Buke servo motor - common fault causes and maintenance methods of servo motor encoders

1. Start the servo motor before work

(1) Measure the insulation resistance (0.5M or more for low-voltage motors).

(2) Measure the power supply voltage, check whether the wiring of the motor is correct, and whether the power supply voltage meets the requirements.

(3) Check whether the starting device is normal.

(4) Check whether the fuse is sufficient.

(5) Check whether the motor has good grounding and zeroing.

(6) Check whether the transmission device is faulty.

(7) Check whether the environment of the motor is normal, and remove combustibles and other sundries.

Second, about the reason for the overheating of the servo motor bearing

The motor itself

(1) The inner and outer rings of the bearing are too tight.

(2) Due to the shape tolerance problem, some parts such as the base, end cover, and shaft do not have good coaxiality.

(3) Improper selection of bearings.

(4) The bearing is not well lubricated or the bearing is not cleaned, and there is dust in the grease.

(5) Current on the shaft

Aspects of use

(1) Improper installation of the equipment, for example, there is no requirement for the coaxiality between the motor shaft and the equipment shaft.

(2) The pulley is pulled too hard.

(3) The bearing is poorly maintained, lacks grease, or dries up and deteriorates after a period of use.

3. What is the reason for the three-phase current imbalance in the servo motor?

(1) Imbalance of three-phase voltage.

(2) The phase branch inside the motor is welded or in poor contact.

(3) The motor winding becomes shorter or the phase is short-circuited to the ground.

(4) Wrong wiring.

Fourth, increase or decrease the speed of the servo motor

The servo motor is a typical closed-loop feedback system, the reducer group is driven by the motor, the terminal (output) drives a linear proportional potentiometer for position detection, the potentiometer feeds back the angular coordinates to the control circuit board with proportional voltage, the board will be compared with the input ground control pulse signal, generate a compensation pulse, and then drive the forward and reverse rotation of the motor, so that the gear set output position. Since the output position of the gear set matches the expected value, the correction pulse will tend to zero, allowing the servo motor to achieve accurate positioning and fixed speed.

5. Observe whether there is a spark between the carbon brush and the commutator when the motor is running and the degree of spark is repaired

1. Only 2 to 4 very small sparks are generated. At this point, if the surface of the commutator is flat, most of the time it can be repaired as is.

2. There is no spark at all. There is no need for repairs.

3. If there are more than four very small sparks and one to three large sparks, you don't have to disassemble the armature, just polish the carbon brush commutator with sandpaper.

4. If there are more than 4 large sparks, the commutator must be sanded with sandpaper, and it must be disassembled from the carbon brush and armature. Polishing carbon brushes replace carbon brushes

6. Repair the commutator

1. The surface of the commutator is obviously uneven (you can see it by touching it by hand), or like in the fourth case, there is a spark in the motor. In this case, it is necessary to disassemble the armature and machine the converter with a precision machine.

2. Basically flat, only very small scratches and sparks, if the second case l mouth should be ground with water sandpaper, Grinding without disassembling the armature 1.The grinding sequence is: first press the outer arc of the commutator to process the wooden tool, and then cut several carbon brushes of different thicknesses with watered sandpaper in a long strip as wide as the commutator (please note that the carbon brush handle and carbon brush groove are removed and marked to ensure that there will be no dilemma during installation) Paste the wooden tool to the commutator with wrapped sandpaper, gently turn the commutator on the shaft for grinding, and use the other hand to operate according to the direction of rotation of the motor. When servicing servo motors, we use different coarse sandpaper and fine sandpaper.

7. How to zero the encoder phase of the servo motor and the magnetic pole phase of the rotor in order to arrange maintenance

1. Incremental encoder phase alignment

The phase of the electronically commutated signal with the incremental encoder UVW coincides with the phase of the rotor poles, i.e., the phase of the electrical angle, as shown below

(1) By applying U in and V current to the UV winding of the motor by using a DC power supply lower than the rated current, the motor shaft is put into a balanced position.

