Browsing by Author "Yeh, SS"

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A new approach to biaxial cross-coupled control
(2000)
Yeh, SS
;
Hsu, PL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Cross-coupled control (CCC) has been developed to improve contouring performance for biaxial contour motion systems. However, it is complicated to apply the CCC to arbitrary contour motion because additional calculations are required to obtain the variable cross-coupling gains. In this paper, a new approach to CCC is proposed to efficiently reduce the computation of cross-coupling gains for arbitrary contour commands. According to the analysis of variable gain cross-coupled control, the magnitude and direction of the contouring error can be used to determine the value and direction to be applied in contour compensation for each axis. Thus, the contouring error vector is used here to derive the new CCC approach. The estimated contouring error vector is defined as a vector from the actual position to the nearest point of the line that passes through the reference position tangentially. Thus, the implementation of CCC becomes much more direct with only one simple formulation for cross-coupling gains. Finally, the experimental results on a CNC machining center show that the proposed CCC approach efficiently reduces the contouring error during arbitrary contour motion. Moreover, the calculations required to obtain the variable gains of the CCC are significantly reduced.
Adaptive-feedrate interpolation for parametric curves with a confined chord error
(2002-03-01)
Yeh, SS
;
Hsu, PL
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電控工程研究所
;
Institute of Electrical and Control Engineering
Recently, modern manufacturing systems have been designed which can machine arbitrary parametric curves while greatly reducing data communication between CAD/CAM and CNC systems. However, a constant feedrate and chord accuracy between two interpolated points along parametric curves are generally difficult to achieve due to the non-uniform map between curves and parameters. A speed-con trolled interpolation algorithm with an adaptive feedrate is proposed in this paper. Since the chord error in interpolation depends on the curve speed and the radius of curvature, the feedrate in the proposed algorithm is automatically adjusted so that a specified limit on the chord error is met. Both simulation and experimental results for non-uniform rational B-spline (NURBS) examples are provided to verify the feasibility and precision of the proposed interpolation algorithm. (C) 2001 Elsevier Science Ltd. All rights reserved.
An optimal and adaptive design of the feedforward motion controller
(1999-12-01)
Yeh, SS
;
Hsu, PL
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電控工程研究所
;
Institute of Electrical and Control Engineering
The zero phase error tracking controller (ZPETC) in motion control, as proposed by Tomizuka et at, renders the desirable zero phase error, but with a limited gain response, Moreover, a ZPETC, which is basically in a feedforward control structure, is very sensitive to modeling error, To improve the tracking accuracy of the ZPETC, this paper presents an optimal ZPETC design with a concise polynomial digital prefilter (DPF), The parameters of this well-designed DPF are obtained through the derived L-2-norm optimization. By cascading the developed DPF to the ZPETC, the resultant optimal ZPETC greatly improves the bandwidth of the tracking control systems while maintaining the zero phase error. Compared with other optimal approaches, the present design leads to much simpler procedures and fewer computations. Furthermore, the proposed optimal ZPETC can be adequately implemented as an adaptive ZPETC by including real-time estimation technique to cope with the external load perturbation and parameter variation, Compared with the other adaptive approaches, the optimal concept is used in the present adaptive ZPETC; and it also renders more accurate results because of its improved magnitude response. Experimental results on a de servo table with different controllers indicate that when there is no loading, the present optimal ZPETC achieves the best tracking performance. Moreover, the adaptive ZPETC achieves the most satisfactory results when an external load is applied.
Analysis and design of integrated control for multi-axis motion systems
(2003-05-01)
Yeh, SS
;
Hsu, PL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In modem manufacturing, the design of multi-axis motion controllers for high-speed/high-precision and complex machining is becoming more critical. In the past, controllers for each axis were, in general, designed individually to obtain desirable tracking accuracy. Although some advanced motion control algorithms have been developed recently, they are mostly applicable to single-axis or biaxial systems. In particular, the design of two-axis integrated control, which includes: 1) feedback loops; 2) feedforward loops; and 3) the cross-coupled control (CCC), achieves significantly improved performance. However, its applications are limited to basic linear and circular contour commands for two-axis systems only. In this paper, system analysis for the multi-axis integrated control structure is proposed in order to achieve tracking and contouring accuracy simultaneously. With the derived contouring error transfer function (CETF), the integrated control design for multi-axis motion systems can be formulated simply as a single-input-single-output (SISO) design. Thus, a robust design with desirable performance for multi-axis motion systems can then be achieved straightforwardly. Moreover, by estimating the contouring error vector, the proposed multi-axis integrated control can be widely applied to general contour commands. Experimental results on a three-axis CNC machining center indicate that both tracking,and contouring accuracy are simultaneously improved by applying the proposed control design.
