Without a kinematic scheme, it is impossible to imagine any type of equipment. We are talking about cars, tractors, machine tools, as well as simpler types of mechanisms. In general, kinematics is a special department in mechanics, which is aimed at studying the properties of the links of mechanisms. Science allows kinematic analysis by studying the trajectories of links, determining points, positions and velocities of elements. Achieving the final result is impossible without justifying the concept of “kinematic scheme”, which will be discussed in this article.
What is a kinematic scheme? Basic concepts
Briefly answer this question, then the kinematic scheme is a certain drawing or document, so to speak, on which all mechanical links with dimensions are shown. Very often, the links in a circuit are called kinematic pairs. If you define the scientific language, then these are conjugated solid elements in the amount of 2 pieces, which, due to the conditions of communication, restrict the movement of each other.
The presence of dimensions is necessary for conducting kinematic analysis, which studies the basics of movement of mechanisms, their trajectory and speed. It is possible to solve kinematics problems both graphically and experimentally.
In general, we are talking about the kinematic scheme when we analyze the type of mechanism. He is called a certain system of bodies, which transforms the movement of some for the required movement of others. The composition of any mechanical element includes links - several solid particles rigidly connected to each other. The link, which is considered motionless, is called the rack.
An element of a kinematic pair or link is a system of surfaces and lines along which one link is in contact with another. This point is also called the interface node.
Fields of application of kinematic schemes
The kinematic scheme is applied in absolutely all areas of industry - machine building, machine tool building, etc. All execution rules are governed by a special document - the so-called GOST.
Scheme execution rules
There are several basic laws for making kinematic drawings:
- The document can be executed both on paper and on electronic media. It is recommended to draw up design schemes on one sheet with the possibility of dividing it into the necessary formats when printing.
- In the case of complex schemes, multimedia tools are allowed, that is, you can show the movement in dynamics in a visual way.
Kinematic drawings are divided into three types: fundamental, structural and functional. The rules for compiling them also differ from each other.
As for the circuit diagrams, then in the figure all kinds of connections between the elements must be plotted. The document is provided in the form of a scan. The basic kinematic scheme, the designation of which the developer indicates in the margin, should be depicted in the outline of the product in axonometric projection. More detailed rules for their preparation can be found in accordance with GOST 2.303 and 2.701.
The main difference between the structural diagrams from the principal is that the first shows the functional parts of the product and the relationship between them. As a rule, they are presented in the form of graphic images or analytical records.
Functional diagrams illustrate the relationships between parts of elements that are represented by simple geometric shapes.
Who regulates the correct mapping?
Compilation rules are spelled out in interstate standardization documents. For the entry into force of this document, most countries voted many years ago. Periodically, changes are made to GOST, this is understandable - scientific progress does not stand still, science is developing, and with it changes and regulatory documents are undergoing. In addition to the main standard, the rules for the implementation of kinematic schemes are spelled out in the Unified System of Design Documentation.
Determination of the structure of mechanisms
As mentioned above, all mechanisms consist of a certain number of kinematic pairs. They are divided into several main ones:
- by type of communication place - to lower and higher;
- by the method of closure;
- relative movement in a pair - on translational, rotational, cylindrical, etc.
Kinematic schemes of mechanisms determine their structure. If we give this concept a definition, then this is the totality of all elements of the device and the relations between them. In addition, in order to determine the structure of the mechanism, it is necessary to establish the composition of the incoming links.
Based on the above classifications, the main types of machine elements that determine its structure are distinguished:
- rack;
- connecting rod;
- crank;
- slider.
Types of mechanisms
There are a large number of different designs. Most often, the mechanisms are divided into:
- lever or rod;
- frictional;
- cam;
- mechanisms with flexible links;
- gear, etc.
Among the main classifications of mechanisms, one is distinguished that subdivides them into three groups:
- functional (according to the principle of the technological process);
- structural (by structure);
- structurally-constructive (by constructive principles).
More details about kinematic schemes will be described using an electric drive as an example.
What is a drive? Its purpose
Before talking about the kinematic scheme of the drive, you need to know what it is. A drive is a special device that drives a machine using an engine. In other words, the mechanism begins to move from the flow of energy, which comes either from the engine, or from additional elements. The kinematic diagram of the gearbox is indispensable in the study of the concept of "drive". This device is a mechanism of worm or gears, which transmits rotation from the engine directly to the shaft of the machine. Its body consists of bearings, shafts and gears.
Kinematic diagram of the drive
In any drive, all elements connected to each other have a certain effect on each other. That is, studying the movement of only one link will not be enough, it is important to take into account their mutual influence. To do this, all the forces in the structure lead to a single point, as a rule, this is the motor shaft . The kinematic circuit of the drive is called equivalent, and the parameters are given.
The schemes of this equipment consist of such basic elements as:
- electric motor;
- open gear;
- gearbox;
- drive shaft of the machine;
- coupling.
This is the classic composition of the kinematic scheme, some elements may be missing.
Kinetic scheme of other mechanisms
Kinematics is a science that studies various designs, therefore, for any type of equipment the scheme is different. Consider a drawing of the most common unit - the machine. Of course, there are a number of other mechanisms, and it can take a lot of time to study their schemes. Images of complex structures are examined in more detail by scientists, mechanics, and kinematics enthusiasts.
A machine is a simple example of a mechanism that is driven by certain forces. The executive bodies of the design are: table, caliper, spindle and other details. The kinematics chains of the machine consist of various gears that are arranged in a specific sequence. Kinematic gear schemes may include belt, gear or worm gears. In the drawing, all elements are indicated by special signs that are prescribed in GOST 3462-61. The kinematic diagram of the machine necessarily includes the steps of the leadscrews, the modules for entering the worms, the engine speed, power, etc.
Modern equipment has not only mechanical transmissions, hydraulic or pneumatic devices are often used, and, accordingly, in the machine passports you can find not kinematic schemes, but combined pneumohydraulic or electric ones.
The modern world of machines and parts is huge, there are thousands of diverse mechanisms and elements. However, each mechanical unit has its own kinematic scheme, whether it is a crane, a car suspension, a metal cutting machine or a drilling rig. Kinematic drawings and design descriptions help to understand the structure and composition of mechanisms, facilitate the process of studying the movement of elements and links in a chain. Thanks to such schemes and the science of kinematics, in general, scientific and technological progress does not stand still, more and more advanced mechanisms, machines and assemblies appear that are actively entering our life.