of the joint became weak; and 3) with learning motion, the fractal dimension of the attractor for knee joint motion exceeded those for the ankle and hip joints.

Biomechanical effect of medial advancement of the supraspinatus tendon. A study in cadavera.

During the repair of some rotator-cuff tears, the torn tendon cannot be freed up adequately to permit reattachment at its original anatomical site of insertion. An option is to advance the site of insertion medially and reattach the tendon to a trough in the sulcus or to the humeral head. The biomechanical effects of such medial advancement on the moment arm of the supraspinatus muscle during glenohumeral elevation were studied in ten fresh-frozen shoulders from cadavera. Medial advancement of the site of insertion of the supraspinatus tendon was simulated by the placement of suture anchors in the sulcus of the proximal part of the humerus at points three, ten, and seventeen millimeters medial to the junction of the supraspinatus tendon and the bone. These distances were chosen not because they represent clinical options but because the large range allowed biomechanical study of medial advancement. Nylon lines were attached to the suture anchors and were passed back through an eyehook at the midpoint of the supraspinatus muscle. The excursion of each line was measured as the humerus was elevated, and the moment arm was estimated from the joint angle and excursion data with use of the principle of virtual work. Three and ten millimeters of medial advancement of the tendon (attachment in the sulcus) had a minimum (non-significant) effect on the moment arm during elevation compared with the value determined for the intact condition. However, seventeen millimeters of medial advancement was found to reduce the moment arm significantly (p < 0.05).

Relationship between Knee Joint Torque, Velocity, and Muscle Activation: Considerations for Musculoskeletal Modeling

The purpose of this study was to determine if the Hill model, used to describe the force-velocity relationship for isolated tetanically stimulated muscle, could be modified and used to describe the torque-velocity behavior of the knee for maximally and submaximally stimulated quadriceps and hamstrings muscles. Fourteen subjects performed both knee flexion and extension movements at 100%, 70%, and 40% of maximum isometric effort. For each effort level, the knee was allowed to move against resistances equal to 75%, 50%, 25%, and 0% of the specified effort level. An electrogoniometer quantified knee angle. Knee velocity was determined by numerically differentiating the joint angle data. Torque-velocity-activation (or effort level) data were determined for each trial. Model parameters were determined to give the best fit to the data for each subject. Average parameter values were determined for each gender and for the entire group. The modified Hill-type model accurately described the relationship between torque, velocity, and muscle activation level for subject-specific parameters but not for parameters averaged across genders or the entire group.

Comparison of two methods for computing abduction moment arms of the rotator cuff

Biomechanical models of the shoulder mechanism require estimates of muscle moment arm magnitude. Some shoulder models have estimated muscle moment arms by assuming an idealized minimum distance path from the origin to insertion that passes around the bony geometry. Alternatively, the principle of virtual work can be used to estimate moment arms from tendon excursion and joint-angle data. The purpose of this study was to determine if these two methods give different estimates of abduction moment arms for the supraspinatus, infraspinatus, and subscapularis muscles. Muscle moment arms were estimated for these muscles on ten fresh frozen cadaver specimens. The results showed a significant difference between the two estimation methods. Average differences were 3.1 mm (10.6%), 3.9 mm (43.9%), and 7.2 mm (70.3%) for the supraspinatus, subscapularis, and infraspinatus muscles, respectively. These results suggest that shoulder models based on the origin-insertion method may give higher rotator cuff muscle force estimates than methods using the slope of the tendon excursion vs joint angle relationship.

Self-Organization of Lower Limb Motion in Human Locomotion

This project was undertaken to demonstrate the modal bifurcation displayed in human locomotion and the nature of motional self-organization found in the lower limb joints via the continuously measured walking and running of subjects on a treadmill for five minutes. The knowledge obtained from this study is as follows: (1) The self-organizational patterns of leg motion differ between walking and running. (2) This pattern shift is achieved based on the joint angular relationship and the change in the dynamical systems controlling the flexion and extension of the ankle and hip joints. The motion pattern is entrained to a final state immediately following the changeover. (3) Chaotic movements were observed in joint-angle time-series data, but the wide variance exhibited in Lyapunov exponent is dependent on the evolution time value set in the calculation. (4) If chaos occur in the lower limb motion of locomotion, we safely achieve locomotion in our everyday life by positively adopting the body and environmental conditions through the utilization of the selfsame chaos.

