How to solve the vibration of servo system? (Classic Q&A 1)

1. When turning on the power and system of a CNC milling machine, the servo motor makes a buzzing sound. After a few minutes of buzzing, the servo motor will heat up. After reducing the rigidity, the buzzing sound stops, but the milled circle does not look like a circle. How should I adjust it?

It should be that the gain settings of several drivers are different, causing the motor to self-excite at different speeds. You can set the parameters of the driver to be tested and the reference driver to be consistent and try again. Have you checked the inertia ratio? Gain is one aspect, but don't ignore inertia.

2. The servo drive controls the servo motor by adjusting the three-loop PID. The noise is relatively loud, but the motor does not vibrate. The carrier frequency is 10KHZ and the current sampling speed is 0.1us. Why?

Cause of noise: Because there is no input pulse filtering, there is noise.

3. What is the reason why the motor cannot start and makes loud noise and vibration?

1. Disconnect the load;

2. Turn it by hand to make sure it is flexible and has no abnormalities;

3. No-load starting experiment;

4. Check the load conditions.

First check if there is a problem with the dynamic balance, which is the sound of the current. Next, check the motor bearings, and finally the driver parameters. In most cases, the bearings are loose or broken.

4. The motor makes abnormal noise when running. What is the reason and how to deal with it?

1. When the stator and rotor rub against each other, a harsh "squeaking" sound will be produced, which is mostly caused by bearing failure. The bearing should be checked and replaced if damaged. If the bearing is not damaged and the bearing is found to be on the inner or outer ring, the bearing and end cover can be inserted or replaced.

2. The motor is running with a phase loss, and the roar is particularly loud. You can turn off the power and then turn it on to see if it can start normally again. If it cannot start, one phase fuse may be broken. Phase loss may also occur if one phase of the switch and contactor contacts is not connected.

3. When the bearing is seriously short of oil, a "hissing" sound can be heard from the bearing chamber. The bearing should be cleaned and new oil should be added.

4. The fan blades hit the shell or there are debris, making a knocking sound. The fan blades should be corrected and the debris around the fan blades should be cleared.

5. When the cage rotor bars are broken or the winding rotor joints are disconnected, there is a sometimes high and sometimes low "buzzing" sound, the speed also slows down, and the current increases, which should be checked and handled. In addition, the length of some motor rotors and stators is not well matched, such as the stator length is much longer than the rotor length, or the end cover bearing hole is too worn, and the rotor has axial movement, which will also produce a "buzzing" sound.

6. The wiring at the beginning and end of the stator winding is wrong, there is a low roar, and the speed also decreases. It should be checked and correct.

The motor is making a lot of noise. What is the reason? How to deal with it?

Reason 1: The bearing clearance inside the motor is large. Solution: Replace the bearing.

Reason 2: Rotor cleaning treatment: Re-repair the stator and rotor.

Reason 3: Loose magnet Solution: Re-bond the magnet.

Reason 4: Motor body deflection Solution: Readjust the body.

Reason 5: The surface of the motor steering gear is oxidized, burned, uneven with oil, and the commutator segments are loose. Solution: Clean the commutator or weld the commutator segments.

Reason 6: The carbon brush is loose and the carbon brush holder is not straight. Solution: Adjust.

5. The motor is noisy. What is the reason? How to solve it?

According to the different ways in which motor noise is generated, it can be roughly divided into three categories:
① electromagnetic noise; ② mechanical noise; ③ aerodynamic noise.

Electromagnetic noise is primarily caused by the radial force of the air gap magnetic field acting on the stator core. It propagates in opposite directions through the magnetic yoke, causing the stator core to vibrate and deform. The second is the tangential force of the air gap magnetic field, which is opposite to the electromagnetic torque and causes the core teeth to deform and vibrate. When the radial electromagnetic force wave is close to the natural frequency of the stator, it will cause resonance, greatly increasing the vibration and noise, and even endangering the service life of the motor.

According to the causes of electromagnetic noise, we can use the following methods to reduce electromagnetic noise.

