Xuesong Mei

Study of the friction error for a high-speed high precision table

Friction is one of the important factors resulting in the contour error of feed servo systems for high-speed, high precision CNC machine tools. A mathematical model of a high speed high precision feed servo table with PID controlling has been established with consideration of friction effects. The friction can be calculated according to the sliding speed and the oil film between the two contact surfaces by using a two-component mixed friction model. The protrusion error occurring at the quadrant boundary in the circular motion is profoundly studied by means of numerical simulation and experiments under different work conditions, and the conclusion that the quadrant protrusion error lags with the rising of the feed rate is obtained. Comparisons between the simulation results and the experimental results demonstrate that with the mathematical model, the dynamics of high speed high precision servo feed systems under PID controlling can be accurately simulated, and the friction error and its characteristics in the course of feeding can be precisely predicted.

Formation of porous structure with subspot size under the irradiation of picosecond laser pulses

A study was presented in this paper on porous structure with microsize holes significantly smaller than laser spot on the stainless steel 304 target surface induced by a picosecond Nd:van regenerative amplified laser, operating at 1064 nm. The target surface variations were studied in air ambience. The estimated surface damage threshold was 0.15 J/cm2. The target specific surface changes and phenomena observed supported a complementary study on the formation and growth of the subspot size pit holes on metal surface with dependence of laser pulse number of 50-1000 and fluences of 0.8 and 1.6 J/cm2. Two kinds of porous structures were presented: periodic holes are formed from Coulomb Explosion during locally spatial modulated ablation, and random holes are formed from the burst of bubbles in overheated liquid during phase explosion. It can be concluded that it is effective to fabricate a large metal surface area of porous structure by laser scanning regime. Generally, it is also difficult for ultrashort laser to fabricate the microporous structures compared with traditional methods. These porous structures potentially have a number of important applications in nanotechnology, industry, nuclear complex, and so forth.

Nanospot soldering polystyrene nanoparticles with an optical fiber probe laser irradiating a metallic AFM probe based on the near-field enhancement effect.

With the development of nanoscience and nanotechnology for the bottom-up nanofabrication of nanostructures formed from polystyrene nanoparticles, joining technology is an essential step in the manufacturing and assembly of nanodevices and nanostructures in order to provide mechanical integration and connection. To study the nanospot welding of polystyrene nanoparticles, we propose a new nanospot-soldering method using the near-field enhancement effect of a metallic atomic force microscope (AFM) probe tip that is irradiated by an optical fiber probe laser. On the basis of our theoretical analysis of the near-field enhancement effect, we set up an experimental system for nanospot soldering; this approach is carried out by using an optical fiber probe laser to irradiate the AFM probe tip to sinter the nanoparticles, providing a promising technical approach for the application of nanosoldering in nanoscience and nanotechnology.

Study on the load distribution of ball screws with errors

A model is developed to analyze the load distribution of ball screws with geometry errors. The load distribution of the contact of the balls and grooves is theoretically investigated under various load conditions. The results demonstrate that the negative geometry errors of the ball screw result in the decrease of the load on balls or guiding grooves, and when the negative errors reach certain value there is no contact between the balls and the groove. On the other hand, if geometry errors of the ball screw are positive, the load increases. If the error heights are assumed to be a normally random distribution, the load distribution without geometry error is the average value of that in random error. It is valuable for equilibrating the load distribution to correct nut grooves. The simulation results show that the model proposed in this paper is significant to the study of the characteristics of ball screws with regard of geometry errors.

Ablation experiment and threshold calculation of titanium alloy irradiated by ultra-fast pulse laser

The interaction between an ultra-fast pulse laser and a materials surface has become a research hotspot in recent years. Micromachining of titanium alloy with an ultra-fast pulse laser is a very important research direction, and it has very important theoretical significance and application value in investigating the ablation threshold of titanium alloy irradiated by ultra-fast pulse lasers. Irradiated by a picosecond pulse laser with wavelengths of 1064 nm and 532 nm, the surface morphology and feature sizes, including ablation crater width (i.e. diameter), ablation depth, ablation area, ablation volume, single pulse ablation rate, and so forth, of the titanium alloy were studied, and their ablation distributions were obtained. The experimental results show that titanium alloy irradiated by a picosecond pulse infrared laser with a 1064 nm wavelength has better ablation morphology than that of the green picosecond pulse laser with a 532 nm wavelength. The feature sizes are approximately linearly dependen...

