Servo motor electronic gear ratio setting method - Database & Sql Blog Articles

Photocoupler

Typically, servo motors use either incremental or absolute encoders. The working principle involves AB phase pulses combined with a Z phase pulse. The AB phase can be thought of as two sets of independent gratings with a 90° phase difference. A full rotation is divided into 2500 equal parts. When the motor rotates forward, the A signal leads the B signal, and vice versa for reverse rotation. As the motor turns, it generates rising and falling edges on both A and B signals, resulting in 10,000 pulses per revolution. The Z phase produces a single pulse per full rotation, which is used for reference or zero-point detection.

To control a motor's rotation, three key factors are required: direction (determined by the AB phase sequence), number of revolutions (measured by the total pulse count), and rotational speed (calculated from the pulse frequency). Let’s calculate the maximum pulse frequency needed. If a servo motor operates at 3000 RPM but can reach up to 5000 RPM, the corresponding pulse frequency would be 5000 RPM × 10,000 PLS / 60 S = 833.333 kHz. This exceeds the maximum output frequency of a typical PLC, which is usually around 200 kHz. In such cases, an electronic gear ratio is introduced to adjust the pulse count.

The electronic gear ratio defines how many pulses the motor needs to complete one revolution relative to the pulses sent by the PLC. It is typically expressed as a numerator over a denominator. The numerator represents the number of pulses the motor requires for one full turn, while the denominator indicates the number of pulses the controller receives. For example, if we set the numerator to 10,000 and the denominator to 1000, then each 1000 pulses from the PLC will make the motor rotate one full revolution. This allows the system to operate within the PLC’s limitations while maintaining accurate control over the motor’s movement.

By adjusting the electronic gear ratio, you can effectively match the motor’s performance with the PLC’s capabilities, ensuring smooth and precise motion control. This method is widely used in industrial automation systems where high-speed and high-precision control are essential.