Machine tool spatial error measurement device and method combining a displacement sensor and a ballbar

Abstract

The present invention discloses a machine tool spatial error measurement device and method combining a displacement sensor and a ball bar. The measurement device includes a planetary gear train structure, a first non-contact displacement sensor, a second non-contact displacement sensor, a third non-contact displacement sensor, a fourth non-contact displacement sensor, a first reference plate, a second reference plate, and a central support. The planetary gear train structure includes a first turntable, a connecting frame, a mounting plate, and a second turntable. The present invention eliminates the flatness error of the reference plate by using two displacement sensors moving along a circular trajectory; and by combining two sets of double displacement sensors forming a planetary gear train, the influence brought by the axial error in the bearing rotation is eliminated, and the Z-axis error of the machine tool is separated. At the same time, in cooperation with the ball bar, the present invention can accurately obtain the three-dimensional error of the machine tool. Since the present invention can eliminate the influence of the flatness error of the reference plate, the present invention has a lower requirement for the flatness of the reference plate, reducing the cost of machine tool spatial error measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field of machine tool error detection, and particularly relates to a machine tool spatial error measurement device and method combining a displacement sensor and a ball bar. Background Technique

[0002] With the continuous development of modern manufacturing industry, the requirements for part machining accuracy are getting higher and higher. As the "processing mother machine" of modern manufacturing industry, improving the machining accuracy of numerically controlled machine tools is of great significance to the development of China's manufacturing industry. The key to improving the machining accuracy of numerically controlled machine tools lies in reducing their spatial errors during the machining process.

[0003] Error compensation is one of the most widely used methods to improve the accuracy of numerically controlled machine tools. The prerequisite for adopting this method is to accurately measure the spatial errors of the machine tool. Due to its advantages such as high detection accuracy, low cost, high detection efficiency, simple installation and convenient operation, the ball bar is widely used in the field of numerically controlled machine tool error detection. Due to the limitation of the structure of the ball bar, only the errors of the machine tool in the X direction and the Y direction can be obtained by conducting a single circular arc test in the XY plane of the ball bar, ignoring the error in the Z direction (that is, the error information obtained by conducting a single circular arc test with the ball bar is incomplete). Therefore, the present invention proposes a method for combining a non-contact displacement sensor and a ball bar to measure the spatial errors of a machine tool. This method can quickly and accurately measure the spatial errors of the machine tool, which is of great significance for improving the machining accuracy of the machine tool. Summary of the Invention

[0004] The purpose of the present invention is to make up for the shortcomings of the incomplete error information of the machine tool obtained by conducting a single circular arc test with the existing ball bar, and to propose a method for combining a non-contact displacement sensor and a ball bar to measure the spatial errors of the machine tool. The present invention can quickly and accurately measure the spatial errors of the machine tool, provide reliable machine tool motion error information, and contribute to the improvement of the machining accuracy of the machine tool.

[0005] In the first aspect, the present invention provides a machine tool spatial error measurement device combining a displacement sensor and a ball bar, including a planetary gear train structure, a first non-contact displacement sensor, a second non-contact displacement sensor, a third non-contact displacement sensor, a fourth non-contact displacement sensor, a first reference plate, a second reference plate and a central support. The planetary gear train structure includes a first turntable, a connecting frame, a mounting plate and a second turntable. During the measurement process, the second reference plate is fixed on the workbench of the measured machine tool. The first turntable is rotatably connected to the spindle of the measured machine tool. The first reference plate is fixed on the spindle of the measured machine tool.

[0006] The described central support is fixed on the second reference plate. The second turntable is rotatably connected to the central support. The second turntable is connected to the mounting plate, and force transmission is only carried out along the tangential direction of the second turntable. The mounting plate and the first turntable are fixed by a connecting frame. A first non-contact displacement sensor and a second non-contact displacement sensor are fixed on the first turntable. A third non-contact displacement sensor and a fourth non-contact displacement sensor are fixed on the mounting plate. Both the first non-contact displacement sensor and the second non-contact displacement sensor face the first reference plate and have the same distance from the central axis of the first turntable. Both the third non-contact displacement sensor and the fourth non-contact displacement sensor face the second reference plate and have the same distance from the central axis of the second turntable.

