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What is the servo motor ?

How to choose a right delta servo motor ? What is the servo motor ?

Let’s start with the structure of the servo motor. The servo motor is also called the actuator motor.,In the automatic control system, servo motor is used as an actuator to receive the electrical signal and Converted the electrical signal to an angular displacement or angular velocity output on the motor shaft. Its main feature is that there is no rotation when the control signal is zero..The servo motor is mainly positioned by pulse. When the servo motor receives one pulse, it will rotate the angle corresponding to one pulse to realize the displacement.Since the servo motor is equipped with an encoder and it can emit pulse, when the servo motor is rotating, the pulses are emitted from servo motor, the pulse received by the servo driver forms a closed loop with the pulse emitted from the servo motor .In this way, the system will know how many pulses sent by the controler to the servo motor.At the same time, how many pulses are returned, so that the rotation of the motor can be accurately controlled to achieve accurate positioning.

  1.Calculate to choose

Calculate the power and speed required by the motor based on the structural form and the speed and acceleration requirements of the final load. It is worth noting that it is usually necessary to select the reduction ratio of the reducer in conjunction with the speed of the selected motor. In the actual selection process, For example, the load is a horizontal motion. Because of the friction coefficient of each transmission mechanism and the uncertainty of the load factor, the formula P=T*N/9549 is often not clearly calculated (the torque cannot be accurately calculated). In practice,We find that the maximum power required to use a servo motor is often the acceleration and deceleration phase. Therefore, the power of the required motor and the reduction ratio of the reducer can be quantitatively calculated by T=F*R=m*a*R (m: load mass; a: Load acceleration; R: load rotation radius F: traction force R: torque radius T: motor torque)..

There are a few points to note:

a) The power surplus factor of the motor (in general, the motor power P=PR/80% PR is calculated by the required power);

b) consider the transmission efficiency of the mechanism;

c) Whether the input and output torque of the reducer are up to standard and have a certain safety factor;

d) Is there a possibility of increasing speed in the later period?

 1.2. Inertia matching

To achieve high-precision control of the load, it is necessary to consider whether the inertia of the motor and the system match.

why the inertia matching is needed, the principle of inertia matching is: considering the system inertia is compared to the motor shaft’s inertia, it should be not more than 10 (Delta servo motor); the smaller the ratio, the better the control stability, but it needs to be a bigger Motor, It will be lower cost performance. If you don’t understand the specific calculation method, please reference to the “Theoretical Mechanics” of the university.

 1.3. Precision requirements

One of the main indicators of our reference motor accuracy is the accuracy of the encoder. For example, the servo motors currently sold by Delta electronic mainly with 17-bit and 20-bit encoders. The number of pulses output by the encoder per revolution of the motor: P=2X (P: number of pulses output per revolution of the motor; X: bits of Encoder ).when the 17-bit motor turn around a rotation , the number of pulses output by the motor encoder is P=217=131072. The angle of rotation per each pulse is ∠= 3600/131072=0.002746580 .when the 20-bit motor turn around a rotation , the number of pulses output by the motor encoder is P=220=1048576.The angle of rotation per each pulse is ∠=3600/1048576=0.00034332270。Obviously, the 20-bit encoder has a smaller angle for each pulse and a higher motor accuracy.

1.4. Control matching

 For example, if the communication mode of the servo controller matches the host controler. For example, the optional control mode of host controler is pulse output, RS485, RS232, wether the servo drive have these functions.