Ball Pass Research Articles

Gaze Behaviors, Estimated Quiet Eye Characteristics, and Decision Making of Nonexpert Assistant Referees Judging Offside Events in Soccer.

The study analyzed the gaze behavior and decision-making performance of 20 soccer assistant referees while judging offside events. Specifically, gaze behaviors, gaze entropy, and estimated quiet eye (eQE; defined as the last fixation prior to the attacker's ball pass) characteristics (i.e.,location, onset, offset, and duration) were analyzed in relation to decision-making accuracy. Although a significant number of fixations were observed on the offside line, the highest viewing time corresponded to the ball carrier. The gaze behavior indicated a high distribution of fixations, as evidenced by high stationary gaze entropy (>90%). The assistant referees also distinguished offside from onside positions above chance. However, they displayed nonprolonged eQE on the offside line. As a result, no significant relationships were found between the eQE characteristics and decision-making accuracy. The study concludes that the absence of more functional gaze behaviors, specifically with longer eQE focused on the offside line, impaired the decision-making accuracy of nonexpert assistant referees in soccer.

Effects of a Strength Training Program on Basic Basketball Skills in Wheelchair Basketball Players

The aim of this study is to investigate the effects of an upper extremity strength training program on basic basketball skills in wheelchair basketball players. The study consisted of a total of 27 wheelchair basketball players (15 in the training group and 12 in the control group). The basic basketball skills were assessed at the beginning and end of the training program with a slalom test, slalom with ball test, layup test, zone shot test, two-point shot test, and pass for accuracy test. The warm-up part of the strength training included the use of wheelchair and passing exercises with a basketball. The special strength program was applied to the training group three times a week for eight weeks. The control group continued with the routine education program. While there was a statistically significant difference in the slalom, slalom with ball, zone shot, and four-meter and eight-meter pass for accuracy tests in the training group (p0.05). It was determined that the basic basketball skills test of the control group did not yield a difference (p>0.05). At the conclusion this research, it was determined that the upper extremity strength training program planned for wheelchair basketball players for eight weeks positively affected their basic basketball skills. It may be recommended to include this program in the warm-up session of the training program in order to improve sportive performance.

Torsional and lateral vibration analysis of wind turbine generator bearing outer ring fault considering unbalanced magnetic pull

Rolling bearings play a critical role in wind turbine generators, operating continuously in an electromagnetic excitation environment. Their fault vibration characteristics are affected by unbalanced magnetic pull (UMP), which has received little attention in previous studies. Moreover, torsional vibration can provide advantages in bearing fault diagnosis, since it has a good signal-to-noise ratio (SNR) and it can be easily measured by the encoder. However, torsional vibration is rarely considered in the existing model of wind turbine generator. Accordingly, this paper proposes a dynamic model with 8 degrees of freedom to analyze the bearing outer ring fault characteristics of wind turbine generator under the influence of UMP, while also taking into account the torsional vibration in the model. The validity of the model is verified through experiments conducted on a test rig. The results displays modulation of the ball pass frequency outer (BPFO) harmonics with both UMP frequency and rotation frequency in lateral vibration, and this phenomenon can also be observed in instantaneous angular speed (IAS) and instantaneous angular acceleration (IAA) signals that represent torsional vibration. Besides, the lateral vibration spectrum reveals two distinct resonance bands, and simulation analysis suggested that the rotor and bearings give rise to low-frequency and high-frequency resonance, respectively. This study provides a reference for bearing faults diagnosis in wind turbine generator.

Skidding behavior of lubricated rolling element bearings under the influence of oil film and radial clearances

Skidding is an inevitable phenomenon in rolling element bearing but accelerates the bearing wear and shortens the bearing life. Recognizing skidding behavior under different clearances will benefit to bearing health monitoring. In this study, an improved bearing dynamic model is developed to investigate its vibration characteristics and skidding behavior taking into all bearing structure components, time-varying oil film characteristics and bearing clearances. A novel method is proposed to include time-varying oil film stiffness and thickness under different clearances into the bearing dynamic model. A fast algorithm is adopted through interpolation during the model solving process. Furthermore, vibration responses and skidding behavior under different clearances are analyzed. Finally, a designed synchronous differential encoder (SDE) system tests the skidding behavior of bearings and verifies the proposed model through measuring the angular velocity of cage transformed by distance test. Numerical result shows that both RMS and ball pass frequency of outer race (BPFO) increase with bearing clearances. The slip ratio represents growth with the increase of bearing clearances, which is verified by the designed experiment with good consistency with the simulation. It can be foreseen that this novel dynamic model with SDE system can be well performed for bearing skidding detection and fault detection.

