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Basic composition, structure and basic principle of CNC machine tools

  1. Program compilation and program carrier

    CNC program is the work instruction for automatic processing of parts by CNC machine tools. Based on the process analysis of the processed parts, determine the relative position of the part coordinate system on the machine coordinate system, that is, the installation position of the part on the machine tool; the dimensional parameters of the relative movement between the tool and the part; the process route of part processing, the process parameters of cutting processing and the action of auxiliary devices, etc. After obtaining all the processing information such as the movement, size, and process parameters of the part, use the standard CNC code composed of text, numbers and symbols to compile the CNC program sheet for part processing according to the prescribed method and format. The work of compiling programs can be done manually; for parts with complex shapes, automatic programming (APT) or CAD/CAM design should be performed on a dedicated programming machine or general-purpose computer.

    The compiled CNC program is stored on a storage carrier that is easy to input into the CNC device. It can be a punched paper tape, a magnetic tape, a disk, etc. Which storage carrier is used depends on the design type of the CNC device.

    1. Input device

    The function of the input device is to transfer the CNC code on the program carrier (information carrier) and store it in the CNC system. Depending on the different control storage media, the input device can be an optical reader, a tape drive or a floppy disk drive, etc. The CNC machine tool processing program can also be directly input into the CNC system manually through the keyboard; the CNC processing program can also be transmitted to the CNC system by the programming computer using RS232C or network communication.

    There are two different ways to input the part processing program: one is to read and process at the same time (when the memory of the CNC system is small), and the other is to read the entire part processing program into the internal memory of the CNC device at one time, and then call it out from the internal memory section by section for processing during processing.

    1. CNC device

    The CNC device is the core of the CNC machine tool. The CNC device takes out or receives one or several sections of the CNC processing program sent by the input device from the internal memory, and after compilation, calculation and logical processing by the logic circuit or system software of the CNC device, it outputs various control information and instructions to control the work of various parts of the machine tool, so that it can perform the prescribed orderly movement and action.

    The contour graphics of the part are often composed of straight lines, arcs or other non-arc curves. During the processing process, the tool must move according to the requirements of the shape and size of the part, that is, move according to the graphic trajectory. However, the input part processing program can only be the data such as the starting point and end point coordinate values ​​of each line segment trajectory, which cannot meet the requirements. Therefore, trajectory interpolation is required, that is, “data point densification” is performed between the starting point and end point coordinate values ​​of the line segment, and the coordinate values ​​of a series of intermediate points are obtained. The pulse signal is output 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).

    1. Drive device and position detection device

    The drive device receives the command information from the CNC device, and after power amplification, it drives the moving parts of the machine tool strictly in accordance with the requirements of the command 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 affecting the processing accuracy, surface quality and productivity of CNC machine tools. The drive device includes two major parts: the controller (including the power amplifier) ​​and the actuator. At present, most DC or AC servo motors are used as actuators.

    The position detection device detects the actual displacement of each coordinate axis of the CNC machine tool, and after inputting it into the CNC device of the machine tool through the feedback system, the CNC device compares the actual displacement value fed back with the set value, and controls the drive device to move according to the command set value.

    V. Auxiliary control device

    The main function of the auxiliary control device is to receive the switch command signal output by the CNC device, compile, logically judge and move, and then drive the corresponding electrical appliances after power amplification, driving the mechanical, hydraulic, pneumatic and other auxiliary devices of the machine tool to complete the switch action specified by the command. These controls include speed change, reversing and start-stop instructions for the spindle moving parts, tool selection and exchange instructions, start and stop of cooling and lubrication devices, loosening and clamping of workpieces and machine tool parts, indexing and indexing of indexing tables and other switch auxiliary actions.

    Due to the characteristics of fast response, reliable performance, easy to use, program and modify programs, and direct start of machine tool switches, programmable logic controllers (PLCs) are now widely used as auxiliary control devices for CNC machine tools.

    VI. Machine Tool Body

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

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