Xiao Jing Yang

Molecular Dynamics Simulations of Sliding Friction of Rigid Sphere with Single Crystal Copper Surface

Using LAMMPS to establish the three-dimensional sliding friction model of the nanoscale diamond hemisphere with the single-crystal copper surface. Simulation and solving the process of sliding friction, research the micro-contact area atomic states change in sliding friction process, and study the friction characteristics change when the rigid sphere sliding on rough surface of the single crystal copper with minute projections. The results indicate that, in the sliding friction process, the lattice of substrate atoms are damaged under the forces of the extrusion which also cause corresponding dislocation and deformation. In the direction of the hemisphere movement, generate the pileup and side stream phenomena, and produce furrows. Friction and normal force rapidly increase with the depth of contact, and then enter into a stable sliding phase. For the thermal motion of atoms, formation of dislocations and the stick-slip effect, the curves of friction and normal force present waves of sawtooth. Small defect on surface of the substrate almost have no effect on the process of sliding friction.

Molecular Dynamics Simulation of Nanoscale Sliding Friction Process between Sphere and Plane

Contact surface of nanoscale sliding friction represent some new features that are different from the macro scale sliding friction, which need to seek new analysis methods. Molecular dynamics simulation is an effective method to describe microscopic phenomena. Therefore, Molecular dynamics method was used to study mechanical behavior of contact surface of nanoscale sliding friction. A molecular dynamics model of hemisphere sphere sliding on rectangular solid plane was built. State change of the micro contact area and friction force variation in the process of sliding friction were observed and analyzed after solution and simulation. The results show that, at the beginning position of the sliding, with different contact depth, contact action region of hemisphere and plane generated the atoms displacement, re-arranged and close-packed accumulation is also different. The deeper the contact depth is, the greater the atoms close-packed accumulation is, and the greater the contact deformation is. In the process of sliding friction, the contact surface of the basal body has produced lattice destruction, surface upheaval and silicon atoms close-packed accumulation, and then formed furrow scratches. At the same time the silicon atoms of the hemisphere generated atomic migration obviously and adhered on the basal body surface. The top of the hemisphere was torn and peeled, which resulted in wear. The deeper contact depth is, the more loss of the material of the hemisphere is, and wear become heavier. The curve of friction force and sliding displacement in different contact depths shows that the deeper contact depth is, the greater friction force is. The friction force increases quickly at the beginning of the sliding. Then the friction force remains steady relatively at stable sliding phase. In subsequent sliding process, due to hemisphere was worn and the original contact surface changed in size, shape and configuration state, friction force decreases obviously. Besides, in process of sliding friction, due to stick-slip effect, friction force appears obviously fluctuations. Moreover, if the sliding speed is large the changes of sliding speed have less effect on friction force when the nanoscale sphere sliding on the plane at the different speeds.

PID+CMAC Neural Network Control of Micro Positioning Platform

Because of some intrinsic properties of the PZT actuator, such as hysteresis, creep and nonlinearity effect, it’s difficult to achieve satisfactory results and control precision for conventional PID controller. In order to improve the control precision of the PZT driven of micro positioning platform, we proposed a CMAC neural network based on PID control scheme, which has the characteristics of realizing feed-forward control and obtaining the inverse dynamic model of controlled object by the CMAC neural network controller, and realizing feedback control by conventional controller, which can ensure the system stability and suppress disturbance. Form MATLAB simulation results, it demonstrates that the CMAC+PID control algorithm can be able to improve the control precision and response time of the system, and enhance the anti-interference ability and robustness, comparing with the traditional digit PID control algorithms.

