Journal of Mechanical Science and Technology 33 (10) (2019) 4605~4613 www.springerlink.com/content/1738-494x(Print)/1976-3824(Online) DOI 10.1007/s12206-019-0903-z Identification of elastomeric isolator parameters on air-borne EO/IR camera with multi-axis gimbal † Sang-won Kim 1,2 , Sung-kie Youn 1 , Ik-jin Lee 1,* and Sang-eun Lee 3 1 Department of Mechanical Engineering, KAIST, Daejeon 34141, Korea 2 EO/IR R&D, Agency for Defense Development, Daejeon 34186, Korea 3 EO/IR R&D Center, LIG Nex1, Gyeonggi-do 16911, Korea (Manuscript Received January 6, 2019; Revised June 24, 2019; Accepted July 7, 2019) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract Stabilization performance of an air-borne EO/IR camera is severely affected mainly by two factors: One is the vibration transmitted from the platform, and the other is the torque disturbance due to mass imbalance of the inner gimbal installed on the camera. Elastomeric isolators are commonly employed in aeronautical equipment due to their ease of installation, light-weight, and excellent dissipation char- acteristics. The dynamic characteristics of an elastomeric isolator are a function of frequency and also of temperature. Therefore, it is very important to obtain accurate parameters for its dynamic characteristics for the control of an EO/IR camera system. The parameters are identified inversely by testing and by using finite element calculation with proper modeling of the isolators. In this paper, the process of identifying the dynamic parameters of the isolators using a simple pilot test and a finite element model of the camera system is pre- sented. A pilot test equipment is built to put real environmental condition (e.g., temperature condition, heat flow condition, etc.) on the elastomeric isolator. Therefore, the characteristics of an elastomer identified on tests are the dynamic values reflecting the temperature environment characteristic. In the process, 3 dB method is introduced for fast and effective parameter identification. On matching the isolator model on FEA to the disturbance transfer model on stabilization control simulator, it is able to narrow the difference between the test and the real condition by using more reliable parameters. Keywords: Elastomeric isolator; Dynamic parameter; Inverse analysis; 3 dB method; EO/IR camera ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction In an air-borne electro-optical equipment, vibration needs to be optimally controlled to suppress line-of-sight (LOS) insta- bility. Mechanical vibration isolators made of elastomers are employed for this purpose. Elastomers have different response characteristics depending on their constituent materials (e.g., organic elastomers, silicon-based elastomers, metals, plastics, and foam materials). In addition, the dynamic characteristics of elastomers are frequency dependent and vary with tempera- ture. For accurate analysis, parameters of an isolator should be correctly identified through a dynamic response test. Elastomeric bushings have been studied in automotive field [1-3]. Gibania and Abrahamsson proposed a correction method for an FE model through a modal test with and with- out mass load condition. Noll et al. studied effects of installa- tion spacing of elastomers. In addition, Kaul inversely identi- fied parameters using different mathematical models of an elastomer based on test results, and presented a suitable elas- tomer model for the operation condition [4]. Zhu et al. identi- fied the parameter of MR damper for single unit using Boun- Wen model [5]. Ripin and Ean compared frequency response characteristics of an engine for the mounting angle based on a sine-sweep profile and found the optimal angle for the mounts [6]. In seismic area, Zhou et al. researched the vibration condi- tion for one direction (vertical isolation) [7]. In aeronautical field [8, 9], Hidalgo and Nabarrete used FEA for various shapes of isolators, and verified the results through tests at different frequencies. Cheng et al. studied an optimization technique for decoupling behaviors using an elastomeric isola- tor between bracket and platform. Rocen and He studied the various vibration condition but test was limited to the compo- nent level [10, 11]. Lee studied a harmonic response analysis method to analyze an air-borne camera [12-15]. As mentioned above, the dynamic parameters of elas- tomeric isolators have been estimated by using the elastomer as a single piece or via a specimen test of the rubber bushing. The analysis process applied to the system is complicated, and some cases have inconvenient processes such as conversion. The simulation and test processes for identifying parameters in the system level are complex. For a system where exciting * Corresponding author. Tel.: +82 42 350 3041, Fax.: +82 42 350 3210 E-mail address: ikjin.lee@kaist.ac.kr † Recommended by Associate Editor Daeil Kwon © KSME & Springer 2019