Introduction to the components of CNC machine tools

CNC machine tools generally consist of a control medium, a numerical control device, a servo system, and a machine tool body.

In order to improve the machining accuracy of the machine tool, a measuring device (namely, the dashed line in the figure above) is added to the above system, which constitutes a block diagram of a closed-loop control CNC machine tool. The working process of the open-loop control system is as follows: The parameters such as displacement amount, displacement speed, displacement direction, and displacement trajectory that control the movement of the table of the machine tool are input to the machine tool numerical control device through the control medium, and the numerical control device calculates the parameters according to these parameter commands. The pulse sequence (containing the above 4 parameters) is then converted by the servo system to amplify, and finally the control table moves according to the required speed, trajectory, direction and distance. In the case of a closed-loop system, there is a misaligned displacement value between the real machine and the machine tool table at the same time when the command value is input. The feedback quantity and the input quantity are compared in the numerical control device. If there is a difference, the difference is indicated. The numerical control device controls the machine tool to move in the direction of eliminating the error.

The various components are briefly described as follows:

1, control media

When CNC machine tools work, workers are not required to shake the handle to operate the machine, but they must automatically perform people's intentions. This must establish a connection between the human and the CNC machine tool. The medium of this connection is called the control medium. (or program media, input media, information carrier).

The commonly used control medium is a standard 8-unit perforation belt, and the commonly used perforation belt is paper, so it is also called a paper belt. Its width is 25.4mm and its thickness is 0.108mm. In addition to having one φ 1.17mm synchronization hole in each row, there can be up to eight φ1.33mm information holes. Different combinations of codes are used for arrays of eight holes per line (a rule for the arrangement of holes in tape, called a code). The perforated tape is input to the tape reader of the numerical control device, and the code of the perforated tape is converted by the tape reader into an electrical signal that can be recognized and processed by the numerical control device, and is transmitted to the numerical control device to complete the input of the instruction information. jobs.

2, numerical control device

The numerical control is the center of the numerical control machine tool. In the ordinary numerical control machine tool, it is generally composed of an input device, a memory, a controller, an arithmetic unit, and an output device. The numerical control device receives the information of the input media, and identifies, stores, and calculates the code, outputs the corresponding command pulse to drive the servo system, and then controls the movement of the machine tool. In the computer numerical control machine tool, because the computer itself contains the above-mentioned unit such as the calculator and the controller, the function of the 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, make the worktable (or slide plate) accurately positioned or make the relative movement according to the specified trajectory, and finally process the parts that meet the requirements of the drawings.

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

4, machine tools

The machine tools in CNC machine tools use general-purpose machine tools at the beginning. They only make changes in terms of automatic transmission, tool rests, or automatic indexing of the table and handles. Practice has proved that CNC machine tools not only affect the accuracy of workpieces due to large cutting amounts, continuous heating, etc., but also because they are automatically controlled, they cannot be manually intervened at any time as in general machine tools. Therefore, its design requirements are more stringent than general-purpose machine tools, and manufacturing requirements are more precise. Therefore, in the design of numerical control machine tools, many new measures such as strengthening rigidity, reducing thermal deformation, and improving accuracy were adopted. As a result, external molding, overall layout, transmission systems, and tool systems of CNC machine tools have taken place. big change.