• 드라이브 ㆍ 컨트롤
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• 제19권2호
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• pp.17-26
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• 2022

Recently, automatic transmissions caused a good improvement in the shift quality of a forklift. An advanced shift control algorithm, which was based on TCU firmware, was applied with embedded control technology and microcontrollers. In the clutch-to-clutch shifting, one friction element is released and the other friction element is activated. During this process, if the release and application timings are not synchronized, an overrun or tie-up occurs and ultimately leads to a shift shock. The TCU, which measures only the speed of the forklift, inevitably applies the open-loop shift control. In this situation, the speed ratio does not change during the clutch fill. The torque phase occurs until the clutch is disengaged. In this study, an offline shift logic of the learning control was proposed. It induced a synchronous shift when the learning control progressed. During this process, the reference current trajectory of the release clutch was corrected and applied to the next upshift. We considered the results of the overrun/tie-up characteristics of the upshift performed immediately before. The vehicle test proved that the deviation in shift quality, which was caused by the difference in the mechanical characteristics of the clutch, could be improved by the learning control.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.263-266
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• 2001

The performance of the powertrain can be analyzed using dynamic models including transient characteristics, and the equations of motion can also be derived from the dynamic models of the powertrain. In this study, the shift transient characteristics of the vehicle equipped with Ravigneaux type planetary gears automatic transmission has been investigated.

• 한국자동차공학회논문집
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• 제6권2호
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• pp.54-66
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• 1998

In a passenger car automatic transmission, the gear ratio is determined by the combination of clutches and brakes, and each element of th planetary gear set is rotated or held stationary by the action of them. In this study, to investigate the shift characteristics of automatic transmission, the equations of motion are derived from the dynamic model of Ravigneaux type planetary gear set and solved analytically. The shift characteristics of each element of planetary gera set during gear ratio change are investigated by considering the torques and velocities of input, reaction and output elements.

• 대한기계학회논문집A
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• 제21권11호
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• pp.1943-1949
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• 1997

In this paper, the analysis of the shift transient characteristics for the Ravigneaux type automatic transmission has been carried out using dynamic models of the automatic trnasmission. It is necessary to understand the overall system including multi-plate clutch, band brake, one way clutch, and planetary gears. The equations of motion are derived from the dynamic models of the automatic transmission. The GUI computer simulation program has been developed to analyze the shift transient characteristics of the vehicle equipped with the Ravigneaux type automatic transmission.

• 대한한방부인과학회지
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• 제19권3호
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• pp.231-245
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• 2006

Purpose : To investigate and compare the characteristics of menstruation in the shift workers and the day workers, and present guidelines for health promotion of the shift-working women. Methods : Questionnaires including general health condition and QSCC II were distributed to shift-working women and day-working women in one university hospital in Gyeonggi-do and 36 questionnaires of shift-working women and 33 of day-working women were analyzed. Results : Day workers were about 5 years older than shift workers on average. There was more irregularity of menstrual cycle and period in day-working group but it is thought to incorrect because of the age problem. There were more women who have dysmenorrhea in day-working group, but the proportion of dysmenorrhea which continues more than 72 hours -which is very suggestive of secondary dysmenorrhea- was higher in shift-working group. Average VAS of dysmenorrhea was nearly the same in two groups. The life of shift-working group was lesser satisfactory than that of day-working group. There were more sleep disturbances in the shift-working group. Sasang constitution was analyzed in both group using QSCC II, and Taeumin were more in shift-working group. Conclusion : As the number of shift-working women increases, needs for oriental medical treatments would increase because it is more natural and lesser invasive managements which women are very interested in. So it is thought to be necessary to understand health problems of shift-working women, and prepare guidelines for managements and treatments to promote the health of shift-working women.

• 한국산업보건학회지
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• 제33권2호
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• pp.206-214
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• 2023

Objectives: To determine the effect of the various type and number of shift work on sociopsychological stress in the university hospital nurses in Seoul, South Korea. Methods: Data was collected through a self-administered questionnaire that included general characteristics, the type and number of shift work in the past 4 weeks and the an sociopsychological stress based on PWI-SF. Logistic regression analysis was conducted to analyze the effect of shift work by types on sociopsychological stress of university hospital nurses using SAS 9.4 and it adjusted general characteristics by the additional models. Results: When the number of night shift work 3 or 4 compared to 0, sociopsychological stress was significantly high(OR=2.16, 95% CI=1.29-3.65). When 5 or more, it was higher(OR=2.39, 95% CI=1.55-3.72). Two continuous night shift work compared to 0 increased sociopsychological stress(OR=2.37, 95% CI=1.49-3.81) and 3 or more even more(OR=2.70, 95% CI=1.72-4.27). If the shift work type changes 14 or 15 times compare to below 11, sociopsychological stress is increased and even higher when 15 or more times but it's not significant after adjusting for covariates. Conclusions: It suggests that workplace with nurse expose to shift work should be on lookout for more than three night shift work, more than two continuous night shift work and more than 14 shift work change which can lead to burnout, absenteeism, depression and decreased productivity.

