• 한국정밀공학회지
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• 제32권12호
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• pp.1049-1054
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• 2015

Nowadays, there are many researches involving structural actuators, which have adjustable stiffness; they are also called variable stiffness actuators (VSA). The VSAs can adjust the characteristics of actuators for various functions and human-machine safety. This paper describes the design and analysis of two types of VSAs. To adjust stiffness, the actuators are controlled by a principle of lever ratio mechanism, by changing a pivot position or a spring position in the structure with springs. To make the principle workable, the designs are simplified by using a ball screw system with a motor. Each structure shows different static properties with variable rates of stiffness. We have also shown the experimental verification of the dynamic performance of the two types of VSAs. This research can be applied to various industrial fields, where humans work in conjunction with robots.

• 한국정밀공학회지
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• 제19권12호
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• pp.109-119
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• 2002

In this paper, mechanism design of optical pickup actuator for fast access is proposed. This actuator is composed of moving magnet type actuator and moving coil type actuator for tracking and fine motion, respectively. Moving magnet type tracking actuator is configurated by two permanent magnets and four air-core solenoids. Additional damper by induced current in tracking actuator can reduce the transient vibration between the coarse seeking servo and fine seeking servo. Variable stiffness can be acquired by applying current to air-core solenoid simply. This actuator can achieve fast access by these additional damper and stiffness. Performance of this actuator is predicted through the FEM, simulation and simple experiment. Settling time for transient vibration is reduced to 14.7% according to simulation result.

• 로봇학회논문지
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• 제12권3호
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• pp.332-338
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• 2017

As an interpretation of existing jamming effects, the main variables affecting the increase in stiffness due to jamming are known as system density, jamming density, pressure, and particulate temperature. The main variable, jamming density, is closely related to the distribution of particle size and contact properties such as particle shape and friction. However, the complexity of these variables makes it difficult to fully understand the mechanism of the jamming effect. In this paper, we focus on the jamming effects of particles that have more elastic properties than particles such as sand and coffee powder, which are commonly used as constituent particles of existing jamming, in order to reduce complicated factors such as temperature and concentrate on jamming effects based on elastic characteristics of particles. It was experimentally explored the possibility of increasing stiffness by mixing particles of different sizes rather than simply increasing the bending stiffness by controlling the particle size. Through simulations and experiments, we found a case where the stiffness of each particle size distribution is larger than the stiffness of each particle size.

• 한국정밀공학회지
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• 제30권3호
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• pp.260-265
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• 2013

To increase the machine accuracy by improving the stiffness of spindle bearings, preload was applied to the spindle bearings. The methods of fixed position preload, convertible preload, constant pressure preload, and variable preload are used to apply the preload to the spindle bearing. The previous studies performed by the author of this study were variable preload methods using rubber pressure and centrifugal force based on mechanical systems. This study proposed a toggle joint mechanism that could be applied to variable preload method using centrifugal force and rubber pressure to increase the preload. Also, a finite element analysis was conducted to predict the deformation of the rubber and change of the preload. And the analysis results showed that the preload by the device using rubber pressure only was increased by the toggle joint mechanism using rubber pressure.

• 소성∙가공
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• 제32권3호
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• pp.129-135
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• 2023

The use of engineering plastic products in internal combustion engine and electric cars to improve stiffness and reduce weight is increasing significantly. Among various lightweight materials, engineering plastics have significant advantages such as cost reduction, improved productivity, and weight reduction. In particular, engineering plastics containing glass fibers are used to enhance stiffness. However, the stiffness of glass fibers can increase or decrease depending on their orientation. Before developing plastic products, optimal designs are determined through injection molding and structural analysis to enhance product reliability. However, reliable analysis of products with variable stiffnesses caused by anisotropy cannot be achieved via the conventional isotropic structural analysis, which does not consider anisotropy. Therefore, based on the previously reported study "the Effect of Impacted Fracture in Glass Fiber Orientation with Injection Molding & Structural Coupled Analysis," this study aims to investigate the structural analysis and degradation mechanisms of various polymers. In particular, this study elucidates the actual mechanism of plastic fracture by analyzing various fracture conditions and their corresponding simulations. Furthermore, the objective of this study is to apply the injection molding and structural coupled analysis mechanism to develop engineering plastic products containing glass fibers. In addition, the study aims to apply and improve the plastic fracture mechanism in actual products by exploring anisotropy and stiffness reduction owing to the unfilled polymer weld line.

