The biological properties of molybdenum are also important, as it is an essential trace element not only for plants but also for animals. Molybdenum is one of the main components of molybdenum flavin protease in nitrogen-fixing bacteria in plants; it is also one of the main components of plant nitrate reductase; it can also stimulate the activity of phosphatase, promote the synthesis and transportation of sugar and starch in crops; it is conducive to early maturity of crops . Molybdenum is one of seven important micronutrients. Molybdenum is also one of the basic components of xanthine oxidase and aldehyde oxidase in the liver and intestine of animals, and also the basic component of heparin sulfite oxidase. Studies have shown that molybdenum has obvious anti-caries effect, and molybdenum has a strong inhibitory effect on the formation of urinary stones. A healthy person weighing 70kg contains 9mg of molybdenum in the body. For humans, molybdenum is the only element known to be essential to humans among the second and third transition elements. Compared with similar transition elements, molybdenum has extremely low toxicity and can even be considered basically non-toxic. Of course, excessive ingestion also accelerates the oxidation of the elastic substance - plasmalogen - in the walls of human arteries. Therefore, in areas with high molybdenum content in the soil, the incidence of cancer is lower, but the incidence of gout and systemic arteriosclerosis is higher. Animals, especially long-horned animals, who eat forages containing excessive molybdenum are prone to stomach problems. Molybdenum Scrap,Metal Molybdenum Scrap,High Purity Molybdenum Waste,Molybdenum Carbide Scrap Jiangsu Lucky Metal Materials Co., Ltd. , https://www.luckymetalmoly.com
Tool) or Parallel Kinematic Machine (Parallel Kinematic
Machine) is a product of the combination of parallel robot technology and modern CNC machine tool technology. It also takes into account many characteristics of machine tools and robots. It can be regarded as a robotized machine tool (can complete the cutting tasks of the machine tool), and can also be regarded as Machine-tooled robots (can do many sophisticated robotic tasks). It can provide the flexibility and flexibility of the robot, and it also has the stiffness and precision of the machine. It is a new type of electromechanical equipment that integrates multiple functions. International academic circles and engineering circles attach great importance to the research and development of parallel machine tools. In the mid-1990s, relevant research institutions and machine tool manufacturers in the United States, Britain, Germany, Russia, Sweden, Switzerland, Japan, and other countries introduced different structural forms one after another. Parallel machine tools with functional features. Parallel machine tools have become a highlight in the development of the machine tool industry.
Since the advent of the parallel machine tool, it has undergone several years of development. It has experienced a rapid development and steady development. With the deepening of people's understanding of parallel machine tools, the research and development work of parallel machine tools is progressing. Gradually stabilized. The researchers realized the unique and unique advantages of the parallel machine tools compared with the traditional machine tools. This encouraged many research institutions and machine tool manufacturers at home and abroad to relentlessly actively engage in the research and development of parallel machine tool technology; on the other hand, After several years of research, the researchers also found that there are some defects in the parallel machine tool. At the same time, the theoretical research and applied technology research of the parallel machine tool are not mature enough, and there are many problems to be overcome. Research institutes and machine tool manufacturers in various countries have reached a consensus on this issue. They believe that this new type of processing equipment, a parallel machine tool, has unique advantages in some respects compared with traditional machine tools. However, at this stage, parallel machine tools cannot be realized. Mass production and marketization, parallel machine tool technology also needs further development and improvement.
Development characteristics and problems
Development characteristics of parallel machine tools
At present, the development trend of parallel machine tools presents the following two characteristics:
(1) Diversity of Parallel Machine Configurations
The diversity of configurations is one of the salient features of parallel machine tools. Each configuration has its own advantages and disadvantages, and each has its own suitable application area. Research on the configuration of parallel institutions has always been a focus of attention. Designing and developing a variety of parallel institutions suitable for different application conditions has always been an important part of institutional scientists' research. In recent years, many scholars have proposed a variety of new institutional configurations, and have systematically discussed the types of institutions and their construction methods. At present, parallel machine tools based on series-parallel hybrid, internal and external sub-hybrid drives, or purely parallel-connected mechanisms with low degrees of freedom are gaining popularity. The most representative parallel machine based on the parallel mechanism with few degrees of freedom is Sweden's Neos.
The Tricept series developed by Robotics, other typical HPI four-bar three-degree-of-freedom machine tools from Comau, Italy, the LINAPOD three-bar machine tool at the Institute of Machine Tools and Manufacturing Equipment Control Technology, Stuttgart University, production engineering and machine tool research at Hanover University, Germany. Developed a three-bar machine for laser machining of steel plates, Sheldon/Van, USA
Someron's Triax three-bar machine tool, Tsinghua University and Jiangdong Machine Tool Plant jointly developed a three-degree-of-freedom hybrid machine tool.
However, due to the appearance of parallel machine tools, there is no special design and development environment. Currently, the design cycle for developing a new type of parallel machine tool is still very long. Therefore, a rapid design and development platform is urgently needed to meet the design of new types of parallel machine tools with increasingly diverse structures. Development requirements.
