How to set the electronic gear ratio of a servo motor

Introduction to servo motors

Servo motors refer to motors that control the operation of mechanical components in servo systems. They are indirect speed-changing devices that assist motors.

Servo motors can control speed and position with high accuracy, and can convert voltage signals into torque and speed to drive the controlled object. The rotor speed of a servo motor is controlled by the input signal and can respond quickly. In automatic control systems, it is used as an actuator and has the characteristics of small electromechanical time constant, high linearity, and starting voltage. It can convert the received electrical signal into angular displacement or angular velocity output on the motor shaft. It is divided into two categories: DC and AC servo motors. Its main feature is that there is no self-rotation when the signal voltage is zero, and the speed decreases uniformly with the increase of torque.

How to understand the electronic gear ratio of the servo motor
Simply put, for example, the electronic gear ratio is 1 (system default), the pulse equivalent is 1mm (that is, the distance the object runs when you send 1 pulse. Note that it is a control pulse, which is the pulse sent by your PLC to the servo amplifier). When you change the electronic gear ratio to 2, the corresponding pulse equivalent becomes 2mm.
It can also be understood that when you give the servo amplifier 1 pulse, when the electronic gear ratio is 1, the servo amplifier runs according to one pulse, when the electronic gear ratio is 2, the servo amplifier runs according to 2 pulses, and so on!

How to set the electronic gear ratio of the servo motor

Setting for the purpose of maximum motor speed

When the servo motor rotates, speed performance is more important than accuracy performance, and it is hoped that the motor speed performance can be fully displayed; while for the rotation resolution requirement is lower. It is recommended to use the following method to set

1) conditions and requirements, assuming that the servo motor rotation speed to be set is 3000R/min, and the number of encoder pulses per revolution is 8192pulse/rev

2) Calculation instructions

Relative to the 3000R/min speed, the pulse frequency is 8192&mes;3000/60=409 600HZ=409.6KHZ.

When the controller pulse output can only be up to 100kHZ, first set the numerator CMX and denominator CDV of the electronic gear ratio to 1, and then send out 10KHZ pulses from the controller JOG rotation as the pulse frequency of 1/10 of the maximum speed. At this time, the servo motor speed is
(10/409.6)&mes;3000≈73R/min.

If the speed is not calculated, the drive speed value can be directly monitored, which should also be 73R/min.

3) Setting method:

The desired speed for a 10KHZ pulse is 3000/min, but the actual speed is 73r/min. To correct the actual speed to 300r/min, the electronic gear ratio must be modified.

73&mes;CMZ/CDV=300 (R/MIN)

Therefore, the CMX numerator can be set to 300, and the CDV denominator can be set to 73.

When the controller's pulse output frequency is 100KHZs, the speed is

3000&mes;[﹙300/73﹚×100000]/409600=3009R/MIN.

All structural conditions are ignored in this example, but the resolution of the transmission part must be considered in actual applications. If the resolution is ignored, the product will eventually become unusable.

How to determine the electronic gear ratio of a servo motor

1. Introduction to electronic gear ratio parameters

The so-called "electronic gear" function has two main applications: one is to adjust the number of command pulses required for the motor to rotate one circle to ensure that the motor speed can reach the required speed. For example, the maximum pulse frequency sent by the host computer PLC is 200KHz. If the electronic gear ratio is not modified, the motor needs 10,000 pulses to rotate one circle, and the maximum speed of the motor is 1200rpm. If the electronic gear ratio is set to 2:1, or the number of pulses per revolution is set to 5000, the motor can reach 2400rpm.

For example: the electronic gear ratio is set to 1:1 or the number of pulses per revolution is set to 10000, and the upper computer PLC sends the highest pulse frequency of 200KHz

2. Calculation of the number of pulses per revolution and the electronic gear ratio

Calculate the number of pulses per revolution or the electronic gear ratio in the following order 1 to 6

Note:

(1) Both the number of pulses per revolution and the electronic gear ratio can limit the command amount required for the servo motor to rotate one circle. The two are complementary, but the priority of the number of pulses per revolution is higher than the electronic gear ratio. The electronic gear ratio will only take effect when the number of pulses per revolution is set to 0. This is what users need to pay attention to. In special cases, if the number of pulses per revolution is calculated to be a decimal, you should consider using the electronic gear ratio.

(2) When P2-02 and P2-03 exceed the setting range, please reduce the numerator and denominator to integers within the setting range before setting. Reduction does not affect the use without changing the ratio.

(3) Unless otherwise specified, the resolution of the motor encoder on the market is 2500P/R.

(4) The command unit does not represent the processing accuracy. Refining the command unit based on the mechanical accuracy can improve the positioning accuracy of the servo. For example, when applying a lead screw, the mechanical accuracy can reach 0.01mm, so the command unit equivalent of 0.01mm is more accurate than the command unit equivalent of 0.1mm.

3. Example of setting electronic gear

Example:

Supplementary explanation of the above example: The number of pulses of the host computer is 5000, which is through the lead screw pitch of 5mm, the pulse equivalent requirement is 0.001mm, so the number of pulses is 5/0.001=5000. The encoder feedback pulse is 131072 per revolution (servo motor), but due to the speed change mechanism, it is 3/2.