Development history of mechanical principles

Development history of mechanical principles

(1) Brief introduction of mechanical principle

The theory of machinery is a subject that studies the structure and motion of mechanisms in machinery, as well as the structure, force, quality and motion of machines. People generally refer to institutions and machines as machines. A mechanism is an assembly consisting of more than two parts, which are movably connected together to realize a specific movement. A machine is composed of one or more mechanisms to do useful work or complete the conversion between mechanical energy and other forms of energy. The main components of this subject are mechanism and mechanical dynamics.

Different machines usually consist of a limited number of commonly used mechanisms.

Therefore, the main mechanisms such as internal combustion engine, compressor and punch are crank-slider mechanisms. The motion of these mechanisms is different from that of general mechanics, which is only related to their geometric constraints, but has nothing to do with their stress, component quality and time. 1875, F. Leroy of Germany separated the above-mentioned problems of * * * from general mechanics and compiled a book "Theoretical Kinematics", which established the foundation of mechanism. Many concepts, viewpoints and research methods put forward in the book are still in use today. 184 1 year, R. Willis of Britain published the Principles of Mechanism. /kloc-since the middle of the 0/9th century, mechanical dynamics has gradually taken shape. The 20th century saw the combination of mechanism and mechanical dynamics.

The mechanical principle of research. 1934, the book Mechanical Principles written by Liu Xianzhou of China was published. 1969, the International Association of Principles of Institutions and Machines (IFTOMM) was established in Poland.

The research object of mechanism is various commonly used mechanisms in machines, such as linkage mechanism, cam mechanism, gear mechanism, screw mechanism and intermittent motion mechanism (such as ratchet mechanism and pulley mechanism). ) and combination mechanism. Its research content is the composition principle and motion certainty of mechanism structure, as well as the motion analysis and synthesis of mechanism. Mechanism only studies the motion of mechanism from the geometric point of view, without considering the influence of force on motion. 1. Machines and institutions

A machine is a combination of artificial objects with definite mechanical motion, which can be used to convert energy, complete useful work or process information to replace and reduce human labor. A mechanism is a combination of artificial objects with definite mechanical motion, which can be used to transmit and transform motion. The relationship between the machine and the mechanism is as follows: 1) Both the machine and the mechanism are the combination of artificial objects, and both have definite mechanical movements; 2) The machine is composed of mechanisms. A simple machine may have only one mechanism, but it usually has multiple mechanisms. For example, the air compressor contains only one linkage mechanism, while the internal combustion engine contains linkage mechanism, cam mechanism, gear mechanism and so on. The difference between a machine and a mechanism is that a single mechanism does not have the function of converting energy or accomplishing useful work, but can only transmit and change motion and power; Machines can do useful work, convert energy or process information. Machinery is the general name of machines and institutions. 2. Components and parts

A part is a unit that constitutes a mechanism and has definite movement, and a part refers to the smallest manufacturing unit that cannot be disassembled again. An assembly can be composed of one part or several different parts, but there is no relative motion between these parts. they

Overall exercise. The difference between a part and a part is that the part is a moving unit and the part is a manufacturing unit. Because the relative motion between the components of the mechanism has nothing to do with the shape and number of components, the shape of components and the shape and size of their sections; Therefore, in the course of Mechanical Principle, the analysis and synthesis of mechanism and the design of mechanical system motion scheme are all studied with components as the smallest unit, and components are represented by simple lines and prescribed symbols. Knowing this clearly, students will not be confused when they learn the drawing content of mechanism motion diagram in the future. 3. Motion chains and mechanisms

Special emphasis should be placed on the concept of kinematic chain and its relationship with mechanism. A kinematic chain is a component system consisting of several components connected by kinematic pairs. If each component in a kinematic chain contains at least two kinematic pair elements, the system in which each component forms a closed end and a closed end is called a closed chain; Otherwise it is called open chain. In a kinematic chain, if one component is fixed as a frame, given the motion law of another component or several components, the motions of other components in the kinematic chain are determined accordingly, and this kinematic chain becomes a mechanism. All institutions have clear campaigns. This point is not clearly stated in most textbooks of mechanical principles at present that the research object of mechanical dynamics is machines or combinations of machines. The research content is to determine the real motion law of the machine under the action of known force and its adjustment, the balance between friction and mechanical efficiency, inertia force and other issues. According to the traditional research method of mechanical principle, the gap between the contact surfaces of components, the elasticity or temperature difference deformation of components and the errors caused by manufacturing and assembly are generally not considered. This is usually feasible for low-speed machines. However, with the development of machinery towards high speed and high precision, it is necessary to study the motion changes caused by the above factors. Therefore, since the 1940s, the problem of mechanism accuracy has been raised. Due to the rapid development of space technology, manipulator and industrial robot, the problem of mechanism accuracy has been paid more and more attention and has become an indispensable part of mechanical principle.

