Calibration device and calibration method for pre-travel of measuring head of in-situ detection system of numerical control machine tool

Abstract

The application discloses a kind of calibration devices of pre-travel of in-situ detection system probe of numerical control machine tool, including trigger probe, trigger probe end is equipped with probe, probe bottom vertical corresponding position is provided with right triangular pyramid table, lengthening rod top end is in contact with right triangular pyramid table bottom and is mutually fixed, lengthening rod bottom end is fixed with magnetic force table seat, limit structure is also provided on the side surface of magnetic force table seat.The application also discloses a kind of calibration method of pre-travel of in-situ detection system probe of numerical control machine tool.The application solves the problem of low pre-travel detection accuracy in prior art.

Description

Technical Field

[0001] This invention belongs to the field of in-situ detection technology of CNC machining accuracy in parts manufacturing process, specifically relating to a calibration device for the probe pre-stroke of a CNC machine tool in-situ detection system, and also relating to a calibration method for the probe pre-stroke of a CNC machine tool in-situ detection system. Background Technology

[0002] In-situ inspection technology for CNC machining accuracy of workpieces eliminates the need for workpiece transfer between machine tools and inspection equipment, avoids manufacturing errors caused by non-alignment of process datums, reduces unnecessary time and material consumption, alleviates labor intensity, and improves productivity. It is of great significance for realizing intelligent, efficient, and high-precision product manufacturing processes.

[0003] Trigger-type probes are a key component of in-situ detection systems. A typical structure of a certain probe model can be found here. Figure 1 During in-situ testing, when probe 1 contacts the workpiece, a trigger signal is generated. The CNC system responds to this signal and records the coordinates of that point. By measuring multiple points as required and processing the data, a test report can be generated.

[0004] The probe measurement sequence is as follows Figure 2 As shown in the diagram, the moment the probe contacts the workpiece is T1, the moment the probe sends a trigger signal is T2, and the moment the CNC system responds to the trigger signal is T3. The probe's pre-stroke is the relative displacement between the probe and the workpiece during the time interval T1 to T3. Related research indicates that the detection error caused by the deviation between the measurement point position recorded by the CNC system and the actual contact position between the probe and the workpiece (i.e., pre-stroke) accounts for over 60% of the total error in in-situ detection. Compensation is an effective means to reduce the impact of probe pre-stroke on in-situ detection accuracy, and the accuracy of the probe pre-stroke measurement calibration value is the determining factor for the level of compensation accuracy.

[0005] Typically, three-dimensional trigger probes can be triggered in any direction within the XY plane (radial) and the +Z direction (axial). Due to the structural characteristics of the probe's triggering mechanism, the probe's pre-travel is not consistent in different triggering directions. Therefore, accurate compensation should be performed specifically along each direction. The axial pre-travel of the probe differs significantly from the pre-travel along other directions, such as... Figure 3 As shown, measurements along the Z-axis (axial direction) of the probe are primarily used to determine the machining allowance and depth of cut of the workpiece. The measurement results directly determine the selection of the workpiece's cutting process parameters and the final machining accuracy. Therefore, the axial pre-travel of the probe must be accurately measured before measurement.

