From computer-aided to intelligent machining: Recent advances in computer numerical control machining research

The aim of this paper is to provide an introduction and overview of recent advances in the key technologies and the supporting computerized systems, and to indicate the trend of research and development in the area of computational numerical control machining. Three main themes of recent research in CNC machining are simulation, optimization and automation, which form the key aspects of intelligent manufacturing in the digital and knowledge based manufacturing era. As the information and knowledge carrier, feature is the efficacious way to achieve intelligent manufacturing. From the regular shaped feature to freeform surface feature, the feature technology has been used in manufacturing of complex parts, such as aircraft structural parts. The authors’ latest research in intelligent machining is presented through a new concept of multi-perspective dynamic feature (MpDF), for future discussion and communication with readers of this special issue. The MpDF concept has been implemented and tested in real examples from the aerospace industry, and has the potential to make promising impact on the future research in the new paradigm of intelligent machining. The authors of this paper are the guest editors of this special issue on computational numerical control machining. The guest editors have extensive and complementary experiences in both academia and industry, gained in China, USA and UK

A Simple Test Method for Large Deformation Bending of Thin High Strain Composite Flexures

A simple test method for large deformation bending of thin composite laminates is investigated using image processing and full-field strain measurements. The assumptions and kinematic equations that represent the test are used to calculate numerically the laminate bending stiffness and strength as well as the curvature and strains at failure. In order to validate the test methodology, a comparison is performed between analytical model predictions and empirical data in terms of computed surface strains versus digital image correlation data and calculated rotation angles of the fixture arms throughout the test versus measured ones. The new test method is then used to calculate the bending stiffness in the D11 and D22 directions as well as failure strains for various thin-ply laminates of interest. These parameters are ultimately compared with predicted values using micromechanics and classical lamination theory analysis. In general, bending stiffness and strain test results and predictions for 0 degree orientation coupons have a maximum difference of 10% and 35%

Two-node curved inverse finite element formulations based on exact strain-displacement solution

The inverse finite element method (iFEM) is an efficient algorithm developed for real-time monitoring of structures equipped by a network of strain sensors. The inverse element for modeling curved beams was previously developed using an approximate solution based on independently interpolated displacement components. In this study, a new formulation is proposed by the development of a least-squares variational principle using the kinematic framework of the curved beam theory. The library of existing iFEM-based elements is expanded by introducing three different inverse curved elements named iCB3, iCB4 and iCB5 respectively. This new formulation has been developed considering the exact solution of the curved beam theory that corresponds to the membrane-bending coupling and the explicit statement of the rigid-body motions. The three inverse elements, which require three, four and five measurement points respectively, extend the practical utility of iFEM for shape sensing analysis of curved structures according to the minimum available quantity of strain sensors. The effectiveness and higher accuracy of the iCB/iFEM methodology compared to other solutions present in literature are demonstrated considering numerical studies on curved beams under static transverse force and distributed loading conditions. For these problems, the effect of strain measurements error, number of sensors and discretization refinement on the solution accuracy is evaluated

Advanced Strategies for Robot Manipulators

Amongst the robotic systems, robot manipulators have proven themselves to be of increasing importance and are widely adopted to substitute for human in repetitive and/or hazardous tasks. Modern manipulators are designed complicatedly and need to do more precise, crucial and critical tasks. So, the simple traditional control methods cannot be efficient, and advanced control strategies with considering special constraints are needed to establish. In spite of the fact that groundbreaking researches have been carried out in this realm until now, there are still many novel aspects which have to be explored

Kinematics and Robot Design II (KaRD2019) and III (KaRD2020)

This volume collects papers published in two Special Issues “Kinematics and Robot Design II, KaRD2019” (https://www.mdpi.com/journal/robotics/special_issues/KRD2019) and “Kinematics and Robot Design III, KaRD2020” (https://www.mdpi.com/journal/robotics/special_issues/KaRD2020), which are the second and third issues of the KaRD Special Issue series hosted by the open access journal robotics.The KaRD series is an open environment where researchers present their works and discuss all topics focused on the many aspects that involve kinematics in the design of robotic/automatic systems. It aims at being an established reference for researchers in the field as other serial international conferences/publications are. Even though the KaRD series publishes one Special Issue per year, all the received papers are peer-reviewed as soon as they are submitted and, if accepted, they are immediately published in MDPI Robotics. Kinematics is so intimately related to the design of robotic/automatic systems that the admitted topics of the KaRD series practically cover all the subjects normally present in well-established international conferences on “mechanisms and robotics”.KaRD2019 together with KaRD2020 received 22 papers and, after the peer-review process, accepted only 17 papers. The accepted papers cover problems related to theoretical/computational kinematics, to biomedical engineering and to other design/applicative aspects

