• Transactions of Materials Processing
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• v.10 no.1
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• pp.59-66
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• 2001

Recently, the technology of incremental forming for sheet metal components has drawn attention for small-batch productions. In the present investigation, a forming tool containing a freely-rotating ball was developed and applied to forming of various shapes with full annealed Al 1050 sheet. Deformation characteristics occurring during forming with this tool was examined through FEM analysis and grid measurement. It was found that deformation modes developed along a straight path and around a corner are close to those of plane-strain and equi-biaxial stretching, respectively, and that cracks occur mostly at corners for the same depth of tool. FEM analysis was successfully applied to this special type of forming process and provided comparable results to the measurements from experiment.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.433-442
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• 1989

Owing to the development of CNC machine tools and automatic programing software, the milling process with ball-end mill has become the most widely used process where three-dimensional precision machining is important. In this study, the ball-end milling process has been analyzed and a cutting force model has been developed to predict the cutting force acting on the ball-end mill on given machining conditions. The development of the model is based on the analysis of geometry of a ball-end mill an the oblique cutting process. The cutting edges of ball-end mills are considered as a series of infinitesimal elements and the geometry of the cutting edge element each cutting edge element is straight. The oblique cutting process in the small cutting edge element has been analyzed as orthogonal cutting process in the plane containing the cutting velocity vector and chip-flow vector. Hence, with the orthogonal cutting data obtained from orthogonal turning test, the cutting forces can be predicted through the model. The predicted cutting forces has shown a fairly good agreement with the test results in various plane cutting conditions.

• Journal of Biosystems Engineering
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• v.27 no.1
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• pp.67-76
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• 2002

This study was conducted to investigate the effects of impact conditions on the acoustic characteristics of a watermelon. The study was crucial to develop a device for nondestructive internal quality evaluation of a watermelon by an acoustic impulse response method. An impact device was constructed with a pendulum to hit the watermelon, a microphone to detect the acoustic impulse responses, and a digital oscilloscope and computer to store and analyze the data. The selected samples were Guemcheon cultivar watermelons(Citrulus Vulgaris Schrad) harvested on Oct. 20,1998. Sixty watermelons were tested on flour different types of sample holders, with four kinds of ball made of different materials, at four bevels of the angular position of the pendulum and distance from the watermelon to the microphone. Since the magnitudes of frequencies obtained by hitting with the steel and rubber ball were relatively small at the bandwidths of above 500 Hz, it was shown that the steel and rubber ball were not suitable far a hitting ball in the pendulum to get informations on internal quality of the watermelon. In case of using broth of the wood and acryl ball, almost the same and good acoustic responses were shown on the wide range of frequency bandwidth. Therefore, it seemed that the acryl ball was more suitable to the test than the wood ball in considering its mechanical properties. The acoustic characteristics of the watermelon were not shown a significant difference between the types of sample holder. The amplitudes of the acoustic signals and the magnitudes of frequencies from the whole samples increased with increase of the angular position of pendulum and with decrease of the distance from the watermelon to the microphone. However, the resonance resonance of the sample were almost the same regardless of the angular positions and the distances.

• Fashion & Textile Research Journal
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• v.20 no.1
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• pp.75-82
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• 2018

This study was attempted to clarify differences in sizes and shapes of foot between 20's and 60-70's women and analyzed the characteristics of elderly women's foot shapes as compared with those of young. The 2D data were 101 elderly and 101 young women in Seoul and Gyeonggi-do. The results are as follows: Firstly, the foot length of the elderly was shorter than that of the young, the foot breadth and the heel width were widened, but the toes breadth became smaller and the deformity of the toe 1 and the first metatarsal part appeared. Secondly, in the Foot Index, there was a significant difference in age group, the young is more than the elderly in the narrow type, standard type, the elderly women showed more than three times the young in the wide type. Thirdly, in the factor analysis for the foot type classification, 'foot length' factors in both age groups were large. Next, young group were influenced by 'toes breadth', lateral ball breadth' factors, elderly group was influenced by the 'lateral ball breadth', 'medial ball breadth' factors. Lastly, in the cluster analysis of the elderly group, the types of sole were classified as W-Type(20.8%, wide foot and toes, large heel), H-type(20.8%, small toes breadth, heel), D-type(31.7%, long length and wide lateral ball) and A-Type(26.7%, which is found only in the elderly, small length and large toes angle). As a result, it is necessary to design the shoes that match the characteristics of the soles of the elderly women.

