• Journal of Korean Neurosurgical Society
• /
• 제46권2호
• /
• pp.144-151
• /
• 2009

Objective: To compare two testing protocols for evaluating range of motion (ROM) changes in the preloaded cadaveric spines implanted with a mobile core type Charite$^{TM}$ lumbar artificial disc. Methods: Using five human cadaveric lumbosacral spines (L2-S2), baseline ROMs were measured with a bending moment of 8 Nm for all motion modes (flexion/extension, lateral bending, and axial rotation) in intact spine. The ROM was tracked using a video-based motion-capturing system. After the Charite$^{TM}$ disc was implanted at the L4-L5 level, the measurement was repeated using two different methods: 1) loading up to 8 Nm with the compressive follower preload as in testing the intact spine (Load control protocol), 2) loading in displacement control until the total ROM of L2-S2 matches that when the intact spine was loaded under load control (Hybrid protocol). The comparison between the data of each protocol was performed. Results: The ROMs of the L4-L5 arthroplasty level were increased in all test modalities (p < 0.05 in bending and rotation) under both load and hybrid protocols. At the adjacent segments, the ROMs were increased in all modes except flexion under load control protocol. Under hybrid protocol, the adjacent segments demonstrated decreased ROMs in all modalities except extension at the inferior segment. Statistical significance between load and hybrid protocols was observed during bending and rotation at the operative and adjacent levels (p< 0.05). Conclusion: In hybrid protocol, the Charite$^{TM}$ disc provided a relatively better restoration of ROM, than in the load control protocol, reproducing clinical observations in terms of motion following surgery.

• 한국자동차공학회논문집
• /
• 제18권3호
• /
• pp.37-42
• /
• 2010

Plastic region tightening is widely used in critical bolted joints in internal combustion engines in order to reduce the engine weight by maximizing the use of load-carrying capacity of bolt. Mechanical behavior of bolt tightened in plastic region under external axial tensile load is investigated for various friction conditions using three dimensional finite element analysis. The behavior of bolt tightened in elastic region as well as that in tensile test are investigated for comparison. Tightening process is simulated by rotating the bolt in order to examine the friction effect realistically. It is revealed that the bolt tightened in plastic region can carry more external load until the joint is opened, and yields at lower bolt load than the bolt tightened in elastic region. The friction coefficient has effect on the yield load, but not on the load-carrying capacity. Moreover, the scatter in the bolt preload due to friction begins with plastic deformation of bolt in the angle tightening control, whereas it begins with the onset of tightening in the torque tightening control. The observations are interpreted with the residual torsional stress in the bolt generated during the tightening.

• 한국정밀공학회지
• /
• 제30권8호
• /
• pp.854-863
• /
• 2013

High-speed spindle systems typically employ angular contact ball bearings, which can resist both axial and radial loading, and exhibit high precision and durability. We investigated the effects of the arrangement of the angular contact ball bearings on the dynamics of high-speed spindle systems. The spindle dynamics were studied with a number of spindle-bearing models, and the location of the bearings was varied, along with the rotational speed and the preload. A finite element spindle model and a bearing model were used, and simulated data showed that the bearing arrangement significantly affected the spindle dynamics. Furthermore, the main effects were due to the cross coupling terms between the transverse and rotational motions of the ball bearings. The coupling stiffness terms were found to influence the spindle dynamics, depending on the mode shapes. An extensive discussion is provided on the effects of the bearing arrangement on the dynamics of the spindle.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2005년도 춘계학술대회 논문집
• /
• pp.907-910
• /
• 2005

Although several artificial disc designs have been developed for the treatment of discogenic low back pain, biomechanical change with its implantation was rarely studied. To evaluate the effect of artificial disc implantation on the biomechanics of functional spinal unit, nonlinear three-dimensional finite element model of L4-L5 was developed with 1-mm CT scan data. Two models implanted with artificial discs, SB $Charit\acute{e}$ or Prodisc, via anterior approach were also developed. The implanted model predictions were compared with that of intact model. Angular motion of vertebral body, force on spinal ligaments and facet joint, and the stress distribution of vertebral endplate for flexion-extension, lateral bending, and axial rotation with a compressive preload of 400 N were compared. The implanted model showed increased flexion-extension range of motion and increased force in the vertically oriented ligaments, such as ligamentum flavum, supraspinous ligament and interspinous ligament. The increase of facet contact force on extension were greater in implanted models. The incresed stress distribution on vertebral endplate for implanted cases indicated that additinal bone growth around vertebral body and this is matched well with clinical observation. With axial rotation moment, relatively less axial rotation were observed in SB $Charit\acute{e}$ model than in ProDisc model.