Enhanced stiffness modeling of manipulators with passive joints

The paper presents a methodology to enhance the stiffness analysis of serial and parallel manipulators with passive joints. It directly takes into account the loading influence on the manipulator configuration and, consequently, on its Jacobians and Hessians. The main contributions of this paper are the introduction of a non-linear stiffness model for the manipulators with passive joints, a relevant numerical technique for its linearization and computing of the Cartesian stiffness matrix which allows rank-deficiency. Within the developed technique, the manipulator elements are presented as pseudo-rigid bodies separated by multidimensional virtual springs and perfect passive joints. Simulation examples are presented that deal with parallel manipulators of the Ortholide family and demonstrate the ability of the developed methodology to describe non-linear behavior of the manipulator structure such as a sudden change of the elastic instability properties (buckling)

Geometric Error Identification for 6DoF Robotic Manipulator Calibration to Improve Absolute Positioning Accuracy

As robotic manipulators become extensively incorporated in various modern industries, there is a growing list of applications for human-to-robot interaction and robot-to-robot collaboration, which requires strong performance on the absolute positioning accuracy of the robot. The lack of accuracy could come from extreme operating environments, manufacturing and assembly errors, dynamic influence from gear compliance and backlash, etc. This thesis tackles the accuracy issue from two aspects: tighter mechanical tolerances and a closer matching kinematics model with the actual robot. For these purposes, according to the geometry of a pneumatically driven six DoF manipulator, a 6D parametric kinematics model is firstly derived. The proposed model is highly flexible in terms of introducing, anywhere in each linkage of the manipulator, any number of virtual mechanical tolerance points that lump effects of dimension and orientation deviations caused by mechanical tolerances. Therefore, concerned mechanical tolerances can be added to the model and studied through Fuzzy arithmetic to analyze their influence on the TCP position. Meanwhile, geometric errors are also the primary source of discrepancies between the nominal model and real hardware. The model can include translational and rotational error parameters that need identification to quantify the effects from the geometric errors at the locations of the virtual mechanical tolerance points. For an effective identification, dependent error parameters are systematically eliminated using QR decomposition. Once the model reduction is completed, the nonlinear least-squares optimization problem using the Gauss-Newton line search method is formulated to identify the remaining independent error parameters. The identification process is eventually verified on the experimental manipulator. In a nutshell, the thesis presents 1) a tolerance analysis tool that offers insights for potential targeted manufacturing improvements to decrease the dominant tolerances, and 2) a capable parameter identification process that rectifies the nominal kinematics model to agree with the hardware.M.S

Optimal synthesis of planar adjustable mechanisms

Adjustable mechanisms provide degrees of flexibility while retaining desirable features of one degree of freedom close-loop mechanisms, such as simplicity, stability, and high speed capabilities. By adjusting linkage parameters, additional phases of motions can be achieved using the same hardware. However, an adjustment to the mechanism adds only one or two additional design positions and divides desired positions into phases , each of which contains only a few positions usually insufficient for industrial applications. In order to extend the design position limitation of adjustable mechanisms, an optimal synthesis method based on link length structural error is developed and applied to kinematic synthesis of adjustable planar mechanisms in this research. Designed with this method, adjustable mechanisms can achieve phases of many design positions with a minimized error. The conveniently-calculated link length structural error effectively reflects the overall difference between generated and desired motions without directly comparing them; and its compact fourth-order polynomial form facilitates the gradient- based optimization process. Link length structural error based optimal synthesis methods are developed for adjustable planar four-bar mechanisms for three typical synthesis tasks. For multi-phase approximate motion generation, standard optimization model is established based on adjustable optimal dyads considering all types of adjustments. For multi-phase continuous path generation, a proper driving dyad is firstly found by an optimization procedure using the full rotation requirement. The driven dyad is then found using the optimization technique for motion generation after calculating all coupler angles. For multi-phase function generation, the coupler length is chosen to carry the structural error and adjustments to the coupler and the side-link lengths are considered. Numerical synthesis examples have demonstrated that the developed method is effective and efficient for multi-phase motion, path, and function generation of planar four-bar linkages with a large number of specified positions in each phase

Robot Manipulators

Robot manipulators are developing more in the direction of industrial robots than of human workers. Recently, the applications of robot manipulators are spreading their focus, for example Da Vinci as a medical robot, ASIMO as a humanoid robot and so on. There are many research topics within the field of robot manipulators, e.g. motion planning, cooperation with a human, and fusion with external sensors like vision, haptic and force, etc. Moreover, these include both technical problems in the industry and theoretical problems in the academic fields. This book is a collection of papers presenting the latest research issues from around the world