DESIGN AND CONTROL OF AN ULTRAPRECISION STAGE USED IN GRATING TILING

In petawatt laser system, the gratings.used to compose pulse compressor are very large in size which can be only acquired currently by arraying small aperture gratings to form a large one instead, an approach referred to as grating tiling. Theory and experiments have demonstrated that the coherent addition of multiple small gratings to form a larger grating is viable, the key technology of which is to control the relative position and orientation of each grating with high precision. According to the turin factors that affect the performance of the grating tiling, a 5-DOF ultraprecision stage is developed for the grating tiling experiment. The mechanism is formed by serial structures. The motion of the mechanism is guided by flexure hinges and driven by piezoelectric actuators and the movement resolution of which can achieve nanometer level. To keep the stability of the mechanism, capacitive position sensors with nanometer accuracy are fixed on it to provide feedback signlas with which to realize closed-loop control, thus the positioning.precision of the mechanism is within several nanometers range through voltage control and digital PID algorithm. Results of experiments indicate that the performance of the mechanism can meet the requirement of precision for grating tiling.

Synthesis of Branched Chains with Actuation Redundancy for Eliminating Interior Singularities of 3T1R Parallel Mechanisms

Although it is common to eliminate the singularity of parallel mechanism by adding the branched chain with actuation redundancy, there is no theory and method for the configuration synthesis of the branched chain with actuation redundancy in parallel mechanism. Branched chains with actuation redundancy are synthesized for eliminating interior singularity of 3-translational and 1-rotational（3T1R） parallel mechanisms. Guided by the discriminance method of hybrid screw group according to Grassmann line geometry, all the possibilities are listed for the occurrence of interior singularities in 3T1R parallel mechanism. Based on the linear relevance of screw system and the principles of eliminating parallel mechanism singularity with actuation redundancy, different types of branched chains with actuation redundancy are synthesized systematically to indicate the layout and the number of the branched chainsinterior with actuation redundancy. A general method is proposed for the configuration synthesis of the branched chains with actuation redundancy of the redundant parallel mechanism, and it builds a solid foundation for the subsequent performance optimization of the redundant actuation parallel mechanism.

Fiber‑Shaped Soft Actuators:Fabrication,Actuation Mechanism and Application

As mechanical devices for moving or controlling mechanisms or systems,actuators have attracted increasing attention in various fields.Compared to traditional actuators with rigid structures,soft actuators made up of stimulus-responsive soft materials are more adaptable to complex working conditions due to soft bodies and diverse control styles.Different from plate-shaped soft actuators,which have the limited deformations between two dimensional(2D)and 3D-configurations such as bending and twisting,fiber-shaped soft actuators(FSAs)own intriguing deformation modes to satisfy diverse practical applications.In this mini review,the recent progress on the controlled fabrication of the FSAs is presented.The advantages and disadvantages of each fabrication method are also demonstrated.Subsequently,the as-developed actuation mechanisms of the FSAs are displayed.Additionally,typical examples of the related applications of the FSAs in different fields have been discussed.Finally,an outlook on the development tendency of the FSAs is put forward as well.

Actuation Mechanism of Two-step Reverse Transformation Behavior in TiNi Alloys Deformed at Parent Phase

The actuation mechanism of TiNi shape memory alloy wires, which were deformed at parent phase followed by a cooling process under constant strain constraint, was investigated. The experimental results show that the two-step reverse martensitic transformation behavior occurs during the heating process, and the temperature range of reverse transformation was obviously widened with the increasing of prestrain. The recovery strain vs temperature curves exhibits an actuation characteristic of linear output recovery strain in a wide temperature range.

Research on Optimal Design of the Transmission Mechanism of a Pressure Meter

The actuating mechanism of a manometer is to magnify and transform the small displacement generated by elastic components, and then the pressure value is indicated by the deflection angle of the pointer. The error between the indicated and actual pressure value can be large without giving sufficient consideration to the displacement of the elastic component and the inherent non-linearity of a actuating mechanism in its traditional design. In this paper, in order to increase the accuracy and rationality of transmission, the elastic component and transmission non-linearity is fitted and the mathematical models are constructed based on centre displacement of elastic instru- ment components. An optimum program is compiled by MATIABS. O, the optimal parameters to compensate the non- linear displacement of a crank link in two groups to spring is obtained. The error analysis of the manometer shows that it is an efficient method to reduce the errors caused by the elastic components and the non-liner characteristic of actuating a mechanism through the optimized design.

Azobenzene Based Photo-responsive Mechanical Actuator Fabricated by Intermolecular H-bond Interaction

Photo-responsive mechanical actuator is a class of stimuli-responsive materials transferring light to mechanical energy through macroscopic transformation.To fabricate photo-responsive mechanical actuator,soft polymeric materials crosslinked with functional bridging structures are desired.Supramolecular interaction is a relatively common way to fabricate crosslinked materials due to its excellent self-assembly performance.And azobenzene and derivatives are ideal candidates of photo-responsive materials because of the unique photo-induced trans-cis isomerization.Here,a new kind of crosslinked materials based on supramolecular interaction between 4,4'-dihydroxyazobenzene and chitosan is reported.Under 355 nm irradiation,the macroscopic bending of polymeric materials occurs rapidly due to the photo-isomerization of 4,4-dihydroxyazobenzene.Meanwhile,the photo-responsive mechanical actuator can also lift weight which is up to 200 times that of the actuator itself,and convert energy from light to mechanical work efficiently.This report suggests a new kind of photo-responsive actuator based on supramolecular interaction and may be helpful to contribute a theoretical basis to the design and synthesis of photo-responsive mechanical actuator suitable for large-scale manufacturing industrialization in future.

