• 한국기계가공학회지
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• 제14권2호
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• pp.67-74
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• 2015

In this study, analysis and experiments were carried out on temperature distributions and thermal deformations in a dry vacuum pump with vertical screws for safe operation. When a vacuum pump is working, it is necessary to get rid of the heat generated by the friction of bearings and the compression of air to prevent the vacuum pump from being damaged by interference between two screws and housing through thermal deformation. Additional cooling was proposed by using oil flow through the inner channel of the rotating axis for lower temperature control of the vacuum pump. Analysis and experimental results were compared in terms of temperature distribution and thermal deformation of the vacuum pump, and two sets of results matched reasonably well. These results for a dry vacuum pump with vertical screws can be used in similar model development and can minimize errors in design and manufacture by providing reasonably accurate prediction in advance.

• The Journal of Advanced Prosthodontics
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• 제9권2호
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• pp.99-103
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• 2017

PURPOSE. The purpose of this study was to achieve more retention and stability and to delay or prevent screw loosening. MATERIALS AND METHODS. Twenty implants (Implantium 3.4 mm, Dentium, Seoul, Korea) were divided into 2 groups (n = 20). In the first group, an adhesive material was applied around the screw of the abutments (test group). In the second group, the screws are soaked in saliva (control group). All the screws were torqued under 30 N/cm, Then, the samples were gone through a cyclic fatigue loading process. After cyclic loading, we detorqued screws and calculated detorque value. RESULTS. In comparison with the control group, all the implant screws in the test group were smeared with the adhesive material, showing significant higher detorque value. CONCLUSION. There are significantly higher detorque values in the group with adhesive. It is recommended to make biocompatible adhesive to reduce screw loosening.

• 대한족부족관절학회지
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• 제10권1호
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• pp.66-70
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• 2006

Purpose: To analyze the clinical and radiological outcome of subtalar arthrodesis using cannulated screws and morselized bone graft. Materials and Methods: Twenty one patients with follow-up of more than 1 year after subtalar arthrodesis were included in this study. Mean age was 40.8 years, and mean follow-up duration was 38 months. Underlying diseases were 19 cases of posttraumatic arthritis (18 calcaneal fractures and 1 talar fracture) and 2 cases of tarsal coalition. Clinically AOFAS ankle-hindfoot score, operation time, complication and satisfaction of patients were analyzed. Radiologically time to union, arthritis of surrounding joints, preoperative and postoperative talar declination angle were analyzed. Results: AOFAS ankle-hindfoot score was improved from preoperative 33 points to postooperative 79 points. Eighteen patients (86%) were satisfied with the results. Mean operation time was 91 minutes. All cases were fixed with 1-2 cannulated screws and morselized bone graft. Mean time to radiologic union was 12.1 weeks. There was 1 case of delayed union. There was no significant perioperative changes in talar declination angles. Conclusion: Subtalar arthrodesis using cannulated screws and morselized bone graft seems to be relatively simple and effective treatment method for subtalar arthritis.

• 항공우주기술
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• 제9권2호
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• pp.129-137
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• 2010

본 논문은 위성용으로 주로 사용되는 소켓헤드 캡 스크류에 대한 국산화 개발 절차를 소개하는 내용이다. 국산화 개발을 위한 소켓헤드 캡 스크류의 제조공정은 MIL-B-7838, ECSS-Q-70-46A, KS W 8168과 같은 항공우주 관련 규격 요구조건을 만족하기 위해서 헤드 포밍 공정, 열처리공정, 전조 공정 및 후처리 공정으로 구성하였다. 그리고 국산화 스크루에 대한 품질 검증을 위하여 여러 가지 종류의 품질검증시험을 성공적으로 완료하였다. 또한, 비국산화 해외 도입 스크류와의 비교 품질시험을 통하여, 국산화 소켓 헤드 캡 스크류 품질이 항공우주용으로 적용 가능한 우수한 품질 성능을 확인 하였다.

• 한국정밀공학회지
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• 제26권8호
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• pp.79-88
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• 2009

This paper presents the analytical stiffness analysis method for a low-DOF planar parallel manipulator. An n-DOF (n<3) planar parallel manipulator to which 1- or 2-DOF serial mechanism is connected in series may be used as a positioning device in planar tasks requring high payload and high speed. Differently from a 3-DOF planar parallel manipulator, an n-DOF planar parallel counterpart may be subject to constraint forces as well as actuation forces. Using the theory of reciprocal screws, the planar stiffness is modeled such that the moving platform is supported by three springs related to the reciprocal screws of actuations (n) and constraints (3-n). Then, the spring constants can be precisely determined by modeling the compliances of joints and links in serial chains. Finally, the stiffness of two kinds of 2-DOF planar parallel manipulators with simple and complex springs is analyzed. In order to show the effectiveness of the suggested method, the results of analytical stiffness analysis are compared to those of numerical stiffness analysis by using ADAMS.

