A space omnidirectional calibration compensation method based on mechanical trigger probe pre-travel error characteristics

Abstract

This invention discloses a spatial omnidirectional calibration compensation method based on the pre-stroke error characteristics of a trigger-type probe, belonging to the field of machine tool in-machine measurement and error compensation. The trigger-type probe pre-stroke error compensation method of this invention, during the calibration work before actual machining and in-machine measurement, establishes a comprehensive pre-stroke error model based on the periodic variation characteristics of the pre-stroke error caused by the distribution of the mechanical sensing structure inside the trigger-type probe, combined with the transmission signal hysteresis and the deflection deformation effect of the probe. It then uses the actual coordinate points obtained from the three-dimensional spatial planning of the calibration measurement points of a high-precision spherical element and the joint analysis of differential dynamics to effectively identify the model parameters. Based on this model, it compensates for the pre-stroke error of each measurement point coordinate during the actual in-machine measurement process, thereby improving the effectiveness of the in-machine measurement results.

Description

Technical Field

[0001] This invention relates to in-machine measurement technology and probe error compensation technology in geometric measurement, specifically a trigger-type probe pre-stroke error compensation method based on the mechanism of probe pre-stroke error generation. Background Technology

[0002] In-machine measurement technology, including integrated touch probes and quick interface functions, integrates measurement sensors with machining equipment such as CNC machine tools. The feed mechanism drives the measurement system to perform precise and controllable movements, enabling efficient measurement of the object being measured. This allows measurement to be integrated into the production process. With in-machine measurement technology, workpieces can be measured and processed in a single setup, avoiding repeated positioning errors, improving workpiece yield, and reducing time costs.

[0003] Mechanically triggered probes remain the most widely used type of probe in machine measurement due to their advantages such as simple structure, low manufacturing cost, and high triggering accuracy. Among these probe structures, three-point motion sensors are commonly used in CNC machine tools and coordinate measuring machines. In this type of sensor, a moving element with three arms is spring-loaded onto three support points. Each of these support points is a break in the circuit. When the stylus connected to the moving element tilts or moves, the circuit opens, generating a signal. Probes using three-point motion sensors exhibit a relatively large triangular characteristic error.

[0004] In the error calibration and compensation process of trigger-type probes, there is an unavoidable type of error caused by its own structure or the measurement process—pre-travel error. Due to the hysteresis effect, the probe will continue to move before receiving the trigger signal. Moreover, after the machine receives the trigger signal, it needs a response time to stop the probe's movement and record the probe coordinates. This actual distance between the actual and measured coordinates is different in different measurement directions and is affected by a variety of factors.

[0005] In the aforementioned pre-stroke error measurement and compensation process, factors inherent in the measurement and calibration process of the trigger probe itself are considered, such as measurement speed, gravity, and the probe's own structure. However, microscopic factors such as friction within the probe's internal structure are difficult to express directly. Furthermore, signal hysteresis and stylus deflection significantly impact the pre-stroke error. Errors caused by the mechanically triggered probe itself are typically difficult to correlate with the macroscopic contact force vector of the measuring ball. Therefore, a methodological breakthrough is needed to construct a comprehensive pre-stroke error model with a mathematical expression. In practical pre-stroke error calibration, scalars are commonly used to compensate for the effective radius of a single measuring ball to offset the influence of the probe's pre-stroke error during measurement. However, due to the three-dimensional nature of in-machine measurement, the pre-stroke error cannot be simply and specifically compensated by scalars; a comprehensive pre-stroke error compensation method in all directions is required. Summary of the Invention

[0006] The purpose of this invention is to provide a pre-stroke error calibration and compensation method for mechanically triggered probes used in on-machine measurement of multi-axis machine tools. By combining signal hysteresis effect, error periodicity characteristics and probe deflection deformation effect, this method provides a more comprehensive description of the pre-stroke error, offering a three-dimensional omnidirectional error compensation method. This improves the compensation accuracy and enhances the on-machine measurement accuracy of the machined workpiece surface.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A spatial omnidirectional calibration compensation method based on the pre-stroke error characteristics of a mechanical trigger probe includes sensor structure analysis of the mechanical trigger probe and description of the influencing factors and periodic characteristics of the pre-stroke error. The three-dimensional lobe periodic effect of the pre-stroke error is extended to the on-machine measurement omnidirectional error compensation steps of actual machine tool workpieces. This method is characterized by the following steps:

