A, numerical control system
It is the core of machine tool automatic processing. It is mainly composed of operating system, main control system, programmable controller and various output interfaces. Among them, the operating system consists of a display and a keyboard. There are many forms of displays, such as digital tubes, CRT and LCD. The main control system is similar to the computer motherboard, and is mainly composed of CPU, memory, controller and other parts. Numerical control system controls mechanical quantities such as position, angle and speed of general objects, as well as physical quantities such as temperature, pressure and flow.
Its control methods can be divided into two categories: data processing control and sequential logic control. According to the read part program, the interpolation operation module in the main controller performs the corresponding tool path interpolation operation after decoding, compiling and other information processing, and controls the displacement of each coordinate axis of the machine tool by comparing with the position and speed feedback signals of each coordinate servo system. Sequential logic control is usually mainly completed by programmable controller PLC, which is coordinated according to the requirements of various actions in the machining process of machine tools, and logically judged according to the detection signals, thus controlling the orderly work of all parts of machine tools.
Second, the servo system
It is the electrical transmission link between CNC system and machine tool body. It is mainly composed of servo motor, drive control system and position detection feedback device. Servo motor is the executive part 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, which is amplified by the power transmission system of the drive control system to drive the motor to run, and the workbench or tool rest is dragged by the mechanical transmission device to move.
Servo system is an important part of CNC machine tools, which is used to realize feed servo control and spindle servo control of CNC machine tools. The function of the servo system is to convert the command information received from the numerical control device into linear displacement or angular displacement of the execution part of the machine tool after power amplification and shaping. Servo system is the last link of CNC machine tools, and its performance will directly affect the accuracy and speed of CNC machine tools and other technical indicators. Therefore, the servo drive device of CNC machine tools is required to have good fast response performance, accurately and sensitively track the digital instruction signals sent by CNC machine tools, and faithfully execute the instructions sent by CNC machine tools, so as to improve the dynamic tracking characteristics and static tracking accuracy of the system.
The servo system consists of two parts: the driving device and the executing mechanism. The driving device consists of a spindle driving unit, a feed driving unit, a spindle servo motor and a feed servo motor. Stepper motor, DC servo motor and AC servo motor are commonly used driving devices.
The measuring element detects the actual displacement values of each coordinate axis of the NC machine tool and inputs them into the NC device of the machine tool through the feedback system. The NC device compares the feedback actual displacement value with the command value, and outputs the displacement command needed to reach the set value to the servo system.
Third, the processing program carrier
When CNC machine tools are working, it is not necessary for workers to directly operate the machine tools. To control CNC machine tools, machining programs must be compiled. The machining program of parts includes the relative motion trajectory of cutter and workpiece on the machine tool, process parameters (feed speed, spindle speed, etc.). ) and auxiliary exercise. Parts processing program is stored in a program carrier with a certain format and code, such as punched paper tape, cassette tape, floppy disk, etc. And the program information is input to the CNC unit through the input device of the CNC machine tool.
Fourth, the numerical control device
Numerical control device is the core of numerical control machine tool. Modern numerical control devices all adopt the form of CNC(ComputerNumericalControl), and generally use multiple microprocessors to realize numerical control functions in the form of programming software, so it is also called SoftwareNC. Numerical control system is a position control system, which interpolates the ideal motion trajectory according to the input data, and then outputs it to the executive parts to process the required parts. Therefore, the numerical control device is mainly composed of three basic parts: input, processing and output. All these tasks are reasonably organized by computer system programs, so that the whole system can work harmoniously.
1. Input device: input numerical control instructions to numerical control devices, and there are different input devices according to different program carriers. There are mainly keyboard input, disk input, direct communication input of CAD/CAM system and DNC (direct numerical control) input connected to the upper computer. At present, many systems still keep the paper tape input form of photoelectric readers.
(1) paper tape input mode. The paper tape photoelectric reader can be used to read the part program and directly control the movement of the machine tool. It can also read the paper tape content into the memory and control the movement of the machine tool with the part program stored in the memory.
(2)MDI manual data input mode. The operator can use the keyboard on the operation panel to input the instructions of the machining program, which is suitable for shorter programs.
In the editing state of the control device, the machining program is input by software and stored in the memory of the control device. This input method can reuse the program. This method is generally used for manual programming.
On the NC equipment with session programming function, different menus can be selected according to the questions prompted on the display, and the relevant size numbers can be input through man-machine dialogue to automatically generate the machining program.
(3) DNC direct numerical control input mode is adopted. The part program is stored in the upper computer, and the NC system receives the subsequent program segments from the computer while machining. DNC mode is mostly used for complex workpieces designed by CAD/CAM software, which directly generates part programs.
