• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.451-454
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• 2003

The Oil Coolers is very important unit for the stable thermal performance in machine tools, semiconductor equipments and high precision measuring systems. To select a proper oil cooler for the temperature control of core unit in a machine, not only cooling ability but also static and dynamic sensitivity of temperature sensors are considered. In this paper, the relationship between cooling ability and inflow oil temperature is identified. The cooling ability is increased with the increase of inflow oil temperature. The oil temperature control errors of a cooler are influenced by mainly sensitivity of temperature sensors and heating velocity in a machine. The validity of error cause analysis for temperature control is proved by real cooling experiments with inflow and outflow temperature sensors.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.1006-1011
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• 2004

Recently, technical trend in machine tools is focused on enhancing of speed, accuracy and reliability. Such high speed usually results in thermal displacement and structural deformation. To minimize such thermal effect, most precision machine tools adopt high precision cooling system. This study proposes a temperature control for an oil cooler system using PI control with fuzzy logic. In a cooler system, the refrigerant flow rate is controlled by rotational speed of the compressor, where the outlet oil temperature is selected as the control variable. The fuzzy control rules iteratively correct PID parameters to minimize the error, difference between the outlet temperature and the reference one. Here, the ambient temperature is used as the reference one. To show the effectiveness of the proposed method, a series of experiments are conducted for an oil cooler system of machine tools, and the results are compared with the ones of a conventional PID control. The experimental results show that the proposed method has advantages of smaller overshoot and smaller steady state error.

• 한국공작기계학회논문집
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• 제13권4호
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• pp.87-94
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• 2004

Recently, technical trend in machine tools is focused on enhancing of speed, accuracy and reliability. The high speed usually results in thermal displacement and structural deformation. To minimize the thermal effect, precision machine tools adopt a high precision cooling system. This study proposes a temperature control for an oil cooler system using Pill control with fuzzy logic. In the cooler system, refrigerant flow rate is controlled by rotational speed of a compressor, and outlet oil temperature is selected as the control variable. The fuzzy control rules iteratively correct PID parameters to minimize the error and difference between the outlet temperature and the reference temperature. Here, ambient temperature is used as the reference one. To show the effectiveness of the proposed method, a series of experiments are conducted for an oil cooler system of machine tools, and the results are compared with the ones of a conventional Pill control. The experimental results show that the proposed method has advantages of faster response and smaller overshoot.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.961-966
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• 2009

This paper presents precise temperature control of oil outlet in an oil cooler with hot-gas bypass control as an industrial refrigerator. The control system was designed for obtaining precise temperature control performance even though abrupt disturbances based on flow rate control of hot-gas bypass. PID controller was adopted in feedback control system. We showed that the gain of PID could be easily determined by using gain-tuning methods without any numerical model. Through some experiments, excellent control performances such as overshoot within 1.7%, steady state temperature error within ${\pm}0.1^{\circ}C$ were established by a simple PI controller. We expect that the system can control the target temperature within error of $0.33^{\circ}C$ under abrupt disturbances.

• 동력기계공학회지
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• 제14권6호
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• pp.89-95
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• 2010

This paper deals with design method of proportional-integral(PI) and feedforward controller for obtaining precise temperature and high energy efficiency of oil cooler system in machine tools. The compressor's speed and opening angle of an electronic expansion valve are controlled to keep reference value of temperature at oil outlet and superheat of an evaporator. Especially, the feedforward controller is added to suppress temperature fluctuation under abrupt disturbances. Through some experiments, the suggested method can control the target temperature within steady state error of ${\pm}0.l^{\circ}C$ and maximum overshoot $0.2^{\circ}C$ under abrupt disturbances.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 추계학술대회
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• pp.233-236
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• 2003

In this Paper, the temperature control error and cooling characteristics of inverter typ coolers are evaluated to predict application validity of coolers under heating pattern and amount The temperature control error of coolers small in 15~70% range of the max. cooling ability. At less than 15% of max. cooling ability has the inverter type cooler a basic temperature control error $\pm0.5^{\circ}C$ and acts as on/off type coolers. The inverter type cooler is unsuitable for precision temperature control under the complex heating pattern. But PID control of cooler including the heating system is an alternative for the case.

