A dynamic compensation system and method for machining thin-walled parts

Abstract

This invention discloses a dynamic compensation system and method for machining thin-walled parts, belonging to the field of precision manufacturing and CNC machining technology. The CNC machining unit drives the tool relative to the workpiece to form a basic machining motion according to the machining program; a node establishment module establishes the local surface normal and local remaining wall thickness information of the tool position node; a relative compliance determination module determines the tool-workpiece relative normal compliance parameters and the forward-looking normal compliance change index; a cutting force acquisition module acquires the normal cutting force component of the current tool position; a retraction prediction module determines the tool position to be compensated based on the current tool position and a preset number of forward tool moves, and determines the predicted normal retraction amount; a compensation generation module generates the target compensation amount; and a compensation execution module compensates the tool relative to the workpiece position in the basic machining motion according to the target compensation amount. This invention is beneficial for improving the machining accuracy and compensation stability of thin-walled parts.

Description

Technical Field

[0001] This invention relates to the fields of precision manufacturing and CNC machining technology, specifically to a dynamic compensation system and method for machining thin-walled parts. Background Technology

[0002] Thin-walled parts are widely used in aerospace, precision equipment, and high-end molds. These parts typically feature small wall thickness, high slenderness ratio, complex local surfaces, and weak structural rigidity. During CNC milling, as material is gradually removed, the remaining wall thickness of the workpiece continuously decreases, and the workpiece's lateral flexibility increases, making it prone to normal yielding under cutting forces. Simultaneously, the cutting tool, tool holder, and their clamping structure also undergo elastic deformation under cutting forces, causing the actual cutting position of the tool relative to the workpiece to deviate from the theoretical cutting position, thus leading to contour errors, dimensional errors, and a decrease in surface quality.

[0003] To address the deformation problem during the machining of thin-walled parts, existing technologies typically employ real-time compensation methods based on displacement detection, predictive compensation methods based on stiffness or flexibility models, and machining error correction methods based on on-machine measurements. While these approaches can improve the machining accuracy of thin-walled parts to some extent, they still have the following shortcomings in practical applications: 1. Existing compensation schemes mostly focus on the detection of the current tool position or the prediction of the deformation of the current tool position, and lack the ability to identify the weak and rigid areas that are about to appear ahead of the machining path, which can easily lead to a lag in compensation response. 2. Existing compensation schemes usually focus on workpiece-side deformation and do not adequately consider the influence of tool-end elastic deformation and tool-workpiece relative displacement, resulting in poor consistency between the compensation model and the actual machining state; 3. Existing compensation schemes lack a unified and systematic control mechanism for compensation triggering and execution under different processing conditions, resulting in insufficient compensation stability.

[0004] Therefore, there is an urgent need to propose a dynamic compensation system for thin-walled part machining, which can combine machining path nodes, tool-workpiece relative normal compliance, forward compliance variation trend and cutting force signal to dynamically compensate the actual cutting position of the tool relative to the workpiece during the machining process of thin-walled parts, thereby improving the machining accuracy and compensation stability of thin-walled parts. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects in the prior art, thereby providing a dynamic compensation system and method for thin-walled part processing.

[0006] A dynamic compensation system for thin-walled part machining, comprising: The CNC machining unit is used to drive the cutting tool to form a basic machining motion relative to the workpiece according to the machining program of the thin-walled part to be machined; The node establishment module is used to read the machining program and discretize the machining path according to the program segment number and tool position number to establish the local surface normal and local remaining wall thickness information of each tool position node. The relative compliance determination module is used to determine the tool-workpiece relative normal compliance parameters corresponding to each tool position node based on the local remaining wall thickness information and the current tool clamping state, and to determine the forward normal compliance change index of the current tool position. The cutting force acquisition module is used to acquire the cutting force signal of the current tool position during the machining process and extract the normal cutting force component along the local surface normal. The retraction prediction module is used to determine the tool position to be compensated based on the current tool position and the preset number of forward tool positions, and to determine the predicted normal retraction amount of the tool position to be compensated based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated and the normal cutting force component of the current tool position. The compensation generation module is used to determine the current machining state based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction amount of the tool position to be compensated, and to generate the target compensation amount when the current machining state belongs to the pre-activation mode or the enhanced compensation mode. The compensation execution module is used to compensate the tool position relative to the workpiece in the basic machining motion according to the target compensation amount, so as to correct the actual cutting position of the tool relative to the workpiece.

