A servo motor is an engine that controls the operation of mechanical components in a servo system ; it is a type of auxiliary motor with indirect speed change.
Servo motors enable highly accurate control of speed and position, converting voltage signals into torque and speed to drive the controlled object.
Servo motor rotor speed is controlled by input signal and can respond quickly. In automatic control systems, it is used as an actuator and has characteristics such as small electromechanical time constant, high linearity, and low starting voltage. It can convert the received electrical signal into angular displacement or angular velocity output on the motor shaft.
Today I'll be sharing with you the debugging methods and precautions for servo motors.
Servo motor debugging method
1. Initialize parameters
Initialize the parameters before wiring.
On the control card: Select the control mode; clear the PID parameters; ensure the enable signal is off by default when the control card is powered on; save this state to ensure that the control card is in this state when it is powered on again.
On the servo motor: set the control mode; enable external control; set the gear ratio of the encoder signal output; set the ratio between the control signal and the motor speed.
Generally, it is recommended that the maximum design speed of the servo be matched with a control voltage of 9V.
2. Wiring
Power off the control card and connect the signal cable between the control card and the servo.
The following lines must be connected: analog output line of the control card, enable signal line, and encoder signal line of the servo output.
After verifying that the wiring is correct, power on the servo motor and control card (and PC).
At this point, the motor should not move and can be easily rotated by external force. If not, check the enable signal settings and wiring.
Rotate the motor with external force to check if the control card can correctly detect changes in the motor position; otherwise, check the wiring and settings of the encoder signal.
3. Try the direction
In a closed-loop control system, if the direction of the feedback signal is incorrect, the consequences will certainly be disastrous.
Enable the servo by turning on the control card. This allows the servo to rotate at a lower speed, which is known as "zero drift".
Most control cards have instructions or parameters for suppressing zero drift. Use these instructions or parameters to see if the motor's speed and direction can be controlled by them.
If it cannot be controlled, check the analog wiring and the parameter settings of the control mode.
If a positive number is provided, the motor rotates forward and the encoder count increases; if a negative number is provided, the motor rotates in reverse and the encoder count decreases.
If the motor is under load and has a limited stroke, do not use this method.
Do not apply excessive voltage during testing; it is recommended to keep it below 1V.
If the directions are inconsistent, the parameters on the control card or motor can be modified to make them consistent.
4. Suppress zero drift
In closed-loop control, the presence of zero drift can have a certain impact on the control effect, and it is best to suppress it.
Carefully adjust the parameters for suppressing zero drift on the control card or servo to bring the motor speed close to zero.
Since zero drift itself has a certain degree of randomness, it is not necessary to require the motor speed to be absolutely zero.
5. Establish closed-loop control
Re-enable the servo enable signal via the control card, and input a small proportional gain on the control card.
As for what constitutes a small value, that's subjective; if you're still unsure, enter the minimum value allowed by the control card. Enable the control card and the servo.
At this point, the motor should be able to roughly perform the actions according to the motion commands.
6. Adjust closed-loop parameters
Fine-tuning the control parameters to ensure the motor moves according to the control card's instructions is a necessary task, and this part relies heavily on experience, so we'll skip the details here.
Precautions for servo motors
1. Servo motor oil and water protection
A: Servo motors can be used in environments where they may be exposed to water or oil droplets, but they are not completely waterproof or oil-proof. Therefore, servo motors should not be placed or used in environments where they are submerged in water or oil.
B: If the servo motor is connected to a reduction gear, an oil seal should be applied when using the servo motor to prevent oil from the reduction gear from entering the servo motor.
C: Do not immerse the servo motor cable in oil or water.
2. Servo motor cable → Reduce stress
A: Ensure that the cable is not subjected to torque or vertical load due to external bending forces or its own weight, especially at cable exits or connections.
B: When the servo motor is moving, the cable (the one that comes with the motor) should be securely fixed to a stationary part (relative to the motor), and it should be extended with an additional cable installed in the cable support to minimize bending stress.
C: Make the bend radius of the cable as large as possible.
3. Permissible shaft end load of the servo motor
A: Ensure that the radial and axial loads applied to the servo motor shaft during installation and operation are within the specified values for each model.
B: Extra care should be taken when installing a rigid coupling, especially since excessive bending loads can cause damage or wear to the shaft end and bearings.
C: It is best to use a flexible coupling so that the radial load is below the allowable value. This is designed specifically for servo motors with high mechanical strength.
D: For information on permissible shaft loads, please refer to the "Permissible Shaft Load Table" (Instruction Manual).
4. Servo motor installation precautions
A: When installing/removing the coupling component from the servo motor shaft, do not strike the shaft end directly with a hammer. (Striking the shaft end directly with a hammer will damage the encoder on the other end of the servo motor shaft.)
B: Strive to align the shaft ends to the optimal state (improper alignment may cause vibration or bearing damage).
DC servo motors can be used in EDM machines, robotic arms, and precision machinery. They can be equipped with a standard encoder and tachometer with a high resolution of 2500P/R, and can also be fitted with a gearbox to bring reliable accuracy and high torque to the mechanical equipment.
It has good speed regulation and the highest output power per unit weight and volume, exceeding that of AC motors and far surpassing that of stepper motors. The multi-stage structure results in less torque fluctuation.
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