A Thermal Error Compensation Method and Device for CNC Machine Tools Considering Temperature-Vibration Coupling

Abstract

The present invention discloses a thermal error compensation method and device for a numerically controlled machine tool considering temperature-vibration coupling, including: (1) obtaining the rotational speed data and voltage-current data of the motorized spindle, and collecting the temperature and vibration data of the motorized spindle through temperature sensors and vibration sensors; (2) calculating the acceleration response matrix of the bearings using the vibration data, so as to obtain the corresponding bearing load coefficients; (3) calculating the heat generation rates of the stator and rotor of the built-in motor and the front and rear bearings using the rotational speed data, voltage-current data and bearing load coefficients of the motorized spindle, and calculating the temperature distribution of the motorized spindle using the heat generation rates and the collected temperature data; (4) repeating steps (2) and (3) for iteration to obtain the final temperature distribution of the mandrel; (5) calculating the thermal elongation of the mandrel using the temperature distribution of the mandrel; (6) performing real-time thermal compensation on the thermal error of the machine tool according to the result of the thermal elongation. The present invention can meet the requirements of long-time high-precision thermal error compensation of the machine tool during machining.

Description

Technical Field

[0001] The present invention belongs to the field of machining process detection and thermal error compensation of numerical control machine tools, and in particular relates to a thermal error compensation method and device for a numerical control machine tool considering temperature-vibration coupling. Background Art

[0002] As the core component of a numerical control machine tool, the operation accuracy of the motorized spindle directly affects the machining accuracy of the machine tool. During the machining process of the machine tool, the motorized spindle rotates at a high speed. Due to electromagnetic loss, friction loss, etc. in the built-in motor and bearings, heat is inevitably generated, resulting in temperature rise, and then causing thermal deformation of the spindle, which affects the machining accuracy. At the same time, during the machining process of the spindle, due to the acting forces such as cutting force and electromagnetic force on the spindle, as well as the slight errors in installation, vibration of the spindle will occur during machining, which will also affect the machining accuracy.

[0003] Moreover, temperature and vibration will affect each other, producing a coupling effect, which has a more complex impact on machining accuracy. Specifically, the temperature rise will cause thermal expansion of the bearing components, affecting the stiffness of the bearings. As the key components connecting the spindle and the housing, the change in the stiffness of the bearings will cause a change in the vibration mode of the spindle. Vibration, on the other hand, will affect the friction of the bearings, thus causing a change in the heat generation rate of the bearings and affecting the temperature change of the bearings.

[0004] For example, the Chinese patent document with the publication number CN109352424A discloses a temperature compensation method for the motorized spindle of a numerical control machine tool, including: collecting the axial center temperature of the motorized spindle of the numerical control machine tool in real time, obtaining the degree of temperature change based on the axial center temperature of the motorized spindle, determining whether the degree of temperature change exceeds the corresponding preset threshold, and when the degree of temperature change exceeds the corresponding preset threshold, obtaining the expansion amount of the motorized spindle based on the axial center temperature of the motorized spindle, and compensating the coordinates of the motorized spindle based on the expansion amount of the motorized spindle.

[0005] The Chinese patent document with the publication number CN105415092A discloses a temperature compensation method for the motorized spindle of a numerical control machine tool, including: using a temperature sensor to measure the temperature of the motorized spindle at different speeds, with a first predetermined time interval between adjacent two measurements, and inputting the real-time temperature into a temperature control device; keeping the motorized spindle at different speeds for a second predetermined time, and using a tool setter to measure the thermal elongation of the motorized spindle at different speeds; establishing a non-linear curve between temperature change and thermal elongation based on the measured real-time temperature and thermal elongation; using the file memory of the PLC to read the temperature in the temperature control device, and calculating the thermal elongation of the motorized spindle based on the linear relationship determined by the tangent of the point corresponding to the temperature on the non-linear curve as the temperature compensation amount; compensating the temperature compensation amount into the external mechanical coordinate offset of the numerical control machine tool.

