Servo motors typically use incremental or absolute encoders, which operate on the principle of one AB phase pulse plus one Z phase pulse. The AB phase pulses can be understood as two independent gratings, each 90° out of phase, dividing a 360° circle into 2500 equal grids. During rotation, when A leads B, it's considered clockwise rotation; conversely, it's counter-clockwise rotation. This generates rising and falling edges for A, rising and falling edges for B, which explains why servo motor specifications describe 2500 lines and 10,000 pulses per revolution. The Z phase generates one pulse per revolution. Therefore, a standard servo motor requires 10,000 pulses per revolution.
To control a rotation, the minimum requirements are: 1. Rotation direction (i.e., the direction of phases A and B); 2. Number of rotations (i.e., number of pulses); 3. Rotation speed (i.e., pulse output frequency). Now let's calculate the highest pulse frequency for servo rotation. Assuming a 3000 RPM servo motor has a maximum speed of 5000 RPM, then the maximum output frequency we need to provide is 5000 RPM * 10000 PLS / 60S = 833.333 kHz. This exceeds the PLC's maximum output frequency of 200 kHz. Therefore, an electronic gear ratio (meaning a defined number of pulses per revolution) is generated under this condition. This value is described by the numerator/denominator. At this point, we can understand that the numerator represents the number of pulses required for the servo motor to complete one revolution, and the denominator is the number of pulses received by the servo controller.
Therefore, when setting the servo controller parameters, we can always set the numerator of the electronic gear ratio to 10000, and the denominator to the desired number of pulses required for the PLC to control the servo to rotate one revolution. Let's assume the electronic gear ratio is 10. After this conversion, we can clearly describe that with a numerator of 10000 and a denominator of 1000, the servo motor rotates one revolution for every 1000 pulses issued by the PLC.
