Yunbo He

A large-stroke flexure fast tool servo with new displacement amplifier

As the rapid progress of science and technology, the free-form surface optical component has played an important role in spaceflight, aviation, national defense, and other areas of the technology. While the technology of fast tool servo (FTS) is the most promising method for the machining of free-form surface optical component. However, the shortcomings of short-stroke of fast tool servo device have constrained the development of free-form surface optical component. To address this problem, a new large-stroke flexible FTS device is proposed in this paper. A series of mechanism modeling and optimal designs are carried out via compliance matrix theory, pseudo-rigid body theory, and Particle Swarm Optimization (PSO) algorithm, respectively. The mechanism performance of the large-stroke FTS device is verified by the Finite Element Analysis (FEA) method. For this study, a piezoelectric (PZT) actuator P-840.60 that can travel to 90 µm under open-loop control is employed, the results of experiment indicate that the maximum of output displacement can achieve 258.3µm, and the bandwidth can achieve around 316.84 Hz. Both theoretical analysis and the test results of prototype uniformly verify that the presented FTS device can meet the demand of the actual microstructure processing.

Geometric model reconstruction through a surface extension algorithm for remanufacturing of twist blades

Purpose Remanufacturing of worn blades with various defects normally requires processes such as scanning, regenerating a geometrical reference model, additive manufacturing (AM) through laser cladding, adaptive machining and polishing and quality inspection. Unlike the manufacturing process of a new part, the most difficult problem for remanufacturing such a complex surface part is that the reference model adaptive to the worn part is no longer available or useful. The worn parts may suffer from geometrical deformation, distortion and other defects because of the effects of harsh operating conditions, thereby making their original computer aided design (CAD) models inadequate for the repair process. This paper aims to regenerate the geometric models for the worn parts, which is a key issue for implementing AM to build up the parts and adaptive machining to reform the parts. Unlike straight blades with similar cross sections, the tip geometry of the worn tip of a twist blade needs to be regenerated by a different method. Design/methodology/approach This paper proposes a surface extension algorithm for the reconstruction of a twist blade tip through the extremum parameterization of a B-spline basis function. Based on the cross sections of the scanned worn blade model, the given control points and knot vectors are firstly reconstructed into a B-spline curve D. After the extremum of each control point is calculated by extremum parameterization of a B-spline basis function, the unknown control points are calculated by substituting the extremum into the curve D. Once all control points are determined, the B-spline surface of the worn blade tip can be regenerated. Finally, the extension algorithm is implemented and validated with several examples. Findings The proposed algorithm was implemented and verified through the exampled blades. Through the extension algorithm, the tip geometry of the worn tip of a twist blade can be regenerated. This method solved a key problem for the repair of a twist blade tip. It provides an appropriate reference model for repairing worn blade tips through AM to build up the blade tip and adaptive machining/polishing processes to reform the blade geometry. Research limitations/implications The extension errors for different repair models are compared and analyzed. The authors found that there are several factors affecting the accuracy of the regenerated model. When the cross-section interval and the extension length are set properly, the restoration accuracy for the blade tip can be improved, which is acceptable for the repairing. Practical implications The lack of a reference geometric model for worn blades is a significant problem when implementing blade repair through AM and adaptive machining processes. Because the geometric reference model is unavailable for the repair process, reconstruction of the geometry of a worn blade tip is the first crucial step. The authors proposed a surface extension algorithm for the reconstruction of a twist blade tip. Through the implementation of the proposed algorithm, the blade tip model can be regenerated. Social implications Remanufacturing of worn blades with various defects is highly demeaned for the aerospace enterprises considering sustainable development. Unlike straight blades, repair of twist blades encountered a very difficult problem because the geometric reference model is unavailable for the repair processes. This paper proposed a different method to generate the reference model for the repair of a twist blade tip. With this model, repair of twist blades can be implemented through AM to build up the blade tip and adaptive machining to subtract the extra material. Originality/value The authors proposed a surface extension algorithm to reconstruct the geometric model for repair of twist blades.

Review and Comparison of High-Dynamic Range Three-Dimensional Shape Measurement Techniques

In the last decade, a significant number of techniques for three-dimensional (3D) shape measurement have been proposed. There are a large number of measurement demands for metallic workpieces with shiny surfaces in industrial applications; however, such shiny surfaces cannot be directly measured using the conventional structured light method. Therefore, various techniques have been investigated to solve this problem over the last few years. Some reviews summarize the different 3D imaging techniques; however, no comprehensive review exists that provides an insight into high-dynamic range (HDR) 3D shape measurement techniques used for shiny surfaces. We present a survey of recent HDR techniques for the digitization of shiny surfaces and classify and discuss the advantages and drawbacks of different techniques with respect to each other.

A Rapid Vibration Reduction Method for Macro–Micro Composite Precision Positioning Stage

A macro-micro composite precision positioning stage is mainly used in microelectronics manufacturing to achieve high velocity, high precision, and large-stroke positioning. The positioning accuracy and working efficiency of the stage are influenced by the inertial vibration caused by motion with high acceleration. This paper proposes an active vibration reduction (AVR) method employing a piezoelectric device for a designed macro-micro motion stage. The design model of the stage is established and its dynamic models are explored. The feasibility of the piezoelectric device as a vibration damper for the designed positioning stage is demonstrated through theoretical analyses, including natural frequency analysis and inertial vibration energy analysis. Furthermore, an optimal design of the stage with the AVR mechanism is established and then verified experimentally. The performance of the AVR method is examined and characterized through investigation of the differences in inertial vibration energy with and without the AVR, and the performance of the proposed method in terms of the vibration amplitude and positioning time is measured at different accelerations, velocities, and strokes. The theoretical and experimental analyses indicate the effectiveness of the proposed vibration reduction method, and this method could be employed in several applications that require vibration reduction.

