Numerical control machine tool thermal error compensation method and device considering temperature vibration coupling

Abstract

The invention discloses a numerical control machine tool thermal error compensation method and device considering temperature vibration coupling, and the method comprises the steps: (1) obtaining the rotating speed data and voltage and current data of an electric spindle, and collecting the temperature and vibration data of the electric spindle through a temperature sensor and a vibration sensor; (2) calculating an acceleration response matrix of the bearing by using the vibration data so as to obtain a corresponding bearing load coefficient; (3) calculating the heat generation rate of the built-in motor stator and rotor and the front and rear bearings by using the rotating speed data, the voltage and current data and the bearing load coefficient of the motorized spindle, and calculating the temperature distribution of the motorized spindle by using the heat generation rate and the collected temperature data; (4) the step (2) and the step (3) are repeated for iteration, and final mandrel temperature distribution is obtained; (5) calculating the thermal elongation of the mandrel by using the temperature distribution of the mandrel; and (6) carrying out real-time thermal compensation on the thermal error of the machine tool according to a thermal elongation result. The requirement for long-time high-precision thermal error compensation of the machine tool in the machining process can be met.

Description

Technical Field

[0001] The invention belongs to the field of machining process detection and thermal error compensation of numerically controlled machine tools, and in particular relates to a method and a device for thermal error compensation of numerically controlled machine tools taking temperature vibration coupling into consideration. Background Art

[0002] As the core component of CNC machine tools, the running accuracy of the electric spindle directly affects the machining accuracy of the machine tool. During the machining process of the machine tool, the electric spindle runs at high speed, and the built-in motor and bearings will inevitably generate heat due to electromagnetic loss and friction loss, causing temperature rise, which in turn causes thermal deformation of the spindle and affects the machining accuracy; at the same time, during the machining process of the spindle, the spindle is subjected to cutting force, electromagnetic force and other forces, as well as slight errors in installation, which will cause the spindle to vibrate during machining, which will also affect the machining accuracy.

[0003] Temperature and vibration will affect each other, resulting in coupling, which will have a more complex impact on machining accuracy. Specifically, temperature rise will cause thermal expansion of bearing components, affecting the stiffness of the bearing. As a key component connecting the mandrel and the housing, changes in the stiffness of the bearing will cause changes in the vibration pattern of the spindle; and vibration will affect the friction of the bearing, thereby causing changes in the heat generation rate of the bearing and affecting the temperature change of the bearing.

[0004] For example, a Chinese patent document with publication number CN109352424A discloses a temperature compensation method for an electric spindle of a CNC machine tool, comprising: real-time acquisition of the axial center temperature of the electric spindle of the CNC machine tool, obtaining the degree of temperature change based on the axial center temperature of the electric spindle, judging whether the degree of temperature change exceeds a corresponding preset threshold, and obtaining the expansion and contraction amount of the electric spindle based on the axial center temperature of the electric spindle when the temperature change exceeds the corresponding preset threshold, and compensating the coordinates of the electric spindle based on the expansion and contraction amount of the electric spindle.

[0005] A Chinese patent document with publication number CN105415092A discloses a temperature compensation method for an electric spindle of a CNC machine tool, comprising: using a temperature sensor to measure the temperature of the electric spindle at different speeds, wherein a first predetermined time is separated between two adjacent measurements, and the real-time temperature is input into a temperature control device; keeping the electric spindle at different speeds for a second predetermined time, and using a tool setting instrument to measure the thermal elongation of the electric spindle at different speeds; establishing a nonlinear curve between temperature change and thermal elongation based on the measured real-time temperature and thermal elongation; using a PLC file memory to read the temperature in the temperature control device, and calculating the thermal elongation of the electric spindle as a temperature compensation amount based on a linear relationship determined by a tangent line of a point on the nonlinear curve corresponding to the temperature; and compensating the temperature compensation amount to the external mechanical coordinate offset of the CNC machine tool.

[0006] In the existing CNC machine tool temperature compensation method, only a single factor such as temperature or vibration is considered, but the coupling effect of temperature and vibration is not considered. Therefore, a new thermal error compensation technology that takes into account the coupling of spindle temperature and vibration is very much needed to improve the machining accuracy of CNC machine tools. Summary of the invention

[0007] The present invention provides a method and device for thermal error compensation of a numerically controlled machine tool taking temperature-vibration coupling into consideration, which can meet the demand for long-term high-precision thermal error compensation of the machine tool during machining.