[0007] Preferably, the machine tool spatial error measuring device combining the displacement sensor and the ball bar further includes a ball bar and a tool cup. The tool cup is fixed on the bottom surface of the first reference plate; the tool cup is coaxially arranged with the main shaft. Conical sockets are provided at the bottom end of the tool cup and the top end of the central support. The ball bar is connected between the conical sockets of the tool cup and the central support. The precision ball at one end of the ball bar is magnetically adsorbed at the bottom end of the tool cup; the precision ball at the other end of the ball bar is magnetically adsorbed at the top end of the central support.

[0008] Preferably, the ball bar is horizontally arranged.

[0009] Preferably, a vertical guide rod is fixed on the side of the second turntable; a limit block is fixed on the side of the mounting plate; a force transmission through groove is provided on the limit block; the vertical guide rod is inserted into the force transmission through groove. The vertical guide rod can freely move along both the axial and radial directions of the second turntable in the force transmission through groove.

[0010] Preferably, the first non-contact displacement sensor is directly above the third non-contact displacement sensor; the second non-contact displacement sensor is directly above the fourth non-contact displacement sensor.

[0011] Preferably, the first non-contact displacement sensor, the second non-contact displacement sensor, the third non-contact displacement sensor, and the fourth non-contact displacement sensor all adopt capacitive displacement sensors.

[0012] Preferably, the first non-contact displacement sensor, the second non-contact displacement sensor, the third non-contact displacement sensor, and the fourth non-contact displacement sensor adopt any one of an inductive displacement sensor, a laser triangulation displacement sensor, a laser confocal sensor, and a laser interferometer.

[0013] The measuring method of this machine tool spatial error measuring device includes the following steps:

[0014] Step 1: The main shaft performs circular interpolation movement driven by the machine tool under test and rotates one week around the central support. During the movement of the main shaft, the third non-contact displacement sensor and the fourth non-contact displacement sensor rotate one week around the central axis of the central support relative to the second reference plate, and the first non-contact displacement sensor and the second non-contact displacement sensor rotate one week around the axis of the main shaft relative to the first reference plate.

[0015] During the movement, the first non-contact displacement sensor and the second non-contact displacement sensor continuously detect the distance from themselves to the first reference plate, and obtain data sets C1 and C2 respectively. The third non-contact displacement sensor and the fourth non-contact displacement sensor continuously detect the distance from themselves to the second reference plate, and obtain data sets C3 and C4 respectively.

[0016] Step 2: Input the data sets C1 and C2 into the double-sensor error extraction method to obtain the flatness error vector R1; input the data sets C3 and C4 into the double-sensor error extraction method to obtain the flatness error vector R2.

[0017] Step 3: Calculate the error vector B1 = C1 - R1. Calculate the error vector B2 = C3 - R2.

[0018] Step 4: Calculate the Z-direction error vector ΔZ of the main shaft = B2 - B1.

[0019] The specific process of calculating the flatness error vector R of the reference plate by the double-sensor error extraction method is as follows:

[0020] The two input data sets are respectively denoted as data set S1 and S2. S1 = {s1(1), s1(2),..., s1(N)}; S2 = {s2(1), s2(2),..., s2(N)}; where, s1(i) is the i-th element of data set S1; s2(i) is the i-th element of data set S2; i = 1, 2,..., N; N is the sampling times of a single non-contact sensor.

[0021] Construct a set S = {s(1), s(2),..., s(N)} according to the data sets S1 and S2; s(i) is a linear combination of s1(i) and s2(i), and its expression is s(i) = s1(i) - s2(i).

[0022] Establish the following flatness error relation:

[0023] s(i) = r(i) - r(i + m1)

[0024] where, r(i) and r(i + m1) are respectively the flatness errors of the detection points where the two non-contact displacement sensors are located at the same moment; m1 is the lag sampling times of the two non-contact displacement sensors for the same sampling position, and its expression is α1 is the phase difference between two non-contact displacement sensors relative to the rotation axis; f is the sampling frequency of the non-contact displacement sensor; ω is the rotational angular velocity of the two non-contact displacement sensors.

[0025] Solve the relational expressions in the solution steps to obtain the flatness error vector R = {r(1), r(2),..., r(N)}.

