Rongqiang Liu

Crashworthiness design optimisation of metal honeycomb energy absorber used in lunar lander

To provide a theoretical basis for metal honeycombs being used as buffering and crashworthy structures in a lunar lander system, this paper investigates the energy absorption properties of hexagonal metal honeycombs, and the size optimisation of the metal honeycomb energy absorber is performed by using response surface method (RSM). Specific energy absorption (SEA) is set as the design objective; the cell length and foil thickness of the metal honeycombs are optimised, while the applied mean crash load is set to not exceed allowable limits. The results demonstrate that this method is effective in solving crashworthiness design optimisation problems. Besides the design optimisation, parametric studies are carried out to investigate the influences of foil thickness and cell length on the metal honeycombs’ crash performances. The pre-processing software Patran is used to build up the finite element models and the explicit solver LS-DYNA is employed to perform the crashworthiness analyses.

Synthesis of Deployable/Foldable Single Loop Mechanisms With Revolute Joints

This paper presents a geometric approach for design and synthesis of deployable/foldable single loop mechanisms with pure revolute joints. The basic kinematic chains with symmetric mobility are first synthesized, and an intuitive geometric method is proposed for the mobility analysis of these kinematic chains. The deployable/foldable single loop mechanisms can be regarded as a combination of the basic kinematic chains with nontrivial mobility intersection, under this approach, the 5R to 8R single loop mechanisms with symmetric mobility are synthesized systematically. The method for determining the positions of the joint axes on polyhedral links is also proposed, so that the mechanism can be fully deployed or fully folded without suffering from physical interference. Under this framework, a class of novel deployable/foldable single loop mechanisms is developed. The computer-aided design models for typical examples are built to illustrate their feasibility. [DOI: 10.1115/1.4004029].

Experimental Study of an EMG-Controlled 5-DOF Anthropomorphic Prosthetic Hand for Motion Restoration

In this paper, we attempted to evaluate the performance of an electromyography (EMG)-controlled 5-DOF prosthetic hand on ten transradial amputees. The proposed prosthesis is composed of a five-fingered hand, a passive wrist, and a customized socket for each subject. The EMG control methods included both a commonly used pattern recognition-based scheme (DD-SVM) and a novel digital encoding strategy (double-channel template matching (DCTM)). A virtual 3D hand platform was developed for training the subjects and rapidly testing the control methods. For each subject, the performance of the EMG control methods was firstly measured by off-line classification accuracy; then, according to the accuracy, a particular control method was selected and embedded in the EMG controller for further validation on ordinary daily life activities. Our experiments were conducted to test not only the hand’s grasp ability but also other multifinger cooperation skills. The result indicated that the subjects of rich control experience can accomplish several intuitive motion control over their hands. However, the kinds of the motions and their relative recognition accuracy may depend on some individual differences, such as the amputation level, the activity of the residual nerve-muscle system, and the richness of control experience. Meanwhile, the proposed digital encoding method, DCTM, which only utilized two channels of EMG, was necessary for those amputees with few available control signals. This paper suggested that the EMG control method should be differently considered according to the particular condition of each subject.

Vibration band gaps in double-vibrator pillared phononic crystal plate

This paper proposes a double-vibrator three-component pillared phononic crystal plate and theoretically studies the properties of vibration band gaps of this plate. The band structures and the displacement fields of the eigenmodes are calculated by the finite element method. Comparing the transmission power spectrums of the vibrations in the plate, the flexural vibration gap is proved more useful than the longitudinal vibration gap. The influence of the lattice constant, the height, and diameter of the pillars on the flexural vibration gaps are investigated. A supercell composed of the uni-vibrator and the double-vibrator unit cells is also investigated, and the analysis shows that the starting frequencies of the gaps in this supercell structure depend on the features of its pillars. This research can be used in the low frequency vibration insulation of plate structures.

Flexural vibration band gaps in a double-side phononic crystal plate

Using the finite element method, we theoretically study the vibration properties of a phononic crystal plate composed of a square array of composite cylindrical pillars on both sides of a thin homogeneous plate. The dispersion relations, the displacement fields of the eigenmodes, and the power transmission spectra are given to estimate the starting and cutoff frequency of the flexural vibration band gaps. We investigate the evolution of the flexural vibration band gaps in the double-side phononic crystal plate, with the height and diameter of the pillars on both sides arranged from a symmetrical distribution to an asymmetrical distribution. Numerical results show that the enlargement of the bandwidth of flexural vibration band gaps in both symmetrical and asymmetrical double-side phononic crystal plates depends strongly on the rise of the cutoff frequency of the gaps. The two pillars with an asymmetrical heights or diameters divide the first flexural vibration band gap into two gaps. These propagation properties of flexural vibration in the double-side plate can be utilized to design low-frequency vibration insulation and band-pass filters.

