An optimization design method of an inner-mounted permanent magnet synchronous motorized spindle for high-precision numerical control machine tools

Abstract

The application provides an optimization design method of an internal permanent magnet synchronous electric spindle for a high-precision numerical control machine tool, and aims at the problem that a conventional electric spindle structure cannot perform real-time adjustment on axial pre-load and radial external load, and performs optimization design on the electric spindle structure from three aspects of high-speed ceramic ball hybrid bearing material, axial pre-load real-time compensation and radial external load real-time compensation. The application can improve dynamic characteristics of a rotor system and can actively inhibit shafting vibration.

Description

An Optimization Design Method for Built-in Permanent Magnet Synchronous Electric Spindle for High-Precision CNC Machine Tools Technical Field

[0001] This invention relates to the field of design of built-in permanent magnet synchronous electric spindles for high-precision CNC machine tools, and particularly to an optimized design method for built-in permanent magnet synchronous electric spindles for high-precision CNC machine tools. Background Technology

[0002] The design level of electric spindles directly affects their operational quality, thus impacting CNC machining capabilities and accuracy. Traditional electric spindle designs often employ axial constant pressure preload or positioning preload, but both have inherent limitations, failing to provide real-time adjustment. Conventional electric spindle designs also cannot compensate for radial external loads in real time or actively suppress shaft vibration. The quality of the electric spindle's shaft system design directly affects the spindle's structural compactness, operational stability, and various key performance indicators, ultimately influencing CNC machining accuracy. Therefore, improving the reliability and stability of the entire shaft system through optimized design of spindle system components has always been a key technical challenge in research both domestically and internationally. Summary of the Invention

[0003] In response to the growing demand for high-precision electric spindle design and to address the aforementioned technical problems, this invention provides an optimized design method for a built-in permanent magnet synchronous electric spindle for high-precision CNC machine tools, which improves the overall structural stability of the electric spindle and achieves active vibration suppression.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] An optimized design method for a high-precision CNC machine tool's built-in permanent magnet synchronous electric spindle includes: designing a high-speed ceramic ball hybrid bearing while simultaneously optimizing the materials of the bearing rolling elements, bearing inner ring, bearing outer ring, and bearing cage; using a double-acting annular hydraulic cylinder for closed-loop feedback control to compensate for axial preload in real time; and using piezoelectric ceramics as actuators for closed-loop feedback control to compensate for radial external load in real time.

[0006] Furthermore, the designed high-speed ceramic ball hybrid bearing uses high-hardness SiN4 ceramic material with a Vickers hardness greater than 1700HV for the rolling elements, 13Cr4Mo4Ni4V alloy steel for the inner ring with a nitriding depth greater than 0.32mm for the surface, 8Cr4Mo4V alloy steel for the outer ring with high-temperature carburizing at 950℃ for the outer ring, and 5% titanium is added to 40CrNiMoA to form a nickel-titanium alloy material with a silver plating layer thickness greater than 0.038mm for the surface.

[0007] Furthermore, the real-time compensation of axial preload using closed-loop feedback control of a double-acting annular hydraulic cylinder includes: querying the axial load data table in real time according to the current operating conditions, feeding back data through an annular force sensor, alternating oil intake in the two chambers of the hydraulic cylinder, continuously adjusting the position of the annular piston push rod, and adjusting the hydraulic thrust to the optimal axial preload value.

[0008] Furthermore, the axial load data table records the relationship between axial preload and the vibration acceleration and temperature of the electric spindle under different speed and torque conditions, and provides a recommended optimal axial preload value.

[0009] Furthermore, the optimal axial preload value is obtained through a pre-experiment method. Under the same working conditions, different axial preload values ​​are adjusted, and the optimal axial preload value is obtained based on the vibration and temperature change trends of the electric spindle.

[0010] Furthermore, the method of using piezoelectric ceramics as actuators for closed-loop feedback control and real-time compensation of radial external loads includes: querying the radial load data table in real time, adjusting the electric field voltage of the piezoelectric ceramic sheet according to the feedback data of the micro force sensor to generate deformation force to compensate for the radial external load in real time, thereby achieving active suppression of radial vibration of the electric spindle.

[0011] Furthermore, the radial load data table is a multidimensional data table created by adding axial preload variables to the axial load data table. The mapping relationship between the radial external load compensation and radial vibration is obtained through pre-experimentation.