Dynamic signal analysis based monitoring for ball screws preload deterioration

The ball screw feed system has been an important part of precision machinery and machine tools. Its preload degradation affects machining accuracy and the issue should be first coped with per manufacturers’ suggestion. The study aims to apply the adaptive order tracking technique and other spectrum analysis schemes as well to differentiate the preload conditions of ball screws. Here varied preload conditions (4 %, 1 % preload and 12um backlash) were considered for monitoring during normal operation. The sideband energy of higher harmonics of ball pass frequency (BPF) are featured to highlight the preload degradation. The control charts together with sideband ratios were established to differentiate preload conditions and single out backlash ball screws.

Use of exercises with increased coordination complexity in the training process of young female volleyball players aged 13-14 years

Background and Study Aim. In the context of training young female volleyball players, understanding the criteria, extent, and impact of exercises with heightened coordination complexity becomes crucial. This study aims to determine the evaluation criteria, scope, and effects of incorporating exercises with elevated coordination demands on the specific athletic readiness of young female volleyball players aged 13–14 years. Material and Methods. The study involved female volleyball players aged 13–14 years (n=24) with an average of 4 years of professional experience. Participants were divided into a control group (n=12) and an experimental group (n=12). Prior to the study, both children and their parents were thoroughly informed about the research procedures, and parental consent was obtained for participation. The coordination exercises were categorized into five groups, each assigned a complexity rating from 1 to 5. The assessment utilized a battery of tests. Results. The findings reveal that coordination training yielded a more pronounced advancement in the development of various coordination abilities among female volleyball players in the experimental group, as compared to those in the control group. A statistically significant enhancement (p<0.05) was evident across all indices of coordination readiness within the experimental group. In contrast, the control group demonstrated notable progress only in 3 out of 10 instances (p<0.05). In the control group, noteworthy increases (p<0.05) were observed in spatial orientation, motor activity restructuring, and response indicators. Female volleyball players in the experimental group exhibited substantial improvement (p<0.05–0.001) across all indicators of technical readiness, including reception, attack hit, serve, and ball pass. Conversely, the control group players showed comparatively less remarkable changes in this aspect of readiness, with significant enhancement (p<0.05) identified in three parameters. Conclusions. The strategic incorporation of exercises with progressively heightened coordination demands emerges as a valuable approach in substantially enhancing the range of coordination abilities among young female volleyball players. Recognizing this factor provides the means to expedite and optimize the mastery of motor skills more effectively.

Predicting Football Team Performance with Explainable AI: Leveraging SHAP to Identify Key Team-Level Performance Metrics

Understanding the performance indicators that contribute to the final score of a football match is crucial for directing the training process towards specific goals. This paper presents a pipeline for identifying key team-level performance variables in football using explainable ML techniques. The input data includes various team-specific features such as ball possession and pass behaviors, with the target output being the average scoring performance of each team over a season. The pipeline includes data preprocessing, sequential forward feature selection, model training, prediction, and explainability using SHapley Additive exPlanations (SHAP). Results show that 14 variables have the greatest contribution to the outcome of a match, with 12 having a positive effect and 2 having a negative effect. The study also identified the importance of certain performance indicators, such as shots, chances, passing, and ball possession, to the final score. This pipeline provides valuable insights for coaches and sports analysts to understand which aspects of a team’s performance need improvement and enable targeted interventions to improve performance. The use of explainable ML techniques allows for a deeper understanding of the factors contributing to the predicted average team score performance.

