• Smart Structures and Systems
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• 제9권2호
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• pp.189-206
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• 2012

This paper focuses on the actuation system combined with a piezoelectric transducer and an electric circuit, which leads to a new insight; the electric actuation system is equivalent to mechanical variable-stiffness actuation systems. By controlling the switch in the circuit, the electric status of the piezoelectric transducer is changed, and consequently a variable-stiffness mechanism is achieved on the electric actuator. This proposed actuator features a shift in the equilibrium point of force, while conventional electrically-induced variable-stiffness actuators feature the variation of the stiffness value. We intensively focus on the equilibrium shift in the actuation system, which has been neglected. The stiffness of the variable-stiffness actuator is periodically modulated by controlling the switch, to suppress the vibration of the system in an open-loop way. It is proved that this electric actuator is equivalent to its mechanical counterpart, and that the electrical version has some practical advantages over the mechanical one. Furthermore, another kind of electrically-induced variable-stiffness actuator, using an energy-recycling mechanism is also discussed from the viewpoint of open-loop vibration control. Extensive numerical simulations provide comprehensive assessment on both electrically-induced variable-stiffness actuators employed for open-loop vibration control.

• Smart Structures and Systems
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• 제24권3호
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• pp.361-377
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• 2019

The stiffness of shape memory alloy (SMA) spring while in actuation is represented by an empirical model that is derived from the logistic differential equation. This model correlates the stiffness to the alloy temperature and the functionality of SMA spring as active variable stiffness actuator (VSA) is analyzed based on factors that are the input conditions (activation current, duty cycle and excitation frequency) and operating conditions (pre-stress and mechanical connection). The model parameters are estimated by adopting the nonlinear least square method, henceforth, the model is validated experimentally. The average correlation factor of 0.95 between the model response and experimental results validates the proposed model. In furtherance, the justification is augmented from the comparison with existing stiffness models (logistic curve model and polynomial model). The important distinction from several observations regarding the comparison of the model prediction with the experimental states that it is more superior, flexible and adaptable than the existing. The nature of stiffness variation in the SMA spring is assessed also from the Dynamic Mechanical Thermal Analysis (DMTA), which as well proves the proposal. This model advances the ability to use SMA integrated mechanism for enhanced variable stiffness actuation. The investigation proves that the stiffness of SMA spring may be altered under controlled conditions.

• Smart Structures and Systems
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• 제13권4호
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• pp.711-730
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• 2014

In this paper the system dynamic influences in actuators with variable stiffness as contemporary used in robotics for safety and efficiency reasons are investigated. Therefore, different configurations of serial and parallel elasticities are modeled by dynamic equations and linearized transfer functions. The latter ones are used to identify the characteristic behavior of the different systems and to study the effect of the different elasticities. As such actuation concepts are often used to reach energy-efficient operation, a power consumption analysis of the configurations is performed. From the comparison of this with the system dynamics, strategies to select and control stiffness are derived. Those are based on matching the natural frequencies or antiresonance modes of the actuation system to the frequency of the trajectory. Results show that exclusive serial and parallel elasticity can minimize power consumption when tuning the system to the natural frequencies. Antiresonance modes are an additional possibility for stiffness control in the series elastic setup. Configurations combining both types of elasticities do not provide further advantages regarding power reduction but an input parallel elasticity might enable for more versatile stiffness selection. Yet, design and control effort increase in such solutions. Topologies incorporating output parallel elasticity showed not to be beneficial in the chosen example but might do so in specific applications.

• 대한기계학회논문집A
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• 제37권10호
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• pp.1195-1200
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• 2013

최근에 들어 로봇과 환경 사이의 상호작용이 다양하게 발생하는 작업에서 가변 강성 액추에이터의 연구가 활발하다. 기존의 다양한 가변 강성 액추에이터가 개발되었지만 크기와 중량 때문에 응용분야를 찾기가 어렵다. 따라서 다양한 분야에 쉽게 이용되기 위해 소형의 가변 강성 액추에이터(miniVSA)를 개발하였다. miniVSA는 모멘트 암 기반의 강성제어 장치와 두 개의 모터로 구성된 구동 장치로 구성된다. 강성제어 장치는 두 캠의 상대 운동을 제어하여 위치와 강성을 동시에 제어할 수 있다. 이를 실험을 통하여 강성 변화를 검증하였다.

• Journal of Mechanical Science and Technology
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• 제20권4호
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• pp.447-454
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• 2006

Hydraulic actuators are important in modern industry due to high power, fast response, and high stiffness. In recent years, hybrid actuation system, which combines electric and hydraulic technology in a compact unit, can be adapted to a wide variety of force, speed and torque requirements. Moreover, the hybrid actuation system has dealt with the energy consumption and noise problem existed in the conventional hydraulic system. Therefore, hybrid actuator has a wide range of application fields such as plastic injection-molding and metal forming technology, where force or pressure control is the most important technology. In this paper, the solution for force control of hybrid system is presented. However, some limitations still exist such as deterioration of the performance of transient response due to the variable environment stiffness. Therefore, intelligent switching control using Learning Vector Quantization Neural Network (LVQNN) is newly proposed in this paper in order to overcome these limitations. Experiments are carried out to evaluate the effectiveness of the proposed algorithm with large variation of stiffness of external environment. In addition, it is understood that the new system has energy saving effect even though it has almost the same response as that of valve controlled system.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.290-295
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• 2005