[0008] A thermal error compensation method for a CNC machine tool considering temperature-vibration coupling comprises the following steps: (1) During the operation of the CNC machine tool, the speed data and voltage and current data of the electric spindle are obtained through the CNC system, and the temperature data and vibration data are collected through multiple temperature sensors and multiple vibration sensors arranged on the electric spindle; (2) Using the vibration data collected by the vibration sensor to calculate the acceleration response matrix of the bearing, the corresponding bearing load coefficient is obtained; (3) using the speed data, voltage and current data of the electric spindle and the bearing load coefficient obtained in step (2) to calculate the heat generation rate of the stator and rotor of the built-in motor and the front and rear bearings, and using the heat generation rate and the temperature data collected by the temperature sensor to calculate the temperature distribution of the electric spindle; (4) Repeat steps (2) and (3) to iterate, and after the iteration is completed, obtain the core shaft temperature distribution from the final electric spindle temperature distribution; (5) Use the temperature distribution of the mandrel to calculate the thermal expansion of the mandrel; (6) Perform real-time thermal compensation on the thermal error of the machine tool based on the results of thermal elongation.

[0009] In step (1), a plurality of temperature sensors and a plurality of vibration sensors are respectively arranged at the front bearing, the built-in motor, and the rear bearing of the electric spindle.

[0010] In step (2), the acceleration response matrix of the bearing is calculated by the modal expansion method. The specific formula is: ; ; ; In the formula, The acceleration response matrix collected by the vibration sensor, i.e., vibration data; The surface displacement mode matrix is ​​obtained by finite element simulation based on the external structural characteristics of the electric spindle. Acceleration modal contribution matrix, is the overall acceleration response matrix of the electric spindle, The overall displacement modal vibration matrix of the electric spindle is obtained by finite element simulation based on the overall structural characteristics of the electric spindle. is the acceleration response expansion matrix of the electric spindle, and the superscript ┬ indicates the generalized inverse of the matrix; Overall acceleration response matrix of the electric spindle Take a subset and get the acceleration response matrix of the bearing .

[0011] In step (3), the heat generation rate of the internal motor stator, rotor and front and rear bearings is calculated using the formula: ; ; ; ; ; In the formula, is the heat generation rate of the internal motor stator and rotor, is the phase voltage of the stator winding of the electric spindle, is the phase current of the stator winding of the electric spindle, is the power factor, is the outer diameter of the stator and rotor, is the inner diameter of the stator and rotor, is the length of the stator and rotor; is the total friction torque of the bearing, is the friction torque caused by the external load, is the friction torque caused by the viscous friction of the lubricant, is the bearing load factor, is the external load on the bearing, is the pitch diameter of the ball bearing, is the lubrication mode coefficient, is the lubricant viscosity, is the spindle speed, is the bearing heat generation rate, is the bearing volume; where, The value of is determined by the bearing acceleration response matrix.

[0012] In step (3), the thermal resistance network method is used to calculate the temperature distribution of the electric spindle, where the first The heat balance equation of a thermal node is: ; In the formula, is the total number of thermal nodes, including multiple thermal nodes respectively arranged on the front bearing, rear bearing, stator and rotor, and core shaft; For the The number of nodes connected to the hot node, For the The temperature of the hot node, For the The hot node is connected to the The temperature of the node, For the The hot node and the connected Thermal resistance between thermal nodes; For the The heat generation rate of the stator and rotor heat nodes corresponds to the heat generation rate of the stator and rotor of the built-in motor. , the front and rear bearing thermal nodes correspond to the bearing heat generation rate ; For the The specific heat capacity of a hot node, For the The density of hot nodes, For the The volume of a hot node, For the The temperature change rate of a hot node.

[0013] In step (4), the specific process of iteration is: First, according to the overall acceleration response matrix of the electric spindle calculated in step (2), Get the vibration response matrix of the bearing , thus the load factor of the bearing The value of is updated, and then the heat generation rate of the bearing thermal node and the temperature value of the bearing thermal node are calculated; Then the thermal deformation of the bearing is calculated, and then the overall displacement modal vibration matrix of the electric spindle is calculated. Update and calculate the updated overall acceleration response matrix of the electric spindle , and iterates back and forth until the temperature values ​​of the bearing temperature nodes calculated twice are less than the set threshold.

[0014] In step (5), the temperature distribution of the mandrel is used to calculate the thermal expansion of the mandrel. The specific formula is: ; ; ; In the formula, For thermal elongation, is the thermal strain of the mandrel, is the length of the mandrel, is the thermal expansion coefficient of the material, is the change of the axial temperature of the mandrel; is the axial temperature distribution function of the mandrel, which is obtained by the temperatures of all the hot nodes of the mandrel obtained by the last iteration; is the initial temperature of the mandrel.