[0006] Currently, there are two methods for measuring the axial pre-travel of a probe: The first is the independent measurement method (hereinafter referred to as the independent method). The probe is mounted on a device equipped with motion control, contact state monitoring, trigger signal recognition, and displacement measurement capabilities to simulate the trigger measurement process of a trigger-type probe and measure its pre-travel. However, considering that the probe's pre-travel is affected by the measurement conditions, the measurement should not be independent of the machine tool's operating environment. The independent method's measurement results cannot accurately reflect the probe's pre-travel during measurement; furthermore, this method uses the moment the probe emits the trigger signal instead of the moment the CNC records the position coordinates during actual measurement as the calculation benchmark for the pre-travel, resulting in a principle error; thirdly, independent measurement equipment is expensive, cumbersome to operate, and has poor engineering adaptability. The second method is the radius of action method. When processing measurement results, it is usually necessary to compensate for the probe radius. Since the probe has a pre-travel, compensating based on the nominal radius of the probe ball during actual measurement is inaccurate. By measuring several points on the surface of a standard sphere and calculating the measuring radius of the standard sphere, the difference between this radius and the nominal radius of the standard sphere is the effective radius of the probe ball including the probe's pre-travel. This compensation method can reduce the impact of the pre-travel on the measurement results to some extent. The effective radius method uses the equivalent average of the pre-travel in each direction to replace the actual pre-travel, thus equalizing the error. However, the pre-travel of a trigger-type probe is not the same in each direction, and can even vary significantly. This idea of ​​compensating with average error is not suitable for axial measurements and is unlikely to effectively improve measurement accuracy. It is particularly important to note that when using a standard sphere as a calibration body, the probe and standard sphere are in point contact during calibration. Due to the friction angle between them, slippage is inevitable, leading to errors in the measurement point data and affecting the calibration accuracy. Furthermore, the more measurement points there are, the more random error components are present in the measurement data, and the larger the data fitting error becomes. Therefore, the number of measurement points should be minimized as much as possible. Summary of the Invention

[0007] The purpose of this invention is to provide a calibration device for the pre-stroke of the probe in the in-situ detection system of CNC machine tools, which solves the problem of low pre-stroke detection accuracy in the prior art.

[0008] Another objective of this invention is to provide a calibration method for the probe pre-stroke of a CNC machine tool in-situ detection system.

[0009] The first technical solution adopted in this invention is a calibration device for the pre-stroke of the probe in the in-situ detection system of a CNC machine tool, including a trigger probe. The trigger probe has a probe at its end, and a truncated triangular pyramid is set at the vertically corresponding position at the bottom of the probe. The top of the extension rod contacts and is fixed to the bottom of the truncated triangular pyramid. The bottom of the extension rod is fixed to the magnetic base. The side of the magnetic base is also provided with a limiting structure.

[0010] The first technical solution of the present invention is further characterized in that,

[0011] The extension rod has a waist-shaped through groove parallel to the length of the rod. The set screw passes through the waist-shaped through groove and is tightened into the screw hole on the magnetic meter base, thereby realizing the connection and fixation between the truncated triangular pyramid and the magnetic meter base.

[0012] The specific structure of the limiting structure is as follows: the vertical edge of the magnetic base, which is equipped with a set screw, is fixed with a vertical stop block and a horizontal stop block.

[0013] Both the standing and lying blocks are rectangular cubes and face the same direction. The standing and lying blocks are parallel to each other and perpendicular to the magnetic base.

[0014] The second technical solution adopted in this invention is a calibration method for the probe pre-stroke of a CNC machine tool in-situ detection system, which is implemented according to the following steps:

[0015] Step 1: Attach the truncated triangular pyramid to the CNC machine tool worktable using a magnetic base;

[0016] Step 2: Adjust the positions of the X-axis, Y-axis and Z-axis of the machine tool, position the probe on the trigger probe at a certain section of the truncated triangular pyramid, and record the Z-axis coordinate Z1 at this time;

[0017] Step 3: Keeping the Z-axis stationary, and moving the X and Y axes in tandem, touch six points evenly distributed along the three sides of the cross-section of the regular triangular pyramid (two points on each side), and record the position coordinates (X, Y, Z) of each measuring point. i Y i ), i = a, b, c, d, e, f, where a, b, c, d, e, f represent the names of the measuring points on the three sides of the measured section;

[0018] Step 4: Calculate the equations of the lines for the three sides of the measured cross-section using the coordinate values ​​obtained in Step 3. This yields the equations of the lines for the three sides of the equilateral triangle of the measured cross-section and the coordinates of the three vertices. The side length L of the measured cross-section is then obtained, as follows:

[0019] Let the equation of line DF be

[0020] y DF =K·x+B

[0021] Where K is the slope of the line, and B is the intercept of the line.

[0022] The coordinates (X) of measuring point a a Y a ) and the coordinates (X) of measuring point b b Y b Substituting these equations into the above formula yields the equation of line DF; similarly, substituting the coordinates (X, Y, F) of the measuring point f into the equation yields the equation of line DF. f Y f ) and the coordinates (X) of measuring point e.e Y e The equation of line DE is obtained; the coordinates (X, Y) of the measuring point d are given. d Y d ) and the coordinates (X) of measuring point c c Y c The equation of line EF is obtained.

