Joint Error Research Articles

A Visual Analytics Approach for Categorical Joint Distribution Reconstruction from Marginal Projections.

Oftentimes multivariate data are not available as sets of equally multivariate tuples, but only as sets of projections into subspaces spanned by subsets of these attributes. For example, one may find data with five attributes stored in six tables of two attributes each, instead of a single table of five attributes. This prohibits the visualization of these data with standard high-dimensional methods, such as parallel coordinates or MDS, and there is hence the need to reconstruct the full multivariate (joint) distribution from these marginal ones. Most of the existing methods designed for this purpose use an iterative procedure to estimate the joint distribution. With insufficient marginal distributions and domain knowledge, they lead to results whose joint errors can be large. Moreover, enforcing smoothness for regularizations in the joint space is not applicable if the attributes are not numerical but categorical. We propose a visual analytics approach that integrates both anecdotal data and human experts to iteratively narrow down a large set of plausible solutions. The solution space is populated using a Monte Carlo procedure which uniformly samples the solution space. A level-of-detail high dimensional visualization system helps the user understand the patterns and the uncertainties. Constraints that narrow the solution space can then be added by the user interactively during the iterative exploration, and eventually a subset of solutions with narrow uncertainty intervals emerges.

Exercises focusing on rotator cuff and scapular muscles do not improve shoulder joint position sense in healthy subjects

Proprioception is essential for shoulder neuromuscular control and shoulder stability. Exercise of the rotator cuff and scapulothoracic muscles is an important part of shoulder rehabilitation. The purpose of this study was to investigate the effect of rotator cuff and scapulothoracic muscle exercises on shoulder joint position sense. Thirty-six healthy subjects were recruited and randomly assigned into either a control or training group. The subjects in the training group received closed-chain and open-chain exercises focusing on rotator cuff and scapulothoracic muscles for four weeks. Shoulder joint position sense errors in elevation, including the humerothoracic, glenohumeral and scapulothoracic joints, was measured. After four weeks of exercise training, strength increased overall in the training group, which demonstrated the effect of exercise on the muscular system. However, the changes in shoulder joint position sense errors in any individual joint of the subjects in the training group were not different from those of the control subjects. Therefore, exercises specifically targeting individual muscles with low intensity may not be sufficient to improve shoulder joint position sense in healthy subjects. Future work is needed to further investigate which types of exercise are more effective in improving joint position sense, and the mechanisms associated with those changes.

TH‐AB‐201‐07: Filmless Treatment Localization QA for the CyberKnife System

Purpose:Accuray recommends daily evaluation of the treatment localization and delivery systems (TLS/TDS) of the CyberKnife. The vendor‐provided solution is a Winston‐Lutz‐type test that evaluates film shadows from an orthogonal beam pair (known as AQA). Since film‐based techniques are inherently inefficient and potentially inconsistent and uncertain, this study explores a method which provides a comparable test with greater efficiency, consistency, and certainty. This test uses the QAStereoChecker (QASC, Standard Imaging, Inc., Middleton, WI), a high‐resolution flat‐panel detector with coupled fiducial markers for automated alignment. Fiducial tracking is used to achieve high translational and rotational position accuracy.Methods:A plan is generated delivering five circular beams, with varying orientation and angular incidence. Several numeric quantities are calculated for each beam: eccentricity, centroid location, area, major‐axis length, minor‐axis length, and orientation angle. Baseline values were acquired and repeatability of baselines analyzed. Next, errors were induced in the path calibration of the CK, and the test repeated. A correlative study was performed between the induced errors and quantities measured using the QASC. Based on vendor recommendations, this test should be able to detect a TLS/TDS offset of 0.5mm.Results:Centroid shifts correlated well with induced plane‐perpendicular offsets (p < 0.01). Induced vertical shifts correlated best with the absolute average deviation of eccentricities (p < 0.05). The values of these metrics which correlated with the threshold of 0.5mm induced deviation were used as individual pass/fail criteria. These were then used to evaluate induced offsets which shifted the CK in all axes (a clinically‐realistic offset), with a total offset of 0.5mm. This test provided high and specificity and sensitivity.Conclusion:From setup to analysis, this filmless TLS/TDS test requires 4 minutes, as opposed to 15–20 minutes for film‐based methods. The techniques introduced can potentially isolate errors in individual joints of the CK robot.Spectrum Medical Physics, LLC of Greenville, SC has a consulting contract with Standard Imaging of Middleton, WI

