Mechanical part of the drive
In accordance with the definition of the electric drive, its mechanical part includes the following elements of the power channel: the movable part of the EMF (motor) - the rotor or the armature; mechanical converter (MP); working element (PO) of the actuator (figure 2.1).
Fig. 2.1. Composition of the mechanical part of the electric drive
In Fig. 2.1 wavy lines are marked "joints" mechanical part with an electromechanical converter on the left and with a technological installation on the right.
The scheme (Figure 2.1, a) - very general. So, for example, in an elevator the rotor of the engine through a reducer, a drum, a cable is connected with a cabin; in the press, the rotor of the motor through the reducer and the crank mechanism is connected with the punch; in a small rolling mill, the rotor of the engine through the reduction gear and the driveshaft is connected to the working roll, etc. In addition to these basic elements, the MP includes various additional elements: couplings, parts of brake units, connecting links, etc.
There are installations where there are no mechanical transmissions (Figure 2.1.6). So, in small fans, the impeller is usually directly connected to the motor shaft, in some electronic pointer clocks, a minute hand is placed on the shaft of the micromotor, etc.
Sometimes actuator combined with a moving part of the engine (Fig. 2.1, in). This is, for example, motor-wheel in some types of vehicles, the MHD pump, in which the role of the moving part of the engine is played by the pumped electrically conductive liquid itself, some centrifuges, etc.
We examined the general nature of the circuits (Figure 2.1), there are many installations with more complex branched kinematic schemes, ever one engine is connected to several working bodies, or several engines work on one mechanism, or, finally, the motors are built in various links of the kinematic chain, as is done in some modern manipulators.
Links of the mechanical part of the electric drive
The design of the mechanical part of the electric drive can be very diverse. However, it contains certain links with common functions for different drives.
The engine as a link of the mechanical part of the drive is a source or consumer of mechanical energy. The mechanical part of the drive includes only the rotating element of the motor - its rotor (or the armature in DC machines), which has a certain moment of inertia (Y), can rotate at a certain speed (w) and develop a driving or braking torque ( M ).
The mechanical converter (MP) carries out the transformation of motion in the mechanical part of the electric drive. With the help of MP, the speed can increase or decrease, the type of motion can change, for example, the transformation of rotary motion into translational motion, etc. Mechanical transmitters include reducers (Fig. 2.2, a), screw, rack-and-pinion (Figure 2.2, 6) or belt drives, a drum with a cable (Figure 2.2, in) The mechanical converter is characterized by a transmission ratio, which is the ratio of the speed at the entrance to speed at the output, mechanical inertia and elasticity of its elements, gaps and friction in the gears and junctions of the converter.
Fig. 2.2. Examples of mechanical motion transducers
The executive or working body (RO) of the production machine realizes the mechanical energy supplied to it into useful work. Most often he is a consumer of energy. This function of the working organ is characteristic for mechanisms that process material, lift or move loads, etc. At the same time, the flow of mechanical power is directed from the engine to the working member. Sometimes the working body can be a source of mechanical energy. In this case, it gives off the mechanical energy stored by the mechanism, for example, during the descent of the load, or entered the mechanism from the outside, for example, with a wind load on the surface of the crane, the earth's surface, the mirror of the antenna device. The flow of mechanical power is directed from the working element to the motor. The working body is characterized by a certain inertia, a working moment with its rotational motion or working force in the forward motion. In each specific mechanism, the RO has its own constructive embodiment. Transmission of mechanical energy from the motor shaft to the working member or vice versa is associated with losses in mechanical links . The cause of losses is friction in bearings, guides, gears, etc. In mechanical links that have elasticity, additional losses occur due to viscous friction in deformable elements. As a result, the flow of power from the source to the consumer gradually decreases. At the same time, the losses of mechanical energy are covered by a source of energy: the motor with a direct energy flow and a working member in the opposite direction.
The task of the electric drive, in the final analysis, consists in the fulfillment of the laws of motion of the working organ specified for technological requirements with the maximum approximation. In the implementation of this task, it is often assumed that the law of motion of the motor rotor is proportional to the specified law for the working body. However, it should be borne in mind that mechanical links can introduce distortions into the transmitted motion. These distortions are due to the fact that the mechanical links have inertia, and also because of energy losses due to gaps and elasticity of the elements forming the links. However, often these distortions are insignificant, and in these cases they can be ignored.Different parts of the mechanical part of the drive can perform different in character movements - rotational (most often, since most motors are rotating), translational, reciprocal, combined (sometimes very complex, as in modern robots).
Thus, the mechanical part in the general case is a system of moving masses rigidly or elastically connected with each other, which are affected by different forces and moments; as created in the electromechanical converter (motor), and caused by the technological process; useful (on the working body), for the overcoming of which the drive is designed; harmful (in all elements of the mechanical part) due to friction. The motion of each mass is characterized by spatial coordinates and their derivatives.
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