[0006] In the existing compensation methods for the temperature of numerically controlled machine tools, only single factors such as temperature or vibration are considered, without considering the coupling effect of temperature and vibration. Therefore, there is a great need for a new type of thermal error compensation technology that takes into account the coupling of spindle temperature and vibration to improve the machining accuracy of numerically controlled machine tools. Summary of the Invention

[0007] The present invention provides a thermal error compensation method and device for numerically controlled machine tools considering temperature-vibration coupling, which can meet the requirements of long-time high-precision thermal error compensation during machining of machine tools.

[0008] A thermal error compensation method for numerically controlled machine tools considering temperature-vibration coupling includes the following steps:

[0009] (1) During the operation of the numerically controlled machine tool, obtain the rotational speed data and voltage-current data of the motorized spindle through the numerical control system, and collect temperature data and vibration data through a plurality of temperature sensors and a plurality of vibration sensors arranged on the motorized spindle;

[0010] (2) Calculate the acceleration response matrix of the bearing using the vibration data collected by the vibration sensor, so as to obtain the corresponding bearing load coefficient;

[0011] (3) Calculate the heat generation rates of the stator and rotor of the built-in motor and the front and rear bearings using the rotational speed data, voltage-current data of the motorized spindle and the bearing load coefficient obtained in step (2), and calculate the temperature distribution of the motorized spindle using the heat generation rates and the temperature data collected by the temperature sensors;

[0012] (4) Repeat steps (2) and (3) for iteration. After the iteration is completed, obtain the temperature distribution of the mandrel from the final temperature distribution of the motorized spindle;

[0013] (5) Calculate the thermal elongation of the mandrel using the temperature distribution of the mandrel;

[0014] (6) Perform real-time thermal compensation for the thermal error of the machine tool according to the result of the thermal elongation.

[0015] In step (1), a plurality of temperature sensors and a plurality of vibration sensors are respectively arranged at the positions of the front bearing, the built-in motor, and the rear bearing of the motorized spindle.

[0016] In step (2), calculate the acceleration response matrix of the bearing by the modal expansion method. The specific formula is:

[0017] ;

[0018] ;

[0019] ;

[0020] In the formula, is the acceleration response matrix collected by the vibration sensor, i.e., the vibration data; is the surface displacement modal vibration mode matrix obtained by finite element simulation according to the external structural characteristics of the motorized spindle, acceleration modal contribution matrix, is the overall acceleration response matrix of the motorized spindle, is the overall displacement modal vibration mode matrix of the motorized spindle obtained by finite element simulation according to the overall structural characteristics of the motorized spindle, is the acceleration response expansion matrix of the motorized spindle, where the superscript ┬ represents the generalized inverse of the matrix;

[0021] For the overall acceleration response matrix of the motorized spindle take a subset to obtain the acceleration response matrix of the bearing .

[0022] In step (3), calculate the heat generation rates of the built-in motor stator and rotor and the front and rear bearings. The formula is:

[0023] ;

[0024] ;

[0025] ;

[0026] ;

[0027] ;

[0028] In the formula, is the heat generation rate of the built-in motor stator and rotor, is the phase voltage of the motorized spindle stator winding, is the phase current of the motorized spindle stator winding, 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 frictional torque of the bearing, is the frictional torque caused by the external load, is the frictional torque caused by the viscous friction of the lubricant, is the bearing load coefficient, is the external load on the bearing, is the pitch diameter of the ball bearing, is the lubrication mode coefficient, is the viscosity of the lubricant, is the spindle speed, is the heat generation rate of the bearing, is the volume of the bearing; where, The value is determined by the acceleration response matrix of the bearing.

