LiMin Zhu

Shanghai Jiao Tong University, Shanghai, Shanghai Shi, China

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Publications (63)51.64 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The high-speed computational performance is gained at the cost of huge hardware resource, which restricts the application of high-accuracy algorithms because of the limited hardware cost in practical use. To solve the problem, a novel method for designing the field programmable gate array(FPGA)-based non-uniform rational B-spline(NURBS) interpolator and motion controller, which adopts the embedded multiprocessor technique, is proposed in this study. The hardware and software design for the multiprocessor, one of which is for NURBS interpolation and the other for position servo control, is presented. Performance analysis and experiments on an X-Y table are carried out, hardware cost as well as consuming time for interpolation and motion control is compared with the existing methods. The experimental and comparing results indicate that, compared with the existing methods, the proposed method can reduce the hardware cost by 97.5% using higher-accuracy interpolation algorithm within the period of 0.5 ms. A method which ensures the real-time performance and interpolation accuracy, and reduces the hardware cost significantly is proposed, and it’s practical in the use of industrial application.
    Chinese Journal of Mechanical Engineering 09/2013; 26(5):940-947. · 0.26 Impact Factor
  • Huan Zhao, LiMin Zhu, Han Ding
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    ABSTRACT: Traditionally, approximation methods are utilized in the parametric interpolation because of the nonanalytic relationship between the spline parameter and the arc length. The approximation error has been considered as the source of the feedrate fluctuation. This paper shows that the discrepancy between the desired tool path and the target trajectory of the motion system is another primary source, and presents a feedback interpolator to eliminate the feedrate fluctuation. To evaluate the initial parameter value for the interpolator, an arc-length based Taylor's expansion with arc-length compensation is proposed, which alleviates greatly the feedrate command error caused by the trajectory deviation. Then, a feedback correction scheme is developed to further reduce the feedrate command error that results from the approximation error. Both computational load analysis and numerical simulations are conducted, and the results show that the present interpolator has very good performance in both efficiency and accuracy, thus is a good choice for high speed and high precision CNC machines.
    International Journal of Machine Tools and Manufacture 01/2013; 75:1–8. · 2.26 Impact Factor
  • Chen Luo, Limin Zhu, Han Ding
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    ABSTRACT: Fixtures are used in almost all modern manufacturing operations. In practice, there is a wide range of specifications on the manufacturing precision and thus different requirements on workpiece locating accuracy during each production process. In view of that, this paper developed a unified signed distance function framework. Under this framework, three systems of sensitivity equations, which link the locator source errors to the resulting workpiece localization error, were derived. Accordingly, unique linear, one-sided quadratic, and two-sided quadratic models have been developed. These three models, distinguished by whether or not taking into account workpiece and/or locator curvature effects, provide a range of locating precision analysis which is illustrated and verified by several examples. The developed modeling technique can handle general fixture locating rather than being limited to certain locating schemes. The proposed models are of practical relevance and have great potential to be applied towards locating scheme evaluation, fixture design, fault diagnosis, and tolerance analysis.
    IEEE Transactions on Automation Science and Engineering 01/2013; 10(4):1166-1172. · 1.67 Impact Factor
  • LiMin Zhu, Han Ding, YouLun Xiong
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    ABSTRACT: By representing the swept envelope of a generic rotary cutter as a sphere-swept surface, our previous work on distance function based tool path optimization is extended to develop the model and algorithm for simultaneous optimization of the tool path and shape for five-axis flank milling. If the tool path is fixed, a novel tool shape optimization method is obtained. If the tool shape is fixed, a tool path optimization method applicable to any rotary cutter is obtained. The approach applies to non-ruled surfaces, and also finds applications in cutter dimension optimization and flank millable surface design. Numerical examples are given to confirm its validity.
    Computer-Aided Design. 12/2012; 44(12):1229–1234.
  • Xu Zhang, Youfu Li, Limin Zhu
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    ABSTRACT: The 3D scene acquisition is becoming increasingly crucial in practical application. In this paper, a new method is proposed to measure the surface of objects, which just require one color pattern image. In our decoding method, advancements are made at two steps. First, color identification is modeled as an unsupervised classification problem and K-means are adopted on a new color feature, called regularized color. It is insensitive to surface orientation, illumination direction and illumination intensity for matte, dull surfaces. Second, a discontinuity-preserving method is proposed in the sequence matching, which is based on the window voting to judge correct correspondences and potential borders.In the experiments, this new color feature is compared with RGB, normalized color, HSI. Their class separability measurements are evaluated by scattering criteria and Bhattacharyya distance. The results show that regularized color has much higher discriminating power than RGB and equivalent performance with HSI. Our matching method is also compared with the traditional local matching methods. The results affirm that ours has higher accuracies on six different objects.