• 대한의용생체공학회:의공학회지
• /
• 제21권3호
• /
• pp.295-301
• /
• 2000

뼈의 성장에 미치는 많은 요소들 중에서 implant의 상대적인 미세운동(relative micromotion)은 뼈의 implant와의 접합을 방해하는 것으로 알려져 왔다. 그런데 이러한 상대적인 운동 및 spinal stability에 직접적으로 영향을 주는 하중조건, spinal material의 물성치, spinal geometry 및 뼈와 implant의 접촉면에서의 마찰계수를 고려하기 위하여, 하나의 titanium interbody cage 가 삽입된 human lumbar segments (L4-L5)의 유한요소 모델이 개발되었다. 이러한 유한요소 모델의 해석을 통하여 상대적인 미세운동, Posterior의 수직적인 변위, von Mises 응력 및 마찰력이 예측되었다. Cancellous bone. annulus fibers 및 ligaments의 기계적인 물성치의 감소 또는 접촉면에서의 마찰계수의 감소는 상대적인 미세운동 (relative micromotion or slip distance)을 증가 시켰다. 접촉면에서의 normal force는 뼈의 밀도 (cancellous bone density) 가 감소하거나 접촉마찰계수가 증가하면 감소했다. 특히 하중조건에 있어서, compressive preload에 대한 torsion의 추가는 접촉면의 anterior부위에서 상대적인 미세운동을 증가 시켰다. 하지만 디스크면적이 증가할수록 상대적인 미세운동은 감소했다. 결론적으로, 접촉면의 기계공학적 거동 (Relative micromotion, stress response, posterior axial displacement and contact normal force)은 접촉면의 마찰계수 뼈의 밀도, 하중조건 및 노화에 따른 형상/물성의 변화에 매우 민감함을 보이고있다.

• Design & Manufacturing
• /
• 제6권1호
• /
• pp.45-51
• /
• 2012

The main goal of this paper is to establish an interference tolerance for determining optimal amount of clearance in the shaft-bearing system supported by radial ball bearings. The 2-D frictional contact model was employed for the FE analysis between the shaft and the inner raceway. Several examples were simulated using different material properties for the solid shaft. Efforts were focused on the deformation applied in the radial direction to select suitable bearings. The analysis results showed that the initial axial preload applied on the bearings plays a significant role to reduce bearing fatigue life. The proposed design parameters obtained by numerical simulations can approximately predict a rate of bearing life reduction as a function of shaft diameter ratio. This analysis can also be used to calculate the optimal initial radial clearance in order to obtain a shaft-bearing system design for high accuracy and long life.

• 한국정밀공학회지
• /
• 제33권1호
• /
• pp.53-61
• /
• 2016

Angular misalignment has a significant effect on the characteristics of angular contact ball bearings (ACBBs). This paper presents an analysis of fatigue life for ACBBs subjected to angular misalignment. A simulation model is developed with de Mul's bearing model and the ISO basic reference rating life model. Simulation is performed to calculate the life of the ACBBs subjected to angular misalignment. The numerical results show that angular misalignment influences the load distribution significantly, thus reducing the bearing rating life. The fatigue life of ACBBs is decreased by angular misalignment regardless of axial preload, external radial load and rotational speed. The results show that angular misalignment should be maintained at less than 1mrad for ACBBs.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2000년도 춘계학술대회논문집
• /
• pp.1051-1057
• /
• 2000

A projected 100 kW APU gas turbine rotor-bearing system has a main outer shaft, which is composed of some numbers of segmented sections for manufacturing and assembly conveniences. For a secure assembly of the segmented sections a tie shaft or inner shaft is installed inside of the outer shaft and a tensional axial preload of 50,000 N is provided to it. In this paper it is intended to set-up a sound modeling method of the APU rotor system, and particularly, the influences of the tie shaft on the rotordynamic characteristics of the entire APU gas turbine rotor-bearing system are investigated. Analysis results show that as a conservative design practice the inner tie shaft should be actively modeled in the rotordynamic analysis of the APU rotor-bearing system, and its effects on the dynamic behaviors of the outer shaft should be thoroughly design-reviewed.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
• /
• pp.440-445
• /
• 1999

One of the important technical issues is how to decrease thermal expansion of ballscrew in proportion to the increase of machining speed. When measuring force of stretch of ballscrew, since not only actual expansion and the value of bending have to be considered, it's impossible to definite the exact value of expansion. In addition, support bearings of ballscrew gain considerable force in axial direction. It also generates thermal expansion on the ballscrew, and deteriorates the bearings. In conclusion, it's impossible to give the pretension enough to absorb the all elongation due to thermal expansion generated during machine running. If gave, bed, column and saddle are all bent to change machine accuracy, and the pretension of support bearing of ballscrew in machine tool.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
• /
• pp.160-166
• /
• 1997

The spindle motor in a computer hard disk drive can be modeled as a rotor-bearing system supported by the base plate. Ball bearing is the crucial element to determine the stiffness of the spindle motor, and its design parameters and operating conditions determine the dynamic characteristics of the spindle motor. In the analysis of a rotor-bearing system with a short shaft like a spindle motor, the stiffness of the base plate as well as ball bearings must be considered accurately to analyze the dynamic charateristics of a spindle motor. In this paper, the lateral and the axial vibration of the spindle motor were analyzed by the transfer matrix method for the dual-shaft rotor-bearing model and by d.o.f lumped parameter model, respectively. The simulation results had good agreements with the experimental modal testing. The dynamic characteristics were fully investigated for the change of the major design parameters of the spindle motor, i.e. the preload of ball bearings and the rotational speed.