• 대한족부족관절학회지
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• 제12권2호
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• pp.180-184
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• 2008

Purpose: To evaluate the result of percutaneous fixation with cannulated screws and Ilizarov external fixator in triplane fracture of the distal tibial epiphysis in children. Materials and Methods: Between May 2004 and December 2007, 14 cases with triplane fractures were treated by percutaneous fixation with cannulated screws and Ilizarov external fixator after underwent CT imaging to assess the fracture pattern, articular disruption and to plan further management. Mean age and follow-up period were 14.1 years old and 15 months respectively. Results: There were satisfactory results in all 14 cases that had excellent reduction and stable fixation. All cases regained full range of movement within 6 weeks. Conclusion: We obtained satisfactory result after percutaneous fixation with cannulated screws and Ilizarov external fixator in triplane fractures of the distal tibial epiphysis in children.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제37권
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• pp.11.1-11.5
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• 2015

Rapid palatal expansion(RPE) with the tooth-born appliance is not sufficient to apply to the patients with periodontal problem or insufficient tooth anchorage, and it leads to tipping of the anchorage teeth and increasing teeth mobility and root resorption. To avoid these disadvantages, we present the case using palatal screws and custommade palatal expander. A 23-year-old patient underwent surgically assisted rapid maxillary expansion with the Hyrax expansion using 4 tent screws. The study models were used to measure the pre-/-post surgical width of the anterior and posterior dental arches with a digital sliding caliper. In the result, the custom-made palatal expander with 4 tent screws is suitable for delivering a force to the mid-palatal suture expansion. And it is low cost, small sized and simply applied. The results indicated that maxillary expansion with the custom-made palatal anchorage device is predictable and stable technique without significant complications in patients.

• Journal of Korean Neurosurgical Society
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• 제56권1호
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• pp.16-20
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• 2014

Objective : Two-dimensional fluoroscopy-based computerized navigation for the placement of pedicle screws offers the advantage of using stored patient-specific imaging data in providing real-time guidance during screw placement. The study aimed to describe the accuracy and reliability of a fluoroscopy-based navigation system for pedicle screw insertion. Methods : A total of 477 pedicle screws were inserted in the lower back of 96 consecutive patients between October 2007 and June 2012 using fluoroscopy-based computer-assisted surgery. The accuracy of screw placement was evaluated using a sophisticated computed tomography protocol. Results : Of the 477 pedicle screws, 461 (96.7%) were judged to be inserted correctly. Frank screw misplacement [16 screws (3.3%)] was observed in 15 patients. Of these, 8 were classified as minimally misplaced (${\leq}2mm$); 3, as moderately misplaced (2.1-4 mm); and 5, as severely misplaced (>4 mm). No complications, including nerve root injury, cerebrospinal fluid leakage, or internal organ injury, were observed in any of the patients. Conclusion : The accuracy of pedicle screw placement using a fluoroscopy-based computer navigation system was observed to be superior to that obtained with conventional techniques.

• 대한기계학회논문집A
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• 제20권1호
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• pp.154-162
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• 1996

Ball screws are commonly used in linear motion feeding systems of various machine tools and automated systems. They are known to have relatively little backlash, high precision and efficiency compared to ordinary lead screws. Furthermore, the effectiveness of ball screw has made it the preferred choice of many newly developed high speed precision feeding units. The motivation of this work is to establish the groove edsigh basis of ball screws for the reduction of contact fatigue failure. In most instances, fatigue failure between ball and shaft groove is due to excessive contact pressure. Especially, the excessive load is causative of plastic flow below the contact surface, which can contribute to surface failure. But, in spite of small load, if groove conformity rate is large, contact pressure is increased and internal shear stress reach the yield value of the material. In such a point, the authors deal with design procedure for deciding the permissible conformity rate of a ball screw groove with the computational evaluation of contact pressure and maximum shear stress.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제32권1호
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• pp.60-64
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• 2006

Backgrounds: Though they are considered as reliable devices, titanium plates and screws have limitations due to some potential problems. To overcome these problems, researches on bioabsorbable materials for internal fixation have been continuing. Recently, there are many clinical trials to apply biodegradable internal fixation devices in oral and maxillofacial surgery. The purpose of this study was to evaluate the clinical results of application of bioabsorbable plates and screws in orthognathic surgery. Methods: Fifty-four patients with dentofacial deformity (17 male patients and 37 female patients) were selected in this study. The patients were treated by internal fixation using bioabsorbable plates and 2.4-mm, 2.0-mm pretapped screws (Biosorb FX, Bionix Implants, Inc., Finland). The patients were evaluated for complications during the follow-up period. Results: Five patients (9.3%) experienced complications. All complications in these cases were infection. No other complications related with physical or mechanical properties of bioabsorbable plates were found such as malunion or nonunion, fractures of plates and loosening of screws. All complications were minor and adequately managed with drainage and supportive care with antibiotics coverage. Conclusions: From the results, the use of these fixation systems in orthognathic surgery will provide a promising alternative titanium fixation in appropriate cases.