Multi coordinate CNC machine tool. Some complex shape parts can not be processed with three coordinate CNC machine tools, such as propeller, aircraft curved surface parts processing, etc. it needs more than three coordinate synthesis movement to process the required shape. Therefore, the multi coordinate CNC machine tool appears, which is characterized by the number of axes controlled by the numerical control device, and the structure of the machine tool is also relatively complex. The number of coordinate axes usually depends on the process requirements of processing parts. Now commonly used is 4, 5, 6 coordinates of CNC machine tools. Computer gong processing, Dongguan computer gong processing, Shenzhen computer gong processing, mechanical parts processing, Guangzhou computer gong processing, figure 1 is a five axis CNC machining schematic diagram. At this time, x, y, Z coordinates can be linked with the rotation of the turntable and the swing of the cutting tool at the same time to process the wing and other parts.
2. Classification according to the motion track of CNC machine tools
According to the relative motion trajectory between the tool and the workpiece that can be controlled, CNC machine tools can be divided into point control CNC machine tools, point position linear control CNC machines, contour control CNC machines, etc. They are as follows:
(1) Point control CNC machine tool. The numerical control device of this kind of machine tool can only control the moving parts of the machine tool to move accurately from one position (point) to another, that is, only the coordinate value of the end of travel is controlled, and no cutting is carried out in the moving process. As for the moving speed and route between the two key points, it depends on the productivity. In order to achieve as high productivity as possible on the basis of accurate positioning, the movement between the two related points first moves quickly to the new position, and then slows down by 1-3 levels to make it approach the positioning point slowly to ensure its positioning accuracy.
This kind of machine tools are mainly CNC coordinate boring machine, CNC drilling machine, CNC punch and CNC measuring machine, and the corresponding CNC device is called point position control device.
(2) Point position linear control CNC machine tool. When this kind of machine tool works, it is necessary to control not only the position (i.e. distance) between two related points, but also the moving speed and route (i.e. trajectory) between the two related points. Its route is generally composed of straight lines parallel to each axis. It is different from the point position control CNC machine tool in that when the moving parts of the machine tool move, it can cut along a coordinate axis (generally, it can also cut along a 45 ° oblique line, such as computer gong machining, Dongguan computer gong machining, Shenzhen computer gong machining, mechanical parts processing, Guangzhou Electric gongs processing, but not along any slope straight line cutting), and its auxiliary functions There are more CNC machine tools than point position control, for example, to increase spindle speed control, cycle feed processing, tool selection and other functions.
This kind of machine tools mainly include simple CNC lathe, CNC boring and milling machine and CNC machining center. The corresponding numerical control device is called point position linear control device.
(3) Contour control CNC machine tool. The control device of this kind of machine tool can control two or more coordinate axes continuously at the same time. During processing, not only the starting point and the end point should be controlled, but also the speed and position of each point in the whole processing process should be controlled, so that the machine tool can process the parts with complex shapes that meet the requirements of drawings. Its auxiliary functions are relatively complete.
This kind of machine tools are mainly CNC lathes, CNC milling machines, CNC grinding machines and electrical machining machines. Its corresponding numerical control device is called contour control device (or continuous control device).
3. According to the control mode of servo system
CNC machine tools can be divided into open-loop and closed-loop according to whether there is a feedback device for the controlled quantity. In the closed-loop system, according to the position of the measuring device, it can be divided into full closed-loop and semi-closed-loop. Based on the open-loop system, an open-loop compensation CNC system is developed.
(1) Open loop control CNC machine tool. In the open-loop control, there is no feedback device for the machine tool (see Fig. 2). The signal sending process of the numerical control device is unidirectional, so there is no system stability problem. Because of the unidirectional flow of the signal, it does not check the actual position of the moving parts of the machine tool, so the machining accuracy of the machine tool is not high, and its accuracy mainly depends on the performance of the servo system. The working process is as follows: the input data is calculated by the numerical control device, and the command pulse is distributed, and the controlled working table is moved by the servo mechanism (the servo element is usually the stepping motor).
This kind of machine tool has the advantages of stable operation, quick response, convenient debugging and simple maintenance, but its control accuracy is limited. It is suitable for medium and small NC machine tools with general requirements.
(2) Closed loop control CNC machine tool. Because the precision of open-loop control can not meet the requirements of precision machine tool and large-scale machine tool, its actual working position must be detected. Therefore, a feedback device is added to the open-loop control CNC machine tool to detect the position of the moving parts of the machine tool at all times during the processing, so as to make it consistent with the position required by the CNC device, so as to achieve high machining accuracy.
The block diagram of closed-loop control system is shown in Fig. 3. In the figure, a is the speed measuring element and C is the position measuring element. When the command value is sent to the position comparison circuit, if the table does not move, there is no feedback in computer gong processing, Dongguan computer gong processing, Shenzhen computer gong processing, mechanical parts processing, Guangzhou computer gong processing, and the command value makes the servo motor rotate. The speed feedback signal is sent to the speed control circuit through a, and the actual displacement of the workbench is fed back to the position by C Set the comparison circuit with the command value, control with the difference value of comparison until the difference is eliminated, and finally realize the accurate positioning of the workbench. This kind of machine tool
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