[0026] Preferably, during the rotation of the main shaft, the ballbar measures the change in the distance between the centers of the two precision balls of itself to obtain the radial error vector ΔR; calculate the X-axis error vector ΔX and Y-axis error vector ΔY of the machine tool to be measured as follows:

[0027] Δx i = Δr i × sinθ i

[0028] Δy i = Δr i × cosθ i

[0029] where, Δr i is the i-th element in the radial error vector ΔR, and Δx i , Δy i are respectively the i-th elements in the X-axis error vector ΔX and Y-axis error vector ΔY. θ i is the rotation angle of the main shaft relative to the initial position at the i-th sampling of the ballbar.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. The present invention uses two displacement sensors moving along a circular trajectory to eliminate the flatness error of the reference plate; and through the combination of two groups of double displacement sensors forming a planetary gear, the influence brought by the axial error in the bearing rotation is eliminated, and then the accurate Z-axis error of the machine tool is separated. At the same time, in cooperation with the ballbar, the present invention can accurately obtain the three-dimensional error of the machine tool.

[0032] 2. The present invention obtains the accurate Z-direction error of the machine tool through the error separation method. Since the influence of the flatness error of the reference plate can be eliminated, the present invention has a lower requirement for the flatness of the reference plate, greatly reducing the cost of machine tool spatial error measurement. Description of the Drawings

[0033] Figure 1 is the structural schematic diagram of the assembly of each part in the present invention;

[0034] Figure 2 is the structural schematic diagram of the first turntable in the present invention;

[0035] Figure 3 is the schematic diagram of the sensor fixture in the present invention;

[0036] Figure 4 Schematic diagram of the limit block in the present invention;

[0037] Figure 5 Schematic diagram of the connecting block in the present invention;

[0038] Figure 6 Schematic diagram of the structure of the second turntable in the present invention;

[0039] Figure 7 Schematic diagram of the mounting plate in the present invention;

[0040] Figure 8 Simulation comparison diagram of the flatness error data calculated by the dual-sensor error extraction method and the theoretical value;

[0041] Figure 9 Comparison diagram of the flatness error data calculated by the dual-sensor error extraction method and the value directly measured by the capacitive displacement sensor.

[0042] Figure 1 In the figure: 1. Mounting plate; 2. Limit block; 3. Connecting rod; 4. Tool cup; 5. Connecting block; 6. First turntable; 7. Spindle; 8. First non-contact displacement sensor; 9. Second non-contact displacement sensor; 10. Sensor fixture; 11. First reference plate; 12. Ball bar; 13. Third non-contact displacement sensor; 14. Fourth non-contact displacement sensor; 15. Second turntable; 16. Central support; 17. Second reference plate. Specific implementation mode

[0043] The present invention will be further described below with reference to the accompanying drawings.

[0044] As Figure 1 shown, a machine tool spatial error measurement device combining a displacement sensor and a ball bar includes a planetary gear train structure, a sensor fixture 10, a first non-contact displacement sensor 8, a second non-contact displacement sensor 9, a third non-contact displacement sensor 13, a fourth non-contact displacement sensor 14, a first reference plate 11, a second reference plate 17, a ball bar 12, a tool cup 4 and a central support 16. The second reference plate 17 is fixed on the workbench of the machine tool to be measured. The central support 16 is fixed at the center position of the top surface of the second reference plate 17. The first non-contact displacement sensor 8, the second non-contact displacement sensor 9, the third non-contact displacement sensor 13 and the fourth non-contact displacement sensor 14 all adopt capacitive displacement sensors.

[0045] The planetary gear train structure is connected between the second reference plate 17 and the spindle 7 of the machine tool to be measured. The planetary gear train structure includes a first turntable 6, a connecting frame, a mounting plate 1, a limit block 2 and a second turntable 15.

[0046] The first turntable 6 is coaxially and rotationally connected to the spindle 7 of the machine tool under test through a bearing. The second turntable 15 is coaxially and rotationally connected to the central support 16 through a bearing.