[0015] A thermal error compensation device for a numerically controlled machine tool taking temperature-vibration coupling into consideration comprises a memory and one or more processors, wherein the memory stores executable codes, and when the one or more processors execute the executable codes, they are used to implement the above-mentioned thermal error compensation method for the numerically controlled machine tool.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention establishes a thermal error compensation model for the electric spindle temperature and vibration coupling, which fully considers the mutual coupling of temperature and vibration, as well as the influence of the temperature and vibration coupling on the thermal deformation of the electric spindle. It solves the limitation of the prior art that only a single factor is considered for thermal error compensation, and effectively improves the compensation accuracy.

[0017] 2. The present invention uses a thermal resistance network method to calculate the temperature distribution of the spindle. Several nodes are set up for the areas that need attention, and uncritical areas are simplified. Therefore, compared with other methods for calculating temperature distribution, it is simpler and more efficient, and the temperature distribution can be calculated more quickly.

[0018] 3. The present invention uses the modal expansion method to calculate the vibration of the main shaft core shaft, which can identify the vibration of the main shaft core shaft relatively quickly and with a high recognition accuracy.

[0019] 4. The present invention performs rapid iteration of temperature-vibration coupling, can calculate the thermal error value of the machine tool in a relatively short time, can realize real-time thermal error compensation, and improve the machining accuracy of the machine tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a flowchart of a method for compensating thermal errors of CNC machine tools taking temperature-vibration coupling into consideration according to an embodiment of the present invention.

[0021] Figure 2 Schematic diagram of the installation positions of the vibration sensor and the temperature sensor in the embodiment of the present invention.

[0022] Figure 3 4 is a flowchart of the iterative process in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0024] like Figure 1As shown, a thermal error compensation method for CNC machine tools considering temperature-vibration coupling comprises the following steps: S01, during the operation of the CNC machine tool, the speed data and the voltage and current data of the electric spindle are obtained through the CNC system, and the temperature data and the vibration data are collected through multiple temperature sensors and multiple vibration sensors arranged on the electric spindle.

[0025] like Figure 2 As shown, the core shaft 2 is a component of the electric spindle 1 and is located at the center of the electric spindle. Three temperature sensors and three vibration sensors are arranged on the surface of the electric spindle 1. Vibration sensor 3, vibration sensor 4, and vibration sensor 5 are respectively arranged at the rear bearing, built-in motor, and front bearing in the vertical direction; temperature sensor 6, temperature sensor 7, and temperature sensor 8 are respectively arranged at the rear bearing, built-in motor, and front bearing in the horizontal direction.

[0026] S02, using the vibration data collected by the vibration sensor to calculate the acceleration response matrix of the bearing, so as to obtain the corresponding bearing load coefficient.

[0027] In this embodiment, the acceleration response matrix of the bearing is calculated by the modal expansion method, and the specific formula is: ; ; ; In the formula, The acceleration response matrix collected by the vibration sensor, i.e., vibration data; The surface displacement mode matrix is ​​obtained by finite element simulation based on the external structural characteristics of the electric spindle. Acceleration modal contribution matrix, is the overall acceleration response matrix of the electric spindle, The overall displacement modal vibration matrix of the electric spindle is obtained by finite element simulation based on the overall structural characteristics of the electric spindle. is the acceleration response expansion matrix of the electric spindle, and the superscript ┬ indicates the generalized inverse of the matrix; Overall acceleration response matrix of the electric spindle Take a subset and get the acceleration response matrix of the bearing .

[0028] S03, using the speed data, voltage and current data of the electric spindle and the bearing load coefficient obtained in step (2) to calculate the heat generation rate of the stator and rotor of the built-in motor and the front and rear bearings, and using the heat generation rate and the temperature data collected by the temperature sensor to calculate the temperature distribution of the electric spindle.

[0029] In this embodiment, the heat generation rate of the stator and rotor of the built-in motor and the front and rear bearings is calculated using the formula: ; ; ; ; ; In the formula, is the heat generation rate of the built-in motor stator and rotor, is the phase voltage of the stator winding of the electric spindle, is the phase current of the stator winding of the electric spindle, is the power factor, is the outer ring diameter of the stator and rotor, is the inner diameter of the stator and rotor, is the length of the stator and rotor; is the total friction torque of the bearing, is the friction torque caused by the external load, is the friction torque caused by the viscous friction of the lubricant, is the bearing load factor, is the external load on the bearing, is the pitch diameter of the ball bearing, is the lubrication mode coefficient, is the lubricant viscosity, is the spindle speed, is the bearing heat generation rate, is the bearing volume; where, The value of is determined by the bearing acceleration response matrix.