[0012] The advantages of this invention compared to the prior art are:

[0013] 1. Traditional bearing components all use ordinary bearing steel materials. This invention simultaneously optimizes the materials of the bearing rolling elements, bearing inner ring, bearing outer ring, and bearing cage. The designed high-speed ceramic ball hybrid bearing uses high-hardness SiN4 ceramic material with a Vickers hardness greater than 1700HV as the bearing rolling element, which has the advantages of light weight, low centrifugal force, low coefficient of linear expansion, low thermal deformation, and enhanced wear resistance. The bearing inner ring material is made of 13Cr4Mo4Ni4V alloy steel with a surface nitriding depth greater than 0.32mm, and the bearing outer ring material is made of 8Cr4Mo4V alloy steel with high-temperature carburizing at 950℃, which can significantly improve its limiting speed and reliability. The bearing cage is made of 40CrNiMoA with 5% titanium to form a nickel-titanium alloy material, which can improve the bearing fatigue life. The silver plating layer on the surface of the bearing cage is thicker than 0.038mm, which can improve self-lubricating performance, reduce wear, and facilitate heat dissipation.

[0014] 2. Traditional electric spindle designs often use axial constant pressure preload or positioning preload, but both have inherent drawbacks and cannot be adjusted in real time. Increasing the axial preload increases the dynamic stiffness of the spindle bearing, which improves radial vibration resistance. However, excessive increases lead to accelerated bearing wear and a significant reduction in bearing life. During high-speed, weak-field operation, motor efficiency decreases, losses increase, axial thermal elongation occurs, and axial deformation is generated. The axial displacement caused by this deformation indirectly increases the original axial preload. The real-time axial preload compensation design in this invention can solve this problem. In reality, the optimal axial preload changes continuously under different speed and torque conditions. Therefore, the optimal axial preload is simultaneously affected by multiple factors, including spindle speed, torque, vibration acceleration, and bearing temperature. It is difficult to solve using theoretical calculation formulas; therefore, the axial load data table created through pre-experimentation is more realistic.

[0015] 3. Conventional electric spindle designs cannot compensate for radial external loads in real time. In the electric spindle design proposed in this invention, when an electric field is applied to the piezoelectric ceramic, the ceramic sheet thins or thickens according to voltage changes, generating deformation force. This characteristic of the piezoelectric ceramic is utilized to compensate for radial external loads in real time. The radial load data table is a multi-dimensional table created by adding axial preload variables to the axial load data table. The mapping relationship between the radial external load compensation and radial vibration is obtained through pre-experimentation, thus more objectively reflecting the true correspondence and achieving better vibration suppression. Attached Figure Description

[0016] Figure 1 shows a schematic diagram of the application positions of axial preload and radial external load;

[0017] Figure 2 is a schematic diagram of the axial preload compensation principle of the electric spindle;

[0018] Figure 3 is a schematic diagram of the radial external load compensation principle of the electric spindle.

[0019] The reference numerals in the attached drawings are as follows: 1. First compensation position for radial external load of electric spindle; 2. Second compensation position for radial external load of electric spindle; 3. Third compensation position for radial external load of electric spindle; 4. Fourth compensation position for radial external load of electric spindle; 5. Axial preload compensation position of electric spindle; 6. Double-acting annular hydraulic cylinder; 7. Annular piston push rod; 8. Annular force sensor; 9. Outer ring of first bearing; 10. Clamping screw; 11. Piezoelectric ceramic plate; 12. Miniature force sensor; 13. Radial push rod; 14. Outer ring of second bearing. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. The invention will now be described in detail with reference to the accompanying drawings.

[0021] As shown in Figure 1, the present invention sets a first compensation position 1 for radial external load of electric spindle, a second compensation position 2 for radial external load of electric spindle, a third compensation position 3 for radial external load of electric spindle, a fourth compensation position 4 for radial external load of electric spindle, and an axial preload compensation position 5 for electric spindle. The compensation position and the number of compensations can be adjusted according to different bearing layouts.