(2) Use an oscilloscope to observe the you and Z signals of the encoder.

(3) Adjust the relative position of the encoder shaft and the motor shaft.

(4) Adjust the encoder by observing the encoder's locking of the relative position of the motor until the U signal of the encoder jumps and the Z signal stabilizes at a high position (the default Z signal is usually low).

(5) After twisting the motor shaft back and forth and letting go, if the Z signal is stable at a higher level every time the motor shaft returns to the equilibrium position freely, the alignment is effective.

2. The phase of the absolute encoder

The phase of an absolute encoder, whether singleturn or multiturn, does not make much difference, in fact, it is important that within one turn, the detection phase of the encoder and the electromechanical angle phase are matched. A very practical approach at the moment is to randomly mount the encoder on the motor shaft, as shown in the figure below, and then use the EEPROM inside the encoder to store the measured phase

(1) Connect the encoder to the motor randomly. That is, the encoder shaft is fixed to the motor shaft, and the encoder housing is fixed to the motor housing.

(2) Guide the motor shaft to an equilibrium position by applying Uin and Vout DC currents to the UV windings of the motor by using a DC power supply lower than the rated current.

(3) The position value of one revolution of the absolute encoder is read by a servo drive and stored in the EEPROM of the encoder, which records the initial stage of the electrical angle of the motor.

(4) The alignment process is complete.

8. Tampering in the process of servo motor maintenance

In terms of feed, the phenomenon of goods channeling is generally due to the feed drive chain backlash or servo drive gain is too large, when the speed measurement signal, the encoder is unstable, such as cracks, poor terminal contact, loose screws, etc., and the goods channeling occurs at the moment of forward movement and reverse movement.

9. Crawling phenomenon occurs when repairing the servo motor

Most of them occur in the starting acceleration section and low-speed feed, which is generally caused by poor lubrication conditions of the feed drive train, low gain of the servo system and excessive external load. Special attention should be paid to the connection between the servo motor and the ball screw, if the connection is loose or the connection itself is defective, such as cracks, it will cause the rotation of the ball screw and the servo motor to be out of sync, resulting in faster or slower feed movements.

10. Vibration phenomenon in servo motor maintenance

When the machine is running at high speed, vibration may occur, which will cause an overcurrent alarm. The problem of machine vibration is generally a speed problem, so we need to look for the problem of the speed loop.

11. Low torque phenomenon occurs when repairing servo motors

It was found that when the servo motor was running at high speed, the torque suddenly dropped from the rated stall torque, which was caused by the thermal damage of the motor windings and the heat of the machine parts. At high speeds, the temperature rise of the motor is large, so it is necessary to use the servo motor correctly before calculating the motor load.

12. The servo motor maintenance position is wrong

If the movement of the servo axis exceeds the position tolerance range (KNDSD100 factory setting PA17:400, the position exceeds the detection range), the servo drive will display the "4" position overload alarm. The main reasons are: the tolerance of the system setting is too small, the gain of the servo system is not set properly, the position detection device is contaminated, the cumulative error of the feed drive chain is too large, and so on.

13. The phenomenon that the servo motor does not rotate during maintenance

The numerical control system has a servo drive, so that the control signal is generally DC + 24V relay coil voltage in addition to the linkage pulse + direction signal. The servo motor does not rotate, the general diagnosis method is: check whether the numerical control system has pulse signal output, check whether the effective signal is connected, observe the system input/output status through the LCD screen, whether the feed shaft starting conditions are met, the servo motor with electromagnetic brake, to ensure that the brake is open, the drive is faulty, the servo motor is faulty, the coupling between the servo motor and the ball screw is faulty or the key has been cut off, etc.

Buke servo motor - common fault causes and maintenance methods of servo motor encoders

Buke servo motor - common fault causes and maintenance methods of servo motor encoders

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