Six-point method for thermal error measurement and identification of spindle of numerical control machine tool

Abstract

The present application relates to the technical fields of spindle thermal error of CNC machine tools, and discloses a six-point method thermal error measurement and identification method for spindle of CNC machine tools, comprising the following steps: step one, changing the measured part of the cylindrical test bar of the spindle of the CNC machine tool into a square shape; step two, performing six-point method thermal error measurement work through the six-point method fixture provided with the eddy current displacement sensor group; step three, performing thermal deformation data sampling, and identifying six thermal errors of the first group of data using a thermal error identification formula; and step four, according to step three, deducing six thermal errors of the nth group of data of the first thermal deformation data sampling. The present application can make up for the defects that the existing measurement technology cannot measure the spindle rotation thermal error, realize complete measurement and identification of the spindle thermal error, improve the accuracy of the established mathematical model, and provide data basis for spindle rotation thermal error compensation.

Description

Technical Field

[0001] This invention relates to the field of thermal error technology for CNC machine tool spindles, and in particular to a six-point method for measuring and identifying thermal errors in CNC machine tool spindles. Background Technology

[0002] Machine tools, as the "mother machines" of manufacturing, directly impact a nation's industrial development level. With the continuous improvement of machining accuracy, controlling the thermal error of machine tool spindles has become increasingly important. Spindle thermal error is a decrease in machining accuracy caused by thermal deformation, which can have a significant impact on high-speed, high-precision machining. Thermal error compensation is an economical and effective method to reduce the impact of thermal errors. In implementing thermal error compensation technology, the compensation amount is predicted and calculated based on an established mathematical model, which is trained using measured data as input. Therefore, the ability to measure and identify target data, and the accuracy of that measurement and identification, directly affect the final compensation effect.

[0003] The most commonly used method for obtaining spindle thermal deformation test data is the five-point method. However, the five-point method can only identify five thermal errors of the spindle, excluding rotational thermal error. This means that the spindle rotational thermal error cannot be compensated when performing thermal error compensation, resulting in a decrease in machine tool machining accuracy. Summary of the Invention

[0004] To address the problems mentioned in the background section, this invention provides a six-point method for measuring and identifying thermal errors in CNC machine tool spindles. This method overcomes the limitations of existing measurement techniques in measuring spindle rotation thermal errors, enabling complete measurement and identification of spindle thermal errors, improving the accuracy of the established mathematical model, and providing data for spindle rotation thermal error compensation.

[0005] To achieve the above objectives, the present invention provides a six-point method for measuring and identifying thermal errors in CNC machine tool spindles, comprising the following steps:

[0006] Step 1: For the CNC machine tool spindle inspection bar, change the tested part of the traditional cylindrical inspection bar to a square shape;

[0007] Step 2: Perform six-point thermal error measurement using a six-point fixture equipped with an eddy current displacement sensor group.

[0008] Step 3: Sample thermal deformation data and use the thermal error identification formula to identify the six thermal errors in the first set of data;

[0009] Step four: Based on step three, derive the six thermal errors of the nth group of data from a single thermal deformation data sampling.

[0010] Preferably, in step two, the eddy current displacement sensor group includes displacement sensor one, displacement sensor two, displacement sensor three, displacement sensor four, displacement sensor five, and displacement sensor six. Displacement sensor one, displacement sensor two, displacement sensor three, and displacement sensor four are installed on the six-point fixture. Displacement sensor five is installed on the opposite side of displacement sensor one. Displacement sensor six is ​​installed on the six-point fixture relative to the center of the end face of the test bar. The eddy current displacement sensor group measures the displacement changes of the target position on the test bar in the X, Y, and Z directions.

[0011] Preferably, before the CNC machine tool spindle undergoes thermal deformation, the width of the inspection bar is H, the center coordinate of the inspection bar is O(0,0), and the initial values ​​measured by each displacement sensor are set to zero before measurement.

[0012] Preferably, in step three, after the CNC machine tool spindle undergoes thermal deformation, the first set of thermal deformation data is sampled. Continuous sampling is performed at positions a and b, representing the symmetrical rotation angles during the spindle's rotation. At position a, the values ​​measured by each sensor are x... 1a 1 x 2a 1 x 3a 1 y 1a 1 y 2a 1 z a 1 At point b, the values ​​measured by each sensor are x. 1b 1 x 2b 1 x 3b 1 y 1b 1 y 2b 1 z b 1 The distance between displacement sensors 1 and 2 along the main shaft axis on the six-point fixture is D. The distance between displacement sensors 3 and 4 along the main shaft axis on the six-point fixture is also D. The length of the square part of the inspection bar is L. The distance from displacement sensor 2 to the bottom surface of the inspection bar is l. The inspection bar is square. During rotation, the change in the width of the inspection bar is superimposed with the thermal offset error. The change in the width of the inspection bar is δ. xθ 1 δ yθ 1 As shown below:

