Metal cutting multi-axis linkage control method and system

Abstract

The application discloses a kind of metal cutting multi-axis linkage control method and system, specifically relates to cutting tool control technical field, for solving the problem that existing technology is when cutting high viscosity metal chip jamming causes moment mutation, servo passive response leads to periodic defects on workpiece surface.The present application acquires spindle torque signal and linkage servo shaft position feedback signal, uses the inconsistency of linkage trajectory curvature change direction and spindle torque signal gradient direction to determine the jamming precursor, when the jamming precursor appears, according to the space included angle of cutting torque direction and transmission chain gap release direction to estimate the speed error in the defect phase interval that the mark on workpiece surface generates, and adjust the feed speed of linkage shaft or workpiece rotation speed in advance to reduce the amplitude of speed error before workpiece rotates to defect phase interval.

Description

Technical Field

[0001] This invention relates to the field of cutting tool control technology, and more specifically, to a multi-axis linkage control method and system for metal cutting. Background Technology

[0002] In the process of cutting metal workpieces using cutting tools, multi-axis linkage control is a fundamental means to achieve efficient cutting of complex cross-section profiles, pipes, or beveled surfaces. Taking multi-axis linkage cutting machine tools as an example, common applications include the linkage between the tool feed axis and the workpiece rotation axis in milling, the combined linkage between tool feed and workpiece posture adjustment in broaching, and the linkage between the feed axis and the workpiece rotation axis in circular sawing. When actually cutting highly ductile materials such as aluminum alloys and copper alloys, the surface of the cut workpiece often shows periodic patterns or bright bands visible to the naked eye, accompanied by instantaneous fluctuations in cutting torque. For these surface defects, the first step on-site is usually to check mechanical factors such as tool runout, spindle bearing clearance, or loose fixtures, and then take measures such as replacing the tool and adjusting the clamping force. In multi-axis linkage cutting equipment, it is a known phenomenon that the output torque of each servo axis fluctuates with the cutting state. Existing control systems mostly deal with torque over-limit situations by setting limiting current or adjusting feed rate. For machining marks that periodically appear on the workpiece surface, there is still a lack of means to actively suppress them from the perspective of multi-axis linkage control.

[0003] In existing cutting processes, for highly viscous metals, when the instantaneous cutting torque changes due to poor chip removal in the cutting chip space, the servo system only relies on passive torque limiting or shutdown protection to respond. The servo axis speed error generated during this response process interacts with the mechanical backlash in the transmission chain, causing undesirable changes in the cutting speed vector, which in turn forms regular defects on the machined surface of the workpiece. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the present invention provides a multi-axis linkage control method and system for metal cutting to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A multi-axis linkage control method for metal cutting includes the following steps: S1: Acquire spindle torque signal and position feedback signal of each linked servo axis during the cutting process; S2: Determine the direction of the cutting arc length change represented by the curvature change of the current linkage trajectory based on the position feedback signal, and obtain the gradient direction of the spindle torque signal along the linkage trajectory. When the direction of the cutting arc length change is inconsistent with the gradient direction, it is determined that there is a sign of blockage. S3: When signs of blockage appear, determine the peak direction of the spindle torque signal when the signs of blockage occur based on the position feedback signal as the cutting torque direction, and obtain the release direction of the transmission chain clearance in the linkage axis coordinate system. Determine the spatial angle between the cutting torque direction and the release direction as the angle, and at the same time determine the current rotation angle position of the workpiece. S4: Determine the geometric relationship between the direction of the velocity error caused by the sudden change in torque and the direction of the linear velocity on the workpiece surface based on the included angle, and determine the starting phase interval of the velocity error imprinting on the workpiece surface based on the current rotation angle position of the workpiece, as the defect phase interval; S5: Before the workpiece rotates into the defect phase range, adjust the feed speed of the linkage shaft or the workpiece rotation speed.

[0006] Furthermore, the spindle torque signal and position feedback signals of each linked servo axis are acquired during the cutting process, including: The spindle torque signal is obtained by utilizing the built-in torque observation function of the spindle drive unit, and the position feedback signal is obtained by utilizing the encoder interface of each linkage servo axis. The spindle torque signal and the position feedback signal are then timestamped using a unified time base.

[0007] Furthermore, based on the position feedback signal, the direction of the cutting arc length change, represented by the curvature change of the current linkage trajectory, is determined, and the gradient direction of the spindle torque signal along the linkage trajectory is obtained. When the direction of the cutting arc length change is inconsistent with the gradient direction, it is determined that a blockage precursor has occurred, including: The motion trajectories of each linked servo axis are synthesized using position feedback signals to obtain the linked trajectory. The curvature of the linked trajectory at the current moment and the curvature change trend over time are calculated. The direction of the increase or decrease of the cutting arc length corresponding to the curvature change trend over time is taken as the direction of the cutting arc length change. The directional derivative of the spindle torque signal along the linked trajectory is obtained to obtain the gradient direction of the spindle torque signal along the linked trajectory. When the direction of the cutting arc length change is opposite to the gradient direction, it is determined that there is a sign of blockage.

[0008] Furthermore, the direction of increase or decrease in cutting arc length corresponding to the curvature change trend over time is taken as the direction of change in cutting arc length. This includes: taking the first-order time derivative of the curvature of the linkage trajectory at the current moment; when the first-order time derivative is positive, the direction of increase or decrease in cutting arc length is determined to be the increasing direction; when the first-order time derivative is negative, the direction of increase or decrease in cutting arc length is determined to be the decreasing direction. The increasing or decreasing direction is taken as the direction of change in cutting arc length.

[0009] Furthermore, when signs of impending blockage appear, the peak direction of the spindle torque signal at the time of the impending blockage is determined based on the position feedback signal as the cutting torque direction, and the release direction of the transmission chain clearance in the linkage axis coordinate system is obtained. The spatial angle between the cutting torque direction and the release direction is determined as the included angle, and the current rotation angle position of the workpiece is determined, including: Taking the moment when the blockage precursor appears as the reference moment, the torque vector direction corresponding to the sampling point where the torque amplitude reaches the local maximum before and after the reference moment is extracted from the spindle torque signal as the cutting torque direction. The motion direction reversal record of each linkage servo axis at the reference moment is obtained from the position feedback signal. The vector direction of the clearance opening direction indicated by the motion direction reversal record in the linkage axis coordinate system is taken as the release direction. The spatial angle between the cutting torque direction and the release direction is calculated. At the same time, the workpiece rotation axis position feedback signal at the reference moment is read to obtain the current rotation angle position of the workpiece.