⑴ Try to use sinusoidal winding to reduce harmonic components;

⑵Choose the appropriate air gap magnetic density, which should not be too high, but too low will affect the utilization rate of the material;

⑶ Select appropriate slots to avoid low-order force waves;

(4) Use rotor skew slots, which are skewed by one stator slot pitch;

⑸The stator and rotor magnetic circuits are symmetrical and even, with tight stacking;

⑹ During the processing and assembly of the stator and rotor, attention should be paid to their roundness and coaxiality;

⑺Be careful to avoid their resonant frequencies.

6. The newly bought motor is the SEW type with a motor and a reducer connected together. It is mainly controlled by PLC and frequency converter, and the speed used is very low, about 25 Hz. The noise feels very loud. There is no problem with the angle of the driving sprocket and the passive sprocket on the machine, the motor base is also firmly fixed, the cooling fan and the protective cover have no scratches, and the explosion-proof brake is also loose. However, the noise is very loud when it starts running, just like the sound of the transformer in the community. Why?

That is the electromagnetic noise (squeaking) unique to the inverter-driven motor. There is no way to eliminate it, but it can be reduced a little by modifying the inverter parameters: increase the carrier frequency a little, and the noise will be smaller. However, increasing the carrier frequency of the inverter will cause the inverter to heat up. The low frequency of about 25 Hz is originally very annoying. Scratching generally has a higher audio frequency. The base is also firmly fixed. It depends on the base. The metal plate will make a louder sound. The load will make a louder sound. Use a screwdriver to hold your ear and listen carefully to where the sound source comes from. If there is no problem with the installation, the motor is often noisy because of a bad bearing. A new one should not be like this. It may have been like this originally. It just needs to run normally. Another problem is control.

7. What is the reason for abnormal noise and heat generation when the servo motor is running?

The abnormal noise is caused by the motor being overloaded, the motor torque being less than the torque required by the load, and the motor stall torque being greater than the torque required by the load. The heat is caused by the motor current being too large (generally, heat is normal). If it is very hot, or the stall time is too long, it is easy to burn the motor (motor demagnetization). To put it bluntly, it is very difficult for a pony to pull a large cart, and it is even more difficult to pull the cart in order to pull the pony, so it will generate heat (increase the current), and it is very difficult to pull the cart (abnormal noise). The abnormal noise is caused by the servo motor bearing being broken, and the heat is caused by the large current. In fact, it is the abnormally large current generated by the servo motor to overcome the vibration of the motor shaft. It is estimated that the motor is broken and needs to be handled as soon as possible, otherwise the fault will expand.

8. What is the problem if the Siemens servo motor makes a buzzing sound?

There are many reasons for this problem in the servo motor. One is that the zero position of the servo motor encoder is inaccurate, that is, the encoder zero position drifts. The second is that the driver is not rigid enough or there is a problem with the parameters. The third is that there may be a problem with the connection of the servo motor power line. The power line of the servo motor cannot be wrong. You can swap it a few times to see. Fourth, there is a problem with the installation of the encoder or the encoder itself. It needs to be carefully checked. If you have the same servo motor and driver, it is best to swap them with each other and try. If there is a problem with the servo motor, it is best to find a professional to repair it. The system and driver failure, the motor itself failure; the matching between the driver and the actual feed system does not reach the optimal value. Usually, it can be eliminated by adjusting the speed loop gain and integral time of the driver. The specific method is:

1) According to the drive module and motor specifications, set the correct current regulator for S2 of the regulator board of the driver.
2) Adjust the integral time Tn adjustment potentiometer of the speed regulator (on the front of the driver) counterclockwise to the limit (Tn≈39ms).
3) Adjust the proportional Kp adjustment potentiometer of the speed regulator (on the front of the driver) to the middle position (Kp≈7~10).
4) After the above adjustments, the screaming sound of the servo motor can be eliminated, but the dynamic characteristics are poor at this time, and the next adjustment is required.
5) Slowly rotate the integral time Tn adjustment potentiometer clockwise to reduce the integral time until the motor vibrates.
6) Slightly rotate the integral time Tn adjustment potentiometer counterclockwise to eliminate the motor vibration sound.
7) Keep the above positions and make a record.
After the above adjustments, the screaming sound of this machine tool is eliminated and the machine tool resumes normal operation.