Maintenance method of servo motor

 What work needs to be done before starting the servo motor
1) Measure the insulation resistance (not less than 0.5M for low-voltage motors).
2) Measure the power supply voltage and check whether the motor wiring is correct and whether the power supply voltage meets the requirements.
3) Check whether the starting equipment is in good condition.
4) Check whether the fuse is suitable.
5) Check whether the motor grounding and zero connection are good.
6) Check the transmission for defects.
7) Check whether the motor environment is suitable, and remove inflammable and other sundries.

What are the causes of overheating of servo motor bearings
Motor itself:
1) The inner and outer rings of the bearing are too tight.
2) There is a problem with the form and position tolerance of the parts, such as the coaxiality of the base, end cover, shaft and other parts is not good.
3) Improper selection of bearing.
4) The bearing is poorly lubricated or the bearing is not cleaned, and there are sundries in the lubricating grease.
5) Shaft current.

Use:
1) The unit is improperly installed, for example, the shaft coaxiality of the motor shaft and the driven device meets the requirements.
2) Pulley is pulled too tight.
3) The bearing is not well maintained, the lubricating grease is insufficient or exceeds the service life, and it is dry and deteriorated.

What is the cause of three-phase current imbalance of servo motor
1) The three-phase voltage is unbalanced.
2) A phase branch in the motor is poorly welded or in poor contact.
3) Motor winding resistance inter-turn short circuit or inter-phase short circuit to ground.
4) Wiring error.

How to control the speed of servo motor
The servo motor is a typical closed-loop feedback system. The reduction gear set is driven by the motor. Its terminal (output end) drives a linear proportional potentiometer for position detection. The potentiometer converts the angle coordinate into a proportional voltage and feeds it back to the control circuit board. The control circuit board compares it with the input control pulse signal to generate a correction pulse, and drives the motor to rotate forward or backward, The output position of the gear set is consistent with the expected value, and the correction pulse tends to zero, so as to achieve the purpose of accurate positioning and speed fixing of the servo motor.

Observe whether there is spark between the carbon brush and the commutator when the motor is running and repair the degree of spark
1. There are only 2-4 tiny sparks. At this time, if the commutator surface is flat, it is not necessary to repair in most cases;
2. No spark, no repair;
3. If there are more than 4 small sparks and 1 to 3 large sparks, it is not necessary to disassemble the armature, but to grind the carbon brush commutator with abrasive paper;
4. If there are more than 4 large sparks, it is necessary to grind the commutator with abrasive paper, and the carbon brush and armature must be removed. Replace the carbon brush and grind the carbon brush.

Repair of commutator
1. The commutator surface is obviously uneven (can be felt by hand) or the spark when the motor is running is the fourth case. At this time, it is necessary to disassemble the armature and process the converter with a precision machine tool;
2. It is basically flat, but there are very small scars or sparks. For example, in the second case, the 1 port is manually ground with water abrasive paper without removing the armature. The grinding sequence is as follows: first, according to the outer circle radian of the commutator, process a wooden tool, cut several water sandpaper of different thicknesses into strips as wide as the commutator, take down the carbon brush (please note that marks are made on the handle of the removed carbon brush and the carbon brush groove to ensure that the left and right are not changed wrong during installation), stick the commutator with a wooden tool wrapped with sandpaper, and gently turn the shaft commutator with the other hand according to the rotation direction of the motor to grind. The order of thickness of abrasive paper used for servo motor maintenance is from coarse to fine. When one piece of abrasive paper is too blind to use, replace it with another thinner abrasive paper until the finest water abrasive paper (or metallographic abrasive paper) is used up.

How to align the encoder phase of servo motor with the rotor magnetic pole phase zero point

1. Phase alignment of incremental encoder
The alignment method between the phase of the UVW electronic commutation signal of the incremental encoder with commutation signal and the rotor magnetic pole phase, or the electrical angle phase, is as follows:
1) Apply a DC power supply to the UV winding of the motor with DC less than the rated current, U in, V out, and orient the motor shaft to a balanced position;
2) Observe the U phase signal and Z signal of the encoder with an oscilloscope;
3) Adjust the relative position of encoder shaft and motor shaft;
4) While adjusting, observe the U-phase signal jump edge of the encoder and the Z signal until the Z signal is stable at the high level (in this case, the normal state of the Z signal is low), and lock the relative position relationship between the encoder and the motor;
5) Twist the motor shaft back and forth, and after letting go, if the Z signal can be stabilized at the high level each time the motor shaft returns to the balance position freely, then the alignment is effective.

2. Phase alignment of absolute encoder
The phase alignment of absolute encoder has little difference between single turn and multiple turns. In fact, it is to align the detection phase of encoder and the phase of motor electrical angle within one turn. At present, a very practical method is to use the EEPROM inside the encoder to store the measured phase after the encoder is randomly installed on the motor shaft. The specific method is as follows:
1) The encoder is installed on the motor randomly, that is, the encoder shaft and motor shaft, as well as the encoder housing and motor housing are consolidated;
2) Apply a DC power supply to the UV winding of the motor with DC less than the rated current, U in, V out, and orient the motor shaft to a balanced position;
3) Use the servo driver to read the single-turn position value of the absolute encoder and store it in the EEPROM which records the initial phase of the electrical angle of the motor inside the encoder;
4) The alignment process ends.

Servo motor maintenance play
Movement occurs during feeding, and the speed measurement signal is unstable, such as cracks in the encoder; Poor contact of wiring terminals, such as loose screws; When the movement occurs at the moment of reversing from the positive direction to the reverse direction, it is generally caused by the reverse clearance of the feed drive chain or the excessive servo drive gain.

Servo motor maintenance creep
Most of them occur in the starting acceleration section or low speed feed, which is generally caused by poor lubrication of the feed drive chain, low servo system gain and excessive applied load. In particular, it should be noted that the coupling used for the connection between the servo motor and the ball screw is not synchronized with the rotation of the ball screw and the servo motor due to the loose connection or the defects of the coupling itself, such as cracks, so that the feed movement is fast and slow.

Servo motor maintenance vibration
When the machine tool is running at high speed, vibration may occur, and then an overcurrent alarm will be generated. The problem of machine tool vibration generally belongs to the problem of speed, so we should look for the problem of speed loop.

Servo motor maintenance torque reduction
When the servo motor runs from the rated locked-rotor torque to high speed, it is found that the torque will suddenly decrease, which is caused by the heat dissipation damage of the motor winding and the heating of the mechanical part. At high speed, the temperature rise of the motor becomes larger, so the load of the motor must be checked before the correct use of the servo motor.

Servo motor maintenance position error
When the servo axis movement exceeds the position tolerance range (KNDSD100 factory standard setting PA17:400, position out-of-tolerance detection range), the servo driver will give the "4" position out-of-tolerance alarm. The main reasons are: the tolerance range set by the system is small; The servo system gain is set improperly; The position detection device is contaminated; The accumulated error of feed transmission chain is too large.

The servo motor does not rotate after maintenance
In addition to connecting pulse+direction signal, there is also enabling control signal from the CNC system to the servo driver, generally DC+24V relay coil voltage. The servo motor does not rotate. Common diagnosis methods include: check whether the numerical control system has pulse signal output; Check whether the enable signal is connected; Observe whether the input/output status of the system meets the starting conditions of the feed shaft through the LCD screen; Confirm that the brake has been turned on for the servo motor with electromagnetic brake; The drive is faulty; The servo motor is faulty; The coupling of servo motor and ball screw fails or the key disengages.

Source: Network