The S series AC spindle servo system is the leading product of Japan's FANUC Corporation in the late 1980s and early 1990s. This product currently has a large amount of domestic ownership. Our factory imported more than a dozen machine tools using this system around 1990. These S series AC spindle servo systems have been close to or in the period of failure. The following will be a brief introduction of the author in the equipment maintenance and repair of a few examples of failures and the treatment methods taken for reference by peers. Example 1: Spindle Servo Unit Display AL-02 Replacing (Excessive Speed ​​Error) When the NC System Sends a Spindle Rotation Command (M03, S1000), the Spindle Rotates at an Extremely Low Speed ​​(45 r/min), and the Spindle Load Table Pointer Has Been To 125%, the spindle servo unit displays the AL-02 alarm. The system's control circuit board was moved to another servo unit of the same type and working, and it was found that the control board was working properly. Therefore, we detected the speed feedback signal of the motor part of the faulty system and found that the signal was not the normal signal as shown in FIG. 1. After opening the tail of the motor, it was found that the mounting screw of the sensor head was loosened and the distance between the sensor surface and the tooth plate increased. After correct installation, troubleshooting.
Figure 1 Speed ​​detector output signal
Figure 2 Speed ​​detector structure
It should be noted that the speed detector of the S series spindle servo motor uses a magneto-resistive encoder (see Figure 2). It consists of a toothed rotor and a magneto-resistive sensor. This type of encoder is based on the physical magnetoresistance effect of semiconductors. When the magnetic flux across the cross-section of the magnetoresistive changes, the resistance of the magnetoresistive resistor changes, and when the toothed rotor rotates, the top and bottom of the tooth rotate alternately across the sensor surface, causing magnetic flux through the semiconductor magnetosensitive element. The pass alternates between high and low so that the potential at the output changes periodically. The distance between the sensor surface and the top of the sensor is 0.15±0.02mm when the sensor is installed. When the sensor is too close, the sensor is easily damaged by the top of the tooth, and if the signal is too far, the signal is too weak. Therefore, maintenance personnel should pay attention when testing. Example 2: When the machine is turned on for a few days after shutdown, F4 (5A fuse protection) burns a machine in our factory for more than ten years. When it is turned on again after a few days of shutdown, the quick-melting fuse F4 (5A) is blown and replaced. After another blow. After inspection, the insurance supplies power to the DC stabilized power supply, the spindle servo unit cooling fan, and the AC motor cooling fan on the printed board. However, the DC regulated power supply on the printed circuit board does not fail. When the spindle servo unit was removed and carefully inspected, it was found that the blades of the axial fan for cooling and the inside of the fan housing had been covered with a very thick layer of oil and dust, causing the cooling fan to be blocked, causing the F4 to be blown and cleaned. After dust, the system returns to normal. Although this is a minor failure, it reminds us that we must pay attention to the daily maintenance of the equipment, especially the old equipment used for many years, must be regularly dust, check the insulation between the terminals, so as to eliminate hidden dangers and avoid electrical failure Keep the equipment running normally and make the equipment play its best role. Example 3: AL-11 alarm when motor brakes The spindle servo unit generates AL-11 alarm (DC side voltage is too high) during high-speed to zero-speed braking, and then the motor coasts to a stop. The main loop of the spindle servo unit is a cross-converter and has energy feedback function. When the main shaft is braked, the main shaft motor works in the generator state, and the kinetic energy of the system evolves into electric energy. The freewheeling diode of the inverter bridge is stored in the storage capacitor C, so that the voltage at both ends thereof rises sharply. The task of the energy feedback circuit is to feed these power back to the grid via the power pipe of the feedback bridge, which saves energy and prevents the voltage across the capacitor C (pump-up voltage) from rising. The role of the resistor R is to limit the energy feedback current, so that the current flowing through the feedback bridge power tube will not be very large, so as to protect the feedback bridge. After investigation, the resistor R has been opened and it is estimated that the current flowing through it is too large. Because the resistance R is open, when the motor is braking, the pump-lift circuit does not discharge circuit, resulting in the voltage across the capacitor C is too high, causing AL-11 alarm. Therefore, we increased its resistance when replacing this resistor, and at the same time we modified the parameter F-20 brake time adjustment) to lengthen the motor braking time, which also reduced the energy feedback current. After this equipment was repaired, it has been operating normally for two years.
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