A body model server for human motion capture and representation.

This paper presents a body model server (BMS) that provides real-time access to the position and posture of a person's torso, arms, hands, head, and eyes. It can be accessed by clients over a network. The BMS is designed to function as a device-independent data-layer between the sensing devices and client applications that require real-time human motion data, such as animation control. It can provide clients with accurate information at up to 40 Hz. For data collection, the model uses four magnetic position/orientation sensors, two data-gloves, and an eye-tracker. The BMS combines the data-streams from the sensors and transforms them into snapshots of the user's upper-body pose. A geometric model made up of joints and segments structures the input. Posture of the body is represented by joint angles. Two unique characteristics of our approach are the use of the implicit, geometric constraints of the sensed body to simplify the computation of the unmeasured joint angles, and the use of time-stamped data that allow synchronization with other data streams, e.g., speech input. This paper describes the architecture of the BMS, including the management of multiple input devices, the representation and computation of the position and joint angle data, and the client-server interface.

End Milling for Articulated Robot Application. 2nd Report. Copy Miling Based on Sensor Feedback Teaching Program.

Copy milling of a sculptured surface has been attempted employing an articulated robot with six degrees of freedom. For this purpose, we developed a sensor feedback teaching system as a previous stage for constructing an off-line teaching system. First, the mathematical model which represents the robot used was established, then kinematic equations and their differential relationships were derived. Joint angles of the robot, which realize adaptive configurations for end milling, were calculated using these equations. In this sensor feedback teaching system, a laser displacement sensor is used to detect the distance between the sensor and the tracing object for copy milling, and joint angles of the robot are determined in order to keep the distance constant. In this way, time series joint angles data are calculated automatically, and the teaching program for the robot is developed. The sensor feedback teaching system was examined by tracing a Mickey Mouse mask. The teaching program developed by this system was executed successfully, and a relief of Mickey Mouse was obtained by experimental copy milling.

Autonomous Robot Calibration for Hand-Eye Coordination

Autonomous robot calibration is defined as the process of determining a robot's model by using only its internal sen sors. It is shown that autonomous calibration of a manip ulator and stereo camera system is possible. The pro posed autonomous calibration algorithm may obtain the manipulator kinematic parameters, external kinematic camera parameters, and internal camera parameters. To do this, only joint angle readings and camera image plane data are used. A condition for the identifiability of the manipulator/camera parameters is derived. The method is a generalization of a recently developed scheme for self- calibrating a manipulator by forming it into a mobile closed-loop kinematic chain.

Measurement of finger joint angles and maximum finger forces during cylinder grip activity

Finger joint angles and finger forces during maximal cylindrical grasping were measured using multi-camera photogrammetry and pressure-sensitive sheets, respectively. The experimental data were collected from four healthy subjects gripping cylinders of five different sizes. For joint angles, an image analysis system was used to digitize slides showing markers. During the calibration of the camera system, both the nonlinear least square and the direct linear transform methods were applied and compared, the former providing the fewer errors; it was used to determine joint angles. Data were collected from the pressure-sensitive grip films by using the same image analysis system as used in the collection of the joint angle data. The method of using pressure-sensitive sheets provided an estimation of the weighted centre of the phalangeal forces. Results indicate that finger flexion angles at the metacarpophalangeal and proximal interphalangeal joints gradually increase as cylinder diameter decreases, but that at the distal interphalangeal joint the angle remains constant throughout all cylinder sizes. It was also found that most of the radio-ulnar deviation and the axial rotation angles at the finger joints deviate from zero, but the deviations are small. For the force measurement, it was found that total finger force increases as cylinder size decreases, and the phalangeal force centres are not located at the mid-points of the phalanges. The data obtained in this experiment would be useful for muscle force predictions and for the design of handles.