[0030] The thermal resistance network method is used to calculate the temperature distribution of the electric spindle. The heat balance equation of a thermal node is: ; In the formula, is the total number of thermal nodes, which is 76. Each bearing includes 3 thermal nodes, the spindle includes 15 thermal nodes, and the rest are thermal nodes of other parts of the electric spindle. For the The number of nodes connected to the hot node, For the The temperature of the hot node, For the The hot node is connected to the The temperature of the node, For the The hot node and the connected Thermal resistance between thermal nodes; For the The heat generation rate of the stator and rotor heat nodes corresponds to the heat generation rate of the stator and rotor of the built-in motor. , the front and rear bearing thermal nodes correspond to the bearing heat generation rate ; For the The specific heat capacity of a hot node, For the The density of hot nodes, For the The volume of a hot node, For the The temperature change rate of a hot node.

[0031] S04, repeating steps S02 and S03 to iterate and obtain the final core shaft temperature distribution.

[0032] like Figure 3 As shown, in the present invention, the specific process of iteration is: First, according to the overall acceleration response matrix of the electric spindle calculated in step S02 Get the vibration response matrix of the bearing , thus the load factor of the bearing The value of is updated, and then the heat generation rate of the bearing thermal node and the temperature value of the bearing thermal node are calculated; Then the thermal deformation of the bearing is calculated, and then the overall displacement modal vibration matrix of the electric spindle is calculated. Update and calculate the updated overall acceleration response matrix of the electric spindle , and iterates back and forth until the temperature values ​​of the bearing temperature nodes calculated twice are less than the set threshold.

[0033] S05, uses the temperature distribution of the mandrel to calculate the thermal expansion of the mandrel. The specific formula is: ; ; ; In the formula, For thermal elongation, is the thermal strain of the mandrel, is the length of the mandrel, is the thermal expansion coefficient of the material, is the change of the axial temperature of the mandrel; is the axial temperature distribution function of the mandrel, which is obtained by the temperatures of 15 hot nodes of the mandrel obtained by the last iteration; is the initial temperature of the mandrel.

[0034] S06, performing real-time thermal compensation for the thermal error of the machine tool according to the result of thermal elongation.

[0035] Based on the same inventive principle, the present invention also provides a CNC machine tool thermal error compensation device that takes temperature-vibration coupling into consideration, comprising a memory and one or more processors, wherein executable code is stored in the memory, and when one or more processors execute the executable code, it is used to implement the CNC machine tool thermal error compensation method mentioned in the above embodiment.

[0036] The effect of the present invention is verified by conducting experiments on the present invention. The experiments show that when the rotation speed is 5000r / min, 8000r / min, 12000r / min, and 15000r / min, the present invention is used to perform real-time thermal error compensation on the machine tool, and the error is reduced by 6.07%, 8.37%, 8.97%, and 10.56% respectively compared with the traditional thermal error compensation that only considers the temperature.

[0037] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for thermal error compensation of CNC machine tools considering temperature-vibration coupling, characterized in that: The following steps are involved: (1) During the operation of the CNC machine tool, the speed data and voltage and current data of the electric spindle are obtained through the CNC system, and the temperature data and vibration data are collected through multiple temperature sensors and multiple vibration sensors arranged on the electric spindle; (2) Using the vibration data collected by the vibration sensor to calculate the acceleration response matrix of the bearing, the corresponding bearing load coefficient is obtained; (3) using the speed data, voltage and current data of the electric spindle and the bearing load coefficient obtained in step (2) to calculate the heat generation rate of the stator and rotor of the built-in motor and the front and rear bearings, and using the heat generation rate and the temperature data collected by the temperature sensor to calculate the temperature distribution of the electric spindle; (4) Repeat steps (2) and (3) to iterate, and after the iteration is completed, obtain the core shaft temperature distribution from the final electric spindle temperature distribution; (5) Use the temperature distribution of the mandrel to calculate the thermal expansion of the mandrel; (6) Perform real-time thermal compensation on the thermal error of the machine tool based on the results of thermal elongation.

