• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 2004년도 춘계학술대회 논문집
• /
• pp.416-423
• /
• 2004

This paper presents the thermal characteristic analysis of a high-speed horizontal machining center with spindle speed of 50,000rpm and feedrate of 120m/fin. The spindle system is designed based on the built-in motor, angular contact ceramic ball bearings, oil-air lubrication and oil-jacket cooling method. The X-axis and Y-axis feeding systems are composed of the linear motors and linear motion guides, and the Z-axis feeding system is composed of the servo-motor, ball screw and linear motion guides. The thermal characteristics such as the temperature distribution, temperature rise, thermal deformation and step response, are estimated based on the finite element model of machining center and the heat generation rates of heat sources related to the machine operation conditions. Especially, the thermal time constant assessed from the step response function is introduced as an index of thermal response characteristics.

• 한국공작기계학회논문집
• /
• 제13권5호
• /
• pp.30-37
• /
• 2004

This paper presents the thermal characteristic analysis of a high-speed horizontal machining center with spindle speed of 50,000rpm and feedrate of 120m／min. The spindle system is designed based on the built-in motor, angular contact ceramic ball bearings, oil-air lubrication and oil-jacket cooling method. The X-axis and Y-axis feeding systems are composed of the linear motors and linear motion guides, and the Z-axis feeding system is composed of the servo-motor, ball screw and linear motion guides. The thermal characteristics such as the temperature distribution, temperature rise, thermal deformation and step response, are estimated based on the finite element model of machining center and the heat generation rates of heat sources related to the machine operation conditions. Especially, the thermal time constant assessed from the step response function is introduced as an index of thermal response characteristics.

• 한국산업융합학회 논문집
• /
• 제17권3호
• /
• pp.84-92
• /
• 2014

In this paper, a novel 5-axis hybrid-kinematic machine tool is introduced and the research results on accuracy improvement of the prototype machine tool are presented. The 5-axis hybrid machine tool is made up of a 3-DOF parallel manipulator and a 2-DOF serial one connected in series. The machine tool maintains high ratio of stiffness to mass due to the parallel structure and high orientation capability due to the serial-type wrist. In order to acquire high accuracy, the methodology of measuring the output shafts by additional sensors instead of using encoder outputs at the motor shafts is proposed. In the kinematic view point, the hybrid manipulator reduces to a serial one, if the passive joints in the U-P serial chain at the center of the parallel manipulator are directly measured by additional sensors. Using the method of successive screw displacements, the kinematic error model is derived. Since a ball-bar is less expensive than a full position measurement device and sufficiently accurate for calibration, the kinematic calibration method of using a ball-bar is presented. The effectiveness of the calibration method has been verified through the simulations. Finally, the calibration experiment shows that the position accuracy of the prototype machine tool has been improved from 153 to $86{\mu}m$.

• Journal of Trauma and Injury
• /
• 제19권2호
• /
• pp.164-172
• /
• 2006

Background: The authors conducted a retrospective study to evaluate the mechanism of injury, the surgical techniques, the clinical features, the combined injuries, the treatment results, and the surgical complications in patients with atlantoaxial fracture/subluxations. Methods: The authors reviewed 71 cervical fracture/dislocations during a four-year period from September 2002 to August 2006. Among them, there were twenty one C1,2 fracture/subluxations. There were thirteen men (mean age : 43.5 years) and eight women (mean age : 50 years). Their follow-up period was at least 6 months, and the mean follow-up period was 9.6 months. Gardner-Wells tongs traction was used in all patients immediately on presentation. Surgical treatment was performed, depending on the pathologic conditions. Results: Of all 21 cases, 14 cases were injured in motor vehicle accidents, 5 were falls, and 2 were miscellaneous. There were four C1 fracture (5.6%), fourteen C2 fracture (66.7%), one C1 and 2 combined fracture (4.8%), and one C1-2 subluxation (4.8%). The C1 fractures in our series were classified as two Jefferson's fractures and two C1 lateral mass fracture. The C2 fractures were classified as one odontoid type I fracture, two odontoid type II fractures, five odontoid type III fractures, one hangman's fracture, and four C2 body tear-drop fractures. Atlantoaxial fractures were associated with six (28.6%) head injuries, four (19.0%) other spinal injuries, two (9.5%) chest injuries, and three (14.3%) spinal cord injuries. Surgical treatment was performed in nine cases, which included anterior odontoid screw fixation in two cases, transarticular screw fixation with iliac bone graft in one case, posterior fixation by using C2 pedicle screw and C3 lateral mass screw in three cases, lateral mass screw fixation C1-2 with iliac bone graft in one case, O(occipito)-C1-3-4 screw fixation in one case, posterior C2-3 wiring with allograft in one case, and halo vest in six cases. Conservative management was used in the rest of the patients in our trials. Bone fusion was complete in all cases. There were no operation-related complication, except one pin site infection in the case of halo vest. Conclusion: In this study, the choice of appropriate treatment according to the fracture types resulted in safe and effective management of unique atlantoaxial fracture/subluxations.

