Browsing by Author "Lee, AC"

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A modified transfer matrix method for the coupling lateral and torsional vibrations of symmetric rotor-bearing systems
(2006-01-03)
Hsieh, SC
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Chen, JH
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Lee, AC
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機械工程學系
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Department of Mechanical Engineering
This study develops a modified transfer matrix method for analyzing the coupling lateral and torsional vibrations of the symmetric rotor-bearing system with an external torque. Euler's angles are used to describe the orientations of the shaft element and disk. Additionally, to enhance accuracy, the symmetric rotating shaft is modeled by the Timoshenko beam and considered using a continuous-system concept rather than the conventional "lumped system" concept. Moreover, the harmonic balance method is adopted in this approach to determine the steady-state responses comprising the synchronous and superharmonic whirls. According to our analysis, when the unbalance force and the torque with nx frequency of the rotating speed excite the system simultaneously, the (n + 1) x and (n - 1) x whirls appear along with the synchronous whirl. Finally, several numerical examples are presented to demonstrate the applicability of this approach. (c) 2005 Elsevier Ltd. All rights reserved.
A novel cross-coupling control design for Bi-axis motion
(2002-11-01)
Shih, YT
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Chen, CS
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Lee, AC
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機械工程學系
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Department of Mechanical Engineering
A new structure of cross-coupling controller for precise tracking in motion control is proposed in this paper. When compared with the conventional cross-coupling system, this new structure has the advantage that the compensators in CCC have a simpler design process than conventional ones and so does its stability analysis. The proposed compensator (or controller) is evaluated and compared experimentally with a traditional uncoupled controller on a microcomputer controlled dual-axis positioning system. The experimental results show that the new structure of cross-coupling controller remarkably reduces contour error. In addition, this new controller can be implemented easily on a majority of motion systems in use today via reprogramming the reference position command subroutine. (C) 2002 Elsevier Science Ltd. All rights reserved.
Asymptotic stability analysis for collocated direct output feedback control of flexible systems
(1997-12-01)
Lee, HK
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Chen, ST
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Lee, AC
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機械工程學系
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Department of Mechanical Engineering
This paper presents a study of asymptotic stability for the control of flexible systems. It shows that when the controller structure is a collocated direct output feedback design with positive definite feedback gain, the number and placement of sensors and actuators are the only factors required to determine necessary and sufficient conditions to ensure closed-loop asymptotic stability. The minimum number of control devices required is dependent on the maximum number of multiple eigenvalues. The positioning of the control devices is restricted by checking several simple subsidiary rank conditions.
Design of a permanent/electromagnetic magnetic bearing-controlled rotor system
(1997-05-01)
Fan, YH
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Lee, AC
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Hsiao, FZ
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機械工程學系
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Department of Mechanical Engineering
This study proposes design procedures for the permanent-magnet-biased magnetic bearings (PEMBs) in rotor systems. Many aspects of designing magnetic bearings are discussed, e.g. the selection of a permanent magnet material, dimensions of electromagnets and permanent magnets, gap length, load capacity and maximum Ampere-turns. Linearization and DC current driver are the two constraints for determining feasible designs. According to an analytical model with a rigid body assumption for the rotor-bearing system, a decentralized output feedback control algorithm is employed to control this inherently unstable magnetic suspension rotor system. Experimental results indicate that the controlled rotor performs well at rotor speeds up to 12,000 rpm. (C) 1997 Published by Elsevier Science Ltd.
Design of a permanent/electromagnetic magnetic bearing-controlled rotor system
(1997-05-01)
Fan, YH
;
Lee, AC
;
Hsiao, FZ
;
交大名義發表
;
機械工程學系
This study proposes design procedures for the permanent-magnet-biased magnetic bearings (PEMBs) in rotor systems. Many aspects of designing magnetic bearings are discussed, e.g. the selection of a permanent magnet material, dimensions of electromagnets and permanent magnets, gap length, load capacity and maximum Ampere-turns. Linearization and DC current driver are the two constraints for determining feasible designs. According to an analytical model with a rigid body assumption for the rotor-bearing system, a decentralized output feedback control algorithm is employed to control this inherently unstable magnetic suspension rotor system. Experimental results indicate that the controlled rotor performs well at rotor speeds up to 12,000 rpm. (C) 1997 Published by Elsevier Science Ltd.
Design of acceleration/deceleration profiles in motion control based on digital FIR filters
(1998-07-01)
Chen, CS
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Lee, AC
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機械工程學系
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Department of Mechanical Engineering
In motion control, the reference commands should pass through the acceleration/deceleration (Acc/Dec) processor before being fed into the servo loop. Consequently, not only can a smooth motion profile be obtained but undesirable vibration can be avoided. In this study, we develop a systematic design procedure for the Acc/Dec processor based on the discrete time finite-impulse-response (FIR) filter design technique with some necessary conditions. Compared with the conventional Acc/Dec scheme, the FIR Acc/Dec scheme poses the advantage that the contouring error can be analyzed. Also, the contouring error caused by the conventional Acc/Dec scheme is evaluated by demonstrating a mapping technique from the conventional Acc/Dec scheme to the FIR Acc/Dec scheme. The proposed Acc/Dec algorithm is quite flexible and efficient, creating space for users to use more sophisticated profiles to more efficiently match the system constraints with minimum contouring errors. Simulation and experimental results verify that the proposed Acc/Dec processor can effectively improve the motion accuracy. (C) 1998 Elsevier Science Ltd. All rights reserved.
