Performance analysis of variable speed hydraulic systems with large power in valve-pump parallel variable structure control

Aiming at the problems, bad low velocity performance and slow response, existing in variable speed hydraulic systems, this study proposes a variable speed hydraulic system in valve-pump parallel variable structure control, in which control structures vary with control requirement. The leaking parallel valve control is applied to improve low-speed performance at the start and stop stages by increasing damping ratios and compensating the reduction of damping ratios due to the friction negative slop; the replenishing parallel valve control is applied to achieve fast response to load disturbance at the uniform stage with high speed; the variable speed pump control is to make full use its high efficiency at other stages. During the regulation process, these control structures switch smoothly and a good speed tracking is achieved, in addition, the pump provides majority of required flow, so the proposed system still can work efficiently as pump control systems. Therefore, the valve-pump parallel variable structure control establishes a flexible control mechanism by two channels of valve control and pump control, and could improve comprehensive performances of variable speed hydraulic systems with large power, such as low-speed performance, rapid response and high efficiency

A New Hydraulic Speed Regulation Scheme: Valve-Pump Parallel Variable Mode Control

© 2013 IEEE. To improve the comprehensive performances of hydraulic speed regulation systems, this paper proposes and develops a new control scheme, valve-pump parallel variable mode control, which can adopt different control modes in different speed regulation stages and can also adjust the weight ratio between pump control and valve control in the control process. In this paper, we design a hydraulic speed regulation in valve-pump parallel variable mode control, explain its principle, establish the system mathematical model, analyze the system parameters, and build a test system to verify regulation performances. The experimental results show that during the speed adjustment process, the switching between different control modes is smooth, the change rule of proportional valve and variable pump is in accordance with the expectation, and the ratio of valve to pump is reasonable, and the proposed scheme can improve the comprehensive performance of speed governing systems. The valve-pump parallel variable mode control could make full use of advantages of valve control and pump control, and will make hydraulic control systems more flexible and suitable and enrich the current control schemes of hydraulic speed regulation systems

Dynamic characteristic analysis of replenishing/leaking parallel valve control systems

To improve the dynamic response of traditional pump control systems, this paper proposes two new control schemes: replenishing parallel valve control (RPVC) and leaking parallel valve control (LPVC). A parallel valve control system using the two control schemes is designed, and its system parameters, control performances and efficiency are analysed and verified by simulation and experiments. Compared to the pump control system, the proposed system has larger damping ratios which vary widely with operating points, and has lower velocity stiffness due to the increase of total leakage coefficients. Both the LPVC and RPVC could contribute to the dynamic response improvement. RPVC is preferred over LPVC because of more stable damping ratios and higher speed stiffness, and these advantages could be further improved by increasing the supply pressure of the control valve, but the LPVC scheme costs lower due to the unnecessary oil supply for the control valve. During the control process, the valve works at a low flow rate, but the pump provides the majority of the system flow, so two parallel valve control systems still have relatively high energy efficiency with rapid response. Therefore, the RPVC and LPVC will enrich the control mode of hydraulic systems

Multistage throttling characteristics of reverse direction impact of pilot operated check valve

The aim of this study was to improve the reverse impact characteristics of large-flow pilot operated check valves, meanwhile reduce oscillation, cavitation and unloading time. Three different main poppets were selected, and the impact pressure and flow were set as 30 MPa and 1000 L/min, respectively. The cavitation phenomenon was explored based on the analysis of gas-liquid two-phase flow by Fluent software, and then experimental verification was performed. Meanwhile, the dynamic characteristics of pilot operated check valves were analyzed by the impact test system. The simulation results showed that the fluid pressure clearly decreased while flowing through the poppet area. The sudden decrease of flow area at the orifice port of the poppet resulted in an increase in flow-velocity, because the cavitation area appears on the side of the main poppet. A stepped throttling structure could effectively reduce the cavitation area, preventing the generation of cavitation. The experimental results showed that the pressure oscillation of a stepped main poppet significantly reduced during the process of unloading, at 28.41 MPa; with a flow gradient of 4.86×105 L/min2; unloading time significantly reduced, for 711 ms; indicating it opened more rapidly and dynamic characteristics was superior. It can be concluded that the stepped throttling structure could effectively reduce the pressure oscillation of a pilot operated check valve during the process of unloading, improve response speed, enhance the impact properties, and reduce cavitation. This verified the correctness of the simulation and the rationality of the cavitation index

Performance analysis of variable speed hydraulic systems with large power in valve-pump parallel variable structure control

Aiming at the problems, bad low velocity performance and slow response, existing in variable speed hydraulic systems, this study proposes a variable speed hydraulic system in valve-pump parallel variable structure control, in which control structures vary with control requirement. The leaking parallel valve control is applied to improve low-speed performance at the start and stop stages by increasing damping ratios and compensating the reduction of damping ratios due to the friction negative slop; the replenishing parallel valve control is applied to achieve fast response to load disturbance at the uniform stage with high speed; the variable speed pump control is to make full use its high efficiency at other stages. During the regulation process, these control structures switch smoothly and a good speed tracking is achieved, in addition, the pump provides majority of required flow, so the proposed system still can work efficiently as pump control systems. Therefore, the valve-pump parallel variable structure control establishes a flexible control mechanism by two channels of valve control and pump control, and could improve comprehensive performances of variable speed hydraulic systems with large power, such as low-speed performance, rapid response and high efficiency

