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한국정밀공학회지제 33 권제 8 호 pp. 655-660 J. Korean Soc. Precis. Eng., Vol. 33, No. 8, pp. 655-660 ISSN 1225-9071(Print), ISSN 2287-8769(Online) August 2016 / 655 http://dx.doi.org/10.7736/kspe.2016.33.8.655 자동귀환서랍의감성품질에대한설계인자영향분석 Effects of Design Parameters on the Ergonomic Quality of a Self-Closing Drawer 서만철 1, 김권희 2, Man Cheol Seo 1 and Kwon Hee Kim 2, 1 고려대학교대학원기계공학과 (Graduate School, Department of Mechanical Engineering, Korea University) 2 고려대학교기계공학부 (School of Mechanical Engineering, Korea University) Corresponding author: kwonhkim@korea.ac.kr, Tel: +82-2-3290-3360 Manuscript received: 2015.11.30. / Revised: 2016.3.29. / Accepted: 2016.5.1. Self-closing drawers are used in high-end products, such as furniture, home appliances, and a range of other storage devices. In this study, a self-closing mechanism is proposed. A system consisting of a friction latch, constant force spring, rotary damper with rack, and pinion is developed. The retracting drawer can be latched at any position and can be reactivated by simple touch. The constant force spring and rotary damper offer smooth closing action. The ergonomic quality of the closing action is quantified by an index based on velocity-time behavior. The effects of various design parameters are analyzed with a dynamics model and experimentally validated by prototype testing. KEYWORDS: Self-Closing drawer ( 자동귀환서랍 ), Ergonomics index ( 감성품질지수 ), ADAMS ( 아담스 ), Dynamics model ( 동역학모델 ), Friction latch ( 마찰잠금장치 ) 1. 서론 자동귀환서랍은가전제품, 의료기구, 차량등감성품질이중요한고가제품에적용이확대되고있다. 1 대부분의경우, 귀환행정의끝부분에서만자동복귀기능이가동되며완충을위한스프링- 댐퍼기구를갖는다. 2-4 이런경우자동귀환작동구간이짧아자동귀환보다는완충의역할이크다고볼수있다. 본연구에서는작동행정전구간의임의위치에서멈출수있고, 단순한조작으로잠금해제와자동귀환재작동이가능한서랍을제시하였다. 5 정하중스프링과로터리댐퍼를사용하여큰범위의 자동귀환거리를구현하였다. 사용자의품질만족도를높이기위해서는서랍이부드럽게닫히고, 최종행정에서충격이발생하지않아야한다. 따라서서랍의운동특성에대한세부적인연구가필요하다. 자동귀환서랍과관련된연구로는회전형댐핑장치에대한연구, 6-9 정하중스프링의특성에대한연구등이있다. 대형냉장고서랍의모터를이용한자동개폐시스템에대한연구를한사례도있다. 10 이연구에서는원가절감을위하여전기장치의사용은배제하고최소의기계부품으로시스템을구성하였다. 서랍의운동특성을예측하기위하여, ADAMS Copyright C The Korean Society for Precision Engineering This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

한국정밀공학회지제 33 권제 8 호 pp. 655-660 August 2016 / 656 Student Edition 11 을이용한동역학시뮬레이션모델을만들고, 시제품시험과비교하여검증하였다. 서랍의운동특성에기반을둔감성품질지수 (Ergonomics Index) 를제안하였고, 직교배열표를이용하여최적의설계인자조합을도출하였다. 2. 자동귀환서랍 2.1 자동귀환구조자동귀환서랍장치의구성을 Fig. 1 에나타내었다. 서랍좌우에각각한쪽끝이고정되는두세트의 3 단슬라이드레일의다른쪽끝은서랍을수용하는프레임내벽에고정된다. 가이드레일프레임쪽고정단에는서랍의구동기구를수용하는고정판 (Base Plate) 이조립된다. 구동기구는마찰잠금장치 (Friction Latch), 로터리댐퍼 (Rotary Damper), 랙과피니언 (Rack and Pinion) 및정하중스프링 (CFS, Constant Force Spring) 등으로구성된다. 정하중스프링의드럼부분은서랍에, 끝부분은가이드판에각각고정되어귀환력을발생시킨다. (a) Isometric view (b) Major components 2.2 주요설계인자자동귀환시서랍에가해지는하중조건을 Fig. 2 에나타내었다. F S 는정하중스프링의하중이며, 다음과같이표현된다. 12,13 FS EI = 2R (1) Fig. 3 에나타낸 R n 은스프링의곡률반경, E 는스프링소재의 Young s Modulus, I 는스프링단면의모멘트이다. 여기서정하중스프링의자유상태곡률반경과보빈의반경은 R n 으로동일하다고가정한다. 정하중스프링의드럼부분은 Drawer, 끝부분은 Base Plate 에각각연결된다. 로터리댐퍼는로터 (Rotor) 와케이스사이에충진된오일의점성으로감쇄력이결정된다. 14-17 로터리댐퍼에장착된피니언은제동토크 T D 로랙의운동을제어한다. 피니언축에는일방향베어링 (One Way Bearing) 이적용되어서랍이열리는방향으로는감쇄력이작용하지않는다. 마찰잠금장치가서랍에가하는제동력 F L 은캠접촉면에코일스프링으로가해지는수직항력 (Latch Contact Force) 과접촉면의마찰계수로결정 2 n (c) Friction latch Fig. 1 Self-Closing drawer system Fig. 2 Forces and torque acting on the rack during selfclosing action with FS: Spring force, FL: Latch friction force and TD: Damper torque

