Method and system for measuring synchronous coaxial error of double five-axis box bottom mirror milling machine tool

Abstract

The application provides a kind of double five-axis box bottom mirror image milling machine tool synchronous coaxial error measurement method and system, comprising: step S1: five displacement sensors are used to measure the tool tip point and tool shaft direction error in synchronous motion simultaneously, and the kinematics model of double five-axis mirror image milling machine tool is established based on the theory of rotation quantity, the kinematics model is based on the unique synchronous coaxial constraint of double five-axis machine tool for measuring trajectory generation;Step S2: using the synchronous coaxial error direct measurement method based on tool shaft measurement, the measurement accuracy and efficiency of coaxial error are improved.The application establishes the synchronous coaxial error model of double five-axis box bottom mirror image milling machine tool based on the synchronous coaxial constraint, and directly evaluates the synchronous coaxial error of double five-axis box bottom mirror image milling machine tool.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of machinery and numerical control machine tools, in particular to a method and system for measuring synchronization coaxial error of a double five-axis box bottom mirror milling machine tool. BACKGROUND

[0002] The rocket tank bottom is the main structure of the launch vehicle, and is a key component affecting the stability of the whole rocket. The overall tank bottom has the characteristics of high size precision and high reliability compared to the currently widely used "block forming + welding" structure. However, the overall tank bottom has a large diameter-thickness ratio, which belongs to a large and ultra-thin part. The mirror milling processing method is currently the only feasible processing method. The mirror milling machine tool is composed of double five-axis machine tools. During processing, one side mills and the other side supports, and it is necessary to maintain relative mirror synchronization motion on both sides of the workpiece at all times. Due to its unique motion form, the absolute accuracy of the single five-axis system is very important, and the high-precision synchronous coaxial motion of the supporting side five-axis relative to the milling side is also important. The synchronization error is manifested as the position error of the tool tip point of the two machine tools, and the coaxial error is manifested as the direction error of the tool axis of the two sides, which directly affects the wall thickness processing precision of the tank bottom part. In order to improve the processing precision of the box bottom mirror milling machine tool, the present application applies for a method for measuring the synchronization coaxial error of a double five-axis box bottom mirror milling machine tool, which measures the synchronization coaxial error of the box bottom mirror milling machine tool to improve the motion precision of the box bottom mirror milling machine tool.

[0003] In the patent CN110539020A, a precision self-diagnosis method for a double five-axis mirror milling machine tool is disclosed. A three-coordinate measuring head, a ball bar instrument, and a line laser profiler are used to diagnose the geometric precision, the spatial profile precision, and the precision of the measurement and control sensor precision of the machine tool, respectively. The method realizes self-evaluation of the running health status of the machine tool. In this method, the quasi-static and dynamic precision of the machine tool itself is evaluated, and the synchronization coaxial precision of the mirror milling machine tool is not evaluated. In the patent CN108614520A, a five-axis structure error measurement method, system, and device for a mirror milling system are disclosed. Through the displacement measurement device integrated on the mirror milling processing head and the geometric motion model of the machine tool, the calculation and feedback compensation of dynamic error are realized, and the synchronization motion precision of the mirror milling machine tool is improved. However, the error model of the synchronization coaxial is not established, and the absolute precision of the five-axis structure is still improved to indirectly ensure the synchronization coaxial precision.

[0004] The existing precision of the box bottom mirror milling mainly focuses on the absolute precision of the single five-axis system, and lacks direct measurement means for the synchronization coaxial precision of the double five-axis. SUMMARY

[0005] In view of the defects in the prior art, the purpose of the present application is to provide a method and system for measuring the synchronization coaxial error of a double five-axis box bottom mirror milling machine tool.

[0006] The application provides a method for measuring synchronization coaxial error of a double five-axis mirror milling machine bed, comprising the following steps:

[0007] Step S1: five displacement sensors are used to measure the tool tip point and tool shaft direction error in synchronous motion, a forward kinematics model of the double five-axis mirror milling machine bed is established based on the screw theory, and the forward kinematics model is used for measuring trajectory generation based on the unique synchronous coaxial constraint of the double five-axis machine bed;

[0008] Step S2: a synchronous coaxial error direct measurement method based on tool shaft measurement is used to improve the measurement accuracy and efficiency of the coaxial error.

[0009] Preferably, in the step S1:

[0010] The forward kinematics model is established as follows:

[0011] Based on the screw theory, a transmission chain model is established, the system comprises a double swing head horizontal five-axis machine as a milling side and a double swing head horizontal five-axis machine bed as a support side, a reference coordinate system WCS of the machine bed is fixed on a bed of the machine bed, a tool coordinate system TCS is fixed at the end of the milling side and moves with the milling side, a support coordinate system SCS is fixed at the end of the support side and moves with the support side, the milling side, the support side and the synchronous coaxial motion chain are established based on the screw theory, and the formula is as follows:

[0012]

[0013] Wherein, [g bt ] and [g bs ] are motion chains from the tool coordinate system TCS and the support side coordinate system SCS to the reference coordinate system WCS, [g st ] is a motion chain from the tool coordinate system to the support side coordinate system, [g bt (0) and [g bs (0) are initial matrices of TCS and SCS relative to WCS; The screw is X1, Y1, Z1, C1 and A1, which represent the positions of the motion axes of the milling side, and X2, Y2, Z2, C2 and A2 represent the positions of the motion axes of the support side.