[0007] Furthermore, the preset number of forward tool positions is determined based on the total system delay, the current feed rate, and the path length between adjacent tool positions. The preset number of forward tool positions is the minimum number of tool positions required to ensure that the cumulative path length along the machining path from the current tool position is not less than the distance the tool moves along the machining path within the total system delay.

[0008] Furthermore, the relative compliance determination module is configured to determine the initial value of the local normal compliance on the workpiece side based on the local remaining wall thickness information of the i-th tool position node, determine the equivalent normal compliance parameter of the tool end based on the current tool clamping state, and determine the local normal compliance parameter of the workpiece side and the tool-workpiece relative normal compliance parameter of the i-th tool position node in the following manner: Cw(i) = μ(i)·Cw0(i); Crel(i) = Cw(i) + Ct(k); Wherein, Cw(i) is the workpiece-side local normal compliance parameter of the i-th tool position node, Crel(i) is the tool-workpiece relative normal compliance parameter of the i-th tool position node, μ(i) is the node correction coefficient of the i-th tool position node, Cw0(i) is the initial value of the workpiece-side local normal compliance of the i-th tool position node, and Ct(k) is the equivalent normal compliance parameter of the tool end under the current tool clamping state k.

[0009] Furthermore, the relative compliance determination module is also configured to determine the forward normal compliance change index of the i-th tool position node based on the workpiece-side local normal compliance parameters of multiple tool position nodes following the current tool position, in the following manner: H(i)=w1·Cw(i+1)+w2·Cw(i+2)+w3·Cw(i+3)-Cw(i); Where H(i) is the forward normal compliance change index of the i-th tool position node, Cw(i) is the workpiece-side local normal compliance parameter of the i-th tool position node, and w1, w2, and w3 are preset weights, satisfying w1>w2>w3.

[0010] Furthermore, the retraction prediction module determines the predicted normal retraction amount of the tool position to be compensated in the following manner: δpred(q) = Crel(q)·Fn(p); Where δpred(q) is the magnitude of the predicted normal retraction of the tool position to be compensated, Crel(q) is the tool-workpiece relative normal compliance parameter of the tool position to be compensated, and Fn(p) is the magnitude of the normal cutting force component of the current tool position.

[0011] Furthermore, the compensation generation module is configured as follows: When the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction of the tool position to be compensated are all less than their respective first thresholds, the current machining state is determined to be in monitoring mode, and no active compensation is output in the monitoring mode. When the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, or the predicted normal retraction of the tool position to be compensated is greater than or equal to the corresponding first threshold, and all three are less than their respective corresponding second thresholds, the current machining state is determined to be in the pre-activation mode, and a feedforward compensation amount is generated based on the predicted normal retraction amount and the pre-activation compensation coefficient, and the feedforward compensation amount is used as the target compensation amount. When the relative normal compliance parameter of the tool-workpiece of the tool position to be compensated, the forward normal compliance change index of the current tool position, or the predicted normal retraction of the tool position to be compensated is greater than or equal to the corresponding second threshold, the current machining state is determined to be in the enhanced compensation mode, and the enhanced compensation amount is generated according to the predicted normal retraction amount and the enhanced compensation coefficient, and the enhanced compensation amount is used as the target compensation amount. Wherein, the enhancement compensation coefficient is greater than the pre-activation compensation coefficient, and the second threshold corresponding to each index is greater than the corresponding first threshold.

[0012] Furthermore, the compensation execution module includes a multi-degree-of-freedom micro-displacement execution module disposed between the spindle and the tool holder. The compensation execution module is used to decompose the target compensation amount into compensation displacement components in each output direction of the multi-degree-of-freedom micro-displacement execution module, and drive the multi-degree-of-freedom micro-displacement execution module to output compensation displacement components corresponding to the local surface normal, so as to correct the actual cutting position of the tool relative to the workpiece. When the target compensation amount exceeds the rated stroke of the multi-degree-of-freedom micro-displacement execution module, the compensation execution module converts the compensation amount exceeding the rated stroke into a CNC machine tool feed axis position compensation command, and outputs the CNC machine tool feed axis position compensation command to the CNC machining unit, so that the CNC machining unit performs position correction on the basic machining motion and works in conjunction with the multi-degree-of-freedom micro-displacement execution module to complete the compensation.