[0029] In step (3), the thermal resistance network method is used to calculate the temperature distribution of the motorized spindle. Among them, the thermal balance equation of the th thermal node on the motorized spindle is:

[0030] ;

[0031] In the formula, is the total number of thermal nodes, including multiple thermal nodes respectively set on the front bearing, rear bearing, stator-rotor and spindle; is the number of nodes connected to the th thermal node, is the temperature of the th thermal node, is the temperature of the th node connected to the th thermal node, is the thermal resistance between the th thermal node and the th node connected to it; is the heat generation rate of the th thermal node. Among them, the thermal nodes of the stator-rotor correspond to the heat generation rate of the built-in motor stator-rotor, and the thermal nodes of the front and rear bearings correspond to the heat generation rate of the bearings; is the specific heat capacity of the th thermal node, is the density of the th thermal node, is the volume of the th thermal node, is the temperature change rate of the th thermal node.

[0032] In step (4), the specific process of iteration is as follows:

[0033] First, according to the overall acceleration response matrix of the motorized spindle calculated in step (2), the vibration response matrix of the bearing is obtained, so as to update the value of the load coefficient of the bearing, and then calculate the heat generation rate of the bearing thermal node and the temperature value of the bearing thermal node;

[0034] Then calculate the thermal deformation of the bearing, and then update the overall displacement mode vibration shape matrix of the motorized spindle, and calculate the updated overall acceleration response matrix of the motorized spindle, and perform reciprocating iteration until the temperature values of the bearing temperature nodes calculated twice are less than the set threshold.

[0035] In step (5), the temperature distribution of the mandrel is used to calculate the thermal elongation of the mandrel, and the specific formula is:

[0036] ;

[0037] ;

[0038] ;

[0039] In the formula, is the thermal elongation, is the thermal strain of the mandrel, is the length of the mandrel, is the coefficient of thermal expansion of the material, is the change value of the axial temperature of the mandrel; is the axial temperature distribution function of the mandrel, obtained from all the thermal node temperatures of the mandrel obtained by the last iteration; is the initial temperature value of the mandrel.

[0040] A thermal error compensation device for a numerically controlled machine tool considering temperature-vibration coupling includes a memory and one or more processors. Executable code is stored in the memory. When the one or more processors execute the executable code, it is used to implement the above-mentioned thermal error compensation method for the numerically controlled machine tool.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The present invention establishes a thermal error compensation model for the temperature and vibration coupling of the motorized spindle, fully considering the mutual coupling effect of temperature and vibration, and the influence of the temperature-vibration coupling effect on the thermal deformation of the motorized spindle. It solves the limitation of only considering a single factor for thermal error compensation in the prior art and effectively improves the compensation accuracy.

[0043] 2. The present invention uses the thermal resistance network method to calculate the temperature distribution of the spindle, sets up several more nodes for key attention in the areas that need to be concerned, and simplifies the non-critical areas. Therefore, it is more simple and efficient than other methods for calculating the temperature distribution and can calculate the temperature distribution more quickly.

[0044] 3. The present invention uses the modal expansion method to calculate the vibration of the spindle mandrel, can identify the vibration of the spindle mandrel relatively quickly, and has a high recognition accuracy.

[0045] 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 achieve real-time thermal error compensation, and improve the machining accuracy of the machine tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a flow chart of a thermal error compensation method for a numerically controlled machine tool considering temperature-vibration coupling according to an embodiment of the present invention.

[0047] Figure 2 This is a schematic diagram of the installation positions of vibration sensors and temperature sensors in an embodiment of the present invention.

[0048] Figure 3 This is a flow chart of the iterative process in an embodiment of the present invention. Detailed implementation manners

[0049] The present invention will be further described in detail below with reference to the drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0050] As Figure 1 shown, a thermal error compensation method for a numerically controlled machine tool considering temperature-vibration coupling includes the following steps:

[0051] S01. During the operation of the numerically controlled machine tool, obtain the rotational speed data and voltage and current data of the motorized spindle through the numerical control system, and collect temperature data and vibration data through a plurality of temperature sensors and a plurality of vibration sensors arranged on the motorized spindle.