[0047] One end of the limit block 2 is fixed to the mounting plate 1 by screws; a force transmission through groove is provided at the other end of the limit block 2; a vertical guide rod is fixed to the side of the second turntable 15; the vertical guide rod is inserted into the force transmission through groove. The vertical guide rod can freely move along the axial and radial directions of the second turntable 15 in the force transmission through groove, preventing the bearing rotational error of the second turntable 15 from affecting the measurement results of the non-contact displacement sensor; a circumferential acting force can be generated between the force transmission through groove and the vertical guide rod along the circumferential direction of the second turntable 15, so that during the process of the spindle 7 performing circular interpolation motion, the four non-contact displacement sensors have a revolution around the central axis of the central support 16 and also have a rotation around the central axis of the spindle 7, and the angular velocity of revolution is equal to the angular velocity of rotation.

[0048] The connecting frame includes a connecting block 5 and a connecting rod 3. The two connecting blocks 5 are respectively fixed to both ends of the connecting rod 3 by screws; one of the connecting blocks 5 is fixed to the first turntable 6 by screws; the other connecting block 5 is fixed to the side of the mounting plate 1 away from the central support 16 by screws.

[0049] A first non-contact displacement sensor 8 and a second non-contact displacement sensor 9 are fixed to the edge of the first turntable 6 by a sensor fixture 10. The mounting plate 1 is located directly below the first turntable 6. A third non-contact displacement sensor 13 and a fourth non-contact displacement sensor 14 are fixed to the edge of the mounting plate 1 by a sensor fixture 10.

[0050] Both the first non-contact displacement sensor 8 and the second non-contact displacement sensor 9 are arranged vertically downward and are at the same distance from the central axis of the first turntable 6. Both the third non-contact displacement sensor 13 and the fourth non-contact displacement sensor 14 are arranged vertically downward and are at the same distance from the central axis of the second turntable 15.

[0051] A first reference plate 11 located directly below the first turntable 6 is fixed to the spindle 7 of the machine tool under test. The rotation trajectories of the first non-contact displacement sensor 8 and the second non-contact displacement sensor 9 relative to the spindle 7 are completely above the top surface of the first reference plate 11. The rotation trajectories of the third non-contact displacement sensor 13 and the fourth non-contact displacement sensor 14 relative to the central support 16 are completely above the top surface of the second reference plate 17.

[0052] The tool cup 4 is fixed to the bottom surface of the first reference plate 11; the tool cup 4 is coaxially arranged with the main shaft 7. The bottom end of the tool cup 4 and the top end of the central support 16 are provided with tapered sockets. The tapered socket at the top end of the central support 16 is specifically a three-point tapered socket. The precision ball at one end of the ball bar 12 is magnetically adsorbed at the bottom end of the tool cup 4; the precision ball at the other end of the ball bar 12 is magnetically adsorbed at the top end of the central support 16.

[0053] During the working process, the main shaft 7 makes a circular interpolation movement around the central support 16, and the ball bar makes a circular interpolation movement along with the main shaft 7 to measure the radial error during the movement of the main shaft. The radial error can be projected onto the X-axis and Y-axis of the space coordinate system.

[0054] Under the action of the planetary gear structure, the first non-contact displacement sensor 8, the second non-contact displacement sensor 9, the third non-contact displacement sensor 13, and the fourth non-contact displacement sensor 14 all have a rotation around the central axis of the first turntable 6 and a revolution around the central axis of the central support. The angular velocities of rotation and revolution are the same. One acquisition cycle is when the turntable rotates 360°.

[0055] The data measured by the first non-contact displacement sensor 8 and the second non-contact displacement sensor 9 include the projection of the rotational error of the first turntable 6 in the Z direction and the flatness error of the first reference plate 11. The data measured by the third non-contact displacement sensor 13 and the fourth non-contact displacement sensor 14 include the projection of the rotational error of the first turntable 6 in the Z direction, the flatness error of the second reference plate 17, and the Z-direction error of the main shaft 7.

[0056] By processing the measurement data of the first non-contact displacement sensor 8 and the second non-contact displacement sensor 9 through the self-derived "dual-sensor error extraction method", and then through the method of vector subtraction, the error curve of the projection of the rotational error of the bearing in the first turntable 6 in the Z direction can be obtained. By processing the measurement data of the third non-contact displacement sensor 13 and the fourth non-contact displacement sensor 14 using the "dual-sensor error extraction method", and then through the method of vector subtraction, the error curve of the coupling of the projection of the rotational error of the bearing in the first turntable 6 in the Z direction and the Z-direction error of the main shaft can be obtained. Subtracting the error curve of the projection of the rotational error of the bearing in the first turntable 6 in the Z direction from this error curve can obtain the accurate Z-direction error of the main shaft.

