Servo motors often experience motor failures due to long-term continuous use or improper user operation, and maintenance is relatively complex. The editor has collected 13 common repair methods for servo motor faults, for everyone to learn and reference.

1、 What are the tasks that need to be done before starting the servo motor

1) Measure insulation resistance (not less than 0.5M for low voltage motors).

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

3) Check if the starting equipment is in good condition.

4) Check if the fuse is suitable.

5) Check if the motor is properly grounded and zeroed.

6) Check if there are any defects in the transmission device.

7) Check if the motor environment is suitable and remove flammable materials and other debris.

2、 What are the reasons for overheating of servo motor bearings

Motor itself:

1) The fit between the inner and outer rings of the bearing is too tight.

2) There are issues with the shape and position tolerances of components, such as poor coaxiality of machine bases, end caps, shafts, and other parts.

3) Improper selection of bearings.

4) Poor lubrication of bearings or incomplete cleaning of bearings, with impurities in the lubricating grease.

5) Axis current.

In terms of usage:

1) Improper installation of the unit, such as the coaxiality of the motor shaft and the dragged device shaft meeting the requirements.

2) The pulley is pulled too tightly.

3) Poor maintenance of bearings, insufficient or expired lubricating grease, and deterioration due to dryness.

3、 What is the reason for unbalanced three-phase current in servo motors

1) Three phase voltage imbalance.

2) Poor welding or poor contact of a certain phase branch inside the motor.

3) Motor winding inter turn short circuit or ground phase short circuit.

4) Wiring error.

4、 How to control the speed of servo motor

A servo motor is a typical closed-loop feedback system, in which the reduction gear set is driven by the motor, and its terminal (output end) drives a linear proportional potentiometer for position detection. The potentiometer converts the angular coordinates 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, generates a correction pulse, and drives the motor to rotate forward or backward, so that the output position of the gear set matches the expected value, and the correction pulse tends to 0, thereby achieving the goal of precise positioning and constant speed of the servo motor.

5、 Observe whether sparks are generated between the carbon brush and commutator during the operation of the motor, and repair them based on the degree of sparks

1. There are only 2-4 extremely small sparks. If the surface of the commutator is flat at this time, most cases do not require repair;

2. It has no sparks and does not require repair;

3. If there are 4 or more extremely small sparks and 1-3 large sparks, there is no need to disassemble the armature, just use sandpaper to grind the carbon brush commutator;

4. If there are more than 4 large sparks, the commutator needs to be ground with sandpaper, and the carbon brush and armature must be removed. Replace the carbon brush and grind it.

6、 Repair of commutator

1. The surface of the commutator is noticeably uneven (which can be felt by hand) or sparks occur during motor operation, as in the fourth scenario. At this point, the armature needs to be disassembled and the converter needs to be machined with a precision machine tool;

2. Basically flat, with minimal scratches or sparks, as in the second case, L mouth 1 can be manually ground with sandpaper without disassembling the armature. The order of grinding is as follows: first, process a wooden tool according to the outer curvature of the commutator, cut several different thicknesses of sandpaper into long strips as wide as the commutator, remove the carbon brush (please make marks on the handle and groove of the removed carbon brush to ensure that it is not changed left or right during installation), use a wooden tool wrapped in sandpaper to firmly attach the commutator, and use the other hand to gently rotate the shaft commutator in the direction of motor rotation for grinding. The order of sandpaper thickness used for servo motor maintenance is from coarse to fine. When one sandpaper is too blind to use, switch to a finer sandpaper until the finest water sandpaper (or metallographic sandpaper) is used up.

7、 How to align the phase of servo motor encoder with the zero point of rotor magnetic pole phase and repair it

1. Phase alignment method 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 electrical angle phase, is as follows:

1) Apply a DC power supply to the UV winding of the motor with a DC current lower 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 between the encoder shaft and the motor shaft;

4) Adjust while observing the transition edge of the encoder U-phase signal and the Z signal until the Z signal stabilizes at a high level (assuming 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 stabilizes at a high level every time the motor shaft returns freely to the equilibrium position, then the alignment is effective.

2. Phase alignment method of absolute encoder

The phase alignment of the absolute encoder is not significantly different for single and multiple cycles. In fact, it aligns the detection phase of the encoder with the phase of the motor electrical angle within one cycle. A very practical method currently is to use the EEPROM inside the encoder to store the measured phase of the encoder randomly installed on the motor shaft. The specific method is as follows:

1) Randomly install the encoder on the motor, that is, fix the encoder shaft and motor shaft, as well as the encoder housing and motor housing;

2) Apply a DC power supply to the UV winding of the motor with a DC current lower than the rated current, U in, V out, and orient the motor shaft to a balanced position;

3) Read the single turn position value of the encoder using a servo driver and store it in the EEPROM that records the initial phase of the motor's electrical angle inside the encoder;

4) The alignment process has ended.

8、 Servo motor maintenance movement phenomenon

During feed, there may be movement and unstable speed measurement signals, such as cracks in the encoder; Poor contact of wiring terminals, such as loose screws; When the movement occurs at the moment of reversal between forward and reverse motion, it is generally due to the reverse backlash of the feed transmission chain or excessive servo drive gain.

9、 Crawling phenomenon during servo motor maintenance

Most of them occur during the acceleration stage or low-speed feed, usually due to poor lubrication of the feed transmission chain, low gain of the servo system, and excessive external load. It is particularly important to note that the coupling used to connect the servo motor and ball screw may cause the rotation of the ball screw and servo motor to be asynchronous due to loose connections or defects in the coupling itself, such as cracks, resulting in fluctuating feed movements.

10、 Vibration phenomenon during servo motor maintenance

When the machine tool is running at high speed, vibration may occur, which will trigger an overcurrent alarm. The vibration problem of machine tools generally belongs to the speed problem, so the speed loop problem should be found.

11、 Servo motor maintenance torque reduction phenomenon

When the servo motor goes from rated locked rotor torque to high-speed operation, it is found that the torque suddenly decreases due to heat dissipation damage to the motor winding and mechanical part heating. At high speeds, the temperature rise of the motor increases. Therefore, before using the servo motor correctly, it is necessary to verify the load of the motor.

12、 Phenomenon of servo motor maintenance position error

When the servo axis movement exceeds the allowable range of position deviation (KNDSD100 factory standard setting PA17:400, position deviation detection range), the servo drive will display a "4" position deviation alarm. The main reasons are: the tolerance range set by the system is small; Improper gain setting of servo system; The position detection device is contaminated; The cumulative error of the feed transmission chain is too large.

13、 The phenomenon of servo motor not turning during maintenance

In addition to connecting pulse and direction signals, the CNC system to the servo drive also has enable control signals, usually DC+24V relay coil voltage. The common diagnostic methods for servo motors not rotating include: checking whether the CNC system has pulse signal output; Check if the enable signal is connected; Observe whether the input/output status of the system meets the starting conditions of the feed axis through the LCD screen; Confirm that the brake of the servo motor with electromagnetic brake has been turned on; Driver malfunction; The servo motor has a malfunction; The coupling between the servo motor and ball screw fails or the key is disconnected.