Development of a dynamics-based NURBS interpolator with real-time look-ahead algorithm

International Journal of Machine Tools and Manufacture, Vol.47, No.15, pp.2246-2262, DEC 2007M. T. Lin, M. S. Tsai and H. T. Yau


Abstract:In this paper, a dynamics-based interpolator with real-time look-ahead (DBLA) algorithm is proposed to generate a smooth and jerk-limited acceleration/deceleration (ACC/DEC) feedrate profile. The interpolator consists of three modules: geometric, dynamics-based, and jerk-limited modules. The geometric module can detect the local maximum/minimum (max/min) curvatures, and divide a NURBS curve into small segments according to the information of sharp corners. The feedrates at the sharp corners are determined based on confined chord errors and curvatures of the curve. The dynamics-based module utilizes a dynamics feedrate modification equation (DFME) to estimate contour errors at the sharp corners and adjusts the feedrates at the locations of the sharp corners. The jerk-limited module plans the feedrate profile of the curve according to the segments’ length and the given jerk limit. Simulations are performed to verify real-time performance of the look-ahead algorithm. Experiments using a PC-based motion controller and an X–Y table are conducted to demonstrate that high-accuracy can be achieved with the proposed dynamics-based interpolator as compared to the adaptive-feedrate and the curvature-based feedrate interpolation algorithms.

Automatic Registration Using Virtual Polar Ball

posted Apr 18, 2011, 9:28 PM by ccu cadcam   [ updated Apr 20, 2011, 2:25 PM ]
Computer-Aided Design and Applications, Vol.4, No.1-4, pp.427-436, 2007H. T. Yau, L. S. Tsou and H. M. Tseng


Abstract:In reverse engineering applications, multiple scanned datasets need to be registered and integrated. However, automatic registration without user intervention is still an open research problem. In this paper, we propose a novel approach, the polar ball algorithm, which can find the corresponding features for automatic registration. Based on the Voronoi diagram and Delaunary triangulation, our approach is unique and invariant to viewpoint, which is critical in finding corresponding features. We utilize this property to obtain automatic registration without user interaction. The result of our registration algorithm is more robust to noise and stable than traditional characteristic point approach. Because the feature polar ball, or “feature ball ” for short, can represent a curved surface region, it can reduce and smooth out the noise effect and represent a feature more reliably.

PC-based controller with real-time look-ahead NURBS interpolator

posted Apr 18, 2011, 7:58 PM by ccu cadcam   [ updated Apr 18, 2011, 9:27 PM ]
Computer-Aided Design and Applications, Vol.4, No.1-6, pp.331-340, 2007H. T. Yau, J. B. Wang, C. Y. Hsu and C. H. Yeh


Abstract:This paper presents a real-time look-ahead NURBS interpolator implemented on a PC-based controller to solve the problems of traditional linear short NC segments. Taking advantage of the designs of the look-ahead function and multi-threads, the NURBS interpolator can obtain enough NC block information and complete feedrate planning before interpolation. Consequently, the computational load is reduced during an interpolation period and unnecessary feedrate acceleration and deceleration can be avoided. The continuous short blocks conforming to the CSB criterion can be fitted into NURBS curves in real-time. S-shaped federate profile for ACC/DEC planning can make the single block achieve C 1 continuity and jerk-limited capability. The simulation and experimental results show that the output contour profiles approach the input NC program models. This indicates that the proposed real-time look-ahead NURBS interpolator is able to provide a satisfactory performance Keywords: NURBS, Interpolator, Real-time, Look-ahead, Continuous Short Blocks. 1.

Fast Bezier interpolator with real-time lookahead function for high-accuracy machining

posted Apr 18, 2011, 7:53 PM by ccu cadcam
International Journal of Machine Tools and Manufacture, Vol.47, No.10, 2007H. T. Yau and J. B. Wang


Abstract:This study presents a real-time fast Bezier interpolation method that solves linearly segmented contour problems that occur during milling using conventional CNC machines. Depending on the length and the CSB criterion, these linearized segments can be regarded as noise, continuous short blocks (CSBs), or G01 blocks. The CSB criterion proposed in this paper is employed to identify CSBs during the NC code interpreting stage. The CSBs are fitted into cubic Bezier curves and interpolated to produce smoother contours in real-time machining. Two different NC programs possessing a large number of short blocks were tested on our PC-based real-time control system. Simulations and experimental results demonstrate that the proposed fast Bezier interpolator (FBI) with real-time lookahead function provides satisfactory performance.