[0013] This invention also includes a method for dynamic compensation in the processing of thin-walled parts, comprising the following steps: S1. Read the machining program of the thin-walled part to be machined, discretize the machining path according to the program segment number and tool position number, establish the local surface normal and local remaining wall thickness information of each tool position node, and drive the tool to form a basic machining motion relative to the workpiece according to the machining program. S2. Based on the local remaining wall thickness information and the current tool clamping state, determine the tool-workpiece relative normal compliance parameter corresponding to each tool position node, and determine the forward normal compliance change index of the current tool position. S3. During the machining process, acquire the cutting force signal of the current tool position and extract the normal cutting force component along the local surface normal. S4. Determine the tool position to be compensated based on the current tool position and the preset number of forward tool positions, and determine the predicted normal retraction amount of the tool position to be compensated based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated and the normal cutting force component of the current tool position. S5. Based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction amount of the tool position to be compensated, determine the current machining state, and generate the target compensation amount when the current machining state belongs to the pre-activation mode or the enhanced compensation mode. S6. Perform compensation according to the current machining state; in monitoring mode, do not perform active compensation; in pre-activation mode or enhanced compensation mode, compensate the tool position relative to the workpiece in the basic machining motion according to the target compensation amount to correct the actual cutting position of the tool relative to the workpiece. S7. If the processing path is not completed, take the next tool position as the new current tool position and repeat steps S3 to S6 until the processing path is completed.

[0014] Furthermore, step S5 specifically includes: When the tool-workpiece relative normal flexibility parameter of the tool position to be compensated, the forward normal flexibility change index of the current tool position, and the predicted normal retreat amount of the tool position to be compensated are all less than their respective corresponding first thresholds, it is determined that the current machining state belongs to the monitoring mode, and no active compensation is output in the monitoring mode; When the tool-workpiece relative normal flexibility parameter of the tool position to be compensated, the forward normal flexibility change index of the current tool position, or the predicted normal retreat amount of the tool position to be compensated is greater than or equal to the corresponding first threshold, and all three are less than their respective corresponding second thresholds, it is determined that the current machining state belongs to the pre-activation mode, and a feedforward compensation amount is generated according to the predicted normal retreat amount and the pre-activation compensation coefficient, and the feedforward compensation amount is used as the target compensation amount; When the tool-workpiece relative normal flexibility parameter of the tool position to be compensated, the forward normal flexibility change index of the current tool position, or the predicted normal retreat amount of the tool position to be compensated is greater than or equal to the corresponding second threshold, it is determined that the current machining state belongs to the enhanced compensation mode, and an enhanced compensation amount is generated according to the predicted normal retreat amount and the enhanced compensation coefficient, and the enhanced compensation amount is used as the target compensation amount; Among them, the enhanced compensation coefficient is greater than the pre-activation compensation coefficient, and the second threshold corresponding to each index is greater than the corresponding first threshold.

[0015] Further, in the pre-activation mode, the target compensation amount is generated in the following manner: |Δtar(q)| = K1·δpred(q); In the enhanced compensation mode, the target compensation amount is generated in the following manner: |Δtar(q)| = K2·δpred(q); Among them, |Δtar(q)| is the magnitude of the target compensation amount of the tool position to be compensated, δpred(q) is the magnitude of the predicted normal retreat amount of the tool position to be compensated, K1 is the pre-activation compensation coefficient, K2 is the enhanced compensation coefficient, and 0 < K1 < K2; the compensation direction of the target compensation amount is opposite to the predicted normal retreat direction of the tool position to be compensated.

[0016] Compared with the prior art, the technical solution of the present invention has the following advantages: The present invention forms a basic machining motion through a numerical control machining unit, and compensates the relative position of the tool to the workpiece in the basic machining motion according to the target compensation amount through a compensation execution module, which can combine the control of the machining program with the dynamic compensation control, and is beneficial to improving the cutting position control accuracy in the machining process of thin-walled parts.