Identification of the unbalance distribution and dynamic characteristics of bearings in flexible rotors
(1996)
Lee, AC
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Shih, YP
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
This paper presents a new method for estimating dynamic characteristics of bearings and unbalance distribution inflexible rotors based on the transfer matrix method for analysing the steady state responses of rotor-bearing systems, in which rotary inertia, gyroscopic and transverse-shear effects are also considered. identification can be realized from the measured response data influenced by bearing characteristics and rotor unbalance using the least-squares method. Justification of the method is presented by numerical simulations.
Identification of the unbalance distribution in flexible rotors
(1997-07-01)
Shih, YP
;
Lee, AC
;
交大名義發表
;
機械工程學系
;
National Chiao Tung University
This paper presents a new method for estimating unbalance distributions of flexible shafts and constant eccentricities of rigid disks based on the transfer matrix method for analyzing the steady-state responses of rotor-bearing systems, in which the transfer matrix of a flexible shaft is derived in a continuous sense with any spatial unbalance distribution. Rotary inertia, gyroscopic and transverse-shear effects are also included. When deflections and deflection angles of one free end are measurable, the unbalance distribution of shafts and disks can be estimated under operating conditions by the proposed method. The main advantage of this identification technique is that only the state vector of the one free end of the rotating shaft need to be measured. Justification of the method is presented by numerical simulations. (C) 1997 Elsevier Science Ltd. All rights reserved.
Identification of the unbalance distribution in flexible rotors
(1997-07-01)
Shih, YP
;
Lee, AC
;
機械工程學系
;
Department of Mechanical Engineering
This paper presents a new method for estimating unbalance distributions of flexible shafts and constant eccentricities of rigid disks based on the transfer matrix method for analyzing the steady-state responses of rotor-bearing systems, in which the transfer matrix of a flexible shaft is derived in a continuous sense with any spatial unbalance distribution. Rotary inertia, gyroscopic and transverse-shear effects are also included. When deflections and deflection angles of one free end are measurable, the unbalance distribution of shafts and disks can be estimated under operating conditions by the proposed method. The main advantage of this identification technique is that only the state vector of the one free end of the rotating shaft need to be measured. Justification of the method is presented by numerical simulations. (C) 1997 Elsevier Science Ltd. All rights reserved.
Modeling and analysis of the intermediate shaft between two universal joints
(1996-01-01)
Sheu, PP
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Chieng, WH
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Lee, AC
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交大名義發表
;
機械工程學系
Unlike a single universal joint, in which the output shaft rotates with a fluctuating speed depending on the misalignment angle, a double universal joint is used to connect two offset shafts. If a double universal joint is correctly arranged with equal joint angles in perfect alignment, the output shaft rotates in a synchronous motion with uniform speed. However, in practice, the intermediate shaft of a double universal joint system suffers from bending moments induced by joint friction and velocity fluctuation induced by the joint angles. These factors distort the linear relationship between the input and output shafts. In this paper, the effects of joint angles and joint friction on the steady-state responses of a double universal joint system are examined. The mass matrix, damping matrix, stiffness matrix, and nonconservative force of a universal joint are derived analytically for finite element modeling. The formulation introduced generates an elementary matrix suitable for the analysis of complex rotor-bearing system's that include double universal joints.
Modeling and diagnosis of motion error of multi-axis machines using a ball bar test
(1996-09-01)
Jeng, SL
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Chieng, WH
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Lee, AC
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交大名義發表
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機械工程學系
The contouring accuracy of a multi-axis machine has a critical effect on the quality of many advanced technology products. One of the best approaches to assessing the contouring performance of machine tools is through double ball bar measurement. During circular interpolation motion, the machine traverses, with two axes at a time, a circular trajectory, with each axis subject to sinusoidal changes in acceleration, velocity, and position. The motion error is measured by detecting the relative distance between a point on the spindle nose and another point on the machine table and plotting this distance in polar coordinates. The present paper derives mathematical models and diagnosis procedures for first and second-order motion error resulting from the active degrees of freedom of a multi-axis machine. The theoretical results are verified by both computer simulation and double ball bar testing experiments.
New direct velocity and acceleration feedforward tracking control in a retrofitted milling machine
(1999-09-01)
Chen, CS
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Lee, AC
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機械工程學系
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Department of Mechanical Engineering
This paper proposes a new feedforward controller called the direct velocity and acceleration feedforward controller (DVAFF) to improve the tracking performance. The controller is adapted to both minimum phase system and nonminimum phase system and it can also take the practical driving capability of actuator and saturation of D/A converter into account by tuning their gains. Simulation and experiment results show that the proposed new DVAFF scheme can effectively improve the motion accuracy.