A new multiobjective tiki-taka algorithm for optimization of assembly line balancing

PurposeThis study aims to propose a new multiobjective optimization metaheuristic based on the tiki-taka algorithm (TTA). The proposed multiobjective TTA (MOTTA) was implemented for a simple assembly line balancing type E (SALB-E), which aimed to minimize the cycle time and workstation number simultaneously.Design/methodology/approachTTA is a new metaheuristic inspired by the tiki-taka playing style in a football match. The TTA is previously designed for a single-objective optimization, but this study extends TTA into a multiobjective optimization. The MOTTA mimics the short passing and player movement in tiki-taka to control the game. The algorithm also utilizes unsuccessful ball pass and multiple key players to enhance the exploration. MOTTA was tested against popular CEC09 benchmark functions.FindingsThe computational experiments indicated that MOTTA had better results in 82% of the cases from the CEC09 benchmark functions. In addition, MOTTA successfully found 83.3% of the Pareto optimal solution in the SALB-E optimization and showed tremendous performance in the spread and distribution indicators, which were associated with the multiple key players in the algorithm.Originality/valueMOTTA exploits the information from all players to move to a new position. The algorithm makes all solution candidates have contributions to the algorithm convergence.

Dynamic Modeling and Analysis of Rotor-Bearing System with Localized Defect in Rotating Machinery

The numerical model is developed to study the vibration response due to the localized defect of ball bearing in rotating machinery. In order to simulate the dynamic response, the equations of motions are developed based on the rotor-bearing system where two identical rotors mounted on symmetric flexible shaft and supported by ball bearings are considered in this model. The presence of defect is introduced on a bearing outer raceway and lubrication effect between bearing components is also included. The numerical results are obtained by applying Runge–Kutta method to solve governing equations of motions. It has been observed that the vibration spectrum of the ball pass frequency outer race and its harmonics for the defect bearing is relatively higher than the good one. Moreover, this dynamic model can effectively enhance the understanding of vibration responses for good and defective bearing.

Nonlinear tribodynamics of an elastic shaft with a flexible bearing outer race

In this paper, a mathematical model of a rotor-bearing system is presented. The model includes modal elastodynamics of a flexible rotor as well as the in-plane radial dynamics of the bearing with a flexible outer race. Elastodynamics of the flexible shaft utilises a solution based on Green's function to provide a computationally efficient approach. The flexible bearing outer race is modelled using Timoshenko beam theory. The system model also includes detailed lubricated contact mechanics of balls-to-races contacts with viscous friction. Therefore, the rotor-bearing analysis represents a detailed multi-physics tribodynamics and modal elastodynamic responses of the system which closely represents broad-band vibration response of such systems in practice, an approach not hitherto reported in the literature. It is also demonstrated that the outer race flexibility changes the location of the stability orbital centres, as well as the spread of limit cycle vibrations. Furthermore, it accentuates the occurrence of multiples of ball pass frequency. The importance of integrated system dynamics and lubricated contact mechanics is highlighted, showing that although the elastodynamic response of the rotor's flexible elements may not be clear in the acquired vibration signal, its effect on energy efficiency of the system can be quite important.

Nonlinear dynamic model for linear guideway with crowning subjected to external load in five directions

The motion accuracy of linear guideway is adversely affected by ball passage vibration (BPV) when rolling balls within carriage move in a loop. Reduced vibration amplitude can be realized by a carriage with crowning design by now. However, few dynamic models are availability for the BPV analysis when linear guideway is subjected to actual external load in five directions. In this paper, a nonlinear dynamic model is proposed to investigate the periodic micro fluctuation of linear guideway with crowning subjected to load in five directions. The idea of coordinate transformation is adopted for the easier derivations of time-dependent and piecewise restoring force function. The different contact states of each ball are described in detail due to load distribution. The numerical simulation is employed to deal with equation of motion and discuss the effects of ball grouping, external load, preload and carriage speed. Experiment is also conducted for the verification of proposed model. The analytical model developed here is promising to clarify the mechanism of BPV from a dynamic perspective and serve the walking parallelism accuracy monitoring of linear guideway.

