How does a servo driver drive a servo motor?
A servo drive, also known as a servo controller or servo amplifier, is a controller used to control servo motors. Its function is similar to that of a frequency converter for ordinary AC motors. It is part of a servo system and is primarily used in high-precision positioning systems. Generally, it controls the servo motor through position, speed, and torque to achieve high-precision positioning of the transmission system. Currently, it represents a high-end product in transmission technology.
Is it driven by amplifying the pulse signal emitted by the PLC?
It's not a simple amplification. The PLC outputs a square wave, while the driver outputs a sine wave. You can think of the PLC's pulses as the servo driver's instructions, like a leader's work order. The servo driver is the executor doing the work; the leader tells the executor to do it this way, but the executor still has to figure out how to do it. The servo driver can be understood as an AC power supply that enables the servo motor to operate. When driving the servo motor, it doesn't simply amplify the PLC's pulses; instead, it understands what these pulses do and then uses PWM to simulate a sine wave to control the servo motor.
Generally, PLCs send pulses, which are PLS pulses, meaning square waves with fixed pulse width and interval. The number of these square waves can be understood as the "step," that is, the "step" the servo motor moves (i.e., how many angles it rotates) after one pulse. Therefore, the more square waves there are, the more angles the servo motor can rotate. So, the servo driver needs to output a waveform that allows the servo motor to rotate by a certain angle. However, servo motors cannot be simply rotated by their structure like stepper motors. They need a position loop to form a closed loop, which means that the encoder pulses measure how much the current motor rotation angle has changed, and then the PID controller adjusts the output voltage and frequency.
In other words, the servo drive compares the received PLC pulses with the encoder pulses fed back from the motor (which can be simply understood as subtraction), then performs PID calculations and outputs a value. This value is then fed into the speed loop and current loop for further calculations. Finally, PWM is used to control the IGBT module, outputting a square wave to simulate a sine wave and control the servo motor's speed to achieve the desired rotation angle. From a fundamental perspective, the control of a servo drive is quite similar to that of a vector frequency converter.