[0023] Solve the system of equations for line DF and DE to obtain the coordinates (X, Y) of point D. D Y D Similarly, by solving the equations of line DE and line EF simultaneously, we can obtain the coordinates (X, Y) of point E. E Y E Solve the system of equations for line DF and EF simultaneously to obtain the coordinates (X, Y) of point F. F Y F According to the formula for the distance between two points, we get...

[0024]

[0025] Step 5: Combining the side length l of the top surface of the regular triangular pyramid and the dihedral angle α between the lateral surface and the base of the pyramid, obtain the theoretical distance Δh between the measured section and the top surface of the pyramid:

[0026]

[0027] Step 6: Move the trigger probe upward along the Z-axis so that the trigger probe probe is higher than the truncated triangular pyramid.

[0028] Step 7: Interpolate the X and Y axes together to position the probe of the trigger probe directly above the top surface of the truncated triangular pyramid.

[0029] Step 8: The CNC machine tool drives the trigger probe to move downward along the Z-axis to touch any point on the top surface of the regular triangular pyramid frustum, and records the Z-axis coordinate Z2 when it is triggered;

[0030] Step 9: Combining the theoretical distance Δh between the measured section and the top surface of the frustum obtained in Step 5, and the Z-axis coordinate Z1 of the frustum surface obtained in Step 2, the axial pre-stroke τ of the trigger probe is obtained.

[0031] τ=△h-[(z2-r)-(z1+r·cosα)]

[0032] In the formula, r is the radius of the probe sphere, and α is the dihedral angle between the lateral surface and the base of the regular triangular pyramid;

[0033] After the measurement is completed, remove the measuring device.

[0034] The beneficial effects of this invention are as follows: 1. This invention calculates the side length of the measured section by touching six measuring points evenly distributed along three sides on any cross-section parallel to the bottom surface of a regular triangular pyramid, thereby obtaining the theoretical distance between the measured section and the top surface of the regular triangular pyramid; the difference between this theoretical distance and the actual measured value between the top surface of the regular triangular pyramid and the measured section is the axial pre-travel of the probe, which is used to compensate and correct the in-situ measurement results, reducing the impact of the pre-travel on measurement accuracy and improving the integrated in-situ detection measurement accuracy. 2. This invention corrects the in-situ detection results based on the measurement calibration results, avoiding measurement errors caused by the difference between the measuring point position touched by the probe and the measuring point position recorded by the CNC system; it also avoids the errors caused by substituting the average value of the pre-travel in various directions of the probe for the actual axial pre-travel in existing methods, thus improving measurement accuracy. 3. The method of this invention measures the pre-travel of the trigger-type probe under actual in-situ detection conditions of a CNC machine tool, and the results truly reflect the pre-travel characteristics of the probe during the measurement process, which can effectively improve measurement accuracy. Furthermore, using a regular triangular pyramid frustum as the measuring instrument requires no other equipment, resulting in low operating costs and ease of operation. 4. Point-by-point measurement is performed using a trigger-type probe, with the measured data serving as the basis for calculating the measurement results. The accuracy of the measured data determines the accuracy of the measurement results. The number of measuring points affects both measurement efficiency and final measurement accuracy. As analyzed above, due to the pre-stroke characteristic of the trigger-type probe, the measured data contains random errors; the more measuring points, the greater the random error, and the lower the final measurement accuracy. Simultaneously, if a standard ball is used to calibrate the probe, the probe and the standard ball are in point contact, and due to the friction angle, slippage can easily occur, leading to deviations between the actual measured data and theoretical data, thus reducing measurement accuracy. This invention only requires collecting two measuring points on each side of the triangular pyramid frustum cross-section, significantly reducing the number of measuring points. Meanwhile, the contact of the probe pre-calibration body is a point-to-line contact, and the measurement path and measurement point position are designed with the friction angle as a constraint, which greatly avoids the measurement point error caused by the measurement point slippage phenomenon and can effectively ensure the accuracy of the pre-stroke calibration measurement process. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the basic structure of a trigger-type probe;

