• Journal of the Korean Society for Precision Engineering
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• v.18 no.2
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• pp.119-125
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• 2001

This paper presents an experimental study on active control of self-excited vibration for a high speed turbomachinery. In order to suppress the self-excited vibration, it is necessary to actively control the air film pressure or the air film thickness. In this study, active pads are used to control the air film thickness. Active pads are supported by pivots containing piezoelectric actuators and their radial position can be actively controlled by applying voltage to the actuators. The transfer characteristics from actuator inputs to shaft vibration outputs are experimentally investigated. In a tilting-pad gas bearing (TPGB), a shaft is supported by the pressurized air film. Four gap sensors were used to measure the vibration of the shaft and PID was used in the feedback control of the shaft vibration. The experimental results show that the self-excited vibration of the rotor can be effectively suppressed if the PID controller gains are properly chosen. As a result we find that the feedback control is effective for suppressing the self-excited vibration of a rotor system using stack-type PZT actuators.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.5
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• pp.614-622
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• 2011

An internal lobe pump is suitable for oil hydraulics of machine tools, automotive engines, compressors, constructions and other various applications. In particular, the pump is an essential machine element of an automotive engine to feed lubricant oil. The subject of this paper is the theoretical analysis of internal lobe pump whose the main components are the rotors: usually the outer one is characterized by lobe with multiple profile(ellipse1, involute and ellipse2) shapes, while the inner rotor profile is determined as conjugate to the other. Also, the design of outer rotor depends on new applications with removing carryover phenomenon. The system generates new lobe profile and calculates automatically the flow rate and flow rate irregularity according to the lobe profile generated. In order to obtain rotor shapes in performance and to find optimize the design parameters, a Taguchi method is proposed in this paper. Results obtained from the analysis enable the designer and manufacturer of oil pump to be more efficient in this field.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.319-324
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• 2003

In general industrial rotating machinery is operated under 3,600 rpm as rotating speed and designed to have critical speed that is above operating speed. So, there was no problem to operate rotating machine under critical speed. But nowadays, they should be operated more than the frist critical speed as usual with the trend of high speed, large scale and hish precision in industries. In case of the large rotor assembly as the trend of large scale, using fitting method of disk or cylinder on shaft is rising for the convenience of assembly and cutting down of manufacturing cost. The shrink fitting is used to assemble lamination part on shaft for manufacturing of rotor of motor or generator in many cases and also is widely used for other machinery. In rotating system, which is compose of rotor and bearing, the critical speed is determined from inertia and stiffness for the rotor and bearings. In case of fitting assembly, analysis and design of the rotor is not easy because the rotor stiffness is determined depend on a lot of factors such as shaft material/dimension, disk material/dimension and assembled interference etc. Therefore designer who makes a plan for hish-speed rotating machine should design that the critical speed is located out of operating range, as dangerous factors exist in it. In order to appropriate design, an accurate estimation of stiffness and damping is very important. The stiffness variation depend on fitting interference is a factor that changes critical speed and if it's possible to estimate it, that Is very useful to design rotor-bearing system. In this paper, the natural frequency variation of the rotor depends on fitting interference between basic shaft and cylinder is examined by experimentation. From the result, their correlation is evaluated quantitatively using numerical analysis that is introduced equivalent diameter end the calculation criteria is presented for designer who design fitting assembly to apply with ease for determination of appropriate interference.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.137-138
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• 2012

본 연구에서는 가스터빈 압축기 로터용 제작 관통볼트의 건전성 검사가 수행됐다. 육안검사, 치수, 재질, 경도 및 피닝처리 등을 검사했으며 GE 볼트와 비교해 건전성을 판단하였다. 평가 결과 제작볼트는 기준범위 이하의 피닝강도로 처리되었다. 이에 숏피닝 강도를 향상시켜 다시 제작된 수정볼트를 재검사했고 모든 항목에서 기준범위에 포함됨을 확인했다. 궁극적으로 본 연구에서 수행된 가스터빈 압축기 로터용 관통볼트의 건전성 검사가 유효함을 확인하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.65-68
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• 2002

