1. A method for detecting dynamic motion errors of a rotating shaft of a five-axis machine tool is characterized by comprising the following steps: comprises the following steps:

firstly, dynamic motion error classification: dividing the dynamic motion error into a dynamic motion error in a servo loop and a dynamic motion error outside the servo loop according to the source and the expression form of the dynamic motion error of the rotating shaft C axis;

secondly, identifying dynamic motion errors:

(1) at different feed rates: a rotating shaft C shaft moves to process a round test piece, and the rotating shaft C shaft and a translation shaft X shaft are linked to process an oval test piece;

(2) sequentially carrying out online measurement and calibration of a three-coordinate measuring machine on the round and oval test pieces respectively;

(3) and identifying corresponding dynamic motion errors based on the dynamic and static motion error separation of the circular and elliptical test pieces in cutting processing.

2. The method for detecting the dynamic motion error of the rotating shaft of the five-axis machine tool according to claim 1, characterized in that: the cutting processing of the round test piece reflects the dynamic motion error outside the servo loop, and the cutting processing of the oval test piece reflects the dynamic motion error inside the servo loop.

3. The method for detecting the dynamic motion error of the rotating shaft of the five-axis machine tool according to claim 1 or 2, characterized in that: the dynamic and static motion error separation process based on the cutting processing of the round and the oval test piece is as follows:

firstly, obtaining a total processing error: p_CMM-P_ideal＝E_t

E_tIndicates the total error of machining, P_ideaRepresenting theoretical value in three coordinates, P_CMMExpressing a calibration value under three coordinates;

then, a quasi-static motion error E is obtained_qs：P_CMM-P_on-machine＝E_qs

P_on-machineRepresenting an online measurement;

the total error of processing is composed of quasi-static motion error and dynamic motion error, finally realizing the separation of dynamic and static errors and identifying the dynamic motion error E_d；E_t-E_qs＝E_d。

4. The method for detecting the dynamic motion error of the rotating shaft of the five-axis machine tool according to claim 1, characterized in that: the dynamic motion error in the servo loop comes from insufficient bandwidth of a servo system and is expressed as an axial following error; the out-of-servo loop dynamic motion errors are derived from elastic deformation of the mechanical structure and are manifested as position and angle errors.

5. The method for detecting the dynamic motion error of the rotating shaft of the five-axis machine tool according to the claim 2 or 3, characterized by comprising the following steps: and step three, performing circle test by using a ball rod instrument at different feeding speeds, and reflecting the C-axis dynamic motion error under the circular track through the change of the length of the ball rod instrument.

6. The method for detecting the dynamic motion error of the rotating shaft of the five-axis machine tool according to claim 5, characterized in that: and step four, establishing a rotary shaft dynamic model, and performing elliptical track dynamic analysis at different feeding speeds to obtain a motion error curve of the elliptical motion track under the influence of different feeding speeds so as to reflect the dynamic motion error in the servo loop.

7. The method for detecting the dynamic motion error of the rotating shaft of the five-axis machine tool according to claim 6, characterized in that: step five, on the basis of the step one to the step four, comparing the cutting result of the round test piece with the round test result of the ball rod instrument, and testing the dynamic motion precision outside the servo loop of the rotating shaft C shaft by using the cutting of the round test piece; and comparing the cutting result of the elliptical test piece with the dynamic analysis result under the elliptical track, and testing the dynamic motion precision in the servo loop of the rotating shaft C shaft by using the cutting of the elliptical test piece.

Background

The five-axis numerical control machine tool can process parts with complex curved surfaces and has wide application in the fields of aerospace, automobile manufacturing and the like. The rotating shaft is used as a key moving part of the five-axis numerical control machine tool, and the moving precision of the rotating shaft is determined by the quasi-static moving error and the dynamic moving error together. In high-speed and high-precision machining, dynamic motion errors have a great influence on the motion precision of a rotating shaft, so that it is necessary to trace and analyze the dynamic motion errors.