(2) Continuous research on the design theory and application technology of parallel machine tools
Although some commercial prototypes of parallel machine tools have been developed and products have been put into practical use, the research on design theory and engineering technology is not mature enough. Currently, the parallel machine tools perform poorly in terms of workability and work performance, compared with traditional CNC machines. There is a certain gap. The research on kinematics design of parallel mechanism, dynamic modeling and analysis of parallel machine tool, accuracy assurance, control technology and other key technologies has been continuously deepened and has achieved certain research results. For example, the conclusions of the kinematics of the Stewart platform developed by Raghavan, the numerical solution of kinematics proposed by Innocenti and Cheok et al.; the geometric analysis of the working space of Gosselin, Merlet, and Ji; and the metamorphism of the working space boundary proposed by Huang Tian and Wang Jinsong et al. Spherical family envelope surface intersection method; multi-scale synthesis method based on isotropic condition (local flexibility), dynamic platform attitude capability, overall flexibility index; Nguyen, Lee, Liu on dynamic modeling and dynamic performance index The theoretical results of the structure, as well as the dynamic optimization design strategy proposed by Xiong Youlun; the relationship between the drive component error and the terminal error established by different methods; various kinematic calibrations, methods to improve the machining accuracy of the machine tool, etc. In short, the key technologies of the parallel machine tools have achieved a lot of valuable theoretical results at home and abroad, and have made great progress in application technology.
Although there are many theoretical results and application techniques related to the design and application of parallel machine tools, these theoretical results and technologies cover many aspects of the design and development of parallel machine tools. They are relatively independent and dispersed, and it is difficult to integrate them organically and cannot be effectively applied to systems. Parallel machine tool design and development. In addition, due to the characteristics of the structure of parallel machine tools, the design of kinematics design, dynamic optimization, and accuracy assurance involve very complex nonlinear problems. There are technical obstacles such as difficult model evolution and difficult data integration among many design links. Therefore, an integrated and integrated parallel machine tool design and development environment is urgently needed to solve the above problems.
Through the analysis of the development status and trends of the current parallel machine tools, it can be seen that the integrated development, integration, and digital parallel machine tool rapid development platform can greatly shorten the design and development cycle of the parallel machine tool, and realize the integration of the latest design theory and application technology. Application and guarantee the integration of the design process, thus promoting the research progress of the parallel machine tool in theory and the process of industrialization in practical application.
But so far, there are few researches related to this at home and abroad. The following researches have involved the following aspects: the integrated design method of parallel machine tools, virtual prototyping environment, virtual design, kinematics simulation and machining simulation.
In 1997, L Molinari
Tosatti et al. proposed an integrated design method for parallel machine tools, proposed the main components of the design environment for parallel machine tools, and used the Stewart platform as an example to perform topological analysis of the Stewart platform, job space evaluation, error analysis, stiffness analysis, and mechanisms. Sensitivity analysis and machine tool dynamics modeling.
In 2001, Marco
Leonesio et al. proposed a virtual prototyping environment for a parallel machine tool that was developed on the basis of commercial software Adams. A three-degree-of-freedom parallel mechanism was used as an example to briefly analyze the motion characteristics and force characteristics of the mechanism prototype.
In 1999, Huang Fulin et al. established the solid model of the Stewart platform mechanism according to the idea of ​​solid geometric modeling, and adopted the painter algorithm. According to the structural characteristics of the Stewart platform mechanism, a blanking algorithm suitable for the mechanism was proposed. At the same time, the Stewart platform mechanism was The phenomenon of interference during the movement was discussed. The kinematics simulation software for the Stewart platform mechanism was finally developed.
In 2000, Han Haisheng took the 3-HSS parallel machine tool as the object, and conducted prototype solid modeling and kinematics simulation in a virtual environment.
In 1998, Liu Xudong developed a kinematics design and performance analysis software for Stewart parallel machine tools using C++ language.
There are also some other researchers who have performed kinematic analysis and simulations on a number of parallel machines based on specific institutions.
Problems in the development of parallel machine tools
In general, the current research of parallel machine tools has the following problems:
1 Foreign research on integrated design methods mainly proposes the components needed in the design of parallel machine tools, such as various commercial software or self-developed software, etc., and did not discuss in depth the integration between the various design links, nor did they propose an integrated integration. The design environment;
2 The studies conducted at home and abroad are only for specific design links to simulate or analyze, and cannot support all aspects of the design of parallel machine tools (for example, Leonesio's virtual prototype environment only supports the simulation and design of institutional prototypes);
3 The research conducted in China is aimed at specific institutions and carries out the simulation and analysis of the organization. Therefore, the software developed is not universal.
In summary, foreign countries have begun to pay attention to the general environment supporting the design of parallel machine tools, and have achieved certain research results (such as the virtual prototype environment of parallel machine tools, etc.), while the domestic still stays in the specific design of specific institutions for simulation and analysis. Stage. The digital rapid development platform for parallel machine tools proposed in this paper can solve the problems existing in the existing research of parallel machine tools at home and abroad, provide an efficient and high-quality development environment for the design of parallel machine tools, and reach the international advanced level in this field.
The significance of the research on digital rapid development platform for parallel machine tools
Parallel Machine Tool (PMT), also known as Virtual Axis Machine