[0022] As shown in Figure 2, the outer circle of the double-acting annular hydraulic cylinder 6 is interference-fitted with the inner circle of the bearing sleeve. The annular piston push rod 7 is installed inside the double-acting annular hydraulic cylinder 6 and can reciprocate. The annular force sensor 8 is bonded and fixed to the annular piston push rod 7 and also bonded and fixed to the outer ring 9 of the first bearing. The double-acting annular hydraulic cylinder 6 alternately feeds oil into its two chambers, pushing the annular piston push rod 7 to act on the annular force sensor 8, applying an axial preload to the outer ring 9 of the first bearing. The magnitude of the applied axial preload force is measured by the annular force sensor 8. Based on the current operating conditions, the axial load data table is queried in real time. Based on the data fed back by the annular force sensor 8, the two chambers of the hydraulic cylinder alternately feed oil, continuously adjusting the position of the annular piston push rod 7 to adjust the hydraulic thrust to the optimal axial preload value.

[0023] The axial load data table records the relationship between axial preload and spindle vibration acceleration and temperature under different spindle speeds and torque conditions, and provides recommended optimal axial preload values. The optimal axial preload value was determined through pre-experimentation, adjusting different axial preload values ​​under the same operating conditions, and based on the trends of spindle vibration and temperature changes.

[0024] As shown in Figure 3, the clamping screw 10 is fixed through a threaded hole on the electric spindle housing. The piezoelectric ceramic sheet 11 is composed of multiple piezoelectric ceramic sheets bonded together. The miniature force sensor 12 is bonded and fixed to the piezoelectric ceramic sheet 11 and also to the radial push rod 13. Under the action of radial external load, the radial push rod 13 directly presses against the outer ring 14 of the second bearing. The clamping screw 10 is used to set the initial radial external load. Under the action of an external electric field, the piezoelectric ceramic sheet 11 will thin or thicken according to the voltage change, thereby generating a deformation force. The deformation force is transmitted to the radial push rod 13 through the miniature force sensor 12. The radial push rod 13 applies a radial external load to the outer ring 14 of the second bearing. The magnitude of the radial external load is measured by the miniature force sensor 12. The radial load data table is queried in real time. Based on the feedback data from the miniature force sensor 12, the deformation force generated by the electric field voltage of the piezoelectric ceramic sheet 11 is adjusted to compensate for the radial external load in real time, thereby achieving active suppression of radial vibration of the electric spindle.

[0025] The radial load data table is a multidimensional data table created by adding axial preload variables to the axial load data table. The mapping relationship between radial external load compensation and radial vibration is obtained through pre-experimentation.

[0026] The optimization design method for a built-in permanent magnet synchronous electric spindle for high-precision CNC machine tools of the present invention includes:

[0027] The designed high-speed ceramic ball hybrid bearing simultaneously optimizes the materials of the bearing rolling elements, inner ring, outer ring, and cage; utilizes a double-acting annular hydraulic cylinder closed-loop feedback control to compensate for axial preload in real time; and employs piezoelectric ceramics as actuators for closed-loop feedback control to compensate for radial external load in real time.

[0028] Furthermore, the designed high-speed ceramic ball hybrid bearing uses high-hardness SiN4 ceramic material with a Vickers hardness greater than 1700HV for the rolling elements, 13Cr4Mo4Ni4V alloy steel with a nitriding depth greater than 0.32mm for the inner ring, 8Cr4Mo4V alloy steel with high-temperature carburizing at 950℃ for the outer ring, and 5% titanium is added to 40CrNiMoA alloy steel to form a nickel-titanium alloy material with a silver plating layer thickness greater than 0.038mm.

[0029] This invention simultaneously optimizes the materials of the bearing rolling elements, bearing inner ring, bearing outer ring, and bearing cage, resulting in bearing rolling elements with advantages such as light weight, low centrifugal force, low coefficient of linear expansion, low thermal deformation, and enhanced wear resistance. The materials of the bearing inner and outer rings significantly improve their limiting speed and reliability. The addition of 5% titanium to 40CrNiMoA to form a nickel-titanium alloy material in the bearing cage can improve bearing fatigue life. The silver plating layer on the surface of the bearing cage with a thickness greater than 0.038mm can improve self-lubricating performance, reduce wear, and facilitate heat dissipation.

[0030] Furthermore, the real-time compensation of axial preload using closed-loop feedback control of a double-acting annular hydraulic cylinder includes: querying the axial load data table in real time according to the current operating conditions, feeding back data through the annular force sensor 8, alternating oil intake in the two chambers of the double-acting annular hydraulic cylinder 6, continuously adjusting the position of the annular piston push rod 7, and adjusting the hydraulic thrust to the optimal axial preload value.