[0052] As Figure 2 shown, the mandrel 2 is a component in the motorized spindle 1 and is located at the center position inside the motorized spindle. A total of three temperature sensors and three vibration sensors are arranged on the surface of the motorized spindle 1. The vibration sensors 3, 4, and 5 are respectively arranged at the positions of the rear bearing, the built-in motor, and the front bearing in the vertical direction; the temperature sensors 6, 7, and 8 are respectively arranged at the positions of the rear bearing, the built-in motor, and the front bearing in the horizontal direction.

[0053] S02. Calculate the acceleration response matrix of the bearing using the vibration data collected by the vibration sensor, so as to obtain the corresponding bearing load coefficient.

[0054] In this embodiment, the acceleration response matrix of the bearing is calculated by the modal expansion method, and the specific formula is:

[0055] ;

[0056] ;

[0057] ;

[0058] In the formula, is the acceleration response matrix collected by the vibration sensor, that is, the vibration data; is the surface displacement modal shape matrix obtained by finite element simulation according to the external structural characteristics of the motorized spindle, acceleration modal contribution matrix, is the overall acceleration response matrix of the motorized spindle, is the overall displacement modal shape matrix of the motorized spindle obtained by finite element simulation according to the overall structural characteristics of the motorized spindle, is the acceleration response expansion matrix of the motorized spindle, and the superscript ┬ represents the generalized inverse of the matrix;

[0059] For the overall acceleration response matrix of the motorized spindle Take a subset to obtain the acceleration response matrix of the bearing .

[0060] S03, use the rotational speed data, voltage and current data of the motorized spindle, and the bearing load coefficient obtained in step (2) to calculate the heat generation rates of the built-in motor stator and rotor and the front and rear bearings, and use the heat generation rates and the temperature data collected by the temperature sensors to calculate the temperature distribution of the motorized spindle.

[0061] In this embodiment, the heat generation rates of the built-in motor stator and rotor and the front and rear bearings are calculated, and the formula is:

[0062] ;

[0063] ;

[0064] ;

[0065] ;

[0066] ;

[0067] In the formula, is the heat generation rate of the built-in motor stator and rotor, is the phase voltage of the motorized spindle stator winding, is the phase current of the motorized spindle stator winding, is the power factor, is the outer diameter of the stator and rotor outer ring, is the inner diameter of the stator and rotor inner ring, is the length of the stator and rotor; is the total frictional torque of the bearing, is the frictional torque caused by the external load, is the frictional torque caused by the viscous friction of the lubricant, is the bearing load coefficient, is the external load on the bearing, is the pitch diameter of the ball bearing, is the lubrication method coefficient, is the viscosity of the lubricant, is the spindle speed, is the heat generation rate of the bearing, is the volume of the bearing; among them, The value of is determined by the acceleration response matrix of the bearing.

[0068] The thermal resistance network method is used to calculate the temperature distribution of the motorized spindle. Among them, the thermal balance equation of the th thermal node on the motorized spindle is:

[0069] ;

[0070] In the formula, is the total number of thermal nodes, which is 76. Each bearing includes 3 thermal nodes, the core shaft includes 15 thermal nodes, and the rest are thermal nodes of other components of the motorized spindle. is the number of nodes connected to the th thermal node, is the temperature of the th thermal node, is the temperature of the th node connected to the th thermal node, is the thermal resistance between the th thermal node and the th thermal node connected to it; is the heat generation rate of the th thermal node. Among them, the stator-rotor thermal nodes correspond to the heat generation rate of the built-in motor stator-rotor , and the front and rear bearing thermal nodes correspond to the heat generation rate of the bearing ; is the specific heat capacity of the th thermal node, is the density of the th thermal node, is the volume of the th thermal node, is the temperature change rate of the th thermal node.

[0071] S04, repeat steps S02 and S03 for iteration to obtain the final temperature distribution of the core shaft.

