Optimization design method of built-in permanent magnet synchronous motorized spindle for high-precision numerical control machine tool

Abstract

The invention provides a built-in permanent magnet synchronous motorized spindle optimization design method for a high-precision numerical control machine tool, and aims to solve the problem that a conventional motorized spindle structure cannot adjust an axial preload and a radial external load in real time. The structure of the motorized spindle is optimally designed from three aspects of high-speed ceramic ball mixed bearing materials, axial preload real-time compensation and radial external load real-time compensation. The dynamic characteristics of the rotor system can be improved, and shafting vibration can be actively inhibited.

Description

Technical Field

[0001] The invention relates to the field of design of built-in permanent magnet synchronous electric spindles for high-precision CNC machine tools, and in particular to an optimization design method of a built-in permanent magnet synchronous electric spindle for high-precision CNC machine tools. Background Art

[0002] The design level of the electric spindle product directly affects the running quality of the electric spindle, thus affecting the CNC machining capability and machining accuracy. The traditional electric spindle structure design often uses axial constant pressure preload or positioning preload, but they all have inherent defects and cannot be adjusted in real time; the conventional electric spindle structure design cannot compensate for the radial external load in real time, and cannot actively suppress the vibration of the shaft system. The quality of the electric spindle shaft system design directly affects the compactness of the spindle structure, operating stability and various key performance indicators, and ultimately affects the CNC machining accuracy. Therefore, how to improve the reliability and stability of the entire shaft system through the optimized design of the spindle system components has always been one of the key technical issues studied at home and abroad. Summary of the invention

[0003] In view of the growing demand for high-precision design of electric spindles and to solve the above-mentioned technical problems, the present invention provides an optimization 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 realizes active vibration suppression.

[0004] In order to achieve the above object, the present invention adopts the following technical scheme: An optimization design method for a built-in permanent magnet synchronous electric spindle for a high-precision CNC machine tool comprises: optimizing the materials of the bearing rolling element, the bearing inner ring, the bearing outer ring and the bearing retainer while designing a high-speed ceramic ball hybrid bearing; using a double-acting annular hydraulic cylinder closed-loop feedback control to perform real-time compensation for the axial preload; using piezoelectric ceramics as an actuator to perform closed-loop feedback control to compensate for radial external loads in real time.

[0005] Furthermore, the bearing rolling elements of the designed high-speed ceramic ball hybrid bearing are made of high-hardness SiN4 ceramic material with a Vickers hardness greater than 1700HV, the bearing inner ring material is made of 13Cr4Mo4Ni4V alloy steel and the surface nitriding depth is greater than 0.32mm, the bearing outer ring material is made of 8Cr4Mo4V alloy steel and is carburized at 950°C, and the bearing retainer is made of nickel-titanium alloy material formed by adding 5% titanium element to 40CrNiMoA, and the surface silver plating layer thickness is greater than 0.038mm.

[0006] Furthermore, the real-time compensation of the axial preload by closed-loop feedback control of the double-acting annular hydraulic cylinder includes: according to the current operating conditions, real-time query of the axial load data table, feedback data through the annular force sensor, alternately supplying oil to 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.

[0007] Furthermore, the axial load data table records the relationship between the axial preload and the vibration acceleration and temperature of the electric spindle under different speed and torque conditions of the electric spindle, and gives a recommended optimal axial preload value.

[0008] Furthermore, the optimal axial preload value is obtained by a preliminary experiment method. Under the same working condition, different axial preload values ​​are adjusted, and the optimal axial preload value is obtained according to the vibration and temperature change trends of the electric spindle.

[0009] Furthermore, the use of piezoelectric ceramics as actuators to perform closed-loop feedback control and real-time compensation of radial external loads includes: real-time query of the radial load data table, and according to the feedback data of the micro force sensor, adjusting the electric field voltage of the piezoelectric ceramic piece 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.

[0010] Furthermore, the radial load data table is a multidimensional data table formed by adding an axial preload variable to the axial load data table, and the mapping relationship between the radial external load compensation amount and the radial vibration is obtained by a preliminary test method.

