Anti-jamming design of economical lathe CNC system
Starting from the aspects of noise transmission path and disturbed equipment, some methods for improving the anti-interference ability of the economical lathe CNC system are proposed, which are to suppress the noise source, block the noise transmission path, and improve the anti-interference ability of the computer part of the CNC system. Practice has proved that flexible use of these methods according to specific conditions can effectively improve the anti-interference ability of the economical lathe CNC system: economical lathe; numerical control system; electromagnetic noise; anti-interference 0 Introduction Economical lathe CNC system 1 is in a harsh environment, from The electromagnetic noise inside and outside the CNC system often interferes with the normal operation of the CNC system, and even causes a malignant accident, and it has to go through many iterations and pay a great price to eliminate the interference. Therefore, the anti-interference design of the numerical control system is particularly important.
Under normal circumstances, there are three conditions for forming electromagnetic interference: a noise source for transmitting noise outward; a path for transmitting electromagnetic noise; and a disturbed device for withstanding electromagnetic interference. In order to ensure that the numerical control system is protected from interference in the electromagnetic environment, it is necessary to take corresponding measures from the design stage: suppress the noise source, directly eliminate the cause of the interference; block the transmission path of the noise; improve the anti-interference ability of the core part of the numerical control system .
1 Suppressing noise sources The noise of the CNC system can be divided into external noise and internal noise. For external noise, it is impossible to eliminate it directly, only to avoid it as much as possible. For internal noise, some measures to eliminate internal and external noise should be eliminated as far as possible. 1.1 Eliminate transient noise switching relays and contacts generated when switching inductive loads Inductive loads such as motors and motors generate high surge voltages with peaks of up to several thousand volts and their pulse power is sufficient to damage semiconductor devices. Moreover, the higher harmonics contained in the surge voltage will invade the numerical control system through the power supply line, the distributed capacitance between the wires, and the insulation resistance, and interfere with the normal operation of the microcomputer. The transient noise can be suppressed by parallel diodes or by connecting to an RC absorption circuit. For example, parallel diodes are connected on the DC relay coils of the machine main motor and the electric tool holder motor, and the RC absorption circuit is connected in parallel to the contactor coil and the motor winding. Practice has proved that the suppression effect of this method is very obvious. In addition, the thyristor zero-crossing switch can be used instead of the AC contactor, which can completely eliminate transient noise 1.2 Eliminate DC power supply noise. Most economical lathe CNC system power supply (+ 5V) is composed of a three-terminal integrated voltage regulator. The circuit is simple and reliable, but the power supply noise from the external AC power grid is weak. The multi-stage filter circuit can be used to enhance the filtering. The medium capacitor C2C4C6 and the inductor Li are used to suppress normal mode noise.
When there is a TTL device in the circuit, the switching action time is 5-10 ns. Under the action of transient current and common impedance, switching noise is generated on the DC power line, which reduces the noise margin of the circuit, resulting in logic circuit and microprocessor. An effective method for reducing the switching noise by using a fault is to connect a 0. 01~0.1F noise-limited tantalum capacitor or a high-frequency non-inductive filter capacitor between the power supply terminal and the ground terminal of each integrated circuit. Install this capacitor on the power input side of the integrated circuit, and minimize the wiring of the capacitor. 1.3 Eliminate the noise of the switching power supply. Currently, the switching power supply is widely used in the numerical control system, but the switching power supply has large noise, wide noise spectrum and high noise. Frequent radiated interference is not completely eliminated. Only isolation, filtering and shielding can be used to block the transmission of noise. The specific method is as follows: reduce the coupling between the switching-level transistor and the power shield. Capacitance to reduce noise generation Inductor coils are used to connect the switching power supply case to the control system housing to reduce common mode noise.
Connecting the line filter to the input of the AC power source not only suppresses the generation of common mode noise and normal mode noise, but also the external power supply noise. The circuit of the line filter is as shown. Among them, the common mode choke. The capacitor C2C3 is used to suppress common mode noise, and the inductor L2 and the capacitor G are used to suppress normal mode noise.
A common mode choke is added to the output to suppress common mode noise. The circuit is as shown. The medium capacitor G should be a tantalum capacitor or a high frequency non-inductive capacitor to suppress normal mode noise.
Install the switching power supply in the metal shielding box and install it as far as possible from other parts of the system to reduce the radiation interference inside the system. 2 Block the noise transmission path. The electromagnetic environment of the CNC system is generally poor, especially nearby. High-frequency transient noise is generated on the common AC grid and control loop when large electrical equipment is started and stopped. These noises are mainly injected into the system through the input power, input signal line and output control circuit of the CNC system. Therefore, measures such as filtering, isolation and shielding must be adopted to block the noise outside the system. Some noises that cannot be eliminated inside the system should also be Filtering, isolation and shielding are used for processing. 21 Use the power supply filter to suppress the input power supply noise. The common mode choke coil LiL2 capacitor C3G attenuates the common mode noise. The capacitor CiC2G attenuates the normal mode noise. In addition, the actual noise of the filter. The suppression effect depends on the method of use. Pay attention to the following three points: the filter should be installed as close as possible to the power input socket, and the incoming and outgoing lines should be twisted and grounded close to the ground potential. The two must be separated and not parallel. The grounding resistance of the filter that can't be bundled together should be as small as possible. It is better to install it directly on the system chassis closest to the system ground terminal, which can better suppress high frequency common mode noise.