[0010] Furthermore, the direction of the torque vector corresponding to the sampling point where the torque amplitude reaches a local maximum before and after the reference time is extracted from the spindle torque signal as the cutting torque direction, including: taking a segment of the spindle torque signal with the reference time as the center of the window, comparing the torque amplitude of adjacent sampling points within the window, determining the sampling point with a torque amplitude greater than the previous sampling point and greater than the next sampling point as the local maximum sampling point, and taking the direction of the torque vector corresponding to the local maximum sampling point in the linkage axis coordinate system as the cutting torque direction.

[0011] Furthermore, based on the included angle, the geometric relationship between the direction of the velocity error caused by the sudden change in torque and the direction of the linear velocity on the workpiece surface is determined, and the starting phase interval for the velocity error to leave an imprint on the workpiece surface is determined according to the current rotational angular position of the workpiece, serving as the defect phase interval, including: The release direction determined by the included angle is taken as the speed error direction. The normal direction of the workpiece surface at the cutting point is calculated based on the current rotation angle position of the workpiece. The speed error direction and the normal direction of the workpiece surface are multiplied to obtain the projection component of the speed error on the normal direction of the workpiece surface. The phase corresponding to the zero-crossing point of the projection component from positive to negative is taken as the imprint start phase. The angle range of the preset width is intercepted along the workpiece rotation direction with the imprint start phase as the starting point as the defect phase interval.

[0012] Furthermore, the normal direction of the workpiece surface at the cutting point is calculated based on the current rotation angle position of the workpiece, including: obtaining the angle value of the workpiece rotation axis at the reference time from the position feedback signal as the current rotation angle position of the workpiece; determining the coordinates of the cutting point in the workpiece coordinate system based on the current rotation angle position of the workpiece and the geometric parameters of the workpiece cross section; and obtaining the normal direction of the workpiece surface by taking the partial derivative of the workpiece cross section shape function at the cutting point.

[0013] Furthermore, before the workpiece rotates into the defect phase range, adjust the feed speed of the linkage axis or the workpiece rotation speed, including: The current angular position of the workpiece rotation axis is obtained in real time from the position feedback signal. The angle difference between the current angular position and the starting boundary of the defect phase interval is calculated. When the angle difference is less than the preset angle threshold, the feed speed of the linkage axis is reduced or the workpiece rotation speed is adjusted to reduce the amplitude of the speed error. After the workpiece rotation axis passes through the defect phase interval, the original feed speed or the original workpiece rotation speed is restored.

[0014] On the other hand, the present invention provides a multi-axis linkage control system for metal cutting, comprising the following modules: The signal acquisition module is used to acquire the spindle torque signal and the position feedback signals of each linked servo axis during the cutting process; The precursor detection module is used to determine the direction of the cutting arc length change represented by the curvature change of the current linkage trajectory based on the position feedback signal, and to obtain the gradient direction of the spindle torque signal along the linkage trajectory. When the direction of the cutting arc length change is inconsistent with the gradient direction, it is determined that a blockage precursor has occurred. The included angle determination module is used to determine the peak direction of the spindle torque signal when the blockage precursor occurs based on the position feedback signal as the cutting torque direction, and to obtain the release direction of the transmission chain clearance in the linkage axis coordinate system when the blockage precursor occurs. The spatial angle between the cutting torque direction and the release direction is determined as the included angle, and the current rotation angle position of the workpiece is determined at the same time. The defect prediction module is used to determine the geometric relationship between the direction of the velocity error caused by the sudden change in torque and the direction of the linear velocity on the workpiece surface based on the included angle, and to determine the starting phase interval of the velocity error imprinting on the workpiece surface based on the current rotation angle position of the workpiece, as the defect phase interval. The speed adjustment module is used to adjust the feed speed of the linkage shaft or the rotation speed of the workpiece before the workpiece rotates into the defect phase range.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. By monitoring the consistency between the direction of curvature change in the linkage trajectory and the gradient direction of the spindle torque signal, pre-clogging signs can be identified, avoiding the limitations of relying solely on torque amplitude thresholds, which are prone to misjudgment and missed detection under variable cutting conditions. In multi-axis linkage cutting scenarios, the increase or decrease of the cutting arc length with the curvature of the linkage trajectory is a normal geometric-mechanical correspondence. However, the accumulation of chips in the chip space of the cutting chamber breaks this correspondence, causing the trend of torque signal change to deviate from the trend of increase or decrease of cutting arc length. Using this deviation as a criterion for pre-clogging signs, the identification of clogging no longer depends on fixed torque limits, but directly reflects the changes in the internal physical state of the cutting process. Therefore, it has a stronger adaptability to material batch differences and tool wear.

[0016] 2. After identifying the signs of blockage, the spatial angle between the cutting torque direction and the transmission chain clearance release direction is further utilized to link the mechanical conditions of the servo axis speed error caused by the sudden torque change with the geometric conditions of the imprint on the workpiece surface. This enables the phase prediction of the defect location, allowing subsequent speed adjustments to be made directly to the defect phase range. By reducing the feed speed of the linkage axis or the workpiece rotation speed in advance within the defect phase range, the speed error amplitude caused by the clearance opening can be reduced, thereby suppressing the formation of periodic patterns at the source, rather than checking or remedying them after the defect occurs. Attached Figure Description

