The servo system is the actuator that translates numerical control information into the feed motion of the machine tool. CNC machine tools combine the advantages of traditional automatic machine tools, precision machine tools and universal machine tools, integrating high efficiency, high precision and high flexibility. The improvement of the technical level of numerically-controlled machine tools mainly depends on the improvement of feed and spindle drive characteristics and the expansion of functions. For this reason, numerical control machine tools have a high level of position control, speed control, servo motors, and mechanical transmission for feed servo systems. The request.
Due to the different processing tasks performed by various CNC machine tools, their requirements for the feed servo system are not the same, but they can generally be summarized as the following aspects.
1. Reversible operation of CNC machine tools. Reversible operation requires flexible forward and reverse operation. During the machining process, the machine tool table is in a random state. According to the requirements of the machining trajectory, forward or reverse movement may be achieved at any time. At the same time, it is required that there should be no backlash and loss of motion when the direction changes. From the energy point of view, the reversible conversion of energy should be realized, that is, the motor absorbs energy from the grid into mechanical energy during the process of operation: when braking, the mechanical inertial energy of the motor should be converted into electrical energy and fed back to the grid for rapid braking. .
2. The wide speed range of CNC machine tools. In order to adapt to different processing conditions, such as the material, type, size, and location of the machined part, the type of the tool, and the cooling method, the feed of the CNC machine tool can be steplessly changed over a wide range. This requires the servo motor has a wide range of speed and excellent speed regulation. After mechanical transmission, the range of change of motor speed can be converted into the range of feed speed. The current state-of-the-art level is that the feed rate is continuously adjustable from 0 to 240 u/min with a feed pulse equivalent of 1 pm.
For general CNC machine tools, the feed speed range of 0 to 24m/min can meet the processing requirements. Usually in this way, the speed is reduced. At zero speed, when the table stops moving, the motor is required to have electromagnetic torque to maintain the positioning accuracy, so that the position servo system is composed of two parts: the speed control unit and the position control link. If the speed control system is also excessively pursuing a speed range that is as large as the position servo control system and it is to work reliably and stably, then speed is generally speaking, for a position control system with a feed speed range of 1:20 000. When the total open-loop position gain is 20-1, as long as the speed control unit has a 1:1 000 speed range, it can meet the needs, which can make the speed control unit circuit simple and reliable. Of course, on behalf of the advanced level of the experimental system in the world today, the speed control unit has reached a speed range of 1:100000.
This requires that the servo system has excellent static and dynamic load characteristics, that is, the servo system should keep the feed speed constant under different load conditions or when cutting conditions change. For a rigid system, the speed is affected little by the changes in load torque. Generally required to withstand the rated torque changes, the static speed drop should be less than 5%, dynamic speed drop should be less than 10%.
Due to the different processing tasks performed by various CNC machine tools, their requirements for the feed servo system are not the same, but they can generally be summarized as the following aspects.
1. Reversible operation of CNC machine tools. Reversible operation requires flexible forward and reverse operation. During the machining process, the machine tool table is in a random state. According to the requirements of the machining trajectory, forward or reverse movement may be achieved at any time. At the same time, it is required that there should be no backlash and loss of motion when the direction changes. From the energy point of view, the reversible conversion of energy should be realized, that is, the motor absorbs energy from the grid into mechanical energy during the process of operation: when braking, the mechanical inertial energy of the motor should be converted into electrical energy and fed back to the grid for rapid braking. .
2. The wide speed range of CNC machine tools. In order to adapt to different processing conditions, such as the material, type, size, and location of the machined part, the type of the tool, and the cooling method, the feed of the CNC machine tool can be steplessly changed over a wide range. This requires the servo motor has a wide range of speed and excellent speed regulation. After mechanical transmission, the range of change of motor speed can be converted into the range of feed speed. The current state-of-the-art level is that the feed rate is continuously adjustable from 0 to 240 u/min with a feed pulse equivalent of 1 pm.
For general CNC machine tools, the feed speed range of 0 to 24m/min can meet the processing requirements. Usually in this way, the speed is reduced. At zero speed, when the table stops moving, the motor is required to have electromagnetic torque to maintain the positioning accuracy, so that the position servo system is composed of two parts: the speed control unit and the position control link. If the speed control system is also excessively pursuing a speed range that is as large as the position servo control system and it is to work reliably and stably, then speed is generally speaking, for a position control system with a feed speed range of 1:20 000. When the total open-loop position gain is 20-1, as long as the speed control unit has a 1:1 000 speed range, it can meet the needs, which can make the speed control unit circuit simple and reliable. Of course, on behalf of the advanced level of the experimental system in the world today, the speed control unit has reached a speed range of 1:100000.
This requires that the servo system has excellent static and dynamic load characteristics, that is, the servo system should keep the feed speed constant under different load conditions or when cutting conditions change. For a rigid system, the speed is affected little by the changes in load torque. Generally required to withstand the rated torque changes, the static speed drop should be less than 5%, dynamic speed drop should be less than 10%.