Introduction to the classification standards and types of CNC machine tools

There are many types of CNC machine tools, which can be classified from different perspectives. Different classification standards correspond to different classifications. I will not state them one by one here. Let's introduce two of the classification methods, that is, according to the movement mode and the control mode. For classification, the specific content is as follows. Numerical control machine tools are classified according to the movement mode, which can be divided into: (1) The point position control system only controls the position of the tool from one point to another, and does not perform cutting during the movement, such as coordinate boring machines, drilling machines, and punching machines. The coordinate position is required to have high positioning accuracy. In order to improve production efficiency, the feed speed set by the machine tool is used for positioning movement. Before approaching the positioning point, it must be graded or continuously decelerated, so that the low speed approaches the end point, thereby reducing the number of moving parts. The inertial overshoot and the positioning error caused by this. No cutting is performed during the positioning movement, so there is no requirement for the motion track. (2) Linear control system The linear control system controls the tool or basic worktable to move at a certain speed along a direction parallel to a certain coordinate axis from one position to another. Also known as point linear movement control system. (3) The contour control system controls two or more coordinate axes at the same time (two-axis, two-axis and a half, three-axis, four-axis, five-axis linkage), it not only controls the start and end points of the moving parts of the machine tool Coordinates, and control the speed, direction and displacement of each point in the entire processing process, that is, control the processing track and process the required contour. The motion trajectory is a straight line, arc, spiral, etc. with any slope. The functions of the numerical control device of this kind of machine tool are complete, which can carry out two-coordinate or even multi-coordinate linkage control, as well as point and linear control. Numerical control machine tools are classified according to the movement mode, which can be divided into: (1) Open-loop numerical control machine tools refer to control systems without feedback. There are no position feedback components in the system, and stepper motors are usually used as actuators. The input data is calculated by the numerical control system, and command pulses are issued. The stepping motor is rotated through a step angle through the ring distributor and the drive circuit, and then the worktable is driven by the transmission mechanism to move a pulse equivalent distance. The moving speed and displacement of the moving part are determined by the frequency of the input pulse and the number of pulses. (2) The semi-closed-loop numerical control machine tool installs an angular displacement detection device (photoelectric encoder or inductive synchronizer) at the end of the drive motor or at the end of the drive screw, and indirectly measures the actual position or the actual position of the actuator by detecting the rotation angle of the motor or screw. The displacement is then fed back to the CNC system. It obtains higher accuracy than the open-loop system, but its displacement accuracy is lower than that of the closed-loop system. Compared with the closed-loop system, it is easy to realize the stability of the system. Most CNC machine tools now widely use this semi-closed-loop feed servo system, and the moving parts of the machine tool with greater inertia are not included in the detection range. (3) The closed-loop numerical control machine tool is directly connected with a detection device on the moving parts of the machine tool, and the measured results are directly fed back to the numerical control system. In fact, the displacement command value is compared with the actual position feedback signal measured by the position detection device in real time, and the difference is controlled according to the difference, so that the moving part can move according to the actual requirements, and finally realize the positioning. (Picture/text http://www.wxdtc.com/)