[0017] Figure 1 This is a flowchart of a multi-axis linkage control method for metal cutting according to the present invention; Figure 2 This is a schematic diagram of the structure of a multi-axis linkage control system for metal cutting according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: Figure 1 This invention provides a multi-axis linkage control method for metal cutting, which includes the following steps: S1: Acquire spindle torque signal and position feedback signal of each linked servo axis during the cutting process; S2: Determine the direction of the cutting arc length change represented by the curvature change of the current linkage trajectory based on the position feedback signal, and obtain the gradient direction of the spindle torque signal along the linkage trajectory. When the direction of the cutting arc length change is inconsistent with the gradient direction, it is determined that there is a sign of blockage. S3: When signs of blockage appear, determine the peak direction of the spindle torque signal when the signs of blockage occur based on the position feedback signal as the cutting torque direction, and obtain the release direction of the transmission chain clearance in the linkage axis coordinate system. Determine the spatial angle between the cutting torque direction and the release direction as the angle, and at the same time determine the current rotation angle position of the workpiece. S4: Determine the geometric relationship between the direction of the velocity error caused by the sudden change in torque and the direction of the linear velocity on the workpiece surface based on the included angle, and determine the starting phase interval of the velocity error imprinting on the workpiece surface based on the current rotation angle position of the workpiece, as the defect phase interval; S5: Before the workpiece rotates into the defect phase range, adjust the feed speed of the linkage shaft or the workpiece rotation speed.

[0020] In the specific implementation of S1, during the multi-axis linkage cutting process of a multi-axis linkage cutting machine tool, the cutting spindle is driven to rotate by the spindle drive unit, and each linkage servo axis drives the tool feed motion component and the workpiece rotation motion component respectively.

[0021] The spindle drive unit integrates a current sensor that continuously monitors the instantaneous three-phase current of the motor driving the tool rotation. The signal processing circuit within the spindle drive unit transforms the instantaneous three-phase current into torque current and excitation current components in a rotating coordinate system based on the field-oriented control principle. The torque current components and the motor output torque value satisfy a linear proportional relationship. The spindle drive unit multiplies the torque current components by a preset motor torque constant to obtain the spindle torque signal. The motor torque constant is a parameter setting value for the spindle drive unit, obtained from the motor nameplate or through calibration tests. A calibration test, for example, involves applying a known torque load to the motor output shaft and recording the corresponding torque current components. A linear fitting is then used to obtain the conversion coefficient between the torque current components and the torque value. The spindle drive unit updates the spindle torque signal at a fixed period, for example, the same as the servo control period of the CNC system, to ensure that the spindle torque signal is synchronized with other signals in time.

[0022] Each linked servo axis is equipped with an incremental encoder or an absolute encoder, which is coaxially mounted with the rotor of the servo motor. For incremental encoders, the encoder outputs A-phase pulse signals, B-phase pulse signals, and Z-phase zero-position pulse signals. The counting circuit inside the servo driver performs a fourfold frequency count on the quadrature pulses of the A-phase and B-phase pulse signals to obtain the current position count value in units of pulse count. This current position count value is then converted to the encoder line count to obtain the rotor's mechanical angle value. This mechanical angle value is then converted to the lead parameter or reduction ratio parameter of the drivetrain to obtain the linear or angular displacement of the linked servo axis, which is output as the position feedback signal. For absolute encoders, the absolute encoder sends the rotor's absolute position value to the servo driver via a communication protocol. After receiving the absolute position value, the servo driver also combines it with the drivetrain lead parameter or reduction ratio parameter to convert the absolute position value into the linear or angular displacement of the linked servo axis. The encoder interface of the linked servo axis refreshes the position feedback signal at a fixed period consistent with the servo control cycle to ensure the real-time nature of the current position information.

[0023] Using a high-precision clock source within the CNC system of a multi-axis linkage cutting machine tool as the reference clock, the CNC system sends synchronization frames to the spindle drive unit and the servo drivers of each linked servo axis at a fixed communication cycle. Each synchronization frame contains the current timestamp of the reference clock. Upon receiving the synchronization frame, the spindle drive unit records its local clock reading and calculates the first deviation between its current reading and the timestamp in the synchronization frame. The time of the reference clock, obtained by adding the first deviation to the sampling time corresponding to the spindle torque signal, is then used as the timestamp of the spindle torque signal. Similarly, upon receiving the synchronization frame, each servo driver records its own local clock reading and calculates the second deviation between its current reading and the timestamp in the synchronization frame. The time of the reference clock, obtained by adding the second deviation to the sampling time corresponding to its own position feedback signal, is then used as the timestamp of the position feedback signal. The spindle torque signal and the position feedback signals of each linked servo axis acquired within the same communication cycle are all assigned timestamps under the same reference clock, achieving timestamp alignment between the spindle torque signal and the position feedback signal using a unified time base. The communication cycle of the synchronization frame is kept consistent with the servo control cycle, so that the timestamp alignment accuracy meets the time synchronization requirements of subsequent linkage trajectory synthesis and torque gradient direction analysis.

[0024] In the specific implementation of S2, the position feedback signal obtained from the step of collecting the spindle torque signal and the position feedback signal of each linkage servo axis during the cutting process includes the linear displacement of the feed axis and the angular displacement of the workpiece rotation axis.

[0025] For the feed axis and workpiece rotation axis involved in the linkage, the angular displacement of the workpiece rotation axis is used as one spatial coordinate of the linkage trajectory, and the linear displacement of the feed axis is used as another spatial coordinate of the linkage trajectory. These two spatial coordinates constitute the linkage trajectory point in a planar coordinate system. At the sampling time corresponding to the unified time base timestamp, the position feedback signal of the feed axis is read as the coordinate value of the linkage trajectory point in the feed direction. The position feedback signal of the workpiece rotation axis is read, and the angular displacement of the workpiece rotation axis is multiplied by the radius of the workpiece at the cutting point to convert it into the arc length value of the cutting point moving along the workpiece surface, which is used as the coordinate value of the linkage trajectory point in the rotational tangent direction. These two coordinate values ​​together determine a spatial position point on the linkage trajectory corresponding to the sampling time. Connecting the spatial position points of all sampling times in chronological order yields the linkage trajectory.

[0026] On the current trajectory, spatial position points at several adjacent sampling times are taken. Using the coordinates of the feed direction as the independent variable and the coordinates of the rotation tangent direction as the dependent variable, a local curve is fitted to obtain a planar curve, which serves as the local trajectory for the current moment. The first and second derivatives of the curve equation of the local trajectory are then calculated.