Analysis and design of the integrated controller for precise motion systems
(1999-11-01)
Yeh, SS
;
Hsu, PL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Recently, feedforward controllers like zero phase error tracking controllers (ZPETC's) and cross-coupled controllers (CCC's) have been developed to effectively reduce tracking error and contouring error, respectively. This paper proposes an integrated controller which combines ZPETC and CCC to achieve both tracking and contouring accuracy. Furthermore, studies indicate that ZPETC and CCC can be designed separately in the present integrated control design, In the provided experimental setup with a servo table, an optimal ZPETC and a robust CCC based on the contouring error transfer function (CETF) were designed to achieve desirable frequency responses and stability, Experimental results show that the proposed integrated controller renders significantly improved accuracy in both tracking and contouring.
Design of precise multi-axis motion control systems
(2000)
Yeh, SS
;
Hsu, PL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In this study, to achieve the multi-axis cross-coupled control (CCC) to render contouring accuracy for arbitrary contour commands, the estimated contouring error vector which is constructed by the tracking error vector and the normalized tangential vector of the trajectory is proposed. Furthermore. this paper introduces the integrated motion systems which combine the feedback loops, the feedforward loops, and the multi-axis CCC to achieve both well tracking and contouring performances. The complete system analysis and the novel formulation of the contouring error transfer function (CETF) for multi-axis systems are also provided to efficiently design the integrated controller. Both motion performance of the resultant tracking and contouring accuracy, and the robustness of desirable stability margins can be thus directly achieved. Experimental results on a 3-axis CNC machine are also provided to prove the validity of the present control design.
Electron-phonon-impurity interference effect in disordered Au56Pd44 and IrO2 thick films
(2005-07-01)
Yeh, SS
;
Lin, JJ
;
Jing, XN
;
Zhang, DL
;
電子物理學系
We have fabricated a series of Au56Pd44 thick films with a wide range of residual resistivity rho(0) varying from 40 to 280 mu Omega cm. The resistivities of these films were measured between 15 and 300 K. We found that at temperatures below about 0.1 theta(D) (theta(D) is the Debye temperature), the interference mechanism between the elastic electron scattering and electron-phonon scattering (the electron-phonon-impurity interference effect) contributes significantly to the measured resistivities. Our results support the current theoretical idea that this interference-mechanism-induced resistivity varies with rho(0)T(2), where T is the temperature. Similar observation has also been made in disordered, conducting transition-metal oxide IrO2 thick films.
Estimation of the contouring error vector for the cross-coupled control design
(2002-03-01)
Yeh, SS
;
Hsu, PL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
In biaxial motion systems, applying the cross-coupled control (CCC) significantly improves contouring accuracy for linear and circular contours. As geometrical and parametric curves become more popular in modern manufacturing, machining processes with multiaxis motion systems are required, however, the available biaxial CCC cannot be directly applied to arbitrary contours with multiaxis machining systems. In this paper, we propose a novel approach for arbitrary contours by estimating the contouring error vector to efficiently determine the variable gains for CCC. Experimental results for a biaxial motion system indicate that the proposed approach efficiently yields variable gains similar to those in traditional CCC. Furthermore, results on a three-axis CNC machining center show that the present approach significantly improves motion accuracy in multiaxis motion systems.
