The composition and working principle of CNC machine tools

The composition and working principle of CNC machine tools

 The numerical control machine tool is composed of several parts such as programming and program carrier, input device, numerical control device (CNC), servo drive and position detection, auxiliary control device, and machine tool body.

 1. Programming and program carrier
 Numerical control program is the work instruction of CNC machine tool to automatically process parts.  Based on the process analysis of the machined parts, determine the relative position of the part coordinate system on the machine tool coordinate system, that is, the installation position of the part on the machine tool; the size parameters of the relative movement of the tool and the part; the process route and cutting processing of the part processing  The process parameters and the actions of auxiliary devices.  After obtaining all the processing information of the part's movement, size, process parameters, etc., use the standard CNC code composed of text, numbers and symbols to compile the CNC program sheet for the part processing according to the specified method and format.  The work of programming can be done manually; for parts with complex shapes, automatic programming (APT) or CAD/CAM design should be carried out on a dedicated programming machine or a general-purpose computer.
 The compiled numerical control program is stored in a storage carrier that is convenient for input to the numerical control device. It can be perforated paper tape, magnetic tape, and disk. Which storage carrier is used depends on the design type of the numerical control device.

 2. Input device
 The function of the input device is to transfer and store the numerical control code on the program carrier (information carrier) into the numerical control system.  Depending on the control storage medium, the input device can be an optoelectronic reader, tape drive, or floppy disk drive.  Numerical control machine tool processing programs can also be directly input into the numerical control system manually through the keyboard; the numerical control processing programs can also be transmitted to the numerical control system by the programming computer using RS232C or using network communication.
 There are two different ways to input the part processing program: one is to read in while processing (when the memory of the numerical control system is small), and the other is to read all the part processing programs into the internal memory of the numerical control device at a time, and then from  The internal memory is called section by section for processing.

 3. Numerical control device
 The CNC device is the core of the CNC machine tool.  The numerical control device fetches or accepts one or several sections of numerical control processing program sent by the input device from the internal memory. After the logic circuit or system software of the numerical control device is compiled, calculated and logically processed, it outputs various control information and instructions to control the machine tool  The work of each part enables it to carry out prescribed and orderly movements and actions.
 The contour graphics of parts are often composed of straight lines, arcs or other non-arc curves, and the tool must move according to the requirements of the shape and size of the part during processing, that is, move according to the graphic trajectory.  However, the input part processing program can only be data such as the starting point and end point coordinate value of each line segment trajectory, which cannot meet the requirements. Therefore, the trajectory interpolation is required, that is, the "data point dense" is performed between the start point and end point coordinate value of the line segment.  Calculate the coordinate values of a series of intermediate points, and output pulse signals to the corresponding coordinates to control the feed speed, feed direction and feed displacement of each coordinate axis (that is, each actuator of the feed motion).

 Four, drive device and position detection device
 The driving device accepts the instruction information from the numerical control device, and after the power is amplified, it drives the moving parts of the machine tool in strict accordance with the requirements of the instruction information to process parts that meet the requirements of the drawing.  Therefore, its servo accuracy and dynamic response performance are one of the important factors that affect the machining accuracy, surface quality and productivity of CNC machine tools.  The driving device includes two parts: controller (including power amplifier) and actuator.  Currently, DC or AC servo motors are mostly used as actuators.
 The position detection device detects the actual displacement of each coordinate axis of the CNC machine tool. After the feedback system is input to the CNC device of the machine tool, the CNC device compares the feedback actual displacement value with the set value, and controls the drive device to set according to the instruction.  Fixed value sports.

 Five, auxiliary control device
 The main function of the auxiliary control device is to receive the switch quantity command signal output by the numerical control device, after compiling, logically discriminating and moving, and then driving the corresponding electrical appliances after power amplification, driving the mechanical, hydraulic, pneumatic and other auxiliary devices of the machine tool to complete the instructions specified  Switch action.  These controls include the speed change, reversing and start and stop commands of the moving parts of the spindle, the selection and exchange commands of the tools, the start and stop of the cooling and lubrication devices, the loosening and clamping of the workpiece and machine tool parts, the indexing table indexing  Wait for switch assist action.
 Because the programmable logic controller (PLC) has the characteristics of fast response, reliable performance, easy to use, programming and modification of the program, and can directly start the machine switch, it has been widely used as an auxiliary control device for CNC machine tools.

 Six, the machine tool body
 The machine tool body of a CNC machine tool is similar to a traditional machine tool, and consists of a spindle drive device, a feed drive device, a bed, a table, and auxiliary motion devices, a hydraulic pneumatic system, a lubrication system, and a cooling device.  However, the CNC machine tools have undergone great changes in the overall layout, appearance, transmission system, tool system structure and operating mechanism.  The purpose of this change is to meet the requirements of CNC machine tools and give full play to the characteristics of CNC machine tools.