Kunhai Cai

A novel voice coil motor-driven compliant micropositioning stage based on flexure mechanism

This paper presents a 2-degrees of freedom flexure-based micropositioning stage with a flexible decoupling mechanism. The stage is composed of an upper planar stage and four vertical support links to improve the out-of-plane stiffness. The moving platform is driven by two voice coil motors, and thus it has the capability of large working stroke. The upper stage is connected with the base through six double parallel four-bar linkages mechanisms, which are orthogonally arranged to implement the motion decoupling in the x and y directions. The vertical support links with serially connected hook joints are utilized to guarantee good planar motion with heavy-loads. The static stiffness and the dynamic resonant frequencies are obtained based on the theoretical analyses. Finite element analysis is used to investigate the characteristics of the developed stage. Experiments are carried out to validate the established models and the performance of the developed stage. It is noted that the developed stage has the capability of translational motion stroke of 1.8 mm and 1.78 mm in working axes. The maximum coupling errors in the x and y directions are 0.65% and 0.82%, respectively, and the motion resolution is less than 200 nm. The experimental results show that the developed stage has good capability for trajectory tracking.

Wrinkling Behaviour of Annular Graphynes under Circular Shearing Load Using Molecular Dynamics Simulations

Graphyne, a novel carbon allotrope, is a two-dimensional lattice of sp2+sp1 hybridization-type carbon atoms, similar to graphene. The initiation and development of wrinkles in single-layer graphynes (α-, β-, γ-, and 6, 6, 12-graphyne) subjected to in-plane circular shearing are investigated. In comparison with graphene, wrinkle pattern and profile characterization in relation to wave number, wavelength and amplitude of graphynes are extensively explored using classic molecular-dynamics (MD) simulations. Unlike graphene, the wave numbers of graphynes increase with increasing rotational angles; the wavelengths reduce correspondingly. The amplitudes show an increasing trend, with some local drops when the rotational angles increase. The drops occur as the positions of the wave numbers increase. Graphynes have superior fracture properties to graphene, despite the densities of graphynes being far lower. The fracture rotational angles depend on the percentages of acetylenic linkages in the graphyne structures: the more acetylenic linkages, the larger the fracture rotational angles. Meanwhile, acetylenic linkages also affect the bond length strains of the graphynes during the wrinkling process. The influences of the temperature on the fracture rotational angles are also examined to obtain further insights into the mechanical properties of such kinds of carbon allotropes. The achieved results can be used as guidelines for the wrinkling control and potential applications of graphynes.

Mechanical properties investigation of monolayer h-BN sheet under in-plane shear displacement using molecular dynamics simulations

The mechanical properties, including wrinkling patterns and fracture behavior, of monolayer h-BN sheets have been investigated using classic molecular dynamics simulations and continuum model. The wrinkling pattern formation and evolution have been first explored. The dependences of the wrinkling shape, amplitude, and wavelength, as well as wrinkling number on shear displacement are extensively elucidated. The influences of geometry and shear load direction, as well as temperature, on the fracture behavior have also been studied to obtain further insights into the properties of the monolayer h-BN sheets.

Development and Testing of a XYZ Scanner for Atomic Force Microscope

Atomic force microscopy (AFM) is a widely used tool in nano measurement and manipulation techniques. However, a traditional AFM system suffers from the limitation of slow scanning rate, due to the low dynamic performance of piezoelectric positioners. As an important part of AFM system, scanner will have a significant impact the result of the scanning imaging and operation. It is well know that high-speed operation of an AFM are increasingly required, and it is also a challenge for the researchers. In this paper, we proposed a parallel kinematic high-speed piezoelectric actuator (PZT) XYZ scanner. The design is aimed at achieving high resonance frequencies and low cross-coupling. The developed stage consists of a parallel kinematic XY stage and a Z stage. The Z stage is mounted on the central moving platform of the XY stage. To achieve the design objective, several parallel leaf flexure hinge mechanisms, arranging symmetrically around the central moving platform of the XY stage, are utilized to provide large stiffness and reduce cross-coupling. For the Z stage, a symmetrical leaf flexure parallelogram mechanism is adopted to achieve high resonance frequencies and decoupling. Then, finite element analysis (FEA) is utilized to validate the characteristics of the XYZ scanner. Finally, extensive experiments are conducted, demonstrating feasibility of the proposed scanner.

Design and stiffness analysis of a XYZ scanning stage

A compact XYZ precision scanning stage is designed in this paper, which is assembled by a XY and a Z precision positioning stages. Each stage is driven by piezoelectric actuator, and guided by symmetric parallel flexible hinges, respectively. These parallel flexible hinges are arranged symmetrically to reduce cross-coupling among X-, Y- and Z-axis. In addition, the theoretical stiffness modeling of the scanner was carried out. According to an effective strain energy method, the stiffness model are obtained, which provides a useful tool to calculate the stiffness of scanner. Furthermore, the characteristics of the XYZ scanner are evaluated in this paper by finite element analysis simulation. The simulation results show that the cross-axis coupling ratio of the proposed scanner is less than 0.91%, indicating excellent decoupling performances. Meanwhile, and the dynamic characteristics are investigated and the results are shown that the design scanner provides the large dynamic bandwidth.

Design of a 6-DOF precision positioning stage: Kinematic analysis and dynamic modeling

A novel 6-DOF precision positioning system is designed in this paper, which is assembled by two type 3-DOF precision positioning stages. Each stage is driven by three piezoelectric actuators (PEAs), and guided by three symmetric T-shape hinges and three elliptical flexible hinges, respectively. The kinematics of this 6-DOF system are investigated. According to an effective kinematic model, the transformation matrix are obtained, which provides a useful tool to predict an output displacement. In addition, the dynamic model of the 6-DOF system is established. The PEAs can be treated as a force generator with a built-in spring-damper component. Furthermore, the characteristics of the 6-DOF system are evaluated in this paper by the FEM simulation. The design structure provides the high dynamic bandwidth. Meanwhile, the experiment is performed to verify the 6-DOF stage has a good characteristic.

Torsional Properties of Boron Nitride Nanocones with Different Cone Heights, Disclination Angles and Simulation Temperatures

The torsional properties of single-walled boron nitride (BN) nanocones at different cone heights, disclination angles and simulation temperatures have been investigated using molecular dynamics (MD) simulation. The simulation results indicate that the torque and average potential energy decrease with the increasing cone height and disclination angle, and the failure torsion angle increases with the increasing cone height and disclination angle. For different simulation temperatures, the torsional behavior of BN nanocones at higher simulation temperature is more serious and earlier to reach a failure point, the maximum torque and average potential energy of the system decrease with the increasing simulation temperature. For different loading rates, the failure torsion angle decreases with the increasing loading rate, so the fracture of BN nanocone occurred earlier with higher loading rate. Therefore, the cone height, disclination angle, simulation temperature and loading rate are considered to be four main influencing factors for the torsional properties of the BN nanocones.