The peripheral interface circuit of the stepping motor driver inside the CNC system and the power supply of the computer circuit can be powered by three filters respectively, which can not only suppress the external power supply interference, but also suppress the mutual interference between the parts. 22 Use the shield transformer to suppress the input power. Most of the internal circuits of the noise-economic numerical control system need to be powered by the transformer. Due to the large coupling capacitance between the primary and secondary, the common transformer has a weaker suppression effect on the common mode noise, and the shielding layer is inserted between the primary and secondary. The shielded transformer has a strong inhibitory effect on common mode noise. The principle is as shown in the figure is the primary common mode noise voltage, C2 is the distributed capacitance between the primary, secondary and shield layers, and C3 is the secondary to ground capacitance. The shield grounding impedance is Z, so that the common mode noise voltage V2 coupled to the secondary is generally small, so V2 is much smaller than V, but as the frequency increases, the impedance of G decreases. Z increases, and the ability to suppress noise is reduced, so the grounding wire of the shield layer should be short and thick. However, the single-layer shielded transformer shown has a weaker ability to suppress the normal mode noise, and the shield winding can be increased and connected to the primary end, and the normal mode noise is filtered by the distributed capacitance between the primary coil and the shield winding.
23 The input and output lines of the input and output lines may also bring noise into the system. For example, the input and output signal lines that control the electric tool holder are the input and output interface circuits of the channel switch of the tool frame motor surge noise entering the system. The optocoupler has a good suppression effect on common mode noise, and G can suppress the normal mode noise.
In the actual machining of the lathe, in order to ensure that the thread is not disordered, the spindle encoder must output the same number of pulses to the system for each revolution of the spindle. However, when the system is connected to an AC drive or other strong interference source, the encoder The output pulse will be severely disturbed and even “eatenâ€. Therefore, the input interface of the encoder pulse should use the differential comparison receiver to suppress the mode noise, and also use high-speed optocoupler to isolate the common mode noise. The circuit is as shown.
Special grounding terminals should be installed on the casing. The power supply filter, shielding transformer, computer shield, etc. should be connected directly to the grounding terminal by using short and thick wires. The smaller the grounding resistance, the stronger the suppression of high-frequency noise. The anti-jamming capability of the computer in the numerical control system of the computer is determined by the circuit design and software design of the computer. Reasonably adopt some software and hardware measures to reduce the noise sensitivity of the computer. Once the interference occurs, the computer can automatically respond accordingly. Processing to minimize the impact of interference.
3.1 Optimized circuit design Most economical CNC systems use MCS-51 series MCUs and extend some peripheral interface circuits to achieve CMOS series chips, such as 80C3180C3227C51282C55, from the perspective of anti-interference and power saving.
The input port of the MCU and the 8255 should be equipped with a pull-up resistor. In particular, the interrupt inlet should be integrated with the integral and shaping circuits, and the output port plus the current driver to enhance the anti-interference ability of the input and output ports. When the expansion chip of the MCU is too much, the bus driver should be used as much as possible to select a large-scale integrated circuit, reduce the number of components used, and reduce the area of ​​the printed circuit board. When designing the circuit board, the layout should be reasonable. Try not to place the MCU and its expansion chip differently. On the printed circuit board, try to widen the power supply and ground wiring, use the bypass capacitor reasonably, and reduce the common impedance noise and switching noise. 3.2 Software anti-jamming measures Anti-interference is also an important task of software design, as long as the computer can run normally, the software is resistant. Interference measures will receive good results.
If the input signal is sampled multiple times, when the multiple sampling results are the same, the input is considered valid; the output signal is scanned multiple times; the backup of the flag and the processing program is set in the RAM area, and the logo is destroyed and restored by the backup program. Processing procedure 1 Wang Wenxi. Digital adjustment technology for machine tools M. Beijing: China Science and Technology Press, 1992189-20ft 3 Xu Jiazheng. Grid interference and monitoring. Electronic Measurement Technology, 1992 (4): 23-27. (Responsible Editor Zhang Qiujuan) 24 suppression of mutual interference between various parts of the CNC system Economical lathe CNC system can be generally divided into computer drive, interface and power supply, etc. 4 parts 2 in space They should be separated as far as possible to reduce mutual interference. In particular, the computer part should be installed separately in a fully enclosed shield to reduce radiated interference. The interface circuit should be installed as close as possible to the system input and output sockets to reduce external noise lines in the system. Internal routing distance.
帮 éµ éµ - Common mode interference caused by poor grounding of the outer casing and mutual interference between the internal circuits of the system rightsreserved, http:// 1994-2 (Jiang Jiannan Anning Guoren! al 2 drive interface circuit and computer connection The line should be twisted or shielded and separated from the power line, motor line and other noise lines. The computer driver and interface should be shielded by different power supply filters. The control signal sent to the drive by the computer should also be via the optocoupler. Isolation 25 Optimized Grounding Designing the correct grounding can better suppress the transmission of noise. For small CNC systems, the internal circuit should be floating, that is, the grounding of the computer, the driver and the external interface are isolated from each other and insulated from the casing. The larger the insulation resistance, the better. This grounding method is beneficial to
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