[0011] The beneficial effects of the present invention compared with the prior art are: 1. Conventional bearing components are all made of ordinary bearing steel. The present invention optimizes the materials of bearing rolling elements, bearing inner rings, bearing outer rings, and bearing retainers at the same time. 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, small centrifugal force, small linear expansion coefficient, small thermal deformation, and enhanced wear resistance. The bearing inner ring material is 13Cr4Mo4Ni4V alloy steel and the surface nitriding depth is greater than 0.32mm. The bearing outer ring material is 8Cr4Mo4V alloy steel and is carburized at 950℃, which can significantly improve its limit speed and reliability. The bearing retainer is formed by adding 5% titanium element to 40CrNiMoA to form a nickel-titanium alloy material, which can improve the fatigue life of the bearing. The thickness of the silver plating layer on the surface of the bearing retainer is greater than 0.038mm, which can improve the self-lubricating performance, reduce wear and facilitate heat dissipation.

[0012] 2. Traditional electric spindle structural designs often use axial constant pressure preload or positioning preload, but they all have inherent defects and cannot be adjusted in real time. When the axial preload is increased, the dynamic stiffness of the spindle bearing increases. The increase in stiffness is beneficial to improving the radial vibration resistance, but when it is increased too much, the bearing wear will increase and the life of the bearing will be greatly reduced. When the motor is running at high speed and weak magnetic field, the efficiency decreases, the loss increases, the axial thermal elongation occurs, and the axial deformation occurs. The axial displacement caused by the deformation will indirectly increase the original axial preload. The real-time compensation design of the axial preload in the present invention can solve this problem. In fact, the optimal axial preload is constantly changing under different speed and torque conditions. Therefore, the optimal axial preload is affected by multiple factors such as the electric spindle speed, torque, vibration acceleration, and bearing temperature. It is difficult to solve it through theoretical calculation formulas. The axial load data table made by the preliminary test method is more in line with reality.

[0013] 3. Conventional electric spindle structural design cannot compensate radial external load in real time. In the electric spindle design proposed by the present invention, when an electric field is applied to the piezoelectric ceramic, the ceramic sheet will become thinner or thicker according to the voltage change to generate deformation force, and this characteristic of piezoelectric ceramic is used to compensate radial external load in real time. The radial load data table is based on the axial load data table, and the axial preload variable is added to form a multidimensional data table. The mapping relationship between the radial external load compensation amount and the radial vibration is obtained by the pre-test method, which more objectively reflects the real corresponding relationship and has a better vibration suppression effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the position where the axial preload and radial external load are applied; Figure 2 This is the principle diagram of the electric spindle axial preload compensation; Figure 3 This is the schematic diagram of the radial external load compensation of the electric spindle.

[0015] Among them, the figures are marked as: the first compensation position 1 of the radial external load of the electric spindle, the second compensation position 2 of the radial external load of the electric spindle, the third compensation position 3 of the radial external load of the electric spindle, the fourth compensation position 4 of the radial external load of the electric spindle, the axial preload compensation position 5 of the electric spindle, the double-acting annular hydraulic cylinder 6, the annular piston push rod 7, the annular force sensor 8, the first bearing outer ring 9, the clamping screw 10, the piezoelectric ceramic sheet 11, the miniature force sensor 12, the radial push rod 13, and the second bearing outer ring 14. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. The present invention is described in detail below in conjunction with the accompanying drawings.

[0017] like Figure 1 As shown, the present invention sets a first compensation position 1 for the radial external load of the electric spindle, a second compensation position 2 for the radial external load of the electric spindle, a third compensation position 3 for the radial external load of the electric spindle, a fourth compensation position 4 for the radial external load of the electric spindle, and a compensation position 5 for the axial preload of the electric spindle. The compensation position and compensation amount can be adjusted according to different layout methods of the bearings.

