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

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Servo motors typically use either an incremental or absolute encoder. The working principle involves AB phase pulses combined with a Z phase pulse. The AB-phase pulses consist of two independent sets of gratings with a 90° phase difference, dividing the full 360° rotation into 2500 equal segments. As the motor rotates, if the A signal leads the B signal, it indicates forward motion, and vice versa. Each rotation generates four edges—rising and falling for both A and B—resulting in 10,000 pulses per revolution. The Z phase provides one pulse per full rotation, which is essential for position reference.

To control a servo motor effectively, three key parameters are required: the direction of rotation (determined by the AB phase sequence), the number of revolutions (based on the pulse count), and the rotational speed (determined by the pulse frequency). Let's calculate the maximum pulse frequency needed. For a 5000 RPM servo motor, the maximum pulse frequency would be 5000 RPM × 10,000 PLS / 60 S = 833.333 KHz. This exceeds the maximum output frequency of most PLCs, which is usually around 200 KHz. In such cases, an electronic gear ratio is used to adjust the pulse distribution.

The electronic gear ratio is expressed as a fraction, where the numerator represents the number of pulses the servo motor requires to complete one full revolution, and the denominator represents the number of pulses the controller can process. For example, if the numerator is fixed at 10,000 (the standard pulse count for one revolution), and the denominator is set to 1000, then the PLC only needs to send 1000 pulses to make the motor rotate once. This allows for better compatibility between the PLC’s capabilities and the servo motor’s requirements, ensuring smooth and accurate control even at high speeds.

By adjusting the electronic gear ratio, users can fine-tune the system to match their specific application needs. Whether it's for high-speed positioning or precise low-speed movement, understanding and configuring this ratio is crucial for achieving optimal performance from the servo motor system.