Elastostatic Stiffness Analysis of a 2PUR-PSR Overconstrained Parallel Mechanism

Chao Yang,Qiaohong Chen,Junhua Tong,Qinchuan Li 한국정밀공학회 2019 International Journal of Precision Engineering and Vol.20 No.4

The elastostatic stiffness performance of a 2PUR-PSR (S: spherical joint; U: universal joint; R: revolute joint; P: prismatic pair) overconstrained parallel mechanism with two rotational and one translational (2R1T) degrees of freedom was studied based on screw theory and strain energy. First, the actuator and constraint wrenches of the mechanism were obtained based on screw theory. Second, by considering the space composite elastic deformation of the rod (including axial tension, and shear, torsional and bending deformation), compact limb stiffness matrixes were obtained in terms of strain energy and Castigliano’s second theorem. Finally, analytic expressions for the overall stiffness matrix of the mechanism and the amplitudes of the actuator and constrained wrenches were obtained based on the virtual-work principle and the balance equation for a moving platform. The relative error between results from the analytical model and the Workbench finite element model is approximately 1.3%, which validates the effectiveness of the proposed elastostatic stiffness model. Unlike traditional stiffness evaluation index, a regional stiffness index was proposed to measure the mechanism’s stiffness performance at various working heights. Using the index, it is possible to determine the optimum stiffness region of a moving platform with known external wrenches.

Kinematics, singularity, and optimal design of a novel 3T1R parallel manipulator with full rotational capability

Yekai Tu,Qiaohong Chen,Wei Ye,Qinchuan Li 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.6

Parallel manipulators (PMs) with 3T1R (three translational and one rotational degrees of freedom) or Schönflies motion are very useful in industry. However, most 3T1R PMs have a limited range of rotation less than 90° while many practical tasks require a large range of rotation over 180°. Furthermore, there are no 3T1R PMs with full rotational capability that has small number of single-DOF joints and fixed actuators. A novel 2-(RRR) 2 RH PM with full rotational capability is proposed, where R and H denote a revolute joint and a helical joint, respectively. The moving platform is connected to the fixed base by two identical (RRR) 2 RH chains, where (RRR) 2 denotes a 2-RRR closed chain. First, kinematic analysis of the proposed 2-(RRR) 2 RH PM, including mobility analysis, inverse and direct kinematics, singularity analysis, and workspace is presented. Second, the local conditioning index is used to evaluate the kinematic performance of the PM. Finally, optimal kinematic design of the 2-(RRR) 2 RH PM is investigated. The 2-(RRR) 2 RH PM has only 16 single-DOF joints and can be actuated by four fixed revolute joints. These features make it a good candidate in many applications.

Dynamic modeling and performance evaluation of a 2UPR-PRU parallel kinematic machine based on screw theory

Chenyang Rao,Lingmin Xu,Qiaohong Chen,Wei Ye 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.6

The orientation ability and accuracy of parallel kinematic machines (PKMs) with two rotational and one translational outputs (2R1T) can be improved with the mechanical structures of 2R1T PKMs with limited degrees of freedom (DOF) limbs, fewer single-DOF joints, and no spherical joints. However, few existing 2R1T PKMs satisfy these conditions. This study proposes a new over-constrained 2UPR-PRU (where U, P, and R represent universal, actuated prismatic, and revolute joints, respectively) PKM with 2R1T DOFs with three limited-DOF limbs, no spherical joints, only 12 single-DOF joints, and one fixed motor. First, mobility, inverse displacement, and singularity analysis are carried out. Inverse dynamic models of the PKM are then established based on screw theory. Velocities, accelerations of limbs and moving platform, and actuation forces are derived. Simulation is carried out to verify the dynamic model, including the comparisons of actuation velocities, accelerations, and forces. Rotational and translational dynamic manipulability ellipsoid indices of the PKM in different operational heights are evaluated. The proposed PKM has good potential for machining work pieces with curved surfaces.