Dynamic modeling, analysis, and experimental study of ball screw pairs with nut spalling faults in electromechanical actuators

Condition monitoring and fault diagnosis on electromechanical actuators (EMAs) have gradually become a research hotspot in the field of aviation, but few studies have examined the failure mechanism of an EMA by establishing a dynamic model. As such, this paper establishes the two-degree-of-freedom radial dynamic models of ball screw pairs under normal and faulty conditions to analyze the dynamic characteristics that may occur in the vibration responses of normal and faulty ball screw pairs. After analyzing the simulation results of the established models, in this study, it is determined that after a spalling fault occurs in the inner raceway of a ball nut, the amplitude at the third harmonic of the ball passage frequency will increase significantly compared with the first and second harmonics of that frequency in the acceleration spectrum of the nut. This phenomenon can be regarded as a characteristic expression of the nut spalling fault in the acceleration spectrum, and it is verified by experiments on an EMA test rig. The experimental results show that this fault characteristic can also be observed even when the screw shaft rotating speed varies from 60 rpm to 420 rpm. However, under high-speed conditions, additional signal processing and noise reduction methods are required to solve the problem of background noise interference.

Eight-DOF Dynamic Modeling of EMA Mechanical Transmission and Spalling Fault Characteristic Analysis

Electromechanical actuators (EMAs), as the critical actuator system of next-generation aircraft, have attracted the attention of many institutions and enterprises around the world. However, due to harsh working conditions, their reliability cannot satisfy the requirements of widespread application in aircraft. Therefore, in order to conduct fault diagnosis on EMAs, in this paper, we establish a comprehensive dynamic model under numerous assumptions to study the fault characteristics that may occur in the displacement and acceleration responses of EMA systems. First, an eight-DOF dynamic model containing typical mechanical components of an EMA is established. Then, by obtaining the impact forces between balls and the spalling fault and the nonlinear relationship between the total elastic restoring forces and the change of ball deformation when the fault occurs, a faulty dynamic model is established. Comparison of the simulation results between the normal and faulty model reveals that the acceleration amplitude at the third harmonic of the ball passage frequency increases when fault occurs. Based on this phenomenon, a numerical calculation method of fault characteristics is proposed. Finally, the effectiveness of the established models and the identified phenomenon are verified by experiments conducted on an EMA test rig in a laboratory environment.

Difference in The Influence of Practice Regulating Passes and Regulating The Game Against The Accuracy of Passing in Junior Football Players

This research aims to find out what exercises are more influential between the practice of regulating passes and the practice of regulating the game against the accuracy of passing in football games in The Extracurricular Students of Private Elementary School Al Wasliyah 30 Martubung Medan In 2021. Participants in this study as many as 20 students with an age range of 10-12 years. Research design is pre-test two group experimental design. This research instrument is a test of passing accuracy in a piece of football. Quantitative descriptive analysis of data, by comparing differences in pretest and postest results. The results of the study in the form of analysis of two research hypotheses. Analysis of the first hypothesis of pre-test data and post-test accuracy of passing ball pass exercise group according obtained thitung = 6.86. From the list of distributions t using the odds of 1-1/2? = 0.975 with degree of freedom (df) n-1 = 9 obtained tcount (0.975) = 2.26. In the hypothesis testing criteria it is stated that in tcount >ttable with ? = 0.05 then Ho accepted Ha rejected. Analysis of the second hypothesis of pre-test data and post-test accuracy of passing ball of the Set Passen exercise group obtained tcount = 5.43. From the list of distributions t using the odds of 1-1/2? = 0.975 with df n-1 = 9 obtained the price t (0.975) = 2.26. In the hypothesis testing criteria it is stated that in tcount >tcount with ? = 0.05 then Ho rejected Ha accepted. Then it can be concluded by using the form of practice of regulating passes and arranging the game can improve the accuracy of passing in football games in The Private Elementary School Football Extracurricular Student Al Wasliyah 30 Martubung Medan Year 2021. This research contributes to subsequent research by being able to use other variables as treatment in the accuracy of football passing. Keywords: Passing, Game, Passing, Accuracy

From soccer video to ball possession statistics

Ball possession statistics in a soccer match is evaluated by counting the number of valid passes by both teams. The valid passes are determined by monitoring the start and end of a ball passing event initiated by a player. In this work, we map pass detection as detection of split and merge of nodes of a flow network. The players and ball represent nodes in the network. A group is formed by the objects (ball and players) which are spatially close to each other. Objects belonging to the same group are allowed to split or merge. We use this group relation to check if the objects split or merge in the sequence of frames. A constraint is added to the network to make sure that two objects can split only if the objects were previously merged. Flow through the split or merge node of the network denotes a ball pass event. Additional nodes like appear and disappear are added to the network to map the possibility that new objects could appear or old objects may disappear to and from the frame. The minimum cost path in the flow network provides the solution for valid pass events. Experimental evaluation shows that our proposal is at least 4% better in estimating ball possession statistics and 8% better in pass detection of a soccer match seen in a broadcast video than that of competitive methods.