[0009] Step 1.1: Based on the external contact force transmission process of the mechanical trigger probe, establish the trigger signal conditions of the internal structure contact point, and use differential equations to solve for the signal hysteresis pre-stroke error caused by the transmission of micro forces and torques inside the probe.

[0010] Step 1.2: Based on the internal symmetrical structure of the mechanical trigger probe, Fourier series is used to describe the periodic characteristics of the pre-stroke error. Combined with the probe deflection and bending effect, a macroscopic pre-stroke error model is established.

[0011] Step 1.3: Through high-precision calibration of the surface point planning and measurement of the spherical element, based on the actual data points and the integral solution process, the comprehensive pre-stroke error model is jointly identified, and the model compensation value is assigned to the directional vectors of the measured point to obtain the three-dimensional comprehensive pre-stroke error compensation result of the measured surface measurement point in the actual on-machine measurement.

[0012] The triggering conditions for establishing the internal structure contact point triggering signal include static analysis of the external probe structure and the internal mechanical structure, and the torque balance condition is used to determine the critical condition for disconnection of the internal contact. The actual triggering force signal at the internal contact is obtained based on the transmission of the contact force vector on the end probe ball through the probe finite element. A pre-stroke error model caused by the signal hysteresis time during the triggering force of the probe reaching the triggering critical process is constructed. A Fourier series model with 3n as the fundamental frequency is constructed based on the triangular symmetric distribution of the internal mechanical structure of the mechanical trigger probe. A pre-stroke error model under the influence of probe deflection is constructed based on the probe distribution and the connection of the probe to the internal mechanical structure. The parameters to be identified in the Fourier series periodic model are determined by calibration tests of a high-precision spherical element based on the model. A comprehensive pre-stroke error compensation model is obtained by solving the signal hysteresis pre-stroke error model through actual calibration points and integration. The three-dimensional pre-stroke error compensation value of the measured workpiece surface point under the actual on-machine measurement posture is determined based on the model.

[0013] The external contact force transmission process of the mechanical trigger probe includes the contact force between the end probe ball and the surface of the workpiece being measured, and the transmission of this force through the finite element stress wave inside the probe. The trigger force characteristics at the internal mechanical structure contact point are obtained as the transmission endpoint. The influence of the transmitted contact force will cause displacement of three pairs of internal contact points. The trigger force allocated to each contact point is calculated separately according to the actual measurement posture, and the contact point most prone to displacement under the trigger force vector at the current moment is obtained as the analysis object at the current measurement point.

[0014] The established trigger signal generation conditions include the change in the balance torque at the internal contact point caused by the probe deflection deformation effect after macroscopic static analysis under the influence of external contact force. Under the trigger threshold set by the probe, the breaking critical point of this balance torque serves as the basis for the intermittent electrical signal change at the contact point, thus triggering the generation of the trigger signal. The transmission of the micro-stress wave inside the probe is solved based on the differential equation caused by velocity and angular velocity between finite elements. The obtained signal hysteresis pre-travel error includes: the distance the probe travels at the contact speed during the transmission time from the contact ball contact through the probe stress wave to the internal contact point, and the distance the probe travels from zero to the time when the contact force is transmitted to each internal contact point and the signal generation condition is broken.

[0015] The internal structure of the mechanical trigger probe is simplified to three pairs of double-contact structures consisting of two rigid support balls and a cylindrical support rod. These three pairs of ball-rod structures are symmetrically distributed at 120°. Based on the actual measurement posture and the installation posture of the probe, trigger force vectors are distributed at six contact points through conduction. When one or more of the contacts are disconnected, the electrical signal state inside the probe changes, and the moment of this change is taken as the moment when the trigger signal is generated.