[0017] The present invention discretizes the tool position nodes of the machining path through a node establishment module, and determines the tool-workpiece relative normal flexibility parameter and the forward normal flexibility change index by a relative flexibility determination module, which can identify the change trend of the weak stiffness area in front of the machining path in advance, and is beneficial to reducing the lag of the compensation response.

[0018] This invention determines the tool-workpiece relative normal compliance parameters based on local remaining wall thickness information and the current tool clamping state through a relative compliance determination module. This allows the compensation model to simultaneously consider the influence of the local normal compliance on the workpiece side and the equivalent normal compliance at the tool end on the actual cutting position of the tool relative to the workpiece, which helps to improve the consistency between the compensation model and the actual machining state.

[0019] This invention uses a cutting force acquisition module and a retraction prediction module to determine the predicted normal retraction amount based on the current tool position, the preset number of forward tool positions, the normal cutting force component, and the tool-workpiece relative normal compliance parameter of the tool position to be compensated. This enables the compensation control to act on the corresponding tool position to be compensated, which helps to reduce compensation lag or compensation misalignment.

[0020] This invention uses a compensation generation module to determine the current machining state based on the tool-workpiece relative normal compliance parameters, the forward normal compliance change index, and the predicted normal retraction amount, and generates a target compensation amount. This reduces unnecessary active compensation and avoids overcompensation while ensuring compensation accuracy.

[0021] This invention compensates for the relative position of the tool to the workpiece in the basic machining motion by means of a compensation execution module based on the target compensation amount. When the target compensation amount exceeds the rated stroke of the multi-degree-of-freedom micro-displacement execution module, the CNC machining unit and the multi-degree-of-freedom micro-displacement execution module work together to complete the compensation, which helps to improve the adaptability of the compensation range and the feasibility of the system. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 A system block diagram for a dynamic compensation system for thin-walled part machining; Figure 2 A flowchart for a dynamic compensation method for machining thin-walled parts. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] This embodiment provides a dynamic compensation system for thin-walled part machining, such as Figure 1 As shown, the system includes a CNC machining unit, a node establishment module, a relative compliance determination module, a cutting force acquisition module, a yield prediction module, a compensation generation module, and a compensation execution module. This system is suitable for dynamic compensation control in CNC milling of weakly rigid structural components such as aerospace blades, thin-shell parts, and thin-walled ribbed parts.

[0029] In this embodiment, the modules can be integrated into the same controller or distributed among the CNC machine tool control system, external compensation controller, sensor acquisition unit, and micro-displacement execution control unit. The modules can interact with each other or transmit control commands via the controller's internal data bus, industrial Ethernet, fieldbus, analog signals, digital signals, or the CNC system's internal data interface.

[0030] A CNC machining unit is used to drive the cutting tool to form basic machining movements relative to the workpiece according to the machining program of the thin-walled part to be machined. The CNC machining unit can be a CNC machine tool control system, a machining center control system, or a machining control unit connected to a CNC machine tool, which can control the predetermined relative movement between the cutting tool and the workpiece according to the machining program.

[0031] The node creation module is used to read the machining program of the thin-walled part to be machined, and to discretize the machining path according to the program segment number and tool position number, and to establish the local surface normal and local remaining wall thickness information of each tool position node.

[0032] Specifically, the node establishment module can read the CAD model, CAM toolpath, and NC machining program of the thin-walled part to be machined, and discretize the machining path according to the program segment number and the tool position sequence number within the segment to obtain the spatial position, local surface normal, and local remaining wall thickness information corresponding to each tool position node. The spatial position of each tool position node is used to characterize the position of the tool position node in the machining path and is used to determine the tool position to be compensated in combination with the tool position advancement relationship in the machining path; the local surface normal is used to extract the normal cutting force component of the current tool position and is used to determine the compensation direction of the target compensation amount in the compensation execution module; the local remaining wall thickness information is used to characterize the local load-bearing state after material removal at the corresponding tool position node and is used to determine the initial value of the local normal compliance on the workpiece side of the corresponding tool position node.

[0033] The relative compliance determination module is used to determine the tool-workpiece relative normal compliance parameters corresponding to each tool position node based on the local remaining wall thickness information and the current tool clamping status, and to determine the forward normal compliance change index of the current tool position.