한국정밀공학회지제 33 권제 8 호 pp. 655-660 August 2016 / 657 Fig. 3 Dimensions of the constant force spring Table 1 Design parameters in 2 levels Design parameter Level 1 Level 2 A Spring force (N) 6.2 8.2 B Damping coefficient (N mm sec/deg) 0.077 0.148 C Latch contact force (N) 3 5 D Friction coefficient (Latch-Rack) 0.32 0.7 된다. 서랍을열었다가놓게되면코일스프링의압축량이최대가되어서랍을고정하는역할을하고, 사용자가서랍을닫는방향으로약간의힘을가하면스프링이좌굴되어서랍이닫히기시작한다 (Fig. 1(c) 참조 ). 이경우에서랍진행방향으로압축스프링이휘어최소의마찰력만존재하게되지만서랍의운동에역시영향을미친다. 서랍의운동특성에영향을주는설계인자들을각 2 수준으로설정하여 Table 1 에정리하였다. 각인자의수준값은제작될시제품을기준으로결정하였다. 3. 1 차모델감성품질평가 3.1 동역학모델설계인자들의영향을평가하기위해 Table 1 에수록된변수들의조합을 Fig. 4 에보인동역학모델에적용하여해석을수행하였다. 모델은서랍, 슬라이드레일, 고정판, 정하중스프링, 로터리댐퍼, 랙, 마찰잠금장치등을포함한다. 서랍의무게는 2 kg, 그리고슬라이드레일의마찰계수는 0.005 를적용하였다. 3.2 감성품질지수서랍의운동특성을수치화하여표현하기위한방법으로감성품질지수를제안하였다. 서랍의총이동거리 S 는시제품을기준으로 280 mm 로설정하고, 서랍이완전히열린상태에서닫히는시간 T 는소비자들의의견을참고하여 2.0 sec 로 Fig. 4 Dynamics model of a self-closing drawer Table 2 Results of simulation for the four parameters in Table 1 RUN A B C D I 1 1 1 1 1 1.05 2 1 1 1 2 0.55 3 1 1 2 2 0.66 4 1 1 2 1 0.76 5 1 2 1 1 0.36 6 1 2 1 2 0.42 7 1 2 2 2 1.17 8 1 2 2 1 0.27 9 2 1 1 1 1.51 10 2 1 1 2 1.36 11 2 1 2 2 0.95 12 2 1 2 1 1.43 13 2 2 1 1 1.13 14 2 2 1 2 0.84 15 2 2 2 2 0.29 16 2 2 2 1 0.97 설정하였다. 처음 250 mm 구간에서등가속도운동을하며, 마지막 30 mm 구간에서등가속도로감속하는것을이상적인거동 V I 로정의한다. 이에따라감성품질지수 (Ergonomics Index) I 는다음과같이표현된다. 1 (2) T 2 I = ( V V ) dt I S 0 여기서 V 는 ADAMS 동역학모델시뮬레이션으로얻어지는서랍의속도를나타낸다. 이상적운동과실제운동의속도그래프에서면적의차이가감성품질지수 I 가되며, 이값은 0 에가까울수록좋다.