[0016] The established Fourier series model is based on the third harmonic as its structural foundation, with the independent variable being the azimuth angle in the XY plane under the probe's local coordinate system. In this coordinate system, the X-axis is collinear with the probe, and the origin is the center point of the measuring ball. Based on the calibration test of the high-precision calibration ball surface measurement points, the identification conditions of the unknown parameters of this part of the model are obtained. Based on the actual coordinate points obtained from the calibration, the azimuth angle changes at the measuring points under the probe's local coordinate system and the machine tool's absolute coordinate system are obtained. Based on the relationship between the azimuth angle and the coordinate points, the Fourier series model is identified, and the complete periodic pre-stroke error under the current working condition is obtained.

[0017] The calibration test of the high-precision calibration ball surface measurement points includes the uniform distribution planning of measurement points on different latitude circles of the front end face of the ball and the uniform distribution planning of measurement points on different latitude circles of the upper end face; according to the displacement of the rotation axis and translation axis of the machine tool, the probe posture changes in linkage and the planned measurement points are uniformly measured.

[0018] The aforementioned probe deflection bending effect is based on the pitch angle obtained by the angle between the contact force vector in the local coordinate system of the probe and the YZ plane. According to the gravity and deflection deformation of the probe, the deflection deformation is decomposed in the vertical and horizontal planes to obtain the deflection changes in the two planes respectively. According to the change of the overall static state of the probe under deflection deformation, the force and torque balance conditions of the contact point are obtained, and the deflection is calculated by simplifying the probe into a cantilever beam structure.

[0019] The established comprehensive pre-stroke error model includes signal hysteresis error, Fourier series periodicity error, and probe deflection pre-stroke error. The joint identification method adopted includes a hybrid calculation of parameter optimization search and differential equation solution. After obtaining the complete comprehensive model, the compensation value obtained from the model is assigned to the three-dimensional omnidirectional measurement result based on the coordinate values ​​of the actual workpiece surface measurement point after subsequent processing and the actual pose of the probe, thus obtaining the compensated actual surface with high measurement accuracy. The method of assigning the model compensation value to the three-dimensional omnidirectional measurement result includes obtaining the pose azimuth and polar angle of the target measuring point in the probe's local coordinate system based on the orientation of the probe's local coordinate system in the machine tool's absolute coordinate system and the coordinate values ​​of each axis of the absolute coordinate system of the measured point. The compensation value is then decomposed through angle projection and assigned to the three-dimensional direction.

[0020] A method for compensating for the pre-stroke error of a mechanically triggered probe includes the following specific steps:

[0021] Step 10.1: Based on the external contact force transmission process of the mechanical trigger probe, establish the trigger signal conditions of the internal structural contact point, and solve for the signal hysteresis pre-stroke error caused by the transmission of micro-forces and torques inside the probe.

[0022] Step 10.2: Based on the internal symmetrical structure of the mechanical trigger probe, Fourier series is used to describe the periodic characteristics of the pre-stroke error. Combined with the probe deflection bending effect, a macroscopic pre-stroke error model is established.

[0023] Step 10.3: Through the calibration test of the high-precision calibrated spherical element, based on the actual data points and the integral solution method, the comprehensive pre-stroke error model is jointly identified, and the model compensation value is assigned to the directional vectors of the measured point to obtain the three-dimensional comprehensive pre-stroke error compensation result of the measured surface measurement point in the actual on-machine measurement.

[0024] A method for calibrating and compensating the pre-stroke error of a mechanically triggered probe used in on-machine measurement of multi-axis machine tools includes a hysteresis effect model of the pre-stroke error, a periodic characteristic model of the pre-stroke error caused by the internal symmetrical structure, and an analysis of the macroscopic probe deflection and bending effect. The compensation value of the comprehensive error model is extended to three dimensions in all directions to achieve specific pre-stroke error compensation. This method is characterized by the following steps:

[0025] Step 1.1: Based on the external contact force transmission process of the mechanical trigger probe, establish the trigger signal conditions of the internal structural contact point, and use differential equations to solve for the signal hysteresis pre-stroke error caused by the transmission of micro-forces and torques inside the probe.