Effects of Defects on the Mechanical Properties of Kinked Silicon Nanowires

Kinked silicon nanowires (KSiNWs) have many special properties that make them attractive for a number of applications. The mechanical properties of KSiNWs play important roles in the performance of sensors. In this work, the effects of defects on the mechanical properties of KSiNWs are studied using molecular dynamics simulations and indirectly validated by experiments. It is found that kinks are weak points in the nanowire (NW) because of inharmonious deformation, resulting in a smaller elastic modulus than that of straight NWs. In addition, surface defects have more significant effects on the mechanical properties of KSiNWs than internal defects. The effects of the width or the diameter of the defects are larger than those of the length of the defects. Overall, the elastic modulus of KSiNWs is not sensitive to defects; therefore, KSiNWs have a great potential as strain or stress sensors in special applications.

Ladderlike Tapered Pillars Enabling Spontaneous and Consecutive Liquid Transport

Directional liquid transport has significant domestic and industrial applications. Tapered objects have theoretically and experimentally been demonstrated to have the ability to spontaneously transport liquids. However, the transporting distance is limited, and consecutively and spontaneously transporting liquids has always been a challenge. In this work we proposed to exploit ladderlike tapered pillars, which are inspired by relay races, to increase the transport distance. These pillars were designed using a developed numerical model and fabricated by a novel alternating etching and coating method followed by wettability enhancement. We demonstrated through experiments that the resulting pillars could consecutively and spontaneously transport a liquid droplet at an average velocity of 0.139 m/s with a maximum acceleration of 5 g. The optimum window of the tilt angle range (0°-25°), contact angle (50°), and the chemical modification time (5 min) were obtained. Such ladderlike tapered pillars are able to improve the water-collection efficiency. These results may provide a new and systematic way to design and fabricate materials and structures for directional liquid transport.

Fine tuning development software for high precision and Multi-Axis Motion Control System

Motion control system is the core component of high density packaging equipment, the characteristics of its movement performance directly determines the performance and quality of the high density packaging equipment. Based on this, this paper presents a method to enhance the dynamic performance and setting performance of motion control system by means of fine tuning for the movement parameters of the movement system, A high performance motion control card is developed for real-time control and real-time data processing on the multi-axis control platform in our experiments. In addition, the high efficient real-time analytical software is developed and applied to the experiments. The interface of the software real-time displays the movement characteristic curve of movements. The experimental results show that in the case of other conditions unchanged, fine tuning for the movement parameters of the motion system brings benefits of lower undershoot and faster settling of motions. Experimental results show that the performance and quality of the high density packaging equipment is greatly improved through the optimization of the motion control parameters of the Multi-Axis Motion Control System.

Modeling study of the dynamics of silicone-phosphor in jet dispensing process for LED packaging

Jet dispensing is one of the key technologies in LED packaging as the consistency of the dispensed volume can directly affect the LED color and quality. Studying the dynamics of silicone-phosphor during the jet dispensing process is of great value. In this paper, a multi-physical model was developed and verified by the experiments. The silicone-phosphor thread profile during the jet dispensing process and break-up time were obtained and analyzed. The effects of piston velocity, nozzle size and dispensing height on the jet dispensing process were studied. It is found that the proper piston velocity is about 2.0 m/s, and the optimized dispensing height is about 10 times of the diameter of the nozzle tip. Nozzle size can speed up the break time but the effect is limited. These findings will be helpful for dispenser design and dispensing technology development in modern LED packaging.

A rapid PID control method for high-speed macro-micro composite positioning stage

Based on the analysis of macro-micro composite driving positioning technology, a high precision macro-micro positioning stage integrated a voice-coil-motor (VCM) and piezoelectric actuator (PZT). The stage can combine the characteristics of large stroke and high acceleration of the VCM and the high precision and heavy load of the PZT. In this paper, a single axis positioning stage is developed to detect the control performance of the macro-micro composite positioning stage. The macro motion of the platform is driven by a VCM to achieve a high acceleration and large stroke motion. The high precision micro motion is driven by the PZT. The double PID control method is used to compensate the positioning error caused by the macro motion. In the positioning process of the macro motion, a double PID control method is used to compensate the position error and suppress vibration and achieve precise and fast positioning targets. The experimental results showed that the positioning accuracy of the positioning stage can be achieved the within 50 nm with the acceleration of 5 g.

A regularized on-line sequential extreme learning machine with forgetting property for fast dynamic hysteresis modeling

Piezoelectric ceramics(PZT)actuator has been widely used in flexure-guided nanopositioning stage because of their high resolution. However, it is quite hard to achieve high-rate precision positioning control because of the complex hysteresis nonlinearity effect of PZT actuator. Thus, an online RELM algorithm with forgetting property(FReOS-ELM) is proposed to handle this issue. Firstly, we adopt regularized extreme learning machine(RELM)to build an intelligent hysteresis model. The training of the algorithm is completed only in one step, which avoids the shortcomings of the traditional hysteresis model based on artificial neural network(ANN) that slow training speed and easy to fall into the local minimum. Then, based on the regularized on-line sequential extreme learning machine(ReOS-ELM), an on-line RELM algorithm with forgetting property(FReOS-ELM) is designed, which can avoid the computational load of ReOS-ELM in the process of adding new data for learning on-line. In the experiment, a real-time voltage signal with varying frequencies and amplitudes is adopted, and the output displacement data of the nanopositioning stage is also acquired and analyzed. The results powerfully verify that the performance of the established hysteresis model based on the proposed FReOS-ELM is satisfactory, which can be used to improve the practical positioning performance for flexure nanopositioning stage.