[0018] like Figure 2 As shown, the outer circle of the double-acting annular hydraulic cylinder 6 is interference-connected with the inner circle of the bearing sleeve, the annular piston push rod 7 is arranged in the double-acting annular hydraulic cylinder 6, and can perform reciprocating motion, and the annular force sensor 8 is bonded and fixed to the annular piston push rod 7, and is also bonded and fixed to the outer ring 9 of the first bearing. The double-acting annular hydraulic cylinder 6 alternately feeds oil through the two chambers, pushes the annular piston push rod 7 to act on the annular force sensor 8, and applies the 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. According to the current operating conditions, the axial load data table is queried in real time, and the feedback data measured by the annular force sensor 8 is measured. The two chambers of the hydraulic cylinder alternately feed oil, and the position of the annular piston push rod 7 is continuously adjusted to adjust the hydraulic thrust to the optimal axial preload value.

[0019] The axial load data table records the relationship between the axial preload and the vibration acceleration and temperature of the electric spindle under different speed and torque conditions, and gives the recommended optimal axial preload value. The optimal axial preload value is obtained by adjusting different axial preload values ​​under the same working conditions through a preliminary experiment, and according to the vibration and temperature change trends of the electric spindle.

[0020] like Figure 3As shown, the clamping screw 10 is fixed through the threaded hole on the housing of the electric spindle, the piezoelectric ceramic sheet 11 is formed by bonding multiple piezoelectric ceramics, the micro force sensor 12 is bonded and fixed to the piezoelectric ceramic sheet 11, and is also bonded and fixed to the radial push rod 13. Under the action of the radial external load, the radial push rod 13 directly supports 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 the external electric field, the piezoelectric ceramic sheet 11 will become thinner or thicker according to the voltage change to generate a deformation force. The deformation force is transmitted to the radial push rod 13 through the micro force sensor 12. The radial push rod 13 applies a radial external load to the outer ring 14 of the second bearing, and the size of the radial external load is measured by the micro force sensor 12. The radial load data table is queried in real time, and the deformation force generated by the electric field voltage of the piezoelectric ceramic sheet 11 is adjusted according to the feedback data of the micro force sensor 12, and the radial external load is compensated in real time to achieve active suppression of the radial vibration of the electric spindle.

[0021] The radial load data table is a multi-dimensional data table made by adding the axial preload variable on the basis of the axial load data table. The mapping relationship between the radial external load compensation amount and the radial vibration is obtained through a preliminary test method.

[0022] The optimization design method of the built-in permanent magnet synchronous electric spindle for high-precision CNC machine tools of the present invention comprises: The designed high-speed ceramic ball hybrid bearing optimizes the materials of the bearing rolling elements, bearing inner ring, bearing outer ring and bearing cage at the same time; uses double-acting annular hydraulic cylinder closed-loop feedback control to perform real-time compensation for axial preload; uses piezoelectric ceramics as actuators for closed-loop feedback control to compensate for radial external loads in real time.

[0023] Furthermore, the bearing rolling elements of the designed high-speed ceramic ball hybrid bearing are made of high-hardness SiN4 ceramic material with a Vickers hardness greater than 1700HV, the bearing inner ring material is made of 13Cr4Mo4Ni4V alloy steel and the surface nitriding depth is greater than 0.32mm, the bearing outer ring is made of 8Cr4Mo4V alloy steel and is carburized at 950℃, and the bearing retainer is made of 40CrNiMoA alloy steel with 5% titanium element added to form a nickel-titanium alloy material, and the surface silver plating layer thickness is greater than 0.038mm.

[0024] The present invention optimizes the materials of the bearing rolling element, the bearing inner ring, the bearing outer ring and the bearing retainer at the same time, so that the bearing rolling element has the advantages of light weight, small centrifugal force, small linear expansion coefficient, small thermal deformation, enhanced wear resistance and the like; the materials of the bearing inner ring and the bearing outer ring significantly improve their limit speed and reliability; the bearing retainer adds 5% titanium element to 40CrNiMoA to form a nickel-titanium alloy material, which can improve the fatigue life of the bearing; the thickness of the silver-plated layer on the surface of the bearing retainer is greater than 0.038 mm, which can improve the self-lubricating performance, reduce wear and facilitate heat dissipation.