• 한국정밀공학회지
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• 제26권3호
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• pp.73-80
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• 2009

In accordance with the trend for high-speed multi-axes, and the increasing technical sophistication of machine tools, thermal deformation has become an important factor in the accuracy of machine tools. It was analyzed that thermal deformation error accounts for about 70% of all errors made with machine tools. For precise temperature control, both cooling and heating should be implemented. A hot gas bypass type cooling cycle method has a simplified structure and temperature control accuracy to with in ${\pm}0.1^{\circ}C$. In this study, the performances of oil cooler system, including temperature controllability according to hot gas floe and preset temperature sustainability according to temperature load, were tested. It is expected that this study will contribute to the development and performances of oil cooler system, which could minimize thermal errors and improve the quality of precision machine tools.

• 융합신호처리학회논문지
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• 제14권3호
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• pp.205-211
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• 2013

최근 공작기계 분야에서 가공속도와 가공정밀도 같은 시스템 성능이 한층 요구되고 있다. 특히 가공속도가 증가함에 따라 공작기계와 수가공 분야의 공작물 가공 부위에 유해한 열 발생을 초래하게 된다. 이 열은 가공 정밀도를 저하시키는 주된 원인으로 작용한다. 따라서 온도를 제어하는 오일쿨러는 공작기계에서 필수적이다. 일반적으로 두 가지 대표적인 제어기법인 핫가스 바이패스방식과 압축기 가변속 제어 방식이 오일쿨러에 채택 되었다. 본 논문에서는 공작기계에 사용하는 핫가스 바이패스 오일쿨러의 정밀한 온도특성을 얻기 위한 퍼지 제어기의 설계와 구현 방법을 다룬다. 출구 오일온도를 설정값과 실내온도로 잘 유지하도록 전자팽창밸브의 개도 각도를 제어하였다. 특히, 퍼지 제어기는 갑작스러운 외란에 의한 온도변화를 억제하는 기능을 포함하고 있다. 몇 가지 실험을 통하여 제안한 방법으로 목표 온도를 ${\pm}0.22^{\circ}C$정상상태 오차 이내로 제어할 수 있었다.

• 설비공학논문집
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• 제23권2호
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• pp.111-119
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• 2011

Recently, the performances of speed and accuracy are enhanced in machine tools. The high speed of the machine tools usually causes harmful thermal displacements on the objects. To reduce the thermal displacements, machine tools generally adopt oil coolers with precise temperature control function. This study aims at precise control of oil outlet temperature in the oil coolers with hot-gas bypass manner based on PI control logic. The control system was designed for obtaining steady state error within ${\pm}0.1^{\circ}C$ and maximum overshoot with 0.8% even though abrupt disturbances are added to the system. We showed that the PI gains could be easily decided by numerical simulations using practical transfer function which got experiments. Also, transient characteristics could be improved significantly by reflecting the inlet temperature of an evaporator to the output of a controller feedforwardly considering periodic abrupt disturbances. Through some experiments, excellent control performances were established by the suggested control.

• 설비공학논문집
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• 제28권12호
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• pp.502-508
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• 2016

An optimized PI controller design method is presented to promote the control performance of an oil cooler system for high precision machine tools. First, a transfer function model of the oil cooler system with a variable rotating speed compressor was obtained by the perturbation method as the first order system with a negligible dead time. Then, the closed-loop control system was described as the second order system with a zero. Its dynamic behaviors are mostly governed by characteristic parameters, the damping ratio, and the natural frequency which is incorporated in PI gains. Next, an optimum integral of the time-weighted absolute error (ITAE) criterion was applied to the second order system. The characteristic parameters can be determined by the given design specifications, percent overshoots and settling times and comparisons with the ITAE criterion. Hence, the PI gains were plainly identified in a deterministic way. Finally, the PI gains were fine-tuned to obtain desirable dynamics in real systems, considering the zero effect and parameter variations. The validity of the proposed method was proven by computer simulations and real experiments for selected cases.