High-precision Equipment Research Articles

Effect of hydrostatic thrust bearing oil pad structure on performance

Background: The hydrostatic thrust bearing is a liquid lubrication technology based on the principle of hydrostatic pressure, characterized by high load-carrying capacity, low friction, and long lifespan. It has been widely applied in precision machinery and the spindles of high-speed, high-precision equipment. The oil pad of the hydrostatic thrust bearing is a crucial component, and its geometric structure significantly influences the bearing performance. During operation, the oil film of the hydrostatic thrust bearing is subjected to high loads and temperatures. If the oil film does not have sufficient strength, it can affect the normal operation of the bearing, leading to accidents. The oil pad structure is a key factor affecting the strength of the oil film. Therefore, the rational design of the oil pad structure is essential to ensure the performance of the hydrostatic bearing and prolong its service life. Objective: This study aimed to summarize the impact of different oil pad structures on the performance of hydrostatic thrust bearings, providing a basis for the future development of hydrostatic thrust bearings. Method: A search for journals, patents, conferences, and papers related to hydrostatic thrust bearings was conducted, and the impact of oil pad structures on hydrostatic thrust bearings was summarized and analyzed. Results: Based on the research findings of numerous scholars, this study summarizes the impact of oil pad structures on the performance of hydrostatic thrust bearings. It describes how the oil pad shape, oil pocket shape, oil pocket depth, and microtextures affect the overall performance of thrust bearings. The research methods employed are analyzed, and a concluding summary is provided regarding the influence of bearing oil pad geometric structures on bearing performance. Conclusion: This paper provides guidance for the design and optimization of the oil pad in hydrostatic thrust bearings. Finally, it outlines the future development trends of the oil pad in hydrostatic thrust bearings and provides prospects for future development trends and key areas of focus for hydrostatic thrust bearings.

A modal momentum method for the identification of structural weak links

In order to meet the demands of weak-link identification of mechanical structures in high-precision equipment, this paper introduces the concepts and equations of modal momentum and modal momentum difference ratio (MMDR), as well as an identification method of weak links based on modal momentum. In this method, the modal data of the mechanical structure is acquired first through experimental modal analysis or finite element analysis. The modal momentum of each measured point is calculated based on the modal data and transformed to the global coordinate system. Then, the MMDRs between the measured point with the largest magnitude of modal momentum and its adjacent measured points are calculated. Weak links are judged if the MMDR exceeds a predefined threshold. Twelve different multi-degrees-of-freedom systems incorporating weak links were designed and then identified using the proposed method. The accuracy of identification is up to 100% for these systems. The method was applied to a double pendulum angle milling head of a five-axis numerically controlled machine tool, and the result reveals that the side plate lacks bending stiffness.

On the Issue of Assigning Dynamic Characteristics of Engineering Equipment in Designing of High-Precision Production

This paper provides a review of the regulatory framework of the permissible value of the vibration level depending on the accuracy of the equipment, a review of the problem of the influence of vibration on the operation of high-precision equipment. Based on the results of the analysis of the identified problem, a lack of initial data from manufacturers of vibration sources in terms of vibration characteristics was identified, and a solution was proposed to obtain the necessary parameters for frequency analysis.

Research on stiffness matching of support structure of high-precision equipment on satellite

Abstract This paper takes the support structure of high-precision equipment on satellites as the research object, and combining it with the characteristics of an actual satellite platform, analyses the stiffness matching between the platform and the load mounting point represented by the axial connecting relay. On this basis, the support structure of two different types of installation points is quantitatively evaluated, the optimal configuration is selected through the analysis result, and the design improvement measures are proposed. It provides a new design idea for the support structure of the same type of high-precision equipment on satellite.

Design of a decision support system to form optimal technological processes for parts machining based on artificial intelligence methods

The object of this study is the process of designing a decision support system for automating the formation of technological processes (TPs) for machining parts of high-precision equipment for the aviation industry. The task of improving the efficiency of the optimization of the process of mechanical processing of parts through the use of a decision support system (DSS) and artificial intelligence methods, which, unlike known analytical approaches, allow describing processes and phenomena that do not have strict formalization, has been solved. DSS consists of three subsystems. The first is an information subsystem for the automated formation of the structure in the technological process of machining parts of high-precision equipment. The second is an information subsystem for optimizing parameters of TP operations by cutting, taking into account the accumulation of tool wear. The third is a subsystem of control and adjustment of operating parameters. In the process of conducting research, an approach was devised for designing optimal technological processes to machine parts of high-precision equipment. The task of designing the structure of technological processes was solved using production rules. The task of determining the optimal parameters of turning and milling operations was solved in a multi-criteria statement. The following objective functions were used: cost of the operation, specific energy consumption for the operation, and productivity of the operation. At the same time, the wear of the tool accumulated over time was taken into account. The solution was obtained by searching for the Pareto-optimal solution using genetic algorithms and artificial neural networks. As a result of the work of DSS, an optimal technological process for machining parts of high-precision equipment for the aviation industry was formed, which made it possible to reduce the production time of one part by 5 % and reduce the total cost of production of the part by 14 %