Study on Friction Torque Loading with an Electro-hydraulic Load Simulator

This article, in order to precisely impose friction on aircraft and weapon actuation systems, presents a new friction loading method characteristic of ＂torque-zero velocity＂ switching control with an electro-hydraulic load simulator. As the general Stribeck friction model has little related to static friction, it proposes a ＂torque-zero velocity＂ switcher, in which a zero-velocity controller is developed to load the static friction and a torque controller the kinetic friction. With the help of mathematical modeling, this article designs a ＂torque-zero velocity＂ switching controller and, correspondingly, provides a ＂dual-threshold judgment＂ algorithm. Simulation results indicate that the proposed method can be successfully used to carry out the static and kinetic friction simulation with an electro-hydraulic load simulator.

A Water Strider Robot with Five Umbrella-Type Footpads

The design of most water strider robots follows the principle that all supporting legs are in a plane,and each supporting leg bears a certain load and the water strider robot can float on the water.To meet this principle,the number of supporting legs and the spacing between each supporting legs of the water strider robot must be increased,which makes the shape of water strider robots look like octopus.This study proposed a novel water strider robot named 5S-robot,which used five new umbrella-type footpads and a centrifugal pump-based actuating mechanism.Motion analysis model and force analysis model of 5S-robot were built.The general consistency between the results of motion experiments and those of numerical simulation verified the former models.For this 5S-robot,the maximum load of 110.5 g and forward speed of 207.1 mm s^(-1)and rotational speed of 1.22 rad s^(-1)were measured,respectively.

Actuation performances of catkin fibers reinforced thiol-acrylate main-chain liquid crystalline elastomer

Liquid crystalline elastomers(LCEs)have been utilized as an important class of smart actuator materials.However,the modest actuation mechanical and robustness performances remain a challenge.Inspired by the specific structures,well mechanical properties and physico-chemical characteristics of some natural plant fibers,a composite of thiol-acrylate main-chain LCE matrix incorporated with catkin fibers is designed and developed.The catkin fibers build a network as reinforcement phase,and demon-strate effective compatibility and integration property with the matrix,their high flexibility can be adapted to the large deforma-tional performance of LCE matrix.The prepared LCE composite demonstrates strong mechanical actuation properties.The mod-ulus and driving force triggered by the stimuli are obviously increased.The tensile strength and fatigue failure resistant prop-erty under high loadings and repeated cycles of thermal actua-tion or photothermal actuation are greatly enhanced.While the stimulus response deformation rate,phase transition temperature and liquid crystal phase structure of the LCE matrix,and so on,do not weaken or change.This work promotes the LCE materi-als’application potential and broadens the application value of natural plant fibers.

Morphology-and ion size-induced actuation of carbon nanotube architectures

Future adaptive applications require lightweight and stiff materials with high active strain but low energy consumption.A suitable combination of these properties is offered by carbon nanotubebased actuators.Papers made of carbon nanotubes(CNTs)are charged within an electrolyte,which results in an electrical field forming a double-layer of ions at their surfaces and a deflection of the papers can be detected.Until now,there is no generally accepted theory for the actuation mechanism.This study focuses on the actuation mechanism of CNT papers,which represent architectures of randomly oriented CNTs.The samples are tested electrochemically in an in-plane set-up to detect the free strain.The elastic modulus of the CNT papers is analyzed in a tensile test facility.The influence of various ion sizes of water-based electrolytes is investigated.During the tests,four parameters that have a significant influence on the mechanical performance of CNT papers were identified:the test conditions,the electrical charging,the microstructure and the ion size.All of these influencing factors point to the mechanically weak inter-tube linking at which the actuation seems to take place.Quadratic voltage-strain correlation suggests a combination of electrostatic and volumetric effects as the possible reason for CNT paper actuation.

Type Synthesis and Dynamics Performance Evaluation of a Class of 5-DOF Redundantly Actuated Parallel Mechanisms

This paper presents a five degree of freedom(5-DOF)redundantly actuated parallel mechanism(PM)for the parallel machining head of a machine tool.A 5-DOF single kinematic chain is evolved into a secondary kinematic chain based on Lie group theory and a configuration evolution method.The evolutional chain and four 6-DOF kinematic chain SPS(S represents spherical joint and P represents prismatic joint)or UPS(U represents universal joint)can be combined into four classes of 5-DOF redundantly actuated parallel mechanisms.That SPS-(2UPR)R(R represents revolute joint)redundantly actuated parallel mechanism is selected and is applied to the parallel machining head of the machine tool.All formulas of the 4SPS-(2UPR)R mechanism are deduced.The dynamic model of the mechanism is shown to be correct by Matlab and automatic dynamic analysis of mechanical systems(ADAMS)under no-load conditions.The dynamic performance evaluation indexes including energy transmission efficiency and acceleration performance evaluation are analyzed.The results show that the 4SPS-(2UPR)R mechanism can be applied to a parallel machining head and have good dynamic performance.