2. The method for thermal error compensation of CNC machine tools considering temperature-vibration coupling according to claim 1, characterized in that: In step (1), a plurality of temperature sensors and a plurality of vibration sensors are respectively arranged at the front bearing, the built-in motor, and the rear bearing of the electric spindle.

3. The method for compensating thermal errors of CNC machine tools considering temperature-vibration coupling according to claim 1, characterized in that: In step (2), the acceleration response matrix of the bearing is calculated by the modal expansion method. The specific formula is: ； ； ； In the formula, The acceleration response matrix collected by the vibration sensor, i.e., vibration data; The surface displacement mode matrix is ​​obtained by finite element simulation based on the external structural characteristics of the electric spindle. Acceleration modal contribution matrix, is the overall acceleration response matrix of the electric spindle, The overall displacement modal vibration matrix of the electric spindle is obtained by finite element simulation based on the overall structural characteristics of the electric spindle. is the acceleration response expansion matrix of the electric spindle, and the superscript ┬ indicates the generalized inverse of the matrix; Overall acceleration response matrix of the electric spindle Take a subset and get the acceleration response matrix of the bearing .

4. The method for compensating thermal errors of CNC machine tools considering temperature-vibration coupling according to claim 3, characterized in that: In step (3), the heat generation rate of the internal motor stator, rotor and front and rear bearings is calculated using the formula: ； ； ； ； ； In the formula, is the heat generation rate of the internal motor stator and rotor, is the phase voltage of the stator winding of the electric spindle, is the phase current of the stator winding of the electric spindle, is the power factor, is the outer diameter of the stator and rotor, is the inner diameter of the stator and rotor, is the length of the stator and rotor; is the total friction torque of the bearing, is the friction torque caused by the external load, is the friction torque caused by the viscous friction of the lubricant, is the bearing load factor, is the external load on the bearing, is the pitch diameter of the ball bearing, is the lubrication mode coefficient, is the lubricant viscosity, is the spindle speed, is the bearing heat generation rate, is the bearing volume; where, The value of is determined by the bearing acceleration response matrix.

5. The method for thermal error compensation of CNC machine tools considering temperature-vibration coupling according to claim 4, characterized in that: In step (3), the thermal resistance network method is used to calculate the temperature distribution of the electric spindle, where the first The heat balance equation of a thermal node is: ； In the formula, is the total number of thermal nodes, including multiple thermal nodes respectively arranged on the front bearing, rear bearing, stator and rotor, and core shaft; For the The number of nodes connected to the hot node, For the The temperature of the hot node, For the The hot node is connected to the The temperature of the node, For the The hot node and the connected Thermal resistance between thermal nodes; For the The heat generation rate of the stator and rotor heat nodes corresponds to the heat generation rate of the stator and rotor of the built-in motor. , the front and rear bearing thermal nodes correspond to the bearing heat generation rate ; For the The specific heat capacity of a hot node, For the The density of hot nodes, For the The volume of a hot node, For the The temperature change rate of a hot node.

6. The method for compensating thermal errors of CNC machine tools considering temperature-vibration coupling according to claim 5, characterized in that: In step (4), the specific process of iteration is: First, according to the overall acceleration response matrix of the electric spindle calculated in step (2), Get the vibration response matrix of the bearing , thus the load factor of the bearing The value of is updated, and then the heat generation rate of the bearing thermal node and the temperature value of the bearing thermal node are calculated; Then the thermal deformation of the bearing is calculated, and then the overall displacement modal vibration matrix of the electric spindle is calculated. Update and calculate the updated overall acceleration response matrix of the electric spindle , and iterates back and forth until the temperature values ​​of the bearing temperature nodes calculated twice are less than the set threshold.

7. The method for thermal error compensation of CNC machine tools considering temperature-vibration coupling according to claim 4, characterized in that: In step (5), the temperature distribution of the mandrel is used to calculate the thermal expansion of the mandrel. The specific formula is: ； ； ； In the formula, For thermal elongation, is the thermal strain of the mandrel, is the length of the mandrel, is the thermal expansion coefficient of the material, is the change of the axial temperature of the mandrel; is the axial temperature distribution function of the mandrel, which is obtained by the temperatures of all the hot nodes of the mandrel obtained by the last iteration; is the initial temperature of the mandrel.

8. A thermal error compensation device for a CNC machine tool taking into account temperature-vibration coupling, comprising a memory and one or more processors, wherein the memory stores executable code, and when the one or more processors execute the executable code, they are used to implement the thermal error compensation method for a CNC machine tool according to any one of claims 1 to 2.

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