[0026] Step 1.2: Based on the internal symmetrical structure of the mechanical trigger probe, Fourier series is used to describe the periodic characteristics of the pre-stroke error. Combined with the probe deflection bending effect, a macroscopic pre-stroke error model is established.

[0027] Step 1.3: Through high-precision calibration of the surface point planning and measurement of the spherical element, based on the actual data points and the integral solution process, the comprehensive pre-stroke error model is jointly identified, and the model compensation value is assigned to the directional vectors of the measured point to obtain the three-dimensional comprehensive pre-stroke error compensation result of the measured surface measurement point in the actual on-machine measurement.

[0028] The present invention is further characterized by:

[0029] Step 1.2 can be implemented in two steps:

[0030] Firstly, due to the macroscopic and global existence of the probe deflection bending effect, the probe is simplified as a cantilever beam for analysis. Based on the probe pose and measurement pose measured on the machine tool, in the established local coordinate system of the probe, the angle between the contact force vector of the probe ball and the vertical plane is used as the independent variable to analyze the force and torque at the contact point of the internal mechanical structure. The equation relationship of each lever arm can be obtained. In particular, the gravity of the probe is also included in the macroscopic force analysis. Based on the deflection formula of the cantilever beam, a deflection effect pre-stroke error model based on the effective lever arm of the contact force is established.

[0031] Then, by incorporating the periodic characteristic expression of the Fourier series error into the established deflection pre-stroke error model, and based on the calibration test of the uniform measuring points on the surface of the high-precision spherical element, the model parameters are identified, and a macroscopic pre-stroke error model is established.

[0032] Step 1.3 can also be implemented in the following way:

[0033] Since the signal hysteresis pre-stroke error model obtained in step 1.1 is constructed based on the stress wave propagation of the probe's finite element triggering force, it involves solving differential equations at each time step, which poses a significant computational obstacle to the parameter identification efficiency of the comprehensive model. The following alternative approach can be used: First, pre-solve the overall hysteresis model within a specified uniform time distribution, and compare and analyze the changing trend of the signal hysteresis. Then, when solving the differential units at all times, the values ​​solved by the differential units can be predicted based on this changing trend, obtaining solution values ​​that meet fidelity requirements. This avoids the massive computation caused by full differential solving, thereby improving the computational efficiency of parameter identification and obtaining model prediction results that are suitable for the actual calibration process.

[0034] Technical principle of the invention:

[0035] The pre-stroke error caused by the internal sensing mechanical structure of the mechanically triggered probe accounts for a large proportion of the total in-machine measurement error. At the same time, the 120° symmetrical distribution of the sensing structure makes this part of the pre-stroke error exhibit periodic variation. Combined with the probe's contact hysteresis effect and the probe deflection effect, this leads to changes in the actual triggering force and the actual contact point, which in turn causes the actual measurement point in the in-machine measurement to deviate from the theoretical measurement point, resulting in changes in the pre-stroke error. Considering a more specific error triggering principle can more comprehensively compensate for this, improve the in-machine measurement accuracy of the machine tool, and make the surface of the measured workpiece closer to the actual machined surface.

[0036] The beneficial effects of this invention are:

[0037] This invention provides a more detailed description of the probe's pre-stroke error and a precise compensation method for in-machine measurement from the perspective of machine tool error transmission. It enriches the in-machine measurement error compensation methods for probes, improves the calibration accuracy of probes, and ensures the measurement accuracy of probes when measuring workpieces during in-machine measurement.

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 A simplified schematic diagram of the internal structure of a mechanical trigger probe;

[0041] Figure 2 This is a schematic diagram of the interaction between differential finite element methods of the probe;

[0042] Figure 3 A schematic diagram of the front face planning for a high-precision ball-shaped marker.