[0013]

[0014] Thermal error δ after removing the influence of test bar width variation x1 δ y 1 δ z 1 ε x 1 ε y 1 The geometric relationship between the values ​​of each sensor in the eddy current displacement sensor group and the values ​​of the sensors is shown below:

[0015]

[0016] Where, δ x δ represents the thermal offset error in the X direction. y Indicates the thermal offset error in the Y direction, δ z ε represents the thermal offset error in the Z direction. x ε represents the thermal tilt error in the X direction. y Indicates the thermal tilt error in the Y direction;

[0017] Spindle thermal rotation error ε z 1 Through the actual angular position ε zθ 1 The difference between the actual angular position ε and the ideal angular position θ is calculated. zθ 1 The calculation formula is as follows:

[0018]

[0019] The ideal angular position is adjusted within the range of 0° to 45°, and the spindle thermal rotation error ε is... z 1 The calculation formula is as follows:

[0020]

[0021] Preferably, the influence of the test bar installation eccentricity error is removed from the six spindle thermal errors calculated in step three, and the X-axis tilt ε of the installation eccentricity error is... sx 1 Offset component δ sx 1 and Y-axis tilt ε sy 1 Offset component δ sy 1 The calculation formula is as follows:

[0022]

[0023] The six thermal error identification formulas are as follows:

[0024]

[0025] Preferably, in step four, following the above steps, when sampling the nth group of thermal deformation data, the values ​​of the six eddy current displacement sensors at the corresponding positions of the X, Y, and Z axes of the test bar at point a are x, x, and x, respectively. 1a n x 2a n x 3a n y 1a n y 2a n z a n At point b, the values ​​measured by each sensor are x. 1b n x 2b n x 3b n y 1b n y 2b n z b n δ x n δ y n δ z n ε x n ε y n ε z n The six thermal errors sampled in the nth data set, and the X-axis tilt ε of the installation eccentricity error sampled in the nth data set. sx n Offset component δ sx n and Y-axis tilt ε sy n Offset component δ sy n Based on the derivation of the six thermal error identification formulas in step four, the formula for sampling the nth group of data is as follows:

[0026]

[0027] Therefore, the present invention employs the above-mentioned six-point method for measuring and identifying thermal errors of CNC machine tool spindles, which has the following beneficial effects:

[0028] (1) The method described in this invention makes up for the deficiency of traditional CNC machine tool spindle thermal error measurement and identification methods that cannot identify spindle rotation thermal error, and obtains all six thermal errors of the spindle.

[0029] (2) The method described in this invention avoids the disadvantage that the measured values ​​of the other five thermal errors are too different from the actual values ​​due to the inability to identify the thermal error of the spindle rotation, and ensures the authenticity and effectiveness of the established thermal error model, providing a data basis for the realization of the thermal error compensation function of the spindle rotation.

[0030] (3) The six-point method fixture described in this invention is easy to use and has high stability. It can achieve accurate acquisition of automated online measurement data by building a measurement system, and has strong practicality.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure of the six-point method fixture assembly according to an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the position of the displacement sensor of the six-point clamp according to an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram illustrating the principle of identifying thermal offset error in the X-axis direction of the main shaft according to an embodiment of the present invention.

[0035] Figure 4 This is a schematic diagram illustrating the principle of identifying thermal tilt error in the X-axis of the spindle according to an embodiment of the present invention.

[0036] Figure 5 This is a schematic diagram illustrating the principle of spindle Z-axis thermal rotation error identification in an embodiment of the present invention.

[0037] Figure 6 This is a curve showing the spindle rotation angle position under ideal conditions according to an embodiment of the present invention;

[0038] Figure 7 This is a schematic diagram of the installation eccentricity offset component according to an embodiment of the present invention;

[0039] Figure 8 This is a schematic diagram of the installation eccentricity tilt component according to an embodiment of the present invention;

[0040] Figure 9 This is a thermal error offset component diagram of an embodiment of the present invention;

[0041] Figure 10 This is a thermal error tilt component diagram of an embodiment of the present invention.