Although there is a lot of research on quasi-static motion errors about the axis of rotation, there is still less research on dynamic motion errors. At present, for the research on the dynamic motion error of a rotating shaft, non-cutting test modes such as instrument measurement and establishment of a dynamic motion axis model are mostly adopted to carry out source tracing analysis on the dynamic motion error of the rotating shaft, however, although the non-cutting test mode is indispensable, more cutting precision of a workpiece is considered in actual processing. Meanwhile, the dynamic precision of the machine tool is often related to the actual processing conditions, so that the source tracing analysis of the dynamic motion error is necessary from the start of test piece cutting.

Disclosure of Invention

The invention provides a method for detecting dynamic motion errors of a rotating shaft of a five-axis machine tool, aiming at overcoming the prior art. The method is used for detecting the change condition of the internal and external dynamic motion errors of the servo loop under the influence of the feeding speed, and can realize effective detection of the internal and external dynamic motion errors of the rotary shaft servo loop.

A method for detecting dynamic motion errors of a rotating shaft of a five-axis machine tool comprises the following steps:

firstly, dynamic motion error classification: dividing the dynamic motion error into a dynamic motion error in a servo loop and a dynamic motion error outside the servo loop according to the source and the expression form of the dynamic motion error of the rotating shaft C axis;

secondly, identifying dynamic motion errors:

(1) at different feed rates: a rotating shaft C shaft moves to process a round test piece, and the rotating shaft C shaft and a translation shaft X shaft are linked to process an oval test piece;

(2) sequentially carrying out online measurement and calibration of a three-coordinate measuring machine on the round and oval test pieces respectively;

(3) and identifying corresponding dynamic motion errors based on the dynamic and static motion error separation of the circular and elliptical test pieces in cutting processing.

Further, the dynamic and static motion error separation process based on the cutting processing of the circular and elliptical test pieces is as follows:

firstly, obtaining a total processing error: p_CMM-P_ideal＝E_t

E_tIndicates the total error of machining, P_ideaRepresenting theoretical value in three coordinates, P_CMMExpressing a calibration value under three coordinates;

then, a quasi-static motion error E is obtained_qs：

P_CMM-P_on-machine＝E_qs

Wherein, P_on-machineRepresenting an online measurement;

the total error of processing is composed of quasi-static motion error and dynamic motion error, finally realizing the separation of dynamic and static errors and identifying the dynamic motion error E_d；E_t-E_qs＝E_d

Compared with the prior art, the invention has the beneficial effects that: .

The existing dynamic motion error non-cutting test mode mostly considers the axial motion error of a motion shaft, the input and the axial motion output of the motion shaft are taken as research objects, but the dynamic motion error not only comprises the axial motion error, but also comprises errors in other positions and angles, and meanwhile, because the dynamic motion error caused by a milling force part cannot be reflected due to the fact that the existing dynamic motion error non-cutting test mode is not subjected to actual cutting test, the existing dynamic motion error non-cutting test mode is not comprehensive enough.

The dynamic motion error is divided into an inner part of the servo loop and an outer part of the servo loop, the former reflects the axial motion error, the latter reflects the error caused by the milling force part, and the cutting test is respectively reflected by the ellipse and the circle test piece. And for the problem that the machining error of the test piece comprises a geometric error, identifying the dynamic motion error through a dynamic and static error separation principle. The method for detecting the dynamic motion error of the rotating shaft of the five-axis numerical control machine tool can be used for detecting the change condition of the internal and external dynamic motion errors of the servo loop under the influence of the feeding speed, can realize effective detection of the internal and external dynamic motion errors of the servo loop of the rotating shaft, and can evaluate the internal and external dynamic precision of the servo loop.

The technical scheme of the invention is further explained by combining the drawings and the embodiment:

drawings

FIG. 1 is a diagram of the process of detecting the dynamic motion error of a rotating shaft of a five-axis machine tool based on cutting of circular and elliptical test pieces according to the invention;

FIG. 2 is a schematic diagram of servo inner and outer dynamic motion errors of a rotating shaft;

FIG. 3 is a drawing of a round specimen and a cutting process of the specimen in the example;

FIG. 4 is a drawing of an oval test piece and a cutting process of the test piece in the example;

FIG. 5 is a schematic diagram of dynamic and static error separation;

FIG. 6 is a graph showing the total error of machining, the quasi-static motion error and the dynamic motion error of the round specimen in the example;

FIG. 7 is a graph showing the total error of machining, the quasi-static motion error and the dynamic motion error of the elliptical test piece in the example;

FIG. 8 is a graph showing measurement patterns and measurement results of a ball bar apparatus in the examples;

FIG. 9 is a rotary shaft dynamics model constructed in the examples;

FIG. 10 is a motion error curve diagram of the dynamic model under the elliptical motion trail in the embodiment.