The Adjustment Analysis Method of the Active Surface Antenna Based on Convolutional Neural Network

Active surface technique is one of the key technologies to ensure the reflector accuracy of the millimeter/submillimeter wave large reflector antenna. The antenna is complex, large-scale, and high-precision equipment, and its active surfaces are affected by various factors that are difficult to comprehensively deal with. In this paper, based on the advantage of the deep learning method that can be improved through data learning, we propose the active adjustment value analysis method of large reflector antenna based on deep learning. This method constructs a neural network model for antenna active adjustment analysis in view of the fact that a large reflector antenna consists of multiple panels spliced together. Based on the constraint that a single actuator has to support multiple panels (usually 4), an autonomously learned neural network emphasis layer module is designed to enhance the adaptability of the active adjustment neural network model. The classical 8-meter antenna is used as a case study, the actuators have a mean adjustment error of 0.00252 mm, and the corresponding antenna surface error is 0.00523 mm. This active adjustment result shows the effectiveness of the method in this paper.

A Picometre-Level Resolution Test Method without Nonlinearity for Heterodyne Interferometer Measurement Electronics

The wide application of displacement measurement in high-precision equipment production and high-precision metrology is placing increasing pressure on the resolution of heterodyne interferometers. However, as the core component of an interferometer, since measurement electronics includes the cross-physical process of photoelectric conversion, its resolution is rarely evaluated, either on an individual level or as a whole. Therefore, in this paper, we propose a picometer resolution test method for measurement electronics, that uses intensity modulation signals based on an AOM to replace the beat frequency interference signals, and an ordinary commercial guide rail to equivalently generate the pm-level displacement of the heterodyne interferometer under laboratory conditions. Based on the detailed analysis of the type of noise in the test device, the correlation between the light intensity and the nonlinear error was established, and nonlinearity was suppressed to 10% of the original level. Furthermore, this test method allows one to perform a 0.1 mrad phase step test at 1 MHz signal frequency, equivalent to a 2.5 pm resolution test in a double-pass heterodyne interferometer. Simultaneously, it can be directly applied to the resolution test for measurement electronics with a center frequency in the range of 1 MHz to 20 MHz.

Current supply status, demand trends and security measures of chromium resources in China

Chromium, a strategic mineral resource in China, is widely used in high-precision equipment manufacturing. As the world’s leading consumer and importer of chromite, China’s external dependence exceeds 99%. The significant imbalance between domestic supply and demand seriously threatens national economic security. This study discusses the state of China’s chromium resource supply from four aspects: the overview of domestic and global chromium resources, China’s chromite production and import volume, the sources of imported chromite, and risk analysis. Considering the chromium industrial chain and factors such as production, consumption, and recovery tendency of chromium-bearing stainless steel, it is forecasted that China’s demand for chromium ore will decline by 2040. This could considerably reduce the security situation of chromium resources. This study proposes five strategies for securing chromium resources: technological innovation, enhancing international cooperation and acquiring overseas resources, constructing a new pattern of “dual circulation” resource guarantee for sea–land transportation, encouraging chromium recycling, and building an emergency management system and strategic reserve mechanism for chromium resources.

Optimization of hybrid platform for high-tech equipment and building vibration mitigation using evolutionary algorithms

