PID control with gravity compensation for hydraulic 6-DOF parallel manipulator

Abstract A novel model-based controller for 6 degree-of-freedom (DOF) hydraulic driven parallel manipulator considering the nonlinear characteristic of hydraulic systems-proportional plus derivative with dynamic gravity compensation controller is presented, in order to improve control performance and eliminate steady state errors. In this paper, 6-DOF parallel manipulator is described as multi-rigid-body systems, the dynamic models including mechanical system and hydraulic driven system are built using Kane method and hydromechanics methodology, the numerical forward kinematics and inverse kinematics is solved with Newton-Raphson method and close-form solutions. The model-based controller is developed with feedback of actuator length, desired trajectories and system states acquired by forward kinematics solution as the input and servovalve current as its output. The hydraulic system is decoupled by local velocity compensation in inner control loop prerequisite for the controller. The performance revolving stability, accuracy and robustness of the proposed control scheme for 6-DOF parallel manipulator is analyzed in theory and simulation. The theoretical analysis and simulation results indicate the controller can improve the control performance and eliminate the steady state errors of 6-DOF hydraulic driven parallel manipulator

Solid-Lubricant, Polymer - Polymeric and Functionalized Fiber- and Powder Reinforced Composites of Ultra-High Molecular Weight Polyethylene

Mechanical and tribotechnical characteristics of solid-lubricant and polymer-polymeric composites of UHMWPE were studied for the sake of design extrudable, wear-resistant, selflubricant polymer mixtures for Additive Manufacturing (AM). Tribotechnical properties of UHMWPE blends with the optimized content of solid lubricant fillers (polytetrafluoroethylene, calcium stearate, molybdenum disulphide, colloidal graphite, boron nitride) were studied under dry sliding friction at different velocities (V=0.3 and 0.5 m/s) and loads (P=60 and 140 N). Also, in order to increase strength and wear-resistance of UHMWPE composites they were reinforced with wollastonite microfibers and aluminum metahydroxide AlO (OH) microparticles preliminary treated (functionalized) in polyorganosiloxane. The comparison on measured mechanical and tribotechnical properties are given with interpretation of the mechanisms of observed phenomenon

Solid-Lubricant, Polymer - Polymeric and Functionalized Fiber- and Powder Reinforced Composites of Ultra-High Molecular Weight Polyethylene

Mechanical and tribotechnical characteristics of solid-lubricant and polymer-polymeric composites of UHMWPE were studied for the sake of design extrudable, wear-resistant, selflubricant polymer mixtures for Additive Manufacturing (AM). Tribotechnical properties of UHMWPE blends with the optimized content of solid lubricant fillers (polytetrafluoroethylene, calcium stearate, molybdenum disulphide, colloidal graphite, boron nitride) were studied under dry sliding friction at different velocities (V=0.3 and 0.5 m/s) and loads (P=60 and 140 N). Also, in order to increase strength and wear-resistance of UHMWPE composites they were reinforced with wollastonite microfibers and aluminum metahydroxide AlO (OH) microparticles preliminary treated (functionalized) in polyorganosiloxane. The comparison on measured mechanical and tribotechnical properties are given with interpretation of the mechanisms of observed phenomenon

Comparison of mechanical and tribotechnical properties of UHMWPE reinforced with basalt fibers and particles

Mechanical and tribotechnical properties of UHMWPE composites reinforced with basalt fibers and particles under dry sliding friction and abrasion were investigated. It is shown that adding of the basalt particles provides higher wear resistance under the dry sliding friction while at abrasion filling by the basalt fibers is more efficient since the wear resistance of the reinforced UHMWPE composites is by 3.7 times higher in contrast with the neat polymer. Wear mechanisms of the polymeric UHMWPE composites under various types of wear are discussed

A Surface-Enhanced Raman Scattering Sensor Integrated with Battery-Controlled Fluidic Device for Capture and Detection of Trace Small Molecules

