Estun servo motor - common faults and solutions of AC servo motors

The AC servo system includes: servo drive, servo motor and a feedback sensor (generally servo motor comes with an optical encoder).

All of these components operate in a controlled, closed-loop system. The driver receives parameter information from the outside, then transmits a certain current to the motor, converts the motor into torque to drive the load, the load moves or accelerates and decelerates according to its own characteristics, the sensor measures the position of the load, makes the driving device compare the set information value and the actual position value, and then makes the actual position value and the set information value consistent by changing the motor current, when the speed change is caused by a sudden change in load, the encoder will immediately respond to the servo drive after learning about this speed change, The drive, in turn, satisfies the change in load by changing the current value supplied to the servo motor and returns to the set speed.

The AC servo system is a fully closed-loop system with a very high response, and the time lag response between load fluctuations and speed correction is very fast.

Estun servo motor - common faults and solutions of AC servo motors

Failure analysis

The following analysis of AC servo motor vibration faults is mainly carried out from the mechanical and electrical aspects.

1. Mechanical aspects

The backlash is too large after the wear of the bearings at both ends of the motor and on the lead screw housing, or the bearing roller elements and cages are severely worn after the lack of grease in the bearing, resulting in excessive loads. Excessive clearance after bearing wear will cause coaxiality error between the center of the motor rotor and the center of the lead screw, which will cause the mechanical system to jitter. Serious wear of the bearing rolling element and cage will cause the friction to increase and lead to "stall", "stall" will not lead to "overload alarm", due to the heavy load, it will increase the response time of the servo system and produce vibration;

If the motor rotor is unbalanced, the dynamic balance of the motor rotor is defective during manufacturing or deteriorates after use, and a vibration source like a "vibrating motor" will be generated;

The bending of the rotating shaft, the bending of the rotating shaft is similar to the unbalanced rotor, in addition to the vibration source, it will also produce the coaxiality error of the center of the rotor of the motor and the center of the lead screw, so that the mechanical transmission system will jitter;

The manufacturing defects of the coupling or the wear after use will cause the coaxiality error of the two parts of the coupling, especially the rigid coupling with casting, due to the poor manufacturing accuracy, it is more likely to produce the coaxiality error and cause vibration;

The poor parallelism of the guide rail during manufacturing will cause the servo system to be unable to reach the specified position to be unable to stay in the designated position, and the servo motor will keep hovering between trying to find the position and the system feedback, so that the motor will vibrate continuously;

The parallelism error between the lead screw and the plane of the guide rail, and the parallelism error between the lead screw and the plane where the guide rail is located during the installation process will also cause the motor to vibrate due to the uneven load;

The lead screw is bent, and the lead screw is bent after the screw is bent in addition to the axial thrust and will be subject to the changing radial force, when the bending is large, the radial force is large, and the radial force is small when bending, and the radial force that should not exist will also cause the mechanical transmission system to vibrate.

2. Electrical aspects

The main reason for the electrical aspect of the AC servo motor is the parameter adjustment of the servo drive.

Load inertia, the setting of load inertia is generally related to the size of the load, too large load inertia parameters will cause the system to vibrate, the general AC servo motor can automatically measure the load inertia of the system;

Speed proportional gain, the larger the set value, the higher the gain, the greater the system stiffness, the parameter value is determined according to the specific servo drive model and load situation, in general, the larger the load inertia, the larger the set value, in the case that the system does not produce vibration, the set value is as large as possible, but the larger the gain, the smaller the deviation, the easier it is to vibrate;

Speed integral constant, under normal circumstances, the larger the load inertia, the larger the set value, the system does not produce vibration, the set value is as small as possible, but reducing the integral gain will make the machine tool slow response, and the rigidity will be worse;

Position proportional gain, the larger the set value, the higher the gain, the greater the stiffness, the same frequency command pulse condition, the smaller the position lag, too large a value may cause motor vibration;

Acceleration feedback gain, when the motor is not rotating, a small offset will be amplified by the proportional gain of the speed ring, and the speed feedback will produce the corresponding torque, making the motor shake back and forth.

Solution

Knowing which aspects will cause vibration faults in AC servo motors, it is difficult to further narrow the scope of faults and lock the cause of faults in actual maintenance, which needs to be comprehensively judged in combination with specific on-site information.

　　1

The fault occurs after the new equipment is started and debugged, the fault that occurs in this period is the most complex, it may be due to the reasons of mechanical manufacturing, it may also be the reason for the incorrect parameter adjustment, which needs to be eliminated step by step, the principle of exclusion is to first eliminate the simple reason, and then eliminate the complex, if the CNC system is equipped with more than two identical drives and AC servo motors, one of the motors vibrates, you can use the simplest "exchange method" to replace the servo drives of the two AC servo motors, This method can be used to quickly determine whether the problem is in the servo drive parameter setting.

　　2

The fault occurs after the equipment has been in operation for a long time, and this situation can basically rule out the problem of the servo drive parameter setting, because if the parameter is not set properly, the problem should have been reflected a long time ago.

　　3

The fault occurs just after starting, if the AC servo motor is just turned on and vibrates, in this case, it can be determined that the mechanical jamming occurs when the CNC system automatically finds the origin of the machine tool, resulting in the motor can not reach the specified position or repeatedly after reaching the specified position, in this case it is generally a mechanical failure.

　　4

The fault occurs when the machine is machining the workpiece, and in such a case, the vibration caused by the increase in load during machining is first considered, and the cause of the increase in load is checked.

　　5

When the fault occurs continuously, it means that the fault cause that causes the motor vibration has always existed, and when the fault occurs irregularly, it means that the fault cause that causes the motor vibration sometimes changes, and if the load does not change greatly, the reason for the servo drive parameter setting can be ruled out basically.

The vibration fault of the AC servo motor is a complex cause in many aspects, and the proportion of motor failure caused by mechanical failure or mechanical failure is found to be large from the actual operation, and it is necessary to master the working principle of the AC servo system when eliminating this kind of fault, understand which reasons are easy to cause motor vibration failure, and at the same time combine the comprehensive judgment of the on-site situation to completely solve the vibration fault of the AC servo motor.

Estun servo motor - common faults and solutions of AC servo motors

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