Optimal control of vibration suppression in flexible systems via dislocated sensor/actuator positioning
(1996-09-01)
Lee, HK
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Chen, ST
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Lee, AC
;
交大名義發表
;
機械工程學系
In this study, we present a new controller design method that not only effectively suppresses vibration in flexible systems, but also has the ability to save control energy. The proposed method allows integrated determination of sensor/actuator locations and feedback gain by minimizing the sum of the integral flexible system energy and the integral control energy. Also, the cost function is characterized by an effective representation of control systems, and is determined via an efficient solution of the Lyapunov equation. The optimization problem is solved by a recursive quadratic programming algorithm. The feasibility of applying this method to a simple and flexible structure confirms the direct relationship between our optimization criterion and effectiveness in vibration suppression. Copyright (C) 1996 Published by Elsevier Science Ltd
Optimum magnetic bearing design considering performance limitations
(1996-09-01)
Hsiao, FZ
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Fan, CC
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Chieng, WH
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Lee, AC
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交大名義發表
Magnetic bearings are subject to three practical performance limitations: the peak force capacity, force slew rate limitation, and displacement sensitivity. In conventional designs, we usually first design a feasible bearing, and then investigate these three limitations. Unfortunately, one usually fails to design the most suitable magnetic bearing in actual cases. In this paper, a methodology for dealing with the performance limitations through the concept of optimum design is presented. The objective functions are to maximize the force slew rate limitation and to minimize the displacement sensitivity under several design constraints. Using the optimization solver software package, we developed a systematic method for determining the characteristics of magnetic hearings. By considering the performance limitations and design constraints, we achieve a better design than that produced using the conventional trial-and-error method.
Path planning for CNC contouring around a corner
(2004-03-01)
Shih, YT
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Chen, CS
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Lee, AC
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機械工程學系
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Department of Mechanical Engineering
Corner motion is a common and important case in contouring applications. If the corner error is well-controlled, a machine can own maximal throughput while maintaining the machining accuracy. In this paper, we investigated corner error yielded by different Acc/Dec processing in the command generation phase. At first, we derive some analytical forms of corner error induced by Acc/Dec processing; both linear and FIR Acc/Dec types are studied. Then a simple method of controlling the corner error without changing the Acc/Dec structure is presented. The method is simply to add some delay time to retard the execution of the second linear command. Although some results here do not explicitly present their final exact analytic expressions, their numerical solutions can be easily solved.
Sensor and actuator placement for modal identification
(1998-09-01)
Shih, YT
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Lee, AC
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Chen, JH
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機械工程學系
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Department of Mechanical Engineering
In modal identification, the use of different actuator and sensor locations results in different frequency response functions (FRFs) and consequently affects the modes shown on the FRF plots. This paper presents a method of placing sensors and actuators to obtain reliable measured data for estimating the modal parameters. The method is based on proposed controllability and observability measures for second-order linear systems, which are suitable for identification purposes and have a physical interpretation on the FRF plots. These measures, combined with an objective criterion, provide a method for ranking the effectiveness of alternative actuator and sensor distributions and hence a rational basis for choosing their locations. The method is applied successfully to the selection of actuator and sensor locations for a set of target modes for the structural characterisation of a simulated system. Finally, an iterative procedure for performing modal surveys is proposed. (C) 1998 Academic Press.
The failure of threaded fasteners due to vibration
(2005-03-01)
Chen, JH
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Hsieh, SC
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Lee, AC
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機械工程學系
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Department of Mechanical Engineering
The main objective of this paper is to study the loosening tendency of a threaded fastener. To achieve the objective, the threaded fastener looseness model is constructed through the following procedures. Firstly, static and dynamic threaded fastener models are derived to find the static and dynamic interior forces respectively. Secondly, for investigating the bolt loosening behaviour, the effects of thread lead angle, initial preload, vibration frequency, and the nature of material on the bolt looseness, the threaded fastener looseness model is constructed by combining the above models with a Karnopp frictional model. The proposed approach not only analyses both the static and the dynamic behaviours of the bolt as well as the bolt loosening but also detects whether the bolt is within the elastic range or not. The approach can serve as a guide for designing a thread fastening procedure to avoid the failure of threaded fasteners due to vibration.
The joint displacement method for multiloop kinematic analysis
(1995-12-01)
Yang, YN
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Chieng, WH
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Lee, AC
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交大名義發表
;
機械工程學系
We present a kinematic formulation, referred to as the joint displacement method. In the kinematic analysis; the closed-loop kinematic chain of interest must be transformed into several open-loop chains by imagining that some joints are relaxed (disconnected), and by replacing them as physical entities with a set of constraint equations. This formulation requires only a minimal number of generalized coordinates, hence it provides;a highly efficient approach for real-time kinematic analysis of spatial mechanisms, heretofore unseen in the literature. For-example, the Jacobian matrix for the RSCR mechanism is 3 x 3 and the CPU time required to perform Gauss elimination is 182 times shorter than that in the traditional link-coordinate method which requires a 17 x 17 Jacobian matrix. This method is applicable to both single loop and multiloop spatial mechanisms with revolute, cylindrical, translational, spherical and universal joints. A general-purpose computer program that implements the joint displacement method has been developed and tested on a variety of mechanisms.