[0014] Preferably, the closed-loop motion chain from the milling side to the support side is used to establish the synchronous coaxial modeling, and the nominal synchronous motion matrix Q synchronous is expressed as:

[0015]

[0016] Wherein P st and O st represent 3x1 nominal position and angle matrices respectively; Q t0To mill the end initial position and tool axis direction of a five-axis machine tool on the side, Q st is a nominal synchronous motion matrix;

[0017]

[0018] wherein E TCP and E TAD respectively represent the tool tip point position and tool axis direction error in the process of synchronous coaxial motion, and respectively represent the actual position and angle matrix affected by multiple error sources such as geometry, temperature, servo, etc.

[0019] Preferably, in the step S2:

[0020] According to the theoretical motion trajectory, a numerical control measurement program is generated and imported into the numerical control system, the numerical control system runs the measurement program, and the measurement device records the measurement data in real time to obtain the actual tool position and tool axis direction (P a ,O a ) of the double five-axis machine tool; based on the double five-axis machine tool kinematic chain and the theoretical measurement trajectory, the nominal tool position and tool axis direction (P, O) are obtained, and the tip point position and tool axis direction error of the double five-axis machine tool are obtained based on the synchronous coaxial model;

[0021] Based on the double five-axis kinematic model, a simultaneous measurement method for the three degrees of freedom of the synchronous position error and the two degrees of freedom of the coaxial error in the process of synchronous coaxial motion of the double five-axis machine tool is proposed, the position deviation of the high-precision standard ball at the tool tip point is measured in real time by three spatial array displacement sensors, and the spatial three-coordinate error information of the center of the tool tip point center ball is obtained by a calibration algorithm; for the coaxial error, the spatial coordinates of the center of the standard ball at the tool axis point are measured simultaneously by another two displacement sensors; the difference between the measurement values of the tool tip point and the tool axis point reflects the influence of the angle error, and the coaxial error is calculated according to the position error of different ball center points.

[0022] Preferably, the coordinate system is calibrated:

[0023] Before measurement, the measurement coordinate system is calibrated to obtain the transformation matrix from the measurement coordinate system to the machine tool reference coordinate system, the rotation axis of the machine tool is placed at the zero position, the standard double ball rod is installed on the milling side spindle, the axis two-degree-of-freedom fine adjustment mechanism of the standard ball is adjusted by the dial gauge and the micrometer to ensure that the centers of the two standard balls are coaxial with the spindle axis, and the eddy current sensor array is installed at the initial position of the support side end through a fixed tool; the space position of the milling side end is moved, the two standard balls are kept in the measurement range of the sensor array, the positions of the five sensors are adjusted, the double balls are kept in the middle interval of the measurement range of the sensor, and the five displacement sensors are set as the zero positions;

[0024] Synchronous coaxial error measurement:

[0025] According to the theoretical motion trajectory, a numerical control measurement program is generated and imported into the numerical control system, the numerical control system runs the measurement program, the measuring device records the measurement data in real time, the actual tool position and tool axis direction of the double five-axis machine tool are obtained, the nominal tool position and tool axis direction (P, O) are obtained based on the double five-axis machine tool motion chain and the theoretical measurement trajectory, and the tip position and tool axis direction error of the double five-axis machine tool are obtained based on the synchronous coaxial model.

[0026] According to the present application, a double five-axis box bottom mirror milling machine tool synchronous coaxial error measurement system is provided, comprising:

[0027] Module M1: five displacement sensors are used to measure the tool tip point and tool axis direction error in synchronous motion, a forward kinematics model of the double five-axis mirror milling machine tool is established based on the screw theory, and the forward kinematics model is used for measurement trajectory generation based on the unique synchronous coaxial constraint of the double five-axis machine tool;

[0028] Module M2: a synchronous coaxial error direct measurement method based on tool axis measurement is used to improve the measurement accuracy and efficiency of the coaxial error.

[0029] Preferably, in the module M1:

[0030] Forward kinematics model establishment:

[0031] Based on the transmission chain modeling of the screw theory, the system includes a double swing head horizontal five-axis machine as a milling side and a double swing head horizontal five-axis machine as a support side, the reference coordinate system WCS of the machine tool is fixed on the bed of the machine tool, the end of the milling side is fixed with a tool coordinate system TCS which moves with the milling side, the end of the support side is fixed with a support coordinate system SCS which moves with the support side, the milling side, the support side and the synchronous coaxial motion chain are established based on the screw theory, and the formula is as follows:

[0032]

[0033] Wherein, [g bt ] and [g bs ] are the motion chains from the tool coordinate system TCS and the support side coordinate system SCS to the reference coordinate system WCS, [g st ] is the motion chain from the tool coordinate system to the support side coordinate system, [g bt (0)] and [g bs (0)] are the initial matrices of TCS and SCS relative to WCS; X1, Y1, Z1, C1, A1 represent the positions of each motion axis of the milling side, and X2, Y2, Z2, C2, A2 represent the positions of each motion axis of the support side.