Design and accuracy analysis of a metamorphic CNC flame cutting machine for ship manufacturing

The current research of processing large size fabrication holes on complex spatial curved surface mainly focuses on the CNC flame cutting machines design for ship hull of ship manufacturing. However, the existing machines cannot meet the continuous cutting requirements with variable pass conditions through their fixed configuration, and cannot realize high-precision processing as the accuracy theory is not studied adequately. This paper deals with structure design and accuracy prediction technology of novel machine tools for solving the problem of continuous and high-precision cutting. The needed variable trajectory and variable pose kinematic characteristics of non-contact cutting tool are figured out and a metamorphic CNC flame cutting machine designed through metamorphic principle is presented. To analyze kinematic accuracy of the machine, models of joint clearances, manufacturing tolerances and errors in the input variables and error models considering the combined effects are derived based on screw theory after establishing ideal kinematic models. Numerical simulations, processing experiment and trajectory tracking experiment are conducted relative to an eccentric hole with bevels on cylindrical surface respectively. The results of cutting pass contour and kinematic error interval which the position error is from–0.975 mm to +0.628 mm and orientation error is from–0.01 rad to +0.01 rad indicate that the developed machine can complete cutting process continuously and effectively, and the established kinematic error models are effective although the interval is within a ‘large’ range. It also shows the matching property between metamorphic principle and variable working tasks, and the mapping correlation between original designing parameters and kinematic errors of machines. This research develops a metamorphic CNC flame cutting machine and establishes kinematic error models for accuracy analysis of machine tools.

Development of an embedded control system by means of dsPIC applied in a 4 DOF robot

In this paper the design and implementation of an embedded control system, using DSCs (Digital Signal Controller) devices of dsPIC type, applied on a four DOF (Degrees Of Freedom) robotic manipulator OWI-535 model is presented. The mathematical model of manipulator is elaborated obtaining joint trajectories to achieve the tracking of a test Cartesian trajectory. A control structure based on a Master/Slave configuration, between two dsPIC30F4013 through SPI (Serial Peripheral Interface) protocol is developed. In such a system, algorithms are implemented: PID (Proportional Integral Derivative) with anti-windup and, generation PWM (Pulse-Width Modulation) and data acquisition, in the DSCs master and slave, respectively. The results are exposed by comparative curves between the desired and real joint trajectories and joint error graphs, generated from real data of the implementation.

Kinematic accuracy research of a novel six-degree-of-freedom parallel robot with three legs

Based on a novel six-degree-of-freedom (DOF) parallel manipulator mechanism, the forward and inverse kinematics have been worked out. This paper addresses the kinematics accuracy problem of the proposed new parallel robot with three legs (TLPM) due to the location of the U joint errors, clearance and driving errors. According to the generalized kinematic mapping of motions in the workspace, the end-effector's exact output error bound for a standard deviation of the components can have a great influence on the pose (position and orientation) error. The stochastic results are presented; for considering both the location errors clearance and driving in the total simultaneous effect of the errors, the superposition principle is not suitable when any of the errors is considerably larger than the last two errors. The accuracy is intensively studied, a laser tracker is applied to calibrate the errors. The models can be built into the controller and used to compensate for the location of the U joint errors, clearance and driving errors. Experimental results show that the robot accuracy is improved and demonstrated the effectiveness of the proposed method.

Sandwich Roof of the Bus – Fatigue and Strength Tests

Lightweight and safe roof of the bus was solved within the MIT CR: FR-TI4/349 project. Several variants of sandwich roof were tested on samples in a prior period. Several errors of adhesive joints occurred during the production of the bus roof. Methyl methacrylate adhesive was tested with respect to the declared adhesive ability for arbitrary surfaces. Standardised shear test of the adhesive joints were made for tuning of the numerical model. The obtained parameters are used forthe numerical model of sandwich roof segment. Roof segments were loaded by four points bending and experimentally obtained data were compared with the results of numerical simulations. Several specimens were subjected to cyclic loading in order to get approximate fatigue life of tested variants.

