Basic composition and working principle of CNC machine tools

CNC machine tool is the abbreviation of digital control machine tool, which is an automatic machine tool with program control system. The control system is capable of logically processing a program having control code or other symbolic instruction specifications, decodes it, and uses a coded digital representation to input the numerical control device through the information carrier. Through the arithmetic processing, various control signals are issued by the numerical control device to control the movement of the machine tool, and the parts are automatically processed according to the shape and size required by the drawings. Titanium Machinery is the main product of the company with rotary top, screw, shaft machining, CNC lathe machining, shank shank and collet post. CNC machine tools have solved complex, precise, small batch and multi-variety. The problem of part processing is a flexible and high-efficiency automatic machine tool, which represents the development direction of modern machine tool control technology and is a typical mechatronic product. CNC machine tools generally consist of a numerical control system, a servo system including a servo motor and a detection feedback device, a main drive system, a high-power control cabinet, a machine tool body, and various auxiliary springs. The dotted line can be used to indicate the basic working process of CNC machining. For CNC machine tools with different functions, the components are slightly different. First, the CNC system It is the core of automatic machining of machine tools. It mainly consists of operating system, main control system, programmable controller and various output interfaces. The operating system consists of a display and a keyboard, and the display has various forms such as a digital tube, a CRT, and a liquid crystal. The main control system is similar to the computer motherboard, and is mainly composed of a CPU, a memory, a controller, and the like. The numerical control system controls the mechanical quantity such as the position, angle and speed of the general object, as well as the physical quantities such as temperature, pressure and flow. The control method can be divided into two categories: data operation processing control and sequential logic control. The interpolation operation module in the main controller is processed according to the read part program, through decoding, compiling and other information processing. The tool path is interleaved and controlled, and the displacement of each coordinate axis of the machine tool is controlled by comparing with the position and speed feedback signals of each coordinate servo system; and the sequential logic control is usually mainly performed by the programmable controller PLC, which is based on the machine tool. Each action in the machining process requires coordination, and logical determination is performed according to each detection signal, thereby controlling the various components of the machine tool to work in an orderly manner. Second, the servo system It is the electric drive connection between the CNC system and the machine body. Mainly composed of servo motor, drive control system and position detection feedback device. The servo motor is the actuator of the system, and the drive control system is the power source of the servo motor. The command signal generated by the numerical control system is compared with the position detection feedback signal as a displacement command, and then driven by the drive control system to drive the motor to operate, thereby dragging the table or the tool holder to move through the mechanical transmission device. The servo system is an important part of the CNC machine tool, which is used to realize the feed servo control and spindle servo control of CNC machine tools. The function of the servo system is to accept the command information from the numerical control device, and then convert it into linear displacement or angular displacement motion of the machine tool executing component after power amplification and shaping processing. Since the servo system is the last link of the CNC machine tool, its performance will directly affect the technical indexes such as the precision and speed of the CNC machine tool. Therefore, the servo drive device of the CNC machine tool is required to have good fast response performance, and accurately and sensitively track the numerical control device. The digital command signal is sent and the instructions from the numerical control device can be faithfully executed to improve the dynamic follow-up characteristics and static tracking accuracy of the system. The servo system consists of two parts: the drive unit and the actuator. The drive unit is composed of a spindle drive unit, a feed drive unit, a spindle servo motor, and a feed servo motor. Stepper motors, DC servo motors and AC servo motors are commonly used drives. The measuring component detects the actual displacement value of each coordinate axis of the CNC machine tool and inputs it into the numerical control device of the machine tool through the feedback system. The numerical control device compares the actual displacement value returned by the numerical control device with the command value, and outputs the set value to the servo system. The required displacement command. Third, the processing program carrier When the CNC machine is working, it is not necessary for the worker to directly operate the machine tool. To control the CNC machine tool, the machining program must be programmed. The part processing program includes the relative motion trajectory of the tool and the workpiece on the machine tool, the process parameters (feedrate spindle speed, etc.) and auxiliary motion. Titanium Machinery is the main product of the company with rotary top, screw, shaft machining, CNC lathe machining, shank shank and collet post. The part processing program is stored in a program carrier with a certain format and code. On the top, such as punched paper tape, cassette tape, floppy disk, etc., the program information is input to the CNC unit through the input device of the numerical control machine tool. Fourth, numerical control device The numerical control device is the core of the CNC machine tool. Modern numerical control devices are all in the form of CNC (Computer Numerical Control). This CNC device generally uses multiple microprocessors to implement numerical control functions in the form of programmed software. Therefore, it is also called Software NC. The CNC system is a position control system that interpolates the ideal motion trajectory based on the input data and outputs it to the parts required to machine the actuator. Therefore, the numerical control device mainly consists of three basic parts: input, processing and output. All of this work is reasonably organized by the computer’s system program, allowing the entire system to work in harmony. 