[0034] Preferably, the synchronous coaxial modeling is established using a closed-loop kinematic chain from the milling side to the support side, the nominal synchronous motion matrix Q synchronous is expressed as:

[0035]

[0036] where P st and O st are 3x1 nominal position and orientation matrices, respectively; Q t0 is the end position and tool axis direction of the milling side five-axis machine tool, Q st is the nominal synchronous motion matrix;

[0037]

[0038] where E TCP and E TAD are the tool tip position and tool axis direction errors during the synchronous coaxial motion, respectively, and are the actual position and orientation matrices affected by multiple error sources such as geometry, temperature, servo, etc.

[0039] Preferably, in the module M2:

[0040] According to the theoretical motion trajectory, a numerical control measurement program is generated and imported into the numerical control system. The numerical control system runs the measurement program, and the measurement device records the measurement data in real time to obtain the actual tool position and tool axis direction (P a , O a ) of the double five-axis machine tool; based on the kinematic chain of the double five-axis machine tool and the theoretical measurement trajectory, the nominal tool position and tool axis direction (P, O) are obtained, and the tip position and tool axis direction errors of the double five-axis machine tool are obtained based on the synchronous coaxial model;

[0041] Based on the double five-axis kinematic model, a simultaneous measurement method for the three degrees of freedom synchronous position error and the two degrees of freedom coaxial error of the double five-axis machine tool during synchronous coaxial motion is proposed. The position deviation of the high-precision standard ball at the tool tip point is measured in real time by three spatial array displacement sensors, and the spatial three-coordinate error information of the center of the tool tip point ball is obtained through a calibration algorithm. For the coaxial error, the spatial coordinates of the center of the standard ball at the tool axis point are measured simultaneously by another two displacement sensors. The difference between the measurement values of the tool tip point and the tool axis point reflects the influence of the angle error, and the coaxial error is calculated according to the position error of different ball center points.

[0042] Preferably, the coordinate system is calibrated:

[0043] Before measurement, calibrate the measurement coordinate system to obtain the transformation matrix from the measurement coordinate system to the machine tool reference coordinate system, place the rotating shaft of the machine tool at the zero position, install the standard double ball bar on the milling side spindle, adjust the two-degree-of-freedom fine adjustment mechanism of the standard ball axis to ensure that the centers of the two standard balls are coaxial with the spindle axis, and install the eddy current sensor array at the initial position of the support side end through a fixing tool;

[0044] Synchronous coaxial error measurement:

[0045] According to the theoretical motion trajectory, a numerical control measurement program is generated and imported into the numerical control system, the numerical control system runs the measurement program, the measurement device records the measurement data in real time, the actual tool position and tool axis direction of the double five-axis machine tool are obtained, the nominal tool position and tool axis direction (P, O) are obtained based on the machine tool motion chain and the theoretical measurement trajectory of the double five-axis machine tool, and the tip position and tool axis direction error of the double five-axis machine tool are obtained based on the synchronous coaxial model.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] 1. The present application is a synchronous coaxial error measurement method for a double five-axis box bottom mirror milling machine tool, based on the unique motion form of the box bottom mirror milling, a synchronous coaxial error measurement model is established, and the precise measurement of the synchronous coaxial error of the double five-axis box bottom mirror milling machine tool is realized.

[0048] 2. The present application can measure the static and dynamic synchronous coaxial accuracy of the double five-axis machine tool without using multiple measurement methods.

[0049] 3. The present application establishes a synchronous coaxial error model for the double five-axis box bottom mirror milling machine tool based on the synchronous coaxial constraint, and directly evaluates the synchronous coaxial error of the double five-axis box bottom mirror milling machine tool. BRIEF DESCRIPTION OF DRAWINGS

[0050] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, with reference to the accompanying drawings:

[0051] Figure 1 Figure 1 is a schematic diagram of the transmission structure of the box bottom mirror milling machine tool;

[0052] Figure 2 Figure 4 is a schematic diagram of the synchronous coaxial error measurement device;

[0053] Figure 3 Figure 5 is a schematic diagram of the synchronous coaxial error of the mirror milling machine tool. DETAILED DESCRIPTION

[0054] The application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the application. These are within the scope of protection of the application.

[0055] Example 1

[0056] The application is to improve the wall thickness machining precision of the box bottom mirror milling machine tool. Based on the unique structure form of the box bottom mirror milling machine tool, the kinematic model of the box bottom mirror milling machine tool is established. Five high-precision displacement sensors are used to measure the tool tip point and tool shaft direction error in synchronous motion at the same time, so as to improve the synchronous coaxial precision of the box bottom mirror milling machine tool.

[0057] According to the application, a method for measuring the synchronous coaxial error of a double five-axis box bottom mirror milling machine tool is provided, which comprises:

[0058] Step S1: five displacement sensors are used to measure the tool tip point and tool shaft direction error in synchronous motion at the same time. A forward kinematics model of the double five-axis mirror milling machine tool is established based on the screw theory. The forward kinematics model is based on the unique synchronous coaxial constraint of the double five-axis machine tool for measuring trajectory generation.

