“Requirements and Optimization Measures for Feed Transmission Mechanism of CNC Machine Tools”
In modern manufacturing, CNC machine tools have become key processing equipment due to their advantages such as high precision, high efficiency, and high degree of automation. The feed transmission system of CNC machine tools usually works with a servo feed system, which plays a crucial role. According to the instruction messages transmitted from the CNC system, it amplifies and then controls the movement of the actuating components. It not only needs to precisely control the speed of the feed movement but also accurately control the moving position and trajectory of the tool relative to the workpiece.
A typical closed-loop controlled feed system of a CNC machine tool is mainly composed of several parts such as position comparison, amplification components, driving units, mechanical feed transmission mechanisms, and detection feedback elements. Among them, the mechanical feed transmission mechanism is the entire mechanical transmission chain that converts the rotational movement of the servo motor into the linear feed movement of the worktable and tool holder, including reduction devices, lead screw and nut pairs, guide components and their supporting parts. As an important link in the servo system, the feed mechanism of CNC machine tools should not only have high positioning accuracy but also have good dynamic response characteristics. The response of the system to tracking instruction signals should be fast and the stability should be good.
To ensure the transmission accuracy, system stability, and dynamic response characteristics of the feed system of vertical machining centers, a series of strict requirements are put forward for the feed mechanism:
I. Requirement for no gap
Transmission gap will lead to reverse dead zone error and affect processing accuracy. To eliminate transmission gap as much as possible, methods such as using a linkage shaft with gap elimination and transmission pairs with gap elimination measures can be adopted. For example, in the lead screw and nut pair, the double-nut preloading method can be used to eliminate the gap by adjusting the relative position between the two nuts. At the same time, for parts such as gear transmissions, methods such as adjusting shims or elastic elements can also be used to eliminate the gap to ensure the accuracy of transmission.
Transmission gap will lead to reverse dead zone error and affect processing accuracy. To eliminate transmission gap as much as possible, methods such as using a linkage shaft with gap elimination and transmission pairs with gap elimination measures can be adopted. For example, in the lead screw and nut pair, the double-nut preloading method can be used to eliminate the gap by adjusting the relative position between the two nuts. At the same time, for parts such as gear transmissions, methods such as adjusting shims or elastic elements can also be used to eliminate the gap to ensure the accuracy of transmission.
II. Requirement for low friction
Adopting a low-friction transmission method can reduce energy loss, improve transmission efficiency, and also help improve the response speed and accuracy of the system. Common low-friction transmission methods include hydrostatic guides, rolling guides, and ball screws.
Adopting a low-friction transmission method can reduce energy loss, improve transmission efficiency, and also help improve the response speed and accuracy of the system. Common low-friction transmission methods include hydrostatic guides, rolling guides, and ball screws.
Hydrostatic guides form a layer of pressure oil film between the guide surfaces to achieve non-contact sliding with extremely small friction. Rolling guides use the rolling of rolling elements on the guide rails to replace sliding, greatly reducing friction. Ball screws are important components that convert rotational motion into linear motion. The balls roll between the lead screw and the nut with a low friction coefficient and high transmission efficiency. These low-friction transmission components can effectively reduce the resistance of the feed mechanism during movement and improve the performance of the system.
III. Requirement for low inertia
To improve the machine tool resolution and make the worktable accelerate as much as possible to achieve the purpose of tracking instructions, the moment of inertia converted to the drive shaft by the system should be as small as possible. This requirement can be achieved by selecting the optimal transmission ratio. Reasonably choosing the transmission ratio can reduce the system’s moment of inertia while meeting the requirements of worktable movement speed and acceleration. For example, when designing a reduction device, according to actual needs, a suitable gear ratio or belt pulley ratio can be selected to match the output speed of the servo motor with the movement speed of the worktable and reduce the moment of inertia at the same time.
To improve the machine tool resolution and make the worktable accelerate as much as possible to achieve the purpose of tracking instructions, the moment of inertia converted to the drive shaft by the system should be as small as possible. This requirement can be achieved by selecting the optimal transmission ratio. Reasonably choosing the transmission ratio can reduce the system’s moment of inertia while meeting the requirements of worktable movement speed and acceleration. For example, when designing a reduction device, according to actual needs, a suitable gear ratio or belt pulley ratio can be selected to match the output speed of the servo motor with the movement speed of the worktable and reduce the moment of inertia at the same time.
In addition, a lightweight design concept can also be adopted, and materials with lighter weight can be selected to make transmission components. For example, using lightweight materials such as aluminum alloy to make lead screw and nut pairs and guide components can reduce the overall inertia of the system.
