Brief introduction to classification standards and types of CNC machine tools, Nanjing Precision Engineering Co., ltd

by:NJPE     2020-01-12

There are many kinds of numerical control machine tools, which can be classified from different angles.  Different classification standards correspond to different classifications, which will not be stated here one by one, today, we will introduce two classification methods, that is, classification according to movement mode and control mode.  The specific contents are as follows. CNC machine tools can be divided :(1) The point control system only controls the tool to move from one point to another, and does not cut during the movement, such as coordinate boring machines, drilling machines and punching machines. The coordinate position is required to have a higher positioning accuracy.  In order to improve the production efficiency, the highest feed speed set by the machine tool is used for positioning movement, and the classification or continuous deceleration shall be carried out before approaching the positioning point, so as to approach the end point at a low speed, thus reducing the inertial overshoot of moving parts and the positioning error caused by it. No cutting is performed during positioning movement, so there is no requirement for motion trajectory. (2) Linear Control system the linear control system is to control the precise movement of the tool or the Foundation table from one position to another along the direction parallel to a certain coordinate axis at a certain speed. Also known as point position linear movement control system. (3) The contour control system controls two or more coordinate axes simultaneously ( Two-axis, two-axis, three-axis, four-axis, five-axis linkage) , It not only needs to control the starting and ending coordinates of the moving parts of the machine tool, but also needs to control the speed, direction and displacement of each point in the whole precision machining process, that is, to control the precision machining trajectory, process the required outline. The motion trajectory is a straight line, arc, spiral line, etc.  of any slope. The function of the numerical control device of this kind of machine tool is the most complete, which can carry out two-coordinate or even multi-coordinate linkage control, and can also carry out point position and straight line control. CNC machine tools can be divided :(1) Open-loop numerical control machine tool refers to the control system without feedback.  There is no position feedback element in the system, and stepping motor is usually used as the actuator. The input data passes through the operation of the numerical control system, sends out the command pulse, and makes the stepping motor turn over a step angle through the ring distributor and the driving circuit, then the transmission mechanism drives the workbench to move a pulse equivalent distance. The moving speed and displacement of the moving part are determined by the frequency and number of input pulses. (2) The semi-closed loop CNC machine tool installs an angular displacement detection device at the end of the drive motor or at the end of the drive screw (Photoelectric encoder or inductosyn) , Indirectly measure the actual position or displacement of the execution part by detecting the rotation angle of the motor or screw, and then feed back to the numerical control system. The accuracy is higher than that of 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. At present, most numerical control machine tools widely use this semi-closed loop feed servo system, and the moving parts of machine tools with large 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 control is carried out according to the difference value, so that the moving parts move according to the actual requirements, finally, accurate positioning is realized. (Figure/text http://www . wxdtc. com /)
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