[0031] The axial load data table records the relationship between axial preload and the vibration acceleration and temperature of the electric spindle under different speed and torque conditions, and provides recommended optimal axial preload values.

[0032] Furthermore, the optimal axial preload value was determined through a pre-experiment method, adjusting different axial preload values ​​under the same working conditions, based on the vibration and temperature change trends of the electric spindle.

[0033] Furthermore, by using piezoelectric ceramics as actuators for closed-loop feedback control, the radial external load is compensated in real time. This includes: querying the radial load data table in real time, adjusting the deformation force generated by the electric field voltage of the piezoelectric ceramic sheet 11 based on the feedback data from the micro force sensor 12, and compensating for the radial external load in real time to achieve active suppression of radial vibration of the electric spindle.

[0034] Furthermore, the radial load data table is a multidimensional data table created by adding axial preload variables to the axial load data table. The mapping relationship between the radial external load compensation and radial vibration is obtained through pre-experiment methods.

Claims

1. A method for optimizing the design of a built-in permanent magnet synchronous electric spindle for high-precision CNC machine tools, characterized in that, include: The designed high-speed ceramic ball hybrid bearing optimizes the materials of the bearing rolling elements, inner ring, outer ring, and cage. It utilizes a double-acting annular hydraulic cylinder with closed-loop feedback control for real-time compensation of axial preload. Piezoelectric ceramics are used as actuators for closed-loop feedback control to compensate for radial loads in real-time. The bearing rolling elements are made of high-hardness SiN4 ceramic material with a Vickers hardness greater than 1700 HV. The inner ring is made of 13Cr4Mo4Ni4V alloy steel with a nitriding depth greater than 0.32 mm. The outer ring is made of 8Cr4Mo4V alloy steel with high-temperature carburizing at 950℃. The cage is made of 40CrNiMoA with 5% titanium added to form a nickel-titanium alloy, and the surface is silver-plated with a thickness greater than 0.038 mm. Real-time radial load monitoring is performed. A radial load data table is used to actively suppress the radial vibration of the electric spindle. This radial load data table is a multi-dimensional table created by adding radial external load variables to the axial load data table. The mapping relationship between the radial external load compensation and radial vibration is obtained through pre-experimentation. The axial load data table records the relationship between axial preload and the electric spindle vibration acceleration and temperature under different speed and torque conditions, and provides a recommended optimal axial preload value. The compensation position and quantity are adjusted according to different bearing layouts. A double-acting annular hydraulic cylinder, through alternating oil intake in its two chambers, pushes an annular piston rod to act on an annular force sensor, applying axial preload to the outer ring of the first bearing. The piezoelectric ceramic plate transmits the deformation force to the radial push rod through a miniature force sensor, and the radial push rod applies a radial external load to the outer ring of the second bearing.

2. The optimized design method for a built-in permanent magnet synchronous electric spindle for high-precision CNC machine tools according to claim 1, characterized in that, The method of using a double-acting annular hydraulic cylinder closed-loop feedback control to compensate for axial preload in real time includes: querying the axial load data table in real time according to the current operating conditions, feeding back data through an annular force sensor, alternately injecting oil into the two chambers of the hydraulic cylinder, and continuously adjusting the position of the annular piston push rod to adjust the hydraulic thrust to the optimal axial preload value.

3. The optimized design method for a built-in permanent magnet synchronous electric spindle for high-precision CNC machine tools according to claim 2, characterized in that, The optimal axial preload value was obtained through a pre-experiment method. Under the same working conditions, different axial preload values ​​were adjusted, and the optimal axial preload value was obtained based on the vibration and temperature change trends of the electric spindle.

4. The optimized design method for a built-in permanent magnet synchronous electric spindle for high-precision CNC machine tools according to claim 1, characterized in that, The method of using piezoelectric ceramics as actuators for closed-loop feedback control and real-time compensation of radial external loads includes: querying the radial load data table in real time, adjusting the electric field voltage of the piezoelectric ceramic sheet according to the feedback data of the micro force sensor to generate deformation force to compensate for the radial external load in real time, thereby achieving active suppression of radial vibration of the electric spindle.

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