[0057] The measuring method of the machine tool spatial error measuring device includes the following steps:

[0058] Step 1: The main shaft 7 performs circular interpolation movement driven by the machine tool under test and rotates one week around the central support 16. During the movement of the main shaft 7, the third non-contact displacement sensor 13 and the fourth non-contact displacement sensor 14 rotate one week around the central axis of the central support relative to the second reference plate 17, and the first non-contact displacement sensor 8 and the second non-contact displacement sensor 9 rotate 360° around the axis of the main shaft 7 relative to the first reference plate 11.

[0059] During the movement process, the first non-contact displacement sensor 8 and the second non-contact displacement sensor 9 continuously detect the distances from themselves to the top surface of the first reference plate 11, and obtain data sets C1 and C2 respectively. The third non-contact displacement sensor 13 and the fourth non-contact displacement sensor 14 continuously detect the distances from themselves to the top surface of the second reference plate 17, and obtain data sets C3 and C4 respectively.

[0060] The ball bar 12 detects the change in the distance between the centers of its two precision balls and obtains the radial error vector ΔR; calculate the X-axis error vector ΔX and Y-axis error vector ΔY of the machine tool under test as follows:

[0061] Δx i =Δr i ×sinθ i

[0062] Δy i =Δr i ×cosθ i

[0063] Where, Δr i is the i-th element in the radial error vector ΔR, that is, the error of the distance between the centers of the balls of the ball bar 12 at the i-th sampling relative to the starting moment. Δx i and Δy i are the i-th elements in the X-axis error vector ΔX and Y-axis error vector ΔY respectively; that is, the X-axis error and Y-axis error of the machine tool under test at the i-th sampling of the ball bar 12. θ i is the rotation angle of the main shaft 7 relative to the initial position at the i-th sampling of the ball bar 12.

[0064] Step 2: According to the data sets C1 and C2, calculate the flatness error vector R1 by the double-sensor error extraction method; according to the data sets C3 and C4, calculate the flatness error vector R2 by the double-sensor error extraction method.

[0065] Step 3: Since the first reference plate 11 is fixedly connected to the main shaft 7, the measured values of the first non-contact displacement sensor 8 and the second non-contact displacement sensor 9 include the flatness error of the first reference plate 11 and the projection of the rotational error of the first turntable 6 in the Z direction. Substituting the flatness error vector R1 into the data set C1, the error vector B1 of the projection of the rotational error of the first turntable 6 in the Z direction (this error is caused by the bearing between the first turntable 6 and the main shaft 7) can be obtained.

[0066] B1 = C1 - R1

[0067] Since the third non-contact displacement sensor 13 and the fourth non-contact displacement sensor 14 are fixedly connected to the first turntable 6, and the second reference plate 17 is installed on the machine tool workbench; therefore, the measured values of the third non-contact displacement sensor 13 and the fourth non-contact displacement sensor 14 include the flatness error of the second reference plate 17, the projection of the rotational error of the first turntable 6 in the Z direction, and the Z-direction error of the main shaft 7. Substituting the flatness error vector R2 into the data set C3, the error vector B2 of the coupling of the projection of the rotational error of the first turntable 6 in the Z direction and the Z-direction error of the main shaft 7 can be obtained.

[0068] B2 = C3 - R2

[0069] Step 4: Since there is only a tangential force transmission between the second turntable 15 and the first turntable 6, the bearing rotational error of the second turntable 15 will not be coupled into the measured values of the four non-contact displacement sensors; therefore, by taking the difference between the error vectors B2 and B1, the Z-direction error vector ΔZ of the main shaft 7 can be accurately obtained.

