Eclipse: An Overactuated Parallel Mechanism for Rapid Machining

Parallel mechanisms with multiple links have been expected to be used in machining because they are higher in rigidity, accuracy, and output power than series mechanisms, such as industrial robots. However, unlike conventional machine tools, which consist of linear and rotary axes, parallel mechanisms have a large number of error factors. In the parallel link mechanism, there is no guide surface that physically guarantees linearity, and all accuracy is determined by the operating performance of the composite axes. This makes it difficult to identify any error factors. Therefore, a kinematics model is devised, and the behavior of the tool tip is checked by inputting the encoder information during the actual operation of a specific axis. Based on the results, we evaluate the machining characteristics of the target machine tool. The target machine tool in this study is a 5-axis machine tool that combines a 3-DOF parallel mechanism consisting of three linear motion axes and a 2-DOF serial mechanism consisting of two rotary axes. In our previous research, we tried to build a forward kinematics model. Although its prediction accuracy was insufficient, it was possible to actually identify the cause of the defect in the quality of the machined surface using the servo position information of the kinematics machine. However, we have not been able to construct an inverse kinematics model that is suitable for calculating the correction position command value to improve the quality of the machined surface. In this study, based on the shape creation theory, we devise and evaluate the kinematics model of a robotic machine tool that has a parallel mechanism. As a result of comparing the kinematics model with the 3D-CAD model in order to evaluate the accuracy of the former, it was confirmed that the proposed method has high simulation accuracy. Then, machining tests were carried out to evaluate the machining accuracy by measuring, based on proposed kinematics model, the machined surfaces in order to identify the mechanism that affects the texture of the machined surface. In addition, we performed a circle interpolation to confirm the effects of reversing the motion of each drive axis on the behavior of the tool tip. As a result, it is considered that the linear motion axis has a large effect on the behavior of the tool tip on the quadrant glitch of each drive axis. It was also found that the effects of the 1st- and 3rd-axes on the behavior of the tool tip are different from those of the 2nd-axis.

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.

Analyses of the inverse and forward positions of a 3-DOF parallel mechanism (PM) along with two rotational DOFs and one translational DOF are presented in this paper. The module of this 2-PRU-PRRU PM is created, and the Jacobian of the 2-PRU-PRRU PM is derived. Boundary, local, and combined singularities are identified based on the Jacobian. The workspace of the 2-PRU-PRRU PM is discussed according to the singularities and condition of a U-joint interference. The 2-PRU-PRRU PM has a simple structure and supplements the 3-DOF PM family with two rotational DOFs and one translational DOF. The 2-PRU-PRRU PM can be applied in the fields of industrial assembly robots, motion simulators, coordinate measuring machines, and parallel machine tools etc.

This paper introduced a three degree-of-freedom planar parallel mechanism which is composed of three branches. In order to give directions for the following engineering design of the mechanism, the inverse kinematics and forward kinematics of this parallel mechanism are analyzed, which shows that analytical equations for the inverse and forward kinematics of the novel parallel mechanism can be obtained. Also, velocity jacobian matrix are presented, based on these matrix, solution formulas about velocity,acceleration and statics of this mechanism are derived. The analysis results show that this novel parallel mechanism can easily realize real-time control and have valuable engineering applications.

This paper describes the research results on telemicromanipulation systems for microlevel tasks. Because of its better manipulation precision, stiffness and speed characteristics, the parallel mechanism micromanipulator was chosen to compose our systems. First, the kinematic analysis of our original manipulator mechanism is performed. Then, the structure of our parallel manipulator, control scheme, and experimental results are shown. Position accuracy and device control characteristics are analyzed and the feasibility of the use of parallel mechanisms for micromanipulator is then discussed. A parallel manipulator motion is restricted by 3 factors: mechanical limits of the passive joints, collision between links and actuators limitations. Results of the numerical workspace analysis considering the above factors are shown. We are proposing the use of dual manipulators for implementing improved real manipulation systems. The first kinematics and workspace analysis of dual systems using the VR simulator are also shown.

A deformation model of a parallel kinematic machine tool

Workspace Analysis of the 4RRR Planar Parallel Manipulator with Actuation Redundancy

Institutional innovation is a challenging task. For parallel mechanisms, a new type of branch structure and a new branch combination scheme can be considered as the innovative design of the topology of the parallel mechanism. At present, there are three main methods for the synthesis of parallel mechanisms, namely, displacement subgroup method, screw theory method and position and orientation characteristic (POC) equations. Degree of freedom analysis is an indispensable part of mechanism synthesis, and is also the foundation of mechanism kinematics. A 5 degrees-of-freedom (DOF) hybrid mechanism was researched in this paper based on a 3-DOF translational parallel mechanism with parallelogram linkage and 2-DOF serial mechanism. Firstly, the characteristics of this topology structure were introduced, and the mobility of the mechanism was analyzed by POC equations. Secondly, according to the space vector relation between the moving platform and the fixed base, the direct kinematics of parallel part were deduced via an analytical method and the inverse kinematics was performed by D-H method. Finally, In order to verify the efficiency of the kinematics algorithm, a set of given arguments about mechanism could be put into the kinematics algorithm to obtain the corresponding changes of displacements and the position of the moving platform. The error of the inverse and direct kinematics was analyzed by an example of machining a complex surface, which shows that the proposed algorithms are effective and have satisfactory computation precision.