Octree-based Virtual Dental Training System with a Haptic Device”, Computer-Aided Design and Applications

posted Apr 18, 2011, 7:48 PM by ccu cadcam
Computer-Aided Design and Applications, Vol.3, No.1-4, pp.415-424, 2006H. T. Yau, L. S. Tsou and M. J. Tsai


Abstract:The virtual dental training system using a haptic device is becoming a very important training tool for dental education. We propose a new approach that utilizes the so-called EP (Edge Proportion) value, local material stiffness and implicit function to develop a novel dental training system which has useful characteristics such as efficient collision detection, stable haptic interaction and accurate sculpting simulation. In the efficient collision detection approach, the oriented bounding box tree and EP value can be quickly updated for collision detection. The EP value is very important in our approach, because it can also be used to compute haptic force and update the tooth model. In the stable haptic interaction approach, we use the spring-damper force model and a simple force filter to obtain stable force feedback. Finally, in the precision sculpting simulation, an implicit function is employed to exactly represent various kinds of dental tools so that accurate calculation of cutter- surface intersection can be realized. The proposed system is highly applicable to virtual dental training and practices. Examples of tooth preparations such as inlay and bridge preparation are demonstrated.

Development of a Dental Training System Based on Point-based Models

posted Apr 18, 2011, 7:45 PM by ccu cadcam   [ updated Apr 18, 2011, 10:07 PM ]
Computer-Aided Design and Applications, Vol.3, No.6, pp.779-788, 2006
H. T. Yau and C. Y. Hsu


Abstract:Recently, a new point-based geometric modeling approach using surfels (surface elements) has been introduced into the field of computer graphics. This new type of 3D model can be used to render complex geometry with less geometric and topological constraints. This paper presents a dental training system which uses surfel models and carries out realistic cutting simulation using a haptic device. We use surfel models to render dental tools and virtual teeth models to get better visual quality with less memory cost. By using surfel models to render dental tools, we can model cutters of many different shapes. The Boolean operation of the surfel model is implemented with local update; the modeling and visual update frequency of the system is about 30Hz. Collision detection and force computation are implemented on an Octree box to simulate physical interactions between a virtual dental tool and a tooth model. Dental training systems based on surfel models can work on any cutter shape. We add the material property to every surfel to simulate different force feedbacks when there is contact with different materials. Adaptive collision detection is performed so that haptic rendering update occurs under 1 kHz. Finally, we use a filter to make the force feedback smooth.

Design and Implementation of Real-time NURBS Interpolation using an FPGA-based Motion Controller

posted Apr 18, 2011, 5:32 PM by ccu cadcam   [ updated Apr 18, 2011, 5:46 PM ]
Computer Aided Design, Vol. 38, No. 10, pp.1123-P.1133, 2006H. T. Yau, M. H. Lin and H. S. Tsai

Abstract:Modern motion control adopts NURBS (Non-Uniform Rational B-Spline) interpolation for the purpose of achieving high-speed and high-accuracy performance. However, in conventional control architectures, the computation of the basis functions of a NURBS curve is very time-consuming due to serial computing constraints. In this paper, a novel FPGA (Field Programmable Gate Array) based motion controller utilizing its high-speed parallel computing power is proposed to realize the Cox-de Boor algorithm for second and higher degrees NURBS interpolation. The motion control algorithm is also embedded in the FPGA chip to implement real-time control and NURBS interpolation simultaneously for multi-axis servo systems. The proposed FPGA-based motion controller is capable of performing the Cox-de Boor algorithm and the IIR (Infinite Impulse Response) control algorithm in about 46 clock cycles, as compared to the 1303 clock cycles by the traditional approach. Numerical simulations and experimental tests using an X-Y table verify the outstanding computation performance of the FPGA-based motion controller. The result indicates that shorter sampling time (10 @ms) can be achieved for NURBS interpolation which is highly critical to the success of high-speed and high-accuracy motion control.

