In the field of orthopedics, it is important to analyze the kinematics of the shoulder joints. In this research group, kinetic analysis of the shoulder joints with high accuracy was made possible using our original image matching method. The aim of this study was to reproduce the relative relationship of bones on 3D-CAD based on 6 degrees of freedom, and analyze the relative relationship between the humeral head and the glenoid cavity. The dynamic glenohumeral kinematics during full axial rotation was analyzed in two rotator cuff tear (RCT) patients before and after arthroscopic rotator cuff repair (ARCR). After kinetic analysis calculates 6 degrees of freedom, the relationship between the scapula and the humerus was reproduced using 3D-CAD, and the distance between the humeral head and the glenoid cavity was estimated. The difference between RCT shoulder and ARCR shoulder during full axial rotation was confirmed. This finding is clinically important as it may provide valuable information as one of the quantitative assessments of RCT shoulders.

The shoulder joint represents the most unstable and complex structure in all of human joints. Shoulder movement involves complex interactions between skeletal system and soft tissues. Understanding these mechanical interactions is important for improving the motor skill in sports and preventing shoulder disorders, such as a dislocation. Musculoskeletal simulation can reveal various mechanical information in human body as non-invasive tools. Several studies have reported that human parts were modeled using finite element method to analyze deformation of soft tissues, and modeled as rigid bodies in multi-body simulation system to reveal the dynamic motion behavior. However, soft tissues related to shoulder joint (e.g., joint capsules and rotator cuff) have not been previously modeled in dynamics simulation system. The aim of this study was to construct anatomical dynamic simulation model of shoulder joint and surrounding tissues by cadaveric specimens. The bones were modeled as rigid bodies using CT scanning of the single cadaver. The joint capsules and rotator cuff were modeled as spring-damper-mass system to connect rigid bone models. The result of dynamics simulation showed the detailed behavior of shoulder joint by contracting rotator cuff muscles.

Up to now, it is still difficult to shoot a table tennis ball in high speeds accompany with designated vertical, horizontal and gyroscopic spins using a commercial table tennis robot (i.e. table tennis machine). Accordingly, we designed and produced a table tennis machine, which can shoot the table tennis ball with a variety of shooting types (e.g. loop, smash, drive, knuckle, chiquita flick). The produced machine has four rollers (two launch rollers and two gyro rollers), where the rotation number and rotation direction of each roller can be adjusted independently. In this study, we perform shooting tests of the developed table tennis machine to evaluate its performance and to study the ball shooting mechanism. From the experimental results, the developed machine has high power to shoot a table tennis ball with maximum speeds over 42 m/s, maximum spin rate over 7,800 rpm accompany with designated spin types (top, back, side, or gyro). Moreover, the direction of the spin axis of the shot ball can be controlled freely within 360 degrees by adjusting the two gyro rollers.

The objective of this study was to construct a finite element model of a table tennis ball, and to devise a method for the construction of the ball model by investigating the factors affecting the behavior of the ball during and after impact. A ball model with viscoelasticity was constructed using the Maxwell model and was composed of shell elements. Normal and oblique impacts with a flat rigid plate were simulated to reveal the relationship between the material properties and the rebound behavior of the ball, that is the deformation, velocity, angle and spin rate, by varying the individual material constants which was composed of the material model of the ball. Impact experiments were also conducted to obtain the rebound behavior of the ball which was ascertained from images taken by a high-speed video camera. Then, a method for the construction of the ball model was proposed based on these relationships and the experimental results of the rebound behavior. The results simulated using the model, constructed by the proposed method, and closely matched the experimental results. The proposed method for constructing the FE model for the table tennis ball may be applicable to quick identification of the material parameters.

The objective of this study was to construct a finite element (FE) model for a table tennis rubber with pimples structure which can accurately estimate the rebound behavior of the ball at impact, and to investigate effects of the structure of the rubber on ball rebound behavior. The rubber is composed by combination of a rubber sheet and a polyurethane foam, and the sheet has complicated structures which are lined up cylindrical pimples. FE models of the sheet and the foam were constructed with non-linearity, strain rate dependency and energy absorption which was expressed based on the results of the static tensile and compression tests and the dynamic compression test. The simulation results for the rebound behavior of the ball, which were calculated from impact analysis between the sheet plate and the ball, quantitatively agreed well the experimental results. FE analysis were conducted using the developed models of the ball and rubber with different diameter of pimples. The simulation results of spin rate do not tend to be proportional to the size of pimple diameter. The trend of the spin rate depends on the amount of impulse during impact which is calculated using the horizontal component of the contact force which contributes to the generation of the spin It was determined that the spin rate has a maximal value when the impulse is the largest.