Nano-Contact Force Calculation Method of Different Tip Radius of Curvature and the Specimen Surface of AFM

Atomic Force Microscope (AFM) works by the force between the probe tip and specimen surface. The nanocontact force between the probe tip and specimen surface has an important influence on the detection surface. Base on the analysis of the working principle of the AFM and nanocontact force calculation model, according to Hamaker assumptions, using continuum method established the theoretical contact force model of the AFM tip. the contact force calculation methods of contact pressure in process has been obtained. The variation of the force between the probe tip and specimen surface has been found by calculation model and programming calculation of Matlab. Provide the basis for improving the accuracy of an atomic force microscope surface inspection and error analysis

Analysis of Micro/Nanoscale Mechanical Properties of Monocrystalline Germanium Using Finite Element Method and Nanoindentation Experiment

The finite element method and nanoindentation experiment are used in this paper, to analysis mechanical properties of monocrystalline germanium on micro/nanoscale. The cloud charts of stress and strain distribution are obtained by finite element method. It is shown that the depth increment of the contact makes the value of stress and strain in the surface layer greater and the area of action larger in the process of nanoindentation of monocrystalline germanium. In the nanoindentation experiment, load and displacement curve is different with different crystal orientations. With the increase of load, contact depth has been increased. The residual deformation depth of three crystal orientations is also different. The results of FEM is is closed to the crystal orientation of [100].

The Design of Feed Drive System of Economical CNC Milling Machine

The feed drive system is important functional components which effects on precision and efficiency of transmission and cost of CNC milling machine tools. So the designe of the feed drive system of economical CNC milling machine tool is researched. Firtsly the general design scheme which includes the transmission scheme and basic parameters of CNC milling machine tool is determined. Then according to the milling force calculated during mill processing, linear rolling guide, ball screw and stepping motor of X axis and Y axis of feed drive system are respectively calculated, selected and checked in detail. Using the Solid works software for 3D modeling and assembly of mechanical parts of feed drive system, By the scheme comparison, selecting the CNC system of Huazhong century star HNC-21 and accomplishing the electrical connection of CNC system.The feed drive system of economical CNC milling machine in the desing is high performance and low cost,and meet accuracy requirement.

The Calibration of Binocular Stereo Vision for the Camera Based on Machine Vision Measurement

Camera calibration is the most important stage of machine vision measurement. The principle and method of camera calibration for binocular stereo vision system are introduced and the left and right CCD are respectively calibrated by using the prepared calibration target and the MATLAB program. Then internal and external camera parameters are obtained by the calibration experiments. The experimental results show that the calibration results have high precision.

Study on a Wireless Temperature and Humidity Monitoring System for Workshop with Constant Temperature Based on SCM

A wireless temperature and humidity monitoring system for workshop with constant temperature based on AT89C52 Single chip microcomputer and nRF905 wireless microchip is studied. The system is consists of base station and slave station. Base station is mainly consists of temperature acquisition module, humidity acquisition module, wireless communicating module and communicating testing module. Good communication protocols play an important role in ensuring the correct monitoring data. So the network topology, communication data form, ad hoc networks protocol, mac protocol and data link layer protocols are discussed for commutation protocol to host computer software. The cost of the system is low and it has a large function area and a good performance. It is able to provide messages of workshop with constant temperature for improving machining accuracy and prolonging the life of equipment in machine shop.

Experimental Research on Mechanical Characteristics in the Process of Nanoscale Sliding Contact

The experiment of mechanical characteristics of sliding contact in nano-scale was researched using nano-indenter. The displacement-friction curves with different loads and sliding velocities were given through the contact effect between diamond indenter and mono-crystalline silicon test-coupon. The three-dimensional AFM morphologies were obtained through scanning contact area by AFM. The research shows that the contact-force and friction increase along with the increment of loads, in condition of sliding with different loads. The friction increases along with the increment of sliding velocity, in condition of different sliding velocities. Otherwise, furrow destruction along with obvious plastic flow is generated with low sliding velocity (100μm/s). However, the oddments accumulate obviously on the verge of nick with high sliding velocity (above 100μm/s), and the phenomenon of oddments accumulating is more obvious along with the increment of sliding velocity.

A Review on Application of Discrete Element Method in Soil Cutting Process

Soil is one of the important mediators in the agricultural production and its particle is a discontinuous, heterogeneity and nonlinear natural geological substance. It is difficult to analyze the soil cutting process by using traditional methods. According to the discrete nature of the agricultural soils, discrete element method based on the discontinuity assumptions can be an alternative to analyze the changes under external forces in the soil cutting process. This article describes the basic principles, its applications and its prospects of the discrete element method, especially in the field of soil cutting.