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Ajou, South Korea

Jeon J.,Inha University | Han C.,Inha University | Han Y.-M.,Ajou Motor College | Choi S.-B.,Inha University
Smart Materials and Structures | Year: 2014

A direct-drive valve (DDV) system is a kind of electrohydraulic servo valve system, in which the actuator directly drives the spool of the valve. In conventional DDV systems, the spool is generally driven by an electromagnetic actuator. Performance characteristics such as frequency bandwidth of DDV systems driven by the electromagnetic actuator are limited due to the actuator response property. In order to improve the performance characteristics of conventional DDV systems, in this work a new configuration for a direct-drive valve system actuated by a piezostack actuator with a flexible beam mechanism is proposed (in short, a piezo-driven DDV system). Its benefits are demonstrated through both simulation and experiment. After describing the geometric configuration and operational principle of the proposed valve system, a governing equation of the whole system is obtained by combining the dynamic equations of the fluid part and the structural parts: the piezostack, the flexible beam, and the spool. In the structural parts of the piezostack and flexible beam, a lumped parameter modeling method is used, while the conventional rule of the fluid momentum is used for the fluid part. In order to evaluate valve performances of the proposed system, an experimental apparatus consisting of a hydraulic circuit and the piezo-driven DDV system is established. The performance characteristics are evaluated in terms of maximum spool displacement, flow rate, frequency characteristics, and step response. In addition, in order to advocate the feasibility of the proposed dynamic model, a comparison between simulation and experiment is undertaken. © 2014 IOP Publishing Ltd.

Han Y.-M.,Ajou Motor College | Choi S.-B.,Inha University
Smart Materials and Structures | Year: 2014

This paper proposes a haptic clutch driven gear shifting assistance device that can help when the driver shifts the gear of a transmission system. In order to achieve this goal, a magnetorheological (MR) fluid-based clutch is devised to be capable of the rotary motion of an accelerator pedal to which the MR clutch is integrated. The proposed MR clutch is then manufactured, and its transmission torque is experimentally evaluated according to the magnetic field intensity. The manufactured MR clutch is integrated with the accelerator pedal to transmit a haptic cue signal to the driver. The impending control issue is to cue the driver to shift the gear via the haptic force. Therefore, a gear-shifting decision algorithm is constructed by considering the vehicle engine speed concerned with engine combustion dynamics, vehicle dynamics and driving resistance. Then, the algorithm is integrated with a compensation strategy for attaining the desired haptic force. In this work, the compensator is also developed and implemented through the discrete version of the inverse hysteretic model. The control performances, such as the haptic force tracking responses and fuel consumption, are experimentally evaluated. © 2014 IOP Publishing Ltd.

Bae W.-S.,Ajou Motor College
Peer-to-Peer Networking and Applications | Year: 2015

Multifunctional high-performance electronic systems in M2M(Machine-to-Machine) industry have been evolving substantially in tandem with the advancement of IT. M2M, standing for machine-to-machine communication, replaces people in cases where human intervention is hardly viable or in such fields as weather, environment or disasters where long-term monitoring is required. Yet, due to the nature of M2M devices involving wireless communication, they are exposed to intruders’ attacks. Thus, the overriding concern in M2M communication is mutual authentication and security. In this context, security communication protocols are considered worth exploring. This paper concerns designing a safe communication protocol by applying hash locks, random numbers and session keys. Instead of arguing for the security of the protocol based on mathematical theorem proving as most previous studies did, the present paper demonstrates the proposed protocol is safe against a variety of intruders’ attacks by formally verifying it using Casper/FDR. In short, the proposed protocol is verified in terms of safety, deadlock and livelock. © 2015 Springer Science+Business Media New York

Oh J.-S.,Inha University | Han Y.-M.,Ajou Motor College | Choi S.-B.,Inha University
Smart Materials and Structures | Year: 2011

This work proposes an active mount for the camera systems of unmanned aerial vehicles (UAV) in order to control unwanted vibrations. An active actuator of the proposed mount is devised as an inertial type, in which a piezostack actuator is directly connected to the inertial mass. After evaluating the actuating force of the actuator, it is combined with the rubber element of the mount, whose natural frequency is determined based on the measured vibration characteristics of UAV. Based on the governing equations of motion of the active camera mount, a robust sliding mode controller (SMC) is then formulated with consideration of parameter uncertainties and hysteresis behavior of the actuator. Subsequently, vibration control performances of the proposed active mount are experimentally evaluated in the time and frequency domains. In addition, a full camera mount system of UAVs that is supported by four active mounts is considered and its vibration control performance is evaluated in the frequency domain using a hardware-in-the-loop simulation (HILS) method. © 2011 IOP Publishing Ltd.

Oh J.-S.,Inha University | Han Y.-M.,Ajou Motor College | Lee S.-R.,Inha University | Choi S.-B.,Inha University
Smart Materials and Structures | Year: 2013

This paper presents a novel 4-degrees-of-freedom (4-DOF) haptic master using a electrorheological (ER) fluid which is applicable to minimally invasive surgery (MIS) systems. By adopting a controllable ER fluid, the master can easily generate 4-DOF repulsive forces with the advantages of a simple mechanism and continuous force control capability. The proposed master consists of two actuators: an ER spherical joint for 3-DOF rotational motion and an ER piston device for 1-DOF translational motion. The generated torque/force models are mathematically derived by analyzing the mechanism geometry and using the Bingham characteristics of an ER Fluid. The haptic master is optimally designed and manufactured based on the mathematical torque/force models. The repulsive torque/force responses are experimentally evaluated and expressed by the first-order and second-order dynamic equations for each motion. A sliding mode controller (SMC), which is known to be robust to uncertainties, is then designed and empirically implemented to achieve the desired torque/force trajectories. It is demonstrated by presenting torque/force tracking results of both rotational and translational motions that the proposed 4-DOF ER haptic master integrated with the SMC can provide an effective haptic control performance for MIS applications. © 2013 IOP Publishing Ltd.

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