Auricular prosthesis is a kind of artificial auricle of repairing physiological defect. This paper studies the problem of forming curve and machining method in auricular prosthesis forming, and puts forward a quick forming method of combining parallel mechanism and NC machine tool. The mathematical model and motion reverse equation of parallel mechanism are established and the structural parameters of Stewart parallel mechanism were designed. Finally, Matlab Software is used in an example to figure out motion function curve of each branch, which verifies the feasibility of this method. In addition, it lays the foundation for further studies of control of parallel mechanism.

This paper presents the structure and geometry of a new translational parallel mechanism. Relations for the analysis of the direct and inverse kinematics problems are derived. An analytical procedure for determining the system’s singular positions is presented and illustrated with examples.

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

A novel parallel mechanism with bifurcated motion is introduced by integrating a discontinuously movable mechanism in the limb design. The mechanism has instantaneously six degrees of freedom at a singularity point. With the discontinuously movable mechanism moving to different motion branches, the parallel mechanism has the ability to evolve into four configurations with different motion characteristics, including 3T motion configuration, 3R motion configuration, 2T1R motion configuration and 2R1T motion configuration. By rigidizing the input joints, the rationality of input scheme for this mechanism is identified based on screw theory. Six motors nearly mounted to the base can sufficiently drive the parallel mechanism to switch between different motion configurations and perform different motions. The forward and inverse kinematics of the mechanism in different configurations are given. The translational motions are independent with each other and decoupled with the rotational motions. Kinematics simulation is performed for the parallel mechanism and the results show that theoretical analyses are correct. The workspace of the parallel mechanism in a general configuration is given. Key words}Discontinuously movable mechanism Parallel mechanism Bifurcated motion Kinematics

In this paper, parallel link mechanisms for multi drive linear motors (MDLMs) are proposed. The multi drive is a control method for linear motors in which a number of moving parts are individually driven on one stator part. Various configurations of parallel link mechanisms which were constructed for MDLMs are proposed. These mechanisms offer a wide range of motion in addition to the existing characteristics that parallel mechanisms provide, namely, rigid mechanisms, high precision, and high speed. Moreover, they are suitable for force control because of their low friction direct drive actuators. In this paper, the kinematic and dynamic characteristics of 2-DOF (xy) and 3-DOF (xy¿) planar parallel link mechanisms are investigated. A singularity analysis and internal force control method for a 3-DOF with 4 redundant moving parts is derived. The condition of dynamic decoupling and the constant inertia design of a 2-DOF with 2 moving parts and a 3-DOF with 4 moving parts are derived. The effectiveness of these analyses is then confirmed by numerical simulation. Based on this analysis, a prototype of the 3-DOF with 4 moving parts is designed and developed.

In this paper, a novel 3-UPU (P and U stand for prismatic and universal joints, respectively) parallel mechanism (PM) and its variant PM are proposed. Both of them have two rotational and one translational (2R1T) degrees of freedom (DOFs) without involving any parasitic motion. Mobility analysis shows that the three constraint forces provided by three limbs of the mechanism are located on the same plane and the mobile platform can translate perpendicular to this plane and rotate around any axis on it. Analysis of the mechanism’s motion characteristics demonstrates that the mobile platform outputs either pure rotation or pure translation. Moreover, the rotational axis can be fixed during the rotation process, which means no parasitic motion is involved. The causes of the motion characteristics are analyzed by the combination of an overall Jacobian matrix, a statistical method, and a geometric method. The PMs only need to translate or rotate once to move from the initial configuration to the final configuration, which allows for easy control of speeds. The relationship between mechanism parameters and singularity is analyzed. A speed control method for the PMs is proposed and a prototype is designed and made. Experiments are conducted to verify the determined motion characteristics, the speed control method, and the singularity analysis.

This paper carries out a comprehensive and systematic comparison study on the kinematic performance of four six degrees of freedom (6-DOF) parallel mechanisms with different topologies, i.e., 6-UPS, 3-(2-UPR)U, 3-(2-UCR)U, and 3-R(2-RPR)U. The research begins by elaborating in detail the similarities and differences among these four parallel mechanisms. By standardizing the definition of the coordinate system for each mechanism, the inverse kinematics and the Jacobian matrix of these four mechanisms are systematically derived. Employing a set of motion/force transmission indices, which are directly obtained from the Jacobian matrix, the kinematic performances of the four mechanisms are thoroughly analyzed and compared within the given workspaces while maintaining the same dimensional parameters for all cases. The comparison study of these four parallel mechanisms extends beyond local transmission indices to also include global transmission indices, covering both position and orientation workspaces, as well as assessments at both the local and global workspace levels. This comprehensive approach ensures a detailed and fair evaluation of their respective kinematic capabilities. The results indicate that the comprehensive kinematic performances of the four parallel mechanisms are similar, and providing a solid theoretical foundation for innovative design and practical guidance for selecting optimal architectures based on specific application requirements.