[0059] Specifically, in the step S1:

[0060] Forward kinematics model establishment:

[0061] Based on the screw theory, the transmission chain modeling system includes a double swing head horizontal five-axis machine as a milling side and a double swing head horizontal five-axis machine as a supporting side. The reference coordinate system WCS of the machine tool is fixed on the bed of the machine tool. The tool coordinate system TCS is fixed at the end of the milling side and moves with the milling side. The supporting coordinate system SCS is fixed at the end of the supporting side and moves with the supporting side. The milling side, the supporting side and the synchronous coaxial motion chain are established based on the screw theory, and the formula is as follows:

[0062]

[0063] Where [g bt ] and [g bs ] are the motion chains from the tool coordinate system TCS and the supporting side coordinate system SCS to the reference coordinate system WCS, [g st ] is the motion chain from the tool coordinate system to the supporting side coordinate system, [g bt (0)] and [g bs (0)] are the initial matrices of TCS and SCS relative to WCS. For the rotation, X1, Y1, Z1, C1, A1 represent the position of each axis of motion on the milling side, and X2, Y2, Z2, C2, A2 represent the position of each axis of motion on the support side.

[0064] Specifically, the synchronous coaxial modeling is established using the closed-loop kinematic chain from the milling side to the support side, and the nominal synchronous motion matrix Q synchronous is expressed as:

[0065]

[0066] where P st and O st represent the 3x1 nominal position and angle matrix, respectively; Q t0 is the initial position and tool axis direction of the milling side five-axis machine tool, and Q st is the nominal synchronous motion matrix.

[0067]

[0068] where E TCP and E TAD represent the tool tip point position and tool axis direction error during synchronous coaxial motion, respectively, and represent the actual position and angle matrix affected by multiple error sources such as geometry, temperature, servo, etc.

[0069] Step S2: using the synchronous coaxial error direct measurement method based on tool axis measurement to improve the measurement accuracy and efficiency of coaxial error.

[0070] Specifically, in the step S2:

[0071] According to the theoretical motion trajectory, a numerical control measurement program is generated and imported into the numerical control system, the numerical control system runs the measurement program, and the measurement device records the measurement data in real time to obtain the actual tool position and tool axis direction (P a , O a ) of the double five-axis machine tool; based on the kinematic chain of the double five-axis machine tool and the theoretical measurement trajectory, the nominal tool position and tool axis direction (P, O) are obtained, and the tip point position and tool axis direction error of the double five-axis machine tool are obtained based on the synchronous coaxial model.

[0072] A simultaneous measurement method for 3-DOF synchronous position error and 2-DOF coaxial error of a double five-axis machine tool in a synchronous coaxial motion process is proposed based on a double five-axis kinematics model. The position deviation of a high-precision standard ball at a tool tip point is measured in real time by three spatial array displacement sensors, and the spatial three-coordinate error information of the ball center of the tool tip point is obtained through a calibration algorithm. For the coaxial error, the spatial coordinates of the ball center of a standard ball at a tool axis point are measured simultaneously by another two displacement sensors. The difference between the measurement values of the tool tip point and the tool axis point reflects the influence of the angle error, and the coaxial error is calculated according to the position error of different ball centers.

[0073] Specifically, coordinate system calibration:

[0074] Before measurement, the measurement coordinate system is calibrated to obtain the transformation matrix from the measurement coordinate system to the machine tool reference coordinate system. The rotation axis of the machine tool is set to zero position, the standard double ball bar is installed on the milling side spindle, the two-DOF fine adjustment mechanism of the standard ball axis is adjusted by the dial gauge and the micrometer to ensure that the ball centers of the two standard balls are coaxial with the spindle axis, and the eddy current sensor array is installed on the support side end in the initial position through a fixed tooling. The milling side end is moved to keep the two standard balls within the measurement range of the sensor array, and the positions of the five sensors are adjusted to keep the double balls within the middle interval of the measurement range of the sensors and set them as the zero positions of the five displacement sensors.

[0075] Synchronous coaxial error measurement:

[0076] A numerical control measurement program is generated according to the theoretical motion trajectory and is imported into the numerical control system. The numerical control system runs the measurement program, and the measurement device records the measurement data in real time to obtain the actual tool position and tool axis direction of the double five-axis machine tool. The nominal tool position and tool axis direction (P, O) are obtained based on the machine tool motion chain and the theoretical measurement trajectory of the double five-axis machine tool, and the tip point position and tool axis direction error of the double five-axis machine tool are obtained based on the synchronous coaxial model.

[0077] Embodiment 2:

[0078] Embodiment 2 is a preferred example of embodiment 1, which more specifically illustrates the present application.

[0079] The present application also provides a double five-axis box bottom mirror milling machine tool synchronous coaxial error measurement system, which can be realized by executing the flow steps of the double five-axis box bottom mirror milling machine tool synchronous coaxial error measurement method, i.e., the double five-axis box bottom mirror milling machine tool synchronous coaxial error measurement method can be understood as the preferred embodiment of the double five-axis box bottom mirror milling machine tool synchronous coaxial error measurement system by those skilled in the art.