Optimization of the growth of the InGaP etch-stop layer by MOVPE for InGaP/GaAs HBT device application
(2006-03-15)
Hsieh, YC
;
Chang, EY
;
Yeh, SS
;
Chang, CW
;
Luo, GL
InGaP has high etching selectivity to GaAs. It can be used as the etch-stop layer to easily fabricate the InGaP/GaAs heterojunction bipolar transistors (HBTs). This process will also increase the uniformity and manufacturability of the HBT devices. However, the InGaP etch-stop layer will increase the energy barrier height that electrons have to overcome flowing from the collector to the subcollector, which will decrease the DC current gain of the device (T. Kobayashi, K. Taira, F. Nakamua, H. Kawai, J. Appl. Phys. 65 (1989) 4898). Therefore, the InGaP etch-stop layer has to be thin enough not to affect the device performance. But the spontaneous formation of the InxGa1-xAsyP1-y intermixing layer between GaAs/InGaP during the metal organic vapour-phase epitaxy (MOVPE) growth will affect the InGaP layer thickness needed as an effective etch-stop layer. In this paper, very thin InGaP layer was achieved with the suppression of InxGa1-xAsyP1-y formation by the optimization of the growth temperature and the gas switching sequence time. An effective 20 angstrom InGaP etch-stop layer was grown at 575 degrees C with interruption time of 3 s. Both STEM and PL data proved that the intermixing InxGa1-xAsyP1-y layer was eliminated and from the selective etching experiment, this 20 angstrom InGaP layer can stand 45 s etching by the H3PO4:H2O2:H2O = 1:1:20 solution. (c) 2005 Elsevier B.V. All rights reserved.
Perfectly matched feedback control and its integrated design for multiaxis motion systems
(2004-09-01)
Yeh, SS
;
Hsu, PL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
For motion systems with multiple axes, the approach of matched direct current gains has been generally, adopted to improve contouring accuracy under low-speed operations. To achieve high-speed and high-precision motion in modern manufacturing, a perfectly matched feedback control (PMFBC) design for multiaxis motion systems is proposed in this paper. By applying stable pole-zero cancellation and including complementary zeros for uncancelled zeros for all axes, matched dynamic responses across the whole frequency range for all axes are achieved. Thus, contouring accuracy for multiaxis systems is guaranteed for the basic,feedback loops. In real applications, the modeling error is unavoidable and the degradation and limitations of the model-based PMFBC exist. Therefore, a newly designed digital disturbance observer is proposed to be included in the proposed PMFBC structure for each axis to compensate,for undesirable nonlinearity and disturbances to maintain the matched dynamics among all axes for the PMFBC design. Furthermore, the feedforward control loops zero phase error tracking controller are employed to reduce tracking errors. Experimental results on a three-axis CNC machining center indicate that both contouring accuracy and tracking accuracy are achieved by applying the present PMFBC design.
The speed-controlled interpolator for machining parametric curves
(1999-04-30)
Yeh, SS
;
Hsu, PL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
Modern CNC systems are designed with the function of machining arbitrary parametric curves to save massive data communication between CAD/CAM and CNC systems and improve their machining quality. Although available CNC interpolators for parametric curves generally achieve contouring position accuracy, the specified feedrate, which dominates the quality of the machining processes, is not guaranteed during motion. Recently, some approximation results concerning motion speed have been reported [Shpitalni M, Koren Y, Lo CC. Computer-Aided Design 1994;26(11):832-838; Bedi S, Ali I, Quan N. Trans ASME J Engng Industry 1993;115:329-336; Chou JJ, Yang DCH. Trans. ASME J Engng Industry 1991;113:305-310; Chou JJ, Yang DCH. Trans ASME J Engng Industry 1992;114:15-22]. In this paper, by deriving a compensatory parameter, the proposed interpolation algorithm has significantly improved curve speed accuracy. In real applications, the proposed algorithm results in: (1) constant speed: and (2) specified acceleration and deceleration (ACC/DEC) to meet the feedrate commands. The motion accuracy and feasibility of the present interpolator have been verified with a provided non-uniform rational B-spline (NURBS) example. (C) 1999 Elsevier Science Ltd. Ail rights reserved.
Theory and applications of the robust cross-coupled control design
(1999-09-01)
Yeh, SS
;
Hsu, PL
;
電控工程研究所
;
Institute of Electrical and Control Engineering
The cross-coupled control (CCC) has been recognized as an efficient motion controller that reduces contouring errors, but theoretical analysis of it is lacking and there is no systematic design approach for obtaining a CCC system with guaranteed central performance. Consequently, the compensators C in CCC are commonly implemented in a PID structure and their contouring accuracy is usually degraded in real applications under different operating conditions. In an attempt to overcome the CCC design limitations described above, this paper introduces a robust CCC design based on a novel formulation: the contouring error transfer function (CETF) leading to an equivalent formulation as in the feedback control design problem. Then, methods in robust control design can be readily employed to achieve robust CCC,vith specified stability margins and guaranteed contouring performance. Furthermore, the proposed design has been verified as being internally stable. All provided experimental results indicate that the proposed robust CCC design consistently renders satisfactory contouring accuracy under different operating conditions.