[0027] The curvature κ is calculated as: κ=|y″| / (1+y′) 2 ) (3 / 2) Where κ represents the curvature of the local trajectory at the current moment, y′ represents the first derivative of the coordinate value in the rotational tangent direction with respect to the coordinate value in the feed direction, y″ represents the second derivative of the coordinate value in the rotational tangent direction with respect to the coordinate value in the feed direction, and |y″| represents the absolute value of y″. The dimension of curvature κ is 1 / mm, y′ is a dimensionless quantity, and the dimension of y″ is 1 / mm.

[0028] Since curvature reflects the degree of bending of the linkage trajectory, and the bending of the linkage trajectory is directly related to the change in cutting arc length, the cutting arc length refers to the length of the arc segment in contact between the tool and the workpiece during the cutting process. When the curvature of the linkage trajectory increases, the cutting arc length increases accordingly; when the curvature decreases, the cutting arc length decreases accordingly. The trend of curvature over time can represent the increase or decrease in cutting arc length.

[0029] The curvature's change over time is obtained by taking its first-order time derivative. Between two adjacent sampling moments, the curvature value at the previous sampling moment is the first curvature value, and the curvature value at the next sampling moment is the second curvature value. Subtracting the first curvature value from the second curvature value yields the difference in curvature. Dividing this difference by the time interval between the two sampling moments gives an approximate value of the first-order time derivative of the curvature at the current moment. If the first-order time derivative is positive, it indicates that the curvature is increasing, the linkage trajectory is becoming more curved, and the corresponding cutting arc length is also increasing. In this case, the direction of increase or decrease in the cutting arc length is the increasing direction. If the first-order time derivative is negative, it indicates that the curvature is decreasing, the linkage trajectory is becoming straighter, and the corresponding cutting arc length is also decreasing. In this case, the direction of increase or decrease in the cutting arc length is the decreasing direction. The increasing or decreasing direction is taken as the direction of change in the cutting arc length.

[0030] The spindle torque signal is acquired at various spatial points along the linkage trajectory and is considered a scalar field on the linkage trajectory. Within this scalar field, the directional derivative of the spindle torque signal along the arc length parameter of the linkage trajectory is calculated; the direction of this directional derivative is the gradient direction. Selecting the current sampling point and its two adjacent sampling points on the linkage trajectory, the spindle torque signal is used as a function of the arc length of the linkage trajectory. The values ​​of the spindle torque signals at adjacent sampling points are differencing, and then divided by the corresponding arc length increment to obtain the directional derivative value of the spindle torque signal along the tangent direction of the linkage trajectory. The arc length increment is calculated using the Euclidean distance between the coordinate difference of two adjacent spatial points in the feed direction and the coordinate difference in the rotation tangent direction. The sign of the directional derivative value indicates the gradient direction: a positive value indicates that the spindle torque signal increases along the positive direction of the linkage trajectory, and the gradient direction points to the positive direction of the linkage trajectory; a negative value indicates that the spindle torque signal increases along the negative direction of the linkage trajectory, and the gradient direction points to the negative direction of the linkage trajectory. The positive direction of the linkage trajectory is determined by the temporal order of the sampling times on the linkage trajectory.

[0031] Compare the direction of change in cutting arc length with the gradient direction. The direction of change in cutting arc length is either increasing or decreasing; increasing corresponds to a trend of increasing cutting arc length, and decreasing corresponds to a trend of decreasing cutting arc length. The gradient direction of the spindle torque signal points to the direction of the linkage trajectory where the spindle torque signal increases. If there is no chip clogging, an increase in cutting arc length will lead to an increase in cutting force, and the spindle torque signal should increase accordingly. The direction of increase in cutting arc length should be consistent with the gradient direction of increase in spindle torque signal. Conversely, the direction of decrease in cutting arc length should be consistent with the gradient direction of decrease in spindle torque signal. If the direction of change in cutting arc length points to increasing, but the gradient direction of spindle torque signal along the linkage trajectory points to the direction of decrease in spindle torque signal, then they point in opposite directions. Alternatively, if the direction of change in cutting arc length points to decreasing, but the gradient direction of spindle torque signal points to the direction of increase in spindle torque signal, they also point in opposite directions. When the direction of change of the cutting arc length is opposite to the direction of the gradient, it indicates that the trend of change of the spindle torque signal contradicts the trend of change of the cutting arc length expected by the curvature change of the linkage trajectory. This means that there are additional non-geometric factors affecting the magnitude of the cutting force, namely, blockage caused by chip accumulation in the chip space. When the direction of change of the cutting arc length is opposite to the direction of the gradient, it is determined that a precursor to blockage has occurred.

[0032] In the specific implementation of S3, the sampling time at which the precursor to blockage occurs is the reference time. The spindle torque signal obtained from the steps of acquiring the spindle torque signal and the position feedback signals of each linked servo axis during the cutting process is a one-dimensional discrete sequence that varies with time. Each sampling point corresponds to a torque amplitude and a sampling time.

[0033] Using the reference time as the center of the window, a segment of the spindle torque signal is captured forward and another segment is captured backward. The durations of these two segments are set according to the sampling period of the spindle torque signal. The forward segment's value is the sampling period of the spindle torque signal multiplied by an integer multiple, and the backward segment's value is the same integer multiple multiplied by the same integer multiple. This integer multiple is set based on the ratio between the control cycle of the spindle drive unit and the cutting time per revolution of the tool; for example, an integer multiple of 5 is used. This ensures that the analysis window covers the complete transition process of torque from increase to decrease before and after the blockage occurs. The forward and backward segments of the spindle torque signal are then combined to form the analysis window.

[0034] Within the analysis window, the torque amplitudes of adjacent sampling points are compared sequentially according to the sampling time. A sampling point is considered a local maximum when its torque amplitude is greater than both the preceding and following sampling points. If multiple local maximum sampling points appear within the analysis window, the sampling point with the largest absolute value of torque amplitude is selected as the sampling point used to determine the cutting torque direction.