Detailed Description

Referring to fig. 1 and 2, a method for detecting a dynamic motion error of a rotating shaft of a five-axis machine tool according to the present embodiment includes the following steps:

firstly, dynamic motion error classification: dividing the dynamic motion error into a dynamic motion error in a servo loop and a dynamic motion error outside the servo loop according to the source and the expression form of the dynamic motion error of the rotating shaft C axis; wherein, the dynamic motion error in the servo loop comes from insufficient bandwidth of the servo system and is represented as an axial following error; the dynamic motion error outside the servo loop comes from the elastic deformation of a mechanical structure and is expressed as a position and angle error; FIG. 2 is a schematic diagram of the dynamic motion error classification of FIG. 1;

secondly, identifying dynamic motion errors:

(1) at different feed rates: a rotating shaft C shaft moves to process a round test piece, and the rotating shaft C shaft and a translation shaft X shaft are linked to process an oval test piece; generally, the two types of dynamic motion errors inside and outside the servo can be respectively reflected by the machining errors of the circular test piece and the elliptical test piece. Only C-axis motion exists during cutting of the round test piece, and the machining precision of the round test piece is not influenced by axial following errors, so that only dynamic motion errors outside a servo loop are reflected; the oval test piece is processed by linkage of the C axis and the X axis, and the processing precision of the oval test piece is influenced by the axial following error, so that the dynamic motion error in the servo loop can be reflected by the oval test piece.

(2) Sequentially carrying out online measurement and calibration of a three-coordinate measuring machine on the round and oval test pieces respectively;

(3) and identifying corresponding dynamic motion errors based on the dynamic and static motion error separation of the circular and elliptical test pieces in cutting processing.

As shown in fig. 5, the principle of separating the dynamic and static motion errors is as follows, the dynamic motion error is identified from the machining error of the test piece, and the quasi-static motion error and the dynamic motion error are required to be separated in order to identify the dynamic motion error, because the quasi-static motion error and the dynamic motion error jointly determine the machining precision of the test piece.

The dynamic and static motion error separation process based on the cutting processing of the round and the oval test piece is as follows:

firstly, obtaining a total processing error: p_CMM-P_ideal＝E_t

E_tIndicates the total error of machining, P_ideaRepresenting theoretical value in three coordinates, P_CMMExpressing a calibration value under three coordinates;

the on-line measurement process involves geometric errors, so that the CMM calibrates the value P_CMMAnd the on-line measured value P_on-machineDeviation between as quasi-static motion error E_qsThen obtaining a quasi-static motion error E_qs：

P_CMM-P_on-machine＝E_qs

P_on-machineRepresenting an online measurement;

the total error of processing is composed of quasi-static motion error and dynamic motion error, finally realizing the separation of dynamic and static errors and identifying the dynamic motion error E_d；E_t-E_qs＝E_d

For better, the dynamic and static motion error separation of the invention based on the cutting processing of the round and the elliptical test pieces is checked, the corresponding dynamic motion error is identified, and for the dynamic motion error, the test of the round test piece and the elliptical test piece under non-cutting is designed;

under different feeding speeds, a ball rod instrument is used for circle testing, and C-axis dynamic motion errors under a circular track are reflected through the change of the rod length of the ball rod instrument; the main shaft side sphere is placed on the axis of the C shaft and is parallel to the X shaft. The test result of the ball rod instrument is only affected by geometric errors and dynamic motion errors caused by servo and mechanical system parameters, and the dynamic motion errors caused by milling force when the actual round test piece is machined cannot be reflected.