[0072] As Figure 3 shown, in the present invention, the specific process of iteration is:

[0073] First, obtain the vibration response matrix of the bearing according to the overall acceleration response matrix of the motorized spindle calculated in step S02, so as to update the value of the load coefficient of the bearing, and then calculate the heat generation rate of the bearing thermal node and the temperature value of the bearing thermal node;

[0074] Next, calculate the thermal deformation of the bearing, and then update the overall displacement modal vibration matrix of the motorized spindle to calculate the updated overall acceleration response matrix of the motorized spindle , and perform iterative calculations until the temperature values of the bearing temperature nodes calculated twice are less than the set threshold value.

[0075] S05. Use the temperature distribution of the mandrel to calculate the thermal elongation of the mandrel. The specific formula is as follows:

[0076] ;

[0077] ;

[0078] ;

[0079] In the formula, is the thermal elongation, is the thermal strain of the mandrel, is the length of the mandrel, is the coefficient of thermal expansion of the material, is the change value of the axial temperature of the mandrel; is the axial temperature distribution function of the mandrel, obtained from the temperatures of 15 thermal nodes of the mandrel obtained by the last iteration; is the initial temperature value of the mandrel.

[0080] S06. Perform real-time thermal compensation for the thermal error of the machine tool according to the result of the thermal elongation.

[0081] Based on the same inventive principle, the present invention also provides a thermal error compensation device for a numerically controlled machine tool considering temperature-vibration coupling, including a memory and one or more processors. When the one or more processors execute the executable code stored in the memory, they are used to implement the thermal error compensation method for the numerically controlled machine tool mentioned in the above embodiments.

[0082] Verify the effect of the present invention and conduct experiments on the present invention. The experiments prove that when the rotational speeds are 5000 r / min, 8000 r / min, 12000 r / min, and 15000 r / min, using the present invention to perform real-time thermal error compensation for the machine tool, the errors are reduced by 6.07%, 8.37%, 8.97%, and 10.56% respectively compared with the traditional thermal error compensation that only considers temperature.

[0083] The above embodiments have described in detail 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 used to limit the present invention. Any modifications, supplements, and equivalent replacements made within the principle scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A thermal error compensation method for CNC machine tools considering temperature-vibration coupling, characterized in that Including the following steps: (1) During the operation of the CNC machine tool, obtain the rotational speed data and voltage and current data of the motorized spindle through the CNC system, and collect temperature data and vibration data through a plurality of temperature sensors and a plurality of vibration sensors arranged on the motorized spindle; (2) Calculate the acceleration response matrix of the bearing using the vibration data collected by the vibration sensor, so as to obtain the corresponding bearing load coefficient; (3) Calculate the heat generation rates of the stator and rotor of the built-in motor and the front and rear bearings using the rotational speed data, voltage and current data of the motorized spindle and the bearing load coefficient obtained in step (2), and calculate the temperature distribution of the motorized spindle using the heat generation rate and the temperature data collected by the temperature sensor; (4) Repeat steps (2) and (3) for iteration. After the iteration is completed, obtain the temperature distribution of the core shaft from the final temperature distribution of the motorized spindle; (5) Use the temperature distribution of the core shaft to calculate the thermal elongation of the core shaft; (6) Perform real-time thermal compensation for the thermal error of the machine tool according to the result of the thermal elongation.

2. The method for compensating the thermal error of a numerically controlled machine tool considering the coupling of temperature and vibration according to claim 1, wherein, In step (1), the plurality of temperature sensors and the plurality of vibration sensors are respectively arranged at the positions of the front bearing, the built-in motor, and the rear bearing of the motorized spindle.

