A servo motor is a device that converts electrical energy into mechanical energy. It can precisely control speed and position and is an important component of a servo system. The working principle of a servo motor is to receive pulse signals to rotate a corresponding angle, while simultaneously sending feedback signals to the controller, thus achieving closed-loop control. Although servo motors have excellent performance, they can still experience malfunctions during use, affecting normal operation.
Based on different fault symptoms and causes, we can classify servo motor faults into the following categories:
1. Power Supply Failure: This type of failure is mainly caused by unstable power supply, overvoltage or undervoltage, short circuit or open circuit, etc. Repair methods include checking and replacing damaged components, adjusting power supply parameters, and installing protective devices. ⚡
2. Encoder Failure: This type of failure is mainly caused by damage, loosening, or contamination of the encoder itself. The encoder is a crucial component for the servo motor's output feedback signal; if it malfunctions, it can lead to position errors or oscillations. Repair methods include cleaning or replacing the encoder, recalibrating, or adjusting parameters.
3. Driver Failure: This type of failure is mainly caused by damage to internal components, overheating, or overload of the driver. The driver amplifies the control signals and outputs them to the motor. If a problem occurs, it can lead to failure to start, abnormal speed, or alarms. Repair methods include checking and replacing damaged components, reducing the temperature or load, resetting or clearing alarms, etc.
4. Sensor Failure: This type of failure is mainly caused by damage, loosening, or contamination of the sensor itself. Sensors are devices used to detect external conditions such as temperature, pressure, and limit switches. If a sensor malfunctions, it can lead to inaccurate data or inability to read data. Repair methods include cleaning or replacing the sensor, reconnecting it, or adjusting its position.
5. Mechanical Failures: These failures are mainly caused by wear, loosening, or breakage of mechanical components such as bearings, gears, and couplings. The mechanical structure connects the motor and load, transmitting motion and force; problems in this area can lead to increased noise, intensified vibration, or jamming. Repair methods include lubricating or replacing worn parts, tightening or aligning loose parts, and replacing broken parts.
6. Control System Failure: This type of failure is mainly caused by problems with the software or hardware of the control system. The control system is a device used to send control signals and receive feedback signals. If problems occur, it can lead to communication failures, incorrect commands, or loss of control. Repair methods include checking and updating the software, replacing or repairing the hardware, and resetting or adjusting parameters.
Repair methods listed
Noise, instability
When customers use servo motors on certain machines, they often encounter problems such as excessive noise and unstable operation of the motor driving the load. When this happens, many users' first reaction is that the servo motor is of poor quality, because sometimes when stepper motors or frequency converter motors are used to drive the load, the noise and instability are much less. On the surface, it does seem to be the servo motor's fault, but after carefully analyzing the working principle of servo motors, we find that this conclusion is completely wrong.
The system oscillates, the motor torque fluctuates, and the load speed fluctuates accordingly. The result, of course, is noise, wear, and instability. However, these are not caused by the servo motor itself. This noise and instability originate from the mechanical transmission device, caused by a mismatch between the servo system's high response speed and the mechanical transmission or response time, i.e., the servo motor responds faster than the time required for the system to adjust to a new torque.
Once the root cause of the problem is found, solving it becomes much easier. For the example above, you can:
(1) Increase mechanical rigidity and reduce system inertia, thereby reducing the response time of mechanical transmission parts, such as replacing V-belts with direct screw drives or using gearboxes instead of V-belts;
(2) Reduce the response speed of the servo system and reduce the control bandwidth of the servo system, such as reducing the gain parameter value of the servo system.
Of course, the above is only one of the reasons for noise and instability. Different solutions will be available for different reasons. For example, noise caused by mechanical resonance can be addressed by resonance suppression and low-pass filtering in the servo motor. In short, the causes of noise and instability are generally not due to the servo motor itself.
Commutator repair
1. If the commutator surface is noticeably uneven (to the touch) or sparks are generated during motor operation, as in case four, remove the armature and machine the converter using a precision machine tool.
2. It is basically flat with only a few scratches or sparks. In the second case, without removing the armature, manually grind port 1 using wet sandpaper. The grinding sequence is as follows: First, process a wooden tool according to the curvature of the commutator's outer circle. Cut several different thicknesses of wet sandpaper into strips the same width as the commutator. Remove the carbon brushes (mark the handles and grooves of the removed carbon brushes to ensure that there is no incorrect left-right change during installation). Attach the commutator using the wooden tool wrapped with sandpaper. With the other hand, gently rotate the commutator shaft in the direction of motor rotation to grind it. The thickness of the sandpaper used for servo motor maintenance should be from coarse to fine. When a piece of sandpaper becomes too dark to use, replace it with another piece of fine sandpaper until the finest wet sandpaper (or metallographic sandpaper) is used up.
Servo motor maintenance vibration
During the feeding process, there is movement, and the speed measurement signal is unstable, such as if the encoder is cracked; or if the wiring terminals have poor contact, such as if the screws are loose; when the movement occurs at the moment of reversal from forward to reverse movement, it is usually caused by the backlash of the feed transmission chain or excessive servo drive gain.
Servo motor repair crawling phenomenon
These problems mostly occur during the starting acceleration phase or at low feed speeds, typically due to poor lubrication of the feed drive chain, low servo system gain, and excessive external load. In particular, it should be noted that the coupling used to connect the servo motor and the ball screw can cause the ball screw and servo motor to rotate out of sync due to loose connections or defects in the coupling itself (such as cracks), resulting in feed motions that are both fast and slow.