[0043] Figure 4 The flowchart for the joint identification of final parameters of the comprehensive pre-travel error model;

[0044] Figure 5 A schematic diagram of the three-dimensional extended pre-stroke error compensation steps; Detailed Implementation

[0045] The present invention will now be described in further detail with reference to the accompanying drawings and formula models. All drawings are merely schematic illustrations of the basic method of the invention, and therefore only show the mechanical trigger probe sensing structure related to the invention and the probe pre-stroke error under the influence of external contact force. A calibration and compensation method for a mechanical trigger probe used in machine tool measurement includes compensation for the probe and pre-stroke error used in in-machine measurement. The compensation method mainly includes the influence of the signal hysteresis effect of the probe pre-stroke error, the internal periodic characteristics and the probe deflection deformation effect on the in-machine measurement accuracy, and model parameter identification and calibration. Its characteristic is that it is performed according to the following steps:

[0046] Step 1.1: Based on the external contact force transmission process of the mechanical trigger probe, establish the trigger signal conditions of the internal structural contact point, and use differential equations to solve for the signal hysteresis pre-stroke error caused by the transmission of micro-forces and torques inside the probe.

[0047] Step 1.2: Based on the internal symmetrical structure of the mechanical trigger probe, Fourier series is used to describe the periodic characteristics of the pre-stroke error. Combined with the probe deflection bending effect, a macroscopic pre-stroke error model is established.

[0048] Step 1.3: Through high-precision calibration of the surface point planning and measurement of the spherical element, based on the actual data points and the integral solution process, the comprehensive pre-stroke error model is jointly identified, and the model compensation value is assigned to the directional vectors of the measured point to obtain the three-dimensional comprehensive pre-stroke error compensation result of the measured surface measurement point in the actual on-machine measurement.

[0049] The present invention is further characterized by:

[0050] Step 1.2 can be implemented in two steps:

[0051] Firstly, due to the macroscopic and global existence of the probe deflection bending effect, the probe is simplified as a cantilever beam for analysis. Based on the probe pose and measurement pose measured on the machine tool, in the established local coordinate system of the probe, the angle between the contact force vector of the probe ball and the vertical plane is used as the independent variable to analyze the force and torque at the contact point of the internal mechanical structure. The equation relationship of each lever arm can be obtained. In particular, the gravity of the probe is also included in the macroscopic force analysis. Based on the deflection formula of the cantilever beam, a deflection effect pre-stroke error model based on the effective lever arm of the contact force is established.

[0052] Then, by incorporating the periodic characteristic expression of the Fourier series error into the established deflection pre-stroke error model, and based on the calibration test of the uniform measuring points on the surface of the high-precision spherical element, the model parameters are identified, and a macroscopic pre-stroke error model is established.

[0053] Step 1.3 can also be implemented in the following way:

[0054] Since the signal hysteresis pre-stroke error model obtained in step 1.1 is constructed based on the stress wave propagation of the probe's finite element triggering force, it involves solving differential equations at each time step, which poses a significant computational obstacle to the parameter identification efficiency of the comprehensive model. The following alternative approach can be used: First, pre-solve the overall hysteresis model within a specified uniform time distribution, and compare and analyze the changing trend of the signal hysteresis. Then, when solving the differential units at all times, the values ​​solved by the differential units can be predicted based on this changing trend, obtaining solution values ​​that meet fidelity requirements. This avoids the massive computation caused by full differential solving, thereby improving the computational efficiency of parameter identification and obtaining model prediction results that are suitable for the actual calibration process.

[0055] See Figure 1 , Figure 1 This is a simplified schematic diagram of the internal structure of a mechanical trigger probe. The deflection and bending effect of the probe stylus is analyzed as a cantilever beam. Taking the vertical plane as an example, the general deflection and bending formula used is: In the formula, P is the effective length between the measuring sphere and the contact point between the internal rigid support sphere and the support cylinder, EI is the equivalent bending stiffness of the probe, and F... TTo effectively measure the contact force, θ is the angle between the contact force and the YZ plane of the local coordinate system of the measuring ball. Figure 1 In the figure, η is the angle by which the probe deviates from the X-axis during measurement, G is the effective weight of the probe, and L is the effective weight of the probe. S Let r1 be the effective length of the probe, r1 be the effective radius of the sphere, and R be the effective radius of the high-precision spherical element. Static analysis of contact force and gravity is performed at all six internal contact points to obtain the expression for the effective length P. Finally, the pre-stroke error δ of the probe deflection deformation in the vertical and horizontal planes under the measurement posture can be calculated. F .