    Optics and Lasers in Engineering 10/2012; 50(10):1416–1422. · 1.92 Impact Factor
  • Xu Zhang, Youfu Li, Limin Zhu
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    ABSTRACT: Color code is widely employed in coded structured light to reconstruct the three-dimensional shape of objects. Before determining the correspondence, a very important step is to identify the color code. Until now, the lack of an effective evaluation standard has hindered the progress in this unsupervised classification. In this paper, we propose a framework based on the benchmark to explore the new frontier. Two basic facets of the color code identification are discussed, including color feature selection and clustering algorithm design. First, we adopt analysis methods to evaluate the performance of different color features, and the order of these color features in the discriminating power is concluded after a large number of experiments. Second, in order to overcome the drawback of K-means, a decision-directed method is introduced to find the initial centroids. Quantitative comparisons affirm that our method is robust with high accuracy, and it can find or closely approach the global peak.
    Applied Optics 08/2012; 51(22):5340-56. · 1.69 Impact Factor
  • Chen Luo, LiMin Zhu, Han Ding
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    ABSTRACT: This paper presents a new method to analyze frictionless grasp immobility based on defined surface-to-surface signed distance function. Distance function's differential properties are analyzed and its second-order Taylor expansion with respect to differential motion is deduced. Based on the non-negative condition of the signed distance function, the first- and second-order free motions are defined and the corresponding conditions for immobility of frictionless grasp are derived. As one benefit of the proposed method, the second-order immobility check can be formulated as a nonlinear programming problem. Numerical examples are used to verify the proposed method.
    Robotica 07/2012; 30(04). · 0.88 Impact Factor
  • Xu Zhang, Limin Zhu, Youfu Li, Dawei Tu
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    ABSTRACT: Gamma distortion is a dominant error source of phase measuring profilometry. It makes a single frequency for the ideal sinusoidal waveform an infinite width of spectrum. Besides, the defocus of the projector-camera system, like a spatial low-pass filter, attenuates the amplitudes of the high-frequency harmonics. In this paper, a generic distorted fringe model is proposed, which is expressed as a Fourier series. The mathematical model of the harmonic coefficients is derived. Based on the proposed model, a robust gamma calibration method is introduced. It employs the multifrequency phase-shifting method to eliminate the effect of defocus and preserve the influence of gamma distortion. Then, a gamma correction method is proposed to correct the gamma distortion with the calibrated gamma value. The proposed correction method has the advantage of high signal-to-noise ratio. The proposed model is verified through experiments. The results confirm that the phase error is dependent on the defocus and the pitch. The proposed gamma calibration method is compared with the state of the art and proves to be more robust to pitch and defocus variations. After adopting the proposed gamma correction method, the phase precision is much enhanced with higher quality in the measured surfaces.
    Journal of the Optical Society of America A 06/2012; 29(6):1047-58. · 1.67 Impact Factor
  • Robotica 01/2012; 30(4):613-625. · 0.88 Impact Factor
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    ABSTRACT: In this paper, a new type of decoupled 2-DOF translational parallel micro-positioning stage is designed to realize the 2-DOF ultra-precision linear motion. The stage consists of two piezoelectric actuators (PZTs) and a monolithic compliant mechanism. The monolithic compliant mechanism adopts two types of compound double parallel four-leaf flexures and a mirror symmetric structure to reduce the input and output cross coupling and parasitic motion. Based on the stiffness matrix method and screw theory, a mathematical model is constructed to analyze the compliant mechanism. The optimal design is performed in view of performance constraints. The design results show good static and dynamic performances of the stage, which are well validated by the simulation of finite-element-analysis (FEA) and experimental results. The experimental results show that the proposed stage has a full range of 40μm × 40μm when the full voltage(100V) is applied on the two PZTs. Besides, the stage only has the maximum cross coupling of -50dB between the two axes, low enough to utilize single-input-single-out(SISO) control strategies for positioning and tracking.
    Robotics and Automation (ICRA), 2011 IEEE International Conference on; 06/2011
  • Xu Zhang, Limin Zhu, Youfu Li
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    ABSTRACT: Determining the correspondence in coded structured light is challenging, but it is very important in one-shot techniques for 3D shape reconstruction. The problem of decoding stripe patterns can be modeled as matching two code sequences. We propose decoding edges indirectly based on the property of the stripe pattern, which can be represented as edge code, color code, or mixed code sequences. While traditional methods match two edge code sequences, indirect decoding matches two color sequences or mixed code sequences. The advantages of the proposed method, including a higher Hamming distance, enforced local coherence, and more code information, make indirect decoding excellent in performance. Previously, the lack of ground truth has prevented direct comparisons of different decoding algorithms. Here we obtain six benchmark datasets using the robust space-time analysis. Five decoding methods are quantitatively evaluated using the ground truth. The comparison results show that our method is robust for complex code situations and that it outperforms the state-of-the-art technique in this area.
