AC Servo Motor Driver

Servo drives are a crucial component of servo systems, causing the vast majority of servo system failures. Tonghang's servo drive series undergoes system testing before production and use. This is a crucial assessment method for servo system safety and stability. As servo drives become more complex, the quality requirements for servo system stability and other parameters continue to increase. Traditional servo drive testing methods rely on manual testing, which is inefficient, costly, and lacks guaranteed accuracy, making them inadequate for current needs. To ensure the factory quality of servo drives, improve product testing efficiency, and enhance the servo drive testing system, we have designed an efficient and reliable servo drive testing system, making us one of the servo system manufacturers with the highest R&D investments in the industry.

Our test system's primary functions are to load the servo motor and configure servo drive parameters to meet test conditions. By controlling the servo drive in real time and collecting torque sensor data, specific test items can be implemented. Results demonstrate that the system can test multiple technical indicators, providing a reliable test system for AC servo drive production.

System Composition and Operating Principle

The AC servo drive test system consists of two parts: hardware and software. The hardware system is divided into three main modules:

Communication module between the host computer and servo drive;

Loading module, which provides the required load for testing;

Acquisition module, which provides servo motor data to the host computer.

The software is divided into three main modules:

Basic servo drive settings module;

Test parameter configuration module;

AC servo drive test module.

The communication module selects appropriate communication equipment to connect the various functional modules, enabling communication between the various devices in the system and ensuring accurate and complete data transmission and the real-time effectiveness of control commands. The data acquisition module, acting as a crucial bridge between software and hardware, transmits collected data to the host computer's data processing module for analysis and judgment of test results. The load application system module applies the appropriate load to the motor under test based on the load value set by the host computer, ensuring that the servo system meets the required load conditions for the test. The basic setup module prepares the AC servo drive for testing, configuring servo drive parameters and performing simple motor tests to ensure proper operation within the test system. The test parameter configuration module configures drive parameters during the test preparation phase to meet control mode and loading state requirements. The test module designs test methods for the relevant test items and controls the drive's operation according to the test methods during the test. This system features a well-designed human-machine interface, allowing users to fully control the AC servo drive test system through the host computer.

System Composition and Operating Principle

The AC servo drive test system consists of two parts: hardware and software. The hardware system is divided into three main modules:

Communication module between the host computer and servo drive;
Loading module that provides the required load for testing;
Acquisition module that provides servo motor data to the host computer.

The software is divided into three main modules:

Servo driver basic configuration module;
Test parameter configuration module;
AC servo driver test module.

The communication module selects appropriate communication equipment to connect the various functional modules, enabling communication between the various devices in the system and ensuring accurate and complete data transmission and the real-time effectiveness of control commands. The data acquisition module, acting as a crucial bridge between software and hardware, transmits collected data to the host computer's data processing module for analysis and judgment of test results. The load application system module applies the appropriate load to the motor under test based on the load value set by the host computer, ensuring that the servo system meets the required load conditions for the test. The basic setup module prepares the AC servo drive for testing, configuring servo drive parameters and performing simple motor tests to ensure proper operation within the test system. The test parameter configuration module configures drive parameters during the test preparation phase to meet control mode and loading state requirements. The test module designs test methods for the relevant test items and controls the drive's operation according to the test methods during the test. This system features a well-designed human-machine interface, allowing users to fully control the AC servo drive test system through the host computer.

System Hardware Design

The hardware system consists of a main control unit, a servo system, and a load loading system.

Communication Module Design
This design module needs to implement data exchange between various devices, ensuring real-time transmission and data accuracy. The data transmission content in this system includes servo drive configuration instructions, motor control instructions, and servo drive status monitoring data. For servo drive configuration instructions, the data transmission process does not have high performance requirements, and the RS485 communication interface can meet them. For motor control instructions and servo drive status monitoring data, high accuracy, good real-time performance, and high data transmission rates are required. Because the servo drive in this design has both CAN and RS485 communication interfaces, CANalystl and Z-TEK equipment were selected to facilitate inter-device data communication for different types of transmission content.