[0056] See Figure 2 , Figure 2 This is a schematic diagram of the interaction between differential finite element components of a trigger-type probe. Each finite element element in the diagram has two surfaces, α and β, where F and M represent the force and torque acting on the surfaces, respectively. The center point of these two surfaces is A. n and B n , where n represents the number of finite element subdivisions, and the contact force Q acting on the end sphere based on nonlinear Hertzian contact theory is... F As the starting point for stress wave transmission, physical transmission occurs between the units of the probe to the six contact points in the sensing structure. Based on the critical threshold value of the preload force of the spring inside the probe distributed to the symmetrical rigid contact points, when Q... F When the internal electrical signal changes due to the increase to the threshold, the time of this process is recorded, and the pre-travel error caused by the signal hysteresis effect is calculated by combining it with the actual touch speed.

[0057] See Figure 3 , Figure 3 This is a schematic diagram of the high-precision spherical calibration front face planning. The red dots in the diagram represent evenly distributed latitude measurement points on the end face. Besides the need for calibration tests on the front face with varying numbers of evenly distributed points at different latitudes, the same group of measurement points also needs to be measured on the upper end face. (The last part, "in Fourier series," appears to be a separate, unrelated sentence fragment and is left untranslated.) In the periodic pre-stroke characteristic description expression based on: a n b n These are the Fourier coefficients. Let be the azimuth angle of the external contact force (the angle of the contact force within the XY coordinate system of the probe), and N be the number of measuring points. The undetermined coefficients in this expression are identified through optimization using the coordinate data of the calibration points, thus yielding the periodic characteristic part δ of the pre-stroke error. m .

[0058] See Figure 4 , Figure 4This is the flowchart for the joint identification of the final parameters of the integrated pre-stroke error model. Since the signal hysteresis effect model is a differential dynamic model, it has an initial motion state vector Y(0). As the initial contact force of the measuring ball gradually increases from t=0, the transmission of stress wave in the measuring needle affects the state vector Y(t) of each unit. With the optimization of the step size and nested optimization, the complete integrated pre-stroke error model can be obtained.

[0059] See Figure 5 , Figure 5 A schematic diagram of the three-dimensional extended pre-stroke error compensation steps after obtaining the model compensation value is shown below. Figure 5 As shown: By utilizing the contact force vector angle between the measuring ball and the measured point, and the touch pose angle, the compensation value output by the model can be decomposed into three dimensions, and the three-dimensional trigger force normal vector n in the global coordinate system can be extracted. actual By using the actual trigger posture (θ, φ) as boundary conditions, the pre-stroke error compensation amount of the three-dimensional spatial probe in-machine measurement at each measuring point and its corresponding dynamic effective trigger radius R can be obtained. dyn Construct the physical contact point Q after three-dimensional compensation actual This can be expressed as: , where P actual To accurately measure the center position of the ball, pre-stroke error compensation is performed between the calibration process and the actual on-machine measurement process to improve detection accuracy.

