Aug 19, 2021
Measure the insulation resistance (for low voltage motor it should not be less than 0.5m).
Measure the power supply voltage, check the motor connection, as well as the power supply voltage.
Examine whether the starting equipment is in good condition.
Check if the fuse is suitable.
Inspect whether the motor is grounded and zeroed.
Check if the transmission device is defective.
Examine the motor environment, and remove inflammable goods and other sundries.
Causes of Overheating of Servo Motor Bearings
The inner and outer ring of the bearing is too tight.
The fault of the shape and position tolerance of parts, in which the coaxiality of the frame, end cover, shaft and other parts is not good.
Improper selection of bearings.
Bearing lubrication is poor or bearing is not clean, and there are sundries in the grease.
Axial current.
Improper installation of the unit. For instance, the shaft of the motor and the dragging device meets the coaxial requirements.
The pulley is pulled too tight.Bearing maintenance is not good, grease is insufficient or over the service life, dry and deteriorated.
Figure 2: The servo motor bearings.
Cause of the Three-Phase Current Imbalance
The imbalance of the three-phase voltage.
Bad welding or bad contact of a phase branch inside the motor.
The short circuit of the motor resistance between windings or the short circuit to the ground phase.
Wiring error.
How to Control the Speed of the Servo Motor
The servo motor is of a typical closed loop feedback system, driven by a motor gear group, the terminal (outputs) of which drives a linear potentiometer position detection. And the potentiometer transforms the coordinate angle into a proportional voltage that is feedback to control circuit boards.
Then the control circuit board compares it with the input pulse signal, generates a corrective impulse, and drives the motor forward or backward. The output position of the gear group is consistent with the expected, and the correction pulse tends to 0, so as to achieve the accurate positioning and constant speed of the servo motor.
Spark between the Carbon Brush and the Commutator
You should observe whether there is a spark between the carbon brush and the commutator when the motor is running and its degree.
Two to four tiny sparks. In most cases, if the surface of the commutator is flat, the repair is unnecessary.
No spark. No need to repair.
More than 4 small sparks, and there are 1 to 3 large sparks. It is not necessary to remove the armature, you should only grind the carbon brush commutator with the sandpaper.
Over than 4 large sparks. You should grand the commutator with the sandpaper. And you must remove them from the armature. Change the carbon brush.
Commutator Repair
The surface of the commutator is obviously uneven or the spark occurs when the motor is running. In this case, the armature should be disassembled and the converter should be machined with precision machine tools.
It is basically flat, only with a small scar or spark. You should grind it with water sandpaper in the case of not removing the armature. The order of grinding is as follows. Process wooden tools according to the outer arc degrees of the commutator, and cut the waterproof abrasive paper into a wide strip as a commutator.
Then you remove the carbon brush, and paste the commutator with wooden tools wrapped with sand paper. You the other hand to gently turn the shaft commutator to grind according to the motor rotation direction. When a piece of sandpaper is too blind to use, then change it with a finer sandpaper, until the use of the finest water sandpaper.
Figure 3: Commutators.
Alignment of Servo Motor Encoder Phase and Rotor Magnetic Pole Phase
Incremental Encoder Phase Alignment
- The alignment method between the phase of the UVW electronic sign of the incremental encoder with commutation sign and the phase of the magnetic pole of the rotor, or the phase of the electrical angle, is as follows:
- Use a DC power supply to the UV windings of the motor through the DC less than the rated current, U in, V out, orientating the motor shaft to a balance position.
- Observe the U and Z signals of the encoder with an oscilloscope.
- Adjust the relative position of the rotary shaft of the encoder and the motor shaft.
- While adjusting, you should observe the jump edge of encoder U and Z signal until Z signal is stable at a high level (the default normal level of Z signal is low here), and lock the relative position relationship between encoder and motor.
- Rotate the motor shaft back and forth. After letting go, if the Z signal can be stable at a high level when the motor shaft freely returns to the balance position each time, the alignment will be effective.
Figure 4: KOYO Solid-shaft Incremental Rotary Encoder TRD-S200B
Absolute Encoder Phase Alignment
There is little difference between the phase alignment of an absolute encoder for a single turn and multiple turns. In fact, the detection phase of the encoder is aligned with the phase of the electromechanical angle within one turn.
At present, a very practical method is to use EEPROM inside the encoder to store the measured phase after the encoder is randomly installed on the motor shaft. The specific methods are as follows.
The encoder is randomly installed on the motor, and the rotary shaft of the encoder and the motor shaft are consolidated, as well as the encoder housing and the motor housing.
You should power on the UV winding of the motor with a DC power supply that is less than the rated current, U in, V out, the motor shaft is orientated to a balance position.
Read the single-turn position value of the absolute encoder with the servo drive and store it into the EEPROM which records the initial phase of the electro-mechanical angle inside the encoder.
The alignment is finished.
Servo Motor Movement
In the feed, the motor occurs channeled phenomenon, resulting in the unstable speed measurement signal, and the encoder cracks. The wiring terminal is in bad contact with the screw, which loosens the screw. When the movement occurs from the positive direction and the opposite direction of the movement of the commutation moment, it is generally due to the extremely large reverse clearance of the feed transmission chain or servo drive gain.
Servo Motor Crawl
Most of them occur in the starting acceleration section or low-speed feeding, generally due to the poor lubrication state of the feeding transmission chain, low gain of the servo system and excessive external load and other factors. In particular, it should be noted that the coupling used by the servo motor and ball screw may occur cracks due to loose connection or coupling itself defects, resulting in ball screw and servo motor rotation to be not synchronized, and unstable feed movement.
Servo Motor Vibration
When the machine is running at high speed, it may vibrate. And then it will produce an overcurrent alarm. The vibration fault of machine tools is generally due to the speed, so the speed ring should be checked.
Servo Motor Torque Reduction
When the servo motor is running from the rated blocked torque to high speed, it is found that the torque will suddenly decrease, which is caused by the heat dissipation damage of the motor windings and the heating of the mechanical part. At high speed, the temperature rise of the motor becomes severe. Therefore, you must inspect the load of the motor before the correct use of the servo motor.
Servo Motor Torque Position Error
When the servo motor movement exceeds the position tolerance range (KNDSD100 factory standard setting is PA17:400), the servo driver will appear "4" position deviation alarm. The main reasons are as follows. The tolerance range set by the system is small. Servo system gain setting is improper. The position detection device is polluted. The cumulative error of the feed transmission chain is too large.
Servo Motor Rotation Failure
In addition to the connecting pulse and direction signal of the CNC system and the servo driver, there is also enable control signal, generally DC+24V relay coil voltage. A servo motor does not rotate, you can troubleshoot it by these methods.
Check whether there is pulse signal output from the numerical control system.
Inspect whether the enabling signal is connected.
Observe if the input/output state of the system meets the starting condition of the feed shaft through the LCD screen.
Confirm that the brake is on for the servo motor with an electromagnetic brake
Examine if the driver is faulty.
Check whether the servo motor fails.
Inspect if the servo motor and ball screw coupling fail or the key release.
