Introduction to Servo Motors
A servo motor is an engine that controls the operation of mechanical components in a servo system; it is a type of auxiliary motor with indirect speed change.
Servo motors enable highly accurate speed and position control, converting 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, they are used as actuators and possess characteristics such as a small electromechanical time constant, high linearity, and low starting voltage. They can convert received electrical signals into angular displacement or angular velocity output on the motor shaft. Servo motors are broadly classified into DC and AC servo motors. Their main characteristic is that they do not rotate when the signal voltage is zero, and their speed decreases uniformly as the torque increases.
How to understand the electronic gear ratio of a servo motor?
Simply put, for example, if the electronic gear ratio is 1 (system default) and the pulse equivalent is 1mm (that is, the distance the object travels when you send one pulse; note that this is the control pulse, the pulse that your PLC sends to the servo amplifier), when you change the electronic gear ratio to 2, the corresponding pulse equivalent becomes 2mm.
This can also be understood as follows: if you give the servo amplifier one pulse, when the electronic gear ratio is 1, the servo amplifier will operate according to one pulse; when the electronic gear ratio is 2, the servo amplifier will operate according to two pulses, and so on!
Servo Motor Electronic Gear Ratio Setting Method
Setting with the aim of achieving the highest motor speed
When a servo motor rotates and speed performance is more important than precision performance, it's desirable to fully represent the motor's speed capabilities; however, when rotational resolution requirements are lower, the following settings are recommended.
1) Conditions and requirements: Assume the desired servo motor rotation speed is 3000 R/min, and the encoder pulse count is 8192 pulses/rev.
2) Calculation instructions
The pulse frequency relative to a speed of 3000 RPM is 8192 × 3000 / 60 = 409600 Hz = 409.6 kHz.
When the controller pulse output can only be up to 100kHz, first set both the numerator (CMX) and denominator (CDV) of the electronic gear ratio to 1. Then, use the 10kHz pulse sent by the controller JOG as the pulse frequency for 1/10 of the maximum speed. At this time, the servo motor speed is...
(10/409.6)×3000≈73R/min
If the rotational speed is not calculated, you can directly monitor the drive speed value, which should also be 73 R/min.
3) Setup method
The desired speed for a 10kHz pulse is 3000 r/min, but the actual speed is 73 r/min. To correct the actual speed to 300 r/min, the electronic gear ratio must be modified.
73×CMZ/CDV=300 (R/MIN)
Therefore, the numerator of CMX can be set to 300, and the denominator of CDV can be set to 73.
The rotational speed when the controller's pulse output frequency is 100 kHz is
3000×［﹙300/73﹚×100000］/409600=3009R/MIN
This example ignores all structural conditions, but in practical applications, the resolution of the transmission part must be considered. If the resolution is ignored, the product will eventually become unusable.
How is the electronic gear ratio of a servo motor determined?
1. Introduction to Electronic Gear Ratio Parameters
The so-called "electronic gear" function has two main applications: First, it adjusts the number of command pulses required for the motor to rotate one revolution, ensuring that the motor speed reaches the required speed. For example, if the maximum pulse frequency sent by the host PLC is 200kHz, without modifying the electronic gear ratio, the motor would require 10,000 pulses to rotate one revolution, resulting in a maximum motor speed of 1200rpm. However, 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 a speed of 2400rpm.
For example: the electronic gear ratio is set to 1:1 or the number of pulses per revolution is set to 10,000, and the maximum pulse frequency sent by the host PLC is 200 kHz.
2. Calculation of pulses per revolution and electronic gear ratio
Calculate the number of pulses per revolution or the electronic gear ratio in the following order 1 to 6.
Notice:
(1) Both the number of pulses per revolution and the electronic gear ratio can limit the number of commands required for the servo motor to rotate one revolution. The two are complementary, but the number of pulses per revolution has a higher priority 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 something that users need to pay attention to. In special cases, if the number of pulses per revolution is calculated to be a decimal, the electronic gear ratio should be considered.
(2) If P2-02 and P2-03 exceed the set range, please simplify the numerator and denominator to integers within the set range before setting. Simplification without changing the ratio will not affect the use.
(3) Unless otherwise specified, the resolution of the motor encoders currently on the market is 2500P/R.
(4) The instruction unit does not represent the machining accuracy. Refining the instruction unit quantity based on the mechanical accuracy can improve the positioning accuracy of the servo. For example, when using a lead screw, the mechanical accuracy can reach 0.01mm, so the instruction unit equivalent of 0.01mm is more accurate than the instruction unit equivalent of 0.1mm.
3. Example of setting up an electronic gear
For example:
Additional explanation for the example above: The host computer outputs 5000 pulses because the lead screw pitch is 5mm and the pulse equivalent requirement is 0.001mm, so the number of pulses is 5/0.001 = 5000. The encoder feedback pulse is 131072 pulses per revolution (servo motor), but due to the speed change mechanism, it is 3/2.
