• The Journal of Korea Robotics Society
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• v.12 no.2
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• pp.194-205
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• 2017

A redundantly actuated planar 3-degree-of-freedom parallel mechanism is analyzed to show its high application potential as a haptic device. Its structure along with the closed form forward position solutions is briefly discussed. Then its geometric and kinematic characteristics via singularity analysis, the kinematic isotropy index, and the input-output force transmission ratio are investigated both for the redundantly actuated cases and for the non-redundantly actuated case. In addition, comparative joint torque simulations of the mechanism with different number of redundant actuations as well as without redundant actuation are conducted to confirm the improved joint torque distribution characteristics. Through these analyses it is shown that the geometric and kinematic characteristics of the redundantly actuated mechanism are superior to the ones of the mechanism without redundant actuation. Thus, it can be concluded that the suggested planar mechanism with redundant actuation has a very high potential for haptic device applications.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.3
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• pp.74-80
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• 2006

This paper deals with the control and fault monitoring of a DDV hydraulic actuation system. A hydraulic servo system has a nonlinear dynamics of an orifice flow through a valve spool. A full nonlinear model for a DDV actuation system is driven, and linearized to a simple model which is convenient for a control loop and fault monitor design. A top level requirement on the performance and safety for the actuation system is introduced. A control system and fault monitoring structure which can meet these requirements are discussed. A simulation package for a DDV actuation system which has a triplex redundant structure is developed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.3
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• pp.81-86
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• 2006

This paper deals with a driving current fault monitor design methodology for a DDV actuation system which has a dual hydraulic power supply system, and triplex electric control capability. A fault existing among these redundant channels should be detected accurately and removed timely, and the remaining channels are to be reconfigured in order to compensate the role of a removed faulty channel. An integrated analysis on the aerodynamics, flight control laws, and DDV actuation system is essential for the design of an actuation system fault monitor. A method to define a fault transient boundary which specifies a maximum travel of an actuation system caused by the first faulty operation is proposed based on the top level requirement on the fault effect specified in MIL-F-8785C.

• Smart Structures and Systems
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• v.9 no.2
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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.

• 제어로봇시스템학회:학술대회논문집
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• 1995.10a
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• pp.219-222
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• 1995

This paper presents a control law of multiple actuation servo systems. Multiple actuation systems have an ability to solve some difficult engineering problems; Coulomb friction, backlash, and disturbance. This fact is shown by basic experiments as well as theoretical analysis. The proposed control strategy remarkably improves the performance comparing with conventional single actuation systems.

• Journal of computational fluids engineering
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• v.17 no.2
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• pp.85-92
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• 2012

Flows over a square cylinder with and without plasma actuation are numerically investigated to see whether plasma actuation can effectively modify vortex shedding from the cylinder and reduce the drag and lift fluctuations. In this study, a plasma synthetic jet actuator is mounted on the rear side of cylinder as a means of direct-wake control. The effect of plasma actuation is considered by adding a momentum forcing term in the Navier-Stokes equations. Results show that the reduction of mean drag and lift fluctuations is obtained for both steady and unsteady actuation. However, the steady actuation is better than the unsteady one in terms of mean drag as well as drag fluctuations. With the strong steady actuation considered, the interaction of two separating shear layers from rear corners is effectively weakened due to the interference of synthetic jets. It results in a merging of synthetic-jet and shear-layer vortices and the increase of vortex shedding frequency. On the other hand, the unsteady actuation generates pulsating synthetic jets in the near wake, but it does not change the vortex shedding frequency for the actuation frequencies considered in this study.

• Aerospace Engineering and Technology
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• v.7 no.1
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• pp.151-160
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• 2008

In this paper, the analysis results of synthetic resonance characteristics are described for the electrohydraulic thrust vector control actuation system. The synthetic resonance is induced by integration of position servo actuation system on the flexible launch vehicle mounting structure. The new resonance mode is synthesized due to composition of hydraulic resonance for electrohydraulic position servo system with inertia load condition and structural resonance for flexible mounting structure. This synthetic resonance can make stability of control system worse by feedback and amplification of control system. The exact nonlinear analysis model of this phenomenon is developed to predict and design a control algorithm for improvement characteristics. The DPF (Dynamic Pressure Feedback) control algorithm has been designed and has excellent resonance suppression capability.

• Smart Structures and Systems
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• v.13 no.4
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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.

• Journal of Magnetics
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• v.22 no.1
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• pp.155-161
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• 2017

This paper presents a new nonmechanical rehabilitation system driven by magnetic force. Typically, finger rehabilitation mechanisms are complex mechanical systems. The proposed method allows wireless operation, a simple configuration, and easy installation on the hand for active actuation by magnetic force. The system consists of a driving coil, driving magnets (M1), and auxiliary magnets (M2 and M3), respectively, at the finger, palm, and the center of coil. The magnets and the driving coil produce three magnetic forces for an active motions of the finger. During active actuations, magnetic attractive forces between M1 and M2 or between M1 and M3 enhance the flexion/extension motions. The proposed system simply improves the extension motion of the finger using a magnetic system. In this system, the maximum force and angular variation of the extension motion were 0.438 N and $49^{\circ}$, respectively. We analyzed the magnetic interaction in the system and verified finger's active actuation.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.6
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• pp.456-465
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• 2003

It is well-known that bio-systems does not calculate inverse dynamics for trajectory planning, but they move by proper modulation of system impedances. Inspired by bio-systems, a biomimetic trajectory planning method is proposed in this work. This scheme is based on employment of redundant actuation which prevails in bio-systems. We discuss that for the generation of the biomimetic trajectory, intelligent structure of bio-systems plays an important role. Redundant actuation and kinematic redundancy fall into such a category of intelligent structure. The proposed biomimetic trajectory planning modulates the complete dynamic behavior such as natural frequencies and damping ratios by using the intelligent structure. Experimental work is illustrated to show the effectiveness of the proposed biomimetic trajectory planning for a five-bar mechanism with redundant actuators.