    Journal of the Optical Society of America A 04/2011; 28(4):651-61. · 1.67 Impact Factor
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    ABSTRACT: A continuous-curvature smoothing algorithm is developed to approximate the linear tool path for high speed machining. The new tool path composed of cubic Bézier curves and lines, which is everywhere G2 continuous, is obtained to replace the conventional linear tool path. Both the tangency and curvature discontinuities at the segment junctions of the linear tool path are avoided. The feed motion will be more stable since the discontinuities are the most important source of feed fluctuation. The algorithm is based upon the transition cubic Bézier curve that has closed-form expression. The approximation error at the segment junction can be accurately guaranteed. The maximal curvature in the transition curve, which is critical for velocity planning, is analytically computed and optimized. The curvature radii of all transition Bézier curves are also globally optimized to pursue the high feed speed by a linear programm model. Therefore, the algorithm is easy to implement and can be integrated into a post-process system.
    Intelligent Robotics and Applications - 4th International Conference, ICIRA 2011, Aachen, Germany, December 6-8, 2011, Proceedings, Part II; 01/2011
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    ABSTRACT: This paper deals with the robust inverse compensation and control for a class of nonlinear systems with unknown asymmetric input backlash. With an analytical expression of the inverse compensation error, a corresponding controller is designed by using the robust adaptive control approach. The developed control law ensures global stability of the whole control system and achieves both stabilization and tracking with desired precision. Simulations performed on an unstable uncertain nonlinear system illustrate and clarify the approach.
    Cybernetics and Intelligent Systems (CIS), 2011 IEEE 5th International Conference onCybernetics and Intelligent Systems (CIS), 2011 IEEE 5th International Conference on; 01/2011
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    ABSTRACT: The aim of this paper is to develop an integral equation based spectral method for prediction of chatter stability in low radial immersion milling. First, the delay-differential equation with time-periodic coefficients governing the dynamic milling process is transformed into the integral equation. Then, the duration of one tooth period is divided into the free vibration and the forced vibration processes. While the former one has an analytical solution, the discretization technique is explored to approximate the solution of the latter one. After the forced vibration duration being equally discretized, the Gauss-Legendre formula is used to discretize the definite integral, in the meantime the Lagrange interpolation is adopted for approximating the state item and the time-delay item by using the corresponding discretized state points and time-delay state points. The approximate Floquet transition matrix is thereafter constructed to predict the milling stability based on the Floquet theory. The benchmark examples are utilized to verify the proposed method. Compared with previous time domain methods, the proposed method enables higher rate of convergence. The results also demonstrate that the proposed method is high-effective.
    IEEE International Conference on Robotics and Automation, ICRA 2011, Shanghai, China, 9-13 May 2011; 01/2011
  • Xu Zhang, Limin Zhu
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    ABSTRACT: A robust method for measuring 3D shapes is proposed, in which only one stripe pattern image is required. To determine edge correspondence, we match color codes instead of edge codes because the former are more stable and immune to the standard deviation of the Gaussian filter in edge detection and width of the color band. The color code is identified by K-means. This method exhibits huge advantages in adaptability and automation over thresholding techniques. The proposed decoding method is compared with two well-known algorithms, dynamic programming and multi-pass dynamic programming. Using ground truth, we evaluate the performance of the methods in measuring three different objects. Quantitative and qualitative comparisons are shown in the experiments, and results affirm that our method is effective and robust.
    Optics and Lasers in Engineering 01/2011; · 1.92 Impact Factor
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    ABSTRACT: This paper presents a distributed multiaxis motion control system based on the IEEE-1394 bus. In the system design, the Unified Modeling Language is employed to illustrate interactions of the objects required in the system. The developed system consists of a set of smart distributed control nodes connected one by one through the IEEE-1394 bus. Each smart node contains four modules, i.e., an IEEE-1394 interface module, a digital signal processor module, a field-programmable gate array module, and a digital-to-analog converter module. It accomplishes its own control task and coordinates with the others through information exchanges, sampling sensor signals, and controlling actuators. A scheduled communication protocol is proposed according to the criteria in terms of bounded time delay and guaranteed transmission. Time delays arising from data processing and message transmission are analyzed. A platform is built, and experiments are conducted to demonstrate the capabilities of the developed distributed control system for real-time communication and synchronous tracking control, which are required for multiaxis applications. The results verify the feasible application of the IEEE-1394 bus to distributed motion control.
