1. The CNC machine tool is generally composed of input and output equipment, numerical control device (CNC), servo unit, driving device (or executive mechanism), programmable controller (PLC) and electrical control device, auxiliary device, machine tool body and measuring device.
(1) input and output devices of CNC machine tool factory.
It is an interactive equipment for machine tool numerical control system and operators to exchange information and realize man-machine dialogue.
The function of the input device is to change the numerical control code on the program carrier into the corresponding electric pulse signal and transmit it into the coexisting population control device.
At present, the input devices of CNC machine tools include keyboard, disk drive, photoelectric reader and so on, and the corresponding program carriers are disk and perforated paper tape.
The output device is a display, and there are two kinds of CRT display or color liquid crystal display.
The function of the output device is that the numerical control system provides the necessary information for the operator through the display.
The information displayed can be the program being edited, coordinate values, alarm signals and so on.
(2) numerical control device (CNC device).
It is the core of computer numerical control system, which is composed of hardware and software.
It receives the pulse signal from the input device, which is compiled, calculated and logically processed by the system software or logic circuit of the numerical control device, and then outputs all kinds of signals and instructions to control all parts of the machine tool. to make it act in a prescribed and orderly manner.
The most basic of these control signals are the feed speed, feed direction and displacement instructions of each axis (that is, the executive parts of the feed motion). There are also spindle speed change, commutation and start-stop signals, select and exchange tool command signals, control coolant and lubricating oil start and stop, control workpieces and machine tool parts to release and clamp.
The auxiliary instruction signal to control the indexing table transposition, etc.
The numerical control device mainly includes microprocessor (CPU), memory, local bus, peripheral logic circuit and interface with other components of the CNC system.
(3) programmable logic controller (PLC).
The CNC machine tool completes the control function through CNC and PLC. Among them, CNC mainly completes the functions related to digital operation and management, such as part program editing, interpolation operation, decoding, position servo control of tool movement and so on.
While PLC mainly completes some actions related to logic operation, it receives the CNC control code M (auxiliary function), S (spindle speed), T (tool selection, tool change) and other switch action information, decodes the switch action information, converts it into the corresponding control signal, and controls the auxiliary device to complete the corresponding switching action of the machine tool, such as clamping of the workpiece, tool replacement, coolant switch and other auxiliary actions.
It also receives instructions from the operation panel of the machine tool. On the one hand, it directly controls the action of the machine tool (such as manually operating the machine tool), on the other hand, it sends part of the instructions to the numerical control device for the control of the machining process.
In the FANUC system, the PLC specially used to control the machine tool is recorded as PMC, which is called the programmable machine tool controller.
(4) Servo unit.
The servo unit receives speed and displacement instructions from the numerical control device.
After being transformed and amplified by the servo unit, these instructions are transformed into the speed, direction and displacement of the feed movement of the machine tool through the driving device.
Therefore, the servo unit is the link between the numerical control device and the machine tool body, which amplifies the weak instruction signal from the numerical control device into the high-power signal to control the drive device.
The servo unit is divided into spindle unit and feed unit. As far as the system is concerned, the servo unit can be divided into open-loop pump system, semi-closed-loop system and closed-loop system.
(5) driving device.
The driving device changes the instruction signal amplified by the servo unit into mechanical motion, and drives the worktable of the machine tool through the mechanical connecting parts, so that the worktable can be accurately positioned or make strict relative motion according to the prescribed locus. The parts that meet the requirements of shape, size and precision are machined.
At present, the commonly used driving devices are DC servo motor and AC servo motor, and AC servo motor is gradually replacing DC servo motor.
The servo unit and the driving device are called the servo driving system, which is the power device of the machine tool. The instructions of the computer numerical control device are implemented by the servo driving system. The servo driving device includes the spindle drive unit (mainly controls the speed of the spindle) and the feed drive unit (mainly controls the speed and position of the feed system).
Servo drive system is an important part of CNC machine tools.
In a sense, the function of CNC machine tools mainly depends on the CNC device, and the performance of CNC machine tools mainly depends on the servo drive system.
(6) Machine tool body.
That is, the mechanical parts of CNC machine tools, including main motion parts, feed motion execution parts (worktable, drag plate and its transmission parts) and supporting parts (bed, column, etc.). It also includes auxiliary devices with the functions of cooling, lubrication, transposition and clamping.
CNC machine tools in machining centers also have tool libraries for storing tools and manipulators for exchanging cutters. The composition of mechanical parts of CNC machine tools is similar to that of ordinary machine tools.
Due to the requirements of high speed, high precision, large cutting parameters and continuous machining, the mechanical parts of CNC machine tools have higher requirements in precision, stiffness, vibration resistance and so on.
In addition, in order to ensure the full play of the function of CNC machine tools, there are some auxiliary systems, such as cooling system, lubrication system, hydraulic (or pneumatic) system, chip removal system, protection system and so on.
