3-DOF Parallel Mechanism Research Articles

Stewart Platform Model with Uncertain Parameters

The paper deals with development of uncertain dynamics model of a six DOF parallel mechanism (Stewart platform) suitable for H-infinity controller design. The model is based on linear state space models of the machine obtained by linearization of the SimMechanics model. The linearization is performed for two positions of the machine in its workspace. It is the nominal position and the position where each link of the machine reaches its maximal length. The uncertainties are then represented as differences between parameters of corresponding state-space matrices. The uncertain state space model is then obtained using upper linear fractional transformation. There are also mentioned several notes regarding H-infinity controller designed according to the obtained model.

A Novel 5-DOF NC Serial-Parallel Machine Tool and its Position Analysis

In this paper, a novel 5 degrees-of-freedom (DOF) numerical control (NC) serial-parallel machine tool is proposed. It can provide 3 translational DOF and 2 rotational DOF. The proposed mechine tool is composed of a 2-TPR/2-TPS special 4-DOF parallel mechanism in series with a rotatable component. The structure of this machine tool is simple. The machine tool can process the workpieces which have complex surfaces.The structural characteristics of this machine tool is introduced. The position inverse solution of this machine tool is deduced by analytical method and the position forward solution of this machine tool is achieved by numerical method.

Dynamic Model of a 3-dof Asymmetric Parallel Mechanism

Most research papers about parallel kinematic chain mechanisms investigate symmetric robot manipulators, in which all the limbs connecting the end-effector to the fixed based are composed by the same sequence of links and joints. Contrarily, in some manipulation tasks the velocity and stiffness requirements are anisotropic. In such cases, the asymmetric parallel kinematic chain mechanisms may offer advantages. This works' main objective is to present the inverse dynamic modeling of a 3-dof asymmetric parallel chain mechanism, conceived as a robot manipulator for pick- and-place operations. The type of kinematic structure of the mechanism constrains the motion of the end-effector to only three translations. First, a brief kinematic modeling is carried out. Then, the inverse dynamic modeling is developed by employing the virtual work principle, considering two assumptions: lumped and distributed masses. Based on the model equations, a motion simulation is performed. The same motion is also analyzed by using the ADAMS computing environment to validate the model equations. After the simulation, the results demonstrated a very good agreement between the analyzed variables provided by the dynamic model and those generated by ADAMS. One can also notice that the input torques calculated by the lumped-mass model are quite close to the torques evaluated by the distributed mass model, and might be sufficient for the future development of a motion control law for the mechanism.

Kinematic Analysis of A 3-DOF Parallel Mechanism for Milling Applications

Parallel mechanisms have been studied during the last two decades, due to the fact that they present some potential advantages in a comparison with serial structures. This work presents the kinematic analysis of a novel 3-dof asymmetric parallel mechanism, purposely conceived for milling applications. In a comparison with the previous proposed concepts, this type of kinematic structure shows some advantages. The architecture is simpler and lighter than Tricept because it has no central passive limb. In addition, only the central active limb needs to satisfy the parallelism and orthogonality conditions. Furthermore, one degree of freedom, associated to the third actuator, is decoupled from the other two. Important issues, related to this type of kinematic structure, such as position and velocity analysis, singularity occurrence prediction and workspace evaluation, are discussed in detail.

A comparison study of two planar 2-DOF parallel mechanisms: one with 2-RRR and the other with 3-RRR structures

SUMMARYThis paper deals with a comparative study of two planar two degrees of freedom parallel mechanisms: one with 2-RRR and the other with 3-RRR structures. For a fair comparison, both 3-RRR and 2-RRR mechanisms are symmetrical. The kinematics and Jacobian matrix of the two mechanisms are studied. Conditioning index, stiffness index and payload index are proposed to compare the condition, stiffness and payload performance of the two mechanisms. The results show that the 2-RRR and 3-RRR mechanisms have the similar condition performance, and the planar 3-RRR mechanism has better payload and stiffness performance than the 2-RRR one.

Design of a 4-DOF hybrid PKM module for large structural component assembly

This paper presents a novel 4-DOF hybrid parallel kinematic machine (PKM), named Bicept, comprising a 2-DOF parallel mechanism plus a 2-DOF rotating head. The PKM is designed as a rigid yet compact module that can act as a robot cell moving along a long track for aircraft structural component assembly, a wing box for example. Dimensional synthesis of the 2-DOF parallel mechanism is carried out to achieve a relatively good kinematic performance within a prescribed task workspace that has a large width/height ratio. Then, using commercial CAE software, rigid body dynamics and stiffness analyses are carried out for motor sizing and performance evaluation of a full-size virtual prototype.

