• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.29.1-29.1
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• 2008

The temperature control system which is using liquid and gaseous nitrogen has been known as the most economical system to simulate space temperature condition due to relatively not expansive price of the liquid nitrogen (less than 0.2 USD per liter). And, among these systems, the closed loop system which circulates compressed nitrogen gas come from sprayed liquid nitrogen by blower and makes a target temperature with heat from an electrical heater and flow rate of liquid nitrogen is prevail all over the world. But, this complete closed loop system requires expansive equipments such as blower, heater, and liquid nitrogen injector, and special maintenance on the system. Therefore, KARI is developing efficient and simple open loop system which utilizes liquid and gaseous nitrogen with eliminating a special blower and other expansive units. In this study, this open loop system with more efficiency and flexibility will be designed and introduced.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.9
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• pp.805-812
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• 2007

This paper present a robust controller design method based on the estimation of velocity disturbance to construct a robust fine seek control system. A loop gain adjustment algorithm is introduced to accurately estimate the velocity disturbance in spite of the uncertainties of fine actuator. A weighting function is optimally selected from a minimum fine seek open-loop gain, calculated by estimating the velocity disturbance. A robust fine seek controller is designed by considering a robust $H_{\infty}$ control problem using the weighting function. The proposed controller design method is applied to the fine seek control system of a DVD rewritable drive and is evaluated through the experimental results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.5 s.98
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• pp.578-585
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• 2005

In this paper, we present a schematic method estimating the tracking vibration quantity occurring in the track-following system of an optical recording device. A tracking loop gain adjustment algorithm is introduced to estimate accurately the tracking vibration quantity in spite of the uncertainties of the tracking actuator, Accordingly, the tracking vibration quantity can be estimated from the tracking error, the controller output, the nominal actuator model, and a compensated gain. An optimal tracking controller can be designed from a minimum tracking open-loop gain calculated by the estimated tracking vibration quantity The proposed vibration quantity estimation and controller design method are applied to the track-following system of an optical recording device and are evaluated through the experimental result.

• International Journal of Control, Automation, and Systems
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• v.5 no.3
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• pp.243-250
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• 2007

This paper presents a systematic method of estimating a velocity disturbance occurring in the fine seek control system of an optical disk drive. A fine seek loop gain adjustment algorithm is introduced to accurately estimate the velocity disturbance in spite of the uncertainties of the fine actuator. The velocity disturbance can be estimated from a measurable velocity, a fine seek controller output, and a compensated fine actuator model. A robust fine seek controller can be designed by considering a minimum fine seek open-loop gain, calculated by the estimated velocity disturbance. The proposed controller design method is applied to the fine seek control system of a DVD rewritable drive and is evaluated through the experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.90-97
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• 1991

A stepping motor can be driven with open-loop or closed-loop control. The major disadvantage of open-loop control is that it is subjected to resonance and instability in certain speed range, and that there is no way to check stalling or error in position. In this paper, a closed-loop control system consisting of a microcomputer, a hybrid stepping motor, a drive, a lead screw, and an encoder which is used as a position sensor is developed. A control program is programmed in assembly language for real time control and the versatile interface adapter(VIA) is used as the interface with the microcomputer. The experimental results of the stepping motor were eliminated on all kinds of inertia load, and maximum start stop pulse rate and maximum slewing pulse rate were also increased about twice respectively.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.680-684
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• 2005

This paper presents a data-based stability analysis of a MIMO linear time-invariant discrete-time system, as an extension of the previous results for a SISO system. In the MIMO case, a similar discussion as in the case of a SISO system is also applied, except that an augmented input and output space is considered whose dimension is determined in relation to both the orders of the input and output vectors and the numbers of inputs and outputs. As certain subspaces of the input and output space, both output data space and closed-loop data space are defined, which contain all the behaviors of a system, respectively, with zero input in open-loop and with a control input in closed-loop. Then, we can derive the data-based stability conditions, in which the open-loop stability can be checked by using a data matrix whose column vectors span the output data space and the closed-loop stability can also be checked by using a data matrix whose column vectors span the closed-loop data space.

