• Journal of Power System Engineering
• /
• v.14 no.2
• /
• pp.34-39
• /
• 2010

Recently, technical trend for machine tools is focused on enhancement of speed and accuracy. High speedy processing causes thermal and structural deformation of objects from the machine tools. Water cooler has to be applied to machine tools to reduce the thermal negative influence with accurate temperature controlling system. Existing On-Off control type can't control temperature accurately because compressor is operated and stopped repeatedly and causes increment of power consumption and decrement of the expected life of compressor. The goal of this study is to minimize temperature error in steady state. In addition, control period of an electronic expansion valve were considered to increment of lifetime of the machine tools and quality of product with a water cooler. PI controller is designed using type of hot-gas bypass for precise control of temperature. Gain of PI is decided easily by method of critical oscillation response, excellent performance of control is shown with 4.24% overshoot and ${\pm}0.2^{\circ}C$error of steady state. Also, error range of temperature is controlled within $0.2^{\circ}C$although disturbance occurs.

• 제어로봇시스템학회:학술대회논문집
• /
• 2004.08a
• /
• pp.1006-1011
• /
• 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.

• Proceedings of the SAREK Conference
• /
• 2009.06a
• /
• pp.961-966
• /
• 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.

• Journal of Institute of Control, Robotics and Systems
• /
• v.3 no.2
• /
• pp.162-168
• /
• 1997

Digital variable structure controller(DVSC) is implemented to control the temperature for the hot water heating circulating pump control system. For the DVSC, a control algorithm is suggested, which using a nonlinear sliding surface and a PID sliding surface outside and inside of steady state error boundary layer, respectively. Smith predictor algorithm is used for the compensation of long dead time. The DVSC of the suggested algorithm yields improved control performance compared with the one of existing algorithm. The system responses with the suggested DVSC shows good responses without overshoot and steady state error inspite of heating load change. By decreasing sampling time, dead time and rise time are increasing, and system output noise by flow dynamics is amplified.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.7 no.4
• /
• pp.461-468
• /
• 1983

The series of experiments have been performed to study the transient heat transfer in air from a suddenly heated vertical thin wire. A platinum wire has been used as a resistance thermometer as well as a heating element to eliminate the disturbances in the measurements. The measured temperature as a function of time is compared with the calculated transient temperature with the aid of a pure conduction equation. The overshoot phenomena in terms of the Nusselt numbers have been detected and it is reasonable to define the delay time at which the onset of convection heat transfer occurs. The measured data are compared with the existing steady-state data and the agreements are reasonable within the comparable ranges.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.1757-1760
• /
• 2005

This paper is concerned with spring back after sheet forming of bulk amorphous alloys in the super cooled liquid state. The temperature-dependence and strain-rate dependence of Newtonian/non-Newtonian viscosities as well as the stress overshoot/undershoot behavior of amorphous alloys are reflected in the thermo-mechanical Finite Element simulations. Hemispherical deep drawing operations are simulated for various forming conditions such as punch velocity, die corner radius, friction, blank holder force, clearance and initial forming temperature. Here, spring back by an instantaneous elastic unloading was followed by thermal deformation during cooling and two modes of spring backs are examined in detail. It could be concluded that the superior sheet formability of an amorphous alloy can be obtained by taking the proper forming conditions for loading/unloading.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2003.10a
• /
• pp.257-260
• /
• 2003

Dynamic simulation program for a smart UAV turbojet engine was developed. The transient simulation program utilized the CMP(Constant Mass flow) method and Euler integration method for integration of excess torque. The transient performance analysis was carried out by increasing from the idle to the maximum rotational speed of the gas generator. To observe engine dynamic behavior, fuel flow was monitored through a step and a ramp increase. When the fuel was increased as a step function the overshoot of the turbine inlet temperature exceeded the limit temperature.

• Transactions of Materials Processing
• /
• v.13 no.8
• /
• pp.696-703
• /
• 2004

The purpose of this study is to examine the bulk/sheet forming characteristics of bulk amorphous alloys in the super cooled liquid state. Recently it is reported that amorphous alloys exhibit stress overshoot/undershoot and non-Newtonian behaviors even in the super cooled liquid state. The stress-strain curves with the temperature-dependences as well as strain-rate dependence of Newtonian/non-Newtonian viscosities of amorphous alloys are obtained based on the previous experimental works. Then, those curves are directly used in the thermo-mechanical finite element analyses. Upsetting and deep drawing of amorphous alloys are simulated to examine the effects of process parameters such as friction coefficient, forming speed and temperature. It could be concluded that the superior formability of an amorphous alloy can be obtained by taking the proper forming conditions.

• Journal of IKEEE
• /
• v.3 no.1 s.4
• /
• pp.109-117
• /
• 1999

This paper describes the quick and precise control of the wafer temperature essential in rapid thermal processing(RTP). The bang-bang plus PID controller structure is introduced to satisfy rapid ramp-up rate and reduce overshoot and steady state error. The controller employs the PID action when the magnitude of the error between reference signal and the output temperature signal is smaller than some prescribed value. To find PID gains, the plant(autoregressive) model is first identified and Kappa-Tau tuning rule is used. The developed controller is applied to experimental RTP apparatus, and performances are evaluated.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.56 no.3
• /
• pp.604-610
• /
• 2007

Injection molding is the most common method of shaping plastic resins for manufacturing a variety of parts. This injection molding is accomplished by injection molding machines (IMM) which consists of a hewer, a reciprocating screw, barrel assembly, and an injection nozzle. The plastic resin is fed to the machine through the hopper and it should be heated to the target melting temperature, which depends on material properties, as closely as possible with very small temperature overshoot in the barrel. Since the barrel, which has temperature dependent specific heat and thermal conductivity in the operating temperature range, is heated by the several electric heater bands, it is not an easy task to control the temperature of the barrel owing to the interference of neighboring heaters and its material properties. Though PID controller with auto-tuning capability is widely adopted in the nm, the auto-tuning process should be carried out whenever the operating temperature is changed significantly. Recently, though the predictive controller is developed and shows good performance, it has drawbacks: 1. Since the heat transfer modeling process is very complicated and should be carried out again when the barrel is changed, it is somewhat inappropriate in the field. 2. The controller performance is not validated in whole operating temperature range. In this paper, cascade type simple PI controller with input restriction is proposed to find the possibility of controlling the barrel temperature in the whole operating temperature range. It is shown by experiment that the proposed controller shows good performance. This result can be applied to design of PI controller with auto-tuning capability.