Recent Patents on Mechanical Engineering - Volume 15, Issue 2, 2022

Background: After a smooth development of life expectancy per capita and fertility in the nineteenth century, the global population increased in size. Along with the demographic shift in the late nineteenth century, the phenomenon of population aging began to appear in developed countries. A survey from UN reports that by 2050, one in six people worldwide will be over 65 years old (16%), compared to 11 (9%) in 2019. According to another survey, 55% of people over the age of 60 suffer from joint diseases, and the number of people suffering from stroke, arthritis and other knee diseases will also increase accordingly. Objective: An overview of the classification and characteristics of today's knee rehabilitation devices and future developments. Methods: This review discusses the existing knee rehabilitation devices, including various products on the market, patents and some conceptual devices, in the context of the structural characteristics of the knee joint and the rehabilitation requirements of different knee conditions or after knee arthroplasty, and systematically introduces their structural features, differences and the rehabilitation effects achieved. Results: A comparative analysis of three types of passive knee rehabilitation devices according to their use was conducted to summarize the typical characteristics. The problems that exist in today's rehabilitation devices are also analyzed, and their development trends are looked forward to. Conclusion: Knee rehabilitation equipment has a high degree of structural richness, but it does not achieve a good balance of convenience, comfort and functionality, and there should be some room for improvement in the materials, volume of the power source and transmission form of the power system. There will be a good development in the future of knee joint recovery.

Background: The bionic water strider robot can achieve sliding, jumping, and other movements on the water surface, having advantages of small size, light weight, flexible movements, and other characteristics. It can detect the quality of water, investigate and search the water surface, and perform some other operations. It has a very broad range of applications and development prospects. Therefore, the trend of biomimetic water strider robots is attracting more and more attention. Objective: This study aimed to review the bionic water strider robot and introduce its classification, characteristics, and development. Methods: This paper reviews various productions and patents related to the bionic water strider robot from 2003 to the present. The sources of the papers include CNKI, Wanfang, Patent publication announcement in China, Web of Science, IEEE, Elsevier, Springer-Verlag, Espacenet, and FPO IP Research & Communities. To obtain the results, an endnote was used for documentation, and citeSapce was used for visual analysis. Results: The mechanical structure of existing bionic water strider robots has been analyzed and compared. Furthermore, the typical characteristics are concluded. The main problems in its development are analyzed, and the development trend is foreseen. Furthermore, the current and future research prospects of the productions and patents on the bionic water strider robot are discussed. Conclusion: The optimization and development of the structure of the bionic water strider robot and the development of associated components help to improve the simulation of the water strider's motion and perform a better task in a complex water surface environment. In the future, with the improvement in the research, the bionic water strider robot will develop into miniaturization, intelligence, and integration.

Background: This study was conducted to explore the temperature rise and distribution of the micro-gap lubricating oil film of the hydrostatic and hydrodynamic thrust bearing, solve the problem of thermal deformation of the friction pair of the hydrostatic and hydrodynamic support, and improve the operation accuracy and stability of the hydrostatic and hydrodynamic thrust bearing. Objective: Combined with the theory of dynamic and static pressure bearings, the problem of lubricating oil film temperature rise is analyzed, and specific research directions are proposed. It is hoped that it will be helpful to improve the research of bearing stability and provide a theoretical basis for the structural design and operational reliability of heavy hydrostatic bearings. Methods: This article summarizes the research status of the oil film temperature rise of hydrostatic and hydrodynamic thrust bearings, especially focusing on the influence of hot oil carrying on the temperature rise of the lubricating oil film, and finally, the specific research directions and methods of the oil film temperature rise are prospected. Results: Current and future developments of the oil film temperature rise of hydrostatic and hydrodynamic thrust bearings are finally provided and discussed. It provides theoretical support for the thermal deformation control of the bearing friction pair, and provides a basis for the highprecision and stable operation of the bearing. Conclusion: Aiming at the research hotspots of lubricating oil film temperature rise and distribution, based on the analysis of the principle of hydrostatic and dynamic pressure bearings, the domestic and foreign literature on the influence of the micro-gap lubricating oil film temperature rise and distribution of hydrostatic and hydrodynamic thrust bearings is collected and analyzed. The research shows that although some research results have been made in this area, current research methods and angle analysis still have certain limitations, so the study of the oil film temperature rise is not comprehensive, and further detailed discussion and analysis are still needed.

