• Title/Summary/Keyword: Contouring accuracy

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Improvement of Corner Contouring Accuracy of CNC Servo Systems with Communication Delay (통신지연을 갖는 CNC 서보 시스템에 대한 모서리 윤곽정확도 향상)

  • Lim, Jong-Hyup;Jee, Sung-Chul
    • Journal of the Korean Society for Precision Engineering
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    • v.28 no.2
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    • pp.168-175
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    • 2011
  • Contouring accuracy of CNC machine tools is very important for high-speed and high-precision machining. In particular, large contour error may occur during corner tracking. In order to reduce the corner contouring error, acceleration and deceleration control or tool-path planning methods have been suggested. However, they do not directly control the corner contouring error. In the meantime, network servo systems are widely used because of their easiness of building and cost effectiveness. Communication latency between the master controller and servo drives, however, may deteriorate contouring accuracy especially during corner tracking. This paper proposes a control strategy that can accurately calculate and directly control the corner contouring error. A prediction control is combined with the above control to cope with communication latency. The proposed control method is evaluated through computer simulation and experiments. The results show its validity and usefulness.

Positioning Control through a Trade-off between Tracking Error and Contour Error for a Feed Drive System in CNC Milling Machine (추적오차 및 윤곽오차의 상호 절충을 통한 CNC 밀링머신 이송장치의 위치제어)

  • Gil Hyeong-Gyeun;Yang Ho-Suk;Lee Gun-Bok
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.14 no.6
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    • pp.1-7
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    • 2005
  • This paper deals with the position control for a feed drive system in CNC milling machine. The study shows that reduction in tacking error does not necessarily increase contouring accuracy, and proposes that a proper control scheme is able to exhibit the optimal tracking and contouring accuracy. The proposed scheme is to fix the parameter of the contouring control, and to find the optimal value of the parameter of the tracking control, which is automatically tuned. The effectiveness of the proposed scheme is confirmed through simulations.

An Integrated Approach to the Analysis and Design of a Three-Axis Cross-Coupling Control System

  • Jee, Sung-Chul;Lee, Hak-Chul
    • International Journal of Precision Engineering and Manufacturing
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    • v.8 no.2
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    • pp.59-63
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    • 2007
  • We propose a controller design analysis for a cross-coupling control system, which is essential for achieving high contouring accuracy in multi-axis CNC systems. The proposed analysis combines three axial controllers for each individual feed drive system together with a cross-coupling controller at the beginning of the design stage in an integrated manner. These two types of controllers used to be separately designed and analyzed since they have different control objectives. The proposed scheme is based on a mathematical formulation of a three-dimensional contour error model and includes a stability analysis for the overall control system and a performance analysis in terms of contouring and tracking accuracy at steady state. A computer simulation was used to demonstrate the validity of the proposed methodology. The performance variation was investigated under different operating conditions and controller gains, and a design range was elicited that met the given performance specifications. The results provide basic guidelines in systematic and comprehensive controller designs for multi-axis CNC systems. A cross-coupling control system was also implemented on a PC-based three-axis CNC testbed, and the experimental results confirmed the usefulness of the proposed control system in terms of contouring accuracy.

Optimal Control for Synchronizing Positions of Multi-Axis Driving System with Cross-Coupled Structure (다축 구동 시스템의 교차식 구조를 이용한 최적 위치동기 제어)

  • 주백석;김성수;홍대희;박진무;조태연
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2001.04a
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    • pp.271-274
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    • 2001
  • The present paper deals with the development of digital contouring controller for multiaxial servosystem. Instead of coordinating the commands to the individual feed drives and implementing closed position loop control for each axis, this work is achieved by the evaluation of a optimal cross-couple compensator aimed specifically at improving contouring accuracy in multi-axial feed drives. The optimal control formulation explicitly includes the contour error in the performance index to be minimized. The contouring control is simulated for straight line. The results show that the proposed controller reduces contouring errors considerably, as compared to the conventional uncoupled control for biaxial systems.