IV. Requirement for high stiffness
A high-stiffness transmission system can ensure resistance to external interference during the processing process and maintain stable processing accuracy. To improve the stiffness of the transmission system, the following measures can be taken:
Shorten the transmission chain: Reducing the transmission links can reduce the elastic deformation of the system and improve the stiffness. For example, using the method of directly driving the lead screw by the motor saves the intermediate transmission links, reduces transmission errors and elastic deformation, and improves the stiffness of the system.
Improve the stiffness of the transmission system by preloading: For rolling guides and ball screw pairs, a preloaded method can be used to generate a certain preload between the rolling elements and the guide rails or lead screws to improve the rigidity of the system. The lead screw support is designed to be fixed at both ends and can have a pre-stretched structure. By applying a certain pre-tension to the lead screw, the axial force during operation can be counteracted and the stiffness of the lead screw can be improved.
A high-stiffness transmission system can ensure resistance to external interference during the processing process and maintain stable processing accuracy. To improve the stiffness of the transmission system, the following measures can be taken:
Shorten the transmission chain: Reducing the transmission links can reduce the elastic deformation of the system and improve the stiffness. For example, using the method of directly driving the lead screw by the motor saves the intermediate transmission links, reduces transmission errors and elastic deformation, and improves the stiffness of the system.
Improve the stiffness of the transmission system by preloading: For rolling guides and ball screw pairs, a preloaded method can be used to generate a certain preload between the rolling elements and the guide rails or lead screws to improve the rigidity of the system. The lead screw support is designed to be fixed at both ends and can have a pre-stretched structure. By applying a certain pre-tension to the lead screw, the axial force during operation can be counteracted and the stiffness of the lead screw can be improved.
V. Requirement for high resonant frequency
A high resonant frequency means that the system can quickly return to a stable state when subjected to external interference and has good vibration resistance. To improve the resonant frequency of the system, the following aspects can be started:
Optimize the structural design of transmission components: Reasonably design the shape and size of transmission components such as lead screws and guide rails to improve their natural frequencies. For example, using a hollow lead screw can reduce weight and improve natural frequency.
Select suitable materials: Select materials with high elastic modulus and low density, such as titanium alloy, etc., which can improve the stiffness and natural frequency of transmission components.
Increase damping: Appropriate increase of damping in the system can consume vibration energy, reduce the resonant peak, and improve the stability of the system. The damping of the system can be increased by using damping materials and installing dampers.
A high resonant frequency means that the system can quickly return to a stable state when subjected to external interference and has good vibration resistance. To improve the resonant frequency of the system, the following aspects can be started:
Optimize the structural design of transmission components: Reasonably design the shape and size of transmission components such as lead screws and guide rails to improve their natural frequencies. For example, using a hollow lead screw can reduce weight and improve natural frequency.
Select suitable materials: Select materials with high elastic modulus and low density, such as titanium alloy, etc., which can improve the stiffness and natural frequency of transmission components.
Increase damping: Appropriate increase of damping in the system can consume vibration energy, reduce the resonant peak, and improve the stability of the system. The damping of the system can be increased by using damping materials and installing dampers.
VI. Requirement for appropriate damping ratio
An appropriate damping ratio can make the system quickly stabilize after being disturbed without excessive attenuation of vibration. To obtain an appropriate damping ratio, the control of the damping ratio can be achieved by adjusting system parameters such as the parameters of the damper and the friction coefficient of the transmission components.
An appropriate damping ratio can make the system quickly stabilize after being disturbed without excessive attenuation of vibration. To obtain an appropriate damping ratio, the control of the damping ratio can be achieved by adjusting system parameters such as the parameters of the damper and the friction coefficient of the transmission components.
In summary, to meet the strict requirements of CNC machine tools for feed transmission mechanisms, a series of optimization measures need to be taken. These measures can not only improve the processing accuracy and efficiency of machine tools but also enhance the stability and reliability of machine tools, providing strong support for the development of modern manufacturing.
In practical applications, it is also necessary to comprehensively consider various factors according to specific processing needs and machine tool characteristics and select the most suitable feed transmission mechanism and optimization measures. At the same time, with the continuous progress of science and technology, new materials, technologies, and design concepts are constantly emerging, which also provides a broad space for further improving the performance of feed transmission mechanisms of CNC machine tools. In the future, the feed transmission mechanism of CNC machine tools will continue to develop in the direction of higher precision, higher speed, and higher reliability.