1. Input device: The numerical control command is input to the numerical control device, and according to different program carriers, there are different input devices. There are mainly keyboard input, disk input, CAD/CAM system direct communication mode input and DNC (direct digital control) input to the upper computer. There are still many systems that still have the paper tape input form of the optical reader. (1) Paper tape input method. The paper tape photoelectric reader can be used to read the part program, directly control the movement of the machine tool, or read the contents of the paper tape into the memory, and control the movement of the machine tool by using the part program stored in the memory. (2) MDI manual data input method. The operator can use the keyboard on the operation panel to input the instructions of the machining program, which is suitable for relatively short programs. In the control device edit state (EDIT), the machining program is input into the memory and stored in the memory of the control device. This input method can be used repeatedly. This method is generally used for manual programming. On the numerical control device with session programming function, different menus can be selected according to the prompts on the display, and the machining program can be automatically generated by inputting the relevant size numbers by means of human-machine dialogue. (3) Adopt DNC ​​direct numerical control input mode. The part program is saved in the upper computer, and the CNC system receives the subsequent block from the computer while processing. The DNC method is mostly used for complex workpieces designed with CAD/CAM software and directly generates part programs. 2. Information processing: the input device transmits the processing information to the CNC unit, and compiles it into a computer-recognizable information. The information processing part gradually stores and processes the information according to the control program, and then sends the position and speed command to the servo through the output unit. System and main motion control section. The input data of the CNC system includes: contour information of the part (starting point, end point, straight line, arc, etc.), machining speed and other auxiliary machining information (such as tool change, shifting, coolant switch, etc.). The purpose of data processing is to complete the insertion. Preparation before the complement operation. The data processing program also includes tool radius compensation, speed calculation, and processing of auxiliary functions. 3. Output device: The output device is connected to the servo mechanism. The output device receives the output pulse of the arithmetic unit according to the command of the controller, and sends it to the servo control system of each coordinate, and drives the servo system through power amplification, thereby controlling the machine tool to move according to the specified requirements. Fifth, the main drive system It is one of the main components for transmitting torque during machine tool cutting. Generally, it is divided into two types: gear stepped speed change and electric stepless speed regulation. Higher grade CNC machine tools require stepless speed regulation to meet various machining process requirements. It mainly consists of spindle drive control system, spindle motor and spindle. Mechanical transmission mechanism and other components. Sixth, strong electric control cabinet It is mainly used to install various electrical components for machine tool power control. In addition to providing input power for numerical control, servo and other weak current control systems, as well as various short-circuit, overload, undervoltage and other electrical protection, mainly in programmable controllers. The output interface of the PLC is connected with the electrical execution components of various auxiliary devices of the machine tool, that is, various AC motors, hydraulic system solenoid valves or electromagnetic clutches for controlling the auxiliary devices of the machine tool, mainly for expanding the joints and expanding the contacts. Contact capacity and so on. In addition, it is also connected to the manual control button of the machine table. The power control cabinet consists of various intermediate relays, contactors, transformers, power switches, terminal blocks and various types of electrical protection components. It is similar to the general ordinary machine tool electrical, but in order to improve the anti-interference of the weak current control system, it is required that all kinds of electromagnetic induction devices such as motors and contactors that are frequently started or switched must be connected to the RC RC absorber. The input of the detection signal requires a shielded cable connection. Seven, auxiliary equipment It mainly includes ATC knife automatic exchange mechanism, APC workpiece automatic change mechanism, workpiece clamping and relaxation mechanism, rotary table, hydraulic control system, lubrication device, overload and limit protection functions. Machine tool processing functions are different from those of Xingxing, and the parts included are different. The auxiliary device is the necessary device to ensure the full play of the functions of the CNC machine tool. The commonly used auxiliary devices include: pneumatic, hydraulic device, chip removal device, cooling, lubrication device, rotary table and numerical control indexing head, protection, lighting, etc. assisting equipments. Eight, machine body It refers to the mechanical structure of CNC machine tools. Compared with the traditional ordinary machine tool, it is also composed of the main transmission mechanism, the feed transmission mechanism, the work table, the bed and the column, but the overall layout, appearance, transmission mechanism, knife system and operating mechanism of the CNC machine tool. There have been great changes in the aspects. The purpose of this change is to meet the requirements of CNC technology and give full play to the characteristics of CNC machine tools. The machine host is the main body of the CNC machine. It includes mechanical components such as bed, base, column, beam, slide, table, headstock, feed mechanism, tool holder and automatic tool changer. Titanium Machinery is the main product of the company with rotary top, screw, shaft machining, CNC lathe machining, shank shank and collet post. It is the mechanical part that automatically completes various cutting operations on CNC machine tools. Compared with traditional machine tools, the main body of CNC machine tools has the following structural features: 1. Adopt new machine tool structure with high rigidity, high shock resistance and small thermal deformation. Generally, the stiffness and shock resistance of the machine tool main body are improved by improving the static stiffness of the structural system, increasing the damping, adjusting the quality of the structural member and the natural frequency, so that the machine tool body can adapt to the need for the CNC machine tool to continuously and automatically perform the cutting process. Measures such as improving machine structure layout, reducing heat generation, controlling temperature rise, and using thermal displacement compensation can reduce the impact of thermal deformation on the machine tool host. 2. The high-performance spindle servo drive and feed servo drive are widely used to shorten the drive chain of the CNC machine tool and simplify the structure of the machine tool drive system. 3. Adopt high transmission efficiency, high precision, gapless transmission and moving parts, such as ball screw nut pair, plastic sliding guide, linear rolling guide, static pressure guide and so on.