Components Of CNC Machine Tools

CNC machine tools are generally composed of control medium, CNC device, servo system and machine tool body.

In order to improve the machining accuracy of the machine tool, a measurement device (that is, the dotted line in the above figure) is added to the above system, thus forming a block diagram of a closed-loop control CNC machine tool. The working process of the open-loop control system is as follows: the displacement, displacement speed, displacement direction, displacement trajectory and other parameters that control the movement of the machine tool table are input to the machine tool CNC device through the control medium, and the CNC device calculates the Give the pulse sequence (including the above four parameters), and then convert and amplify by the servo system, and finally control the worktable to move according to the required speed, track, direction and distance. If it is a closed-loop system, at the same time when the command value is input, the actual displacement of the machine table is detected by the feedback. The feedback value and the input value are compared in the CNC device. If there is a difference, the second difference is explained. The numerical control device controls the machine tool to move in the direction of eliminating errors.

The components are briefly described as follows:

1. Control Medium

When the CNC machine tool is working, there is no need for the worker to operate the machine tool by rocking the handle, but it is necessary to automatically execute people’s intentions. This must establish some kind of connection between the person and the CNC machine tool. (Or program medium, input medium, information carrier).

The commonly used control medium is 8 units of standard perforated tape, and the commonly used perforated tape is paper, so it is also called paper tape. It has a width of 25.4mm and a thickness of 0.108mm. In addition to a synchronous hole of 1.17mm, each line can have up to 8 information holes of 1.33mm. Different codes are represented by the arrangement and combination of 8 holes in each row (the rules of the arrangement of holes on the paper tape are called codes). Input the punched tape to the belt reader of the numerical control device, and then the belt reader converts the code on the punched belt into an electrical signal that can be recognized and processed by the numerical control device, and transmits it to the numerical control device, thus completing the input of the instruction information jobs.

2. CNC Device

The numerical control device is the center of the numerical control machine tool, which is generally composed of an input device, a memory, a controller, an arithmetic unit and an output device in an ordinary numerical control machine tool. The numerical control device receives the information of the input medium, and recognizes, stores, and calculates its code, and outputs the corresponding command pulse to drive the servo system, and then control the movement of the machine tool. In a computer numerical control machine tool, since the computer itself contains the above-mentioned units such as an arithmetic unit and a controller, the function of its numerical control device is completed by a computer.

3. Servo System

The role of the servo system is to convert the pulse signal from the numerical control device into the movement of the moving parts of the machine tool, so that the worktable (or slide) can be accurately positioned or strictly relative to the specified trajectory, and finally the parts that meet the requirements of the drawing are processed.

In the servo system of CNC machine tools, commonly used servo drive components include power stepper motors, electro-hydraulic pulse motors, DC servo motors and AC servo motors.

4. Machine Tool

The machine tools in the CNC machine tools use general-purpose machine tools at the beginning, but only make some changes in terms of automatic speed change, tool holder or table automatic indexing and handles. Practice has proved that CNC machine tools cannot only affect the accuracy of the workpiece due to the large amount of cutting and the continuous heating, and because of the automatic control, they cannot be manually intervened at any time as in general machine tools. Therefore, its design requirements are stricter than general-purpose machine tools, and its manufacturing requirements are more precise. Therefore, in the design of CNC machine tools, many new measures to strengthen rigidity, reduce thermal deformation, and improve accuracy have been adopted, so that the external shape, overall layout, transmission system and tool system of CNC machine tools have occurred.

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