Surface plasmon polaritons assisted diffraction in periodic subwavelength holes of metal films with reduced interplane coupling

Metal films grown on Si wafer perforated with a periodic array of subwavelength holes have been fabricated and anomalous enhanced transmission in the mid-infrared regime has been observed. High order transmission peaks up to Si(2,2) are clearly revealed due to the large dielectric constant contrast of the dielectrics at the opposite interfaces. Si(1,1) peak splits at oblique incidence both in TE and TM polarization, which confirms that anomalous enhanced transmission is a surface plasmon polaritons (SPPs) assisted diffraction phenomenon. Theoretical transmission spectra agree excellently with the experimental results and confirm the role of SPPs diffraction by the lattice.Comment: 4 pages, 5 figures, 26 reference

Fluorescent Nanoparticle-Based Indirect Immunofluorescence Microscopy for Detection of Mycobacterium tuberculosis

A method of fluorescent nanoparticle-based indirect immunofluorescence microscopy (FNP-IIFM) was developed for the rapid detection of Mycobacterium tuberculosis. An anti-Mycobacterium tuberculosis antibody was used as primary antibody to recognize Mycobacterium tuberculosis, and then an antibody binding protein (Protein A) labeled with Tris(2,2-bipyridyl)dichlororuthenium(II) hexahydrate (RuBpy)-doped silica nanoparticles was used to generate fluorescent signal for microscopic examination. Prior to the detection, Protein A was immobilized on RuBpy-doped silica nanoparticles with a coverage of ∼5.1×102 molecules/nanoparticle. With this method, Mycobacterium tuberculosis in bacterial mixture as well as in spiked sputum was detected. The use of the fluorescent nanoparticles reveals amplified signal intensity and higher photostability than the direct use of conventional fluorescent dye as label. Our preliminary studies have demonstrated the potential application of the FNP-IIFM method for rapid detection of Mycobacterium tuberculosis in clinical samples

A novel homozygous mutation in LSS gene possibly causes hypotrichosis simplex in two siblings of a Tibetan family from the western Sichuan province of China

Aim: Hypotrichosis simplex (MIM 146520) is a rare form of monogenic hereditary alopecia. Several genes have been identified as being associated with the disease, including LPAR6, LIPH, and DSG4. LSS encoding lanosterol synthase (LSS) has been shown to cause hypotrichosis simplex, but the related mechanisms have not been elucidated to date. This study aims to find mutations in LSS from a Chinese family, among which a 21-year-old male patient and his 9-year-old sister were affected by hypotrichosis simplex.Methods: Dermoscopy and histological analysis were used to examine patients’ scalps, while exome sequencing was used to find the mutations in LSS.Results: The hair loss was only detected on the scalp of the proband and his sister, while other ectodermal structures were normal with no systemic abnormalities. Further, the exome sequencing identified a new homozygous mutation NM_002340.6 (LSS_v001):c.812T>C (p.(Ile271Thr)) in the LSS gene of the proband, which was also found in his sister. In addition, a heterozygous mutation of LSS was found in their asymptomatic parents. Finally, the possible protein structure of the mutational LSS was predicted.Conclusion: The hypotrichosis simplex reported here could be an autosomal recessive disease in this family. The mutation on LSS might reduce the enzyme activity of LSS, thus leading to the disease

Relevance of JAK2V617F positivity to hematological diseases - survey of samples from a clinical genetics laboratory

<p>Abstract</p> <p>Background</p> <p>JAK2V617F is found in the majority of patients with Ph- myeloproliferative neoplasms (MPNs) and has become a valuable marker for diagnosis of MPNs. However, it has also been found in many other hematological diseases, and some studies even detected the presence of JAK2V617F in normal blood samples. This casts doubt on the primary role of JAK2V617F in the pathogenesis of MPNs and its diagnostic value.</p> <p>Methods</p> <p>In the present study, we analyzed JAK2V617F positivity with 232 normal blood samples and 2663 patient blood, bone marrow, and amniotic fluid specimens obtained from a clinical genetics laboratory by using a simple DNA extraction method and a sensitive nested allele-specific PCR strategy.</p> <p>Results</p> <p>We found JAK2V617F present in the majority (78%) of MPN patients and in a small fraction (1.8-8.7%) of patients with other specific hematological diseases but not at all in normal healthy donors or patients with non-hematological diseases. We also revealed associations of JAK2V617F with novel as well as known chromosomal abnormalities.</p> <p>Conclusions</p> <p>Our study suggests that JAK2V617F positivity is associated with specific hematological malignancies and is an excellent diagnostic marker for MPNs. The data also indicate that the nested allele-specific PCR method provides clinically relevant information and should be conducted for all cases suspected of having MPNs as well as for other related diseases.</p