• International Neurourology Journal
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• v.22 no.4
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• pp.228-236
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• 2018

Neuromodulation was introduced for patients with poor outcomes from the existing traditional treatment approaches. It is well-established as an alternative, novel treatment option for voiding dysfunction. The current system of neuromodulation uses an open-loop system that only delivers continuous stimulation without considering the patient's state changes. Though the conventional open-loop system has shown positive clinical results, it can cause problems such as decreased efficacy over time due to neural habituation, higher risk of tissue damage, and lower battery life. Therefore, there is a need for a closed-loop system to overcome the disadvantages of existing systems. The closed-loop neuromodulation includes a system to monitor and stimulate micturition reflex pathways from the lower urinary tract, as well as the central nervous system. In this paper, we reviewed the current technological status to measure biomarker for closed-loop neuromodulation systems for voiding dysfunction.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2A
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• pp.154-167
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• 2006

Today's IEEE 802.11 WLANs(Wireless LANs) provide multiple transmission rates so that different rates can be exploited in an adaptive manner depending on the underlying channel condition in order to maximize the system performance. Many rate adaptation schemes have been proposed so far while most(if not all) of the commercial devices implement a simple open-loop rate adaptation scheme(i.e., without feedback from the receiver), called ARF(Automatic Rate Fallback) due to its simplicity. A key problem with such open-loop rate adaptation schemes is that they do not consider the collision effect, and hence, malfunction severely when many transmission failures are due to collisions. In this paper, we propose a novel rate-adaptation scheme, called CARA(Collision-Aware Rate Adaptation). The key idea of CARA is that the transmitter station combines adaptively the Request-to-Send/Clear-to-Send(RTS/CTS) exchange with the Clear Channel Assessment(CCA) functionality to differentiate frame collisions from frame transmission failures cause by channel errors. Therefore, compared with other open-loop rate adaptation schemes, CATA is more likely to make the correct rate adaptation decisions. Through extensive simulation runs, we evaluate our proposed scheme to show that our scheme yields significantly higher throughput performance than the existing schemes in both static and time-varying fading channel environments.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.10
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• pp.1796-1803
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• 2006

This Paper describes a systematic method for designing the $H_{\infty}$ controller for the inverted pendulum which is a nonlinear and single-input double-outputs system. In particular, the open-loop system is conbined with a pre-filter to shape the open-loop transfer function for the sensitivity function ind the complementary sensitivity function to be kept the desirable frequency characteristics. Consequently, the loop shaping technique of the open-loop transfer function reduces the impacts of the model uncertainties, measurement noises and exogenous disterbances on the dynamic characteristics of the inverted pendulum. The results of simulation and experiment show the efficiency of the proposed control method comparing with conventional PID control method.

• Design & Manufacturing
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• v.15 no.3
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• pp.56-61
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• 2021

The increase in automation facilities in the injection molding industry is a very important process control item. The most important item when constructing an unmanned machine using a take-out robot is the "mold opening stroke" of the mold. The injection molding machine control method is divided into hydraulic type and electric type, and there have been few studies on the mold opening distance according to the control method. In this study, the correlation was confirmed by increasing the injection speed to 20, 50, 80, and 100% for the three types of hydraulic control method, open loop and close loop, and electric control method. Through the experiment, the following results were obtained. (1) It can be seen that the reproducibility is excellent with the electric, close loop, and open loop control methods. (2) When the injection speed is set to 50%, the mold opening distance is 263.10~263.27 mm, which is the most reproducible. (3) As a result of ANOVA, both injection speed and mold opening distance showed a significant difference in the hydraulic control method (p<0.05), but it was verified through experiments that there was no significant difference in the electric control method. Based on these results, when electric control is selected rather than hydraulic control, the reproducibility of the mold opening distance is excellent, so it is thought that the taking-out robot can take the object out of the mold more safely.