    IEEE Transactions on Industrial Electronics 01/2011; · 5.17 Impact Factor
  • Gang Zheng, Limin Zhu, Qingzhen Bi
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    ABSTRACT: Strategies for cutter size optimisation and interference-free tool path generation are proposed for five-axis flank milling of centrifugal impellers. To increase the material removal rate and provide a stronger tool shank during flank milling, the cutter size is first maximised under a set of geometric constraints. The tool path is then globally optimised in accordance with the minimum zone criterion for the determined optimal cutter size. Aside from the local interference of the cutter with the design surface, the global interferences with the hub surface and the adjacent blade surface are also considered in the optimisation models. Interference is indicated by the signed distance from the sampled point on the blade surface to the tool envelope surface. This distance is calculated without constructing the envelope surface. On the basis of the differential property of the distance function, we choose a sequential linear programming method in implementing the optimisations. This approach applies to generic rotary cutters, such as cylindrical and conical tools. Simulations are conducted to obtain the optimal cutter size and generate an interference-free tool path for a practical impeller. Simultaneously, a software module that can generate tool envelope surfaces and verify geometric errors is used to validate the proposed method.
    International Journal of Production Research 01/2011; · 1.46 Impact Factor
  • Guo-Ying Gu, LiMin Zhu, Ying Feng
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    ABSTRACT: IEEE 1394 is a high-efficiency communication network to guarantee timely data transmission and perform excellent network interconnection. In this paper, an IEEE-1394-based smart motion control card is presented, which is constructed by the hardware structure of the combination of a digital signal processor (DSP) and a field-programmable gate array (FPGA). The former DSP module implements an IEEE-1394 controller, a servo controller and memory mapping for FPGA access, while the FPGA module is utilized to achieve the logical functions containing quadrature-encoder-pulse (QEP) circuit, feedback count, direction decoder, addressing mapping, DAC pre-processing circuit and I/O interface. For real-time communication, an ISA/IEEE-1394 interface board for the host is designed and the Ardence Real-time Extension (RTX) is adopted for deterministic control of Windows XP-based systems. As a meaningful attempt, an experimental platform is established to evaluate the communication performance of the IEEE-1394 interface. The experimental results show excellent real-time communication performance, which demonstrates the feasible application of the IEEE 1394 interface for distributed motion control systems.
    Intelligent Robotics and Applications - 4th International Conference, ICIRA 2011, Aachen, Germany, December 6-8, 2011, Proceedings, Part II; 01/2011
  • Guo-Ying Gu, LiMin Zhu, Chun-Yi Su
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    ABSTRACT: Piezo-actuated positioning stages are widely ap- plied in many industrial applications for nanometer or sub- nanometer displacement resolution. However, the non-smooth hysteresis nonlinearity inherent to the piezoelectric material usually degrades the tracking performance of the controlled system. The challenge is that there is no general method to design control laws with general hysteresis models. The control algorithms are always developed based on a specific hysteresis model. In this paper, an ellipse-based hysteresis model is used to describe the hysteresis behaviors observed on the piezo-actuated positioning stages. The benefit for such a model lies on the fact that the expressions of the model are completely analytical and can be determined easily by a set of parameters. It is therefore convenient to fuse this model with the available robust control approach to mitigate the effects of hysteresis. To illustrate this advantage, a discontinue-projection-based robust adaptive controller is specifically designed, which guarantees the global stability of the closed control system and achieves excellent tracking performance within a desired precision. Simulation performed on a piezo-actuated positioning stage validates the effectiveness of the developed control approach. Index Terms— Piezo-actuated positioning stage, ellipse-based hysteresis, robust adaptive control
    Information and Automation (ICIA), 2011 IEEE International Conference onInformation and Automation (ICIA), 2011 IEEE International Conference on; 01/2011
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    ABSTRACT: In this paper, a NURBS hardware interpolator based on FPGA is designed to perform the feedrate profile scheduling, de-Boor Cox calculation and second-order Talor expansion to realize real-time interpolation. Look-ahead algorithm including curve-scanning, feedrate adjustment and acceleration/deceleration planning is implemented in the computer to release the computational load of the interpolator, whereas a motion control card with DSP+FPGA architecture receives the pre-processed results from the look-ahead circuit through PCI bus, and sequently performs the interpolation task in the FPGA and position servo control in the DSP. Experiments are carried out to verify the feasibility of this interpolator. The results imply the FPGA can finish the interpolation within 0.5ms, meanwhile its resource utilization and the calculation speed can compromise to satisfy the practical application.
    Intelligent Robotics and Applications - 4th International Conference, ICIRA 2011, Aachen, Germany, December 6-8, 2011, Proceedings, Part II; 01/2011

Publication Stats

218 Citations
51.64 Total Impact Points

Institutions

  • 2004–2013
    • Shanghai Jiao Tong University
      • • State Key Laboratory of Mechanical Systems and Vibration
      • • Department of Mechanical Engineering (ME)
      • • School of Mechanical Engineering
      Shanghai, Shanghai Shi, China
  • 2010–2011
    • Shanghai University
      • Department of Precision Mechanical Engineering
      Shanghai, Shanghai Shi, China