[0035] Obtain the torque vector corresponding to the local maximum sampling point. The torque vector is the directional representation of the spindle torque signal in space. Its amplitude is the torque amplitude, and its direction is determined by the sign of the components of the spindle torque on each coordinate axis of the linkage axis coordinate system. The linkage axis coordinate system is a spatial coordinate system established with the motion directions of each linkage servo axis participating in the linkage as the coordinate axis directions. In the linkage axis coordinate system, the movement direction of the feed axis constitutes one coordinate axis direction, and the tangential direction of the workpiece rotation axis constitutes another coordinate axis direction. The spindle torque signal itself is a scalar. The direction of the torque vector corresponding to the spindle torque signal is determined by the decomposition relationship of the tool cutting force in the linkage axis coordinate system: the projection of the cutting force applied by the tool to the workpiece in the feed direction is the feed force component, the projection of the cutting force applied by the tool to the workpiece in the tangential direction of the workpiece rotation is the tangential force component, and the resultant force of the feed force component and the tangential force component is the total cutting force. The direction of the total cutting force is the direction of the torque vector. The feed force component is obtained through the torque current component of the feed axis servo drive, and the tangential force component is calculated by converting the spindle torque signal and the tool radius. The conversion relationship is that the tangential force component equals the spindle torque signal divided by the tool radius. The feed force component and the tangential force component are vector synthesized, and the direction of the resultant vector in the linkage axis coordinate system is taken as the cutting torque direction.

[0036] Each servo driver of a linked servo axis records the sign of its speed command value in each control cycle. When the sign of the speed command value in the current control cycle is opposite to that in the previous control cycle, it indicates that the axis has reversed its motion direction. The servo driver records the time of the reversal and the motion direction before the reversal, forming a motion direction reversal record. At the reference time, the motion direction reversal records of each linked servo axis are read. If a linked servo axis has a motion direction reversal record near the reference time, the reversal with the closest reversal time to the reference time is taken, and the motion direction before the reversal is reversed to obtain the gap opening direction. The gap opening direction represents the position of the transmission chain gap in the linked axis coordinate system. The unit vector direction of the gap opening direction in the linked axis coordinate system is taken as the release direction. If a linked servo axis does not have a motion direction reversal record near the reference time, the transmission chain of that axis has not undergone a gap opening process, and the release direction of that axis is taken as the zero vector. If the release direction of all linked servo axes is the zero vector, the zero vector in the linked axis coordinate system is directly taken as the release direction, and the spatial angle is zero degrees.

[0037] The cutting torque direction and the release direction are both converted to unit vectors in the linkage axis coordinate system. The spatial angle θ is calculated as: θ = arccos(F·R); where θ represents the spatial angle, F represents the cutting torque direction converted to a unit vector in the linkage axis coordinate system, R represents the release direction converted to a unit vector in the linkage axis coordinate system, · represents the dot product of the two unit vectors, and arccos represents the inverse cosine function. The spatial angle ranges from 0 degrees to 180 degrees, and its dimension is degrees.

[0038] From the position feedback signals obtained by collecting the spindle torque signal and the position feedback signals of each linked servo axis during the cutting process, the position feedback signal of the workpiece rotation axis at the reference time is read. The position feedback signal of the workpiece rotation axis at the reference time is the current rotation angle position of the workpiece.

[0039] In the specific implementation of S4, the spatial angle, cutting torque direction, release direction, and current workpiece rotation angle position have already been obtained in step S3. Step S4 uses these parameters to predict the phase interval in which the defect will occur. The speed error caused by the sudden change in torque essentially originates from the instantaneous opening of the transmission chain gap. When the gap opens, the actual movement direction of the servo axis deviates from the command direction, and the deviation direction is the release direction of the gap opening.

[0040] The speed error direction is directly taken from the release direction obtained in step S3. The release direction is a vector direction represented in the linkage axis coordinate system. The linkage axis coordinate system uses the movement direction of the feed axis and the tangent direction of the workpiece rotation axis as coordinate axes. The release direction has a clear component representation in the linkage axis coordinate system. This vector direction is also the direction of the actual movement deviation of the servo axis when the gap is opened, which is the speed error direction.

[0041] After determining the direction of the speed error, it is necessary to assess the degree of influence of the speed error direction on the surface quality of the workpiece. Defects on the machined surface of the workpiece, such as periodic bright bands or textures, are essentially the result of the deviation of the tool's normal position relative to the workpiece being imprinted on the workpiece surface. Only the projection component of the speed error in the normal direction of the workpiece surface will change the instantaneous normal distance between the tool and the workpiece.

[0042] The workpiece cross-sectional geometric parameters are known in advance. These parameters describe the shape of the workpiece's cross-sectional profile; for example, a rectangular cross-section workpiece has a rectangular cross-section. Taking a circular cross-section workpiece as an example, the expression for the cross-sectional profile function of a circular cross-section workpiece in the workpiece coordinate system is given by the equation of a circle at any point on the workpiece's cross-sectional profile. Taking the partial derivative of this equation with respect to the coordinate variables yields the partial derivative of the workpiece's cross-sectional profile function at the cutting point. The vector direction formed by these partial derivatives is the normal direction of the workpiece surface. The coordinates of the cutting point in the workpiece coordinate system are determined by the workpiece's current rotation angle position and the workpiece cross-sectional geometric parameters. The current rotation angle position comes from the workpiece rotation axis position feedback signal read in step S3 at the reference time. By superimposing the current rotation angle position of the workpiece with the initial angle reference in the workpiece cross-sectional geometric parameters, the azimuth angle of the cutting point relative to the workpiece's geometric center is obtained. Combined with the cross-sectional dimensions in the workpiece cross-sectional geometric parameters, the coordinate values ​​of the cutting point in the workpiece coordinate system are solved.

[0043] After obtaining the coordinates of the cutting point in the workpiece coordinate system, the gradient of the workpiece cross-sectional shape function at that coordinate is calculated. The direction of the gradient vector is the normal direction of the workpiece surface. In numerical calculations, the gradient of the workpiece cross-sectional shape function is obtained by taking the partial derivatives of the two components of the cutting point coordinates. The direction of the vector formed by the two partial derivatives in the workpiece coordinate system is the normal direction of the workpiece surface. This vector direction is then normalized to a unit vector.

