Servo motor are primarily used for precise positioning, unlike ordinary motors. Typically, when we talk about controlling a servo, we are referring to its position control. While servo motors can also operate in speed and torque control modes, these are less commonly used.
Speed control is usually implemented with inverters and is often used in scenarios requiring rapid acceleration and deceleration or precise speed control. Unlike standard inverters, servo motors can achieve thousands of revolutions within a short span due to their closed-loop system, providing stable and accurate speed control. Torque control focuses on managing the servo motor's output torque, taking advantage of the servo’s fast response time. In both cases, the servo drive functions similarly to a frequency converter, typically using analog control.
Position control remains the primary application of servo motors. This involves managing both speed and position to control how quickly the servo motor reaches a specific point and halts precisely.
A Servo Motor Driver regulates the distance and speed of the servo motor based on the frequency and number of pulses it receives. For instance, if a servo motor completes one revolution for every 10,000 pulses, then if a PLC sends 10,000 pulses per minute, the motor rotates at 1 rpm. If it sends 10,000 pulses per second, the motor rotates at 60 rpm.
PLC systems manage the servo motor by controlling pulse output. The most common method is using PLC transistor outputs, especially in low-end PLCs. Mid- and high-end PLCs, however, communicate the pulse quantity and frequency to the servo drive. Both methods achieve the same result but through different channels.
Programming PLCs varies between manufacturers; for example, Japanese PLCs use instructions, while European ones use function blocks. The fundamental process is consistent, as both types manage the output channel, pulse count, frequency, acceleration, deceleration, and read motion parameters like whether the servo drive has reached its position or triggered a limit.
In summary, regardless of the PLC type, the goal remains the same: controlling these physical parameters and reading the servo motor's movement data, even though the implementation varies between systems.