Benefits of enhanced techniques combining negentropy, spectral correlation and kurtogram for bearing fault diagnosis

In condition monitoring based on vibrations for rotating machines fault detection, one of the typical symptoms is the presence of repetitive transients, which are characterized by impulsive and cyclostationarity signature. The approach quite popular nowadays in the industry for their detection is time–frequency techniques. Those techniques are mainly analysis tools instead of processing tools, and in any case, they are unable to offer a versatile methodology that applies to all mechanical signals in all circumstances. On the one hand, the paper is motivated by ideas borrowed from thermodynamics, where transients are seen as departures from a state of equilibrium; it is proposed to measure the negentropy of the squared envelope (SE) and the squared envelope spectrum (SES) of the signal. On the other hand, the paper proposes an adequate approach to exploit methods such as spectral correlation and kurtogram. The work’s main objective is to investigate connections in those approaches to capture the signature of this repetitive behavior. The methodology used in this paper proposes to display as images all three proposed techniques. The impulsive events are then detected and localized in frequency by high values of the squared envelope spectrum (SES) infogram in some frequency bands. In order to analyze the signal in the frequency domain, the Short-Time Fourier Transform (STFT) is then used. The STFT is suggested in this study due to its simplicity and high flexibility. For fault, such as bearings, Kurtogram was demonstrated to be efficient. However, kurtosis based on temporal signals is effective under some conditions; its performance is low in the presence of a low signal-to-noise ratio. The paper analyzed the case of Ball Pass Frequency Inner Race (BPFI), where bearings are housed in a casing allowing the shaft to rotate while driven by a variable speed electric motor. A radial load is applied using a hydraulic cylinder, and different sizes of defects are realized. For fault like BPFI, the negentropy gives more information even for a shallow size of fault and allows a prompt fault detection, and it can also be used for fault localization. The paper demonstrated that results obtained from negentropy through infograms combining with spectral correlation could significantly extend the domain of the applicability of the Kurtogram.

Vibration characteristics and condition monitoring of internal radial clearance within a ball bearing in a gear-shaft-bearing system

Internal radial clearance is a key factor influencing bearing fatigue life. Moreover, bearings inevitably suffer from various wears and tears, which result in gradual increase of clearance and shorten bearing life. Monitoring bearing clearance changes using vibration can effectively indicate the bearing wear and provide good leading time to perform maintenances. Previous studies show that vibration at ball pass frequency on outer race (BPFO) can be based for clearance monitoring. However, such clearance induced vibration has not been well understood, especially under complicated dynamic interactions such as in a gearbox system. To fill this gap, this paper presents a nonlinear gear-shaft-bearing-housing vibration model with fourteen degree of freedom (DOF) to investigate the vibration responses under the dynamic gear meshing force and progressively changed radial clearances at first. Then, the model was verified through a two-stage spur gearbox. Furthermore, bearing characteristics with different radial clearances under the influence of gear are revealed and indicator based on modulation signal bispectrum-sideband estimator (MSB-SE) was proposed. Finally, vibration data from a run-to-failure gearbox test rig was utilized to verify the effectiveness of the MSB-SE indicator for bearing clearances monitoring. Simulation results show that BPFO is modulated on gear meshing frequency (GMF) and BPFO amplitude from envelope spectrum increases with bearing clearances under the influence of gear meshing. Indicator based on MSB-SE, possessing the capability of purifying the interferences of gear meshing and strong noises, is effective to capture the variance of bearing clearances. The experiment based on a run-to-failure gearbox test rig provided evidence for the effectiveness of the proposed indicator, which is more accurate than BPFO amplitude from conventional envelope analysis and time-domain indicators, such as RMS and kurtosis. These findings are of significance for bearing fault diagnosis and maintenance.

