Kinematic Analysis and Verification of a New 5-DOF Parallel Mechanism

This paper first designs a new 5-DOF parallel mechanism with 5PUS-UPU, and then analyses its DOF by traditional Grubler–Kutzbach and motion spiral theory. It theoretically shows that the mechanism meets the requirement of five dimensions of freedoms including three-dimensional movement and two-dimensional rotation. Based on this, the real mechanism is built, but unfortunately it is found unstable in some positions. Grassmann line geometry method is applied to analyze its unstable problem caused by singular posture, and then an improving method is put forward to solve it. With the improved mechanism, closed loop vector method is employed to establish the inverse position equation of the parallel mechanism, and kinematics analysis is carried out to get the mapping relationships between position, speed, and acceleration of moving and fixed platform. Monte Carlo method is used to analyze the workspace of the mechanism, to explore the influencing factors of workspace, and then to get the better workspace. Finally, an experiment is designed to verify the mechanism working performance

Research on a Fiber Corner Compensation Algorithm in a 3D Printing Layer of Continuous Fiber-Reinforced Composite Materials

Fused filament fabrication (FFF) 3D printing technology for continuous fiber-reinforced composite (CFRC) printing has become a trend. This article is based on ‘independent extrusion’ FFF CFRC printing. The continuous fiber-reinforced filament (CFRF) printing solution is the contour offset method for obtaining executable g-code. When the CFRCF prints at the corner, it is found that the actual CFRC printing trajectory is inconsistent with the ideal laying trajectory. The causes of the error are analyzed, and an angle optimization algorithm is proposed. The corner optimization algorithm is verified by theoretical analysis and experimental analysis. From the experimental results, the corner optimization algorithm improves the 30° angle fit of CFRF printing by 90% and reliability has also been improved. When the printing length is 127,200 mm, there are 960 printing corners, and the failure rate is 0

Research on Continuous Machining Strategy for Five-Axis Machine Tool: Five-Axis Linkage to Four-Axis Linkage

The article presents a novel strategy for enhancing the efficiency of machines that are used for complex structure machining. It proposes a low-cost five-axis four-linkage milling system as an alternative to the more expensive five-axis five-linkage system. Kinematic analysis of the machine tool is conducted to establish a correlation between the tool location data and the displacement of kinematic axes. An interpolation algorithm is then devised to determine a four-axis linkage milling strategy. The theoretical errors of the interpolation trajectory are observed to be reduced following the transformation. The research employs impeller processing as a case study, wherein the five-axis linkage machining path is translated into a more efficient five-axis four-linkage path using the interpolation algorithm. The practical application of this novel milling strategy confirms its effectiveness in processing the integral impeller within acceptable efficiency parameters. The results provide a theoretical foundation for the practical application of the low-cost five-axis four-linkage machining strategy in high-precision five-axis five-linkage machine tools

I Ks Protects from Ventricular Arrhythmia during Cardiac Ischemia and Reperfusion in Rabbits by Preserving the Repolarization Reserve

Introduction: The function of the repolarization reserve in the prevention of ventricular arrhythmias during cardiac ischemia/reperfusion and the impact of ischemia on slowly activated delayed rectifier potassium current (IKs) channel subunit expression are not well understood. Methods and Results: The responses of monophasic action potential duration (MAPD) prolongation and triangulation were investigated following an L-768,673-induced blockade of I Ks with or without ischemia/reperfusion in a rabbit model of lef

Preparation and Process Parameter Optimization of Continuous Carbon Fiber-Reinforced Polycarbonate Prepreg Filament

Continuous fiber-reinforced composite 3D printing (CFRC 3DP) has become a hot topic of interest for many experts and scholars. Continuous fiber-reinforced prepreg filament (CFRPF) for printing needs to be prepared in advance. In this paper, on the basis of the resin fusion impregnation theory, a fabrication device was designed for continuous carbon fiber-reinforced polycarbonate prepreg filament (CCFRPF). Then, according to the orthogonal test and the TOPSIS entropy weight optimization theory, the optimization method for CFRPF/PC preparation process parameters was proposed, and the relationship between the preparation process parameters and the performance indexes was discussed. The results show that when preparing CCFRPF/PC, the weight of diameter performance index is the largest, about 0.75. The optimal combination of process parameters for CCFRPF/PC is, respectively, 285 °C for the outlet mold temperature, 305 °C for the impregnation mold temperature, and 1 m/min for the winding speed. In this case, the diameter, roundness, minimum curvature radius and tensile strength of 0.375 mm, 29.4 μm, 9.775 mm and 1298 MPa were achieved, respectively

Research on the Simulation Model of Continuous Fiber-Reinforced Composites Printing Track

The rapid development of additive manufacturing technology (AM) is revolutionizing the traditional continuous fiber-reinforced polymer (CFRP) manufacturing process. The combination of FDM technology and CFRP technology gave birth to continuous fiber reinforced thermoplastic composites (CFRTPC) 3D printing technology. Parts with complex structure and excellent performance can be fabricated by this technology. However, the current research on CFRTPC printing mainly focuses on printing equipment, materials, and the improvement of mechanical properties. In this paper, the CFRTPC 3D printing track errors are investigated during the printing process, and it is found that the polytetrafluoroetylene (PTFE) tube in the nozzle of the printer head is often blocked. Through detailed analysis, a line-following mathematical model reflecting the deviations of the CFRTPC printing track is established. According to the characteristics of the fiber and its track during actual laying, a modified line-following model, without the minimum curvature point, is further proposed. Based on this model, the actual printing track for the theoretical path is simulated, the process tests are carried out on the printing track at different corner angles, and the relevant rules between the parameters of the model and different corner angles are obtained. The mathematical model is verified by experiments, and the clogging problem of the printer head caused by the fiber track error is solved, which provides theoretical support for the rational design of the fiber track in CFRTPC printing