[0060] Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0061] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A spatial omnidirectional calibration compensation method based on the pre-stroke error characteristics of a mechanically triggered probe, characterized in that, This includes the analysis of the sensing structure of the mechanical trigger probe and the description of the influencing factors and periodic characteristics of the pre-stroke error. The three-dimensional lobe periodic effect of the pre-stroke error is extended to the on-machine measurement omnidirectional error compensation process for actual machine tool workpieces. The method is characterized by the following steps: Step 1.1: Based on the external contact force transmission process of the mechanical trigger probe, establish the trigger signal conditions of the internal structure contact point, and use differential equations to solve for the signal hysteresis pre-stroke error caused by the transmission of micro forces and torques inside the probe. Step 1.2: Based on the internal symmetrical structure of the mechanical trigger probe, Fourier series is used to describe the periodic characteristics of the pre-stroke error. Combined with the probe deflection and bending effect, a macroscopic pre-stroke error model is established. Step 1.3: Through high-precision calibration of the surface point planning and measurement of the spherical element, based on the actual data points and the integral solution process, the comprehensive pre-stroke error model is jointly identified, and the model compensation value is assigned to the directional vectors of the measured point to obtain the three-dimensional comprehensive pre-stroke error compensation result of the measured surface measurement point in the actual on-machine measurement.

2. The spatial omnidirectional calibration compensation method based on the periodic characteristics of the pre-stroke error of a mechanical trigger probe according to claim 1, characterized in that, The triggering conditions for establishing the internal structure contact point triggering signal include static analysis of the external probe structure and the internal mechanical structure, and the torque balance condition is used to determine the critical condition for disconnection of the internal contact. The actual triggering force signal at the internal contact is obtained based on the transmission of the contact force vector on the end probe ball through the probe finite element. A pre-stroke error model caused by the signal hysteresis time during the triggering force of the probe reaching the triggering critical process is constructed. A Fourier series model with 3n as the fundamental frequency is constructed based on the triangular symmetric distribution of the internal mechanical structure of the mechanical trigger probe. A pre-stroke error model under the influence of probe deflection is constructed based on the probe distribution and the connection of the probe to the internal mechanical structure. The parameters to be identified in the Fourier series periodic model are determined by calibration tests of a high-precision spherical element based on the model. A comprehensive pre-stroke error compensation model is obtained by solving the signal hysteresis pre-stroke error model through actual calibration points and integration. The three-dimensional pre-stroke error compensation value of the measured workpiece surface point under the actual on-machine measurement posture is determined based on the model.

3. The spatial omnidirectional calibration compensation method based on the periodic characteristics of the pre-stroke error of a mechanical trigger probe according to claim 1, characterized in that, The external contact force transmission process of the mechanical trigger probe includes the contact force between the end probe ball and the surface of the workpiece being measured, and the process of the force being transmitted through the finite element stress wave inside the probe, obtaining the trigger force characteristics at the internal mechanical structure contact point as the transmission endpoint. The transmitted contact force will cause displacement of the three pairs of internal contact points. The trigger force allocated to each contact point is calculated separately according to the actual measured pose. The contact point most likely to be displaced under the trigger force vector at the current moment is obtained as the analysis object at the current measurement point.

4. The spatial omnidirectional calibration compensation method based on the periodic characteristics of the pre-stroke error of a mechanical trigger probe according to claim 1, characterized in that, The established trigger signal generation conditions include the change in the balance torque at the internal contact point caused by the probe deflection deformation effect after macroscopic static analysis under the influence of external contact force. Under the trigger threshold set by the probe, the breaking critical point of this balance torque serves as the basis for the intermittent electrical signal change at the contact point, thus triggering the generation of the trigger signal. The transmission of the micro-stress wave inside the probe is solved based on the differential equation caused by velocity and angular velocity between finite elements. The obtained signal hysteresis pre-travel error includes: the distance the probe travels at the contact speed during the transmission time from the contact ball contact through the probe stress wave to the internal contact point, and the distance the probe travels from zero to the time when the contact force is transmitted to each internal contact point and the signal generation condition is broken.

5. The spatial omnidirectional calibration compensation method based on the periodic characteristics of the pre-stroke error of a mechanically triggered probe according to claim 1, characterized in that, The internal structure of the mechanical trigger probe is simplified to three pairs of double-contact structures consisting of two rigid support balls and a cylindrical support rod. These three pairs of ball-rod structures are symmetrically distributed at 120°. Based on the actual measurement posture and the installation posture of the probe, trigger force vectors are distributed at six contact points through conduction. When one or more of the contacts are disconnected, the electrical signal state inside the probe changes, and the moment of this change is taken as the moment when the trigger signal is generated.