For surface-enhanced Raman scattering (SERS) sensors, one of the important issues is the development of substrates not only with high SERS-activity but also with strong ability to capture analytes. However, it is difficult to achieve the two goals simultaneously especially when detecting small molecules. Herein a compact battery-controlled nanostructure-assembled SERS system has been demonstrated for capture and detection of trace small molecule pollutants in water. In this SERS fluidic system, an electrical heating constantan wire covered with the vertically aligned ZnO nanotapers decorated with Ag-nanoparticles is inserted into a glass capillary. A mixture of thermo-responsive microgels, Au-nanorods colloids and analyte solution is then filled into the remnant space of the capillary. When the system is heated by switching on the battery, the thermo-responsive microgels shrink, which immobilizes the analyte and drives the Au-nanorod close to each other and close to the Ag-ZnO nanotapers. This process has also created high-density “hot spots” due to multi-type plasmonic couplings in three-dimensional space, amplifying the SERS signal. This integrated device has been successfully used to measure methyl parathion in lake water, showing a great potential in detection of aquatic pollutants

The molecular record of metabolic activity in the subsurface of the Río Tinto Mars analog

In the subsurface, the interplay between microbial communities and the surrounding mineral substrate, potentially used as an energy source, results in different mineralized structures. The molecular composition of such structures can record and preserve information about the metabolic pathways that have produced them. To characterize the molecular composition of the subsurface biosphere, we have analyzed some core samples by time-of-flight secondary ion mass spectrometry (ToF-SIMS) that were collected in the borehole BH8 during the operations of the Mars Analog and Technology Experiment (MARTE) project. The molecular analysis at a micron-scale mapped the occurrence of several inorganic complexes bearing PO3-, SOx(2to4)-, NOx(2,3)-, FeOx(1,2)- SiO2-, and Cl-. Their distribution correlates with organic molecules that were tentatively assigned to saturated and monounsaturated fatty acids, polyunsaturated fatty acids, saccharides, phospholipids, sphingolipids, and potential peptide fragments. SOx- appear to be mineralizing some microstructures larger than 25 microns, which have branched morphologies, and that source SO3-bearing adducts. PO3-rich compounds occur in two different groups of microstructures which size, morphology, and composition are different. While a group of >40-micron sized circular micronodules lacks organic compounds, an ovoidal microstructure is associated with m/z of other lipids. The NO2-/NO3- and Cl- ions occur as small microstructure clusters (<20 microns), but their distribution is dissimilar to the mineralized microstructures bearing PO3-, and SO3-. However, they have a higher density in areas with more significant enrichment in iron oxides that are traced by different Fe-bearing anions like FeO2-. The distribution of the organic and inorganic negative ions, which we suggest, resulted from the preservation of at least three microbial consortia (PO4-, and NO2-/NO3-mineralizers PO4-lipid bearing microstructures), would have resulted from different metabolic and preservation pathway

The Design and Testing of a PEA Powered Ankle Prosthesis Driven by EHA

Several studies have shown that actuation concepts such as Serial elastic actuator (SEA) can reduce peak power and energy consumption in ankle prostheses. Proper selection and design of the actuation concepts is important to unlock the power source potential. In this work, the optimization design, mechanical design, control scheme, and bench experiments of a new powered ankle&ndash;foot prosthesis is proposed. The actuation concept of this prosthesis is parallel elastic actuator (PEA) composed of electro-hydrostatic actuator (EHA) as the power kernel and a unidirectional parallel spring as the auxiliary energy storage element. After the appropriate motor and transmission ratio was selected, a dynamic model of the PEA prosthesis was built to obtain the appropriate spring parameters driven by biological data. The design of the hydraulic and mechanical system and the controller were provided for the implementation of the designed system. Bench experiments were performed to verify the performance. The results showed that the designed prosthesis meets the biomechanical dynamics requirements. This result emphasizes the feasibility of the EHA as a power source and actuator and provides new ideas for the design of ankle&ndash;foot prostheses