[0042] Figure Labels

[0043] 1. Inspection bar; 2. Six-point method fixture; X1. Displacement sensor one; X2. Displacement sensor two; Y1. Displacement sensor three; Y2. Displacement sensor four; X3. Displacement sensor five; Z. Displacement sensor six. Detailed Implementation

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0045] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. The terms "set," "install," and "connect" should be interpreted broadly; for example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two elements. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0046] Example

[0047] In this embodiment, a VDL-600A vertical CNC machining center from Dalian Machine Tool Factory was selected. The CNC system brand is FANUC, model 0i-mateTD. Machine tool parameters: X-axis travel: 850mm; Y-axis travel: 550mm; Z-axis travel: 540mm; worktable area: 550*1100mm; maximum spindle speed: 8000rpm; spindle taper: BT-40.

[0048] Parameters of square inspection bar 1: Material: 7075 aluminum alloy; Length: 210mm; Width: 20mm; Radius of cylindrical part: 10mm; Length of cylindrical part: 70mm; Surface roughness: RA4 grade.

[0049] The ML33 eddy current displacement sensor from Milon has the following parameters: linear range: 0.5mm~2.5mm; standard sensitivity: 2.5V / mm; measurement accuracy: 0.001mm; response frequency: 10HZ; voltage: ±15V.

[0050] The TEST5910 displacement acquisition system from Tester has the following parameters: frequency: 10Hz; voltage: 220V; sampling frequency: 1MHz; number of channels: 16.

[0051] Measurement conditions: The spindle speed is fixed at 5100 rpm, the acquisition system samples at a frequency of 10 Hz, and the spindle continues to rotate until the machine tool reaches a thermal steady state and stops rotating.

[0052] like Figure 1 As shown, the method for measuring and identifying six thermal errors of CNC machine tool spindles according to the present invention includes the following steps:

[0053] Step 1: For the CNC machine tool spindle inspection bar 1, the measured part of the traditional cylindrical inspection bar 1 is changed to a square shape to reflect the change in spindle rotation thermal error.

[0054] Step two involves performing a six-point thermal error measurement using a six-point fixture equipped with an eddy current displacement sensor group. The eddy current displacement sensor group includes displacement sensor X1, displacement sensor X2, displacement sensor Y1, displacement sensor Y2, displacement sensor X3, and displacement sensor Z.

[0055] Specifically, such as Figure 2 As shown, four precision displacement sensors (non-contact type) are placed at certain intervals along the same circular cross-section in the X and Y directions passing through the center of the inspection bar 1. These are displacement sensor X1, displacement sensor X2, displacement sensor Y1, and displacement sensor Y2. Displacement sensor X3 is placed opposite displacement sensor X3 in the X direction, close to the worktable. Displacement sensor Z is placed on the six-point fixture relative to the center of the end face of the inspection bar 1. These sensors are used to measure the displacement changes in the X, Y, and Z directions at the target position on the inspection bar 1. The width of the inspection bar 1 is considered fixed at H, regardless of whether it is affected by thermal deformation. Before thermal deformation of the machine tool spindle, the width H of the inspection bar 1 is 20mm, and the center coordinate of the inspection bar 1 is O(0,0). The initial values ​​measured by the sensors are set to zero before measurement.

[0056] Step 3: Sample thermal deformation data and use the thermal error identification formula to identify the six thermal errors in the first set of data.

[0057] Specifically, after the CNC machine tool spindle undergoes thermal deformation, the first set of thermal deformation data is sampled. The CNC machine tool spindle rotates at 5100 rpm, and the first set of data collected after 1 minute is used for calculation. Continuous sampling is performed at positions a and b, representing the symmetrical rotation angles during the spindle rotation process. At position a, the values ​​measured by each sensor are x... 1a 1 x 2a 1 x 3a 1 y 1a 1 y 2a 1 z a1 At point b, the values ​​measured by each sensor are x. 1b 1 x 2b 1 x 3b 1 y 1b 1 y 2b 1 z b 1 The square inspection bar 1 has a width H = 20mm. The distance between the two sensors arranged along the Z direction on the six-point clamp 2 is D = 80mm. The total length of the square part of the inspection bar 1 is L = 140mm. The distance from the displacement sensor 4 to the bottom surface of the inspection bar 1 is l = 100mm. The error geometry diagram is shown below. Figure 3 , Figure 4 , Figure 5 As shown, since the test bar 1 is square, the change in the width of the test bar 1 during rotation will be superimposed on the thermal offset error, resulting in a width change δ of the test bar 1. xθ 1 δ yθ 1 As shown in equation (1):

[0058]

[0059] Thermal error δ after removing the influence of the width variation of test bar 1 x 1 δ y 1 δ z 1 ε x 1 ε y 1 The geometric relationship between the values ​​of each sensor and the values ​​is shown in equation (2):

[0060]

[0061] Where, δ x δ represents the thermal offset error in the X direction. y Indicates the thermal offset error in the Y direction, δ z ε represents the thermal offset error in the Z direction. x ε represents the thermal tilt error in the X direction. y This indicates the thermal tilt error in the Y direction.

