The basic components of the processing technology system of CNC machine tools include processing program carriers, CNC devices, servo drive devices, machine tool main bodies and other auxiliary devices.
When the processing program carrier CNC machine tool is working, workers do not need to directly operate the machine tool. To control the CNC machine tool, a high-speed CNC machine tool must prepare a processing program. The part processing program includes the relative motion trajectory of the machine tool and the workpiece, process parameters (feed amount, spindle speed, etc.) and auxiliary motion, etc. The part processing program is stored in a certain format and code on a program carrier, such as punched paper tape, cassette tape, floppy disk, etc., and the program information is input into the CNC unit through the input device of the CNC machine tool. CNC device CNC device is the core of CNC machine tools. Modern CNC devices all adopt the form of CNC (Computer Numerical Control). This CNC device generally uses multiple microprocessors to implement CNC functions in the form of programmed software, so it is also called Software NC.
The CNC system is a position control system that interpolates the ideal motion trajectory based on input data, and then outputs it to the execution component to process the required parts. Therefore, the CNC device is mainly composed of three basic parts: input, processing and output. All these tasks are rationally organized by the computer system program so that the entire system works in a coordinated manner.
1) Input device: Input CNC instructions to the CNC device. Depending on the program carrier, there are different input devices. Mainly include keyboard input, disk input, CAD/CAM system direct communication input and DNC (direct numerical control) input connected to the superior computer. There are still many systems that still retain the paper tape input form of photoelectric readers.
(1) Paper tape input method. You can use a paper tape photoelectric reader to read the part program and directly control the movement of the machine tool. You can also read the contents of the paper tape into the memory and use the part program stored in the memory to control the movement of the machine tool.
(2) MDI manual data input method. The operator can use the keyboard on the operation panel to input instructions for the processing program, which is suitable for relatively short programs. In the editing state (EDIT) of the control device, use software to input the processing program and store it in the memory of the control device. This input method can reuse the program. This method is generally used in manual programming. On a CNC device with conversational programming function, you can select different menus according to the questions prompted on the display, use human-machine dialogue method, enter the relevant size figures, and the processing program can be automatically generated.
(3) Adopt DNC ??direct numerical control input method. The part program is saved in the superior computer, and the CNC system receives subsequent program segments from the computer while processing.
The DNC method is mostly used when complex workpieces are designed using CAD/CAM software and part programs are directly generated.
2) Information processing: The input device transmits the processing information to the CNC unit and compiles it into information that can be recognized by the computer. The information processing part gradually stores and processes it according to the provisions of the control program, and then passes the output unit Send position and speed commands to the servo system and main motion control part. The input data of the CNC system includes: the contour information of the part (starting point, end point, straight line, arc, etc.), processing speed and other auxiliary processing information (such as tool change, speed change, coolant switch, etc.). The purpose of data processing is to complete the insertion Preparatory work before complement 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 accepts 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. After power amplification, it drives the servo system to control the movement of the machine tool according to the specified requirements. Servo and measurement feedback system The servo system is an important part of CNC machine tools and 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 CNC device into linear displacement or angular displacement motion of the machine tool execution 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 accuracy and speed of the CNC machine tool and other technical indicators. Therefore, the servo drive device of the CNC machine tool is required to have good rapid response performance and accurately and sensitively track the CNC device. The digital command signal sent out can faithfully execute the instructions from the CNC device, improving the dynamic following characteristics and static tracking accuracy of the system. The servo system consists of two parts: the driving device and the actuator. The driving device consists 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 drive devices. The measuring element detects the actual displacement value of each coordinate axis of the CNC machine tool and inputs 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 command value, and outputs to the servo system the set value. The required displacement instruction. Main body of machine tool The main body of machine tool is the main body of CNC machine tool. It includes mechanical components such as bed, base, columns, beams, slides, worktables, spindle boxes, feed mechanisms, tool rests, and automatic tool changers. It is a mechanical part that automatically completes various cutting processes 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 stiffness, high earthquake resistance and small thermal deformation. Methods such as improving the static stiffness of the structural system, increasing damping, adjusting the mass and natural frequency of structural parts are usually used to improve the stiffness and earthquake resistance of the machine tool main body, so that the machine tool main body can adapt to the needs of CNC machine tools for continuous and automatic cutting processing. Taking measures such as improving the structural layout of the machine tool, reducing heat generation, controlling temperature rise, and using thermal displacement compensation can reduce the impact of thermal deformation on the main machine tool.
2) Extensive use of high-performance spindle servo drives and feed servo drives shortens the transmission chain of CNC machine tools and simplifies the structure of the machine tool's mechanical transmission system.
3) Use high transmission efficiency, high precision, and gap-free transmission devices and moving parts, such as ball screw nut pairs, plastic sliding guide rails, linear rolling guide rails, static pressure guide rails, etc.