Background: Recent reviews on tooth modification of involute cylindrical gear are presented. Gear pairs are widely employed in motion and power transmission systems. Manufacturing and assembling errors of gear parts, time-varying mesh stiffness, and transmission error of gear pair usually induce vibration, noise, non-uniformly load distribution, and stress concentration, resulting in earlier failure of gear. Tooth modification is regarded as one of the most popular ways to suppress vibration, reduce the noise level, and improve the load distribution of gear pairs. Objective: The objective of this study was to provide an overview of recent research and patents on tooth modification methods and technology. Methods: This article reviews related research and patents on tooth modification. The modification method, evaluation, optimization, and machining technology are introduced. Results: Three types of modifications are compared and analyzed, and influences of each on both static and dynamic performances of gear pair are concluded. By summarizing a number of patents and research about tooth modification of cylindrical gears, the current and future development of research and patent are also discussed. Conclusion: Tooth modification is classified into the tip or root relief along with tooth profile, lead crown modification along tooth width, and compound modification. Each could be applied in different ways. In view of design, optimization under the given working condition to obtain optimal modification parameters is more practical. Machining technology and device for modified gear is a key to get high-quality performance of the geared transmission. More patents on tooth modification should be invented in the future.

Background: The flow rate distribution in the flat tubes of a micro-channel evaporator is essential for its heat transfer performance. Due to a large number of flat tubes in a microchannel evaporator, the flow rate distribution is often difficult to determine. Objective: An evaporator test rig was constructed to study the quantification of the refrigerant mass flow rate distribution in a two-pass evaporator without destroying its structure. Methods: A heat transfer performance test rig for a two-pass evaporator was utilized. Subcooled refrigerant R134a was pumped into the inlet header, and infrared thermography was used to obtain the cloud map of the wall temperature distribution on the surface of the evaporator. The flow rate distribution in each flat tube was calculated based on an analysis that combines the heat balance between the air side and the refrigerant side with the effectiveness-Number of Transfer Units (ε- NTU) method. Results: The flow rate distribution was found to be in good agreement with the evaporator wall temperature distribution. The difference between the calculated and measured total mass flow rates was less than 15.9%, which proves that the method is simple and effective. And the unevenness of flow rate distribution in the 1^st and 2^nd pass is 0.13 and 0.32, respectively. Conclusion: This method is simple and effective, and does not destroy the structure of the microchannel evaporator. However, it is only suitable for cases in which there exists a subcooled zone in a pass, and is not applicable to a pass in which the refrigerant is only in a single-phase or a two-phase state.

Background: Cr4Mo4 V steel is widely used in high-temperature bearings because of its excellent high-temperature performance. Based on the research status of Cr4Mo4 V nationally and internationally, this paper explores its mechanical properties and friction properties at high temperatures. Objective: To characterize the composition, microstructure, and properties of Cr4Mo4 V steel and explore its tensile properties, hardness, and friction properties at high temperatures. Methods: Many methods are adopted, including chemical element analysis, metallographic analysis, hardness test, tensile test, damping test, and friction test. Results: Cr4Mo4 V has a tempered martensite microstructure. The hardness and maximum tensile strength of Cr4Mo4 V decrease with increasing temperature. The grain of the Cr4Mo4 V steel after heating becomes refined, and the grain boundary increases. At room temperature, the surface friction coefficient and wear rate of Cr4Mo4 V steel decrease. Moreover, a Cr4Mo4 V steel-ceramic ball shows the best friction resistance. At high temperatures, the friction coefficient and wear of Cr4Mo4 V steel first decrease with increasing temperature and then increase sharply at 200°C. Conclusion: With an increase in temperature, the hardness, breaking force, and tensile strength of Cr4Mo4 V bearing steel decrease, whereas the friction property increases. By analyzing the threedimensional morphology of different wear samples, the optimal working temperature of Cr4Mo4 V steel bearing is determined as 200°C.

Background: Due to the influence of external wind speed and their flight speed, the droplets sprayed by the plant protection Unmanned Aerial Vehicles (UAV) have serious drift and volatilization. Objective: The aim was to study the atomization characteristics of the fan-shaped atomizing nozzle of UAV under different inlet pressures and in different internal cavity diameters. Methods: Firstly, the Realizable k- turbulence model, DPM discrete phase model, and TAB breakup model are used to make a numerical simulation of the spray process of the nozzle. Then, the SIMPLE algorithm is used to obtain the droplet size distribution diagram of the nozzle atomization field. At last, the related test methods are used to study its atomization performance and the changes of atomization angle and droplet velocity under different inlet pressures and in different internal cavity diameters; the distribution of droplet size is also discussed. Results: The research results show that when the diameter of the internal cavity is the same, as the inlet pressure increases, the spray cone angle of the nozzle and the droplet velocity at the same distance from the nozzle increase. As the distance from the nozzle increases, the droplet velocity decreases gradually, the droplet size distribution moves to the direction of small diameter, and the droplets in the anti-drift droplet size area increase. Under the same inlet pressure, as the diameter of the internal cavity increases, the spray cone angle first increases and then decreases, and the droplet velocity at the same distance from the nozzle increases. As the distance from the nozzle increases, the droplet velocity decreases gradually, the droplet size distribution moves to the direction of large diameter, and the size of the large droplets increases, thereby, not meeting the condition of anti-drift volatilization effect. Conclusion: Under the parameters set in this study, i.e., when the inlet pressure was 0.6 MPa, and the internal cavity diameter was 2 mm, the best atomization result was obtained.

