Скачать с ютуб Machine Theory - Video 1 - Introduction to Mechanisms (links, linkages, kinematic pairs, joints) в хорошем качестве

Machine Theory - Video 1 - Introduction to Mechanisms (links, linkages, kinematic pairs, joints)

#Mechanical_Engineering This video is part of the lectures related to the machine dynamics topic. It is the first video of the Introduction section. This video is going to introduce mechanisms or linkages. To achieve the learning outcomes enumerated previously, the video is divided in four parts. First we are going to define what are mechanisms. We are going to focus on the useful definition of mechanisms and not recalling the historical definitions. It will not be able to understand what is a mechanism without having a deep understanding of links, kinematic pairs, and kinematic chains. Thus, in the second part of this video, we are going to define what are links, kinematic pairs, and kinematic chains. Then, we will give some examples and some applications, in the third and fourth parts, respectively. Examples will help you to have a feeling about the definition of mechanisms. You will be able to recognize which mechanical system is a mechanism and which is not. Applications will give a feeling about the usefulness of mechanisms. A mechanism is a mechanical system that is made of links or rigid bodies. Rigid bodies or links are mechanical parts that conserves their shapes while moving or subjected to forces. The distance between any two points, of a link or a rigid body, remains always constant and does not change. Angles within a rigid body, or a link, also does not change. In a mechanism, the links are assembled or connected together, using joints, or kinematic pairs. The kinematic pairs are contact points, lines or surfaces, between links, that reduce or block some relative degree of freedom. These two conditions build a kinematic chains. A kinematic chain is assemblage of links using kinematic pairs or joints. In a mechanism, we should also have a link, considered as a reference for mechanism’s motion. This link is also called the ground or the frame. A mechanism is a kinematic chain having a grounded link. The ground or the frame, is not necessary a static non moving link. It is rather a link that is considered as a reference for the mechanism’s kinematics. In other words, the kinematics of the mechanism is studied, relatively to the link, which is chosen as a reference or the ground. A mechanism receives an input motion. This means, that one link (or more) will be controlled by an external source of energy. In response to this input, the mechanism will move in completely determined and controlled way. The output is the motion of one link (or more). A mechanism is a kind of motion transformer. It receives an input motion and it gives back another output motion. Let’s have some examples of kinematic pairs or joints. Also, here, we will focus, on examples used in planar mechanisms. The first example is the pin or revolute joint. The pin joint blocks the two relative translations. Links can only rotate relatively to each other. Each link can rotate independently of each other. The rotation speed and direction of one link is independent of the other link’s rotation speed and direction. Prismatic joints connect two links by cancelling the relative rotation and one relative translation. Thus, one link can only translate in one direction relatively to the second link. It is possible to have one link translating and the other static. Or also, it is possible that the two links translate. Cam joints are obtained by simple or direct contact between two bodies or links. Cam joints allow one translation and one rotation. Gear joints are obtained by contact between teethed bodies or links. Gear joints also allow one relative translation and one relative rotation. Any device or machine that moves, or have a sub-system moves, contains one mechanism or more. A bike for example employs a mechanism to transform the feet motion of the rider to a rotation motion of the rear wheel. The mechanism uses a crank, a crank set, a chain, and a cassette. An automobile involves several mechanisms. The gear box is an example of these mechanisms. Manual transmission systems use compound gears trains to provide torque multiplication. Also in a car, the gas engine uses slider-crank mechanisms to transform the reciprocal motion of the piston, induced by the gas explosion, to a rotational motion. Construction equipment, fitness equipment, robots, involve many mechanisms. Mechanisms are around us, in almost all machines. Their application is wide and versatile.