Trajectory Tracking Control of a Real Redundant Manipulator of the SCARA Type

Modeling, control and implementation of a real redundant robot with five Degrees Freedom (DOF) of the SCARA (Selective Compliant Assembly Robot Arm) manipulator type is presented. Through geometric methods and structural and functional considerations, the inverse kinematics for redundant robot can be obtained. By means of a modification of the classical sliding mode control law through a hyperbolic function, we get a new algorithm which enables reducing the chattering effect of the real actuators, which together with the learning and adaptive controllers, is applied to the model and to the real robot. A simulation environment including the actuator dynamics is elaborated. A 5 DOF robot, a communication interface and a signal conditioning circuit are designed and implemented for feedback. Three control laws are executed in: a simulation structure (together with the dynamic model of the SCARA type redundant manipulator and the actuator dynamics) and a real redundant manipulator of the SCARA type carried out using MatLab/Simulink programming tools. The results, obtained through simulation and implementation, were represented by comparative curves and RMS indices of the joint errors, and they showed that the redundant manipulator, both in the simulation and the implementation, followed the test trajectory with less pronounced maximum errors using the adaptive controller than the other controllers, with more homogeneous motions of the manipulator.

Multi-sensor data fusion methods for indoor localization under collinear ambiguity

Sensor node localization in mobile ad-hoc sensor networks is a challenging problem. Often, the anchor nodes tend to line up in a linear fashion in a mobile sensor network when nodes are deployed in an ad-hoc manner. This paper discusses novel node localization methods under the conditions of collinear ambiguity of the anchors. Additionally, the work presented herein also describes a methodology to fuse data available from multiple sensors for improved localization performance under conditions of collinear ambiguity. In this context, data is first acquired from multiple sensors sensing different modalities. The data acquired from each sensor is used to compute attenuation models for each sensor. Subsequently, a combined multi-sensor attenuation model is developed. The fusion methodology uses a joint error optimization approach on the multi-sensor data. The distance between each sensor node and anchor is itself computed using the differential power principle. These distances are used in the localization of sensor nodes under the condition of collinear ambiguity of anchors. Localization error analysis is also carried out in indoor conditions and compared with the Cramer–Rao lower bound. Experimental results on node localization using simulations and real field deployments indicate reasonable improvements in terms of localization accuracy when compared to methods likes MLAR and MGLR.

It's not just my fault: Neural correlates of feedback processing in solo and joint action

People often coordinate their actions with others’ in pursuit of shared goals, yet little research has examined the neural processes by which people monitor whether shared goals have been achieved. The current study compared event-related potentials elicited by feedback indicating joint errors (resulting from two people's coordinated actions) and individual errors (resulting from one's own or another person's observed actions). Joint errors elicited a reduced feedback-related negativity (FRN) and P3a relative to own errors, and an enhanced FRN relative to observed errors. In contrast, P3b amplitudes did not differ between joint and individual errors. These findings indicate that producing errors together with a partner influences neural activity related to outcome evaluation but has less impact on activity related to the motivation to adapt future behaviour.

System Hazard Platform: Case Study NASA Field Joint Failure

<p class="1Body">NASA became overconfident with consecutive successful flights with no major failures leading up to Flight 25 of the Space Shuttle Challenger and failed to correctly apply quality assurance to reanalyze the possibilities of failure when extreme cold weather was present for what would become the last Challenger launch. System Hazard Analysis applied correctly to analyze the failure rate patterns of the NASA Space Shuttle Challenger Solid Rocket Booster field joints may have prevented the launch of the tragic Flight 25, where there was a total loss of aircraft and seven astronauts were killed in the accident. The steps of System Hazard Analysis will be explained that if followed may have provided the data necessary for NASA to correct the field joint error prior to instead of after the Challenger explosion.</p>

Comparison of Proprioception in Injured and Uninjured Knee Joints among Male Professional Footballers

Background: Football is the world's most popular sport. There are over 240 million registered players worldwide and many more recreational footballers. The knee is a complex joint with many components making it vulnerable to a variety of injuries. The study has investigated the effect of knee proprioception error on injured and uninjured male professional footballers.Methods: This was a cross sectional comparative study with hundred and six (106) male professional footballers were selected for the study as per the selection criteria. Hundred and eighteen injured and ninety four uninjured knee samples were analysed for this study. Photographic analysis method was used to evaluate proprioception error at inner, middle and outer range of knee joint. Proprioception error of knee joint was measured at inner range, middle range and outer range for injured and uninjured groups. Data analysis found that there is significant difference in proprioception error between the groups.Result: Comparative study was performed using independent t’ test for proprioception error between knee injured and uninjured groups. P<0.05 were considered as significant difference in effect for this study. The means of knee injured and uninjured groups were 6.08 and 5.55 respectively with t’ value 2.21 and degree of freedom 634. The study found that proprioception error has significant difference in effect on knee injury, with P< 0.03*.Conclusion: The study concluded that proprioception error was varied between knee injured and uninjured groups. Proprioception error of knee joint was more among injured male professional footballers compared to the uninjured footballers.&nbsp