[0044] The velocity error direction is converted to a unit vector in the linkage axis coordinate system, the workpiece surface normal direction is converted to a unit vector in the workpiece coordinate system, and the unit vector in the linkage axis coordinate system is converted to the workpiece coordinate system through a coordinate transformation matrix. The coordinate transformation matrix is ​​determined by the current rotation angle position of the workpiece, and the elements of the transformation matrix are the trigonometric function values ​​of the workpiece rotation angle.

[0045] The projection component P of the speed error onto the workpiece surface normal is calculated as: P = V·N; where P represents the projection component of the speed error onto the workpiece surface normal, V represents the unit vector of the speed error direction transformed into the workpiece coordinate system, N represents the unit vector of the workpiece surface normal direction in the workpiece coordinate system, and · represents the dot product of the two unit vectors. P is a dimensionless scalar with a value ranging from -1 to 1. When P is positive, it indicates that the speed error points inward into the workpiece, i.e., the tool deviates inward into the workpiece, resulting in overcutting; when P is negative, it indicates that the speed error points outward from the workpiece, i.e., the tool deviates away from the workpiece, resulting in undercutting.

[0046] The values ​​of the projection component P as a function of the workpiece's rotation angle are recorded during one full rotation. Using the workpiece's rotation angle as the x-axis and the value of the projection component P as the y-axis, a series of discrete sampled values ​​of the projection component P at fixed angular intervals along the workpiece circumference are obtained. The fixed angular interval is calculated based on the sampling period of the workpiece's rotation axis position feedback signal and the workpiece's current rotation speed. The conversion method is that the fixed angular interval equals the product of the workpiece's current rotation speed and the sampling period, then converted to angle units. In the discrete sampled value sequence, starting from the workpiece's current rotation angle position, the sampled values ​​of the projection component P corresponding to each angular interval are scanned sequentially according to the workpiece's rotation direction. When the signs of two adjacent sampled values ​​are positive and negative respectively, it indicates that the projection component P has crossed zero from positive to negative within the angular interval corresponding to these two sampled values. The median of the two angular positions corresponding to the positive and negative sampled values ​​is taken, or the precise angular position of the zero-crossing point is obtained through linear interpolation of the positive and negative sampled values. This angular position is used as the starting phase of the imprint.

[0047] The preset width is an angle range calculated based on the decay time of the servo axis speed error after the gap is opened. The speed error caused by the gap opening does not disappear instantaneously, but gradually decays with the position adjustment action of the servo controller. The duration of the decay process is related to the gain parameters of the servo controller and the inertia parameters of the drive train. The preset width is set as follows: by applying a step-shaped position deviation command to the servo driver, the time required for the actual position of the servo axis to transition from the initial value to the new steady-state value is recorded as the transition time. The transition time reflects the speed at which the servo controller corrects sudden position deviations. Multiplying the transition time by the current rotational speed of the workpiece axis yields the angle value spanned by the speed error on the workpiece circumference, and this angle value is used as the preset width. The size of the preset width is adjusted according to the actual servo parameters and the workpiece rotational speed; the higher the rotational speed or the slower the servo response, the larger the preset width should be.

[0048] Starting from the initial phase of the imprint, a predetermined angular range of width is intercepted along the workpiece rotation direction as the defect phase interval. The defect phase interval is a continuous angular range, with its starting boundary at the initial phase of the imprint and its ending boundary at the initial phase of the imprint plus the predetermined width. The defect phase interval reflects the workpiece rotation angle segment where the speed error caused by a sudden change in torque will produce an imprint on the workpiece surface, providing clear spatial coordinates for step S5 to adjust motion parameters in advance within the defect phase interval.

[0049] When implementing S5, the defect phase interval has been determined in step S4. Step S5 uses the defect phase interval to pre-adjust the motion parameters of the linkage shaft to avoid speed errors caused by sudden torque changes from leaving marks on the workpiece surface.

[0050] From the position feedback signals obtained through the steps of acquiring spindle torque signals and position feedback signals of each linked servo axis during the cutting process, the position feedback signal of the workpiece rotation axis is continuously read at each sampling moment, and the current sampled value of the position feedback signal is taken as the current angular position of the workpiece rotation axis. The current angular position of the workpiece rotation axis changes periodically with the workpiece rotation, ranging from 0 degrees to 360 degrees, and is incremented again from 0 degrees after each 360-degree rotation.

[0051] The angle difference D is calculated as: D = θstart - θcurrent; where D represents the angle difference, θstart represents the angle value corresponding to the starting boundary of the defect phase interval, and θcurrent represents the angle value corresponding to the current angular position of the workpiece rotation axis. The dimension of the angle difference is degrees. The starting boundary of the defect phase interval has been determined as the imprint starting phase in step S4.

[0052] The preset angle threshold is a lead time set based on the servo controller's response time and the current rotational speed of the workpiece axis. The preset angle threshold is set by multiplying the servo controller's speed loop response time by the current rotational speed of the workpiece axis, and using this lead time as the preset angle threshold. The servo controller's speed loop response time is obtained by inputting a speed step command to the servo controller and recording the time required for the actual speed to change from the initial value to 95% of the command value. This recorded time reflects how quickly the servo controller responds to changes in speed commands. The current rotational speed of the workpiece axis is obtained by dividing the difference between two adjacent sampling moments of the workpiece axis's position feedback signal by the sampling period. The preset angle threshold is dynamically adjusted as the current rotational speed of the workpiece axis changes; the higher the rotational speed, the larger the preset angle threshold, ensuring sufficient time for speed adjustment.

