Papers by Keyword: Parallel Mechanism

Abstract: A novel internal force decoupling control strategy of hyper-redundant shaking table based on stiffness matrix is proposed in this paper. The linear models of electro-hydraulic servo system and mechanical system are built by considering the shaking table moving in a small range around the zero point. Internal forces are given through a transformation of cylinder forces which can be acquired from the pressure sensors. By meshing top platform of the shaking table in different directions, the stiffness matrix between the redundancy displacements and internal forces are given through dynamics equations including inertia and shear parts. The IFDC controller is designed to feedback the redundancy displacement caused by internal forces to the input current of the servovalve. Simulation results show that the proposed method is capable to reduce internal forces effectively.

Abstract: The paper deals with a workspace problem of the 3 RRR planar parallel mechanism, used as parallel robot structure. Depending on the dimensional parameters and constructive characteristics, the authors search to depict the shape and particularities of the mechanism workspace of a 3 RRR planar parallel mechanism. This characterization of the mechanism workspace depending on the dimensional parameters can be usefull in mechanism designing accorded to some functional particularities and also can help in avoiding singular configurations.

Abstract: The paper presents some authors results regarding working quality inside workspace of a 3 DoF, 3 RRR planar parallel mechanism, used as parallel robot structure. Namely we deal with singularities avoidance inside workspace as is wide known in scientific literature this represents a major disadvantages of these mechanisms. To this purpose, the configuration determinant notion has been used as principal mechanism work parameter.

Abstract: Solving forward displacement is the difficulty of the 6-SPS parallel kinematics calculations, to make sure solving forward displacement easily, in this paper, added a initial multi-DOF drive to the 6-SPS parallel mechanism's moving platform in the ADAMS environment to make kinematical simulation, to get simulation of inverse kinematics solution and strike a theoretical inverse kinematics solution in the MATLAB environment, and prove the correctness of simulation of inverse solution. The inverse simulation position be used as input parameters to drive this parallel mechanism, by the solving forward displacement, results showed that the forward displacement is consist with the initial-DOF-driven values, indicating it is correct. It proves the use of these methods can be simply and easily calculate the required 6-SPS parallel mechanism positive solution, which can provide the reference of such institutions' solving forward position and control.

Abstract: Kinematics analysis of mechanism refers to analysis for pose、speed and acceleration of mobile platform of spatial 3-RPS parallel mechanism. In this paper, mathematical model of spatial 3-RPS parallel mechanism is primarily built, and the close loop equation is adopted for the positional posture analysis of the mobile platform, then the positional posture of mobile paltform is acquired. Finally, kinematical simulation will be acquired by software Adams, which makes sense in kinematical performance of spatial 3-RPS parallel mechanism.

Abstract: A heavy-load positioner with series-parallel mechanism was put forward according to the heavy-load positioner’s task demand. Two rotational DOFs were realized by the spherical 3-DOF mechanism with a restricted embranchment instead of traditional gear-driven mechanism, the other by the serial part. The mechanism has the advantages of large workspace, good flexibility and high stiffness-to-weight ratio. The kinematics, statics and singularity of the positioner mechanism were analyzed. The mathematic model of the positioner mechanism was established. Combining the workspace demand of the positioner, dimension optimization of the mechanism was researched. Finally, the kinematics,statics and the singularity analysis of the positioner mechanism was verified through virtual prototype designed with one group of satisfied dimensions.

Abstract: Force sensor based on the six degree of freedom (6-DoF) Stewart platform is universal for wide applications. Mechanism errors are significant for its measuring accuracy. However, because of the multi-variables and the complicated forms, it is difficult to solve the expression directly. The Monte Carlo method is proposed based on the analysis of the system structure and the mathematical model. The effect of mechanism errors on the measurement accuracy was assessed. With this method, a complex accuracy expression of the sensor could be avoided. It also provided a theoretical basis for designing the sensor of the Stewart platform.

Abstract: This paper addresses forward and inverse kinematics of a specific class of serial-parallel manipulators, known as 2(6-UPU) manipulators. This manipulator composed of two modules which consist of elementary manipulators with the parallel structure of Stewart Platform. At first, the Kinematics Model of the hybrid manipulator is obtained. As there is a highly nonlinear relations between joint variables, and position and orientation of the end effectors, the inverse kinematic problem of these manipulators is quite complicated to solve. In this study, wavelet based neural network (WNN) with its inherent learning ability, is used to solve the inverse kinematic problem. Also, proposed wavelet neural network is applied to approximate the paths of mid and upper plates in circle and spiral trajectories. Finally, the results of simulation show high accurate performance of proposed method.

Abstract: The human wrist has three rotational DOFs. Elbow muscle group work together to drive the wrist joint. According to the above characteristics of human wrist, parallel mechanism with three rotational DOFs of the imitation of human wrist is built. Traditional method for calculating DOF based on arithmetic is not that accurate. The method for analysis of DOF based on theory of constraint screw is explained. According to theory of constraint screw, the parallel mechanism built was analyzed. All the kinematic pairs in the mechanism will be expressed with screws so that the common constraints and the over constraints will be obtained. Through analysis above, the DOFs of the mechanism can be calculated and which a few degrees of freedom of the mechanism will be known. The new method avoids the disadvantages of the traditional method.

Abstract: A bran-new style coordinate measuring system with 3-PUU parallel mechanism and its advantages was proposed which could realize 3D measurement with only one linear grating and two precision guides. Firstly, measuring space with a 0.05mm error of structure parameter as target was explored based on 6 bars direct kinematics model, workspace and error model, and then the principle of maximum measuring space was presented to elaborate the relationship between measuring space and length of bar. Then in order to enlarge the scale of measuring space of Coordinate Measuring Machine (CMM), improve the measuring accuracy and flexibility of CMM, the key dimensions and positional parameters of CMM were optimization designed according to the direct kinematics model and the principle of maximum measuring space. Finally the deformation of key components was processed by Finite Element Method (FEM) according to the motion characteristics and parameters of the new CMM prototype, so that the affect of deformation to measuring accuracy can be controlled and decreased. Results are shown that the measuring space of CMM is 1100mm in x axis, 535mm in y axis, 426mm in z axis; deformation of beam is the main reason to influence the measuring accuracy and should be offset after calibration.