• Safety and Health at Work
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• 제15권1호
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• pp.102-109
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• 2024

Background: In today's modern world, longer working hours, shift work, and working at night have become major causes of the disruption of our natural circadian rhythms. This study aimed to investigate the effects of the type of shift work (rotating vs. fixed day), duty period (on-duty vs. off-duty), and working period within each shift (nighttime vs. daytime) on the circadian rhythm characteristics of nurses who provide direct patient care. Methods: This cross-sectional study used a purposive sampling method. Cosinor analysis was applied to analyze the actigraphy data of nurses providing direct patient care for seven consecutive days. The linear mixed effects model was then used to determine any variances between shift type, duty period, and working period within each shift for the nurses. Results: The mesor value did not differ according to nurses' shift type, duty period, and working period within each shift. The amplitude was statistically higher in on-duty nurses and in daytime working hours. The acrophase was significantly delayed in nighttime working hours. As well as nurses in rotating shift had experience. Conclusion: Our findings revealed that the peak activity of nurses occurs significantly later at night while working and nurses working during nighttime hours may have a weaker or less distinct circadian rhythm. Thus, this study suggests that limits be placed on the number of rotating nighttime shifts for nurses.

• 한국산업보건학회지
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• 제29권4호
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• pp.550-561
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• 2019

Objectives: The purpose of this study is to provide basic data for the improvement of the working environment for health prevention and related countermeasures for shift workers. This study was conducted based on the Fifth Korean Working Conditions Survey (KWCS), which analyzed the health effects of shift work forces and compared them with preceding studies. Methods: By analyzing secondary rates using raw data from the 5th KWCS, 4,870 (9.7%) of the 50,184 total study subjects were divided into shift work and 45,314 (90.3%) non-shift work groups based on the response to shift status. Variables that could affect work health issues were identified and corrected. A cross-analysis was conducted to examine demographic characteristics (gender, age, and education level) of the workers and occupation characteristics (monthly net earnings, employment type, occupation, working period up to now, workplace scale, type of work system, and weekly working hours). In order to find the work health issue ratio between the shift and non-shift work groups, logistic regression was analyzed and the association with health problems according to shift type by gender was looked at through cross-analysis. Results: According to the surveys conducted from the 1st KWCS (2006) to the 5th KWCS (2017), the proportion of shift workers continued to increase. Also, muscular pains in the lower limbs (hips, legs, knees, feet, etc.) (OR=1.135, 95%CI 1.031-1.251), headaches, eyestrain (OR=1.580, 95% CI 1.428-1.748), anxiety (OR=1.715, 95% CI 1.402-2.099), difficulty falling asleep (OR=1.391), and other problems (OR=7.392) were reported. In addition, back pain, muscular pains in shoulders, neck and/or upper limbs, muscular pains in lower limbs (hips, legs, knees, feet, etc.), headaches, eyestrain, depression, anxiety, overall fatigue resulted in significant results for both male and female shift workers. Depression and anxiety were higher in female shift/circulation compared to males. Conclusions: The social nets for the health and safety of shift workers should be explored in a variety of ways, including management and supervision of shift sites, attempts to reorganize and improve the shift system, development of workers' health recovery programs, promotion, systematic treatment, and compensation systems.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.639-646
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• 2002

In this paper, thrust equations for a rubber belt CVT are derived by considering the geometry and mechanism of the mechanical actuators. In order to solve the thrust equations, an algorithm to calculate the speed ratio is suggested for the given driver speed and load torque based on the actuator characteristic equations and existing formula for the belt thrust forces. Experiments are performed to investigate the driver speed-load torque-speed ratio characteristics at a steady state. The speed and torque efficiencies are measured and used to modify the actuator equations. It is found that the modified equations well predict the steady state characteristics. In addition, the shift dynamic model for a rubber belt CVT is derived experimentally. Simulation results of the CVT shift dynamics are in good accordance with the experiments and it is noted that different coefficients are required to describe the CVT shift dynamics for the upshift and the downshift.

• 대한기계학회논문집A
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• 제22권3호
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• pp.654-662
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• 1998

Shift quality of an automatic transmission in a vehicle is mainly affected by transient pressures in the hydraulic system during shifting. In this study, dynamic modelings of the hydraulic system and the power train of an automatic transmission are made systematically by a bond-graph method. The dynamic characteristics of the line pressures and clutch/brake pressures during shiftings are investigated by simulations and verified by experiments. The effects of clutch/brake pressures on the shift torque are also investigated through driving simulation.