Acquisition Module Design

This design module needs to collect speed and torque data from the motor under test, ensuring high accuracy, stability, and strong anti-interference capabilities.

The acquisition module uses a micro-range torque sensor and its accompanying torque, speed, and power meter as data acquisition equipment. This sensor offers excellent performance, capable of detecting both torque and speed and shaft force, with high accuracy, excellent stability, and strong anti-interference capabilities, meeting the performance requirements. The torque sensor is connected to the working end of the servo motor, and the power meter's RS485 communication interface is connected to the control board's RS485 communication interface, forming the system's data acquisition module.

Load Application Module Design

This design module applies a load to the motor. The load value is set by a host computer input or a manual adjustment knob, ensuring consistent, stable load output with low error.

The load application module consists of a hysteresis brake, a hysteresis controller, and a control board. The test system requires safe and stable load application to the motor. Hysteresis brakes offer the advantage of maintaining a nearly constant torque regardless of slip speed, and can control high torque output with low current. Therefore, this loading system was designed with a hysteresis brake. The load value set by the host computer is received via an RS485 interface, and after data processing, an analog value representing the actual torque value is output. For 24 VDC... In addition to direct voltage regulation, voltage-controlled hysteresis brakes generally employ more refined current control. Hysteresis brake torque regulation and control is achieved by adjusting the DC current flowing through the electromagnetic coil to determine the output torque. Torque and current are linearly related, and the use of a constant current source minimizes drift errors caused by external brake factors. The control board is a key module in the load-applying system, providing the motor load. This load-applying board utilizes the STM32F103ZET6 as the control board's processing core, featuring two analog outputs, three RS485 interfaces, an RS232 interface, an RS422 interface, a CAN interface, an LED module, and a pushbutton module. Because the hysteresis controller requires an input voltage range of 0-5V, the analog output circuitry is designed by combining the STM32F103ZET6 chip's internal DA converter with an op amp circuit. The LED module, combined with the pushbutton module, implements functions such as mode switching, parameter setting, and control board status display.

Software Design

System Software Design

The system host computer was developed using the Qt platform, leveraging Modbus and CAN open communication protocols to transmit and receive data and control commands, ultimately displaying them on the user interface. Based on an analysis of specific functional real-time requirements, task modules were divided into real-time and non-real-time tasks. Process data objects in the CAN open protocol were used to ensure accurate and timely completion of real-time tasks.

System Functional Module Design

This software system adopts a modular design concept. Based on the overall system requirements, the software functions are divided into a device connection module, a servo drive basic configuration module, a test condition configuration module, and a test module.

Device Connection Module Design

When the host computer software is launched, a communication settings dialog box will be displayed. In this dialog box, select the desired communication port, communication rate, device scan range, etc.
1) Connect/Disconnect: When connecting, select the communication method and set communication parameters. When disconnecting, some functions can be used offline.
2) Server Driver Selection: Automatically scan and identify the communication address of the connected device within the communication address range, or directly enter the communication address to connect.

Basic Settings Module Design

The servo drive basic settings module uses the MODBUS communication protocol (8-bit data, 1-bit even parity, 1-bit stop bit, ASCII code). Its main functions include:

1) Parameter Editing: Displays the connected servo drive parameters and allows modification of selected parameters. Each parameter is briefly described.

2) Alarm Information: Displays current alarm information and historical alarm records, and can reset current alarms and clear historical alarm records as needed.

3) IO Monitoring: Displays servo drive input and output signal information.

4) Data Monitoring: Displays servo drive and motor information, such as motor speed, torque, reference pulses, feedback pulses, and deviation pulses.

5) Offset Adjustment: Zeros analog input signals (speed, torque).

5) Advanced Functions: Enables motor zero position detection and load inertia detection.

6) Trial Run: JOG Operation and forward/reverse rotation testing;
7) Factory Reset: Resets the servo drive to factory settings and updates the host computer's parameter list.
8) File Import/Export: Files serve as storage and data sources for parameter lists.

