China Servo Drives & Motors Manufacturer
Tonghang specializes in industrial automation products such as servo drives and servo motors. These products cover low-, medium-, and high-voltage series, with a wide power range from 100W to 22kW. Tonghang has successfully developed a variety of bus-based servo drives, including EtherCAT, CANOpen, and MECHATROLINK III. They also offer servo systems for tapping machines and servo control systems for industrial high-speed doors. Furthermore, they can develop customized servo products tailored to the needs of individual industries.
Our address
Building 3, No.398 Hanghai Road, Yuyue Town, Deqing County, Huzhou City, Zhejiang Province, China
Phone Number
8613385726890
krystalshen@hzth-edrive.com
Research on the method of eliminating interference of servo drive
Tonghang was proposed during the improvement of the automatic positioning system for press brakes to eliminate interference issues with servo drives. Stability and reliability are fundamental requirements for a system. However, the use of servo motors in large press brake control systems, due to the need for precise positioning, has led to significant interference issues. To eliminate interference, the main causes and coupling pathways of interference were analyzed. Hardware anti-interference technologies, such as grounding, isolation transformer filtering, magnetic ring demagnetization, and isolation resistors, were employed to eliminate interference paths in the system, ensuring normal commissioning and operation.
During the improvement of the press brake control system, we encountered interference caused by the use of servo motors. We summarized the process of resolving this interference. During the installation of the electrical cabinet, the failure to separate power and signal cables, coupled with the operation of the servo motor drive, generated significant electromagnetic interference on sensitive components (sensors) and their signal conditioning circuits in the system.
An anti-interference solution for the servo system was developed through experimental methods to improve system stability and reliability. In recent years, with the advancement of various disciplines and technologies, servo drives in AC servo control technology, as controllers for servo motors, have become widely used. However, due to the characteristics of their operation, interference becomes a significant problem. It can be coupled to sensitive equipment through conduction and radiation. Therefore, it is imperative to address and propose a series of effective anti-interference measures through experimental methods to improve the stability and reliability of the system and test equipment.
Causes of system interference
Hardware interference elimination method
1. Grounding and Magnetic Ring Demagnetization
Magnetic ring demagnetization is primarily intended to address interference caused by the fact that the motor driver's power line and the external PLC's signal line were not separated during the precise positioning of the press brake during this design process.
Common-mode magnetic rings are used to address the various interference sources encountered during the press brake design process. Common-mode interference current acts between the signal line and the ground line, flowing halfway through each signal line in the same direction, with the ground line serving as a common return path. The principle behind common-mode magnetic rings is the common-mode inductor, which is essentially a bidirectional filter: on the one hand, it filters out common-mode electromagnetic interference on the signal line, and on the other hand, it suppresses its own electromagnetic interference, preventing it from affecting the normal operation of other electronic equipment in the same electromagnetic environment.
The image shows the internal circuit diagram of a common common-mode inductor. In actual circuit design, multi-stage common-mode circuits can also be used to further filter out electromagnetic interference.
2. Isolation Transformer Filtering
An isolation transformer is constructed of an iron core, copper wire, leads, and other insulating materials. Its input and output are independent, with no common line. Unlike autotransformers, isolation transformers are widely used in the electronics industry, industrial and mining enterprises, and for control power supplies for general circuits in mechanical equipment, as well as for safety lighting and indicator lights.
This article examines interference suppression for isolation transformers used in servo drives with 2000N, 7.5kW output motors. This isolates the PLC power supply in the control power supply from other power sources (power supply, switching power supply, and other relay control power supplies), effectively isolating the primary and secondary sides. Furthermore, the high high-frequency loss of the iron core suppresses high-frequency noise from entering the control circuit. Using an isolation transformer to suspend the secondary side relative to ground is only suitable for applications with a small power supply range and short lines. In this case, the system's capacitive current to ground is too low to pose a risk to personnel. An isolation transformer is a 1:1 transformer with a single-phase 220V primary and a single-phase 220V secondary. Alternatively, a three-phase primary is used. 380V, the secondary is also three-phase 380V. As shown in the figure.
3. Isolation Resistors
Isolating interference using small resistors is not a common method and isn't suitable for all circuits. This article combines several methods to propose a method to eliminate servo interference on the controller, which in turn affects the screen output. A 125-ohm resistor is added between the PLC communication lines and the screen communication lines, as shown in the figure.
Summary
This article discusses the debugging process of a press brake automatic positioning system. Due to the need to improve positioning displacement and incorporate a servo drive, to eliminate the interference caused by the servo drive on the debugging system, hardware anti-interference technologies such as grounding, isolation transformer filtering, magnetic ring demagnetization, and isolation resistors were employed to cut off the interference path in the system, thereby ensuring normal debugging and operation of the system.
Research on Servo Drive Reliability Enhancement Test Technology
Tonghang designed a reliability hardening test scheme based on the servo drive application environment. Using different stress types to stimulate servo drive failure modes and mechanisms, the scheme identified the product's stress limits. Servo drive testing verified that the proposed hardening test scheme can fully expose product weaknesses, providing a basis for design improvements and a reference for reliability assessments of other products in the industry.
Servo systems are core components of industrial robots. As the driving device within the servo system, the reliability of the servo drive directly impacts the reliability and operational capabilities of the entire robot. Applying reliability hardening test technology to servo drive design and development can effectively address the conflict between high product reliability, low development costs, and short lead times. Therefore, this research is of great significance to the development of servo drive reliability hardening test technology. This paper, based on the servo drive application environment, determined a hardening stress application method, identified the product's stress limits, fully exposed product weaknesses, and discovered product failure modes and performance degradation. Through a "test-improve-retest" approach, potential defects were gradually addressed, ultimately improving the reliability of the servo drive.