• 대한치과보철학회지
• /
• 제55권3호
• /
• pp.251-257
• /
• 2017

목적:본 연구에서는 long internal connection 형태의 임플란트 지대주를 내부 연결 길이에 변화를 주어 임플란트-지대주 결합부의 안정성을 비교 평가해 보고자 하였다. 재료 및 방법: Long internal connection의 임플란트(Replus system, $4.7{\times}11.5mm$)를 각각 지대주의 길이에 따라 4개의 군(1, 2, 3, 4 mm 군)으로 나누었고 총 20개의 시편을 사용하였다. 시편을 레진에 매몰하여 고정시키고 100 N의 힘으로 임플란트 장축에 대해 30도의 각도에서 $1.0{\times}10^6$ 번의 반복하중을 가한 후 하중 전 후의 풀림회전력의 차이를 계산하여 95% 유의수준에서 Kruskal-Wallis 검정 방법을 통해 통계 분석하였다. 결과:지대주 내부 길이에 따른 풀림 회전력의 통계적 유의성은 나타나지 않았으며 (P > .05) 어떤 시편에서도 완전한 나사 풀림이나 나사 파절은 관찰되지 않았다. 결론: 내측 연결 임플란트에서 지대주 내부길이에 따른 나사 풀림의 정도는 차이가 나지 않았다.

• 대한치과보철학회지
• /
• 제55권2호
• /
• pp.151-155
• /
• 2017

목적: 이 연구의 목적은 새로운 타이타늄 구성요소를 가진 지르코니아 지대주의 나사 제거력의 변화에 대해 알아보는 것이다. 내부연결 임플란트를 위한 새로운 지르코니아 지대주의 동적하중 후 지대주 나사의 제거력을 기존의 타이타늄 지대주와 비교하여 분석하였다. 재료 및 방법: 내측연결 임플란트와 타이타늄 지대주, 타이타늄 구성요소를 가진 지르코니아 지대주를 준비하였다. 12개의 내부연결형 임플란트에 6개의 타이타늄 지대주를 연결하고(대조군), 6개의 타이타늄 구성요소를 가진 지르코니아 지대주(실험군)를 30 Ncm의 토크로 연결한 후 동적하중 전후의 나사 제거력을 측정하였다. 동적 만능재료시험기를 사용하여 연결체의 장축과 30도 각도를 이루도록 하고 300 N 하중크기로 100만번의 하중이 가해졌다. 동적하중 전후의 지대주 나사 제거력을 t검정을 통해 신뢰구간 95%로 통계적 유의성을 검증하였다. 결과: 두 그룹 모두에서 동적하중 후 나사 풀림을 보이지 않았다. 동적 하중 전후의 나사 제거력은 두 그룹 모두에서 통계적으로 유의한 차이가 있게 나타났다(P < .05). 동적 하중 전후의 나사 제거력 차이는 대조군에서 $-7.25{\pm}1.50Ncm$, 실험군에서 $-7.33{\pm}0.93Ncm$ 로 나타났다. 통계분석 결과 두 군간에 나사 제거력 차이에서는 유의한 차이를 보이지 않았다(P > .05). 결론: 이 실험의 결과에 한하여 타이타늄 구성요소를 사용한 지르코니아 지대주의 동적하중 후 지대주 나사 제거력의 변화는 타이타늄 지대주와 통계학적으로 유의한 차이를 보이지 않았다.