Except for file operations, all other functions are implemented through programming to access the servo status data communication address, parse Modbus data packets, and control UI controls.

Test Condition Configuration Module Design

To meet the test conditions for AC servo drive testing, the following functional designs were implemented:

1) Load Setting: The load value is set on the host computer and input into the load loading system according to the communication protocol. After processing, the required test load is applied to the motor.

2) Control Mode Setting: The servo drive has five control modes (speed control, position control, home control, position interpolation control, and torque control). The corresponding control mode is set according to the test requirements. The CAN open protocol's Service Data Objects (SDOs) are used to transmit non-time-critical data (parameters). The corresponding control mode and test-related parameters are set by modifying the data dictionary.

Test Module Design

During the test, the system needs to control the servo drive's operation in real time until the test is complete. Any control lag during the test will affect the test results, making real-time data transmission crucial to the system. The CAN open communication protocol offers advantages in motion control, especially synchronous control, so it was used for data transmission. Its process data objects (PDOs) are often used to transmit time-critical process data (setpoints, control words, status information, etc.).

PDO mapping is performed on time-critical process data involved in the test. Based on this mapping, control commands are sent to the servo drive at regular intervals according to the test requirements, enabling real-time control of the servo drive and completing the test operation.

Test results are evaluated based on sensor data and the AC servo drive's technical specifications to determine whether the device under test meets the specified technical standards.

Main Control Program Design

The test system is divided into basic configuration, test environment configuration, test implementation, and test results.

The software system has permissions, requiring users to log in to access the system. After initialization, the user enters the human-machine interface, which contains multiple functional screens with user-friendly switching. The main process of the software system involves configuring the AC servo drive in the basic settings interface. After confirming that the servo system is functioning properly, the user enters the specific test item interface, selects the test item, and uses the load loading system to configure the required load. The test module then configures the relevant test parameters. During the test, the test parameters and load are adjusted according to the required parameters, and the data is recorded. After the test is completed, the data is analyzed to determine the test results. Depending on the test process, the user can exit or conduct another test item.

Experimental Results and Analysis

Speed ​​Fluctuation Test

Test Requirements: With the motor at no load and rated speed, perform forward and reverse rotation tests at multiple speed steps for closed-loop speed drives. The servo drive motor is tested at steady-state speeds of -200 rpm, 600 rpm, -1000 rpm, and 2000 rpm to verify the smoothness of the motor's operating speed.

Test Indicators: When the system is running at no load, the lower the speed, the greater the system resistance and the greater the speed fluctuation. When the motor is rated at 3000 rpm, the fluctuation rate should not exceed 1% when running at high speeds greater than 2000 rpm; when running at medium speeds between 1000 rpm and 2000 rpm, the fluctuation rate should not exceed 3%; and when running at low and medium speeds between 0 and 1000 rpm, the fluctuation rate should not exceed 0.000 rpm above 200 rpm. 3%.

Test steps: Connect the drive under test to the system, power on the drive, launch the host computer software, configure the drive parameters, and perform a test run to ensure proper operation. Once the motor is operating normally, switch the host computer software to the test mode, set the load to no-load, the control mode to speed mode, and configure the relevant test parameters. Once the test is ready, click the speed fluctuation test. The driver will control the motor according to the test requirements. Wait for the test to complete and obtain the motor speed curve and test results.

Test result analysis: The fluctuation of the curve at medium and low speeds does not exceed 3%, and the AC servo drive runs smoothly within the range. The speed fluctuation test of the AC servo drive has passed.

Conclusion

Based on servo drive testing requirements, Tonghang has built a test system specifically for AC servo drives in accordance with the "General Technical Requirements for AC Servo Drives." This design isolates different functional modules, minimizing system complexity while maintaining system functionality and facilitating future development. The system boasts a rational hardware and software design, robust functionality, and an intuitive and user-friendly human-machine interface. The comprehensive display features meet practical needs. We design servo drives tailored to your specific needs. Please contact us for purchasing inquiries.