In this paper, an ideal fuzzy logic control (FLC) algorithm is designed for micro vibration control of a hybrid platform which is placed on a second floor of the building subjected to traffic-induced ground vibrations. A hybrid platform is one that can be utilized to safeguard high precision equipment from vibrations caused by traffic, machinery, and natural hazards like earthquakes while it is situated with in the building structure. A fuzzy system is employed to obtain the appropriate control force of active actuators, and the fuzzy system is then optimized using four evolutionary algorithms (EAs), which are population-based metaheuristic algorithms that were inspired by the nature. A microgenetic algorithm (µ-GA), particle swarm optimization (PSO), differential evolutionary algorithm (DEA), and cuckoo search algorithm (CSA) are used to optimize the FLC knowledge base and rule base. To illustrate the capabilities of the proposed method in traffic-induced vibration control of a hybrid platform, a three-degree-of freedom (3-DOF) structure along with the platform is taken into account. Finally, utilizing the Bolt, Beranek and Newman (BBN)-vibration criteria and the absolute velocity of hybrid platform as the objective, the efficiency of the hybrid platform microvibration control is evaluated. The simulation results obtained from these novel EAs indicated that the actively controlled platform is efficacious in reducing microvibration of high-tech equipment. Based on the results, the PSO algorithm optimized fuzzy controller outperforms the other methods in terms of velocity levels of second floor of the building and hybrid platform.

Research on Partial Reduction of Non-Essential Capabilities of Initiating Devices for Complex Mechanical Equipment Systems

Currently, modern spacecraft use high-precision equipment that is sensitive to shock impacts. In this regard, there is a need to create initiating devices with reduced impact. This task determined the vector of development of electromechanical release devices that do not contain pyrotechnic means in their design. Along with new challenges, there are the constant problems of reducing weight, increasing holding force, and reducing response time. The paper presents an analysis of the possibility of upgrading initiating devices in order to improve its characteristics. A team of engineers conducts research using computational and experimental methods. During the work, samples of mechanisms were made and tested to confirm their performance.

Research on Tolerance Optimization of High Precision Equipment Assembly Based on Error Transfer Prediction Model

In this paper, the assembly error transfer prediction model was established based on the error transfer attribute and the error transfer path of the assembly process. The assembly accuracy prediction was realized by combining error variation inequality, constraint inequality and mathematical statistics method. Aiming at the lowest processing cost of high-precision equipment assembly, the assembly accuracy required the reliability of index, the value interval of tolerance item and the principle of tolerance selection as constraints, the tolerance optimization model was established. The tolerance optimization of high-precision equipment assembly was carried out by combining the penalty function method and the improved genetic algorithm. Finally, taking gear oil pump assembly as an example, according to the reliability calculation formula of assembly accuracy, the reliability is 97.35%. Compared with the processing cost before and after optimization, the processing cost decreased by 12.13% after optimization, and the assembly accuracy reliability increased by 1.65%. The correctness and effectiveness of assembly accuracy prediction and tolerance optimization are verified.

Evaluation of Aircraft Emissions at Bucharest Henri Coanda Airport

This study presents the influence of aircraft movements on air quality by highlighting the contribution of landings and/or takeoffs at Henri Coanda Airport, Bucharest. An experimental campaign was carried out using a mobile laboratory equipped with reference instruments for the main air pollutants (NO-, NO2, NOx, SO2, CO, and O3) and a meteorological station to measure wind speed and direction, air temperature, pressure, and relative humidity at a height of 10 m above the ground. The mobile testing laboratory was located inside the airport near the passenger embarking area, and measurements were carried out for 7 days. Air sampling was carried out at a height of 3.5 m above the ground. Pollutant levels were continuously measured throughout the measurement period, with high-precision equipment and a 10-second interval. The results obtained showed an increase in pollutant concentrations during takeoffs and/or landings, providing an initial assessment of gaseous pollutant levels and hourly distribution. Airport authorities can use this assessment to balance aircraft and passenger movements to minimize human exposure to gaseous pollutants. Furthermore, this study used the Pearson correlation between each pollutant and meteorological parameters to establish the best conditions for passengers to be present on the airport premises. The results showed that wind speed and direction directly influence the distribution of gaseous pollutants, especially during landings and takeoffs.

Damage evolution model and failure mechanism of continuous carbon fiber-reinforced thermoplastic resin matrix composite materials

