Common Fault of Gear Pump - Reason Analysis and Elimination Method
Digital control machine tools, commonly known as numerical control (NC) machine tools, are advanced electromechanical systems that integrate mechanical, electrical, hydraulic, pneumatic, microelectronic, and information technologies. These machines have been widely used in modern manufacturing for over three decades. Typically, multiple motors drive the system, with each axis—such as the spindle and feed mechanisms—controlled independently. Due to the diverse nature of workpieces, processes, and tools, the movement speed of various components must be adaptable. Therefore, the main motion of the machine tool, particularly the spindle, needs to support variable speed control.
The spindle speed control system often employs an AC spindle system. With the advancement of variable frequency technology, AC drives can now meet the performance demands of CNC machines. The main motor usually drives the spindle through a belt or a combination of belts and gear reductions within the spindle housing, allowing for greater torque. Thanks to the wide speed range and stepless speed adjustment capabilities of modern spindle motors, the design of the spindle housing has become significantly simpler.
**Application Technology Requirements for CNC Machine Tools**
1. **Motor Requirements**
Usually, a variable frequency motor is used, or a standard motor equipped with a fan to ensure adequate cooling at low frequencies. The motor should also support a wide speed range.
2. **Inverter Technical Requirements**
- **High Low-Frequency Torque**: A vector inverter is typically used to provide 150% of rated torque at low frequencies (1–10 Hz).
- **Fast Torque Response and High Speed Accuracy**: Vector inverters offer excellent dynamic response, adjusting output torque quickly based on load changes to maintain stable spindle speed.
- **Fast Deceleration and Stopping**: CNC machines generally require short acceleration and deceleration times. The deceleration time depends on the external braking resistor or unit.
- **Motor Parameter Self-Learning**: After selecting a vector inverter, it's essential to perform self-learning of motor parameters to ensure accurate internal data for vector control. Required parameters include rated power, frequency, speed, voltage, and current. If the rated speed is not listed on the motor nameplate, it can be estimated empirically. Self-learning should be done under no-load conditions for maximum accuracy.
- **Frequency and Operation Commands**: The inverter’s frequency and operation commands are derived from the CNC controller. These are usually provided via analog reference or multi-step speed signals, with multi-speed priority. Analog inputs can be either voltage or current-based, and the inverter can process both.
3. **Anti-Interference Issues**
While inverters are designed with strong anti-interference capabilities, they can still act as sources of interference. In CNC systems, this can disrupt the controller, causing operational issues. To mitigate this, magnetic rings can be added to the inverter’s output lines to reduce high-frequency radiation. Imported CNC systems often have better immunity against such disturbances.
This article discusses the application of ECOM series high-performance vector inverters in a CNC machine tool factory in Shenyang. It highlights how these inverters improve speed control and efficiency in CNC systems.
**System Components**
- EACON Inverter
- Braking Resistor (100Ω/520W)
- 5.5KW Adjustable Speed Motor
- CNC System
**Frequency Converter and CNC Parameters**
For a 5.5kW CNC lathe:
- Motor Rated Power: 5.5kW
- Rated Frequency: 50Hz
- Rated Voltage: 380V
- Rated Current: 11A
- Rated Speed: 1440r/min
- Gear Ratio: 1:1.5
- Material Processed: 45# steel
**Actual Performance**
- Spindle Speed: 200r/min (frequency ~9–10Hz)
- Spindle Speed: 450r/min (frequency ~22Hz)
**Features of EC3000 Series Inverter**
The EC3000 series uses advanced flux control technology, offering high torque at low speeds, precise speed control, and cost-effective performance. It includes features like sensorless vector control, large starting torque (0.5Hz/150%, 0Hz/180%), adjustable carrier frequency, analog interface compatibility, strong overload capacity, and multiple output signals for monitoring.
**Debugging Results**
Testing has shown that the EC3000 series inverter meets all spindle control requirements. Its advanced flux algorithm ensures smooth torque output even at low speeds, replacing traditional rolling bearing designs. The compact and simple structure enables true stepless speed control. The spindle speed is controlled via an external analog signal, allowing different machining processes (e.g., roughing, finishing) to use varying speeds. The start-stop signal is also managed by the CNC system, enhancing automation and extending tool life.
**Conclusion**
Traditional AC servo systems, imported vector inverters, and specialized motors come with high costs. However, the EC3000 series offers superior performance, including low starting current, wide speed range, energy efficiency, stability, precision, and comprehensive protection features. With its high cost-effectiveness, the EC3000 series has quickly gained popularity in CNC applications, providing a reliable and efficient alternative.
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