2. Information processing: the input device transmits the machining information to the CNC unit and compiles it into information that can be recognized by the computer. The information processing part stores and processes it step by step according to the provisions of the control program, and then sends the position and speed instructions to the servo system and the main motion control part through the output unit. The input data of numerical control system includes: contour information of parts (starting point, ending point, straight line, arc, etc. ), machining speed and other auxiliary machining information (such as tool change, speed change, coolant switch, etc.). ). The purpose of data processing is to complete the preparatory work before interpolation operation. The data processing program also includes tool radius compensation, speed calculation and auxiliary function processing.
3. Output device: the output device is connected with the servo mechanism. The output device receives the output pulse of the arithmetic unit according to the instruction of the controller and sends it to the servo control system of each coordinate. After power amplification, the servo system is driven to control the machine tool to move according to the specified requirements.
Verb (abbreviation for verb) main transmission system
It is one of the main components that transmit torque in the cutting process of machine tools. Generally divided into gear stepless speed regulation and electrical stepless speed regulation. High-grade CNC machine tools require stepless speed regulation to meet the requirements of various processing technologies. It is mainly composed of spindle drive control system, spindle motor and spindle mechanical transmission mechanism.
Six, high voltage control cabinet
It is mainly used to install various electrical components for high-voltage control of machine tools. In addition to providing input power for weak current control systems such as numerical control and servo, as well as various electrical protections such as short circuit, overload and undervoltage, it is mainly used as a bridge between the output interface of programmable controller PLC and the electrical executive components of various auxiliary devices of machine tools, that is, various AC motors, solenoid valves or electromagnetic clutches that control the auxiliary devices of machine tools, which mainly play a role in expanding contact dispersion and contact capacity.
In addition, it is also connected with the related manual buttons on the machine tool console. The high-voltage control cabinet consists of various intermediate relays, contactors, transformers, power switches, terminals and various electrical protection elements. Similar to ordinary machine tools, but in order to improve the anti-interference of weak current control system, it is required that various electromagnetic induction devices such as motors and contactors that are frequently started or switched must be connected in parallel with RC resistance-capacitance absorbers, and various detection signals should be connected with shielded cables.
Seven. ancillary equipment
It mainly includes ATC tool automatic exchange mechanism, APC workpiece automatic conversion mechanism, workpiece clamping and loosening mechanism, turntable, hydraulic control system, lubricating device, overload and limit protection functions, etc. The machining function of machine tools is different from that of Xing Xing, and the parts included are also different. In order to ensure the full play of the functions of CNC machine tools, auxiliary equipment is essential. Commonly used auxiliary devices include: pneumatic and hydraulic devices, chip removal devices, cooling and lubricating devices, rotary tables and numerical control indexing heads, protection, lighting and other auxiliary devices.
Eight, machine tool body
Refers to the mechanical structure entity of CNC machine tools. Compared with the traditional common machine tool, it is also composed of main transmission mechanism, feed transmission mechanism, workbench, lathe bed and column, but the overall layout, appearance modeling, transmission mechanism, tool system and operating mechanism of CNC machine tools have changed greatly. The purpose of this change is to adapt to the requirements of CNC technology and give full play to the characteristics of CNC machine tools.
Machine tool host is the main body of CNC machine tools. It comprises a lathe bed, a base, an upright post, a cross beam, a sliding seat, a workbench, a spindle box, a feeding mechanism, a tool rest and an automatic tool changing device. It is a mechanical part that automatically completes all kinds of cutting processing on CNC machine tools. Compared with traditional machine tools, the main body of CNC machine tools has the following structural characteristics:
1. Adopt a new machine tool structure with high rigidity, high earthquake resistance and small thermal deformation. Usually, methods such as improving the static stiffness of structural system, increasing damping and adjusting the mass and natural frequency of structural parts are used to improve the stiffness and seismic capacity of machine tool body, so that the machine tool body can meet the needs of continuous automatic cutting of CNC machine tools. The influence of thermal deformation on the main engine can be reduced by improving the structural layout of machine tools, reducing heating, controlling temperature rise and adopting thermal displacement compensation.
2. The wide application of high-performance spindle servo drive and feed servo drive device shortens the transmission chain of CNC machine tools and simplifies the structure of mechanical transmission system of machine tools.
3. Adopt transmission devices and moving parts with high transmission efficiency, high precision and no clearance, such as ball screw nut pair, plastic sliding guide rail, linear rolling guide rail and hydrostatic guide rail.