Real-time NURBS interpolation using FPGA for high speed motion control

posted Apr 18, 2011, 5:26 PM by ccu cadcam   [ updated Apr 18, 2011, 10:09 PM ]
Computer Aided Design, Vol.38, No.10, pp. 1123-1133, 2006H. T. Yau, M. T. Lin and M. S. Tsai


Abstract:Modern motion control adopts NURBS (Non-Uniform Rational B-Spline) interpolation for the purpose of achieving high-speed and high-accuracy performance. However, in conventional control architectures, the computation of the basis functions of a NURBS curve is very time-consuming due to serial computing constraints. In this paper, a novel FPGA (Field Programmable Gate Array) based motion controller utilizing its high-speed parallel computing power is proposed to realize the Cox–de Boor algorithm for second and higher degrees NURBS interpolation. The motion control algorithm is also embedded in the FPGA chip to implement real-time control and NURBS interpolation simultaneously for multi-axis servo systems. The proposed FPGA-based motion controller is capable of performing the Cox–de Boor algorithm and the IIR (Infinite Impulse Response) control algorithm in about 46 clock cycles, as compared to the 1303 clock cycles by the traditional approach. Numerical simulations and experimental tests using an X–Y table verify the outstanding computation performance of the FPGA-based motion controller. The result indicates that shorter sampling time (10 μs) can be achieved for NURBS interpolation which is highly critical to the success of high-speed and high-accuracy motion control.

A New Combinational Approach to Surface Reconstruction with Sharp Features

posted Apr 18, 2011, 5:21 PM by ccu cadcam
IEEE Transaction on Visualization and Computer Graphics, Vol.12, Issue 1, pp. 73-82, ISSN: 1077-2626, 2006C. C. Kuo and H. T. Yau

Abstract:This paper presents a new combinatorial approach to surface reconstruction with sharp features. Different from other postprocessing methods, the proposed method provides a systematic way to identify and reconstruct sharp features from unorganized sample points in one integrated reconstruction process. In addition, unlike other approximation methods, the reconstructed triangulated surface is guaranteed to pass through the original sample points. In this paper, the sample points in the sharp regions are defined as characteristic vertices (c-vertices), and their associated poles (c-poles) are used as a "sculptor" to extract triangles from a Delaunay structure for the sharp features. But, for smooth surface regions, an efficient region-growing scheme is used for triangle extraction and connection. Since only the c-poles associated with the sharp regions are used to participate in the Delaunay computation with the sample points, the proposed algorithm is adaptive in the sense that, given a sampled object with less sharp features, the triangulation becomes more efficient. To validate the proposed algorithm, some detailed illustrations are given. Experimental results show that it is robust and highly efficient.

Development of Command-Based Iterative Learning Control Algorithm With Consideration of Friction, Disturbance, and Noise Effects

posted Apr 18, 2011, 5:14 PM by ccu cadcam
IEEE Transactions on Control Systems Technology, Vol.14, No.3,  511 - 518 ISSN: 1063-6536, 2006M.S. Tsai, M.H. Lin, and H.T. Yau

Abstract:In this brief, a command-based iterative learning control (ILC) architecture is proposed to compensate for friction effect and to reduce tracking error caused by servo lag. In contrast to a feedback-feedforward control structure, the proposed methodology utilizes the learning algorithm that updates the input commands based on the tracking errors from the previous machining process. The effects of noise accumulations from each learning process of the ILC are analyzed by formulating the equivalent error dynamic and updated command equations, and the P-type ILC with a zero-phase filter is applied to alleviate noise and disturbance effects. It is shown that, for tracking a circle, the quadrant protrusions caused by friction can be reduced substantially by the updated command containing a concave shape located at the crossing of the zero velocity. Finally, analytical simulation and experimental results demonstrate that the command-based ILC algorithm can enhance the tracking performance significantly.