[0053] When the angle difference is less than the preset angle threshold, the motion parameters of the linkage axis are adjusted by either reducing the feed rate of the linkage axis or adjusting the workpiece rotation speed to a value different from the current rotation speed. The amplitude of the speed error refers to the absolute value of the projection component of the speed error obtained in step S4 onto the workpiece surface in the normal direction. The larger the amplitude of the speed error, the greater the actual position deviation of the servo axis when the gap is open, and the higher the risk of leaving marks on the workpiece surface. The method of reducing the feed rate of the linkage axis is to send a speed command lower than the current speed command value to the servo driver of the feed axis. The reduction amount is determined by the ratio of the amplitude of the speed error to the feed rate during normal cutting before the appearance of blockage precursors. For example, multiplying this ratio by the current feed rate command value gives the amount of feed rate reduction, and subtracting the reduction amount from the current feed rate command value gives the adjusted feed rate command value. After the feed rate is reduced, the instantaneous feed amount at the cutting point within the defect phase interval decreases, the actual position deviation of the servo axis when the gap is open decreases accordingly, and the amplitude of the speed error decreases accordingly. The method to adjust the workpiece rotation speed is to send a modified rotation speed command to the servo driver of the workpiece rotation axis. The modified rotation speed reduces the instantaneous rotation speed of the workpiece rotation axis when the workpiece rotates to near the starting phase of the imprint within the defect phase interval. This reduces the relative ratio between the linear velocity of the workpiece surface and the speed error at the moment the gap opens, thus weakening the degree to which the speed error produces an imprint on the workpiece surface.

[0054] The method for determining whether the workpiece rotation axis has passed through the defect phase interval is as follows: continuously read the position feedback signal of the workpiece rotation axis, compare the current angular position of the workpiece rotation axis with the angle value corresponding to the termination boundary of the defect phase interval, and determine that the workpiece rotation axis has passed through the defect phase interval when the current angular position of the workpiece rotation axis is greater than the angle value corresponding to the termination boundary of the defect phase interval. The termination boundary of the defect phase interval has been determined in step S4 as the imprint start phase plus a preset width.

[0055] After the workpiece rotation axis passes through the defect phase interval, the original feed rate or original workpiece rotation speed is restored. The original feed rate refers to the feed rate command value sent to the servo driver of the feed axis before the signs of blockage appear, and the original workpiece rotation speed refers to the speed command value sent to the servo driver of the workpiece rotation axis before the signs of blockage appear. The storage circuit inside the CNC system continuously stores the current feed rate command value and speed command value as a backup at fixed intervals during normal cutting. When it is necessary to restore the original feed rate or original workpiece rotation speed, the most recently stored feed rate command value and speed command value are read from the storage circuit inside the CNC system. The read feed rate command value is sent as the original feed rate to the servo driver of the feed axis, or the read speed command value is sent as the original workpiece rotation speed to the servo driver of the workpiece rotation axis.

[0056] Example 2: Figure 2 A schematic diagram of a multi-axis linkage control system for metal cutting according to the present invention is provided. The multi-axis linkage control system for metal cutting includes the following modules: The signal acquisition module is used to acquire the spindle torque signal and the position feedback signals of each linked servo axis during the cutting process; The precursor detection module is used to determine the direction of the cutting arc length change represented by the curvature change of the current linkage trajectory based on the position feedback signal, and to obtain the gradient direction of the spindle torque signal along the linkage trajectory. When the direction of the cutting arc length change is inconsistent with the gradient direction, it is determined that a blockage precursor has occurred. The included angle determination module is used to determine the peak direction of the spindle torque signal when the blockage precursor occurs based on the position feedback signal as the cutting torque direction, and to obtain the release direction of the transmission chain clearance in the linkage axis coordinate system when the blockage precursor occurs. The spatial angle between the cutting torque direction and the release direction is determined as the included angle, and the current rotation angle position of the workpiece is determined at the same time. The defect prediction module is used to determine the geometric relationship between the direction of the velocity error caused by the sudden change in torque and the direction of the linear velocity on the workpiece surface based on the included angle, and to determine the starting phase interval of the velocity error imprinting on the workpiece surface based on the current rotation angle position of the workpiece, as the defect phase interval. The speed adjustment module is used to adjust the feed speed of the linkage shaft or the rotation speed of the workpiece before the workpiece rotates into the defect phase range.

[0057] All calculations involved in the embodiments are dimensionless numerical calculations, and the preset parameters and thresholds in the calculations are set by those skilled in the art according to the actual situation.

[0058] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0059] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and inventive constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. A multi-axis linkage control method for metal cutting, characterized in that, Includes the following steps: S1: Acquire spindle torque signal and position feedback signal of each linked servo axis during the cutting process; S2: Determine the direction of the cutting arc length change represented by the curvature change of the current linkage trajectory based on the position feedback signal, and obtain the gradient direction of the spindle torque signal along the linkage trajectory. When the direction of the cutting arc length change is inconsistent with the gradient direction, it is determined that there is a sign of blockage. S3: When signs of blockage appear, determine the peak direction of the spindle torque signal when the signs of blockage occur based on the position feedback signal as the cutting torque direction, and obtain the release direction of the transmission chain clearance in the linkage axis coordinate system. Determine the spatial angle between the cutting torque direction and the release direction as the angle, and at the same time determine the current rotation angle position of the workpiece. S4: Determine the geometric relationship between the direction of the velocity error caused by the sudden change in torque and the direction of the linear velocity on the workpiece surface based on the included angle, and determine the starting phase interval of the velocity error imprinting on the workpiece surface based on the current rotation angle position of the workpiece, as the defect phase interval; S5: Before the workpiece rotates into the defect phase range, adjust the feed speed of the linkage shaft or the rotation speed of the workpiece.

2. The multi-axis linkage control method for metal cutting according to claim 1, characterized in that, Acquire spindle torque signals and position feedback signals of each linked servo axis during the cutting process, including: The spindle torque signal is obtained by utilizing the built-in torque observation function of the spindle drive unit, and the position feedback signal is obtained by utilizing the encoder interface of each linkage servo axis. The spindle torque signal and the position feedback signal are then timestamped using a unified time base.

3. The multi-axis linkage control method for metal cutting according to claim 1, characterized in that, The direction of the cutting arc length change, represented by the curvature change of the current linkage trajectory, is determined based on the position feedback signal. The gradient direction of the spindle torque signal along the linkage trajectory is also acquired. When the direction of the cutting arc length change is inconsistent with the gradient direction, a precursor to blockage is identified, including: The motion trajectories of each linked servo axis are synthesized using position feedback signals to obtain the linked trajectory. The curvature of the linked trajectory at the current moment and the curvature change trend over time are calculated. The direction of the increase or decrease of the cutting arc length corresponding to the curvature change trend over time is taken as the direction of the cutting arc length change. The directional derivative of the spindle torque signal along the linked trajectory is obtained to obtain the gradient direction of the spindle torque signal along the linked trajectory. When the direction of the cutting arc length change is opposite to the gradient direction, it is determined that there is a sign of blockage.

