• Journal of Drive and Control
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• v.15 no.4
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• pp.55-60
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• 2018

Force-controlled electro-hydrostatic actuators have to exhibit high backdrivability, to quickly compensate for force control errors caused by externally disturbed rod movement. To obtain high backdrivability, the servomotor for driving the hydraulic pump, should rotate exactly to such a revolution to compensate for force control errors, compressing or decompressing cylinder chambers. In this study, we proposed a modified velocity control structure, including a robust internal-loop compensator (RIC)-based velocity controller, for the servomotor to improve backdrivability of a force-controlled EHA. Performance improvement was confirmed experimentally, wherein sinusoidal velocity disturbance was applied to the force-controlled EHA, with constant reference input. Its dynamic force control errors reduced effectively, with the proposed control scheme, compared to test results with a conventional motordriver, for motor velocity control.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.723-725
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• 2004

An iterative robust control design for PZT using Gaussian wavelet networks is proposed. A Gaussian wavelet network with accurate approximation capability is employed to approximate the nonlinear hysteresis dynamics of PZT systems by using an iterative control algorithm. Depending on the finite number of wavelet basis functions which results in unavoidable approximation errors, a robust control law is provided to guarantee the stability of the closed-loop nano positioning system. Finally, the effectiveness of the robust control approach is illustrated through comparative simulations on a PZT.

• International Journal of Control, Automation, and Systems
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• v.3 no.3
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• pp.387-396
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• 2005

The Rotational/Translational Actuator (RTAC) benchmark problem considers a fourth-order dynamical system involving the nonlinear interaction of a translational oscillator and an eccentric rotational proof mass. This problem has been posed to investigate the utility of a rotational actuator for stabilizing translational motion. In order to experimentally implement any of the model-based controllers proposed in the literature, the values of model parameters are required which are generally difficult to determine rigorously. In this paper, an approach to the least-squares estimation of the parameters of a system is formulated and practically applied to the RTAC system. On the other hand, this paper shows how to model a nonlinear system as a linear uncertain system via nonparametric system identification, in order to provide the information required for linear robust $H_\infty$ control design. This method is also applied to the RTAC system, which demonstrates severe nonlinearities, due to the coupling from the rotational motion to the translational motion. Experimental results confirm that this approach can effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.6
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• pp.773-780
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• 1999

A digital tracking controller is proposed for micro electrostatic actuator with input nonlinearity, where disturbance observer is utilized in cooperation with inverse function. Generally the disturbance observer is announced to be robust to modeling uncertainty, and external disturbance. But, when the nonlinearity exists in the systems, the disturbance observer may not directly be applied to that system, because the nonlinearity may destabilize the overall system. Therefore, first, we linearize the nonlinear input characteristics of micro electrostatic actuator by the use of inverse function. Secondly, we apply disturbance observer to approximately linearized system for eliminating the residuals of nonlinearity and the modeling uncertainty. Then, we get the good properties of the disturbance rejection as well as the robustness due to the own nature of disturbance observer. In this case, we propose a sufficient condition for the robust stability of overall systems. Furthermore, we discuss the problem that may be exposed when disturbance observer is applied to the internally stable system with saturation, and analyze two methods to overcome input saturation problem in the sense of internal stability. Simulations have been carried out to show the effectiveness of the proposed controller.

• Proceedings of the IEEK Conference
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• 1999.06a
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• pp.1117-1120
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• 1999

In this paper, we design the H$\infty$ optimal controller satisfying robust stability and performance in spite of the plant uncertainty for an electro-mechanical actuator system and analyze the controller in frequency domain. H$\infty$ optimal controller K was designed using iteration algorithm suggested by DOYLE. Using the controller in an electro-mechanical actuator system, the joint with very small coupling rigidity coefficient was used to vary the control parameter. The plant unstructured uncertainty was assumed to be a multiplicative type.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.11
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• pp.1477-1483
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• 2020

The stability guarantee of wireless network based control systems is still challenging due to the lossy links and node failures. This paper proposes a hierarchical cluster-based network protocol called robust wireless sensor and actuator network (R-WSAN) by combining time, channel, and space resource diversity. R-WSAN includes a scheduling algorithm to support the network resource allocation and a control task sharing scheme to maintain the control stability of multiple plants. R-WSAN was implemented on a real test-bed using Zolertia RE-Mote embedded hardware platform running the Contiki-NG operating system. Our experimental results demonstrate that R-WSAN provides highly reliable and robust performance against lossy links and node failures. Furthermore, the proposed scheduling algorithm and the task sharing scheme meet the stability requirement of control systems, even if the controller fails to support the control task.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.932-937
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• 2002

The polyimide nozzle and silicon restrictor inside a thermal micro actuator have been fabricated using state of the art laser micromachining methods. Numerical models of fluid dynamics inside the actuator chamber and nozzle are presented. The models include fluid flow from reservoir, bubble formation and growth, ejection through the nozzle, and dynamics of refill through restrictor. Since high tapered nozzle and restrictor are very important parameters for overall actuator performance design, a special setup for the beam delivery system has been developed. The effects of variations of nozzle thickness, diameter, taper angles, and restrictor shapes are simulated and some results are compared with the experimental results. It is fecund that the fluid ejection through the thinner and high tapered nozzle is more steady, fast, and robust and the tapered restrictor shows more satisfying refill than the zero taper one.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.1
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• pp.70-75
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• 2010

The objective of this paper is to propose a new velocity measurement method for an electro-mechanical fin actuator. The model of the electro-mechanical fin actuator includes uncertainties such as unknown disturbances and parameter variations in flight condition. So, an electro-mechanical fin actuator system needs robust control algorithm which requires not only position information but also velocity information. Usually, analog tachometers have been used for velocity feedback in an electro-mechanical fin actuator. However, using these types of sensors have problems such as the cost, space, and malfunction. These problems lead to propose a new velocity measurement method using linear type Hall-effect sensor. In order to verify the proposed method, several experiments are performed using Model Following Sliding Mode Controller(MFSMC). It is shown that the MFSMC with a new velocity measurement method using linear type Hall-effect sensor can satisfy the requirements without using of velocity sensor.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.10
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• pp.988-993
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• 2009

In this paper, we deal with a tracking gain-up controller design problem to control effectively the shake of tracking actuator after a track seek. A minimum tracking gain-up open-loop gain can be calculated by estimating the shake of tracking actuator and a desired transient specification is considered to diminish effectively the shake of actuator. A tracking gain-up controller is designed by considering a robust $H_{\infty}$ control problem with a regional stability constraint. The proposed tracking gain-up controller design method is applied to the track-following system of a DVD recording device and is evaluated through the experimental results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.5
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• pp.385-393
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• 2004

This paper proposes a swing-arm type dual-stage actuator, which consists of a PZT actuator for fine motion and a VCM(voice coil motor) for coarse motion, for an SFF ODD(small form factor optical disk drive), in order to achieve fast access speed and precise track-following control. Over the past few decades there have been a lot of researches related to the VCM and dual-stage actuator. In this paper, we focus our attention on the design and control of the PZT actuator. Due to the dual cantilever structure. the PZT actuator can generate precise translational tracking motion at its tip to which an optical pickup is attached. and the effect of hysteric behavior of the PZT element is reduced. The dynamic model of the PZT actuator is derived by using the Hamilton's principle, and verified by comparing it with the experimental frequency response. The sliding mode control is designed in order to be robust against modeling uncertainties. Simulations and experimental results confirm the effectiveness of the suggested control scheme.