In a high speed spindle system, it is very important to monitor the state of rotating rotor. Particularly in active control spindle system, the position sensor must provide feedback to the control system on the exact position of the rotor. In order to monitor the state of a high speed spindle exactly, High accuracy and wide frequency bandwidth of sensors are important. This paper describes the factors which has an effect on performances of inductive position sensor. We also report the experimental results that characterize the performances of the inductive position sensor.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.212-216
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• 2004

Bearingless motors are the rotational electric machine which utilize a common magnetic structure for rotation and magnetic suspension. Since the bearing function is combined with the motor, the shaft length can be shortened resulting in higher critical speeds. Relationship between suspension force and current of bearingless motor is clearly derived by prior research. However, relationship between displacement of rotor and suspension force is not precisely defined. In this paper, we present model of bearingless motor describing the radial force variation due to the movement of the rotor. Using a distributed magnetic circuit and maxwell stress tensor, we derived a mathematical expression for the radial force. For a slotless bearingless motor, we are able to find an analytical model presented in the form of stiffness. For a slotted motor, we can compute the stiffness by semi-analytical analysis. This model is validated by a finite-element-analysis.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.470-473
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• 1995

There exist two critical in application of the magnetic bearing system. One is the control axis interference caused by gyroscopic effect and the other is the vibration caused by the unbalance on the rotor. To solve both problems at the same time, first, a centralized full-state feedback controller based on the LQR control theory was designed to compensate for the gyroscopic effect. Second, disturbance rejection control input based on the observer was designed to avoid the vibration causer by the unbalanced rotor. Balancing input computer accroding to LQR and output of the observer were derived in term of rotational speed. Effectiveness of the on-line balancing was verified through numerical simulation. The developed observer-based controller was also applied to the linear and nonlinear magnetic bearing systems.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.355-360
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• 1995

In order to align the shaft, the dialgauge method has used as a means of solution until now. The method using a dialgauge require a great deal of labour and money due to making by hand, the accurate alignmentis not up to the expectation. For aligning the shaft, all the rotor must come to accord. It means that the moment of the point of coupling must keep being "Zero". The ideal measurement method as to material on the zero is used by straingauge which can gauge the moment at any point of the shaft. Also, the dialgauge method cannot be compared with straingauge measurement method, form the viewpoint, which can gauge in short time.hort time.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.769-772
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• 1995

Most turbo machines, which operate at high speeds, such as gas turbines, jet engines, pumps, and compressors are prone to perrturbing vibrations. The best vibration control method for rotors is to eliminate destabilizing factors. Careful balancing application of "more stable" oil-lubricated bearing, such as tilting pad bearings or use of anti-swirl devices in seals, are examplse of passive vibration control methods. the use of magnetic bearing is an active control method. An obvious advantage of active control is that it provides damping (or modifies system stiffness or other parameters) only when there is a need for that, i.e., in emergency states, while not affecting the rotor normal operational conditions. Moreover, active control methods provide exact position control through on-line control. In this study, a magnetic actuator, digital contrliier using DSP, and bipolar operational power supply/amplifiers were developed to show the effectiveness of reducing robot vibration. Also the curve fitting procedure to obtain the transfer function of frequency dependent component was developed. Results presented in this dissertation will provide a well-defined technical parameters in designing magnetic damper system.er system.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.229-232
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• 1997

In this paper, the case study of reducing rotational errors is done for a grinding spindle with an active magnetic bearing system. The rotational errors acting on the magnetic bearing spindle are due to mass unbalance of rotor, runout, grinding excitation and unmodeled nonlinear dynamics of electromagnets. For the most case, the electrical runout of sensor target is big even in well-finished surface; this runout can cause a rotation error amplified by feedback control system. The adaptive feedforward method based on LMS algorithm is discussed to compensate this kind of runout effects, and investigated its effectiveness by numerical simulation and experimental analysis. The rotor orbit size in both bearings is reduced about to 5 pin due to lX rejection by feedforward control up to 50,000 rpm.