[0080] According to the application, a synchronous coaxial error measurement system of a double five-axis mirror milling machine tool is provided, as shown in Figures 1-3 , comprising:

[0081] Module M1: five displacement sensors are used to measure the tool tip point and tool axis direction error in synchronous motion, a forward kinematics model of the double five-axis mirror milling machine tool is established based on the screw theory, and the forward kinematics model is based on the synchronous coaxial constraint unique to the double five-axis machine tool for trajectory generation;

[0082] Specifically, in the module M1:

[0083] Forward kinematics model establishment:

[0084] Based on the screw theory, the transmission chain modeling system includes a double swing head horizontal structure five-axis machine as a milling side and a double swing head structure horizontal five-axis machine tool as a support side, the reference coordinate system WCS of the machine tool is fixed on the bed of the machine tool, the end of the milling side is fixed with a tool coordinate system TCS which moves with the milling side, the end of the support side is fixed with a support coordinate system SCS which moves with the support side, the milling side, the support side and the synchronous coaxial motion chain are established based on the screw theory, and the formula is as follows:

[0085]

[0086] Where [g bt ] and [g bs ] are the motion chains from the tool coordinate system TCS and the support side coordinate system SCS to the reference coordinate system WCS, [g st ] is the motion chain from the tool coordinate system to the support side coordinate system, [g bt (0)] and [g bs (0)] are the initial matrices of TCS and SCS relative to WCS; is a screw, X1, Y1, Z1, C1, A1 represent the positions of each motion axis of the milling side respectively, and X2, Y2, Z2, C2, A2 represent the positions of each motion axis of the support side respectively.

[0087] Specifically, the synchronous coaxial modeling is established using the closed-loop motion chain from the milling side to the support side, and the nominal synchronous motion matrix Q synchronous is expressed as:

[0088]

[0089] Where P st and O st represent 3×1 nominal position and angle matrix respectively; Q t0 is the initial position of the end of the five-axis machine tool of the milling side and the tool axis direction, and Q st is the nominal synchronous motion matrix.

[0090]

[0091] wherein E TCP and E TAD represent the position of the tool tip and the tool axis orientation error in the process of simultaneous on-axis motion, respectively, and represent the actual position and angle matrix affected by multiple error sources such as geometry, temperature, servo, etc.

[0092] Module M2: using the simultaneous on-axis error direct measurement method based on tool axis measurement, improving the measurement accuracy and efficiency of on-axis error.

[0093] Specifically, in the module M2:

[0094] According to the theoretical motion trajectory, a numerical control measurement program is generated and imported into the numerical control system. The numerical control system runs the measurement program, and the measurement device records the measurement data in real time to obtain the actual tool position and tool axis orientation (P a ,O a ) of the double five-axis machine tool; based on the double five-axis machine tool kinematic chain and the theoretical measurement trajectory, the nominal tool position and tool axis orientation (P, O) are obtained, and the tool tip position and tool axis orientation error of the double five-axis machine tool are obtained based on the simultaneous on-axis model;

[0095] Based on the double five-axis kinematic model, a simultaneous measurement method for 3 degrees of freedom of simultaneous position error and 2 degrees of freedom of on-axis error in the process of simultaneous on-axis motion of the double five-axis machine tool is proposed. The position deviation of the high-precision standard ball at the tool tip point is measured in real time by three displacement sensors arranged in space. The spatial three-coordinate error information of the center of the tool tip point ball is obtained through the calibration algorithm. For the on-axis error, the spatial coordinates of the center of the standard ball at the tool axis point are measured simultaneously by another two displacement sensors. The difference between the measurement values of the tool tip point and the tool axis point reflects the influence of the angle error. The on-axis error is calculated according to the position error of different ball center points.

[0096] Specifically, coordinate system calibration:

[0097] Before measurement, the measurement coordinate system is calibrated to obtain the transformation matrix from the measurement coordinate system to the machine tool reference coordinate system. The rotation axis of the machine tool is placed at the zero position. The standard double ball bar is installed on the milling side spindle. The axis double-degree-of-freedom fine adjustment mechanism of the standard ball is adjusted by the dial gauge and the micrometer to ensure that the centers of the two standard balls are coaxial with the spindle axis. The eddy current sensor array is installed at the initial position of the support side end through a fixed tool. The milling side end is moved to keep the two standard balls within the measurement range of the sensor array. The positions of the five sensors are adjusted to keep the double balls within the middle interval of the measurement range of the sensors, and the positions are set as the zero positions of the five displacement sensors.

[0098] Synchronous coaxial error measurement:

[0099] According to the theoretical motion trajectory, a numerical control measurement program is generated and imported into the numerical control system. The numerical control system runs the measurement program, and the measurement device records the measurement data in real time to obtain the actual tool position and tool axis direction of the double five-axis machine tool. Based on the double five-axis machine tool kinematic chain and the theoretical measurement trajectory, the nominal tool position and tool axis direction (P, O) are obtained. Based on the synchronous coaxial model, the tip position error and tool axis direction error of the double five-axis machine tool are obtained.

[0100] Example 3:

[0101] Example 3 is a preferred example of Example 1, which more specifically illustrates the present application.

[0102] The present application proposes a kind of box bottom mirror image milling machine tool synchronous coaxial error measurement method, five high-precision displacement sensors are used to measure tool tip point and tool axis direction error in synchronous motion, which avoids the influence of repeated installation error. First, the kinematic model of double five-axis mirror image milling machine tool is established based on the theory of rotation, and the model is based on the unique synchronous coaxial constraint of double five-axis machine tool for measurement trajectory generation;Next, a direct measurement method based on tool axis measurement is proposed, which improves the measurement accuracy and efficiency of coaxial error.

