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Iterative Learing Reference Trajectory Modification For Contouring Performance Enhancement Of Industrial Machine Tool Feed Drive Systems

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In industrial applications, highly accurate mechanical components are generally re- quired to produce advanced mechanical and mechatronic systems. Most of them are produced by computer numerical control (CNC) machine tools. A fundamental mo- tion in CNC machine tools is a drive axial movement to track a desired trajectory. Not only are there tracking errors in each drive axis, but there are also contour errors, which are directly related to the machined shape of a workpiece, and therefore must be considered in controller design. Although most existing contouring controllers are based on feedback control and estimated contour error, it is generally difficult to replace the feedback controller in commercial CNC machine tools. In order to improve the contouring performance for commercial CNC machine tools, this thesis presents an iterative learning contouring controller (ILCC) design with two contour error estimation approaches.

The proposed method is implemented in three types of CNC machine tool feed drive systems. First, a laboratory biaxial feed drive system is used to prove the propo- sed methods performance (Chapter 3) with an estimated contour error correction.
Then, an ILCC is applied to a three-axis commercial CNC machine tool (Chapter 4) to improve the contour error estimation. Last, a machine tool with a linear motor mechanism is used as an example of an advanced machine tool (Chapter 5). Descrip uons of the physical system configurations and system parameters are presented in Chapter 2

An ILCC that considers both tracking and contour errors is proposed in Chapter 3. The proposed control steratively modifies the reference trajectory of each drive axis to reduce the contour error. The proposed controller can be directly applied to commercial machines currently in use without requiring any modification of their original controllers. The proposed method has been experimentally verified through a biaxial feed drive system on a sharp-corner trajectory, which normally leads to a large contour error around the corner due to the discontinuity. A comparison with a conventional ILCC (CILCC) was done in order to evaluate its performance. The experimental results show that the contour error converges within a few iterations and the maximum contour error can be reduced by 49.2% in comparison with the CILCC. The limitation is that this method is only effective for a low-curvature tra- jectory. It requires more iterations to track a high-curvature trajectory.

An ILCC that considers the actual contour error compensation (ACEC) with linear interpolation and the Bézier reposition trajectory (BRT) is proposed in Chapter 4 to improve upon the method presented in Chapter 3. The ACEC enhances tracking performance for a high-curvature trajectory by correcting the reference input with an actual contour error value, and the BRT enables smooth velocity transitions be- tween discrete points in the reference trajectory. For the performance analysis, the proposed controller was implemented in a commercial three-axis CNC machine tool and several experiments were conducted on the basis of typical 3D sharp-corner and half-circular trajectories. The experimental results show that the proposed control- ler could reduce the maximum and mean contour errors by 45.11% and 54.48% on average, compared with the ILCC with estimated contour error. In comparison
with the ILCC with ACEC, the maximum and mean contour errors are reduced by 20.54% and 26.92%, respectively. However, this method is not effective for circu- lar trajectories. It will be improved by the circular interpolation method in the next chapter

To improve the effectiveness of the proposed method in an advanced commercial CNC machine tool system, circular interpolation is designed. It is implemented in a CNC machine tool with a linear motor mechanism in Chapter 5. An ILCC that considers ACEC with linear and circular interpolation enhances the contouring performance of linear motor CNC machine tool feed drive systems. The proposed control iteratively modifies the reference trajectory of each drive axis to reduce the contour error. The proposed controller can be directly applied to a commercial CNC machine tool with a linear motor mechanism currently in use without requiring any modification of the original controller. The comparisons between linear and circular interpolation were simulated in both "air-cutting" and machining conditions. The simulation was conducted for non-smooth rhomboidal and circular trajectories. The effectiveness of the proposed method has been experimentally verified with a rhom- boidal trajectory. The results show that the proposed controller could reduce the maximum and mean contour errors by 94.58% and 88.67% on average, compared with the original controller. In addition, the proposed method improved the cont- rol input variance by 37.9%, and consequently, the consumed energy was reduced by 11.7% compared with the original NC program. Concluding remarks and future works are described in Chapter 6.

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Ketersediaan

Informasi Detail

Judul Seri

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No. Panggil

TA-2180219.1

Penerbit

Japan : Toyohashi University Of Technology., 2018

Deskripsi Fisik

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Bahasa

English

ISBN/ISSN

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Klasifikasi

NONE

Tipe Isi

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Tipe Media

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Tipe Pembawa

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Edisi

S3/Doctoral Thesis/2018

Subjek

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Info Detail Spesifik

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Pernyataan Tanggungjawab

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Versi lain/terkait

Lampiran Berkas

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