Component parts of the mechanism - Applied Mechanics

Components of the mechanism

Mechanisms, regardless of function and design, have a common structural basis. They consist of links - bodies involved in the transformation of motion. Link - part or group of rigidly connected parts (solid link). In addition, the links can be flexible (cables, belts, chains), liquid or gaseous.

Rack - fixed link or link conventionally taken as a stationary one. The stand can be a frame, a housing, a mechanism board, etc. Relative to the rack, the parameters of movement of the mechanism (displacement, speed, etc.).

From the mobile links, depending on their location in the chain of the mechanism, the input and output links are allocated. The input link is the link to which the movement from the engine is reported, the output - the link making the movement for which the mechanism is intended. The remaining mobile links of the mechanism are called intermediate . Mechanisms can have several input and output links. For example, a vehicle differential with one input link receiving traffic from the engine has two output links connected to the rear or front wheels.

The input link is the leader (driving) link. The remaining mobile links of the mechanism that perform the required unambiguously defined movements are called slaves . This classification is used in the structural study of the mechanism. When analyzing the dynamics of the mechanisms, the separation of the links into the leading and the slave units is carried out according to the sign of the elementary work of the forces acting on the link. In the leading links this work is positive, for the slaves - negative or zero. Therefore, the input link, which in the structural analysis on the basis of the action is the leading one, can be both the driving and the driven, depending on the sign of the elementary work of the forces acting on the link, under dynamic analysis at different sections of the motion.

The positions of all links of the mechanism with respect to the fixed link (racks) are given by generalized coordinates - independent variables that fully and unambiguously determine the position of the mechanism. The number of generalized coordinates corresponds to the number of degrees of freedom of the mechanism. In Fig. 1.1 shows the structural diagram of a flat hinged four-link. Here 1-4 are the links; A, B, C, D - kinematic pairs. The position of the hinged four-link mechanism having one degree of freedom is completely and unambiguously determined by specifying one coordinate (angles of -

Fig. 1.1

crank gate 1 ), which you can take as a generalized coordinate.

Any independent coordinates can be taken as generalized coordinates. The link whose coordinates are selected as generalized coordinates of the mechanism is called the starting link . In most cases, it coincides with the input link. However, sometimes to simplify the analysis for the initial link it is more convenient to take an intermediate or even an output link.

The links in the mechanisms are interconnected movably. The movable connection of two adjoining links, allowing their relative motion, is called a kinematic pair . The points, lines, surfaces along which the links touch, are called kinematic pairs .

thematic pictures

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