[0103] Step description:

[0104] 1. Forward kinematic model establishment.

[0105] 1.1 Transmission chain modeling based on rotation theory. Take the transmission structure of box bottom mirror image milling as an example, that is, the system includes a five-axis machine with A-C double swing head horizontal structure as milling side and a five-axis machine with A-C double swing head structure as supporting side, and the code of machine tool structure is [w-A2-C2-Z2-Y2-X2-b-X1-Y1-Z1-C1-A1-t]. The reference coordinate system (WCS) of the machine tool is fixed on the bed of the machine tool. The end of the milling side is fixed with a tool coordinate system (TCS) which moves with the milling side, and the end of the supporting side is fixed with a supporting coordinate system (SCS) which moves with the supporting side. Based on the rotation theory, the milling side, the supporting side and the synchronous coaxial motion chain are established, and the formula is as follows:

[0106]

[0107] Wherein, [g bt ] and [g bs ] are the motion chains from tool coordinate system TCS and supporting side coordinate system SCS to reference coordinate system WCS. [g st ] is the motion chain from tool coordinate system to supporting side coordinate system. [g bt (0) and [g bs(0) are the initial matrices of TCS and SCS relative to WCS. are the positions of the axes of motion on the milling side, and X2, Y2, Z2, C2, A2 and Figure 1 are the positions of the axes of motion on the support side, respectively. Figure 1 are the positions of the axes of motion on the support side, respectively.

[0108] 1.2 Synchronous Coaxial Motion Modeling. Synchronous coaxial modeling is established using the closed-loop kinematic chain from the milling side to the support side. The nominal synchronous motion matrix can be expressed as:

[0109]

[0110] where P st and O st are the 3x1 nominal position and orientation matrices, respectively.

[0111]

[0112] where E TCP and E TAD are the tool tip position and tool axis orientation error during synchronous coaxial motion, respectively, and are the actual position and orientation matrices affected by multiple error sources such as geometry, temperature, servo, etc.

[0113] 2. Synchronous Coaxial Error Measurement Method Based on Tool Axis Measurement.

[0114] 2.1 Measurement Principle

[0115] The NC measurement program is generated according to the theoretical trajectory and imported into the NC system. The NC system runs the measurement program, and the measurement device records the measurement data in real time to obtain the actual tool position and tool axis orientation (P a , O a ) of the double five-axis machine tool. Based on the kinematic chain of the double five-axis machine tool and the theoretical measurement trajectory, the nominal tool position and tool axis orientation (P, O) are obtained, and based on the synchronous coaxial model, the tool tip position and tool axis orientation error of the double five-axis machine tool are obtained.

[0116] Based on the double five-axis kinematic model, a simultaneous measurement method for the 3-DOF synchronous position error and the 2-DOF coaxial error of the double five-axis machine tool during synchronous coaxial motion is proposed. The basic measurement principle is as follows: Figure 2The position deviation of the high-precision standard ball at the tool tip point is measured in real time by three displacement sensors arranged in space, and the spatial three-coordinate error information of the tool tip point center (ball center) is obtained by a calibration algorithm. For the coaxial error, a similar method is used to calculate the spatial coordinates of the ball center of the standard ball at the tool axis point by another two displacement sensors. The difference between the measurement values of the tool tip point and the tool axis point reflects the influence of the angular error, because the projection distance of the angular error in the tool axis direction varies with the tool axis position, and therefore the coaxial error can be calculated according to the position error of different ball centers.

[0117] 2.2 Coordinate system calibration

[0118] Before measurement, the measurement coordinate system needs to be calibrated to obtain the transformation matrix from the measurement coordinate system to the machine tool reference coordinate system. First, the rotating shaft of the machine tool is placed at the zero position. The standard double-ball bar is installed on the milling side spindle, and the two-degree-of-freedom fine adjustment mechanism of the standard ball axis is adjusted by the dial gauge and the micrometer to ensure that the ball centers of the two standard balls are coaxial with the spindle axis. The eddy current sensor array is installed at the initial position of the support side end through a fixed tooling. Then, the spatial position of the milling side end is moved, the two standard balls are kept within the measurement range of the sensor array, the positions of the five sensors are fine adjusted, the two balls are kept within the middle interval of the measurement range of the sensors, and they are set as the zero positions of the displacement sensors 1, 2, 3, 4, and 5.

[0119] 2.3 Synchronous coaxial error measurement

[0120] A numerical control measurement program is generated according to the theoretical motion trajectory and is imported into the numerical control system. The numerical control system runs the measurement program, and the measurement device records the measurement data in real time to obtain the actual tool position point and tool axis direction of the double five-axis machine tool. Based on the machine tool motion chain and the theoretical measurement trajectory of the double five-axis machine tool, the nominal tool position point and tool axis direction (P, O) are obtained, and based on the synchronous coaxial model, the tool tip point position and tool axis direction error of the double five-axis machine tool are obtained.

