There are many types of CNC machine tools, which can be classified from different angles, different classification standards corresponding to different classifications, today by me to introduce you to two of the classification methods, that is, according to the movement and control mode for classification, the specific content of the following.
CNC machine tools can be divided into, according to the movement mode
(1) point position control system
Only control the position of the tool to move from one point to another, and in the process of moving without cutting process, such as coordinate boring machine, drilling machine and punching machine. The coordinate position is required to have high positioning accuracy, in order to improve productivity, the highest feed speed set by the machine tool is used for positioning movement, before approaching the positioning point to be graded or continuous speed reduction in order to converge to the end point at low speed, thus reducing the inertial overshoot of the moving parts and the positioning error caused by this. No cutting process is performed during the positioning movement, so there is no requirement for the motion trajectory.
(2) Linear control system
Linear control system is to control the precise movement of the tool or base table from one position to another at a certain speed, along a direction parallel to a coordinate axis. It is also called point position linear movement control system.
(3)Contour control system
Is the control of two or more coordinate axes at the same time (two-axis, two-and-a-half-axis, three-axis, four-axis, five-axis linkage), it is not only to control the starting and ending coordinates of the moving parts of the machine tool, but also to control the speed, direction and displacement of each point of the entire machining process, that is, to control the trajectory of processing, processing the required contour. Motion trajectory is any slope of the straight line, arc, spiral line, etc.. This type of machine tool CNC device is the most complete, able to carry out two coordinates or even multi-coordinate linkage control, but also able to point and linear control.
CNC machine tools according to the movement, can be divided into.
(1) open-loop CNC machine tools
Refers to the control system without feedback, no position feedback elements within the system, usually using stepper motors as the actuator. The input data through the numerical control system of computing, issued a command pulse, through the ring distributor and drive circuit, so that the stepper motor turned a step angle, and then through the transmission mechanism to drive the table to move a pulse equivalent distance. The moving speed and displacement of the moving parts are determined by the frequency and number of pulses of the input pulse.
(2) Semi-closed-loop CNC machine tools
Install angular displacement detection device (photoelectric encoder or induction synchronizer) at the end of the drive motor or at the end of the drive screw to indirectly measure the actual position or displacement of the actuating part by detecting the angle of the motor or screw, and then feedback to the CNC system. Obtain higher accuracy than the open-loop system, but its displacement accuracy is lower than that of the closed-loop system, and it is easy to achieve system stability compared with the closed-loop system. Now most CNC machine tools are widely used this semi-closed-loop feed servo system, inertia of the machine tool moving parts are not included in the detection range.
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