Background: High-temperature alloys, such as the nickel-based alloy, have become the main materials for core components in the aerospace field because of their high strength and good toughness. Therefore, how to improve the machining accuracy and stability of electrochemical machining (ECM) of small deep holes on nickel-based alloy is an important topic for studies. The instantaneous high-density current during the pulse width of pulse ECM is beneficial to the dissolution of nickel-based alloy. Many experts and scholars have studied pulse ECM of small deep holes. Objective: The purpose of this article is to propose and design a positive and negative pulse (PANP) power supply to study the accuracy and stability of ECM of small deep holes on the nickel-based alloy. Methods: First of all, an H-bridge composed of four MOSFET switches is designed to achieve PANP output in the main circuit of the power supply. Then, this article discusses the influence of the ratio of positive and negative pulses on short circuits, the influence of the ratio of positive and negative pulses on the mass removal rate, and the influence of the electrolyte concentration and pulse width on the mass removal rate. Finally, according to the obtained optimal parameters, the influence of the electrolyte pressure on the average radial overcut of hole depth is analyzed. Results: The experimental results show that the short-circuit frequency is reduced by more than 50% compared with non-negative pulses power supply; the ratio of positive and negative pulses, pulse width, and electrolyte concentration and pressure were optimized by experiments in order to improve the mass removal rate of the workpiece and the average radial overcut of hole depth. Conclusion: The designed PANP power supply can improve the machining accuracy and stability of ECM of small deep holes on the nickel-based alloy.

Background: In recent years, a kind of drilling method of solid-liquid separation combined with pulsating vacuum formed by vibrating screen and compressed air injection has emerged in oil drilling, which profoundly improves the gas, solid, and liquid separation ability of the drilling fluid vibration screen. Objective: Based on the above ideas, a kind of hydrocyclone used for gas-liquid separation with the pulsating feed boundary was proposed. The separation performance of gas-liquid hydrocyclone may change significantly due to the mixed pulsation of the gas-liquid fluid transported by the jet pump. Therefore, the flow characteristics of the pulsating feed hydrocyclone need to be analyzed and explored to provide basic data for further improvement of the structure. Methods: The development status of cyclone separators are summarized through related literature and patent investigation. The Computational Fluid Dynamics (CFD) software ANSYS Fluent 2019 R3 is used to analyze the flow field characteristics and optimize the parameters of the hydrocyclone with stable feed. Then, the programming by the User-Define-Function (UDF) of Fluent is used to simulate the flow field of the separator under the condition of pulsating feed. Meanwhile, the flow field analysis and parameter optimization are carried out accordingly. Results: The optimal parameters in a stable state and pulsed state are obtained from the analysis of the efficiency curve. The results show that the flow field can be stabilized in the pulsating feed state, and the sinusoidal pulsing with a frequency of 0.4 Hz is used to achieve the highest separation efficiency, i.e., 85.5%. Conclusion: The separators with pulsating feed and stable feed have similar flow field characteristics, and the optimal structural parameters under pulsating feed are obtained. Compared with the stable feed condition, the pulsating feed condition can connect multiple cyclone separators, which can separate more drilling fluid in unit time and improve the work efficiency. It has strong practicability, which provides a critical foundation for structure optimization in the future.

Background: In this paper we have developed an intelligent control law for the control of mobile manipulator robots by investigating the various techniques proposed in the literature. Thus, we have adopted a hybrid approach integrating part of classical and advanced automation in order to create an efficient control structure that can cope with a certain level of complexity. Our research logic is based on the process of keeping in mind that the control system must comply with the constraints imposed during the implementation of the control architecture. Objective: This paper aims to develop a control law in order to guarantee a certain level of performance and, more precisely, during a trajectory tracking application for mobile handling missions. The developed control law guarantees robustness with respect to external disturbances and parametric uncertainties due to the modelling of the system. Methods: In this paper, a study of the basic concepts of robotics and robot modelling is presented in order to set up the dynamic model used for the elaboration of the command. A sliding-mode controller based on a radial base function neural network with minimum parameter learning is developed for the Pelican robot as a two link robot manipulator. This approach, which combines a Radial Base Function Neuronal Network (RBFNN) and a Sliding Mode Control (SMC), is presented for the tracking control of this class of systems with unknown nonlinearities. The centres and outputs weights of the RBFNN are updated via online learning in accordance with the adaptive laws, allowing the control output of the neural network to approach the equivalent control in the sliding mode in the predetermined direction. The Lyapunov function is used to develop the adaptive control algorithm based on the RBFNN model. To reduce computational load and increase real-time arm performance, an RBFNN-based on the SMC with the Minimum Parameter Learning (MPL) method is designed. Results: Neural network sliding mode control is designed to underline the effectiveness of the approach to control the manipulator. This method of control ensure the tracking trajectories. Conclusion: The results of the simulation for the manipulator arm presented demonstrates the effectiveness of the modelling strategy, the correction and the robustness of the control approach.