MT Chap1 Introduction

2020-02-27 194浏览

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3.1.1 General Information 1. The Concept of Machinery (1) Mechanism A mechanism is a device, which produces specific mech anical motions. Thus, the function of a mechanism is to transmit and modify a motion. We often use a drawing with some simple lines and symbols to d escribe the mechanism, and it is called kinematical diagram. (2) Machine A machine is a device which produces specific mechanical motions, and it can transmit or modify mechanical energy, materials and information. A machine may be a mechanism or a combination of mechani sms capable of transmitting or modifying motion and mechanical energy. (3) Machinery In the viewpoint of kinematics, mechanism and machine h ave no difference，so mechanisms and machines are generally called mac hinery in mechanical engineering. There is no energy transforming and mo difying in a mechanism, for example, mechanical watch is a mechanism bu t not a machine, because it can not transform energy.
4.Fig.1-1 Internal combustion engine and scheme(内燃机及其机构简图) 1—piston(活塞) 2—coupler(连杆) 3—crank shaft(曲轴) 4、5、6—gear(齿轮) 7—cam(凸轮) 8—follower(推杆) 9—lever(杠杆) 10—valve(气门) 11—frame(缸体)
5.2.Composition of Machines A machine consists of prime power, transmission system and working system. A modern machine also contains a control system. Fig.1-2 shows the block diagram of composition of a machine. Fig.1-2 Composition of machine(机器组成示意图)
6.Fig.1-3b shows a diagram of an automatic gate. Fig.1-3a shows the composition of the driver. The prime power is electromotor 3 which has a high speed. But gate 2 needs a low speed to work, so we have to install gear mechanisms and chain mechanisms to modify the speed of electromotor 3. The reducer 4 and chain driver 5 are transmission system. Gate 2 consisting of the parallel linkages is called working system. Fig.1-3 Automatic gate (电动大门示意图) 1—driver(驱动器) 2—gate (大门) 3—electromotor(电动机) 4—reducer(减速器) 5—chain driver(链传动) 6—rollers(滚轮)
7.Fig.1-4 Constitute of the coupler(连杆的组成) 1—body of the coupler(连杆体) 2—bearing(小端轴承) 3—bearing bush(轴瓦) 4—head of the coupler(连杆头) 5—bolt(螺栓) 6—nut(螺母) 7—washer(垫圈)
8.1.2 Teaching Content and Object of the Course 1. Research Object of the Course The research object of the course is the theory of machin ery, and machinery contains mechanisms and machines. Ther efore, the theory of mechanisms and machines is the importan t content of this course. The piston, coupler, crank, cam, gear and so on shown in Fig.1-1 are smallest motion units, and they are called links. Th e motion of links is an important content for us.
9.1.3 Purpose of This Course 1. Purpose The machinery is closely related to human life, economic construction, and national defense construction, so mechanical industry can reflect a industry level of a country and a level of science and technology. Although there are a lot of machines, the mechanisms consisting machines are finite. So on the basis of finite mechanisms to design some new machine is a creative work. It is also the purpose of this course. This course is the basis of some other subsequent courses, such as Machinery Design, Advanced Kinematics and Dynamics of Mechanisms, Mechanical Manufacture, etc. So the purpose of this course is also to lay the foundation for the further machine design.
10.2. Conclusion 1) Machinery is very important to develop the economy. 2) Theory of Mechanism and Machines is very useful to design machin es. 3) Mechanism is a device which can transmit and modify motion. 4) The kinematical diagram is a simple form to describe the mechanis ms. 5) A machine may be a mechanism or combination of mechanisms cap able of transmitting or modifying motion and mechanical energy. 6) Machinery is the generic term of mechanisms and machines. 7) A link is a smallest kinematical unit of a machine from the point of vie w of the movement. 8) An element is a smallest manufacturing unit of a machine. 9) Theory of Machines and Mechanisms is a basic course, and it is a p art of machinery design.
11.Thanks for Your Attention