[0036] Figure 2 This is a timing diagram of the trigger-type probe's contact testing operation;

[0037] Figure 3 This is a schematic diagram of a CNC machine tool equipped with a trigger probe;

[0038] Figure 4 This is a schematic diagram illustrating the measurement principle of the trigger-type probe axial pre-stroke measurement method of the present invention;

[0039] Figure 5(a) is a schematic diagram of the measuring device for the trigger-type probe axial pre-stroke measurement method of the present invention;

[0040] Figure 5(b) is a schematic diagram of the measuring device of the trigger-type probe axial pre-stroke measurement method of the present invention from another perspective. Figure 5(b) is the left view of Figure 5(a).

[0041] Figure 6 This is a detailed enlarged view of the neutral position stop 7 and the horizontal position stop 9 of the calibration device for the probe pre-stroke of the CNC machine tool in-situ detection system of the present invention;

[0042] Figure 7 This is a measurement schematic diagram of Embodiment 2 of the present invention.

[0043] In the diagram, 1. Probe; 2. Trigger probe; 3. Regular triangular pyramid frustum; 4. CNC machine tool worktable; 5. Extension rod; 6. Magnetic base; 7. Vertical stop; 8. Set screw; 9. Horizontal stop. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0045] The calibration device for the probe pre-stroke of the CNC machine tool in-situ detection system of the present invention is described in the following document: Figure 1 , Figure 3 As shown in Figures 5(a) and 5(b), the device includes a trigger probe 2, with a probe 1 at the end of the trigger probe 2. A truncated triangular pyramid 3 is provided at the vertically corresponding position at the bottom of the probe 1. The top of the extension rod 5 contacts and is fixed to the bottom of the truncated triangular pyramid 3. The bottom of the extension rod 5 is fixed to the magnetic base 6. A limit structure is also provided on the side of the magnetic base 6.

[0046] The extension rod 5 has a waist-shaped through groove parallel to the length of the rod. The set screw 8 passes through the waist-shaped through groove and is tightened into the screw hole on the magnetic meter base 6, thereby realizing the connection and fixation between the regular triangular pyramid 3 and the magnetic meter base 6.

[0047] The specific structure of the limiting structure is as follows: the magnetic base 6 is equipped with a set screw 8, and the vertical edge is fixed with a vertical stop block 7 and a horizontal stop block 9.

[0048] Both the upright stop 7 and the horizontal stop 9 are rectangular cubes and face the same direction. The upright stop 7 and the horizontal stop 9 are parallel to each other and perpendicular to the magnetic base 6. For example... Figure 6As shown, the plane ghij on the upright stop 7 and the plane klmn on the horizontal stop 9 are perpendicular to each other. This structure allows for positioning of the truncated triangular pyramid in both upright and horizontal positions. When adjusting the orientation of the truncated triangular pyramid 3, loosen the set nut 8 and rotate the truncated triangular pyramid 3 and the extension rod 5 connected together around the axis of the set nut 8. When the side wall of the extension rod 5 contacts the plane ghij on the upright stop 7, tighten the set nut 8; this is the upright installation position. If the extension rod 5 is rotated around the axis of the set nut 8 until its side wall contacts the plane klmn on the horizontal stop 9, tighten the set nut 8; this is the horizontal installation position. Figure 6 This is a measurement schematic diagram of Embodiment 2 of the present invention. The thin dashed line represents the cross-section and path measured by the probe, and the dotted line represents the probe's path when touching the top surface of the truncated triangular pyramid after measuring the cross-section. During measurement calibration, first, the truncated triangular pyramid is reliably installed at the top of the extension rod 5, ensuring that the bottom surface of the truncated triangular pyramid is perpendicular to the axis of the extension rod; loosen the set screw 8, adjust the angle of the extension rod 5 according to the posture of the probe to be calibrated, and tighten the set screw 8 after accurate positioning; finally, attach the entire device to a suitable position on the CNC machine tool worktable 4 to begin measurement calibration.

