A deformation model of a parallel kinematic machine tool

A novel 6-SSP parallel machine tool and a novel 4SPS+UPU parallel machine tool are presented, and a novel CAD approach is proposed to machine a 3D free-form surface in its normal direction by using the two parallel machine tools. First, by adopting the CAD geometry constraint and dimension-driving technique, the simulation mechanisms of a 6-SSP parallel manipulator with 6-DOF and a 4SPS+UPU parallel manipulator with 5-DOF are created. Second, a 3D free-form surface and a guiding plane of tool path are constructed above the moving platform of the two simulation mechanisms. Third, the tool axis of simulation parallel machine tool is retained perpendicular to the 3D free-form surface. In the light of two prescribed tool paths, the driving limbs and the pose of the moving platform of parallel machine tools are solved automatically and visualized dynamically.

In the development of robots and machine tools, in addition to conventional and serial structures, parallel mechanism-based kinematic structures have been used over a longer period of time. Aside from a number of advantages, the irregular shape and relatively small dimensions of the workspace formed by parallel mechanisms rank among the major weaknesses of their application. Accordingly, this fact has to be taken into consideration in the process of designing parallel mechanism-based robots or machine tools. This paper describes the categorization of criteria for the conceptual design of parallel mechanism-based robots or machine tools, resulting from workspace analysis as well as the procedure of their defining. Furthermore, it also presents the designing methodology that was implemented into the program for the creation of a robot or machine tool space model and the optimization of the resulting solution. For verification of the criteria and the programme suite, three common (conceptually different) mechanisms with a similar mechanical structure and kinematic characteristics were used.

A fuzzy interpolation method is proposed to simplify the calibration process for parallel machine tools. Either inverse or forward kinematic models need to be used in the traditional calibration methods to perform the identification and compensation of the pose errors for parallel machine tools. Instead of using a model, the proposed method presents a modeless technique combined with the fuzzy interpolation method to obtain the same or higher calibration accuracy when a small workspace is adopted.

A 5-Degree of Freedom (DOF) 5-UPS/PRPU fully parallel machine tool (PMT) was introduced. Based on the original edition of CNC system, the concise motion control algorithm was deduced by analyzing the identical feature between two Euler angles of 5-UPS/PRPU PMT and two swing angles of conventional 5-axis cutter swing machine tool. Then by using the formula of the inverse kinematic solution of the PMT, the length of the driving axis in the joint space can be calculated. The new CNC system software based on this algorithm was developed and it has been applied successfully to the 5-DOF PMT in our laboratory.

A review of parallel kinematic machine tools: Design, modeling, and applications

This research is investigated on the multi-objective performance optimization of a parallel robotic machine tool which is expected to be applied as a next generation of computer numerical control (CNC) machine. The system configuration and the kinematic model are detailed introduced. The performance maps including dexterity and workspace are generated and illustrated. The multi-objective optimal performance indices are investigated based on the integration of the evolutionary algorithm and Pareto frontier sets. The developed technologies and approaches are generic and also feasible for the design, modeling and improvement of other parallel kinematic machines.

Skull stiffness of children is of great significance to protect brain tissues during traffic accidents. In this paper, the effects of skull stiffness on traumatic brain injury (TBI) are investigated by using a validated 6-year-old child head finite element (FE) model according to Chinese standard GB/T 24550-2009 Results showed that the HIC value, intracranial pressure, Von Mises stress and shear strain of brain tissue increased with the decrease of skull stiffness during the impact of FE model with engine hood. Therefore, the injury risk of the child head decreases with the increase of skull stiffness. And the skull with higher stiffness can provide a better protection for brain tissues during traffic accidents.

Parallel kinematic machines (PKMs) have been attracting attention in research institutes as well as in the machine tool industry because of their structural rigidity due to their closed kinematic loops and their conceptual capabilities in high dimensional accuracy. During performance evaluation of the first prototypes of parallel machine tools, it turned out that their accuracy has not yet reached industrial application level. Against this background, the accuracy behaviour of a hexapod milling machine, located at the Laboratory for Machine Tools and Production Engineering (WZL) at Aachen University of Technology, and accuracy-related design issues have been extensively studied. Based on these investigations, strategies for kinematic calibration and error compensation have been developed.

The main objective of this work is to check the compatibility of Finite element method (FEM) to determine the modal parameters of the rotor system and to compare the results with analytical method. Current work is an attempt to implement different finite element (FE) models for the estimation of modal parameters. Two different order elements from Beam, Axisymmetric and Solid FE models are considered. The analysis is carried out on the rotor system and the accuracy of the results and the computation time of the FE models are estimated. The FE results are compared with the analytical method. It is observed that FE model can be used to simulate even at higher order frequencies, which is a limitation of analytical model. The analysis shows that the FE results closely match with analytical method and also the study summarizes that proper choosing of FE helps in developing rotor models in both a desirable accuracy and efficiency. Finally, a Campbell diagram is generated using the analytical method and FEM. The critical speeds are also calculated from the Campbell diagram. The closeness of the results between the two methods is checked.

This paper provides a study of workspace analysis of reconfigurable parallel machine tool (PMT). A reconfigurable PMT is established in either telescoped drive form or railway linear drive form by the same modules but different assembly modes. In the architecture of the PMT, an angle-variable module is designed to change the setting-angle in X and Z orientation for working more efficiently. In the workspace analysis of the PMTs of two drive models, inverse kinematics solution is given, and the effect of setting-angle of spherical joint on PMT has been investigated and the spherical joint setting-angle selection method has been proposed. A comparison result is supplied to show the difference of workspace between these two kinds of PMTs.