3. The method for compensating the thermal error of a numerically controlled machine tool considering temperature-vibration coupling according to claim 1, wherein, In step (2), calculate the acceleration response matrix of the bearing by the modal expansion method. The specific formula is: ； ； ； In the formula, is the acceleration response matrix collected by the vibration sensor, that is, the vibration data; is the surface displacement modal shape matrix obtained by finite element simulation according to the external structural characteristics of the motorized spindle, the acceleration modal contribution matrix, is the overall acceleration response matrix of the motorized spindle, is the overall displacement modal shape matrix of the motorized spindle obtained by finite element simulation according to the overall structural characteristics of the motorized spindle, is the acceleration response expansion matrix of the motorized spindle, where the superscript ┬ represents the generalized inverse of the matrix; The overall acceleration response matrix of the motorized spindle Take a subset to obtain the acceleration response matrix of the bearing .

4. The NC machine tool thermal error compensation method considering temperature-vibration coupling according to claim 3, characterized in that In step (3), calculate the heat generation rates of the stator and rotor of the built-in motor and the front and rear bearings. The formula is: ； ； ； ； ； In the formula, is the heat generation rate of the built-in motor stator and rotor, is the phase voltage of the electric spindle stator winding, is the phase current of the electric spindle stator winding, 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 frictional torque of the bearing, is the frictional torque caused by the external load, is the frictional torque caused by the viscous friction of the lubricant, is the bearing load coefficient, is the external load on the bearing, is the pitch diameter of the ball bearing, is the lubrication mode coefficient, is the viscosity of the lubricant, is the spindle speed, and is the heat generation rate of the bearing, is the volume of the bearing; where, The value of is determined by the acceleration response matrix of the bearing.

5. The method for compensating the thermal error of a numerically controlled machine tool considering the coupling of temperature and vibration according to claim 4, characterized in that, In step (3), the thermal resistance network method is used to calculate the temperature distribution of the motorized spindle. Among them, the thermal equilibrium equation of the th thermal node on the motorized spindle is: ； In the formula, is the total number of thermal nodes, including multiple thermal nodes respectively set on the front bearing, rear bearing, stator-rotor, and core shaft; is the number of nodes connected to the th thermal node, is the temperature of the th thermal node, is the temperature of the th node connected to the th thermal node, is the thermal resistance between the th thermal node and the th thermal node connected to it; is the heat generation rate of the th thermal node, where the stator-rotor thermal node corresponds to the heat generation rate of the built-in motor stator-rotor, and the front and rear bearing thermal nodes correspond to the bearing heat generation rate ; is the specific heat capacity of the th thermal node, is the density of the th thermal node, is the volume of the th thermal node, is the temperature change rate of the th thermal node.

6. The thermal error compensation method for a numerically controlled machine tool considering temperature-vibration coupling according to claim 5, characterized in that In step (4), the specific process of the iteration is: First, obtain the overall acceleration response matrix of the motorized spindle calculated in step (2). Obtain the acceleration response matrix of the bearing , thereby updating the value of the load coefficient of the bearing , and then calculating the heat generation rate of the bearing thermal node and the temperature value of the bearing thermal node; Next, calculate the thermal deformation of the bearing, and then update the overall displacement modal shape matrix of the motorized spindle to calculate the updated overall acceleration response matrix of the motorized spindle , and perform iterative calculations until the temperature values of the bearing temperature nodes calculated twice are less than the set threshold value.

7. The thermal error compensation method for a numerically controlled machine tool considering temperature-vibration coupling according to claim 4, characterized in that In step (5), use the temperature distribution of the core shaft to calculate the thermal elongation of the core shaft. The specific formula is: ； ； ； Wherein, is the thermal elongation, is the thermal strain of the mandrel, is the length of the mandrel, is the coefficient of thermal expansion of the material, is the change value of the axial temperature of the mandrel; is the axial temperature distribution function of the mandrel, obtained from all the thermal node temperatures of the mandrel obtained by the last iteration; is the initial temperature value of the mandrel.

8. A thermal error compensation device for a CNC machine tool considering temperature-vibration coupling, including a memory and one or more processors. Executable code is stored in the memory. When the one or more processors execute the executable code, it is used to implement the CNC machine tool thermal error compensation method according to any one of claims 1-2.

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