[0062] Spindle thermal rotation error ε z 1 It can be obtained through the actual angular position ε zθ 1 The difference between the actual angular position ε and the ideal angular position θ is calculated. zθ1 The calculation formula is shown in equation (3):

[0063]

[0064] Due to the square structure of test bar 1, the calculated actual angular position value varies between 0° and 45°, while the ideal angular position varies between 0° and 360°. For ease of calculation, the range of the ideal angular position is adjusted to 0° to 45°. The adjusted ideal angular position variation curve is shown below. Figure 6 As shown; spindle thermal rotation error ε z 1 The calculation formula is shown in equation (4):

[0065]

[0066] During the thermal error measurement process, the fixed installation eccentricity error generated during the installation of the test bar 1 is superimposed on the thermal offset error and thermal tilt error in the X and Y directions of the spindle. Therefore, it is necessary to remove the influence of the installation eccentricity error of the test bar 1 from the six spindle thermal errors calculated above. The geometric diagram of the installation eccentricity error is shown below. Figure 7 , Figure 8 As shown, the X-direction tilt ε of the installation eccentricity error sx 1 Offset component δ sx 1 and Y-axis tilt ε sy 1 Offset component δ sy 1 The calculation formula is shown in equation (5):

[0067]

[0068] The final six thermal error identification formulas are shown in equation (6):

[0069]

[0070] Figure 9 This is a thermal error offset component diagram according to an embodiment of the present invention. Figure 10 This is a thermal error tilt component diagram of an embodiment of the present invention.

[0071] Step four: Based on step three, derive the six thermal errors of the nth group of data from a single thermal deformation data sampling.

[0072] Specifically, following the steps above, when sampling the nth set of thermal centrifugal data, the first set of data collected n minutes later is used for calculation. The values ​​of the six eddy current displacement sensors at the corresponding positions of the X, Y, and Z axes of the test bar 1 at point a are x, x, and x, respectively. 1a nx 2a n x 3a n y 1a n y 2a n z a n At point b, the values ​​measured by each sensor are x. 1b n x 2b n x 3b n y 1b n y 2b n z b n δ x n δ y n δ z n ε x n ε y n ε z n The six thermal errors sampled in the nth data set, and the X-axis tilt ε of the installation eccentricity error sampled in the nth data set. sx n Offset component δ sx n and Y-axis tilt ε sy n Offset component δ sy n Based on formula (6), the formula for sampling the nth group of data is shown in formula (7):

[0073]

[0074] The CNC machine tool spindle rotated at 5100 rpm for 450 minutes, collecting a total of 450 sets of thermal error data. The identified X-axis thermal offset error data is as follows:

[0075] [0,0.06655,0.0845,-0.00635,-0.20485,-0.3377,-0.362,-0.2775,……,-11.2063,-11.2063,-11.182,-11.0978,-11.2729,-11.3149,-11.2729,-11.3149] (Unit: μm).

[0076] The X-axis thermal tilt error data is in array:

[0077] [0,0.000018,-0.00608,-0.00916,-0.00927,-0.00932,-0.01238,-0.01847,……,0.028332,0.028332,0.031392,0.025326,0.028314,0.031338,0.028314,0.031338](Unit:″).

[0078] The Y-axis thermal offset error data is in array:

[0079] [0,0.13635,-0.0164,0.0941,0.0941,0.20395,0.34005,0.29805,……,4.05165,3.9674,4.03525,3.8569,4.1615,4.00965,4.00965,4.1195] (Unit: μm).

[0080] The Y-axis thermal tilt error data is in array:

[0081] [0,-0.000054,0.006048,0.002988,0.002988,-0.000054,-0.00009,0.002934,……,-0.05251,-0.04644,-0.04646,-0.04338,-0.05555,-0.04948,-0.04948,-0.05252](Unit:″).

[0082] The Z-axis thermal elongation error data is in array:

[0083] [0,-0.27,-0.6744,-1.0116,-1.2812,-1.5512,-1.888,-2.0904,……,-9.9796,-9.9124,-9.9124,-9.9796,-10.182,-10.182,-10.0472,-9.9796] (Unit: μm).

[0084] The Z-axis thermal rotation error data is in array:

[0085] [0,-0.00568,-0.00943,-0.01183,-0.00925,-0.00897,-0.01256,-0.01874,……,0.095912,0.090215,0.091628,0.091267,0.092101,0.09023,0.09033,0.090993](Unit:″).