Modeling and Simulation of Hydraulic Power Take-Off Based on AQWA

The AQWA software is often used to perform hydrodynamic analysis, and it is highly convenient for performing frequency domain simulations of Pelamis-like wave energy converters. However, hydraulic power take-off (PTO) must be simplified to a linear damping model or a Coulomb torque model when performing a time domain simulation. Although these simulation methods can reduce the computational complexity, they may not accurately reflect the energy capture characteristics of the hydraulic PTO. By analyzing system factors such as the flow and pressure of each branch of the hydraulic PTO, the output torque of the hydraulic cylinder to the buoy, and the electromagnetic torque of the generator, a relatively complete hydraulic PTO model is obtained, and the model is applied to AQWA using the FORTRAN language. Comparing and analyzing the simulation results of the linear damping model, the Coulomb torque model, and the hydraulic PTO, we found that the simulation results obtained by the linear damping model are quite different from those of the hydraulic PTO, while the torque characteristics, kinematic characteristics and energy capture characteristics of the Coulomb torque model are closer to those of the hydraulic PTO model. Therefore, it is more appropriate to simplify hydraulic PTO to a Coulomb torque model based on AQWA

CircFKBP5 Suppresses Apoptosis and Inflammation and Promotes Osteogenic Differentiation

ABSTRACT: Objectives: Dental pulp stem cells (DPSCs) are a type of mesenchymal stem cell possessing self-renewal and multilineage differentiation capabilities. The dysfunction of DPSCs is related to the pathologic process of pulpitis. The participation of circular RNAs (circRNAs) in DPSC differentiation has been identified. This work focussed on exploring the functions and mechanism of circFKBP5 in DPSC dysfunction evoked by lipopolysaccharide (LPS). Materials and methods: The viability and apoptosis of human DPSCs (hDPSCs) were determined using Cell Counting Kit-8 assay and flow cytometry. Inflammation was analysed by measuring the release of inflammatory cytokines. The osteogenic differentiation of hDPSCs was investigated by performing alkaline phosphatase (ALP) staining and alizarin red S staining and detecting the changes of ALP and runt-related transcription factor 2 (RUNX2) proteins. The dual-luciferase reporter, RNA immunoprecipitation (RIP), and pull-down assays were used to confirm the binding between miR-708-5p and circFKBP5 or G-protein-coupled receptor (GPCR)–kinase interacting protein 2 (GIT2). Results: CircFKBP5 expression was decreased in hDPSCs and, functionally, reexpression of circFKBP5 attenuated LPS-induced apoptosis, inflammation, and inhibition of proliferation ability and osteogenic differentiation in hDPSCs. Mechanistically, circFKBP5 acted as a sponge for miR-708-5p, which was verified to target GIT2. LPS induced miR-708-5p expression in hDPSCs, and knockdown of miR-708-5p protected against LPS-evoked hDPSC dysfunction. Besides, GIT2 expression was decreased in hDPSCs after LPS treatment. Rescue experiments showed that GIT2 could mediate the protective functions of circFKBP5 on hDPSCs under LPS treatment. Conclusions: CircFKBP5 could protect against LPS-induced apoptosis, inflammation, and osteogenic differentiation inhibition in hDPSCs via the miR-708-5p/GIT2 axis

Modeling and Simulation of Hydraulic Power Take-Off Based on AQWA

The AQWA software is often used to perform hydrodynamic analysis, and it is highly convenient for performing frequency domain simulations of Pelamis-like wave energy converters. However, hydraulic power take-off (PTO) must be simplified to a linear damping model or a Coulomb torque model when performing a time domain simulation. Although these simulation methods can reduce the computational complexity, they may not accurately reflect the energy capture characteristics of the hydraulic PTO. By analyzing system factors such as the flow and pressure of each branch of the hydraulic PTO, the output torque of the hydraulic cylinder to the buoy, and the electromagnetic torque of the generator, a relatively complete hydraulic PTO model is obtained, and the model is applied to AQWA using the FORTRAN language. Comparing and analyzing the simulation results of the linear damping model, the Coulomb torque model, and the hydraulic PTO, we found that the simulation results obtained by the linear damping model are quite different from those of the hydraulic PTO, while the torque characteristics, kinematic characteristics and energy capture characteristics of the Coulomb torque model are closer to those of the hydraulic PTO model. Therefore, it is more appropriate to simplify hydraulic PTO to a Coulomb torque model based on AQWA