Many people believe that servo drive is the same thing as a frequency drive, but these two are completely different drives. While variable frequency drives without encoder modules adjust the frequency and amplitude of a 3-phase voltage signal to control a motor, servo drives do almost the same, but with greater accuracy. Servo drives usually have a built-in encoder into the motor, which makes changes to the voltage signal to meet specific requirements. But this is not the only difference between frequency and servo drive.
Servo drive is a special type of drive (electronic amplifier) and is usually used to power electric servo mechanisms. It receives a command signal from the control system, amplifies it and transmits electric current to a servo motor. Then, the servo motor produces a motion that is same as the command signal. In some cases, the command signal is the desired velocity, but it can also represent the desired torque. The servo motor uses a sensor, which reports the actual status of the motor back to the servo drive. Then, the servo drive compares the actual motor status with the motor status demanded by the command signal. It then changes the voltage frequency of the motor and corrects it if needed.
If the control system is properly configured, the servo motor will rotate at a velocity, which is identical with the velocity signal being received from the servo drive. To achieve the desired results, few parameters can be adjusted: damping, feedback gain, stiffness, etc. This process is known as performance tuning. The latest servo drives are suitable to many different types of motors.
Variable Frequency Drive
The variable frequency drive, or simply known as VFD, is an electronic device that can control and protect the AC motor speed. It is not a cheap investment, but is surely a worthy one. The variable frequency drive provides huge cost savings in a long run and also extends the motor life. This electronic devices is able to control the motor speed during start and stop cycles, as well as during run cycles. It consists of a DC circuit, an AC to DC converter and a DC to AC inverter. Usually, variable frequency drives are used to adjust control, absolute speed control and in applications that need energy savings. Unlike servo drive, the variable frequency drive converts constant frequency and voltage input power to adjustable frequency and voltage source for AC induction motor speed control.