As a new composite material with high strength, toughness, and heat resistance, the continuous fiber-reinforced polyaryl ether sulfone ketone (PPESK) thermoplastic resin matrix composite (CFRP) has a wide temperature range, which is attributed to the complex temperature sensitivity of the matrix. The failure evolution characteristics under different conditions are not clear yet, which significantly limits its development and application to high-precision equipment. In this work, in order to deeply explore the full three-dimensional (3D) multi-scale multi-physics damage evolution mechanism of the CFRP over a wide temperature range, macroscale cross-temperature stretching/bending experiments, computer tomography (CT) scanning, and microscale scanning electron microscopy (SEM) are performed to effectively capture the overall damage morphology and local fiber/matrix damage failure characteristics of the material. The results show that the reinforcement with continuous fibers increases the tensile strength of the CFRP by 14–45 times and its bending strength by 2–6 times compared to those of the PPESK matrix in the cross-temperature domain. Moreover, the main failure mechanism of the CFRP in the cross-temperature domain is matrix crushing and fiber fracture at room temperature and fiber fretting slip and matrix viscous flow at high temperatures. This further explains the deformation mechanism of the CFRP, which can maintain its stability at high temperatures (low elongation at break: 1%–1.2%). The unique trans-temperature regional energy evolution and continuous fiber reinforcement of the material matrix resin PPESK lay the synergic stability of the high temperature performance and damage morphology of the CFRP. In particular, a cell model is constructed to further reveal the damage evolution characteristics of the matrix, fiber, and interface of the CFRP at the micro-scale. Combined with the failure mode theory and the performance degradation mechanism of composite materials, the temperature influence factor is introduced to formulate a multi-scale full 3D temperature-dependent damage evolution constitutive model of the CFRP over a wide temperature range. The constitutive model of the CFRP is incorporated in finite element software, and the simulation results are compared with the experimental ones for validation. The results show that the model developed in this work can effectively characterize the complex mechanical damage morphology and progressive failure characteristics of the CFRP over a wide temperature range.

Оптико-электронная система для оперативного контроля прямолинейности железнодорожных рельсов

The paper considers principles of operation of the optical electronic devices designed for operational high-precision control of the railway rails rolling surface straightness. It provides a description of the functional scheme proposed by the authors of the optical electronic devices of the triangulation type with structured illumination, where the rolling surface straightness is assessed based on analyzing the images of the rail cross sections registered by a linear camera. A technical solution is proposed that could significantly increase control and reliability of its results, as well as ensure image registration of the rail cross sections, where the distance between them is not exceeding 1 mm with the measurement car speed of 180 km/h. Mathematical expressions were obtained to study the optical electronic devices proposed scheme influence on the threshold sensitivity of control over the points' position along the rail rolling surface. To reduce the control results error, methods of the coordinates' subpixel refinement of the structured illuminated peaks registered coordinates were used. In the course of numerical experiments, the error root-mean-square deviation dependence in measuring the rail surface points' coordinates on the signal-to-noise ratio and the structured illumination peaks width values was studied. Requirements are formulated to components of the triangular type optical electronic devices, which could be introduced in design and development of the high-precision equipment for operational control of the railway track rolling stock straightness

Ultra-low frequency active vibration isolation in high precision equipment with electromagnetic suspension: Analysis and experiment

High performance vibration isolation requirement in the ultra-low frequency band for high precision equipment becomes more and more stringent. An active vibration isolation method is investigated to broaden the frequency band of isolation and improve the performance, in which an electromagnetic suspension is adopted to provide a static lifting force and an active control force. Naturally, the suspension is accompanied by a controllable negative stiffness. Two factors that might cause instability of the suspension system, i.e., the bias current and the base disturbance, are analyzed to give the stable region. The matching relationship between the currents in the upper and lower coils, and the mapping rules among the current, relative displacement, force and stiffness are discussed, respectively. The maximum base disturbance that the system can withstand is analyzed. On the basis of the theoretical analysis, the active position stabilization and vibration control methods are built and the performance is evaluated. Furthermore, experiments were conducted to verify the effectiveness of the active vibration isolation method. Numerical and experimental results demonstrate that the electromagnetic suspension is able to improve the vibration isolation performance in the ultra-low frequency range, where the transmissibility is below 0 dB in the entire frequency band and the initial vibration isolation frequency is less than 1Hz.

Dynamic characteristic analysis of pressure pulsations of a pump turbine in turbine mode utilizing variational mode decomposition combined with Hilbert transform