Association of polymorphisms in bone morphogenetic protein receptor-1B gene exon-9 with litter size in Dorset, Mongolian, and Small Tail Han ewes

Jianlei Jia,Qian Chen,Lin-sheng Gui,Jipeng Jin,Yongyuan Li,Qiaohong Ru,Shengzhen Hou 아세아·태평양축산학회 2019 Animal Bioscience Vol.32 No.7

Objective: The present study was to investigate the association of polymorphisms in exon-9 of the bone morphogenetic protein receptor-1B (BMPR-1B) gene (C864T) with litter size in 240 Dorset, 232 Mongolian, and 124 Small Tail Han ewes. Methods: Blood samples were collected from 596 ewes and genomic DNA was extracted using the phenol: chloroform extraction method. The 304-bp amplified polymerase chain reaction product was analyzed for polymorphism by single-strand conformation polymorphism method. The genotypic frequency and allele frequency of BMPR-1B gene exon-9 were computed after sequence alignment. The χ2 independence test was used to analyze the association of genotypic frequency and litter size traits with in each ewe breed, where the phenotype was directly treated as category. Results: The results indicated two different banding patterns AA and AB for this fragment, with the most frequent genotype and allele of AA and A. Calculated Chi-square test for BMPR-1B gene exon-9 was found to be more than that of p value at the 5% level of significance, indicating that the population under study was in Hardy-Weinberg equilibrium for all ewes. The χ2 independence test analyses indicated litter size differences between genotypes was not the same for each breed. The 304-bp nucleotide sequence was subjected to BLAST analysis, and the C864T mutation significantly affected litter size in singletons, twins and multiples. The heterozygosity in exon-9 of BMPR-1B gene could increase litter size for all the studied ewes. Conclusion: Consequently, it appears that the polymorphism BMPR-1B gene exon-9 detected in this study may have potential use in marker assisted selection for litter size in Dorset, Mongolian, and Small Tail Han ewes.

A Gene Cluster for the Biosynthesis of Dibenzodioxocinons in the Endophyte Pestalotiopsis microspora, a Taxol Producer

( Yanjie Liu ),( Longfei Chen ),( Qiaohong Xie ),( Xi Yu ),( Anqing Duan ),( Yamin Lin ),( Biyun Xiang ),( Xiaoran Hao ),( Wanwan Chen ),( Xudong Zhu ) 한국미생물생명공학회(구 한국산업미생물학회) 2019 Journal of microbiology and biotechnology Vol.29 No.10

The fungal products dibenzodioxocinones promise a novel class of inhibitors against cholesterol ester transfer protein (CEPT). Knowledge as to their biosynthesis is scarce. In this report, we characterized four more dibenzodioxocinones, which along with a previously described member pestalotiollide B, delimit the dominant spectrum of secondary metabolites in P. microspora. Through mRNA-seq profiling in gα1Δ, a process that halts the production of the dibenzodioxocinones, a gene cluster harboring 21 genes including a polyketide synthase, designated as pks8, was defined. Disruption of genes in the cluster led to loss of the compounds, concluding the anticipated role in the biosynthesis of the chemicals. The biosynthetic route to dibenzodioxocinones was temporarily speculated. This study reveals the genetic basis underlying the biosynthesis of dibenzodioxocinone in fungi, and may facilitate the practice for yield improvement in the drug development arena.

Tex3: An 2R1T Parallel Manipulator with Minimum DOF of Joints and Fixed Linear Actuators

Lingmin Xu,Qinchuan Li,Junhua Tong,Qiaohong Chen 한국정밀공학회 2018 International Journal of Precision Engineering and Vol.19 No.2

A new 2R1T (R: rotation, T: translation) parallel manipulator (PM), called Tex3, is proposed. The Tex3 PM is a 2PUR-PRU PM consisting of 9 joints with 12 DOFs (degrees of freedom), and can be actuated by fixed linear actuators. Mobility analysis shows that it is an RPR-equivalent PM whose finite motion is the product of a rotation (R) followed by a translation (P) and another rotation (R). Inverse position and velocity analyses are discussed. Furthermore, the local transmission index and good transmission workspace are used to evaluate the motion/force transmissibility of the proposed PM. The singularity loci of the proposed PM are obtained according to the motion/force transmissibility, corresponding to the inverse, forward and combined kinematic singularity. The constraint singularity is also discussed. Finally, link parameters are optimized to obtain an improved good transmission workspace. Because of its minimum DOF of joints and fixed linear actuators, the Tex3 PM has good kinematic performance and is suited to the high-speed machining of workpieces with curved surfaces.