Trends in the use of Servo motor control technology in industry

The industrial revolution 4.0 is booming, promoting automation in all areas of production. With the ability to precisely control position, speed and torque, Servo motors play a key role in today’s automation trend. In this article, RX Tradex will provide you with in-depth information about the “Trend of using Servo motor control technology in industry“, helping you choose the optimal automation solution, improve product performance and quality.

1. System configuration of servo motor

A typical servo motor control system consists of three main components:

• Controller: This is the brain of the system, usually a PLC (Programmable Logic Controller) or a dedicated motion controller. The controller is responsible for sending control signals to the motor controller based on specific operating requirements. It has sophisticated programming and control capabilities to ensure the system works efficiently.
• Motor Driver: This device receives the signal from the controller and adjusts the power fed to the servo motor, adjusting the speed, position and torque as required. Motor controllers typically use advanced technologies such as IGBT (Insulated Gate Bipolar Transistor) to ensure high performance and fast response, minimizing energy loss and increasing system durability.
• Rotary Pulse Encoder (Encoder): Provides feedback on the position and speed of the motor. This information is sent back to the controller for comparison with the command signal, which in turn makes the necessary adjustments. The encoder can be either proportional or absolute type, depending on the exact requirements of the application. Proportional encoders are commonly used in applications that require high speed accuracy, while absolute encoders are important in applications that need to know exactly where the motor shaft is even when power is lost.

2. Servo motor structure

In industry, servo motors usually use brushless DC motors. The structure of the servo motor consists of the main parts:

• Rotor: It is a permanent magnet with a strong magnetic field, which acts as the rotating part of the motor.
• Stator: Contains separate coils, powered in an appropriate sequence to rotate the rotor. The movement of the rotor depends on the frequency, phase, polarity, and current flowing through the stator winding.
• Sensor: Usually a rotational pulse encoder, which provides feedback on the position and speed of the rotor.
• Engine housing: Protects the internal components from environmental factors.

Function of servo motor controller

The servo motor controller is responsible for:

• Power supply: The right amount, the right time for the servo motor to control the position, speed and torque.
• Communication with Motion Controller: To execute control commands from the main system.
• Read the feedback from the rotary pulse encoder: Real-time adjustment for the closed control loop circuit.
• Input/Output Signal Processing: Includes safety device, input mode, and operating status signals.

The precise power supply and control make servo motors operate efficiently and reliably in industrial applications.

3. Power control for servo motor

Servo motor electrical controllers use transistors with isolated control poles (IGBTs) to control energy. IGBTs enable fast switching with large currents, ideal for servo motor control, which improves system performance and reliability.

4. Servo motor control signal

The servo motor control signal can be analog DC voltage, pulse range, or data packet transmitted over the network. The controller receives signals from the motion control program to perform certain forms of movement. The use of modern communication protocols such as EtherCAT and PROFINET also helps to increase integration and control more precisely.

5. Feedback in servo motor system

The servo system operates in a closed-loop circuit, where the actual position, velocity, and torque of the motor are compared to the motion command. The controller adjusts the motor in real-time to eliminate deviations, ensuring that the motor always performs as required

The feedback cycle – error determination – error suppression is called a closed control loop circuit.

6. Control loop circuit

The control loop circuit in the servo motor system plays an important role, which is controlled by the servo motor controller or the motion controller, or both depending on the specific requirements of the application. In order to achieve the desired movement, it can be divided into circuits that control position, velocity and torque.

Not all control applications need all three types of control loop circuits. Many applications use only current loops and speed loops to control the operating speed. However, many more complex applications require all three types of circuit to ensure accuracy and meet precise positioning needs.

Position Control Loop: A position control loop circuit that manages and adjusts the absolute angular position of an axle or actuator. When the servo motor changes position, the rotary pulse encoder sends the actual position feedback. The position loop circuit compares the placement and the actual position, and adjusts the motor to minimize the positioning error based on the alignment parameter.

Velocity Loop: A speed loop circuit that manages the velocity and direction of rotation of a servo motor. The controller adjusts the velocity to ensure that the variable velocity and operating conditions are achieved. For example, in the case of heavy loads, the engine can increase torque to maintain speed.

Torque Control Loop Circuit (Current Loop): The torque control loop circuit that manages the rotational force generated by the servo motor. By measuring the current flowing through the stator winding, the controller adjusts the current to meet the torque requirement of the application. This helps to achieve optimum torque under different conditions of the production process.

7. Rotational pulse coding responder

The rotary pulse encoder is a critical piece of hardware in the servo motor system, which is responsible for responding to information about the speed and position of the motor. Typically, this encoder is integrated or attached to a servo motor. However, in some applications, the rotary pulse encoder can be installed separately from the motor to capture detailed parameters that affect the operation of the system.

There are two main forms of rotational pulse encoders:

7.1. Proportional Rotation Pulse Encoder

The proportional rotation pulse encoder works on an optical principle, using a clear glass disc with radiant symmetrical lines printed evenly spaced. This disc is fixed to the shaft of the servo motor and rotates together with the rotor of the motor. The lines on the disc are detected by a photoelectric sensor. Each time there is a change from light to dark or vice versa, the output of the sensor changes, corresponding to the rotation speed of the motor. This output signal, also known as the Phase A signal, not only indicates the speed, but also determines the direction of rotation. To know the direction of rotation, the encoder needs to use a second optical sensor, which is placed at a certain distance from the first sensor.

When the direction of rotation changes, the pulses from the second sensor will be out of phase by 90 degrees from the first sensor. This is called a 1/4 cycle phase delay. By comparing these two phase-out pulse sequences, we can determine the direction of rotation of the engine. In addition to the Phase A and Phase B signals, a proportional rotation pulse encoder can also have a third output called Phase Z. This signal emits only a single pulse per revolution, which is used to determine the origin or reference position. The signal from the Z Phase is the starting point for calculating the absolute position by counting the number of pulses from the known position.

7.2. Absolute Rotation Pulse Encoder

The absolute rotational pulse encoder also uses a transparent disk, but instead of printed lines, it has transparent and opaque areas arranged in binary code. Each bit of encryption is a separate region on the disk, and the optical sensors simultaneously read all of these regions. The data from the disc is unique and corresponds to each angular position of the motor shaft. This data can be sent from the encoder in parallel or converted to serial data.

The number of bits in the data specifies the angular resolution of the rotational pulse encoder. For example, a 12-bit rotational pulse encoder will produce 4096 different codes when spinning a 360-degree turn; This means that each time the engine shaft rotates 0.088 degrees, it will produce a different code. Other factors can also affect the actual accuracy, so 20-bit encoders are not uncommon either. Another method for determining absolute location is to combine a proportional rotational pulse encoder with a special hardware and software memory, rather than using an expensive disk of absolute encoders. This device uses the retained momentum from the encoder to create a virtual absolute position in hardware memory, keeping this information even when the system loses power. Both types of absolute rotational pulse encoders provide the necessary position feedback for the servo motor controller.

8. Conclusion

Servo motor control technology is increasingly widely applied in industry thanks to its precise control, high performance and high reliability. Hopefully, with the content of the above article, RX Tradex has provided you with detailed information about the system configuration, motor structure, power control, control signal, feedback, control loop circuit and rotation pulse coding responder of the Servo motor. In addition, if you want to learn more about advanced automation solutions or update the latest manufacturing trends in the electronics industry, don’t miss the opportunity to participate in the largest and only international exhibition NEPCON Vietnam organized by RX Tradex of the year. Register here to participate.