(2) All stages of machinery

1. primitive machinery

In ancient times, humans created and used primitive stand-alone machines such as levers, pulleys, inclined planes and screws. In the process of building pyramids in Egypt, rolling logs were used to carry huge stones. Archimedes used a screw to lift water to a high place, which is the ancestor of today's screw conveyor. The Chinese nation has a long history of civilization, with many inventions in machinery and its own characteristics in the design and application of some special machinery. Such as compass, water drain, seismograph, etc. , all have unique functions. Compass is one of China's ancient cultural treasures and an outstanding representative of ancient scientific and technological achievements. The south guide car skillfully uses the gear transmission mechanism. No matter which direction the car goes, Woodenhead's arm on the car always points to the south. This invention fully embodies the great wisdom of the ancients and is the pride of China people. Primitive machinery is only driven by manpower, animal power and water power. Its function is to reduce human physical labor, and it is the driving force that restricts the development of machinery. 2. Traditional machinery

/kloc-In the 8th century, Watt invented the steam engine, which opened the curtain of the industrial revolution. The steam engine has brought great power to mankind, and various power-driven machinery such as textile machines and lathes have sprung up. /kloc-the invention of internal combustion engine and motor in the 0/9th century is another technological revolution. In most cases, electricity replaces steam, and independent motors are installed on machine tools and textile machines. The invention of the internal combustion engine made it possible for cars and airplanes to appear. Compared with primitive machinery, traditional machinery has its own "heart"-power drive, whose function is not only to reduce human physical labor, but more importantly to replace human physical labor.

3. Modern machinery

In the second half of the 20th century, the invention of computers was an epoch-making event in the history of scientific development. With the advent of computers, robots, as a typical representative of modern machinery, are more and more widely used in industrial production, undertaking tasks that many people cannot complete. The combination of electronic technology and computer technology with machinery makes the machinery more and more automatic and intelligent, and the machinery can even run normally without human operation. Modern machinery is developing in the direction of active control, informationization and intelligence, which will greatly improve human production and life. Compared with traditional machinery, modern machinery has its own "brain"-control system, whose function can not only replace human physical labor, but also replace human mental labor. [ 1]

The development of production has promoted the development of the discipline of mechanical principles. The development of disciplines in turn provides favorable conditions for the development of production and promotes the development of production. With the development of science and technology, in order to better meet the actual needs of production and the requirements of mechanical automation, it is necessary to constantly innovate some new institutions, so the mechanism science with institutional innovation as the main content has developed rapidly. Such as multi-bar and multi-degree-of-freedom planar linkage mechanism, spatial mechanism, various combined mechanisms (including all kinds of combined mechanisms with flexible members), mechanical, electrical and hydraulic integrated mechanisms, etc., are all under study, and some have been applied. At the same time, bionic machines such as robots and manipulators have developed rapidly, including robots and manipulators working under special conditions such as high temperature, high pressure, toxicity and radioactivity. For example, a robotic arm on a spacecraft for recovering satellites; Robots that install equipment in nuclear power plants; Robots working in the deep seabed, etc. In addition, the development of micro-technology has also created some micro-machinery. For example, scalpels that can operate in human abdominal cavity and even micro robots that can crawl in human blood vessels have been used.

In order to analyze and design these new machines, the discipline of mechanical principles has developed many new theories and methods in recent years, and introduced some different mathematical and mechanical tools, especially the popularization and application of computers, which provided extremely favorable conditions for the development of the discipline of mechanical principles. Computer-aided analysis, computer-aided design and optimization design (including multi-objective optimization design) have developed rapidly and become mature.

Due to the development of machinery in the direction of high speed, high precision, high load and high efficiency, some new topics have been put forward for the discipline of mechanical principle and some new research fields have been opened up. For example, for high-speed and heavy-duty machinery, it is necessary to study not only its motion performance, but also its dynamic performance. Sometimes it is necessary to consider the influence of elastic deformation, mass distribution, connection gap and friction in machinery on mechanical work, and consider the vibration, impact and balance of machinery.

(3) Future prospects

In recent years, the development of mechanical principle is very rapid. Great progress has been made in both basic principles and research methods. There are also some new innovations in the types of institutions, some of which have broken through the scope of traditional institutions, entered the so-called "generalized institutions" and created institutions with links such as gas, liquid, light and electricity. At present, there are combination mechanisms composed of three basic mechanisms, and there are also combination mechanisms including flexible members. A lot of work has been done in the research of spatial combination mechanism. In addition, some combined mechanisms with special motion and dynamic performance are also studied. With the development of machinery towards high speed and heavy load, the research of mechanical dynamics has developed rapidly. Due to the wide application of electronic computers, the computer-aided analysis and computer-aided design of mechanisms have developed rapidly. From the development of the discipline of mechanical principles, it can be seen that the need of production development is the main driving force for the development of this discipline. The development of disciplines in turn promoted the development of production and improved the level of production. It can be predicted that with the continuous improvement of production requirements for technological modernization, the discipline of mechanical principles will continue to develop rapidly. [2]