[0025] Furthermore, the real-time compensation of the axial preload is performed by closed-loop feedback control of the double-acting annular hydraulic cylinder, including: according to the current operating conditions, real-time query of the axial load data table, feedback of data through the annular force sensor 8, alternating oil supply to the two chambers of the double-acting annular hydraulic cylinder 6, and continuous adjustment of the position of the annular piston push rod 7, so as to adjust the hydraulic thrust to the optimal axial preload value.

[0026] The axial load data table records the relationship between the axial preload and the vibration acceleration and temperature of the electric spindle under different speed and torque conditions of the electric spindle, and gives the recommended optimal axial preload value.

[0027] Furthermore, the optimal axial preload value is obtained by adjusting different axial preload values ​​under the same working conditions through a preliminary experiment method, based on the vibration and temperature variation trends of the electric spindle.

[0028] Furthermore, piezoelectric ceramics are used as actuators to perform closed-loop feedback control and real-time compensation of radial external loads, including: real-time query of the radial load data table, adjusting the deformation force generated by the electric field voltage of the piezoelectric ceramic piece 11 according to the feedback data of the micro force sensor 12, and real-time compensation of the radial external load to achieve active suppression of the radial vibration of the electric spindle.

[0029] Furthermore, the radial load data table is a multi-dimensional data table formed by adding the axial preload variable on the basis of the axial load data table, and the mapping relationship between the radial external load compensation amount and the radial vibration is obtained by a preliminary test method.

Claims

1. An optimization design method for a built-in permanent magnet synchronous electric spindle for a high-precision CNC machine tool, characterized in that: include: The designed high-speed ceramic ball hybrid bearing optimizes the materials of the bearing rolling elements, bearing inner ring, bearing outer ring and bearing cage at the same time; uses double-acting annular hydraulic cylinder closed-loop feedback control to perform real-time compensation for axial preload; uses piezoelectric ceramics as actuators for closed-loop feedback control to compensate for radial external loads in real time.

2. The optimization design method of a built-in permanent magnet synchronous electric spindle for a high-precision CNC machine tool according to claim 1 is characterized in that: The bearing rolling elements of the designed high-speed ceramic ball hybrid bearing are made of high-hardness SiN4 ceramic material with a Vickers hardness greater than 1700HV, the bearing inner ring material is made of 13Cr4Mo4Ni4V alloy steel and the surface nitriding depth is greater than 0.32mm, the bearing outer ring material is made of 8Cr4Mo4V alloy steel and is carburized at 950℃, and the bearing cage is made of nickel-titanium alloy material formed by adding 5% titanium element to 40CrNiMoA, and the surface silver plating layer thickness is greater than 0.038mm.

3. The optimization design method of a built-in permanent magnet synchronous electric spindle for a high-precision CNC machine tool according to claim 1 is characterized in that: The real-time compensation of the axial preload by closed-loop feedback control of the double-acting annular hydraulic cylinder includes: according to the current operating conditions, real-time query of the axial load data table, feedback data through the annular force sensor, alternately supplying oil to 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.

4. The optimization design method of a built-in permanent magnet synchronous electric spindle for a high-precision CNC machine tool according to claim 3 is characterized in that: The axial load data table records the relationship between the axial preload and the vibration acceleration and temperature of the electric spindle under different speed and torque conditions of the electric spindle, and gives a recommended optimal axial preload value.

5. The optimization design method of a built-in permanent magnet synchronous electric spindle for a high-precision CNC machine tool according to claim 4 is characterized in that: The optimal axial preload value is obtained by a preliminary experiment method. Under the same working condition, different axial preload values ​​are adjusted, and the optimal axial preload value is obtained according to the vibration and temperature change trends of the electric spindle.

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

7. The optimization design method of a built-in permanent magnet synchronous electric spindle for a high-precision CNC machine tool according to claim 6 is characterized in that: The radial load data table is a multidimensional data table formed by adding an axial preload variable to the axial load data table. The mapping relationship between the radial external load compensation amount and the radial vibration is obtained by a preliminary test method.

Images