ニューロサージカル ･ モーションベースの開発

Neurosurgical motion base is a 8 DOF robotic arm for positioning a surgical tool. In this paper, its overview, kinematics, prototype implementation, mechanical evaluation and clinical set-up test using a patient phantom model are described. The neurosurgical motion base is developed as a mount-type surgical robot on a conventional surgical head frame, therefore, it is possible to realize a quick installation. In our concept, the neurosurgical motion base holds and positions a cutting-edge surgical tool including a sensor feedback suction tool and a 3D endoscope. In the neurosurgical motion base, a 4 DOF active mechanism is introduced for precise positioning of a surgical tool, and a 4 DOF passive mechanism is introduced for adjusting the robot position on the head frame. By introducing a new 3 DOF parallel mechanism into the active part of neurosurgical motion base, high rigidity and accuracy can be realized, and also it is possible to locate all actuators on the base part for a capability of sterilization. From mechanical evaluations, it was revealed that accuracy and rigidity of the developed robot were 0.04 mm and 6.5 N/mm respectively. In addition, by an installation test on a patient phantom model, a feasibility of the developed robot was positively shown.

応答曲面法によるパラレルメカニズム型加工機のキャリブレーション(機械要素,潤滑,設計,生産加工,生産システムなど)

This study proposes a calibration method of parallel mechanisms for machine tools by response surface methodology (RSM). RSM finds the optimum solution by employing a response surface that approximates an input-output relationship of a certain problem. The methodology obtains the response surface from a small number of data that are selected by experimental design. The present study approximates a relationship between the target postures and the output errors of a parallel mechanism by response surface. Furthermore, the calibrated control values are obtained from the response surface. It is beneficial that the output errors of a parallel mechanism can be estimated from a small number of measured data by RSM because the measurement of its posture is so difficult. This study shows the proposed method can distinctly improve the positioning accuracy of a spatial 3 dof parallel mechanism from a small number of the measured data by numerical simulation, and the availability of the proposed method is actually confirmed by the calibration of a machine tool consisting of the parallel mechanism.

Accuracy Analysis and Calibration of a Special 3-DOF Parallel Mechanism

Kinematic calibration is an effective way to improve machine accuracy. An improved error analysis and calibration method is verified through simulation, and it solves the kinematics calibration problem of a special 3-DOF parallel mechanism used in a forging manipulator’s bench clamp. Based on its forward and inverse kinematic model, the workspace is obtained, and kinematic accuracy analysis of the mechanism is carried out to obtaine the influences of all error sources of the mechanism on the terminal pose errors. The Jacobian matrix is obtained by using differential method. Simulation result shows that the difference between the identification value and the true value of the kinematic parameter error is less than 5%, which proves the effectiveness of the new accuracy analysis and calibration method for this special parallel mechanism.

Kinematic Performance and Accuracy Analysis of New Type 3-DOF Parallel Mechanism

Hybrid series-parallel mechanism, which contains the advantages of both series and parallel mechanisms, is used more and more widely in the manufacturing equipment for parts with complex free curved face. A 3-DOF parallel 3-PSP mechanism, which can realize one translational and two rotational motions, is proposed. The 3-PSP mechanism has accompanying motions. According to the analysis of motion mode, tilt-torsion angle for describing the motion of moving platform is adopted instead of traditional Euler angle, and based on that, kinematic model is built to solve the complete kinematic problem including accompanying motions and passive joint variables. Furthermore, the range of the joint, velocity characteristic, and accuracy characteristic are analyzed to demonstrate that the 3-PSP mechanism is fully suitable for parallel module in hybrid series-parallel frame which can fulfill the requirement of the complex parts in aerial, space, and automotive fields.

Stiffness modeling of a family of 6-DoF parallel mechanisms with three limbs based on screw theory

The stiffness modeling of a family of six degrees of freedom (DoF) parallel mechanisms with configurations of 3-RUPU is presented. The mobility of the mechanisms is firstly analyzed, and then the stiffness analysis and modeling of the family of mechanisms is developed by a novel screw-theory based method. The method employs screw theory as a tool for force analysis and deformation analysis. Based on the developed stiffness model, two global flexibility indices, which refer to the maximum and minimum singular values of compliance matrix, are introduced to evaluate the compliance of parallel mechanisms. Finally, a case study is presented to demonstrate the effectiveness of the method in analyzing and evaluating the stiffness behavior of the presented parallel mechanisms.

STRUCTURAL SYNTHESIS AND VARIATION ANALYSIS OF A FAMILY OF 6-DOF PARALLEL MECHANISMS WITH THREE LIMBS

STRUCTURAL SYNTHESIS AND VARIATION ANALYSIS OF A FAMILY OF 6-DOF PARALLEL MECHANISMS WITH THREE LIMBS

Autoderivation of Topological Graphs for Type Synthesis of Planar 3DOF Parallel Mechanisms

The autoderivation of valid topological graph (TGs) of planar 3DOF parallel mechanisms is studied systematically based on topology embryonic graphs (TEGs) and arrays. First, some TEGs without any binary links are constructed, some paths with only binary links are distributed over the TEGs, and some valid TGs of the planar 3DOF PMs are derived. Second, a complicated derivation of the TG is transformed into an easy derivation of array. Third, some programs are compiled in VB, all valid arrays corresponding to nonisomorphic TGs are derived automatically, and some invalid arrays corresponding to the isomorphic TGs and invalid TGs are determined by compiled programs. Finally, many valid TGs of planar 3DOF PMs with various basic links are derived from valid arrays.

