• 제어로봇시스템학회논문지
• /
• 제15권7호
• /
• pp.675-682
• /
• 2009

Instead of direct driving like BLDC, the induction principle is adopted as a driving one for planar stage. The stage composed of four linear induction motors put in square type is activated by two-axial forces; low-frequency attractive force and thrust force of the linear induction motors. Here, the modified vector control whose new inputs are q-axis current and dc current biased to three phase current instead of d-axis current or flux current is applied extensively to overall motion of the stage. For the developed system, the precision step test and the constant velocity test are tried to guarantee its feasibility for TFT-LCD pattern inspection. However, to exclude a discontinuity due to phase shift and minimize a force ripple synchronized with the command frequency, the initial system is revised to the antagonistic structure over the full degree of freedom. Concretely describing, the porous air bearings guide an air-gapping of the stage up and down and a pair of liner induction motors instead of single motor are activated in the opposite direction each other. The performances of the above systems are compared from trapezoid tracking test and sinusoidal test.

• 대한인간공학회지
• /
• 제8권2호
• /
• pp.3-18
• /
• 1989

Two sets of isometric pushing and pulling experiments were performed by two male and two female susbjects. One set of experiments involoved isometric hand pushing and pulling in a standing erect posture, in which the thigh and pelvic regions of the subjects were braced to achieve the greatest strength. Another set of experiments involved isometric hand pushing and pulling in a free posture, in which the subjects elected their preferred postures to attain the largest strength at each of thred handle heights (low-66cm ; mid-109cm ; and high-152cm). It was shown from isometric pushing and pulling experiments in a standing erect poture that the rectus abdominis and the erector spinae muscles were acting as an antagonistic pair with respect to the L5/S1 intervertebral joint, and that the integrated EMG and the muscle force were linearly related. However, the relationships between the integrated EMG and the muscle force during isometric pushing and pulling in a free posture were not well-correlated. It is proposed that the integrated EMG results should be carefully interpreted for tasks of pushing and pulling at various handle heights.

• The Journal of Advanced Prosthodontics
• /
• 제8권1호
• /
• pp.43-52
• /
• 2016

PURPOSE. This study was conducted to evaluate the effects of full-coverage all-ceramic zirconia, lithium disilicate glass-ceramic, leucite glass-ceramic, or stainless steel crowns on antagonistic primary tooth wear. MATERIALS AND METHODS. There were four study groups: the stainless steel (Steel) group, the leucite glass-ceramic (Leucite) group, the lithium disilicate glass-ceramic (Lithium) group, and the monolithic zirconia (Zirconia) group. Ten flat crown specimens were prepared per group; opposing teeth were prepared using primary canines. A wear test was conducted over 100,000 chewing cycles using a dual-axis chewing simulator and a 50 N masticating force, and wear losses of antagonistic teeth and restorative materials were calculated using a three-dimensional profiling system and an electronic scale, respectively. Statistical significance was determined using One-way ANOVA and Tukey's test (P<.05). RESULTS. The Leucite group ($2.670{\pm}1.471mm^3$) showed the greatest amount of antagonist tooth wear, followed by in decreasing order by the Lithium ($2.042{\pm}0.696mm^3$), Zirconia ($1.426{\pm}0.477mm^3$), and Steel groups ($0.397{\pm}0.192mm^3$). Mean volume losses in the Leucite and Lithium groups were significantly greater than in the Steel group (P<.05). No significant difference was observed between mean volume losses in the Zirconia and Steel groups (P>.05). CONCLUSION. Leucite glass-ceramic and lithium disilicate glass-ceramic cause more primary tooth wear than stainless steel or zirconia.

• 한국정밀공학회지
• /
• 제28권1호
• /
• pp.115-122
• /
• 2011

Recently, we have proposed a hypothesis that spinal structures have a stress sensor driving feedback mechanism, In the human spine, spinal structure could react to modify muscular action in such a way so as to equalize stress at the disc, therefore reduce the risk of injury, In this analysis, abdominal muscle and abdominal pressure, which were not included in the previous study, were added to identify those effects in spine stability during upright stance posture for the case where the intervertebral disc plays the role of mechanoreceptor, The musculoskeletal FE model was consisted with detailed whole lumbar spine, pelvis, sacrum, coccyx and simplified trunk model. Muscle architecture with 46 local muscles containing paraspinal muscle and 6 rectus abdominal muscles were assigned according to the acting directions. The magnitude of 4kPa was considered for abdominal pressure. Minimization of the nucleus pressure deviation and annulus fiber average tension stress deviation was chosen for cost function. Developed model provide nice coincidence with in-vivo measurement (nucleus pressure). Analysis was conducted according to existence of co-activation of abdominal muscle and abdominal pressure. Antagonistic activity of abdominal muscle produced stability of spinal column with relatively small amount of total muscle force. In contrast to the abdominal muscle, effect of abdominal pressure was not clear that was partly depending on the assumption of constant abdominal pressure.