Method of Calculating the Assembly Error Transfer Path Based on JSS Matrix

Joint surface error is described by small displacement torsors theory, error transfer properties of common assembly joint surface are analyzed. Assembly joint surface symbols with engineering semantics are defined to describe the type of joint surface and cooperate relationship. Combined with the polychromatic sets theory, joint surface and error relationship contour matrix(called joint surface symbols(JSS) matrix) that can describe assembly relationship, joint surface type and error transfer properties is established. Assembly error transfer path search method based on JSS matrix is proposed, the actual error transfer property matrix of joint surface is established, and the method of obtaining the transfer path of each error component is discussed. In view of the uncertainty problem in parallel error transfer path, highest precision is put forward as the basis of distinguishing error transfer effective path, then the effective error transfer paths of error component which is associated with the assembly precision requirements are obtained based on the error model that is established based on Jacobian-torsor theory. The feasibility and practicability of the research method is verified by an example of a typical assembly error transfer path solution.

Shoulder Joint Angle Errors Caused by Marker Offset

The International Society of Biomechanics (ISB) has recommended a standardization of the definition of the joint coordinate system (JCS) and use of a sequential rotation to describe human shoulder joint rotation. Markers attached to the surface of the body may move during the process of motion data capture, resulting in an offset from their initial location. This leads to a change of the JCS and therefore affects the calculated shoulder joint angles. In this research study, we presented a simple marker offset model to quantify the shoulder joint errors for both static poses and dynamic activities. Specific conditions of different offsets and elbow flexion angles were studied. Results showed that the errors should not be neglected when the shoulder elevation angle was near -90° and 90°, or elbow flexion was very small. Attention should be paid to these errors for such activities especially walking and throwing.

Simulation Research on Motion Reliability of Joystick-Control Mechanism in Excavator

Motion precision is an important evaluating index to evaluate the quality of the mechanisms. On the premise of fully studying the motion of joystick in the excavator, a new kind of joystick-control mechanism is proposed. The dynamics simulation model of the mechanism is constructed by ADAMS, so the dimension error and initial angle error of joint in the installation is analysed. Random sampling method are adopted to simulate the error of position of two key points, the simulation of transverse and longitudinal swing of is completed, and the effect on the motion precision of joystick is compared which is made by error of each direction of two key adjusting points. The motion reliability of the joystick-control mechanism is calculated, combined with the stress-strength interference theory.

Efficient tracking of human poses using a manifold hierarchy

In this paper a 3D human pose tracking framework is presented. A new dimensionality reduction method (Hierarchical Temporal Laplacian Eigenmaps) is introduced to represent activities in hierarchies of low dimensional spaces. Such a hierarchy provides increasing independence between limbs, allowing higher flexibility and adaptability that result in improved accuracy. Moreover, a novel deterministic optimisation method (Hierarchical Manifold Search) is applied to estimate efficiently the position of the corresponding body parts. Finally, evaluation on public datasets such as HumanEva demonstrates that our approach achieves a 62.5–65mm average joint error for the walking activity and outperforms state-of-the-art methods in terms of accuracy and computational cost.

Efficiency of dairy farms participating and not participating in veterinary herd health management programs