[0086] Therefore, the present invention adopts the above-mentioned six-point method for measuring and identifying thermal errors of CNC machine tool spindles, which can make up for the shortcomings of existing measurement technologies that cannot measure spindle rotation thermal errors, realize complete measurement and identification of spindle thermal errors, improve the accuracy of the established mathematical model, and provide data basis for spindle rotation thermal error compensation.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A six-point method for measuring and identifying thermal errors in CNC machine tool spindles, characterized in that: Includes the following steps: Step 1: For the CNC machine tool spindle inspection bar, change the tested part of the traditional cylindrical inspection bar to a square shape; Step 2: Perform six-point thermal error measurement using a six-point fixture equipped with an eddy current displacement sensor group. Step 3: Sample thermal deformation data and use the thermal error identification formula to identify the six thermal errors in the first set of data; Step four: Based on step three, derive the six thermal errors of the nth group of data from a single thermal deformation data sampling. In step two, the eddy current displacement sensor group includes displacement sensor one, displacement sensor two, displacement sensor three, displacement sensor four, displacement sensor five, and displacement sensor six. Displacement sensor one, displacement sensor two, displacement sensor three, and displacement sensor four are installed on the six-point fixture. Displacement sensor five is installed on the opposite side of displacement sensor one. Displacement sensor six is ​​installed on the six-point fixture relative to the center of the end face of the test bar. The eddy current displacement sensor group measures the displacement changes in the X, Y, and Z directions of the target position on the test bar. Before thermal deformation occurs in the CNC machine tool spindle, the width of the inspection bar is... H The center coordinate of the test bar is O(0,0). Before measurement, the initial values ​​measured by each displacement sensor are set to zero. In step three, after the CNC machine tool spindle undergoes thermal deformation, the first set of thermal deformation data is sampled. Continuous sampling is performed at positions a and b, representing the symmetrical rotation angles during the spindle's rotation. At position a, the values ​​measured by each sensor are as follows: x 1a 1 , x 2a 1 , x 3a 1 , y 1a 1 , y 2a 1 , z a 1 At point b, the values ​​measured by each sensor are as follows: x 1b 1 , x 2b 1 , x 3b 1 , y 1b 1 , y 2b 1 , z b 1 The distance between displacement sensor 1 and displacement sensor 2 along the main shaft axis on the six-point fixture is... D The distance between displacement sensors three and four along the main shaft axis on the six-point fixture is... D The length of the square part of the test bar is L The distance from displacement sensor two to the bottom surface of the test bar is l The test bar is square. During rotation, the change in the width of the test bar is combined with the thermal offset error, resulting in a change in the width of the test bar. , As shown below: Thermal error after removing the influence of test bar width variation , , , , The geometric relationship between the values ​​of each sensor in the eddy current displacement sensor group and the values ​​of the sensors is shown below: in, This indicates the thermal offset error in the X direction. This indicates the thermal offset error in the Y direction. This indicates the thermal offset error in the Z direction. This indicates the thermal tilt error in the X direction. Indicates the thermal tilt error in the Y direction; Spindle thermal rotation error By actual angular position relative to ideal angle position θ The difference is calculated to determine the actual angular position. The calculation formula is as follows: Adjust the ideal angular position within the range of 0° to 45°, and reduce the spindle thermal rotation error. The calculation formula is as follows: Remove the influence of the test bar installation eccentricity error from the six spindle thermal errors calculated in step three. The X-axis tilt of the installation eccentricity error is then considered. Offset components and Y-axis tilt Offset components The calculation formula is as follows: The six thermal error identification formulas are as follows: 。 2. The six-point thermal error measurement and identification method for CNC machine tool spindles according to claim 1, characterized in that: In step four, following the same logic as above, when sampling the nth set of thermal deformation data, the values ​​measured by the six eddy current displacement sensors at the corresponding positions in the X, Y, and Z directions of the test bar at point a are respectively... x 1a n , x 2a n , x 3a n , y 1a n , y 2a n , z a n At point b, the values ​​measured by each sensor are as follows: x 1b n , x 2b n , x 3b n , y 1b n , y 2b n , z b n , δ x n δ y n δ z n ε x n ε y n , ε z n The six thermal errors sampled in the nth data set, and the X-axis tilt of the installation eccentricity error sampled in the nth data set. Offset components and Y-axis tilt Offset components Based on the derivation of the six thermal error identification formulas in step four, the formula for sampling the nth group of data is as follows: 。

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