[0070] ΔZ = B2 - B1

[0071] The specific process of the dual-sensor error extraction method is as follows:

[0072] The two input data sets are respectively denoted as data set S1 and data set S2. S1 = {s1(1), s1(2),..., s1(N)}; S2 = {s2(1), s2(2),..., s2(N)}; where s1(i) is the change value of the distance measured by one of the non-contact displacement sensors for the i-th sampling of the reference plate relative to the detection value at the starting moment; s2(i) is the distance change value measured by the other for the i-th sampling of the reference plate. i = 1, 2,..., N; N is the number of samplings, and its expression is: N = 2π / Δθ; Δθ is the sampling radian interval, and its expression is

[0073] The theoretical derivation of eliminating the coupling error is as follows:

[0074] The data sets S1 and S2 respectively correspond to the distance change data s1(θ) and s2(θ) between two non-contact displacement sensors and the reference plate. For the convenience of description, here, the first capacitive displacement sensor 8 and the second capacitive displacement sensor 9 are taken as examples. The first capacitive displacement sensor 8 is the first non-contact displacement sensor, and the second capacitive displacement sensor 9 is the second non-contact displacement sensor; both the data s1(θ) and s2(θ) are affected by the flatness error of the reference plate and the projection ΔZ(θ) of the rotary error of the turntable in the Z direction, and their expressions are shown as follows.

[0075]

[0076] In Equation (1): r(θ) is the flatness error of the reference plate, and ΔZ(θ) is the projection of the rotary error of the turntable in the Z direction (in this embodiment, it is the vertical direction); α1 is the installation angle between the first non-contact displacement sensor and the second non-contact displacement sensor relative to the rotation axis of the turntable (that is, the angle between the line connecting the first non-contact displacement sensor to the rotation axis of the turntable and the line connecting the second non-contact displacement sensor to the rotation axis of the turntable); the installation angle α1 is an integer multiple of the sampling radian interval Δθ; θ is the rotation angle of the turntable. With Figure 1 the sensor positions installed as shown, when the turntable rotates counterclockwise (from the top-down perspective), α1 is positive, and when the turntable rotates clockwise (from the top-down perspective), α1 is negative.

[0077] Construct a linear combination s(θ) of the data collected by the two non-contact displacement sensors, and introduce a coefficient c1, as shown in the equation:

[0078] s(θ) = s1(θ) + c1s2(θ) Equation (2)

[0079] Substitute Equation (1) into Equation (2) and simplify to obtain Equation (3):

[0080] s(θ) = r(θ) + c1r(θ + α1) + ΔZ(θ)(1 + c1) Equation (3)

[0081] Let the coefficient of the ΔZ(θ) term in Equation (3) be 0, and the value of the sensor calibration coefficient c1 can be determined as shown in Equation (4):

[0082] c1 = -1 Equation (4)

[0083] When the coefficient c1 takes -1, the projection ΔZ(θ) of the rotary error of the turntable in the Z direction can be eliminated, so that s(θ) = r(θ) - r(θ + α1), and r(θ) can be obtained by solving.

[0084] Perform data processing on the measurement data obtained in Step 1 to obtain an accurate flatness error value of the flat plate. The specific process is as follows:

[0085] 3-1. Construct the discrete parameter m1 of the installation angle α1 of two non-contact displacement sensors, as shown in Equation (5):

[0086] m1 = α1 / Δθ Equation (5)

[0087] 3-2. Construct the discrete linear combination s(i) as shown in Equation (6):

[0088] s(i) = s1(i) + c1s2(i) Equation (6)

[0089] 3-3. Obtain the relationship between the constructed linear combination s(i) and the flatness error as shown in Equation (7):

[0090] s(i) = r(i) - r(i + m1) Equation (7)

[0091] Equation (7) is the discretized form of Equation (3). r(i) is the height difference of the measured point relative to the starting detection point of the first non-contact displacement sensor at the i-th detection of the first non-contact displacement sensor; r(i + m1) is the height difference of the measured point relative to the starting detection point of the first non-contact displacement sensor at the i-th detection of the second non-contact displacement sensor.

[0092] 3-4. Write the equation as a linear equation system as shown in Equation (8).

[0093] AR = S Equation (8)

[0094] In the equation, A is a sparse singular matrix, determined by the installation angle α1. R = {r(1), r(2),..., r(N)}; S = {s(1), s(2),..., s(N)}.

[0095]

[0096] 3-5. Solve the equation to obtain the flatness error vector R.

