A novel decoupled parallel mechanism with two translational and one rotational degree of freedom and its performance indices analysis

Abstract

Less degrees of freedom parallel mechanism is widely used in many fields with its unique advantages. A decoupled parallel mechanism with 2 degree-of-freedom translation and 1 degree-of-freedom rotation is presented, and its performance evaluation indices analysis is performed. By the constraint screw method, the motion feature of the mechanism and its number of degree of freedom are analyzed. The constrained equations of the mechanism are established according to the constrained conditions of the pole length. The analytical expression of the forward and inverse position for the mechanism is deduced, and the expression of the Jacobian matrix is derived, which validated the decoupling feature of the mechanism. The singularity of the mechanism is also carried out. The performance evaluation indices for the decoupled parallel mechanism are discussed and the corresponding performance indices analysis of the proposed decoupled parallel mechanism is executed. The novel decoupled parallel mechanism presented herein enriches the parallel mechanism structure, and the definition and analysis of the performance evaluation indices should be meaningful for the further design and optimization of the decoupled parallel mechanism.

An approach for mobility and force/motion transmissibility analysis of parallel mechanisms based on screw theory and CAD technology

“…In this step, several info sets are used to store the extracted and generated information in a five-element data structure, that is, ''ID-Object-Attribute-Type-Value.'' (3) Attach the generated information of step (2) as SolidWorks attributes to the conceptual model, and formulate the formulas of the bases of twist/wrench subspaces of the limbs using equation ( 1). ( 4) Compute the basis elements of twist/wrench subspaces of the limbs numerically by assigning the coordinates of position and direction vectors of joint axes (obtained using the SolidWorks API) into the formulas generated in step (3), and evaluate the mobility and force/motion transmissibility performance of the PM as a whole by assigning the generated data to corresponding formulas in the algorithm library.…”

“…The 3- R (SS) 2 mechanism, also known as the Delta PM, is composed of three R(SS) 2 limbs in which there is a closed loop in the form of a spatial parallelogram connected by four spherical joints. As shown in Figure 21, the closed loop denoted by (SS) 2 can be treated as four serially linked 1-DOF R/P joints, and the skeleton elements within the conceptual model are described as follows: (1) s 1 , i , s 2 , i , l 2 , i , and n 1 , i are unit vectors along the joint orientation axes of the i th R(SS) 2 limb. (2) p 1 , i , p 2 , i , and p 3 , i are position vectors of the joint position points denoted by P 1 , i , …”

“…As shown in Figure 21, the closed loop denoted by (SS) 2 can be treated as four serially linked 1-DOF R/P joints, and the skeleton elements within the conceptual model are described as follows: (1) s 1 , i , s 2 , i , l 2 , i , and n 1 , i are unit vectors along the joint orientation axes of the i th R(SS) 2 limb. (2) p 1 , i , p 2 , i , and p 3 , i are position vectors of the joint position points denoted by P 1 , i , P 2 , i , and …”

“…By using the process shown in Figure 4 or selecting limbs from the library which contains the bases of twist/wrench subspaces of typical closed loop limbs such as (SS) 2 , (UU) 2 , and (RR) 2 , etc., the info sets of the bases of twist/wrench subspaces of the i th R(SS) 2 limb can be formulated in the interface shown in Figure 15, and the formulas of each screw elements can be…”

Dynamic Modeling and Mobility Analysis of the 3-R(RRR)R+R Antenna Mechanism

“…However, due to the coupling relationship of each branch of the parallel mechanism, it is difficult to achieve complete motion decoupling; besides, the motion range of the parallel mechanism is limited. 11 Due to the non-circular reflector of polarization type antenna, when the antenna moves in azimuth and pitch, the reflector rolls along with the movement, which changes the phase center of the antenna. Thus, the signal transmission of noncircular polarization antenna is affected.…”