6. The spatial omnidirectional calibration compensation method based on the periodic characteristics of the pre-stroke error of a mechanically triggered probe according to claim 2, characterized in that, The established Fourier series model is based on the third harmonic as its structural foundation, with the independent variable being the azimuth angle in the XY plane under the probe's local coordinate system. In this coordinate system, the X-axis is collinear with the probe, and the origin is the center point of the measuring ball. Based on the calibration test of the high-precision calibration ball surface measurement points, the identification conditions of the unknown parameters of this part of the model are obtained. Based on the actual coordinate points obtained from the calibration, the azimuth angle changes at the measuring points under the probe's local coordinate system and the machine tool's absolute coordinate system are obtained. Based on the relationship between the azimuth angle and the coordinate points, the Fourier series model is identified, and the complete periodic pre-stroke error under the current working condition is obtained.

7. The spatial omnidirectional calibration compensation method based on the periodic characteristics of the pre-stroke error of a mechanical trigger probe according to claim 6, characterized in that, The calibration test of the high-precision calibration ball surface measurement points includes the uniform distribution planning of measurement points on different latitude circles of the front end face of the ball and the uniform distribution planning of measurement points on different latitude circles of the upper end face; according to the displacement of the rotation axis and translation axis of the machine tool, the probe posture changes in linkage and the planned measurement points are uniformly measured.

8. The spatial omnidirectional calibration compensation method based on the periodic characteristics of the pre-stroke error of a mechanical trigger probe according to claim 1, characterized in that, The aforementioned probe deflection bending effect is based on the pitch angle obtained by the angle between the contact force vector in the local coordinate system of the probe and the YZ plane. According to the gravity and deflection deformation of the probe, the deflection deformation is decomposed in the vertical and horizontal planes to obtain the deflection changes in the two planes respectively. According to the change of the overall static state of the probe under deflection deformation, the force and torque balance conditions of the contact point are obtained, and the deflection is calculated by simplifying the probe into a cantilever beam structure.

9. The spatial omnidirectional calibration compensation method based on the periodic characteristics of the pre-stroke error of a mechanical trigger probe according to claim 1, characterized in that, The established comprehensive pre-stroke error model includes signal hysteresis error, Fourier series periodicity error, and probe deflection pre-stroke error. The joint identification method adopted includes a hybrid calculation of parameter optimization search and differential equation solution. After obtaining the complete comprehensive model, the compensation value obtained from the model is assigned to the three-dimensional omnidirectional measurement result based on the coordinate values ​​of the actual workpiece surface measurement point after subsequent processing and the actual pose of the probe, thus obtaining the compensated actual surface with high measurement accuracy. The method of assigning the model compensation value to the three-dimensional omnidirectional measurement result includes obtaining the pose azimuth and polar angle of the target measuring point in the probe's local coordinate system based on the orientation of the probe's local coordinate system in the machine tool's absolute coordinate system and the coordinate values ​​of each axis of the absolute coordinate system of the measured point. The compensation value is then decomposed through angle projection and assigned to the three-dimensional direction.

10. A method for compensating for the pre-stroke error of a mechanically triggered probe, characterized in that, The specific steps include the following: Step 10.1: Based on the external contact force transmission process of the mechanical trigger probe, establish the trigger signal conditions of the internal structural contact point, and solve for the signal hysteresis pre-stroke error caused by the transmission of micro-forces and torques inside the probe. Step 10.2: Based on the internal symmetrical structure of the mechanical trigger probe, Fourier series is used to describe the periodic characteristics of the pre-stroke error. Combined with the probe deflection bending effect, a macroscopic pre-stroke error model is established. Step 10.3: Through the calibration test of the high-precision calibrated spherical element, based on the actual data points and the integral solution method, the comprehensive pre-stroke error model is jointly identified, and the model compensation value is assigned to the directional vectors of the measured point to obtain the three-dimensional comprehensive pre-stroke error compensation result of the measured surface measurement point in the actual on-machine measurement.

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