An-Chen Lee

A novel cross-coupling control design for Bi-axis motion

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.

A CAD/CAM system from 3D coordinate measuring data

SUMMARY A CAD/CAM system with some new numerical methods is presented in this paper. This system mainly consists of two stages. In stage 1, the least squares method is applied to fit a best form of parametric surface to a set of data points obtained from a 3D coordinate measuring machine, with the errors caused by the probe compensated. In stage 2, from the best form of parametric surface obtained in stage 1, a new efficient method—adaptive path planning—which has better performance than the old parametric method is developed to generate the cutter path. By application of adaptive path planning, machining time can be reduced. By transforming the cutter contact path to the cutter location path, the curvature method for detecting gouging is presented by which a tool path with gouging avoidance can be generated.

Design of acceleration/deceleration profiles in motion control based on digital FIR filters

Abstract 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.

Analysis of cutting forces in ball-end milling

Abstract A cutting force model for ball end milling is developed, the model being based mainly on the assumption that the cutting force is equal to the product of the cutting area and the specific cutting force. The formulation of the cutting area is derived from the geometry of the mill and the workpiece, whilst the specific cutting force is obtained by third-order curve-fitting of data measured in experiments. The model established in this paper predicts the cutting forces in ball-end milling much more accurately than do previous models.

ANALYSIS OF CHATTER VIBRATION IN THE END MILLING PROCESS

Abstract This paper continues the work of a previous paper by the authors. A different approach is applied, which adopts frequency domain analysis by linearizing the nonlinear equations to investigate the dynamic behavior in the milling process. A new relationship among the limiting axial depth of cut, workpiece fundamental natural frequency and spindle speed is constructed, and the obtained stable region is also consistent with that of the previous paper.

Analysis of chatter vibration in a cutter-workpiece system

Abstract The phenomenon of chatter vibration in milling has been investigated by many authors, but the consideration of workpiece has never been paid any attention to. In this paper, this defect has been excluded by involving workpiece dynamic effect on chatter vibration. A general form of time domain simulation and a simplified form of frequency domain analysis referred as circle criterion will be proposed to examine such a system. The new phenomenon of chatter vibration is derived by both of these methods and experiments also demonstrate the validity of this new phenomenon.

A Modified Transfer Matrix Method for Linear Rotor-Bearing Systems

The steady-state responses of linear flexible rotor-bearing systems are analyzed by the modified transfer matrix method. The transfer matrix has the advantage of solving the problems in frequency domain with fixed matrix size. This makes the method more economical in analyzing a large degree-of-freedom rotor system than many time-marching integrating methods. In this paper, the modifications of transfer matrix method include that the transfer matrix of shaft is derived from the “continuous system” concept instead of conventional “lumped system” concept, and the paper tries to extend the transfer matrix method to fit synchronous elliptical orbit and nonsynchronous multi-lobed whirling orbit. To demonstrate the applications of the method, three examples are presented; two synchronous and one nonsynchronous.

Design of a Permanent~Electromagnetic Magnetic Bearing-controlled Rotor System

Abstract 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.

Run-by-Run Process Control of Metal Sputter Deposition: Combining Time Series and Extended Kalman Filter

By the time series model, this paper constructed the disturbance model for the aluminum sputter deposition process and derived the extending Kalman filter (EKF) controller based on this new disturbance model. Experimental results reveal that ARI(3,1) model appropriately characterizes the dynamic behavior of the disturbance for the processes. The EKF controller which includes information of process noise and measurement noise is able to regulate the model coefficients automatically as the target is replaced or degrades. In this paper, the d-EWMA controller, time-varying d-EWMA controller, age-based d-EWMA controller, and EKF controller have been applied to aluminum sputter deposition processes for predicting deposition rates and comparing their performances. The application of the EKF controller here is proven to improve the estimating accuracy of the aluminum sputter deposition process significantly, regardless of whether the deposition rates are measured at each run or not.

Estimation of linearized dynamic characteristics of bearings using synchronous response

Abstract This paper presents a new method for estimating linearized dynamic characteristics of bearings using a priori information about the rotor. The rotor-bearing systems considered here are composed of a flexible shaft, which may be changed stepwise along the axial direction, and multiple rigid disks supported on anisotropic bearings. The main feature of this estimation technique is that it eliminates the need to measure the external input force. Since the system considered here is driven by an unbalance force, the steady state of the rotor will contain only a synchronous frequency component. By applying a Fourier transform to the measured displacement, we can obtain the coefficients of the sine and cosine terms with respect to the synchronous frequency. Finally, we formulate the normal equation by using the relations between these coefficients and the known system. parameters; the characteristics of the bearings are then estimated by the least-squares method. The theoretical development of the method is presented together with simulation and experimental results.