4. The multi-axis linkage control method for metal cutting according to claim 3, characterized in that, The direction of change of cutting arc length corresponding to the curvature change trend over time is taken as the direction of change of cutting arc length. This includes: taking the first time derivative of the curvature of the linkage trajectory at the current moment; when the first time derivative is positive, the direction of change of cutting arc length is determined to be the increasing direction; when the first time derivative is negative, the direction of change of cutting arc length is determined to be the decreasing direction. The increasing or decreasing direction is taken as the direction of change of cutting arc length.

5. The multi-axis linkage control method for metal cutting according to claim 1, characterized in that, When signs of impending blockage appear, the peak direction of the spindle torque signal at the time of the blockage is determined based on the position feedback signal as the cutting torque direction. The release direction of the transmission chain clearance in the linkage axis coordinate system is also obtained. The spatial angle between the cutting torque direction and the release direction is defined as the included angle. Simultaneously, the current rotational angle position of the workpiece is determined, including: Taking the moment when the blockage precursor appears as the reference moment, the torque vector direction corresponding to the sampling point where the torque amplitude reaches the local maximum before and after the reference moment is extracted from the spindle torque signal as the cutting torque direction. The motion direction reversal record of each linkage servo axis at the reference moment is obtained from the position feedback signal. The vector direction of the clearance opening direction indicated by the motion direction reversal record in the linkage axis coordinate system is taken as the release direction. The spatial angle between the cutting torque direction and the release direction is calculated. At the same time, the workpiece rotation axis position feedback signal at the reference moment is read to obtain the current rotation angle position of the workpiece.

6. The multi-axis linkage control method for metal cutting according to claim 5, characterized in that, Extracting the direction of the torque vector corresponding to the sampling point where the torque amplitude reaches a local maximum before and after the reference time from the spindle torque signal as the cutting torque direction includes: taking a segment of the spindle torque signal with the reference time as the center of the window, comparing the torque amplitude of adjacent sampling points within the window, determining the sampling point with a torque amplitude greater than the previous sampling point and greater than the next sampling point as the local maximum sampling point, and taking the direction of the torque vector corresponding to the local maximum sampling point in the linkage axis coordinate system as the cutting torque direction.

7. The multi-axis linkage control method for metal cutting according to claim 1, characterized in that, The geometric relationship between the direction of the velocity error caused by the sudden change in torque and the direction of the linear velocity on the workpiece surface is determined based on the included angle. The starting phase interval for the velocity error to leave an imprint on the workpiece surface is then determined based on the current rotational angular position of the workpiece, serving as the defect phase interval, including: The release direction determined by the included angle is taken as the speed error direction. The normal direction of the workpiece surface at the cutting point is calculated based on the current rotation angle position of the workpiece. The speed error direction and the normal direction of the workpiece surface are multiplied to obtain the projection component of the speed error on the normal direction of the workpiece surface. The phase corresponding to the zero-crossing point of the projection component from positive to negative is taken as the imprint start phase. The angle range of the preset width is intercepted along the workpiece rotation direction with the imprint start phase as the starting point as the defect phase interval.

8. The multi-axis linkage control method for metal cutting according to claim 7, characterized in that, The normal direction of the workpiece surface at the cutting point is calculated based on the current rotation angle position of the workpiece, including: obtaining the angle value of the workpiece rotation axis at the reference time from the position feedback signal as the current rotation angle position of the workpiece; determining the coordinates of the cutting point in the workpiece coordinate system based on the current rotation angle position of the workpiece and the geometric parameters of the workpiece cross section; and obtaining the normal direction of the workpiece surface by taking the partial derivative of the workpiece cross section shape function at the cutting point.

9. The multi-axis linkage control method for metal cutting according to claim 1, characterized in that, Before the workpiece rotates into the defect phase range, adjust the feed speed of the linkage axis or the workpiece rotation speed, including: The current angular position of the workpiece rotation axis is obtained in real time from the position feedback signal. The angle difference between the current angular position and the starting boundary of the defect phase interval is calculated. When the angle difference is less than the preset angle threshold, the feed speed of the linkage axis is reduced or the workpiece rotation speed is adjusted to reduce the amplitude of the speed error. After the workpiece rotation axis passes through the defect phase interval, the original feed speed or the original workpiece rotation speed is restored.

10. A multi-axis linkage control system for metal cutting, used to implement the multi-axis linkage control method for metal cutting as described in any one of claims 1-9, characterized in that, Includes the following modules: The signal acquisition module is used to acquire the spindle torque signal and the position feedback signals of each linked servo axis during the cutting process; The precursor detection module is used to determine the direction of the cutting arc length change represented by the curvature change of the current linkage trajectory based on the position feedback signal, and to obtain the gradient direction of the spindle torque signal along the linkage trajectory. When the direction of the cutting arc length change is inconsistent with the gradient direction, it is determined that a blockage precursor has occurred. The included angle determination module is used to determine the peak direction of the spindle torque signal when the blockage precursor occurs based on the position feedback signal as the cutting torque direction, and to obtain the release direction of the transmission chain clearance in the linkage axis coordinate system when the blockage precursor occurs. The spatial angle between the cutting torque direction and the release direction is determined as the included angle, and the current rotation angle position of the workpiece is determined at the same time. The defect prediction module is used to determine the geometric relationship between the direction of the velocity error caused by the sudden change in torque and the direction of the linear velocity on the workpiece surface based on the included angle, and to determine the starting phase interval of the velocity error imprinting on the workpiece surface based on the current rotation angle position of the workpiece, as the defect phase interval. The speed adjustment module is used to adjust the feed speed of the linkage shaft or the rotation speed of the workpiece before the workpiece rotates into the defect phase range.

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