Servo motor electronic gear ratio calculation method

The electronic gear ratio of the servo motor is to enlarge or reduce the pulse frequency received by the servo to the upper computer. One of the parameters is the numerator and the other is the denominator. For example, if the numerator is larger than the denominator, it is enlarged. For example, if the upper computer input frequency is 100HZ, the electronic gear ratio is set to 1 and the denominator is set to 2, the actual servo running speed is performed according to the 50HZ pulse. The input frequency of the upper computer is 100HZ, the electronic gear ratio is set to 2, and the denominator is set to 1. Then the actual running speed of the servo is performed according to the pulse of 200HZ. The electronic gear ratio is relative to the mechanical gear meshing and the gear ratio of the gear pair. It is also a form of shaftless transmission that is often said.

Taking a motor with a 17-bit encoder as an example, the servo amplifier transmits 131072 pulses to the servo motor every revolution of the servo motor, and the encoder feeds 131072 pulses to the servo amplifier. If we want the motor to rotate at 20r/s, if we do not set the electronic gear ratio, we will send 2621440 pulses per second to the servo amplifier, ie the pulse frequency is 2621440HZ. However, the devices that send pulses, such as PLCs, have a limit on the transmission pulse frequency, which is generally 200KHZ or 500KHZ. At this time, we introduce the concept of electronic gears to reduce the frequency of pulses to the servo amplifier.

The encoder of the servo motor is generally 2000 lines or 2500 lines, that is, it can generate 2000 or 2500 pulses in one revolution, and the servo driver performs 4 times frequency processing on this pulse, so the motor can generate 8000 or 10000 in one revolution. The pulse, that is, the resolution is 8000 or 10000.

motor model

Encoder line number

Motor encoder resolution

Sanyo P2, P5 motor

2000

8000

Dahao servo

2500

10000

Take the Sanyo servo motor as an example: When the controller sends a pulse to the driver, the angle at which the servo motor rotates is

After the secondary transmission, the angle of the frame movement is converted to the motor and the secondary transmission ratio is inversely proportional. For example, if the secondary transmission ratio is 1/4, then the angle of the motor rotation is 4 times that of the transmission shaft. . Frame gear size:

At present, there are mainly two kinds of gears on the market: the angles that need to be rotated when the frame is moved by 0.1 mm are 0.36° and 0.45°. Most machines use a 0.36° gear.

In summary, the formula for the electronic gear ratio can be found as follows

With the screw structure, the calculation of the electronic gear ratio is slightly different.

Because in general, there is a 1:1 belt drive between the motor and the screw shaft, and the pitch of the screw is M mm/turn, then the calculation formula is

When the servo motor rotates, the speed performance is heavier than the precision performance, and it is desirable to fully express the motor speed performance; and when the rotation resolution is low. The following methods are recommended.

Suppose the servo motor rotation speed to be set is 3000R/min, and the number of pulses per encoder is 8192 pulses/rev.

The pulse frequency is 8192 & TImes relative to 3000R/min; 3000/60=409 600HZ=409.6KHZ

When the pulse output of the controller can only be up to 100kHZ, the molecular part CMX and the denominator part CDV of the electronic gear ratio are first set to 1, and then the 10KHZ pulse is sent by the controller JOG to be the pulse frequency of the maximum speed of 1/10. At this time, the servo motor speed is

(10/409.6) & TImes; 3000≈73R/min

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

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

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

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

The speed of the controller's pulse output frequency is 100KHZs.

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

In this example, all structural conditions are ignored, and the resolution of the transmission part must be considered in practical applications. If the variability is ignored, the product will not be used.

Servo motors are commonly used in machining control and operation. At this time, the machining accuracy requirements should be prioritized over the speed. When the accuracy is reached, the speed problem is considered. Therefore, the setting of the electronic gear ratio must give priority to the output pulse of the controller can not be arbitrarily amplified, because the output pulse frequency will affect the resolution. It is recommended to prioritize the setting of the electronic gear ratio.

Assume that the rated speed of the servo motor to be set is 3000R/MIN. The encoder pulse is 8192 pulses/rev per revolution; the maximum frequency of the controller pulse output is 100KHZ; the servo motor link deceleration mechanism, input pulse: output pulse = M: N = 3; The ball shaft of the mechanism output shaft linking mechanism has a lead of 10 mm.

The resolution of the servo motor driven by the speed reduction mechanism is

(10/8192) × (1/3) ≈ 0.0004069 (mm / pulse) = 0.4069 μm / pulse

The number of pulses per revolution of the lead screw is

10/0.0004069≈24576(pulse/rev)

If you want the output slew rate of the controller to be 1μm/pulse, the number of pulses per revolution of the lead screw becomes 10/0.001=10000pulse/rev

10000×(CMX/CMD)=24576pulse/rev

The controller sends a pulse servo to receive the pulse

Therefore, the CMX molecule can be set to 24576, the CDV denominator can be set to 10000, and so on.

(100000×24576×60)/(8192×10000)=1800r/min

1800r/min "3000r/min. Therefore, the motor rotation speed cannot reach 3000r/min, but the resolution of the servo motor will achieve the desired effect.