Change of Direction Biomechanics in a 180-Degree Pivot Turn and the Risk for Noncontact Knee Injuries in Youth Basketball and Floorball Players

Background: Studies investigating biomechanical risk factors for knee injuries in sport-specific tasks are needed. Purpose: To investigate the association between change of direction (COD) biomechanics in a 180-degree pivot turn and knee injury risk among youth team sport players. Study Design: Cohort study; Level of evidence, 2. Methods: A total of 258 female and male basketball and floorball players (age range, 12-21 years) participated in the baseline COD test and follow-up. Complete data were obtained from 489 player-legs. Injuries, practice, and game exposure were registered for 12 months. The COD test consisted of a quick ball pass before and after a high-speed 180-degree pivot turn on the force plates. The following variables were analyzed: peak vertical ground-reaction force (N/kg); peak trunk lateral flexion angle (degree); peak knee flexion angle (degree); peak knee valgus angle (degree); peak knee flexion moment (N·m/kg); peak knee abduction moment (N·m/kg); and peak knee internal and external rotation moments (N·m/kg). Legs were analyzed separately and the mean of 3 trials was used in the analysis. Main outcome measure was a new acute noncontact knee injury. Results: A total of 18 new noncontact knee injuries were registered (0.3 injuries/1000 hours of exposure). Female players sustained 14 knee injuries and male players 4. A higher rate of knee injuries was observed in female players compared with male players (incidence rate ratio, 6.2; 95% CI, 2.1-21.7). Of all knee injuries, 8 were anterior cruciate ligament (ACL) injuries, all in female players. Female players displayed significantly larger peak knee valgus angles compared with male players (mean for female and male players, respectively: 13.9°± 9.4° and 2.0°± 8.5°). No significant associations between biomechanical variables and knee injury risk were found. Conclusion: Female players were at increased risk of knee and ACL injury compared with male players. Female players performed the 180-degree pivot turn with significantly larger knee valgus compared with male players. However, none of the investigated variables was associated with knee injury risk in youth basketball and floorball players.

A time-dependent dynamic model for ball passage vibration analysis of recirculation ball screw mechanism

Ball passage vibration arising during recirculation of rolling elements is a limitation of high-precision performance associated with ball screw. A relatively deep understanding of this phenomenon when rolling balls leave load area and enter circulation channel has been achieved by now. However, few mechanical models are established for calculation of rolling ball contact deformation and force inside nut while moving by taking into account transient phase at import and export of circulation channel. In this work, we present a general time-dependent dynamic model for description of ball motion and axial periodic micro fluctuation within ball screw subjected to external load. The numerical simulation is employed to deal with equation of motion including segmented restoring force function. Effects of applied load, preload and screw rotational speed on dynamic response are discussed theoretically. Reduced vibration amplitude may be realized by small ball diameter and phase difference between ball groupings. Proposed model is experimentally illustrated.

Friction Forces in a Linear-Guideway Type Recirculating Ball Bearing Under Grease Lubrication

Abstract This paper deals with friction forces in a linear-guideway type recirculating ball bearing (linear bearing) under grease lubrication. During the experiments, the friction force, temperature, and electric contact voltage of a grease lubricated linear bearing (test bearing) without seals were measured. Experimental results showed that the measured friction forces of the test bearing were fluctuated with the ball passage period. The measured time-average friction force FAVG (measured FAVG) was nearly constant when the grease filling rate x (=grease filling volume/internal space of the bearing) ≥0.13, while the measured FAVG decreased as x decreased when x < 0.13. In addition, the measured temperatures were almost constant, and the measured contact voltages indicated that the contacts of the balls and raceways were electrically insulated by the grease film. Next, the expressions of friction forces due to differential slip (FD), elastic hysteresis loss (FE), and rolling traction (FRT) were shown. The calculated FD + FE + FRT for the test bearing was almost equal to the measured FAVG around the grease filling rate of x = 0, while in cases where x > 0, the measured FAVG was greater than the calculated FD + FE + FRT. This means that when x > 0, an agitating resistance (FA) from the grease might cause the measured FAVG to be greater than the calculated FD + FE + FRT. Finally, an expression for the friction force of a linear bearing, FAVG = FD + FE + FRT + FA (which can estimate the measured ones) is proposed.