I. Servo Driver Faults and Repairs
Common servo driver repair, testing, and methods:
1. When checking the current monitoring output of the driver with an oscilloscope, it was found to be entirely noise and could not be read.
Cause of the fault: The current monitoring output is not isolated from the AC power supply (transformer).
Solution: Use a DC voltmeter to check and observe.
2. A motor travels faster in one direction than in the other;
(1) Cause of failure: The phase of the brushless motor is wrong.
Solution: Detect or identify the correct phase.
(2) Cause of failure: The test/deviation switch is in the test position when not in use for testing.
Solution: Set the test/deviation switch to the deviation position.
(3) Cause of failure: The position of the deviation potentiometer is incorrect.
Solution: Reset.
3. Motor stall;
(1) Cause of failure: The polarity of the speed feedback is incorrect.
Solution: You can try the following methods.
a. If possible, switch the position feedback polarity switch to the other position. (This is possible on some drivers.)
b. If using a speed measuring machine, swap the TACH+ and TACH- connections on the driver.
c. If using an encoder, swap the connections of ENC A and ENC B on the driver.
d. In HALL speed mode, swap HALL-1 and HALL-3 on the driver, and then swap Motor-A and Motor-B.
(2) Cause of failure: The encoder power supply is lost when the encoder speed feedback is being processed.
Troubleshooting: Check the 5V encoder power supply connection. Ensure this power supply can provide sufficient current. If using an external power supply, ensure this voltage is connected to the driver signal ground.
4. The LED light is green, but the motor is not moving;
(1) Cause of failure: Motors in one or more directions are prohibited from operating.
Solution: Check the +INHIBIT and -INHIBIT ports.
(2) Cause of the fault: The command signal is not grounded to the driver signal.
Solution: Connect the command signal ground and the driver signal ground.
5. After powering on, the driver's LED light does not illuminate;
Cause of the fault: The power supply voltage is too low, below the minimum voltage requirement.
Solution: Check and increase the power supply voltage.
6. The LED light flashes when the motor rotates;
(1) Cause of the fault: HALL phase error.
Troubleshooting: Check if the motor phase setting switch (60°/120°) is correct. Most brushless motors have a 120° phase difference.
(2) Cause of failure: Hall sensor malfunction
Solution: Detect the voltage at Hall A, Hall B, and Hall C while the motor is running. The voltage values should be between 5VDC and 0V.
7. The LED light remains red at all times;
Cause of the fault: A fault exists.
Troubleshooting: Causes: Overvoltage, undervoltage, short circuit, overheating, driver disabled, HALL invalid.
II. Servo Driver Operating Modes
The servo driver offers the following selectable operating modes: open-loop mode, voltage mode, current mode (torque mode), IR compensation mode, Hall speed mode, encoder speed mode, tachometer mode, and analog position loop mode (ANP mode). (Not all of these modes are available in all driver models.)
1. Open-loop mode
The input command voltage controls the output load rate of the driver. This mode is used for brushless motor drivers and is the same as the voltage mode for brushed motor drivers.
2. Voltage Mode
The input command voltage controls the driver's output voltage. This mode is used for brushed motor drivers and is the same as the open-loop mode for brushless motor drivers.
3. Current Mode (Torque Mode)
The input command voltage controls the driver's output current (torque). The driver adjusts the load rate to maintain the command current value. This mode is typically included if the servo driver can operate in speed or position loop mode.
4. IR Compensation Mode
Input commands control motor speed. IR compensation mode can be used to control the speed of motors without speed feedback. The driver adjusts the load rate to compensate for fluctuations in output current. When the command response is linear, this mode is less accurate than closed-loop speed mode under torque disturbances.
5. Hall Speed Mode
The input command voltage controls the motor speed. This mode utilizes the frequency of the Hall sensor on the motor to form a speed closed loop. Due to the low resolution of the Hall sensor, this mode is generally not used for low-speed motion applications.
6. Encoder speed mode
The input command voltage controls the motor speed. This mode utilizes the frequency of encoder pulses on the servo motor to form a speed closed loop. Due to the encoder's high resolution, this mode can be used for smooth motion control at various speeds.
7. Speed measuring machine mode
The input command voltage controls the motor speed. This mode utilizes an analog tachometer on the motor to form a speed closed loop. Because the voltage of the DC tachometer is analog and continuous, this mode is suitable for very high-precision speed control. Of course, it is also susceptible to interference at low speeds.
8. Simulated Position Loop Mode (ANP Mode)
The input command voltage controls the motor's rotational position. This is essentially a speed mode that provides position feedback in analog devices (such as adjustable potentiometers, transformers, etc.). In this mode, the motor speed is proportional to the position error, and it features a faster response and smaller steady-state error.