A method for continuous box-girder bridge structure finite element (FE) model updating based on static-load testing is proposed. The procedure includes field static-load testing, FE modeling, FE model (parameter) updating, etc. Based on this procedure, the structure FE model updating for an expressway 5-span pre-stressed concrete continuous box-girder bridge is conducted. And the bridge structure static FE model, which is consistent with the static-load testing actual measure response, is gained. The updated FE model (parameter) is foundation of structural performance evaluation for the bridge.

Purpose – In former work, test results of cracks in aluminium panels under cyclic shear buckling showed that cracks in the tensile stress field of a buckle propagate. The main influencing factor for the crack growth rate is the maximum principle stress. A simplified approach for crack propagation analyses based on this finding showed limitations for application on larger cracks because it disregarded the increasing out-of-plane deformation for larger cracks as well as stress redistributions. The purpose of this paper is to improve the results of the simplified approach with the help of finite element method (FEM). Design/methodology/approach – An approach for crack propagation based on FEM is presented taking into account the mutual interaction of cracks and buckling. The finite element (FE) model, which is described in detail, respects the boundary conditions of the test-set-up. Different initial crack positions, loads and panel thicknesses are analyzed. Results of the stress intensity factors KI calculated by the ABAQUS® FE model provide a function which is used to run a crack propagation analysis based on Forman law. Findings – The results of the FE-based crack propagation solution are in good agreement with test results and improve the prediction of the simplified approach. It is not restricted in terms of panel thickness, crack position or applied shear load. Research limitations/implications – Limitations of the FE-based crack propagation solution compared to the experimental results are discussed. These are, the sensitivity of crack propagation analyses to initial crack length and deviations of the experimental settings from the ideal FE model. Originality/value – The interaction of cracks and buckling in aluminium shells is mainly disregarded both in research and industrial work, but can be of interest considering, accidental damages in fuselage side shells. Cracks propagate under shear load as it was shown in former work. The FE modeling of the tests presented in this paper proves the mutual interactions of crack propagation and buckling deformation.

Thermally induced vibration (TIV) of composite laminate subjected to suddenly applied heating is studied using finite element (FE) method in this paper. Some Python programs written by the authors are used to process the data of the analysis flow, and complete the pre- and post-process of FE models used in the four analyses. An equivalent displacement method is proposed to calculate equivalent temperature load. Dynamic responses of six composite laminates with different sizes are analyzed with solid FE models and shell FE models. The results gotten by FE method are in close proximity to that gotten by classic theory and shear theory under certain conditions. It is proved that the TIV analysis method proposed in this paper is reliable and efficient. The TIV analysis with FE method based on equivalent displacement method can solve the dynamic response of a structure due to sudden changes of temperature or suddenly applied heating.

Given the functional complexities of soft tissues and organs, it is clear that computational simulations are critical in their understanding and for the rational basis for the development of therapies and replacements. A key aspect of such simulations is accounting for their complex, nonlinear, anisotropic mechanical behaviors. While soft tissue material models have developed to the point of high fidelity, in-silico implementation is typically done using the finite element (FE) method, which remains impractically slow for translational clinical time frames. As a potential path toward addressing the development of high fidelity simulations capable of performing in clinically relevant time frames, we review the use of neural networks (NN) for soft tissue and organ simulation using two approaches. In the first approach, we show how a NN can learn the responses for a detailed meso-structural soft tissue material model. The NN material model not only reproduced the full anisotropic mechanical responses but also demonstrated a considerable efficiency improvement, as it was trained over a range of realizable fibrous structures. In the second approach, we go a step further with the use of a physics-based surrogate model to directly learn the displacement field solution without the need for raw training data or FE simulation datasets. In this approach we utilize a finite element mesh to define the domain and perform the necessary integrations, but not the finite element method (FEM) itself. We demonstrate with this approach, termed neural network finite element (NNFE), results in a trained NNFE model with excellent agreement with the corresponding "ground truth" FE solutions over the entire physiological deformation range on a cuboidal myocardium specimen. More importantly, the NNFE approach provided a significantly decreased computational time for a range of finite element mesh sizes. Specifically, as the FE mesh size increased from 2744 to 175,615 elements, the NNFE computational time increased from 0.1108 s to 0.1393 s, while the "ground truth" FE model increased from 4.541 s to 719.9 s, with the same effective accuracy. These results suggest that NNFE run times are significantly reduced compared with the traditional large-deformation-based finite element solution methods. We then show how a nonuniform rational B-splines (NURBS)-based approach can be directly integrated into the NNFE approach as a means to handle real organ geometries. While these and related approaches are in their early stages, they offer a method to perform complex organ-level simulations in clinically relevant time frames without compromising accuracy.

This paper describes the design, construction, and experimental results of the Eclipse, a novel 6 d.o.f. parallel mechanism designed for rapid machining. The Eclipse is designed to be capable of performing 5-face machining while retaining the advantages of high stiffness, high accuracy, and compact size characteristic of parallel mechanisms. We describe the kinematic structure of the Eclipse, including computational procedures for the forward and inverse kinematics, as well as results of workspace, stiffness, and singularity analysis. The Eclipse has 8 actuators. The overactuation is necessary in order to eliminate kinematic singularities present in the internal workspace of the mechanism. Experimental results obtained with a prototype capable of machining plastic stock are described. We conclude with a summary of what we believe are some of the criticial issues in designing parallel mechanism-based machine tools.