Liang Yingchun

Design and Testing of a Nanometer Positioning System

This paper presents the design and implementation of a positioning system with a dc servomotor and ball-screw mechanism used to realize high-precision positioning over a wide travel range with nanometer level positioning error and near zero overshoot. Instead of the popular dual-model control strategy and friction compensation, a high-gain proportional-integral-derivative controller is used to realize a single-step point-to-point positioning. The controller parameters are obtained by placing closed-loop poles according to the macrodynamics of a ball-screw mechanism only to avoid identification of microdynamics and friction modeling. In order to suppress the overshoot caused by actuator saturation in long-stroke positioning, a trajectory planning method is applied to calculate the input of the closed-loop system. Experimental and simulation results demonstrate that single-step precision positioning responses to different size commands are achieved without producing any large overshoot. In point-to-point positioning from 100 mm down to 10 nm, the positioning error is within 2 nm and the response dynamics is satisfactory.

Molecular dynamics simulation on mechanical property of carbon nanotube torsional deformation

In this paper torsional deformation of the carbon nanotubes is simulated by molecular dynamics method. The Brenner potential is used to set up the simulation system. Simulation results show that the carbon nanotubes can bear larger torsional deformation, for the armchair type (10,10) single wall carbon nanotubes, with a yielding phenomenon taking place when the torsional angle is up to 63?(1.1rad). The influence of carbon nanotube helicity in torsional deformation is very small. The shear modulus of single wall carbon nanotubes should be several hundred GPa, not 1?GPa as others report.

High-precision micro-displacement actuatorand its application in polar astronomical telescope

High-precision tiling technology is an effective way to fabricate large-aperture astronomical telescope. Based on the application of micro-displacement actuator in the area of large-aperture astronomical telescope, the principle of tiling mirrors and the characteristic of micro-displacement actuator were presented at first. Secondly, the mechanical structures and working principles of typical micro-displacement actuators were reviewed according to the ground-based large-aperture astronomical telescope constructed. The key technologies for micro-displacement actuator in polar low-temperature environment were analyzed emphatically, which include mechanical structure design in low-temperature, anti-ice and deicing technology, material for micro-displacement actuator, lubrication technology in low-temperature and control of actuator. Moreover, the key technologies that should be solved were summarized for the application of micro-displacement actuator in Antarctic astronomical telescope and the prospect for the micro-displacement actuator in Antarctic area was proposed in terms of the future development trend.

Deposition mechanism of nano-structured single-layered C36 film on a diamond (100) crystal plane

The Brenner–LJ potential is adopted to describe the interaction between C36 clusters and diamond surface, and the deposition mechanism of multi-C36 clusters on the diamond surface is also studied by using the method of molecular dynamics simulation. The simulation results show that the competition effects of two interactions, i.e. the interaction between cluster and cluster and the interaction between cluster and crystal plane, are studied, and then the influence of these competition effects on C36 cluster deposition is analysed. The finding is that when an incident energy is appropriately chosen, C36 clusters can be chemically adsorbed and deposited steadily on the diamond surface in the form of single-layer, and in the deposition process the multi-C36 clusters present a phenomenon of energy transmission. The experimental result shows that at a temperature of 300K, in order to deposit C36 clusters into a steady nano-structured single-layered film, the optimal incident energy is between 10 and 18 eV, if the incident energy is larger than 18 eV, the C36 clusters will be deposited into an island nano-structured film.

CONTROLLER RESEARCH ON EMB SYSTEM OF GRINDING MACHINE SPINDLE

In order to solve the difficult that achieves the high stiffness and high rotational speed of grinding machine system supported by electromagnetic bearing(EMB)at the same time because of the EMBs nonlinearity,electromagnetic force as the input and electromagnetic force formula,electromagnet and power amplifier are integrated to electromagnetic force com- ponents,On the basis of thinking of relationship and effects above,the excited current is calculated inversely in order to ensure controller output signal.The advantages of this method are that the calculation of electromagnetic force and the controller design can be considered separately without considering the nonlinearity.The experimental results show that the two indexes can be achieved at the same time and the effects come from electromagnetic force perturbation can be overcame by means of being adopted H_∞controller with elec- tromagnetic force components.

Energy conversion of nano-cantilever beam with forced vibration in low vacuum housing

The study of damping as the micro-resonator is vibrating has been a most important aspect which effects and pushes the development of resonator. The most effective measure to achieve high working capability is to encapsulate the resonator structure in housing where air is rarefied. However, in most cases, it is very difficulty to realize the absolute vacuum in the housing. Therefore, it is important to study the effect of damping for resonator. In this paper, nano-cantilever beam which is widely used in resonator is analyzed, and molecular dynamics simulation method is used to study energy conversion problem when the beam is encapsulated in different vacuum degree housing. The width and high of the nano-cantilever beam is equal and is 2.172nm, and the length is 10.860nm. By adopting Tersoff function, potential energy between beam atoms is calculated. After relaxation, it is found that the length of beam is shorten about three percent, and the area of cross section is increased slightly, furthermore the area of cross section on two end sides is lightly more than the area of the middle cross section of the beam. On the other hand, the distortion of the beam with forced vibration is simulated on the condition that the pressure in the housing is from 1000pa to 1pa. From experimental data we can found that the losing energy for collision between air molecules and beam atoms is gradually decreased with the pressure reduced. In the same condition, the losing energy is almost linear increasing with the time increased. The line slope was decreased from 0.03934362 at 1000pa pressure to 0.00003964 at 1pa pressure. When the pressure in the housing js reduced to zero, namely absolute vacuum, the energy got by the beam from outside force is changed periodically with the time change. For the energy from beam gravity is at 10-12 ev degree, the gravity effect for whole beam system is so small that it can be neglected as well as the macro-structure. The above-mentioned results are useful to design and optimize the parameters of nano-structure, and provide the academic foundation for MEMS/NEMS developing

An Improved Diagonalization Multiplier Method and Its Applications

Benefiting from the constrainted variable metric method (CVMM) we developed an new optimal algorithm called Generalized constrainted quasi-Newton method (GCQNM)on the basis of the Diagonalization multiplier method (DMM). It was successfully used in finite element-optimal design of maehine tool parts involving both static and dynamic constraints and good numerical results are achieved.