And establishing a rotary shaft dynamic model, and performing elliptic motion trajectory dynamic analysis at different feeding speeds to obtain a motion error curve of an elliptic motion trajectory under the influence of different feeding speeds so as to reflect dynamic motion errors in a servo loop. Because the dynamic model does not contain quasi-static errors and only takes axial motion as model output, the motion error curve only reflects dynamic motion errors in the servo loop.

Further, on the basis of the test, comparing the cutting result of the round test piece with the round test result of the ball rod instrument, tracing the dynamic motion error outside the servo loop, testing the influence of different feeding speeds on the dynamic error outside the servo loop, and obtaining the dynamic motion precision outside the servo loop for testing the C axis of the rotating shaft by using the cutting of the round test piece; and comparing the cutting result of the elliptic test piece with the dynamic analysis result under the elliptic orbit, tracing the dynamic motion error in the servo loop, testing the influence of different feed speeds on the dynamic error in the servo loop, and obtaining the dynamic motion precision in the servo loop for testing the rotating shaft C axis by using the cutting of the elliptic test piece.

The invention is further described below by way of examples:

the embodiment is operated on a JDGR400 five-axis numerical control machine tool. According to the technical route shown in fig. 1, the dynamic motion error inside and outside the servo loop of the rotating shaft C axis is detected and analyzed by tracing.

The first step, using the C axis of the rotating shaft as the research object, as shown in fig. 2, dividing the dynamic motion error of the rotating shaft into the dynamic motion error in the servo loop and the dynamic motion error outside the servo loop according to the source and the representation form of the dynamic motion error of the rotating shaft; wherein, the dynamic motion error in the servo loop comes from insufficient bandwidth of the servo system and is represented as an axial following error; the dynamic motion error outside the servo loop comes from the elastic deformation of a mechanical structure and is expressed as a position and angle error;

and secondly, as shown in fig. 3 and 4, respectively processing a round test piece by the motion of a rotating shaft C shaft and processing an oval test piece by the linkage of the rotating shaft C shaft and a translation shaft X shaft at different feeding speeds. Wherein the feeding speeds are respectively 200mm/min, 300mm/min, 400mm/min and 500 mm/min. In the processing process, the rotating speed of the main shaft is 5000r/min, the cutting depth is 5mm, and the processing conditions are kept the same except that the feeding speed is changed. In the cutting of the round test piece, fig. 3a shows the round test piece, the radius of the round test piece is 100mm, the length, width and height of the adopted blank material are 205mm, 205mm and 25mm respectively, and fig. 3b shows the processing process of the round test piece. In the cutting of the oval test piece, fig. 4a shows the oval test piece, the major diameter of the oval test piece is 100mm, the minor diameter is 50mm, and fig. 4b shows the machining process of the oval test piece, and the length, the width and the height of the adopted blank material are 205mm, 105mm and 25mm respectively.

And thirdly, sequentially carrying out online measurement and Coordinate Measuring Machine (CMM) calibration on the circular test piece and the elliptical test piece respectively.

And fourthly, as shown in fig. 5, identifying the dynamic motion error from the machining error of the test piece according to the dynamic and static motion error separation principle. The errors of the circular test piece and the elliptical test piece are respectively shown in fig. 6 and 7, the total machining error (shown in fig. 6 a), the quasi-static motion error (shown in fig. 6 b) and the dynamic motion error (shown in fig. 6 c) of the circular test piece, the total machining error of the elliptical test piece is shown in fig. 7a, the quasi-static motion error is shown in fig. 7b and the dynamic motion error is shown in fig. 7 c. Wherein, the dynamic motion error increases along with the increase of the feeding speed, and the quasi-static motion error is kept unchanged; FIGS. 6 and 7 show the corresponding errors for feed rates of 200mm/min, 300mm/min, 400mm/min and 500mm/min, respectively.

Then, a source tracing analysis is performed based on the identified dynamic motion error.