Nanoscale Electrodes for Flexible Electronics by Swelling Controlled Cracking

Nanogap electrodes are realized using pre-patterned electrodes and a swelling controlled cracking method. Parallel fabrication of nanogap electrodes on flexible substrates can be achieved using this method. This swelling-controlled cracking method is promising for fabricating high-performance flexible electronics. UV photodetectors with ZnO nanoparticle-bridged nanogap electrodes exhibit high responsivity and external quantum efficiency.

Thermal error compensation on a computer numerical control machine tool considering thermal tilt angles and cutting tool length

The present error compensation technology of computer numerical control machine tools ignores radial thermal tilt angle errors of the spindle, while the thermal-induced offset is closely related to the tilt angle and the handle length. To solve this problem, three models of spindle thermal errors are proposed for the thermal yaw, pitch angles and elongation, and error compensation is performed based on the thermal tilt angles and cutting tool length. A five-point method was applied to measure the spindle thermal drifts at different speeds by eddy current sensors, which could effectively analyse the changes in the position-pose of the errors. Fuzzy clustering and correlation analysis were applied to group and optimise the temperature variables and select the variables sensitive to thermal errors in order to depress the multicollinearity of the temperature variables and improve the stability of the model. Finally, the thermal offset compensation was conducted in three directions. The results indicate that back propagation has a better capability for nonlinear fitting, but its generalisation is far less than that of time series. While the structure of multiple linear regression analysis is simple, its prediction accuracy is not satisfied. Time series adequately reflects the dynamic behaviours of the thermal error, and the prediction accuracy can reach 94%, with excellent robustness under different cutting conditions. The thermal error compensation equation that includes thermal tilt angles and cutting tool length is suitable for actual conditions and can accurately describe the space-pose of the thermal deformation and improve the machining accuracy.

A Decoupling Control Algorithm for Unwinding Tension System Based on Active Disturbance Rejection Control

This paper presents a new control methodology based on active disturbance rejection control (ADRC) for designing the tension decoupling controller of the unwinding system in a gravure printing machine. The dynamic coupling can be actively estimated and compensated in real time, which makes feedback control an ideal approach to designing the decoupling controller of the unwinding system. This feature is unique to ADRC. In this study, a nonlinear mathematical model is established according to the working principle of the unwinding system. A decoupling model is also constructed to determine the order and decoupling plant of the unwinding system. Based on the order and decoupling plant, an ADRC decoupling control methodology is designed to enhance the tension stability in the unwinding system. The effectiveness and capability of the proposed methodology are verified through simulation and experiments. The results show that the proposed strategy not only realises a decoupling control for the unwinding system but also has an effective antidisturbance capability and is robust.

Tension controller design for unwinding tension system based on active disturbance rejection control

A unique controller based on active disturbance rejection control (ADRC) method is presented to strengthen the stability of the tension in unwinding system of gravure printing machines. The uniqueness of the ADRC design is that both the internal dynamics and the external disturbances can be actively estimated and compensated in real time, which makes the feedback control to be an ideal candidate to design controller of the unwinding system. In this study, a nonlinear mathematical model is established according to the unwinding systems working principle, and the order of the unwinding system is constructed. Based on the order and dancer roll model, an ADRC controller and a tension observer are designed to enhance the stability of the tension in unwinding system respectively. The results of simulation show that the proposed tension controller has better robustness and disturbance rejection than traditional PID controller in tension control of the unwinding system.

Research status and application prospects of manufacturing technology for micro–nano surface structures with low reflectivity

The light trapping surface of micro–nanostructure can significantly improve the performance of optical transmission and can greatly reduce the broadband domain of material surface reflectivity, which means the material surface absorptivity on wide-spectrum signal is enhanced. Several commonly used methods for manufacturing micro–nano surface of light trapping structure with low reflectivity are introduced first, including chemical etching, mechanical grooving, reactive ion etching, common long-pulse laser grooving, and ultra-fast pulse laser processing. This is followed by a comparison of the advantages and disadvantages of these methods. Among these methods, ultra-fast pulse laser processing is an ideal manufacturing technology for fabrication of light trapping structures. The research status of the micro–nano manufacturing technology of structured surfaces for light trapping with low reflectivity is reviewed, and emphasis is given to their application prospects. The research directions and trends of the micro–nano manufacturing technology of structured surfaces for light trapping with low reflectivity are summarized, and broad application prospects and research value in many fields, such as solar cells, solar water heater, building wave-absorbing materials, information acquisition of mechanized equipments, high-radiation heat exchange equipment, solar heating equipment, and solar air conditioner, are pointed out.