[0121] Those skilled in the art know that, in addition to implementing the system provided by the present application and each device, module, unit thereof in the form of pure computer readable program code, the same function can also be realized by logically programming the method steps in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system provided by the present application and each device, module, unit thereof can be considered as a hardware component, and the devices, modules, units included therein for realizing various functions can also be considered as structures within the hardware component; the devices, modules, units for realizing various functions can also be considered as both software modules realizing methods and structures within hardware components.

[0122] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other at will without conflict.

Claims

1. A method for measuring the synchronous coaxial error of a dual five-axis box-bottom mirror milling machine, characterized in that, include: Step S1: Five displacement sensors are used to simultaneously measure the tool tip point and tool axis direction error during synchronous motion. Based on the screw theory, a forward kinematic model of the dual five-axis mirror milling machine is established. The forward kinematic model is based on the unique synchronous coaxial constraint of the dual five-axis machine for measurement trajectory generation. Step S2: Use a direct measurement method for synchronous coaxial error based on tool axis measurement to improve the measurement accuracy and efficiency of coaxial error; In step S1: Establishment of the forward kinematic model: Based on screw theory, the transmission chain modeling system includes a double-swivel horizontal five-axis machine tool as the milling side and a double-swivel horizontal five-axis machine tool as the support side. The reference coordinate system (WCS) of the machine tool is fixed to the machine bed. A tool coordinate system (TCS) is fixed at the end of the milling side and moves with the milling side. A support coordinate system (SCS) is fixed at the end of the support side and moves with the support side. Based on screw theory, the kinematic chains of the milling side, support side, and synchronous coaxial kinematic chains are established, as expressed by the following formulas: Among them, [g bt ] and [g bs [g] These are the motion chains from the tool coordinate system (TCS) and the support-side coordinate system (SCS) to the reference coordinate system (WCS). st ] is the motion chain from the tool coordinate system to the support side coordinate system, [g bt (0)] and [g bs [0] is the initial matrix of TCS and SCS relative to WCS; For the spin, X1, Y1, Z1, C1, A1 represent the positions of each motion axis on the milling side, and X2, Y2, Z2, C2, A2 represent the positions of each motion axis on the support side. Synchronous coaxial modeling is established using a closed-loop kinematic chain from the milling side to the support side, with the nominal synchronous motion matrix Q. synchronous Represented as: Where P st and O st Let Q represent the nominal position and angle matrices of 3×1, respectively; t0 Q represents the initial position of the end face of the five-axis milling machine and the direction of the tool axis. st This is the nominal synchronization motion matrix; Among them, E TCP and E TAD These represent the errors in the tool tip position and tool axis direction during synchronous coaxial motion, respectively. and These represent the actual position and angle matrices affected by multiple error sources, including geometry, temperature, and servo.

2. The method for measuring the synchronous coaxial error of a dual five-axis box-bottom mirror milling machine according to claim 1, characterized in that, In step S2: A CNC measurement program is generated based on the theoretical motion trajectory and imported into the CNC system. The CNC system runs the measurement program, and the measuring device records the measurement data in real time to obtain the actual tool position point and tool axis direction (P) of the dual five-axis machine tool. a O a The nominal tool position point and tool axis direction (P,O) are obtained based on the machine tool kinematic chain and theoretical measurement trajectory of the dual five-axis machine tool, and the tip position and tool axis direction error of the dual five-axis machine tool are obtained based on the synchronous coaxial model. Based on the kinematic model of a dual five-axis machine tool, a method for simultaneously measuring the synchronous position error (3 degrees of freedom) and the coaxial error (2 degrees of freedom) during synchronous and coaxial motion is proposed. Three displacement sensors arranged in a spatial array are used to measure the position deviation of a high-precision standard sphere at the tool tip in real time. A coordinate system calibration algorithm is used to obtain the spatial three-coordinate error information of the sphere's center at the tool tip. For the coaxial error, two additional displacement sensors simultaneously measure the spatial coordinates of the standard sphere's center at the tool axis. The difference between the measurements at the tool tip and tool axis reflects the influence of the angular error, and the coaxial error is calculated based on the position errors of different sphere centers.

3. The method for measuring the synchronous coaxial error of the dual five-axis box-bottom mirror milling machine according to claim 2, characterized in that: The coordinate system calibration algorithm includes: Before measurement, the measurement coordinate system is calibrated to obtain the transformation matrix from the measurement coordinate system to the machine tool reference coordinate system. The rotation axis of the machine tool is placed at the zero point. The standard double ball joint is installed on the milling side spindle. The axis of the standard ball is adjusted by a dial indicator and a micrometer. The dual-degree-of-freedom fine adjustment mechanism ensures that the center of the two standard balls is coaxial with the spindle axis. The eddy current sensor array is installed at the support end of the initial position by a fixing fixture. The spatial position of the milling side end is moved to keep the two standard balls within the measurement range of the sensor array. The position of the five sensors is adjusted so that the double ball is kept within the middle interval of the sensor's measurement range and set as the zero position of the five displacement sensors. Synchronous coaxial error measurement: A CNC measurement program is generated based on the theoretical motion trajectory and imported into the CNC system. The CNC system runs the measurement program, and the measuring device records the measurement data in real time to obtain the actual tool position point and tool axis direction of the dual five-axis machine tool. The nominal tool position point and tool axis direction (P, O) are obtained based on the machine tool motion chain of the dual five-axis and the theoretical measurement trajectory. The tip position and tool axis direction error of the dual five-axis machine tool are obtained based on the synchronous coaxial model.