[0049] The calibration method for the probe pre-stroke of the CNC machine tool in-situ testing system shall be implemented according to the following steps:

[0050] Step 1: Attach the truncated triangular pyramid 3 to the CNC machine tool worktable 4 using the magnetic base 6;

[0051] Step 2: Adjust the positions of the X-axis, Y-axis and Z-axis of the machine tool, position the probe 1 on the trigger probe 2 at a certain section of the regular triangular pyramid 3, and record the Z-axis coordinate Z1 at this time;

[0052] Step 3: Keeping the Z-axis stationary, and moving the X and Y axes in tandem, touch six points evenly distributed along the three sides of the cross-section to be measured on the regular triangular pyramid 3, i.e., two points on each side, and record the position coordinates (X, Y, Z) of each measuring point. i Y i ), i = a, b, c, d, e, f, where a, b, c, d, e, f represent the names of the measuring points on the three sides of the measured section;

[0053] Step 4: Calculate the equations of the lines for the three sides of the measured cross section using the coordinate values ​​obtained in Step 3. This yields the equations of the lines for the three sides of the equilateral triangle of the measured cross section and the coordinates of the three vertices. The side length L of the measured cross section is then obtained, as detailed below:

[0054] Let the equation of line DF be

[0055] y DF =K·x+B

[0056] Where K is the slope of the line, and B is the intercept of the line.

[0057] The coordinates (X) of measuring point a a Y a ) and the coordinates (X) of measuring point b b Y b Substituting these equations into the above formula yields the equation of line DF; similarly, substituting the coordinates (X, Y, F) of the measuring point f into the equation yields the equation of line DF. f Y f ) and the coordinates (X) of measuring point e. e Y e The equation of line DE is obtained; the coordinates (X, Y) of the measuring point d are given. d Y d ) and the coordinates (X) of measuring point c c Y c The equation of line EF is obtained.

[0058] Solve the system of equations for line DF and DE to obtain the coordinates (X, Y) of point D. D Y D Similarly, by solving the equations of line DE and line EF simultaneously, we can obtain the coordinates (X, Y) of point E. E Y E Solve the system of equations for line DF and EF simultaneously to obtain the coordinates (X, Y) of point F. F Y F According to the formula for the distance between two points, we get...

[0059]

[0060] Step 5: Combining the side length l of the top surface of the regular triangular pyramid and the dihedral angle α between the lateral surface and the base of the pyramid, obtain the theoretical distance Δh between the measured section and the top surface of the pyramid:

[0061]

[0062] Step 6: Move the trigger probe upward along the Z-axis so that the trigger probe probe is higher than the truncated triangular pyramid.

[0063] Step 7: X-axis and Y-axis interpolation are linked to position the probe 1 of the trigger probe 2 directly above the top surface of the truncated triangular pyramid.

[0064] Step 8: The CNC machine tool drives the trigger probe 2 to move downward along the Z-axis to touch any point on the top surface of the regular triangular pyramid frustum, and records the Z-axis coordinate Z2 when it is triggered;

[0065] Step 9: Combining the theoretical distance Δh between the measured section and the top surface of the frustum obtained in Step 5, and the Z-axis coordinate Z1 of the frustum surface obtained in Step 2, the axial pre-stroke τ of the trigger probe is obtained.

[0066] τ=△h-[(z2-r)-(z1+r·cosα)]

[0067] In the formula, r is the radius of the probe sphere, and α is the dihedral angle between the lateral surface and the base of the regular triangular pyramid;

[0068] After the measurement is completed, remove the measuring device.