• 한국산업보건학회지
• /
• 제15권1호
• /
• pp.61-70
• /
• 2005

This study investigated the spinal loads(L5/S1 disc compression and shear forces) predicted from four biomechanical models: one EMG model and three optimization models. Three objective functions used in the optimization models were to miminize 1) the cubed muscle forces : MF3, 2) the cubed muscle stress : MS3, 3) maximum muscle intensity : MI. Twelve healthy male subjects participated in the isometric voluntary exertion tests to six directions : flexion/extension, left/right lateral bending, clockwise/ counterclockwise twist. EMG signals were measured from ten trunk muscles and spinal loads were assessed at 10, 20, 30, 40, 50, 60, 70, 80, 90%MVE(maximum voluntary exertion) in each direction. Three optimization models predicted lower L5/S1 disc compression forces than the EMG model, on average, by 31%(MF3), 27%(MS3), 8%(MI). Especially, in twist and extension, the differences were relatively large. Anterior-posterior shear forces predicted from optimization models were lower, on average, by 27%(MF3), 21%(MS3), 9%(MI) than by the EMG model, especially in flexion(MF3 : 45%, MS3 : 40%, MI : 35%). Lateral shear forces were predicted far less than anterior-posterior shear forces(total average = 124 N), and the optimization models predicted larger values than the EMG model on average. These results indicated that the optimization models could underestimate compression forces during twisting and extension, and anterior-posterior shear forces during flexion. Thus, future research should address the antagonistic coactivation, one major reason of the difference between optimization models and the EMG model, in the optimization models.

• 로봇학회논문지
• /
• 제12권4호
• /
• pp.419-424
• /
• 2017

Twisted string actuators (TSAs) are tendon-driven actuators that provide high transmission ratios. Twisting a string reduces the length of the string and generates a linear motion of the actuators. In particular, TSAs have characteristic properties (compliance) that are advantageous for operations that need to interact with the external environment. This compliance has the advantage of being robust to disturbance in force control, but it is disadvantageous for precise control because the modeling is inaccurate. In fact, many previous studies have covered the TSA model, but the model is still inadequate to be applied to actual robot control. In this paper, we introduce a modified variable radius model of TASs and experimentally demonstrate that the modified variable radius model is correct compared to the conventional variable radius string model. In addition, the elastic characteristics of the TSAs are discussed along with the experimental results.

• 대한기계학회논문집A
• /
• 제41권8호
• /
• pp.771-782
• /
• 2017

본 논문은 노약자들의 발목근력보조를 위한 착용형 로봇에 대해서 서술하였다. 기존 착용형 로봇들은 보행 시 필요한 근력을 보조하기 위해 대부분 모터와 감속기를 사용하였다. 하지만 모터와 감속기의 조합은 무게가 무거울 뿐만 아니라 감속기 치차의 마찰때문에 실제 사람의 근육과 달리 강성과 토크를 동시에 제어하기 어려운 한계가 있다. 따라서 본 연구에서는 모터/감속기 조합보다 가볍고 안전하며 근력을 보조하는 힘을 충분히 발휘할 수 있는 Mckibben 공압 근육을 사용하였다. 발목의 피칭 모션에 이용되는 종아리 가자미근 및 앞정강근의 힘을 한 쌍의 공압 근육을 사용한 상극구동으로 보조하였으며, 상극구동제어를 위해 상극구동 모델 파라미터들을 실험적으로 도출하였다. 사용자의 보행의지를 판단하고자 발바닥에 부착된 압력변위센서로 압력과 압력중심위치를 측정하여 발바닥의 하중과 발목토크를 계산하였고, 이를 기반으로 공압 근육 관절의 강성과 토크를 동시에 제어하였다. 최종적으로, 트레드밀에서 근전도 신호를 측정하여 발목근력보조로봇의 성능을 실험적으로 입증하였다.

• 한국운동역학회지
• /
• 제25권1호
• /
• pp.49-56
• /
• 2015

Objectives : The purpose of this study was to present quantitative data and basic references to decrease the accident risk of soccer instructors. Methods : To obtain data, we conducted an investigation on how H/Q ratio affects the dynamic stability of the lower extremity at the time of drop landing. The study targeted 13 soccer players from C University who have not had any injuries or wounds in the lower extremity joints and in any other parts of their bodies over the last 6 months. By using CMIS (USA), the players were divided into two groups according to H/Q ratios higher and lower than 69%, respectively. The subjects in each group were instructed to perform a drop landing. Results : The H/Q ratio did not affect the maximal flexion angle of the knee joints at the time of drop landing. In addition the dominant group with a relatively high H/Q ratio was observed to have increased time to reduce shock and to efficiently absorb the ground reaction force during drop landing. Also, the dominant group with a relatively high H/Q ratio utilized the strong performances of the antagonistic muscles around the hamstrings and the controlled rotatory powers of the thighs that were applied to the tibias supported by the ground. Finally, H/Q ratio, load factors, and mean and maximum EMG were significantly negatively related, whereas GRFx showed a positive relationship. In fact, these factors all affected the impact of the load from the H/Q ratio to the knee joints. Conclusion : From these findings it can be concluded that unbalanced H/Q ratio can be considered as a predictor of knee joint injury at the time of drop landing.