Mastering the dynamic characteristics of the pressure pulsations is necessary to ensure high efficiency and security, and extend the life span of the pump turbine (PT) and the pumped storage system. In this research work, the experimental investigation was conducted with the aid of the high-precision equipment to measure the pressure pulsation signals from a PT in the turbine direction. The variational mode decomposition (VMD) and Hilbert marginal spectrum (HMS) are adopted to improve the extraction capabilities of dynamic characteristics in the signals. Through carrying out the VMD, the pressure pulsation signals can be decomposed into several modes. By calculating the average instantaneous frequencies, energy ratios, and correlation coefficients of these modes, the dominant modes are determined, and the trends of the values of root mean square of them with load at typical monitoring points can reflect the dynamic transition of the internal flow status. To be specific, the entire load range can be segmented into three load areas to analyze different physical sources of pressure pulsations. In the low load area, they are mainly induced by the unstable flows of blade passing frequency (BPF) in the vaneless area (VA) and the low-frequency vortex strips in the draft tube (DT). In the intermediate load area, they are mainly caused by the low-frequency vortex strips in the DT. In the high load area, they are mainly caused by the phenomenon of rotor-stator interaction in the VA. By conducting the HMS based on VMD, it can be found that the head changes will affect the amplitudes of dominant frequencies of pressure pulsation signals. Based on the current signal processing results, the high-sensitivity indexes can be used to characterize the generation and dynamic propagation of pressure pulsations.

Characterizing elastic parameters of isotropic thin plates using impedance tube and transmission loss measurements: a numerical inverse method

Thin plates are widely used in various engineering applications, including aerospace, automotive, and construction industries. The mechanical properties of these plates, such as Young's modulus, Poisson's ratio, and structural damping, are essential in determining their acoustic performance. While there are various methods for measuring these properties individually or simultaneously, accurately obtaining them can be difficult due to the thin plate's delicate structure and the need for high precision and sensitive equipment. In this paper, we present a numerical inverse method for characterizing the elastic parameters of isotropic thin plates using transmission loss measurements obtained from an impedance tube and clamped circular specimen. The proposed method is compared to the Oberst beam technique (ASTM E756-05), and demonstrated through several examples ultimately allowing for the prediction of diffused field transmission loss obtained through intensity measurements in a small reverberant room.

A novel piezoelectric-based active-passive vibration isolator for low-frequency vibration system and experimental analysis of vibration isolation performance

Low-frequency vibration is the core problem that hinders high-precision equipment's positioning accuracy and control accuracy. This paper presents an active-passive integrated vibration isolator based on piezoelectric ceramics to solve the vibration problem. An active-passive vibration isolator with a piezoelectric actuator in the active part and a damping buffer in the passive part is designed, and its dynamic simplified model is established. The feedforward and feedback control system is established, the active controller is designed, and the vibration isolation performance of the active-passive vibration isolator is high. And it can effectively achieve vibration isolation from 5 Hz to 500 Hz, verified by experiment and the worst vibration isolation effect can still achieve 30% attenuation of the excitation amplitude. This kind of active-passive vibration isolator improves the passive vibration isolation low-frequency vibration isolation effect, dramatically reduces the resonance peak of the system, and broadens the frequency band. It can be extensively applied to low-frequency vibration systems, such as aerospace and high-precision equipment.

Manufacturing of dies and an experimental study on the cold-press surface-texture forming process

Surface texturing can significantly improve the service performance of joint surfaces. However, the fabrication techniques for micro- and nanoscale structures require high-precision equipment and involve complicated processes. An efficient and practicable cold-press forming technique for surface-texture fabrication was proposed. First, the feasible methods for fabricating cold-pressed dies with surface textures were introduced. Three methods for preparing cold-pressing dies having microembossment arrays were explored. The preparation of dies via through-mask electrochemical machining on an alloy steel surface was deemed feasible. Then, the process parameters of cold-press surface-texturing were calculated using the sliding line method. The application of single microembossment to cold pressing of brass verified the validity of the models. Ultimately, cold-pressing experiments were performed using an array microembossment die. A surface texture of 1000 pits was formed in ∼3 s, and the desired quality was achieved. The experimental results showed that cold pressing of surface textures could be accomplished using the manufactured dies at a low cost and high efficiency.

Low-frequency broadband multidirectional vibration isolation by piezoelectric smart platform with active control

A high-precision equipment is very sensitive to vibration, even micro vibration. How to isolate the low-frequency broadband multidirectional vibration remains a challenge. As the main component of piezoelectric smart vibration isolation model, the piezoelectric stack consists of a piezoelectric actuator, a piezoelectric sensor, and a rubber layer. The numerical results obtained by the finite element method agree well with theoretical solutions. The vibration attenuates rapidly under displacement and velocity feedback control with negative gains. As the control gain decreases, the vibration isolation band is extended to lower frequency. A piezoelectric smart multidirectional vibration isolation platform model is further proposed by inclined installation of two piezoelectric stacks. A spring-like structure is designed to exert a preload pressure on these piezoelectric stacks. After optimization on the control gain, the platform can isolate vibration from 0 to 3000 Hz in multiple directions.