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Contour Control Algorithm for Parallel Machine Tool (병렬형 공작기계를 위한 윤곽제어 알고리즘)

  • 이승환;홍대희;최우천;송재복
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2002.10a
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    • pp.1003-1006
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    • 2002
  • In machining free-form curves with a machine tool equipped with parallel device, improving contouring accuracy is very important. In this paper, we present contouring control algorithm far parallel machine tool. The relation between the error in Joint space and the error in catesian space is evaluated, and we estimate contouring error vector which efficiently determines the variable gains for the cross coupled control. To show the validity of the algorithm, the contouring control is simulated for free form contour trajectory in cubic parallel machine tool model.

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Optimal Tuning of Biaxial Servomechanisms Using a Cross-coupled Controller (상호결합제어기를 이용한 2축 서보메커니즘의 최적튜닝)

  • Bae Ho-Kyu;Chung Sung-Chong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.10 s.253
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    • pp.1209-1218
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    • 2006
  • Precision servomechanisms are widely used in machine tool, semiconductor and flat panel display industries. It is important to improve contouring accuracy in high-precision servomechanisms. In order to improve the contouring accuracy, cross-coupled control systems have been proposed. However, it is very difficult to select the controller parameters because cross-coupled control systems are multivariable, nonlinear and time-varying systems. In this paper, in order to improve contouring accuracy of a biaxial servomechanism, a cross-coupled controller is adopted and an optimal tuning procedure based on an integrated design concept is proposed. Strict mathematical modeling and identification process of a servomechanism are performed. An optimal tuning problem is formulated as a nonlinear constrained optimization problem including the relevant controller parameters of the servomechanism. The objective of the optimal tuning procedure is to minimize both the contour error and the settling time while satisfying constraints such as the relative stability and maximum overshoot conditions, etc. The effectiveness of the proposed optimal tuning procedure is verified through experiments.

Design of a 3-Axis Cross-Coupling Control System Considering Both Contouring and Tracking Performance (윤곽제어 및 위치추종 성능을 고려한 3축 연동제어 시스템 설계)

  • Lee H.;Jee S.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2006.05a
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    • pp.137-138
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    • 2006
  • This paper proposes a controller design analysis for three-axis CNC systems considering both contouring and tracking performance. The proposed analysis inclusively combines axial controllers for each individual feed drive system together with cross-coupling controller at the beginning design stage as an integrated manner. These two controllers used to be separately designed and analyzed since they have different control objectives. The proposed scheme includes a stability analysis for the overall control system and a performance analysis in terms of contouring and tracking accuracy. Computer simulation is performed and the results show the validity of the proposed methodology.

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5-Axis Cross-Coupling Control System Based on a Novel Real-Time Tool Orientation Error Model (새로운 실시간 공구방향오차 모델에 기초한 5 축 연동제어 시스템)

  • Byun, Je-Hyung;Jee, Sung-Chul
    • Journal of the Korean Society for Precision Engineering
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    • v.27 no.8
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    • pp.48-53
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    • 2010
  • 5-axis CNC machining now is getting popular because it can deal with complex shapes such as impeller, turbine blade and propeller without additional equipment or process, proving a set of various tool orientations. CAM software related to 5-axis machining is being developed quickly so that users can take advantage of potential capacities of 5-axis machine tools. However, only a few researches can be found in the area of control strategy development for 5-axis machining. This paper proposes a 5-axis cross-coupling control system based on a novel tool orientation error model. The proposed tool orientation error model provides accurate information on the tool orientation error in real time, which in turn enables directly controlling the tool orientation accuracy. The proposed control system also employs a contour error model to calculate the contour error and reflect it in the control as well. The accuracy of the proposed tool orientation error model is verified and the performance of the 5-axis cross-coupling control system in terms of both contouring and tool orientation accuracy is evaluated through computer simulations compared with existing 5-axis control systems.