This paper compares farm efficiencies between dairies who were participating in a veterinary herd health management (VHHM) program with dairies not participating in such a program, to determine whether participation has an association with farm efficiency. In 2011, 572 dairy farmers received a questionnaire concerning the participation and execution of a VHHM program on their farms. Data from the questionnaire were combined with farm accountancy data from 2008 through 2012 from farms that used calendar year accounting periods, and were analyzed using Stochastic Frontier Analysis (SFA). Two separate models were specified: model 1 was the basic stochastic frontier model (output: total revenue; input: feed costs, land costs, cattle costs, non-operational costs), without explanatory variables embedded into the efficiency component of the error term. Model 2 was an expansion of model 1 which included explanatory variables (number of FTE; total kg milk delivered; price of concentrate; milk per hectare; cows per FTE; nutritional yield per hectare) inserted into the efficiency component of the joint error term. Both models were estimated with the financial parameters expressed per 100kg fat and protein corrected milk and per cow. Land costs, cattle costs, feed costs and non-operational costs were statistically significant and positive in all models (P<0.01). Frequency distributions of the efficiency scores for the VHHM dairies and the non-VHHM dairies were plotted in a kernel density plot, and differences were tested using the Kolmogorov–Smirnov two-sample test. VHHM dairies had higher total revenue per cow, but not per 100kg milk. For all SFA models, the difference in distribution was not statistically different between VHHM dairies and non-VHHM dairies (P values 0.94, 0.35, 0.95 and 0.89 for the basic and complete model per 100kg fat and protein corrected milk and per cow respectively). Therefore we conclude that with our data farm participation in VHHM is not related to overall farm efficiency.

Bayesian Nonparametric Instrumental Variables Regression Based on Penalized Splines and Dirichlet Process Mixtures

We propose a Bayesian nonparametric instrumental variable approach under additive separability that allows us to correct for endogeneity bias in regression models where the covariate effects enter with unknown functional form. Bias correction relies on a simultaneous equations specification with flexible modeling of the joint error distribution implemented via a Dirichlet process mixture prior. Both the structural and instrumental variable equation are specified in terms of additive predictors comprising penalized splines for nonlinear effects of continuous covariates. Inference is fully Bayesian, employing efficient Markov chain Monte Carlo simulation techniques. The resulting posterior samples do not only provide us with point estimates, but allow us to construct simultaneous credible bands for the nonparametric effects, including data-driven smoothing parameter selection. In addition, improved robustness properties are achieved due to the flexible error distribution specification. Both these features are challenging in the classical framework, making the Bayesian one advantageous. In simulations, we investigate small sample properties and an investigation of the effect of class size on student performance in Israel provides an illustration of the proposed approach which is implemented in an R package bayesIV. Supplementary materials for this article are available online.

On Theoretical and Empirical Aspects of Marginal Distribution Choice Models

In this paper, we study the properties of a recently proposed class of semiparametric discrete choice models (referred to as the marginal distribution model (MDM)), by optimizing over a family of joint error distributions with prescribed marginal distributions. Surprisingly, the choice probabilities arising from the family of generalized extreme value models of which the multinomial logit model is a special case can be obtained from this approach, despite the difference in assumptions on the underlying probability distributions. We use this connection to develop flexible and general choice models to incorporate consumer and product level heterogeneity in both partworths and scale parameters in the choice model. Furthermore, the extremal distributions obtained from the MDM can be used to approximate the Fisher's information matrix to obtain reliable standard error estimates of the partworth parameters, without having to bootstrap the method. We use simulated and empirical data sets to test the performance of this approach. We evaluate the performance against the classical multinomial logit, mixed logit, and a machine learning approach that accounts for partworth heterogeneity. Our numerical results indicate that MDM provides a practical semiparametric alternative to choice modeling.This paper was accepted by Eric Bradlow, special issue on business analytics.

A calibration method of kinematic parameters for serial industrial robots

Purpose– Calibrating kinematic parameters is one of the efficient ways to improve the robot's positioning accuracy. A method based on the product-of-exponential (POE) formula to calibrate the kinematic parameters of serial industrial robots is proposed. The paper aims to discuss these issues.Design/methodology/approach– The forward kinematics is established, and the general positioning error model is deduced in an explicit expression. A simplified model of robot's positioning error is established as both the error of reference configuration and the error of rigid displacement of the base coordinating system with respect to the measuring coordinating system are equivalently transferred to the zero position errors of the robot's joints. A practical calibration model is forwarded only requiring 3D measuring based on least-squares algorithm. The calibration system and strategy for calibrating kinematic parameters are designed.Findings– By the two geometrical constrains between the twist coordinates, each joint twist only has four independent coordinates. Due to the equivalent error model, the zero position error of each joint can cover the error of reference configuration and rigid displacement of the robot base coordinating system with respect to the measuring coordinating system. The appropriate number of independent kinematic parameters of each joint to be calibrated is five.Originality/value– It is proved by a group of calibration experiments that the calibration method is well conditioned and can be used to promote the level of absolute error of end effector of industrial robot to 2.2 mm.