4. A system for measuring the synchronous coaxial error of a dual five-axis box-bottom mirror milling machine, characterized in that, include: Module M1: Employs five displacement sensors to simultaneously measure the tool tip point and tool axis direction error during synchronous motion. Based on screw theory, it establishes a forward kinematic model of the dual five-axis mirror milling machine. The forward kinematic model is based on the unique synchronous coaxial constraint of the dual five-axis machine for measurement trajectory generation. Module M2: Uses a direct measurement method for synchronous coaxial error based on tool axis measurement to improve the measurement accuracy and efficiency of coaxial error; In module M1: Establishment of the forward kinematic model: Based on screw theory, the transmission chain modeling system includes a double-swivel horizontal five-axis machine tool as the milling side and a double-swivel horizontal five-axis machine tool as the support side. The reference coordinate system (WCS) of the machine tool is fixed to the machine bed. A tool coordinate system (TCS) is fixed at the end of the milling side and moves with the milling side. A support coordinate system (SCS) is fixed at the end of the support side and moves with the support side. Based on screw theory, the kinematic chains of the milling side, support side, and synchronous coaxial kinematic chains are established, as expressed by the following formulas: Among them, [g bt ] and [g bs [g] These are the motion chains from the tool coordinate system (TCS) and the support-side coordinate system (SCS) to the reference coordinate system (WCS). st ] is the motion chain from the tool coordinate system to the support side coordinate system, [g bt (0)] and [g bs [0] is the initial matrix of TCS and SCS relative to WCS; For the spin, X1, Y1, Z1, C1, A1 represent the positions of each motion axis on the milling side, and X2, Y2, Z2, C2, A2 represent the positions of each motion axis on the support side. Synchronous coaxial modeling is established using a closed-loop kinematic chain from the milling side to the support side, with the nominal synchronous motion matrix Q. synchronous Represented as: Where P st and O st Let Q represent the nominal position and angle matrices of 3×1, respectively; t0 Q represents the initial position of the end face of the five-axis milling machine and the direction of the tool axis. st The nominal synchronization motion matrix; Among them, E TCP and E TAD These represent the errors in the tool tip position and tool axis direction during synchronous coaxial motion, respectively. and These represent the actual position and angle matrices affected by multiple error sources, including geometry, temperature, and servo.

5. The system for measuring the synchronous coaxial error of a dual five-axis box-bottom mirror milling machine according to claim 4, characterized in that, In module M2: A CNC measurement program is generated based on the theoretical motion trajectory and imported into the CNC system. The CNC system runs the measurement program, and the measuring device records the measurement data in real time to obtain the actual tool position point and tool axis direction (P) of the dual five-axis machine tool. a O a The nominal tool position point and tool axis direction (P,O) are obtained based on the machine tool kinematic chain and theoretical measurement trajectory of the dual five-axis machine tool, and the cusp position and tool axis direction error of the dual five-axis machine tool are obtained based on the synchronous coaxial model. Based on the kinematic model of a dual five-axis machine tool, a method for simultaneously measuring the synchronous position error (3 degrees of freedom) and the coaxial error (2 degrees of freedom) during synchronous and coaxial motion is proposed. Three displacement sensors arranged in a spatial array are used to measure the position deviation of a high-precision standard sphere at the tool tip in real time. A coordinate system calibration algorithm is used to obtain the spatial three-coordinate error information of the sphere's center at the tool tip. For the coaxial error, two additional displacement sensors simultaneously measure the spatial coordinates of the standard sphere's center at the tool axis. The difference between the measurements at the tool tip and tool axis reflects the influence of the angular error, and the coaxial error is calculated based on the position errors of different sphere centers.

6. The system for measuring the synchronous coaxial error of a dual five-axis box-bottom mirror milling machine according to claim 5, characterized in that: The coordinate system calibration algorithm includes: Before measurement, the measurement coordinate system is calibrated to obtain the transformation matrix from the measurement coordinate system to the machine tool reference coordinate system. The rotation axis of the machine tool is placed at the zero point. The standard double ball joint is installed on the milling side spindle. The axis of the standard ball is adjusted by a dial indicator and a micrometer. The dual-degree-of-freedom fine adjustment mechanism ensures that the center of the two standard balls is coaxial with the spindle axis. The eddy current sensor array is installed at the support end of the initial position by a fixing fixture. The spatial position of the milling side end is moved to keep the two standard balls within the measurement range of the sensor array. The position of the five sensors is adjusted so that the double ball is kept within the middle interval of the sensor's measurement range and set as the zero position of the five displacement sensors. Synchronous coaxial error measurement: A CNC measurement program is generated based on the theoretical motion trajectory and imported into the CNC system. The CNC system runs the measurement program, and the measuring device records the measurement data in real time to obtain the actual tool position point and tool axis direction of the dual five-axis machine tool. The nominal tool position point and tool axis direction (P, O) are obtained based on the machine tool motion chain of the dual five-axis and the theoretical measurement trajectory. The tip position and tool axis direction error of the dual five-axis machine tool are obtained based on the synchronous coaxial model.

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