• Smart Structures and Systems
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• 제24권3호
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• pp.303-317
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• 2019

Magneto-rheological fluid (MRF) rotatory dampers are normally used for controlling the constant rotation of machines and engines. In this research, such a device is proposed to act as variable stiffness device to alleviate the rotational oscillation existing in the many engineering applications, such as motor. Under such thought, the main purpose of this work is to characterize the nonlinear torque-angular displacement/angular velocity responses of an MRF based variable stiffness device in oscillatory motion. A rotational hysteresis model, consisting of a rotatory spring, a rotatory viscous damping element and an error function-based hysteresis element, is proposed, which is capable of describing the unique dynamical characteristics of this smart device. To estimate the optimal model parameters, a modified whale optimization algorithm (MWOA) is employed on the captured experimental data of torque, angular displacement and angular velocity under various excitation conditions. In MWOA, a nonlinear algorithm parameter updating mechanism is adopted to replace the traditional linear one, enhancing the global search ability initially and the local search ability at the later stage of the algorithm evolution. Additionally, the immune operation is introduced in the whale individual selection, improving the identification accuracy of solution. Finally, the dynamic testing results are used to validate the performance of the proposed model and the effectiveness of the proposed optimization algorithm.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2004년도 춘계학술대회 논문집
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• pp.773-777
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• 2004

The variable-gauge wheelset drives on the variable railways. It doesn't need to replace or move the carriages to another bogie parts. This paper is for dynamic analysis of the variable-gauge wheel set. 3D-Virtual Mock-up. program was developed to verify the operating mechanism and understand dynamic characteristics for German RAFIL- V variable-gauge wheel set. When the system is going through the width-variable railway, its safety depends on the stiffness and velocity. So the numerical and contact model of this system were developed. This solution is useful to analyze dynamic characteristics for variable-gauge wheelset.

• 한국군사과학기술학회지
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• 제21권3호
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• pp.331-341
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• 2018

This study proposes an integrated serial spring-damper mechanism as a dual pulse generation system. Compared to the traditional dual pulse generation system, which used multiple springs and a damper to generate a dual pulse critical for impact testing of naval equipments, currently used separated serial spring-damper mechanism is comprised of two components: an air spring, and a damper. The proposed mechanism combines the two components into one integrated system with a unique design that lets simply changing the volume and the pressure of the air tank, and the length of the annular pipe adjust the stiffness and damping constants for testing, eliminating the need to have multiple sets of air springs and dampers. Simulations using MatLab and Simulink were conducted to verify the feasibility of this design. The results show the potential of an integrated serial spring-damper mechanism as a more convenient and flexible mechanism for dual pulse generation system.

• Earthquakes and Structures
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• 제22권1호
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• pp.95-107
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• 2022

This paper introduces a novel, rigorous, and efficient probabilistic methodology for the performance-based optimal design (PBOD) of semi-active tuned mass damper (SATMD) for seismically excited nonlinear structures. The proposed methodology is consistent with the modern performance-based earthquake engineering framework and aims to design reliable control systems. To this end, an optimization problem has been defined which considers the parameters of control systems as design variables and minimization of the probability of exceeding a targeted structural performance level during the lifetime as an objective function with a constraint on the failure probability of stroke length damage state associated with mass damper mechanism. The effectiveness of the proposed methodology is illustrated through a numerical example of performance analysis of an eight-story nonlinear shear building frame with hysteretic bilinear behavior. The SATMD with variable stiffness and damping have been designed separately with different mass ratios. Their performance has been compared with that of uncontrolled structure and the structure controlled with passive TMD in terms of probabilistic demand curves, response hazard curves, fragility curves, and exceedance probability of performance levels during the lifetime. Numerical results show the effectiveness, simplicity, and reliability of the proposed PBOD method in designing SATMD with variable stiffness and damping for the nonlinear frames where they have reduced the exceedance probability of the structure up to 49% and 44%, respectively.

• Earthquakes and Structures
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• 제12권4호
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• pp.425-436
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• 2017

Vibration control using a tuned mass damper (TMD) is an effective technique that has been verified using analytical methods and experiments. It has been applied in mechanical, automotive, and structural applications. However, the damping of a TMD cannot be adjusted in real time. An excessive mass damper stroke may be introduced when the mass damper is subjected to a seismic excitation whose frequency content is within its operation range. The semi-active tuned mass damper (SATMD) has been proposed to solve this problem. The parameters of an SATMD can be adjusted in real time based on the measured structural responses and an appropriate control law. In this study, a stiffness-controllable TMD, called a leverage-type stiffness-controllable mass damper (LSCMD), is proposed and fabricated to verify its feasibility. The LSCMD contains a simple leverage mechanism and its stiffness can be altered by adjusting the pivot position. To determine the pivot position of the LSCMD in real time, a discrete-time direct output-feedback active control law that considers delay time is implemented. Moreover, an identification test for the transfer function of the pivot driving and control systems is proposed. The identification results demonstrate the target displacement can be achieved by the pivot displacement in 0-2 Hz range and the control delay time is about 0.1 s. A shaking-table test has been conducted to verify the theory and feasibility of the LSCMD. The comparisons of experimental and theoretical results of the LSCMD system show good consistency. It is shown that dynamic behavior of the LSCMD can be simulated correctly by the theoretical model and that the stiffness can be properly adjusted by the pivot position. Comparisons of experimental results of the LSCMD and passive TMD show the LSCMD with less demand on the mass damper stroke than that for the passive TMD.