Determination of Narrow Coal Pillar Width and Roadway Surrounding Rock Support Technology in Gob Driving Roadway

In order to determine the rational width of coal pillars and study the surrounding rock control technology of gob side entry driving with a narrow coal pillar, this paper first calculates the width of narrow coal pillar according to limit equilibrium theory; after that, the lateral support pressure and plastic zone development of the goaf is analyzed by numerical simulation to determine the rational width of reserved coal pillar; finally, through the ring breaking deformation regulation of surrounding rock of the gob side entry, the deformation and failure characteristics of the gob-side roadway during excavation and the influence of mining on the deformation and failure of the gob-side roadway are analyzed. The research results show that, combined with theoretical analysis and numerical simulation, the width of narrow coal pillar is decided to be 10 m; the deformation of the coal pillar side of the gob side roadway is much bigger than the roof subsidence, the deformation of the solid coal wall and the floor deformation; after the bolt support design of the gob side roadway, the deformation and damage of the gob side roadway during the driving period is small; during mining, the deformation of the narrow coal pillar wall is the key factor to determine the stability of the gob roadway; under the bolt support scheme, the overall deformation and failure of surrounding rock of the goaf roadway is small, and the control effect of the surrounding rock of the goaf roadway is good

Divergent molecular mechanisms for potassium channel remodeling in animal models of heart disease.

<p>AV, atrioventricular; ICM, ischemic cardiomyopathy; ND, not determined; -, no change.</p><p>*Weak bands limited the reliability of the measurement.</p>‡<p>KCNQ1.2, a truncated isoform of canine KCNQ1, was increased and may suppress I_Ks in a dominant-negative fashion.</p

Efficacy of intravenous plus intrathecal/intracerebral ventricle injection of polymyxin B for post-neurosurgical intracranial infections due to MDR/XDR Acinectobacter baumannii: a retrospective cohort study

Abstract Background Post-neurosurgical intracranial infections caused by multidrug-resistant or extensively drug-resistant Acinetobacter baumannii are difficult to treat and associated with high mortality. In this study, we analyzed the therapeutic efficacy of intravenous combined with intrathecal/intracerebral ventricle injection of polymyxin B for this type of intracranial infection. Methods This retrospective study was conducted from January 2013 to September 2017 at the Second Affiliated Hospital, Zhejiang University School of Medicine (Hangzhou,China) and included 61 cases for which cerebrospinal fluid (CSF) cultures were positive for multidrug-resistant or extensively drug-resistant A. baumannii after a neurosurgical operation. Patients treated with intravenous and intrathecal/intracerebral ventricle injection of polymyxin B were assigned to the intrathecal/intracerebral group, and patients treated with other antibiotics without intrathecal/intracerebral injection were assigned to the intravenous group. Data for general information, treatment history, and the results of routine tests and biochemistry indicators in CSF, clinical efficiency, microbiological clearance rate, and the 28-day mortality were collected and analyzed. Results The rate of multidrug-resistant or extensively drug-resistant A. baumannii infection among patients who experienced an intracranial infection after a neurosurgical operation was 33.64% in our hospital. The isolated A. baumannii were resistant to various antibiotics, and most seriously to carbapenems (100.00% resistance rate to imipenem and meropenem), cephalosporins (resistance rates of 98.38% to cefazolin, 100.00% to ceftazidime, 100.00% to cefatriaxone, and 98.39% to cefepime). However, the isolated A. baumannii were completely sensitive to polymyxin B (sensitivity rate of 100.00%), followed by tigecycline (60.66%) and amikacin (49.18%). No significant differences in basic clinical data were observed between the two groups. Compared with the intravenous group, the intrathecal/intracerebral group had a significantly lower 28-day mortality (55.26% vs. 8.70%, P = 0.01) and higher rates of clinical efficacy and microbiological clearance (95.65% vs. 23.68%, P < 0.001; 91.30% vs. 18.42%, P < 0.001, respectively). Conclusions Intravenous plus intrathecal/intracerebral ventricle injection of polymyxin B is an effective regimen for treating intracranial infections caused by multidrug-resistant or extensively drug-resistant A. baumannii

Comparison of waveforms between the Sham (2-d) and Infarct (2-d) groups after bolus injection of epinephrine.

<p>The only morphological differences in peri-infarct MAP were identified in the Infarct (2-d) group. (<b>A</b>) ECG Lead II waveforms showing that both groups had a comparable degree of heart rate increase. (<b>B</b>) MAP recorded at the peri-infarct epicardial zone showing that after the adrenergic challenge, the MAP of the Infarct (2-d) group had a dramatic shortening of MAPD30, whereas the MAPD90 was only minimally changed. (<b>C</b>) Direct overlapping of MAP showing that the MAP of the Infarct (2-d) group demonstrates more prominent triangulation.</p