[0069] The method for measuring the pre-travel (axial) of a trigger-type probe uses a truncated triangular pyramid as the measuring instrument. (See [link to documentation]). Figure 3 , Figure 4 Figure 5 Figure 6 The principle is that the distance Δh between any cross-section and the top surface of a regular triangular pyramid can be determined by the side length of the cross-section, the side length of the top surface, and the dihedral angle between the lateral surface and the base of the regular triangular pyramid. Six points evenly distributed along the circumference are touched on a cross-section of the regular triangular pyramid, and the coordinate values ​​of each point are linearly fitted to obtain the side length of the measured cross-section. Then, the distance between the measured cross-section and the top surface of the regular triangular pyramid is measured. Finally, considering the influence of the probe radius on the measurement results, the pre-stroke (axial) of the trigger probe is:

[0070] τ=△h-[(z2-r)-(z1+r·cosα)]

[0071] In the formula, r is the radius of the probe measuring ball, α is the dihedral angle between the side and the base of the regular triangular pyramid, Z2 is the Z-axis position coordinate corresponding to the top surface of the regular triangular pyramid, Z1 is the Z-axis position coordinate corresponding to the measured section, and Δh is the theoretical distance between the measured section and the top surface of the frustum.

[0072] After the measurement is completed, remove the measuring device.

[0073] Example 1

[0074] This embodiment measures the axial pre-travel of a Renishaw LP2 trigger probe. It is mounted vertically. Figure 3 On the CNC machine tool shown, the probe axis is the Z-axis of the CNC machine tool.

[0075] Clean the surfaces of the regular triangular pyramid frustum and the probe, attach the measuring device to a suitable position on the CNC machine tool worktable 4, ensuring it is within the working stroke of the trigger probe 2 in all directions; complete the touch test on a certain section of the regular triangular pyramid frustum and record the coordinates of each measuring point; calculate the lengths of the three sides of the measured section; under the control of the NC program, measure the distance between the measured section and the top surface of the regular triangular pyramid frustum; finally, calculate the axial pre-stroke of the probe.

[0076] Comparison of experimental results

[0077] The measurement results using the calibration method of this invention and the measurement results using the radius of action method are shown in Table 1 below.

[0078] Table 1 Axial pre-travel for different measurement methods

[0079]

[0080] A comparison reveals that the pre-travel obtained by the radius-of-action method is greater than that obtained by the method of this invention. Since the radial pre-travel of the probe is greater than the pre-travel when triggered axially, the radius-of-action method, which employs the error averaging approach, will cause the axial pre-travel measurement value to be affected by the pre-travel in other directions, resulting in a significant error. Experiments show that using this as the pre-travel compensation value will affect the in-situ detection accuracy. According to relevant literature, when measuring the same type of probe as in this example using the independent device method, the axial pre-travel is approximately 0.002 mm, far smaller than the result obtained by this method. This is because the independent device method makes the probe measurement independent of its operating conditions, and it uses the moment the probe emits the trigger signal instead of the moment the CNC records the position coordinates during actual measurement as the calculation benchmark for the pre-travel. This means the measurement result cannot reflect the true situation of the probe pre-travel during measurement and is not suitable for on-site compensation of the pre-travel of trigger-type probes.

[0081] Example 2

[0082] See Figure 7 The probe is mounted horizontally, with its axis aligned with the X-axis of the CNC machine tool.

[0083] First, loosen the set screw 8, rotate the truncated triangular pyramid 90° around the axis of the set screw, and make the extension rod contact the horizontal position stop 9. After it is in place, tighten the fastening screw 8 and attach it to the appropriate position on the machine tool worktable to ensure that it is within the travel range of the trigger probe 2 in all directions.

[0084] Then, control the movement of each axis of the machine tool, position the trigger probe at the cross section of the truncated triangular pyramid, and perform a trial touch test, recording the X-axis coordinate X1 at the time of triggering. Figure 7 (The position indicated by the thin dashed line);

[0085] By interpolating along the Z and Y axes, six evenly distributed points (two points on each side of the cross section) are measured, and the position coordinates of each point (Z-axis and Y-axis) are recorded. i Y i );

[0086] The obtained coordinate values ​​are fitted and calculated to obtain the straight line equations and vertex coordinates of the three sides of the measured cross section, and finally the side length L of the cross section is calculated.

[0087] Adjust the axes of the machine tool so that the probe is moved away from the truncated triangular pyramid in the X direction;

[0088] The probe is positioned within the top surface area of ​​the frustum by interpolation along the Z and Y axes.

[0089] The X-axis is used to touch the vertex of a regular triangular pyramid, and the X-axis coordinate X2 is recorded when the probe is triggered.

