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휠체어용 리클라이너의 중력보상 메커니즘 최적화 설계 기법
김세영,김광준,박철훈,박찬훈,허필원,구광민 대한기계학회 2024 大韓機械學會論文集A Vol.48 No.1
본 연구에서는 휠체어용 리클라이너의 구동 힘을 최소화할 수 있도록 가스 스프링의 설치 위치를 조정하여 중력보상 메커니즘을 최적화하는 방법을 제안하였다. 리클라이너는 좌판 양측에 있는 평행사변형 링크 구조를 통해 등판과 발판이 서로 동기화되어 같은 방향과 각도로 움직이도록 구현되었으며, 해당 평행사변형 링크 내부에 힘 방향이 서로 교차되도록 설치된 가스 스프링과 리니어 구동기의 조합 힘을 통해 탑승자 정하중이 보상되도록 설계되었다. 가스 스프링의 최적 설치 위치는 리클라이닝 모션 시 수동기계 요소에 의한 중력보상을 최대화하고 동시에 능동 구동기의 평균 발생힘을 최소화시키는 목적 함수와 해당 기계요소들의 스펙과 설치조건을 각각 구속 및 경계 조건으로 갖는 비선형 최적화 알고리즘을 도입해 계산하였다. 이때, 전역 최적해를 얻기 위해 다양한 초기값을 사용하였으며, 결과적으로 가스 스프링의 수동 힘을 최대한 활용하면서 구동기가 낼 수 있는 최대 힘을 넘지 않는 조건을 만족하도록 중력보상이 이루어졌다. 해당 최적화 과정은 평행사변형 링크 구조를 포함하는 다양한 자세변환 시스템에서 활용될 수 있을 것으로 기대한다. In this study, gravity compensation of a wheelchair recliner was optimized to minimize the driving force of a recliner by adjusting the installation position of gas springs. The combined force of the gas spring and linear actuator compensate for the static load of occupant, where the force directions of the active and passive power sources cross each other inside the parallelogram links of the recliner. The optimal installation of the gas springs were determined via a non-linear optimization algorithm. The objective function of the algorithm involves simultaneous maximization of gravitational torque compensation by the gas springs and minimization of the average generated force of the linear actuators. The results showed that gravity compensation satisfies the condition of not exceeding the maximum force that the actuator can generate while maximizing the use of the passive force of the gas springs. The proposed optimization is expected to be used in various mechanical systems including parallelogram link structures.
Analysis of Body Slip and Seat Pressure in Powered Wheelchairs with Two-Slide Recline System
Yunhee Chang,Yong Cheol Kim,Ki Tae Nam,Jung Sun Kang,Bo Ra Jeong,Eung-Pyo Hong 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.3
Recline and tilt functions are the most desirable features for relieving seating pressure to decrease the risk of pressure ulcers. This study presents a new recline mechanism for a powered wheelchair for users sitting for a long duration. We analyzed the effect of a developed two-slide mechanism. In this study, body slip distance and buttock pressure were measured during wheelchair reclining and repositioning using a three-dimensional motion analysis and a pressure measurement system in 10 healthy subjects. Non-slide, one-slide, and two-slide versions were compared. During reclining, the total slip distance along the backrest with two slides was 40.6 mm, which was 77% and 44% smaller than non-slide and one-slide backrests, respectively. The slip variation of the non-slide was 38 mm at the beginning of recline in the initial seated position, and the slip distance tended to decrease as the recline angle increased. However, in the two-slide backrest, the average slip distance per 10° interval was only 5.1 ± 1.1 mm. In addition, we observed a similar slip in repositioning as in reclining, and the slip distance along the seat also decreased most in the two-slide backrest. The buttock pressure gradually decreased from 100° to 150° and then increased again from 160°, but the two-slide backrest showed a tendency to decrease at larger angles of recline and decreased by 59% of the maximum pressure. This study confirms that the two-slide system reduces body slip and buttock pressure, and it is expected that risk factors caused by the long-term use of a wheelchair can be minimized.