• The Journal of Advanced Prosthodontics
• /
• 제10권4호
• /
• pp.300-307
• /
• 2018

PURPOSE. To investigate the fatigue and fracture resistance of computer-aided design and computer-aided manufacturing (CAD/CAM) ceramic molar crowns on dental implants and human teeth. MATERIALS AND METHODS. Molar crowns (n=48; n=8/group) were fabricated of a lithium-disilicate-strengthened lithium aluminosilicate glass ceramic (N). Surfaces were polished (P) or glazed (G). Crowns were tested on human teeth (T) and implant-abutment analogues (I) simulating a chairside (C, crown bonded to abutment) or labside (L, screw channel) procedure for implant groups. Polished/glazed lithium disilicate (E) crowns (n=16) served as reference. Combined thermal cycling and mechanical loading (TC: $3000{\times}5^{\circ}C/3000{\times}55^{\circ}C$; ML: $1.2{\time}10^6$ cycles, 50 N) with antagonistic human molars (groups T) and steatite spheres (groups I) was performed under a chewing simulator. TCML crowns were then analyzed for failures (optical microscopy, SEM) and fracture force was determined. Data were statistically analyzed (Kolmogorow-Smirnov, one-way-ANOVA, post-hoc Bonferroni, ${\alpha}=.05$). RESULTS. All crowns survived TCML and showed small traces of wear. In human teeth groups, fracture forces of N crowns varied between $1214{\pm}293N$ (NPT) and $1324{\pm}498N$ (NGT), differing significantly ($P{\leq}.003$) from the polished reference EPT ($2044{\pm}302N$). Fracture forces in implant groups varied between $934{\pm}154N$ (NGI_L) and $1782{\pm}153N$ (NPI_C), providing higher values for the respective chairside crowns. Differences between polishing and glazing were not significant ($P{\geq}.066$) between crowns of identical materials and abutment support. CONCLUSION. Fracture resistance was influenced by the ceramic material, and partly by the tooth or implant situation and the clinical procedure (chairside/labside). Type of surface finish (polishing/glazing) had no significant influence. Clinical survival of the new glass ceramic may be comparable to lithium disilicate.

• 대한소아치과학회지
• /
• 제37권2호
• /
• pp.226-232
• /
• 2010

영구치의 매복은 다양한 빈도로 보고되며, 인구 집단의 약 5.6~18.8%에서 발생한다. 그 중에서 하악 제2대구치의 맹출장애 빈도는 약 0.06%, 하악 제1대구치는 약 0.01%로 매우 드물게 나타난다. 영구 대구치는 기능적으로 저작을 위한 중요한 교합적 지지를 제공하며 안면의 조화로운 성장발육에 중요한 역할을 담당한다. 영구 대구치의 매복시 발생되는 문제점으로는 구치부의 개방교합과 대합치의 정출, 인접치의 치근흡수와 기울어짐, 낭종의 형성, 심할 경우 하안면고경의 감소 등 여러 가지 문제점이 유발될 수 있다. 매복치의 치료 방법으로는 우선적으로 외과적노출술을 생각해 볼 수 있으며, 외과적노출술 후에 추가적인 인위적 아탈구로 자발적맹출을 기대해 볼 수도 있다. 자발적맹출이 관찰되지 않으면 교정적 강제 견인이나 외과적재위치술을 고려해 볼 수 있으며, 최악의 경우에는 발치 후 보철치료를 준비해야 할 것이다. 맹출장애를 보이는 치아의 조기진단과 치료는 중요한 의미를 갖는데, 늦은 시기에 발견될 경우 자발적 맹출력이 감소되어 치료의 성공률도 감소하고, 치료기간도 증가하며 임상적으로 다양한 합병증을 야기하기 때문이다. 따라서, 하악 제1대구치의 맹출장애를 조기에 발견할 경우 우선적으로 맹출유도를 고려해 볼 필요가 있다. 다음 두 증례는 매복된 하악 제1대구치에 대하여 외과적 노출술을 시행 후 자발적 맹출을 기대하였으나 상반된 결과를 얻었기에 보고하는 바이다.