• Structural Engineering and Mechanics
• /
• 제26권3호
• /
• pp.343-361
• /
• 2007

This article presents a numerical tool for dimensioning two-threaded fasteners connecting prismatic parts subjected to fatigue tension loads that are coplanar with the screw axis. A simplified numerical model is developed from unidirectional finite elements, modeling the connected parts and screws with bent elements and the elastic contact layer between the parts with springs. An algorithm updating the contact stiffness matrix, calculating forces and displacements at each node of the structure and thus normal stresses in the screws in both static and fatigue is further developed using C language. An experimental study is also conducted in parallel with the numerical approach to validate the developed model assumptions, the numerical model and the 3D finite element results. Since stiffness values for the compressive zones in the parts are analytically difficult to determine, a statistical software method is used, from which a tuning factor is derived for identifying these stiffness values. The method is also applied to set out the influence of each parameter on the fatigue behaviour of each screw. Finally, the developed model will be used to establish a new, sophisticated, fast and accurate tool for dimensioning bolted mechanical structures.

• The Journal of Korean Physical Therapy
• /
• 제31권6호
• /
• pp.333-338
• /
• 2019

Purpose: Although previous studies on the screw-home movement (SHM) for autopsy specimen and walking of living persons conducted, the possibility of acquiring SHM based on inertial measurement units received little attention. This study aimed to investigate the possibility of measuring SHM for the non-weighted bearing using a micro-electro-mechanical system-based wearable motion capture system (MEMSS). Methods: MEMSS and camera-based motion analysis systems were used to obtain kinematic data of the knee joint. The knee joint moved from the flexion position to a fully extended position and then back to the start point. The coefficient of multiple correlation and the difference in the range of motion were used to assess the waveform similarity in the movement measured by two measurement systems. Results: The waveform similarity in the sagittal plane was excellent and the in the transverse plane was good. Significant differences were found in the sagittal plane between the two systems (p<0.05). However, there was no significant difference in the transverse plane between the two systems (p>0.05). Conclusion: The SHM during the passive motion without muscle contraction in the non-weighted bearing appeared in the entire range. We thought that the MEMSS could be easily applied to the acquisition of biomechanical data on the knee related to physical therapy.

• 대한치과교정학회지
• /
• 제49권3호
• /
• pp.188-193
• /
• 2019

Objective: The aim of this finite element study was to clarify the mechanics of tooth movement in palatal en-masse retraction of segmented maxillary anterior teeth by using anchor screws and lever arms. Methods: A three-dimensional finite element method was used to simulate overall orthodontic tooth movements. The line of action of the force was varied by changing both the lever arm height and anchor screw position. Results: When the line of action of the force passed through the center of resistance (CR), the anterior teeth showed translation. However, when the line of action was not perpendicular to the long axis of the anterior teeth, the anterior teeth moved bodily with an unexpected intrusion even though the force was transmitted horizontally. To move the anterior teeth bodily without intrusion and extrusion, a downward force passing through the CR was necessary. When the line of action of the force passed apical to the CR, the anterior teeth tipped counterclockwise during retraction, and when the line of action of the force passed coronal to the CR, the anterior teeth tipped clockwise during retraction. Conclusions: The movement pattern of the anterior teeth changed depending on the combination of lever arm height and anchor screw position. However, this pattern may be unpredictable in clinical settings because the movement direction is not always equal to the force direction.

• 대한치과보철학회지
• /
• 제41권4호
• /
• pp.393-404
• /
• 2003

Statement of problem. Higher incidence of prosthetic complications such as screw loosening, screw fracture has been reported for posterior single tooth implant. So, there is ongoing research regarding stability of implant-abutment interface. One of those research is increasing the implant diameter and prosthetic table width to improve joint stability. In another part of this research, internal conical type implant-abutment interface was developed and reported joint strength is higher than traditional external hex interface. Purpose. The purpose of this study is to compare stress distribution in single molar implant between external hex butt joint implant and internal conical joint implant when increasing the implant diameter and prosthetic table width : 4mm diameter, 5mm diameter, 5mm diameter/6mm prosthetic table width. Material and method. Non-linear finite element models were created and the 3-dimensional finite element analysis was performed to see the distribution of stress when 300N static loading was applied to model at $0^{\circ},\;15^{\circ},\;30^{\circ}$ off-axis angle. Results. The following results were obtained : 1. Internal conical joint showed lower tensile stress value than that of external hex butt joint. 2. When off-axis loading was applied, internal conical joint showed more effective stress distribution than external hex butt joint. 3. External hex butt joint showed lower tensile stress value when the implant diameter was increased. 4. Internal conical joint showed lower tensile stress value than external hex butt joint when the implant diameter was increased. 5. Both of these joint mechanism showed lower tensile stress value when the prosthetic table width was increased. Conclusion. Internal conical joint showed more effective stress distribution than external hex joint. Increasing implant diameter showed more effective stress distribution than increasing prosthetic table width.