A new planar 3-DOF parallel mechanism with continuous 360-degree rotational capability

This paper presents a novel three degrees of freedom (3-DOF) planar parallel mechanism with a 360-degree rotational capability, which can be used as a positioning device. A high rotational capability is necessary to reduce process time and to apply the mechanism to various fields such as micro-machining and printed circuit board (PCB) depaneling. The proposed mechanism has the advantage of a continuous rotational capability over existing planar parallel mechanisms with limited rotation. The position and velocity kinematics are derived, and the singularities are analyzed based on the Jacobian matrices. The workspace can be determined not to have a singularity inside, and the kinematic variables for enlarging the singularity-free workspace are determined. The application example on the PCB depaneling process is proposed for future work.

A Foldable 3-DOF Parallel Mechanism With Application to a Flat-Panel TV Mounting Device

This paper deals with a new 3-degree-of-freedom (DOF) parallel mechanism for a flat-panel TV mounting device with two rotations and one translation. The most important operational requirements of this device are that it should support the heavy weight of the flat-panel TV and should be foldable to save space between the flat panel and the wall. An asymmetric parallel structure that has three kinematic chains with internal four-bar linkage is proposed to meet such requirements. Kinematic modeling was performed along with actuator sizing. Finally, the mechanism was developed and tested to show its effectiveness as a flat-panel TV mounting device.

Optimum Kinematic Design of the 4R 2-DOF Parallel Mechanism

This paper analyzes the kinematic optimization design of the 4R 2-DOF parallel mechanism taking into account the force transmissibility. Three indices are introduced to reflect the force transmissibility. Based on these indices and their performance charts, the optimization design process with respect to the workspace is presented in detail. The results show that the designed mechanism is not only far from every singularity but also has good force transmissibility in its workspace. These kinematic optimization indices can be extended to other parallel mechanisms.

Design, implementation, and performance evaluation of a 4-DOF parallel robot

SUMMARYThis paper deals with the design, implementation, and performance evaluation of a new type of 4-DOF parallel mechanism providing three translations and one rotation for high-speed handling and machining. This parallel mechanism is named H4. A necessary condition and system configuration of the H4 are also described. Hardware and kinematics of the H4 is addressed and the manipulability ellipsoid which is one of the widely used methods to examine the design of parallel mechanisms is addressed. The performance evaluation is carried out to demonstrate the H4 robot. The simulation and experimental results show that three different controllers, the PD, PD + velocity feed-forward, and dynamic compensation controller, dramatically improve the trajectory tracking accuracy.

Kinematic modeling of a 5-DOF parallel mechanism for semi-spherical workspace

This paper presents the architecture synthesis and the kinematic modeling of a new five-degree-of-freedom parallel manipulator. The proposed mechanism is a 3T2R device intended to position and orient a line in space. It has been originally designed for a medical application in which the aforementioned line corresponds to the axis of a surgical needle. The mechanism is characterized by an asymmetric arrangement of its legs and wider mobility ranges than usually obtained with a parallel structure. Its inverse and forward kinematic models are derived, together with the assembly modes complying with the practical limitations of the mechanism.

Stiffness Modeling of the Tricept Robot Using the Overall Jacobian Matrix

Taking the 3DOF parallel mechanism within the Tricept robot as an example, this paper presents an analytical approach for the stiffness modeling of parallel kinematic machines having a properly constrained passive limb. The stiffness model is formulated using the 6×6overall Jacobian. It takes particular interest in the precise formulation of the bending stiffness matrix of the properly constrained passive limb by considering the compatibility conditions of the system. Stiffness evaluation of a sample Tricept robot is carried out using two global indices obtained from singular value decomposition of the compliance matrix.

Design and Analyses of a Novel 3-DOF Parallel Mechanism

Considering panels as links and creases as revolute joints,a cube paper fold can be taken as a novel 3-DOF parallel mechanism,based on the concept of mechanisms.The parallel mechanism consists of a base plate,a movable platform,and four connecting legs.The connecting legs have the same structure and each of them contains a closed-loop subchain,which is special six-bar spherical metamorphic mechanism.The configuration design of the new parallel mechanism is introduced.The parallel mechanism employs only revolute joints and has characteristics of symmetric structure.The mechanism characteristic,general configuration and mobility of the closed-loop subchain are introduced.The mobility of the closed-loop subchain is analyzed by using screw theory.The six-bar spherical metamorphic mechanism is replaced by a generalized kinematic pair,and the terminal constraints of the connecting legs are investigated by applying concept of generalized kinematic pair and screw theory.Considering the symmetrical structure of the parallel mechanism,the mobility characteristics of the movable platform are analyzed.The moving platform has three degrees of freedom,i.e.two degrees of rotational freedom and one degree of translational freedom,with respect to the base plate.The moving platform can rotate with continuously rotational axes.