Fifthly, as shown in fig. 8a, under different feeding speeds, a ball rod instrument is used for circle testing, and C-axis motion errors under a circular track are reflected through the change of the rod length of the ball rod instrument; in the test process, the C shaft rotates for a circle at the feeding speeds of 200mm/min, 300mm/min, 400mm/min and 500mm/min respectively, 4 groups of tests are carried out totally, a main shaft side round ball is placed on the axis of the C shaft, the club length of the club instrument is 100mm and is parallel to the X shaft, and the test result of the club instrument circle shows that as shown in figure 8b, the change situation of the club length of the club instrument is not changed along with different feeding speeds;

and sixthly, building a dynamic model of the rotating shaft C shaft as shown in fig. 9, wherein the dynamic model of the machine tool rotating shaft C shaft is as shown in fig. 9. The C-axis rotating mechanism mainly comprises a motor drive, a gear, a worm gear and a worm and an execution component, and converts the output torque of the motor into the rotating angle of a C axis. The dynamic model has three degrees of freedom which are respectively the motor rotation angles theta_mAngle of rotation theta of worm and gear_wAnd the angle of rotation theta of the turntable_tThe kinetic differential equation is shown below:

in the formula, the motor driving part: t is_mIs an outputTorque, J_mIs moment of inertia, c_mIs a viscous damping coefficient, f_mIs Coulomb friction torque, θ_mIs a rotation angle. A gear transmission part: t is_gTo output torque, c_gIs a viscous damping coefficient, R_gIs a transmission ratio, c_igIs the internal damping coefficient. A worm gear portion: t is_wTo moment of inertia, J_wIs moment of inertia, c_wIs a viscous damping coefficient, f_wIs a coulomb friction torque, R_wIs a transmission ratio, c_iwIs the internal damping coefficient, theta_wThe rotation angle of the worm gear and the worm. An execution section: j. the design is a square_tIs inertia, c_tIs a viscous damping coefficient, f_tIs Coulomb friction torque, θ_tIs the rotation angle of the turntable.

The elliptical trajectory dynamics analysis was performed at different feed rates, wherein the feed rates were 200mm/min, 300mm/min, 400mm/min, 500mm/min, respectively. Obtaining a motion error curve of the elliptical motion trajectory under the influence of different feeding speeds, as shown in fig. 10, wherein the peaks in the curve correspond to error curves with feeding speeds of 200mm/min, 300mm/min, 400mm/min and 500mm/min from bottom to bottom respectively.

And seventhly, comparing the cutting result of the round test piece with the round test result of the ball rod instrument, wherein the dynamic motion error of the round test piece is increased along with the increase of the feeding speed, and the length of the ball rod instrument is not changed. This is because the cue stick instrument cannot reflect the dynamic motion error caused by the milling force received when the actual round test piece is machined. The dynamic error of the round test piece processed at different feed speeds is mainly changed by the milling force, namely the influence of the different feed speeds on the dynamic error outside the servo loop is mainly caused by the change of the milling force. With the increase of the feeding speed, the milling force is increased, and the milling force acts on the movement of the rotating shaft C shaft, so that the mechanical structure is elastically deformed, and finally the dynamic error outside a servo loop of the mechanical structure is increased. Therefore, the out-of-servo-loop dynamic motion accuracy of the rotating shaft C axis can be checked by cutting the round test piece.

The dynamics analysis result under the elliptical orbit shows that the increase amplitude of the motion error is far smaller than the increase amplitude of the actual machining error along with the increase of the feeding speed. Thus, the feed speed has a much greater effect on the dynamic error outside the servo loop than inside the servo loop. Compared with a ball arm instrument circular track test, the circular track is realized only by the independent rotation of the rotating shaft C shaft, and the elliptic track is realized by the linkage of the rotating shaft C shaft and the X shaft. The difference between the two is that in an elliptical trajectory, the axial following hysteresis of the feed shaft causes motion errors. Therefore, in the multi-axis interlocking motion, the feed speed is considered to affect the motion accuracy mainly by the characteristic of the axial follow-up hysteresis of the feed shaft. Therefore, the dynamic motion precision in the servo loop of the rotating shaft C axis can be checked by cutting the elliptical test piece.

The present invention is not limited to the above embodiments, and those skilled in the art can make various changes and modifications without departing from the scope of the invention.