• Tribology and Lubricants
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• v.30 no.4
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• pp.205-211
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• 2014

Recent studies emphasize the importance of pivot stiffness in the analysis of tilting pad bearings (TPBs). The present paper develops a finite element model of the pad pivot and compares the predicted pivot stiffness to the results of Hertzian contact model calculations. Specifically, a finite element analysis generates tetrahedral mesh models with ~40,000 nodes for a ball-socket pivot and ~50,000 nodes for a rocker-back pivot. These models assume a frictionless boundary condition in the contact area. Increasing the applied loads on the pad in conjunction with increasing time steps ensures rapid convergence during the nonlinear numerical analysis. Predictions are performed using the developed finite element model for increasing the differential diameters between the pad pivot (or ball) and the bearing housing (or socket). The predictions show that the pivot contact area increases with decreasing differential diameters and increasing applied loads. Further, the maximum deformation occurring at the pivot center increases with increasing differential diameters and increasing applied loads. The pivot stiffness increases nonlinearly with decreasing differential diameters and increasing applied loads. Comparisons of results of the developed finite element model to those of Hertzian contact model calculations assuming a small contact area show that the latter model underestimates the pivot stiffnesses predicted by the finite element models of the ball-socket and rocker-back pivots, particularly for small differential diameters. This result implies the need for cautionduring the design of pivot stiffness by the Hertzian contact model.

• Korean Journal of Applied Biomechanics
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• v.17 no.4
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• pp.83-88
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• 2007

The purpose of this study was to investigate the ball velocity changes depending on the different linear momentum of putter head. For this study, two different moving conditions(25cm free fall and 35cm free fall) of putter head were set. And two different types of ground conditions were used which are artificial grass green($180cm{\times}600cm{\times}1cm$) and glass green($40cm{\times}130cm{\times}1cm$). Movements of putter head and ball were recorded with 2 HD video cameras(60 Hz, 1/500s shutter speed). Small size control object($18.5cm{\times}18.5cm{\times}78.5cm$) was used in this study. Ball and putter head velocities were calculated by the First Central Difference Method(Hamill & Knutzen, 1995). Linear momentum of ball and putter head were calculated with mass and its velocities. Before impact, the velocity of the putter head of 35cm free fall was about 30% greater than that of the putter head of 25cm free fall. Linear momentum of putter head of 35cm free fall was about 0.355-0.364kg m/s and 25cm free fall was 0.251 kg m/s. After impact, putter head lost its linear momentum about 14-19% and adjusting time of putter head after impact would be 0.1 second. After 0.1 second, putter moved the route same as before impact. Maximum ball velocities were appeared 0.08s-0.10s after impact no matter what the ground conditions are. Ball velocities struck by 35cm free fall were 30 % faster than 25cm free fall. Linear momentum of ball struck by putter head was greater than that of expected amount because the moving ball has translational energy and rotational energy. Future study must treat three things. One is ball must struck by the different putters with different materials. Another is two-piece ball and three-piece ball should be used for the same condition studies. The other is height of center of rotation of club should be changed. In this study, the height of center of rotation of club head is 71cm from the ground. But recently many golfers used the long putter. Therefore next study should apply the different height of center of rotation of club head.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.119-126
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$ balls were fabricated using different raw materials, sintering aids and sintering conditions, Commercially available Si3N4 ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 9.525mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) mjcrostructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$Phase.

• Tribology and Lubricants
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• v.19 no.3
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• pp.123-132
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• 2003

The effect of surface texture on elastohydrodynamic lubrication (EHL) point contact of a ball Joint mechanism in small reciprocating compressors is studied numerically by using multigrid method. Pressure and film thickness profiles have been calculated for surface roughness with waviness of different orientations and transverse ridge and dent at minimum and maximum Hoes M parameter conditions. The influence of the amplitude and the wavelength of the surface roughness was also studied. Results show that the oblique waviness with orientation angle of 30$^{\circ}$generates the smallest minimum film thickness as compared with those of longitudinal, transverse, and other oblique roughness. The influence of transverse waviness on the minimum film thickness is smaller than for the longitudinal waviness case.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.6
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• pp.484-491
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• 2002

We developed a new type of human-sized BWR (biped walking robot) driven by a new actuator based on the ball screw which has high strength and high gear ratio. Each leg of the robot is composed of three pitch joints and one roll joint. In all, a 10 degree-of-freedom robot with two balancing joints was developed. A new type of actuator for the robot is proposed, which is composed of four bar link mechanism driven by the ball screw. The robot overcomes the limit of the driving torque of conventional BWRs. The BWR was designed to walk autonomously by adapting small DC motors for the robot actuators and has a space to board DC battery and controllers. In the performance test, the BWR performed sitting-up and down motion, and walking motion. Through the test, we found the possibility of a high performance biped-walking.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.564-571
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• 2003

This research investigates how characteristics of ball bearing affect non-repeatable runout(NRRO) in a HDD spindle system at elevated temperature. It shows that the elevated temperature results in the increase of bearing contact angle and the decrease of bearing deformation due to the different thermal expansion rate of the components of the HDD spindle system. The increase of contact angle at elevated temperature is so small that the variation of bearing frequencies is negligible. On the other hand, the decrease of bearing deformation at elevated temperature reduces the stiffness of ball bearing and the natural frequencies of HDD spindle system consequently, which changes the amplitude and the frequency distribution of NRRO.