Servo system structure
A servo system mainly consists of two parts: a servo driver and a servo motor. The servo motor has actuators, feedback components, and brake components.
Test Equipment Introduction
The reliability hardening test equipment is used to test the reliability of servo drives. It consists of three main components: a liquid nitrogen rapid temperature chamber, a pneumatic 3-axis 6-degree-of-freedom (6DOF) shaker and test system housed within the chamber, and an electrical cabinet and control system. This equipment systematically applies step stress to the product to rapidly stimulate design flaws, expose weaknesses, and determine the product's operating and failure limits. The reliability hardening test platform's testing capabilities are as follows:
Temperature range: -100 to 200°C,
Temperature ramp rate: 60°C/min,
Cooling method: Liquid nitrogen,
Vibration method: Pneumatic 3-axis 6DOF,
Frequency range: 5 Hz to 10 kHz.
Test Plan Design
Based on the servo drive's application environment and actual operating conditions, three stress types were designed: temperature stress, vibration stress, and voltage cycling stress. These stress types are used to stimulate the servo drive's failure modes and mechanisms. The following briefly describes the mechanisms and modes of failure induced by these three stress types:
Temperature Stress
Temperature stress can act on a servo drive through low temperatures, high temperatures, and temperature cycling, affecting its mechanical, physical, chemical, and electrical properties. Failure modes triggered by temperature and cycling include: wire stretching or loosening, poor contact, parameter drift and poor circuit stability, circuit board opens and shorts, and loose components. A cross-section of a low-temperature step stress test is shown in the figure.
Vibration Stress
Vibration stress directly uses external forces to induce resonance in the servo drive's internal components and their interconnected parts, potentially causing performance deterioration or failure, loosening, wear, or loss of structural leads, and amplifying minor defects and damage. Failure modes induced by vibration include circuit board opens and shorts, loose components, cold solder joints, open solder joints, poor bonding, and mechanical defects. A cross-section of a vibration step stress test is shown in the figure.
Voltage Cycling Stress
Voltage cycling can trigger failures in servo drive components sensitive to voltage fluctuations, including voltage regulators, diodes, transistors, and relays. Failure modes triggered by voltage cycling include intermittent failure, performance degradation, circuit malfunction, short circuits, and insulation aging. Stress application is performed in a step-by-step manner, with the step stress limit exceeding the design value and allowing for sufficient margin. The test step length can be flexibly adjusted based on the product application. Furthermore, in vibration environmental stress testing, the dwell time at each step stress level is generally set to 5 to 10 minutes to determine the product's damage and operating limits. In temperature environmental stress testing, the power-off temperature dwell time should be determined based on the servo's temperature equilibrium. If extreme stress is used to induce failure during temperature cycling testing, the dwell time at the endpoint temperature should not be extended until the servo drive has fully reached temperature equilibrium (maximum 90%).
Fault Detection
The function and performance testing of the servo drive is determined according to the servo drive design and testing principles. Function and performance testing should be performed before, during, and after the test. If the servo drive exhibits any of the following conditions during the reliability enhancement test, it will be considered to be malfunctioning or failing:
1) The servo drive loses any essential function.
2) The servo drive's performance parameters are out of tolerance.
3) Mechanical parts, structural components, or components exhibit cracks, breaks, or damage that could affect the function, performance, or structural integrity of the servo drive control system.
4) The servo drive has fault warning and protection features that will sound an alarm when an anomaly occurs, causing the servo motor to stop operating. In the fault and protection alarm states, the front panel LED displays the alarm code AL.XXX, and the servo motor will not turn on.
Test Verification Results
In the laboratory, we conducted tests using a 400 W servo drive from a certain brand according to the designed servo drive hardening test plan. Two failures occurred during the test, confirming the product's operating limits and quickly identifying design weaknesses. The test plan was effective. The specific failure types are as follows:
Temperature Stress Failure
Failure Symptom 1: During a low-temperature step stress test of the servo drive, the temperature dropped to -20°C. The servo drive displayed fault code AL161, indicating a thermal protection circuit failure. After returning the sample to room temperature, the fault code was resolved and the sample resumed normal operation.
Failure Analysis: The servo drive triggered the low-temperature protection circuit.
Failure Solution: This fault is caused by a design feature of the servo drive. Replacing the temperature sensor in the servo drive's low-temperature protection circuit with a 10 kΩ resistor resolved the fault.
Failure Symptom 2: During a low-temperature step stress test of the servo drive, the temperature was reduced to -55°C for 5 minutes. The IPM power supply voltage exceeded the upper limit of 16.5 V, reaching 20.5 V. The -12VA controller power supply voltage exceeded the upper limit of 10.8 V, reaching 16.7 V, causing the drive to trip and shut down.
Failure Analysis: The lower arm of the W phase of the servo drive's IPM (intelligent power module) failed.
Failure Solution: The servo drive's IPM The incoming components were defective. After replacing the components, the sample returned to normal operation.
Vibration Stress Failure
Failure Symptom 1: During a vibration step stress test on the servo drive, the vibration level reached 40 g. The servo drive displayed fault code AL 220. After vibration was stopped and the sample was restarted, the servo drive display panel digital tube did not light up. The bus voltage was monitored at 305 V, the IPM power supply voltage was 0 V, and the controller power supply (+12VA) was 0 V.
Failure Analysis: The NTC thermistor pin in the servo drive circuit was broken.
Solution: Replace the NTC thermistor. Avoid collision and bending of components during soldering, production, and transportation.