[0097] For the effectiveness and feasibility of the "dual-sensor error extraction method", use MATLAB software to conduct a simulation experiment on the theory of eliminating coupling errors. First, set the flatness error curve of the first reference plate as:

[0098]

[0099] The projection error curve of the rotary error of the turntable in the Z direction is:

[0100]

[0101] Then, the non-contact displacement sensor was simulated to sample the above error curve to obtain s(i). The sparse singular matrix A in the linear equations is only determined by the installation angle α1, which can be obtained after the installation angle of the sensor is determined. In this simulation experiment, α1 = 45° was set. Thus, the linear equations AR = S were obtained. The least squares method was used to solve them, and finally, Figure 8 and Figure 9 . Figure 8 represents the comparison diagram of the reference plate error curve and the theoretical error curve, Figure 9 represents the amplitude difference diagram of the reference plate error curve and the theoretical error curve. From Figure 8 and Figure 9 it can be seen that the "dual-sensor error extraction method" can accurately obtain the flatness error curve of the reference plate.

Claims

1. A machine tool spatial error measurement device combining a displacement sensor and a ballbar, characterized in that: It includes a planetary gear train structure, a first non-contact displacement sensor (8), a second non-contact displacement sensor (9), a third non-contact displacement sensor (13), a fourth non-contact displacement sensor (14), a first reference plate (11), a second reference plate (17), a central support (16), a ballbar (12) and a tool cup (4); the planetary gear train structure includes a first turntable (6), a connecting frame, a mounting plate (1) and a second turntable (15); during the measurement process, the second reference plate (17) is fixed on the workbench of the machine tool to be measured; the first turntable (6) is rotatably connected to the main shaft (7) of the machine tool to be measured; the first reference plate (11) is fixed on the main shaft (7) of the machine tool to be measured; The central support (16) is fixed on the second reference plate (17); the second turntable (15) is rotatably connected to the central support (16); the second turntable (15) is connected to the mounting plate (1), and it only transmits force along the tangential direction of the second turntable (15); the mounting plate (1) is fixed to the first turntable (6) through the connecting frame; the first non-contact displacement sensor (8) and the second non-contact displacement sensor (9) are fixed on the first turntable (6); the third non-contact displacement sensor (13) and the fourth non-contact displacement sensor (14) are fixed on the mounting plate (1); both the first non-contact displacement sensor (8) and the second non-contact displacement sensor (9) face the first reference plate (11), and the distances from the center axis of the first turntable (6) are the same; Both the third non-contact displacement sensor (13) and the fourth non-contact displacement sensor (14) face the second reference plate (17), and the distances from the center axis of the second turntable (15) are the same; the four non-contact displacement sensors have a revolution around the central axis of the central support (16), and at the same time, there is also a rotation around the central axis of the main shaft (7), and the angular velocity of revolution is equal to the angular velocity of rotation; The tool cup (4) is fixed on the bottom surface of the first reference plate (11); the tool cup (4) is coaxially arranged with the main shaft (7); there are conical sockets at the bottom end of the tool cup (4) and the top end of the central support (16); the ballbar (12) is connected between the conical sockets of the tool cup (4) and the central support (16); the precision ball at one end of the ballbar (12) is magnetically adsorbed at the bottom end of the tool cup (4).

2. The machine tool spatial error measuring device combining a displacement sensor and a ballbar according to claim 1, characterized in that: The ballbar (12) is horizontally arranged.

3. The machine tool spatial error measuring device combining a displacement sensor and a ballbar according to claim 1, characterized in that: A vertical guide rod is fixed on the side of the second turntable (15); a limit block (2) is fixed on the side of the mounting plate (1); a force transmission through groove is formed on the limit block (2); the vertical guide rod is inserted into the force transmission through groove; the vertical guide rod can freely move along the axial and radial directions of the second turntable (15) in the force transmission through groove.

4. A machine tool spatial error measuring device combining a displacement sensor and a ballbar, characterized in that: The first non-contact displacement sensor (8) is directly above the third non-contact displacement sensor (13); the second non-contact displacement sensor (9) is directly above the fourth non-contact displacement sensor (14).

5. The machine tool spatial error measuring device combining a displacement sensor and a ballbar according to claim 1, characterized in that: The first non-contact displacement sensor (8), the second non-contact displacement sensor (9), the third non-contact displacement sensor (13) and the fourth non-contact displacement sensor (14) all adopt capacitive displacement sensors.

