1. Machining Accuracy Accuracy is a crucial performance indicator that machine tools must guarantee. The positional accuracy of the position servo control system largely determines the machining accuracy of CNC machine tools. Therefore, positional accuracy is an extremely important indicator. To ensure sufficient positional accuracy, it is necessary to correctly select the open-loop amplification factor in the system and to impose accuracy requirements on the position detection element. Because in a closed-loop control system, it is difficult to distinguish between the error of the detection element itself and the deviation of the detected quantity, the accuracy of the feedback detection element often plays a decisive role in the system's accuracy. It can be said that the machining accuracy of CNC machine tools is mainly determined by the accuracy of the detection system. The smallest displacement that a displacement detection system can measure is called its resolution. Resolution depends not only on the detection element itself but also on the measurement circuit. When designing CNC machine tools, especially high-precision or large and medium-sized CNC machine tools, the detection element must be carefully selected. The resolution or pulse equivalent of the selected measurement system is generally required to be an order of magnitude higher than the machining accuracy. In short, a high-precision control system must be guaranteed by a high-precision detection element. For example, the accuracy of linear inductive synchronizers commonly used in CNC machine tools can reach ±0.0001mm, or 0.1µm, with a sensitivity of 0.05µm and a repeatability of 0.2µm; while the accuracy of circular inductive synchronizers can reach 0.5N, with a sensitivity of 0.05N and a repeatability of 0.1N. 2. Open-Loop Amplification Factor In a typical second-order system, the damping coefficient x = 1/2(KT) - 1/2, and the steady-state speed error e(∞) = 1/K, where K is the open-loop amplification factor, often referred to as the open-loop gain in engineering. Clearly, the open-loop amplification factor of the system is one of the important parameters affecting the static and dynamic performance of the servo system. Generally, the amplification factor of the servo mechanism in CNC machine tools is taken as 20–30 (1/S). Servo systems with K < 20 are usually called low amplification factors or soft servo systems, mostly used for point-to-point control. Systems with K > 20 are called high amplification factors or hard servo systems, applied to contour machining systems. If, to avoid affecting the surface roughness and accuracy of the machined parts, it is desirable that the step response does not oscillate, i.e., a larger value is required, and the open-loop gain K should be smaller. Conversely, if the system's speed is prioritized, a smaller x is desired, i.e., an increased open-loop gain is desirable, and simultaneously, an increase in the K value can improve the system's steady-state accuracy. Therefore, the selection of the K value must be considered comprehensively. In other words, a higher system gain is not always better. When the input speed changes abruptly, a high gain may lead to drastic output fluctuations, subjecting mechanical devices to significant shocks, and potentially causing system stability issues. This is because in high-order systems, system stability is subject to a specific range of K values. Low-gain systems also have certain advantages, such as easier system adjustment, simpler structure, less sensitivity to disturbances, and better surface roughness. 3. Improving Reliability CNC machine tools are high-precision, high-efficiency automated equipment; failures result in even greater losses. Therefore, improving the reliability of CNC machine tools is particularly important. Reliability is one of the main quantitative indicators for evaluating reliability. It is defined as the probability that a product will perform its intended function under specified conditions and within a specified time. For CNC machine tools, the specified conditions refer to environmental conditions, working conditions, and operating methods, such as temperature, humidity, vibration, power supply, interference intensity, and operating procedures. The intended function mainly refers to the machine tool's functionalities, such as its various functions and servo performance. Mean Time Between Failures (MTBF) is the average time from one failure to the next for a repairable device or system that can continue to operate after repair or replacement of parts. CNC machine tools commonly use it as a quantitative indicator of reliability. Since the adoption of microcomputers in CNC devices has greatly improved reliability, the reliability of servo systems has become relatively prominent. Failures mainly originate from servo components and mechanical transmission parts. Generally, the reliability of hydraulic servo systems is lower than that of electrical servo systems. Electromagnetic components such as solenoid valves and relays have poor reliability and should be replaced with contactless components whenever possible. Currently, the reliability of CNC machine tools is not very high due to limitations in component quality, manufacturing processes, and cost. To ensure CNC machine tools are well-received by factories, their reliability must be further improved to enhance their usability. When designing servo systems, components must be selected according to design technical requirements and reliability criteria, and rigorous testing and inspection must be conducted. Close attention must be paid to mechanical interlock devices to minimize failures caused by mechanical components. 4. Wide Speed ​​Range In CNC machine tool machining, servo systems require a sufficiently wide speed range for the feed drive to simultaneously meet high-speed rapid traverse and single-step jogging. Single-step jogging is often used as an auxiliary working method for adjusting the worktable. For the servo system to achieve smooth feed at low speeds, the speed must be greater than the "dead zone." The "dead zone" refers to the phenomenon where, due to static friction, the motor cannot overcome this friction and cannot rotate under very small inputs. Additionally, mechanical backlash can also cause the motor to rotate while the slide does not move; these phenomena can also be described using the "dead zone." Let the dead zone range be 'a'. Then the minimum speed Vmin should satisfy Vmin≥a. Since a≤dK, where d is the pulse equivalent (mm/pulse) and K is the open-loop amplification factor, then Vmin≥dK. If we take d=0.01mm/pulse and K=30×1/S, then the minimum speed Vmin≥a=30×0.01mm/min=18mm/min. The selection of the maximum speed of the servo system must consider the mechanical limits of the machine tool and the actual machining requirements. While higher speed can improve productivity, it also places higher demands on the drive. In addition, from the perspective of system control, there is also a detection and feedback issue, especially in computer control systems, where the software processing time must be considered. Since fmax=fmax/d, where: fmax is the pulse frequency of the maximum speed, kHz; vmax is the maximum feed rate, mm/min; d is the pulse equivalent, mm. Let D be the speed range, D = vmax/vmin, then fmax = Dvmin/d = DKd/d = DK. Since the reciprocal of the frequency is the interval between two pulses, the reciprocal of the highest frequency fmax is the minimum interval tmin, i.e., tmin = 1/DK. Clearly, the system must complete the position detection and control operations within tmin through hardware or software. For the highest speed, the value of vmax is constrained by tmin. A good servo system often has a speed range D of 800–1000. The most advanced level today is continuous adjustment of the feed rate from 0 to 240 m/min under the condition of pulse equivalent d = 1µm. 5. Conclusion The above aspects analyze the servo performance requirements of CNC machine tool position servo systems and propose reliability indicators for stable system operation. The research results can be used for the design of servo CNC systems and for the retrofitting of existing CNC machine tools to improve their working accuracy.