Novel 2R3T and 2R2T parallel mechanisms with high rotational capability

SUMMARYLarge rotational angles about two axes for parallel mechanisms (PMs) with two rotational and three translational (2R3T) degrees of freedom (DOFs) or two rotational and two translational (2R2T) DOFs are demanded in some industries, such as parallel machine tools and multi-axis 3D printing. To address the problem, this paper focuses on the structural synthesis of new 2R3T and 2R2T PMs with high rotational capability. First, two new moving platforms are proposed based on the concepts of decoupled and configurable design. By means of the proposed platforms and Lie group theory, a series of 2R2T and 2R3T PMs are synthesized. Then the inverse kinematics and velocity relationship of one of the synthesized 2R3T PMs are presented. Finally, the rotational capability of the same 2R3T PM is analyzed. The result shows that by means of actuation redundancy, the studied 2R3T PM indeed possesses the high rotational capability about two axes, even though interferences and singularities are taken into consideration.

The Kinematics Analysis of the 3-PTT Parallel Machine Tools

This paper presents the kinematics for 3-PTT parallel machine tools, the kinematic is analytically performed, the forward and inverse position kinematic equations are explicit functions and workspace is derived and there is no singularity configuration and kinematic coupling in the whole workspace. The manipulability analytical of the parallel machine tool is investigated by the Jacobian matrix.

The Prediction of Surface Roughness of Parallel Machine Tools Based on the Neural Network

Because the parallel machine tool have high speed, high precision, high rigidity and the mechanical structure is simple, the parallel machine tool have been used in many field widely. In the research and application of parallel machine, the effect of processing parameter on machine processing is the most important problem. In the paper the improved artificial neural network is applied to the roughness prediction model of parallel machine tools, the model predict the roughness when the feed rate, spindle speed, processing angle and machining force are changed effectively.

Workspace Comparison Study of Two Plane-Symmetry Parallel Machine Tools

Workspaces of two plane-symmetry parallel machine tools whose limbs are composed of the revolute joint, the prismatic joint and the spherical joint were studied comparatively in this paper. Firstly, manipulators of the plane-symmetry 3-RPS parallel machine tool and the plane-symmetry 3-SPR parallel machine tool were introduced, and their simulation manipulators were given. Secondly, the workspaces of the plane-symmetry 3-RPS parallel machine tool and the plane-symmetry 3-SPR parallel machine tool were solved and expressed in the same figure on the basis of the computer aided geometric technique method, respectively. Lastly, indices measuring the workspace were defined, and workspaces of the plane-symmetry 3-RPS parallel machine tool and the plane-symmetry 3-SPR parallel machine tool were analyzed comparatively from two aspects: positional workspace and posture angle.

Modeling and Simulation of the Dynamics of the Milling of Ball End Milling

A dynamic modal of the milling of ball end milling is presented for the simulation and analyzing the influence of the milling parameters on milling in order to avoid the vibration. The milling cutter and constrains are simplified to be a system with the two modes of vibration, the modal is developed considering effective cutting area of the cutting edge and regenerative effect, which directly reflects the cutter-in and the cutter-out. The mode testing and identifying determine the equation coefficients. It is found that reducing the milling depth can improve the stability and avoid self-excited vibration milling when the depth less than the critical milling depth, the frequency of the milling system will change while changing the rotate speed of the spindle, the self-excited is prone to occur when the frequency is close to the natural frequency. The results of simulation are benefit of the milling and optimal design of the parallel machine tools.

Algorithm for the Inverse Kinematics Calculation of Cross Rods Parallel Machine Tools Based on Lie-Algebras

In order to solve the problems that traditional kinematics model built by the method of D-H parameters can only reflect relative movements between adjacent components and can't express directly the spatial poses of every component relative to static platform, Lie-algebras is used this paper to establish the product of exponential formula of forward direct kinematics of every branch chains. The elimination method and Paden - kahan sub-problems are used to calculate joint variables. Then the quick and intuitive inverse algorithm of cross rods parallel machine tools is acquired. The algorithm provides reliable proofs for the analysis of error compensation, kinematics interference and singularity. Finally we prove our theory with an example of an actual parallel machine tool.