The main difference between CNC machine tools and traditional machine tools is that they have their own "brain"—the CNC system—allowing them to operate manually like traditional machine tools. Many people wonder how much the quality of this "brain" affects the performance of a CNC machine tool. This article, compiled from various sources, aims to provide some helpful information.
To understand the impact of CNC systems on CNC machine tools, it's essential to first understand their structure. A CNC system primarily consists of a human-machine interface (HMI), a CNC core, a programmable logic controller (PLC), and drivers. The HMI handles human-machine interaction ; the CNC core is the heart of the system, responsible for trajectory calculation, position adjustment, and related controls such as acceleration, tool data, zero-point offset, and various complex machine tool functions. The PLC controls the machine tool's logic, including the tool magazine and hydraulic systems; and the drivers are the actuators that adjust the motor's current and speed loops to ensure rapid and accurate execution of commands from the CNC core.
For CNC machine tools, a CNC system is not merely an accessory, but a complete solution, encompassing both hardware and software. Only when hardware and software are combined, and when the human-machine interface, CNC core, programmable logic controller (PLC), and drives within the CNC system work together to control the machine tool, can high precision and high quality be guaranteed. Therefore, the quality of the CNC system directly impacts the accuracy and efficiency of the CNC machine tool.
Generally, a "good CNC system" as defined by the public will be equipped with a servo motor. A good CNC system can offer users a variety of motor types to choose from, such as high-dynamic motors and high-inertia motors . Users can select motors with different characteristics according to the different requirements of the machine tool. Good servo motors usually also have higher encoder resolution; the higher the resolution, the smaller the speed fluctuation. Motors with high-resolution encoders will be controlled more smoothly and with higher precision.
Industry insiders know that there are many elastic connections (such as flexible couplings) between motors and machinery. These elastic elements can introduce subtle errors during machine tool transmission. However, the system only knows the motor's feedback and not the transmission errors, thus affecting the actual control accuracy. To address this, the CNC system can be connected to a linear encoder as a direct measurement system, forming a "fully closed loop." This allows the system to directly obtain the actual feedback from the machinery through the encoder for control and adjustment, thereby improving the machine tool's accuracy.
Today, many CNC systems can achieve computational precision exceeding the nanometer level. This means that CNC systems can provide higher control accuracy, thereby achieving more ideal interpolation trajectories. Furthermore, machine tools inevitably experience vibrations during production due to external environmental interference, such as from cooling equipment, hydraulic equipment, or other machine tools. These types of problems can generally be detected by measuring positional deviations with a linear encoder, but are difficult to suppress or eliminate by adjusting the machine tool's dynamic response parameters. CNC machine tools, however, can often suppress external interference using methods similar to Siemens APC (Advanced Position Control) positioning control functions, thereby further improving machine tool machining performance.
During an interview at CCMT2018, Mr. Li Jinhe, Assistant President of Yamazaki Mazak (China) Co., Ltd., mentioned that the human-machine interface (HMI) function of the seventh-generation CNC system, after more than 20 years of development, is increasingly demonstrating its superior practicality. In today's world of advanced computers, many CNC machines still require human operation, while Mazak's control system allows for program editing through everyday conversational language, providing convenience for users and significantly reducing labor costs. From this perspective alone, the CNC system demonstrates its extraordinary superior performance.
Although the core of a CNC machine tool lies in the machine tool itself, and good mechanical performance is the foundation, a good, high-quality CNC system can bring out the machine tool's excellent mechanical performance even better, achieving the goal of adding the finishing touch.
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