Hydraulic actuators are important in modern industry due to high power, fast response, and high stiffness. In recent years, hybrid actuation system, which combines electric and hydraulic technology in a compact unit, can be adapted to a wide variety of force, speed and torque requirements. Moreover, the hybrid actuation system has dealt with the energy consumption and noise problem existed in the conventional hydraulic system. Therefore, hybrid actuator has a wide range of application fields such as plastic injection-molding and metal forming technology, where force or pressure control is the most important technology. In this paper, the solution for force control of hybrid system is presented. However, some limitations still exist such as deterioration of the performance of transient response due to the variable environment stiffness. Therefore, intelligent switching control using Learning Vector Quantization Neural Network (LVQNN) is newly proposed in this paper in order to overcome these limitations. Experiments are carried out to evaluate the effectiveness of the proposed algorithm with large variation of stiffness of external environment. In addition, it is understood that the new system has energy saving effect even though it has almost the same response as that of valve controlled system.

• Smart Structures and Systems
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• 제3권1호
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• pp.89-114
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• 2007

Two aspects of the design of a small-scale smart wing are addressed in this work, related to the ability of the wing to modify its cross section assuming the shape of two different airfoils and to the possibility of deflecting the profiles near the trailing edge in order to obtain hingeless control surfaces. The actuation is provided by one-way shape memory alloy wires eventually coupled to springs, Shape Memory Alloys (SMAs) being among the most promising materials for this kind of applications. The points to be actuated along the profiles and the displacements to be imposed are selecetd so that they satisfactorily approximate the change from an airfoil to the other and to result in an adequate deflection of the control surface; the actuators and their performances are designed so that an adequate wing stiffness is guaranteed, in order to prevent excessive deformations and undesired airfoil shape variations due to aerodynamic loads. The effect of the pressure distributions, calculated by way of the XFOIL software, and of the actuators loads, is estimated by FE analyses of the loaded wing. Two prototypes are then realised incorporating the variable airfoil and the hingeless aileron features respectively, and the verification of their shapes in both the actuated and non-actuated states, supported by image analysis techniques, confirms that interesting results are achievable with the proposed lay out and design considerations.

• Wind and Structures
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• 제30권2호
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• pp.211-217
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• 2020

Vibrations of a wind turbine blade have a negative impact on its performance and result in failure of the blade, therefore an approach to effectively control vibration in turbine blades are sought by wind industry. The small domestic horizontal axis wind turbine blades induce flap wise (out-of-plane) vibration, due to varying wind speeds. These flap wise vibrations are transferred to the structure, which even causes catastrophic failure of the system. Shape memory alloys which possess physical property of variable stiffness across different phases are embedded into the composite blades for active vibration control. Previously Shape memory alloys have been used as actuators to change their angles and orientations in fighter jet blades but not used for active vibration control for wind turbine blades. In this work a GFRP blade embedded with Shape Memory Alloy (SMA) and tested for its vibrational and material damping characteristics, under martensitic and austenite conditions. The embedment portrays 47% reduction in displacement of blade, with respect to the conventional blade. An analytical model for the actuated smart blade is also proposed, which validates the harmonic response of the smart blade.

• 대한기계학회논문집A
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• 제39권4호
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• pp.361-367
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• 2015

논문에서는 인간과의 안전한 접촉이 가능한 내부형 연속체로봇에 대한 설계개념과 로봇 말단장치의 운동특성실험을 제시한다. 인간의 근육과 유사한 상극구동방식으로 작동하는 공압인공근육을 연속체로봇의 백본 및 구동장치로 사용하기 때문에, 외부환경과의 부드러운 접촉과 강한 접촉을 선택적으로 제어할 수 있는 로봇 관절에서의 가변강성이 가능하다. 그러나 내부형 연속체로봇은 백본소재의 굽힘운동을 예측하기 어렵기 때문에 로봇 말단장치에서의 자세를 추정하기 어렵다. 이를 해결하기 위해 3 축 가속도계와 3 축 자이로스코프를 이용한 칼만필터 방법을 제안하고 개발된 내부형 연속체 로봇의 자세추정에 적용하여 실제 실험을 통해서 제안된 방법의 효율성을 검증하였다.

• 대한기계학회논문집
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• 제17권1호
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• pp.90-100
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• 1993

본 연구에서는 압전 감지기/작동기를 이용한 복합적층판의 진동제어해석을 위 하여 판요소를 사용한 능률적인 유한요소코드 개발에 있다. 운동방정식은 고전 적층 판이론과 Hamilton의 법칙을 이용하여 유도하며 압전방정식으로부터 전기적-기계적 연 계를 고려한 감지식과 작동식을 구한다.각식들은 유한요소 보간함수에 의하여 절점 변위에 대한 행렬방정식으로 변환된다. 요소마다 하나의 전기적 자유도를 가진 4-절 점 12-자유도 판요소를 사용하여 효율적인 계산을 가능하게 하였다. 압전 감지기/작 동기를 도입함에 있어 하나의 전극에 대해 압전 감지기/작동기는 하나의 감지/작동전 압을 갖는다. 각 요소에 전극번호를 부가함으로써 다양한 형상의 전극을 쉽게 모델 링하였으며 전극의 특성도 충분히 고려하였다. 전기적 하중에 의한 압전보의 변형과 변형에 대한 감지전압에 대한 계산을 수행하여 기존의 연구와 비교함으로써 본 프로그 램의 타당성을 확인하였다. 나아가 여러가지 전극형상에 대한 복합재료 평판의 시간 영역과 주파수영역에서 응답을 계산하였다.