Why servo motor need encoder, how does it work?

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Servo motors are one kind of a closed-loop system, it is made of a servo motor, shaft, potentiometer, drive gears, amplifier, and an encoder, Servo motors can be widely used in robots, CNC machines, CNC routers, printing, food machine,  servomotors( encoder motor ) can be popular in modern industry, because servo motor has good performance in accuracy, precision, speed, torque, direction of rotation of motors, super low error rate, etc.

This servo motor encoder(also called electric motor encoder, encoder in servo motor,servo motor with encoder) allows control systems to adjust motor parameters in real-time, The encoder in the servo motor decides these above features. In this article, we’ll introduce why the servomotor can become people’s priority from the encoder's point when facing the choose servo motor

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1. The encoder in servo motor helps the servo motor to finish the position measurement. 

An electric motor encoder is one kind of sensor for position feedback of the motor, this feedback of the servo motor encoder is sent to the controller which uses this information to adjust the power supplied to the motor to achieve the desired position. 

Position control means maintaining and controlling the precision position of the servo motor shaft. The controller will do the accurate position measurement according to encoder feedback. This measurement can guarantee repeatability, accuracy, and smooth motion.

Precision controlling is super important in robotics, CNC machines, and other automatic system. Here please note: The electric motor encoder can not control the motor directly, it only provides the information to the controller. The servo motor can work without any purpose if there is no encoder. There is no feedback to the controller, the motor is out of the controller.

2. The encoder in servo motor helps the servo motor to finish the Speed measurement.

The controller controls the servo motor speed via the encoder speed loop and decides the output current or voltage. The controller will input a certain speed to let the servo motor work, and the electric motor encoder measures the servomotor's speed. The controller compares the target speed with the actual speed right now and then decides whether the motor needs to adjust the speed or not. Application: conveyor belts and printing presses.

Here we need to note: The higher the resolution of the encoder, the more accuracy speed when the controller adjusts the speed.

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3. The encoder in servo motor helps the servo motor finish the torque measurement.

This kind of measurement belongs to a non-contact measurement method that does not damage or affect the measured object, servo motor encoder can be widely used in complex shapes and high temperatures.

The electric motor encoder calculates the output torque of the motor through the relative rotation angle between the rotor and stator and achieves precise control of the torque by controlling the current of the motor.

4. The encoder in servo motor helps the servo motor to finish error correction.

If your servo motor has some problems, the zero point calibration of the encoder is a very important step to ensure the motor's accuracy and normal operation. It includes the mechanical calibration method, parameter adjustment method, automatic calibration method, and button calibration method. The servo motors can be back to the standard status via these methods.

The encoder in servo motor helps servo motor to finish work repeatability.

Normally, the encoder has the ability to repeat the exact information with the same accuracy. Moreover, the measurement accuracy can be supposed to be 2-10 times than standard accuracy. 


5. The encoder in servo motor helps 2 sets of servo motors to finish synchronization.

There are many requirements for the synchronization movement of servo motors in many applications, requiring two or even more, including multi-axis printing lines, cranes, systems gantries, and conveyor systems. Each controller commands its respective motor to the same speed/position and then uses encoder feedback to drive the differential speed to zero.

How does motor encoders work?

When we say how does encoder works, it is necessary to introduce the encoder type.

Based on the measurement mechanism, the encoder has an incremental encoder and an absolute encoder;

Based on the movement, the encoder has a linear encoder, rotary encoder;

Based on the sensing technologies, the encoder has optical encoders, magnetic encoders, capacitive encoders, and quadrature encoders.

These encoder in servo motor has the same working principle.

An encoder belongs to a high-precision sensor, offering some information to let the controller control the movement of a motor. The encoder achieves precise control of the motor via sensing motor position, motor speed, and motor acceleration. 

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1. Encoder signal conversion

servo motor encoder usually use photoelectric signals, electromagnetic signals, or Hall sensors to change the physical phenomenon into electrical signals by the motor rotation.

2. Deal with the Encoder signal.

Dealing with the encoder in servo motor signal is to amplify, and filter the electrical signal so that the circuit can correctly identify and process the signal in the future. The signal is usually in the unit of resolution or frequency.

3. Encoder signal output

After processing the signal of the encoder in servo motor, the signal needs to be output to the control system through the interface circuit, and the control system can control the motor according to the encoder signal. 

4. Encoder signal and motor drive control

After the control system receives the encoder signal, The control system achieves accurate control of the motor's speed, position, and acceleration by adjusting the voltage, current, or frequency.

The servo encoder changes the physical signal by the rotation of the motor into electrical signals, and outputs the signal to the control system after processing, to make sure the servo motor can work in a high accuracy, more strady. 

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In a word, an encoder helps the servo motor to finish the closed-loop system, it can use the resolution to give feedback to the controller and command the servo motor to convert a series of high accuracy positions, exact speed, suitable torque, and suitable speed. 

RicoCNC provides a wide range of servo motor with encoder with different brands. like Panasonic,SANYO DENKI, YASKAWA, Bosch Rexroth, Mitsubishi, Schneider, etc brand. If you are looking for them, do not hesitate to contact us.

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