[0090] Data processing: Based on the obtained X-coordinate X1 of the measured section, the side length L of the measured section, and the X-coordinate X2 of the top surface of the frustum, the pre-stroke (axial) of the probe is calculated according to the axial pre-stroke calculation formula of the trigger probe given by the method of this invention.

[0091] After the measurement is completed, remove the measuring tool and fill in the calculated probe pre-stroke into the compensation table of the in-situ detection data processing software.

Claims

1. A calibration method for a pre-travel of a probe of an in-situ detection system of a numerical control machine tool, characterized in that, The application discloses a calibration device for a pre-stroke of a probe of an in-situ detection system of a numerical control machine tool. Step 1: the right triangular pyramid table (3) is adsorbed on the numerical control machine tool workbench (4) through the magnetic table seat (6); i=a, b, c, d, e, Step 3, keep Z axis fixed, X axis and Y axis linkage, touch 6 points on the measured section of the positive triangular prism table (3) which are evenly distributed on the three edges, i.e. 2 points on each edge, and record the position coordinates of each measuring point X i , Y i ), a, b, c, d, e, f f wherein, Supposing that the equation of the straight line DF is indicates the name of each measuring point on the three edges of the measured section; Step 4, the straight line equation of the three edges of the measured section is calculated respectively according to the series of coordinate values obtained in step 3, the straight line equation of the three edges of the measured section and the three vertex coordinates of the equilateral triangle are obtained, and then the edge length of the measured section is obtained L , as follows: Step 6: the trigger probe is moved upwards along the Z axis, so that the trigger probe is higher than the right triangular pyramid table; wherein K is the slope of the straight line and B is the intercept of the straight line, The coordinates of the measuring points a , X a , Y a , and the coordinates of the measuring point b X b , Y b are brought into the above equation, i.e. the equation of the straight line DF is obtained; in the same way, the coordinates of the measuring points f , X f , Y f and the coordinates of the measuring point e X e , Y e are brought into the equation, i.e. the equation of the straight line DE is obtained; the coordinates of the measuring point d X d , Y d and the coordinates of the measuring point c X c , Y c are brought into the equation, i.e. the equation of the straight line EF is obtained; Solving the equations of straight lines DF and DE simultaneously gives the coordinates of point D X D , Y D ) Similarly, solving the equations of straight lines DE and EF simultaneously gives the coordinates of point E X E , Y E ) Solving the equations of straight lines DF and EF simultaneously gives the coordinates of point F X F , Y F ) and the distance between the two points is given by Step 5, combine the top face edge length of the right triangular frustum l and the dihedral angle of the right triangular frustum side face and the bottom face α to get the theoretical distance between the measured cross section and the frustum top face h : Step 7: the X axis and the Y axis are interlocked to position the probe (1) of the trigger probe (2) directly above the top surface of the right triangular pyramid table; After the measurement is completed, the measurement device is removed. Step 8, the numerical control machine drives the trigger probe (2) to move downward along the Z axis to touch any point on the top surface of the right triangular prism table, and record the Z axis coordinate when the trigger is triggered Z 2; Step 9, combine the measured section obtained in step 5 with the theoretical distance between the top surface of the cone and the measured section h Step 2, the Z axis coordinate of the cone surface obtained in step 2 Z 1, obtain the axial pre-travel of the trigger probe , wherein r R is the radius of the probe ball, α is the dihedral angle between the side and the base of the regular triangular pyramid. The lengthening rod (5) is provided with a waist-shaped through groove parallel to the length direction of the rod, and a close screw (8) is screwed into a screw hole in the magnetic table seat (6) through the waist-shaped through groove, so that the right triangular pyramid table (3) and the magnetic table seat (6) are connected and fixed.

2. The method of claim 1, wherein, The vertical block (7) and the horizontal block (9) are both long cuboid shapes and are consistent in direction, and the vertical block (7) and the horizontal block (9) are parallel to each other and perpendicular to the magnetic table seat (6).

3. The method of calibrating the pre-travel of the probe of an in-situ detection system of a CNC machine tool according to claim 2, characterized in that, ​ 4. The method of claim 3, wherein the method further comprises: ​

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