Maintenance and transformation technology of the h

2022-08-16
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NC machine tool maintenance and transformation technology

practice without theoretical guidance is blind practice, and theory without practice is empty theory. There are tens of thousands of engineering and technical personnel engaged in the electrical design, application and maintenance technology of CNC machine tools in China. However, due to the complexity, diversity and variability of this technology and the constraints of some objective environmental factors, a mature and complete theoretical system has not been formed in the electrical maintenance technology of CNC machine tools. Nowadays, with the rapid development of control theory and automation technology, especially the rapid development of microelectronics technology and computer technology, CNC technology is also developing synchronously and rapidly. The PC based, open and diversified, complex and high intelligent structure of CNC system has not only brought great changes to its application from concept to practice, but also brought great changes to its maintenance theory, technology and means. Therefore, it is impossible for an article in the form of a lecture to completely express the electrical maintenance technology theory of CNC machine tools, which has formed a special discipline. This paper only summarizes and sorts out the experience of many years of practical exploration and colleagues in the industry, in order to benefit the development of the theory of this discipline and the practice of engineering technicians

first, when it comes to maintenance, we must first understand our maintenance objects in general. 1. Overview of the electrical control system of CNC machine tools. The entire electrical control system of a typical CNC machine tool is shown in Figure 1

(1) data input device is a necessary device to input command information and various application data into the CNC system. It can be a perforated tape reader (rarely used), a 3.5in floppy disk drive, a CNC keyboard (general input operation), a hard disk and drive device equipped with a CNC system (for the storage and protection of a large amount of data), a tape drive (rarely used), a PC computer, etc

(2) the center of CNC machine tool of CNC system, which decodes and calculates all the received function instructions, and then sends out various required motion instructions and control instructions of various machine tool functions in an orderly manner until the end of motion and functions. CNC systems have perfect self diagnosis ability. In daily use, we should pay more attention to the strict operation according to the regulations, and the daily maintenance is mainly to protect the hardware use environment and prevent the system software from being broken and stored and data processing

(3) the programmable logic controller is the logic control center of all functions of the machine tool. It logically sorts all kinds of motion and function instructions from CNC, so that they can operate accurately, harmoniously and orderly; At the same time, all kinds of information and working status from the machine tool are transmitted to the CNC, so that the CNC can send further control instructions in time and accurately, so as to realize the control of the whole machine tool. Contemporary PLC is mostly integrated in CNC system, which mainly refers to the integration of control software, while PLC hardware often adopts distributed structure in large-scale systems. The integration of PLC and CNC is realized by software interface. Generally, the system assigns various communication information between them to their fixed storage addresses respectively, and the system monitors the information status of all addresses in real time, analyzes and judges according to the current status of each interface signal, and then makes further control commands to complete the control of motion or function. PLCs from different manufacturers have different PLC languages and different language expressions. Therefore, the premise of trying to be familiar with the PLC program of a machine tool is to be familiar with the PLC language of the machine tool first

(4) the spindle drive system receives the drive command from the CNC, outputs the drive signal to drive the main motor to rotate through speed and torque (power) adjustment, and receives speed feedback to implement speed closed-loop control. It also notifies CNC of various actual working states of the spindle through PLC to complete the control of various functions of the spindle. The spindle drive system itself has many parameter settings, which directly affect the rotation characteristics of the spindle, some of which cannot be lost or changed, such as the parameters indicating the motor specifications, and some of which can be adjusted according to the operating state, such as zero drift, etc. Generally, CNC also has machine tool data related to the spindle, which has the same function as the parameters of the spindle drive system. Therefore, pay attention to choose one of the two and do not conflict

(5) the feed servo system receives the speed command provided by the CNC for each moving coordinate axis, outputs the drive signal to drive the servo motor to rotate through the speed and current (torque) adjustment, realizes the movement of the machine tool coordinate axis, and receives the speed feedback signal to implement the speed closed-loop control. It also communicates with CNC through PLC to report the current working state and accept the control of CNC. The correct adjustment of the speed regulator of the feed servo system is the most important. The optimal adjustment should be made under the condition of open-loop position, which not only does not rush, but also maintains certain hard characteristics. It is restricted by the mechanical characteristics of the coordinate axis of the machine tool. Once the state of the guide rail and the mechanical transmission chain changes, the speed loop regulator needs to be readjusted

(6) with the non extrusion of PLC functions, electrical hardware circuits can be cut off by technology suppliers. The main tasks of electrical hardware circuits are power generation and control circuits, isolation relay parts and various executive appliances (relays, contactors), and few relay logic circuits exist. However, some imported machine tool cabinets also use special combined relays with certain logic control. Once such components fail, in addition to replacement, they can also be removed and replaced by PLC logic. However, this requires not only a clear understanding of the working principle of the special electrical appliance, but also a deep understanding of the PLC language and program of the machine tool

(7) the machine tool (electrical part) includes all motors and solenoid valves, which generate great friction between the upper and lower end faces and the support of the experimental machine, brakes, various switches, etc. They are the executors of various actions of machine tools and the reporters of various realistic states of machine tools. Most of the possible main faults here are the damage of the electrical parts themselves and the disconnection or fracture of the connecting wires and cables. (8) Speed measurement is usually completed by the tachometer assembled in the spindle and feed motor. It matches the actual speed of the motor into a voltage value and sends it back to the servo drive system as a speed feedback signal, which is compared with the commanded speed voltage value, so as to realize the accurate control of speed. Pay attention to the matching connection of the speed measurement feedback voltage here, and do not disassemble the speed measurement machine. The speed out of control caused by this is mostly caused by the reverse connection or disconnection of the speed measurement feedback line

(9) position measurement earlier machine tools used linear or circular synchronous sensors or rotary transformers, while modern machine tools mostly used grating ruler and number

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