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

In order to improve the machining accuracy of the machine tool, the above system and then add a measuring device (i.e., the dashed part of the above figure), so as to constitute a closed-loop control of CNC machine tool block diagram. Open-loop control system works like this: the control of the machine table movement displacement, displacement speed, displacement direction, displacement trajectory and other parameters through the control medium input to the machine tool CNC device, the CNC device according to these parameters instruction calculation to derive the feed pulse sequence (containing the above four parameters), and then by the servo system conversion amplification, *** control table according to the required speed, trajectory, direction and distance movement, direction and distance. If the closed-loop system, the input command value at the same time, feedback *** machine table between the real one has the error between the displacement value, feedback and input quantity in the CNC device for comparison, if there is a difference, that two differences, the CNC device to control the machine tool towards the elimination of the direction of the error movement.

The components are briefly described as follows:

1, control medium

CNC machine tool work, do not need workers to shake the handle to operate the machine tool, but to automatically execute people's intentions, which must be established between the human and CNC machine tool some kind of link, the medium of this link is called the control medium (or program medium, input medium, information carrier).

Commonly used control medium is 8 units of standard perforated tape, and commonly used perforated tape is paper, so also known as paper tape. Its width is 25.4mm, 0.108mm thick, each line must have a φ1.17mm synchronization hole in addition to *** more than 8 φ1.33mm information holes. With each row of 8 holes with or without the arrangement of the combination to indicate different codes ( the arrangement of holes on the paper tape regulations, called code ). The perforated tape input to the CNC device of the tape reader, and then by the tape reader to perforate the code on the tape converted to the CNC device can be identified and processed by the electrical signal, and transmitted to the CNC device, will complete the command information input work.

2, CNC device

CNC device is the hub of CNC machine tools, in general CNC machine tools by the input device, memory, controller, operator and output device. CNC device to receive information from the input medium, and its code to identify, store, computing, output the corresponding command pulse to drive the servo system, and then control the machine action. In the computer numerical control machine tool, because the computer itself that contains the operator, controller and other units, so the role of its numerical control device by a computer to complete.

3, servo system

The role of the servo system is to convert the pulse signal from the CNC device into the movement of the moving parts of the machine, so that the table (or skate) *** positioning or according to the prescribed trajectory for strict relative movement, *** processing of parts in line with the requirements of the drawings.

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

4、Machine tool

CNC machine tools in the machine tool, at the beginning of the stage of using general-purpose machine tools, only in the automatic speed change, tool holder or table automatic indexing and handle to make some changes. Practice has proved that: CNC machine tools in addition to the cutting amount of large, continuous processing more heat, such as the impact on the accuracy of the workpiece, and because it is automatically controlled, in the processing can not be like in the general-purpose machine tool can always intervene by hand. So its design requirements than general-purpose machine tools more stringent, manufacturing requirements more precise. Therefore, later in the design of CNC machine tools, the use of many new measures to strengthen rigidity, reduce thermal deformation, improve accuracy, etc., so that the external shape of CNC machine tools, the overall layout, transmission systems and tooling systems have undergone great changes.