Optimizing the qusai-static folding and deploying of thin-walled tube flexure hinges with double slots

The thin-walled tube flexure(TWTF) hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven’t been completely solved, which restricts their applications. An optimal design method for the qusai-static folding and deploying of TWTF hinges with double slots is presented based on the response surface theory. Firstly, the full factorial method is employed to design of the experiments. Then, the finite element models of the TWTF hinges with double slots are constructed to simulate the qusai-static folding and deploying non-linear analysis. What’s more, the mathematical model of the TWTF flexure hinge quasi-static folding and deploying properties are derived by the response surface method. Considering of small mass and high stability, the peak moment of quasi-static folding and deploying as well as the lightless are set as the objectives to get the optimal performances. The relative errors of the objectives between the optimal design results and the FE analysis results are less than 7%, which demonstrates the precision of the surrogate models. Lastly, the parameter study shows that both the slots length and the slots width both have significant effects to the peak moment of quasi-static folding and deploying of TWTF hinges with double slots. However, the maximum Mises stress of quasi-static folding is more sensitive to the slots length than the slots width. The proposed research can be applied to optimize other thin-walled flexure hinges under quasi-static folding and deploying, which is of great importance to design of flexure hinges with high stability and low stress.

Crashworthiness Analysis on Alternative Square Honeycomb Structure under Axial Loading

Hexagonal metal honeycomb is widely used in energy absorption field for its special construction. However, many other metal honeycomb structures also show good energy absorption characteristics. Currently, most of the researches focus on hexagonal honeycomb, while few are performed into different honeycomb structures. Therefore, a new alternative square honeycomb is developed to expand the non-hexagonal metal honeycomb applications in the energy absorption fields with the aim of designing low mass and low volume energy absorbers. The finite element model of alternative square honeycomb is built to analyze its specific energy absorption property. As the diversity of honeycomb structure, the parameterized metal honeycomb finite element analysis program is conducted based on PCL language. That program can automatically create finite element model. Numerical results show that with the same foil thickness and cell length of metal honeycomb, the alternative square has better specific energy absorption than hexagonal honeycomb. Using response surface method, the mathematical formulas of honeycomb crashworthiness properties are obtained and optimization is done to get the maximum specific energy absorption property honeycomb. Optimal results demonstrate that to absorb same energy, alternative square honeycomb can save 10% volume of buffer structure than hexagonal honeycomb can do. This research is significant in providing technical support in the extended application of different honeycomb used as crashworthiness structures, and is absolutely essential in low volume and low mass energy absorber design.

Topology structure synthesis and analysis of spatial pyramid deployable truss structures for satellite SAR antenna

Many attentions for structural synthesis are paid to planar linkages and parallel mechanisms, while design novel pyramid deployable truss structure(PDTS) of satellite SAR mainly depends on experience of designer. To design novel configuration of PDTS, a two-step topology structure synthesis and analysis approach is proposed. Firstly, a conceptual configuration of PDTS is synthesized. Weighted graph and weighted adjacency matrix are established to realize topological description for PDTS. Graph properties are then summarized to distinguish differentia between PDTS and other type structures. According to graph properties, a procedure for synthesis conceptual configuration of PDTS is presented. Secondly, join relationship of components in a PDTS is analyzed. Kinematic chain and corresponding incidence/adjacency matrix are employed to analyze join relationship of PDTS. Properties and simplified rules of kinematic chain are extracted to construct kinematic chain. A procedure for construction kinematic chain of PDTS is then established. Finally, with this two-step approach all 11 rectangular pyramid deployable structures whose folded state is planar are discovered and their kinematic chains are constructed. Based on synthesis results, a novel deployable support structure for satellite SAR is designed. The proposed research can be applied to obtain some novel PDTSs, which is of great importance to design some novel deployable support structures for satellite SAR antenna.

Parametric Design and Multiobjective Optimization of Maglev Actuators for Active Vibration Isolation System

The microvibration has a serious impact on science experiments on the space station and on image quality of high resolution satellites. As an important component of the active vibration isolation platform, the maglev actuator has a large stroke and exhibits excellent isolating performance benefiting from its noncontact characteristic. A maglev actuator with good linearity was designed in this paper. Fundamental features of the maglev actuator were obtained by finite element simulation. In order to minimize the coil weight and the heat dissipation of the maglev actuator, parametric design was carried out and multiobjective optimization based on the genetic algorithm was adopted. The optimized actuator has better mechanical properties than the initial one. Active vibration isolation platforms for different-scale payload were designed by changing the arrangement of the maglev actuators. The prototype to isolate vibration for small-scale payload was manufactured and the experiments for verifying the characteristics of the actuators were set up. The linearity of the actuator and the mechanical dynamic response of the vibration isolation platform were obtained. The experimental results highlight the effectiveness of the proposed design.

Type synthesis of deployable/foldable articulated mechanisms

This work intends to deal with the type synthesis problem of deployable/foldable articulated mechanisms. The type synthesis in this kind of mechanism design can be factorized into two stages: the first stage is the topological synthesis of which the properties of mechanism are reflected by the graph; the second stage is the kinematic synthesis which aims at finding a set of mechanisms with the desired kinematic properties. According to the folded morphology, the compact form for deployable units are first classified into three categories: linear compact structure, planar compact structure and hybrid compact structure. Then we can enumerate the topological structures of these three categories and synthesize their combinations. Different from kinematic synthesis of general industrial robot which amounts to find the set of robotic mechanisms such that the end-effector of which has the desired mobility, the kinematic synthesis of deployable mechanism is to find out the set of mechanisms which can be folded onto the desired compact form in which the mechanism is taking up the minimum geometric volume. If a mechanism has at least one inverse solution to the desired compact form for the given set of parameters and there is finite mobility between the deployed and folded configurations, that is the mechanism we are looking for.