한국정밀공학회지제 33 권제 8 호 pp. 655-660 August 2016 / 658 Fig. 6 Experimental setup Fig. 5 Predicted velocities for Run 8 and Run 15 compared with ideal curve 3.3 1 차모델평가결과 Table 1 의주요설계인자들의영향을분석하기위하여 Table 2 의변수조합을기준으로해석을진행하고감성품질지수를평가하였다. Table 2 의결과로 8 번실험이가장낮은인덱스값을갖는것을알수있다. Table 2 에서가장낮은인덱스값을갖는 8 번과 15 번실험의속도 - 시간그래프를이상적속도 V I 와비교하여 Fig. 5 에나타내었다. 8 번의경우속도패턴이나서랍이닫히는데까지걸리는시간은이상적속도그래프와대체적으로유사하나완전히닫히기직전에급가속과바운딩 (Bounding) 이발생하는것을확인할수있다. Fig. 7 Measured and predicted velocities for the Run 8 condition in Table 2 compared with ideal curve 4. 모델검증 해석으로예측되는결과와시제품에대한실험결과를비교하여동역학해석모델을검증하였다. 18,19 실험장치의구성은 Fig. 6과같다. 흔들림이가장적은서랍의중앙에가속도센서를부착하고서랍이움직이는동안측정된데이터는아두이노 (Arduino) 마이크로컨트롤러를통해 0.025 sec 간격으로 PC에기록되었다. 가속도센서는 MPU6050으로입력전압 3.3V, 차단주파수 250 Hz, 분해능 1/16384 (LSB/G), 측정범위 ±4 (G) 이다. 시제품은 Table 2의 8번실험조건을기준으로제작하였다. Fig. 7은시제품시험결과와 ADAMS 시뮬레이션결과를이상적인속도 V I 와비교하여보이고있다. 실험결과와동역학모델의해석결과가대체적으로일치하는것을알수있다. Fig. 8 Dynamics model of drawer with an added springdamper assembly 5. 2 차모델 5.1 정지완충장치의추가 Fig. 7 에서확인할수있듯이서랍이닫히면서바운딩이나타난다. 이에대한대책으로정지완충장치 (Stop Damper) 의적용을검토하였다. 스프링 - 댐퍼시스템으로구성되는정지완충장치는 Fig. 8 에보인것과같이서랍의전체작동행정 280 mm 중마지막 30 mm 구간에서부드러운닫힘을유도하기위하여서랍외부프레임에고정된다.

한국정밀공학회지제 33 권제 8 호 pp. 655-660 August 2016 / 659 Table 3 Design parameters in 2 levels Design parameter Level 1 Level 2 A Spring force (N) 6.2 8.2 B Damping coefficient (N mm sec/deg) 0.077 0.148 C Latch contact force (N) 3 5 D Friction coefficient (Latch-Rack) 0.32 0.7 E Spring stiffness (Stop Damper), (N/mm) 0.15 0.3 F Damping coefficient (Stop Damper), (N sec/mm) 0.02 0.04 G Drawer load (kg) 0 5 Table 4 L8(2 7 ) orthogonal array Run A B C D E F G I 1 1 1 1 1 1 1 1 1.02 2 1 1 1 2 2 2 2 0.98 3 1 2 2 1 1 2 2 1.02 4 1 2 2 2 2 1 1 1.12 5 2 1 2 1 2 1 2 0.66 6 2 1 2 2 1 2 1 0.88 7 2 2 1 1 2 2 1 1.05 8 2 2 1 2 1 1 2 0.14 Fig. 10 Predicted velocity for the Run 8 condition in Table 4 compared with ideal curve 큰요소이기때문인것으로보인다. 이외에도다른변수들의영향력이적지않아변수들의적절한조합이중요함을판단할수있다. 가장이상적인조합은 Run 8 과일치한다. Fig. 10 은 Table 4 의 Run 8 에대한해석결과와이상적인속도선도를비교한것이다. 낮은평가지수가표현하는것처럼서랍의거동이이상적인형태에가까운것을알수있다. 6. 결론 Fig. 9 Mean value analysis for the parameters in Table 4 5.2 직교배열표 2차모델에서는 Table 1의기존설계변수들에정지완충장치의스프링강성계수 K, 감쇄계수 C 및서랍적재중량 (Load) 등을추가하여 Table 3와같이실험조건을설정하였다. Table 4에보인것과같이 L8(2 7 ) 직교배열표를이용하여총 7개의 2 수준인자들에대한동력학해석을수행하고감성품질지수 I 를평가하였다. 20 Fig. 9에서감성품질지수에가장큰영향을미치는인자들은정하중스프링의힘인데, 이는서랍의진향방향으로작용하는하중조건중가장 서랍의자동귀환기구를고안하고, 여러변수들이서랍의운동특성에끼치는영향을평가하기위해동역학해석을진행하였다. 서랍의운동특성을감성품질지수로평가하기위한인덱스를제시하였다. 1 차실험을통해가장좋은조합을찾아내었고, 그조합과동일한조건으로만들어진시제품에대한실험을통하여해석모델을검증하였다. 2 차시험에서는정지완충장치를추가하여운동특성이개선된모델을제시하였다. Figs. 5 와 10 의비교로 I 값이 0 에가까울수록이상적서랍운동에가까우며, 제안된감성품질지수가효과적임을확인할수있다. 후기 이논문은 2014 년도정부 ( 미래창조과학부 ) 의재원으로한국연구재단의지원을받아수행된기초연구사업임 (No.2007-0056094).

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