6. The machine tool spatial error measuring device combining a displacement sensor and a ballbar according to claim 1, characterized in that: The first non-contact displacement sensor (8), the second non-contact displacement sensor (9), the third non-contact displacement sensor (13) and the fourth non-contact displacement sensor (14) adopt any one of an inductive displacement sensor, a laser triangulation displacement sensor, a laser confocal sensor and a laser interferometer.

7. A method for measuring the spatial error of a machine tool by combining a displacement sensor and a ballbar, characterized in that: Adopt a machine tool spatial error measurement device combining a displacement sensor and a ball bar as described in claim 1; the measurement method includes the following steps: Step 1: The spindle (7) performs a circular interpolation movement under the drive of the measured machine tool and rotates one week around the central support (16); during the movement of the spindle (7), the third non-contact displacement sensor (13) and the fourth non-contact displacement sensor (14) rotate one week around the central axis of the central support relative to the second reference plate (17), and the first non-contact displacement sensor (8) and the second non-contact displacement sensor (9) rotate one week around the axis of the spindle (7) relative to the first reference plate (11); During the movement, the first non-contact displacement sensor (8) and the second non-contact displacement sensor (9) continuously detect the distances from themselves to the first reference plate (11) and respectively obtain data sets C1 and C2; the third non-contact displacement sensor (13) and the fourth non-contact displacement sensor (14) continuously detect the distances from themselves to the second reference plate (17) and respectively obtain data sets C3 and C4; Step 2: Input the data sets C1 and C2 into the dual-sensor error extraction method to obtain the flatness error vector R1; input the data sets C3 and C4 into the dual-sensor error extraction method to obtain the flatness error vector R2; Step 3: Calculate the error vector B1 = C1 - R1; calculate the error vector B2 = C3 - R2; Step 4: Calculate the Z-direction error vector ΔZ of the spindle (7) = B2 - B1; The specific process of calculating the flatness error vector R of the reference plate by the dual-sensor error extraction method is as follows: (1) Denote the two input data sets as data set S1 and data set S2 respectively; S1 = {s1(1), s1(2),..., s1(N)}; S2 = {s2(1), s2(2),..., s2(N)}; where, s1(i) is the i-th element of data set S1; s2(i) is the i-th element of data set S2; i = 1, 2,..., N; N is the sampling times of a single non-contact sensor; (2) Construct a set S = {s(1), s(2),..., s(N)} according to data sets S1 and S2; s(i) is a linear combination of s1(i) and s2(i), and its expression is s(i) = s1(i) - s2(i); (3) Establish the following flatness error relation: s(i) = r(i) - r(i + m1) Among them, r(i) and r(i + m1) are respectively the flatness errors of the detection points where two non-contact displacement sensors are located at the same moment; m1 is the number of lag samples of the two non-contact displacement sensors for the same sampling position, and its expression is α1 is the phase difference between the two non-contact displacement sensors relative to the rotation axis; f is the sampling frequency of the non-contact displacement sensor; ω is the rotational angular velocity of the two non-contact displacement sensors; (4) Solve the relation in step (3) to obtain the flatness error vector R = {r(1), r(2),..., r(N)}.

8. A method for measuring the spatial error of a machine tool by combining a displacement sensor and a ballbar, characterized in that: A tool cup (4) is fixed to the bottom surface of the first reference plate (11); the tool cup (4) is coaxially arranged with the main shaft (7); a tapered socket is provided at the bottom end of the tool cup (4) and the top end of the central support (16); the ball bar (12) is connected between the tapered sockets of the tool cup (4) and the central support (16); During the rotation of the main shaft (7), the ball bar (12) detects the change in the distance between the centers of the two precision balls of itself to obtain the radial error vector ΔR; the X-axis error vector ΔX and the Y-axis error vector ΔY of the machine tool under test are calculated as follows: Δx i = Δr i × sinθ i Δy i = Δr i × cosθ i where, Δr i is the i-th element in the radial error vector ΔR, and Δx i , Δy i are the i-th elements in the X-axis error vector ΔX and the Y-axis error vector ΔY, respectively; θ i is the rotation angle of the main shaft (7) relative to the initial position during the i-th sampling of the ballbar (12).

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