[0034] The current tool clamping status can be obtained from the CNC system tool list, tool change record, manually input information, or tool clamping measurement results. The current tool clamping status may include at least one of the following: tool number, tool type, tool extension length, tool holder type, clamping length, and clamping method. The relative compliance determination module can determine the clamping status number k based on the current tool clamping status and retrieve the corresponding tool end equivalent normal compliance parameter Ct(k) from a pre-calibrated tool end equivalent normal compliance parameter library. The tool end equivalent normal compliance parameter library can be pre-established through static stiffness calibration, modal testing, or trial cutting calibration.

[0035] In this embodiment, the relative compliance determination module determines the initial value of the local normal compliance on the workpiece side based on the local remaining wall thickness information of the i-th tool position node, and determines the equivalent normal compliance parameter of the tool tip based on the current tool clamping state, and then determines it in the following manner: Cw(i) = μ(i)·Cw0(i); Crel(i) = Cw(i) + Ct(k); Wherein, Cw(i) is the workpiece-side local normal compliance parameter of the i-th tool position node, Crel(i) is the tool-workpiece relative normal compliance parameter of the i-th tool position node, μ(i) is the node correction coefficient of the i-th tool position node, Cw0(i) is the initial value of the workpiece-side local normal compliance of the i-th tool position node, and Ct(k) is the equivalent normal compliance parameter of the tool end under the current tool clamping state k.

[0036] Generally, the smaller the local residual wall thickness, the weaker the local load-bearing capacity of the corresponding tool position node, and the larger the initial value of the local normal compliance on the workpiece side. The node correction coefficient can be determined based on the first piece trial cut, light cut test, or pre-calibration results.

[0037] The relative compliance determination module can also determine the forward normal compliance variation index of the current tool position based on the workpiece-side local normal compliance parameters of multiple subsequent tool position nodes. Specifically, the forward normal compliance variation index of the i-th tool position node can be determined as follows: H(i)=w1·Cw(i+1)+w2·Cw(i+2)+w3·Cw(i+3)-Cw(i); Where H(i) is the forward normal compliance change index of the i-th tool position node, Cw(i) is the workpiece-side local normal compliance parameter of the i-th tool position node, and w1, w2, and w3 are preset weights, satisfying w1>w2>w3. When the forward normal compliance change index is large, it indicates that the workpiece-side normal compliance of several tool position nodes in front of the current tool position is on an upward trend, and the system can enter the pre-activation mode or the enhancement compensation mode in advance. When the number of subsequent tool position nodes of the current tool position is less than the preset number, the relative compliance determination module can determine the forward normal compliance change index based on the actual number of subsequent tool position nodes, or shorten the forward window.

[0038] The cutting force acquisition module is used to acquire the cutting force signal at the current tool position during machining and extract the normal cutting force component along the local surface normal. The cutting force acquisition module can be connected to a cutting force sensor, strain sensor, or piezoelectric sensor, which can be installed in the tool holder, spindle, fixture, or workpiece support. Based on the local surface normal at the current tool position, the cutting force acquisition module converts the acquired cutting force signal into a normal cutting force component along the local surface normal.

[0039] The retraction prediction module is used to determine the tool position to be compensated based on the current tool position and the preset number of forward tool positions, and to determine the predicted normal retraction amount of the tool position to be compensated based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated and the normal cutting force component of the current tool position.

[0040] In this embodiment, the current tool position is denoted as p, and the tool position to be compensated is denoted as q. The tool position to be compensated is the tool position node corresponding to the current tool position after moving forward a preset number of tool positions along the machining path. The preset number of tool positions is used to ensure that the compensation amount generated by the system corresponds to the machining position when the compensation command is actually applied, thereby reducing compensation lag or compensation misalignment.

[0041] The preset number of forward tool positions can be determined based on the total system delay, the current feed rate, and the path length between adjacent tool positions. Specifically, the preset number of forward tool positions is the minimum number of tool positions required to ensure that the cumulative path length moved forward along the machining path from the current tool position is not less than the distance the tool moves along the machining path within the total system delay. The total system delay can include sensor sampling delay, filtering delay, control calculation delay, and execution response delay.

[0042] In the case of equally spaced tool positions, the preset forward tool position number ΔN can be determined as follows: ΔN = ceil(τ·vf / Ls); Where ceil() represents the floor function, τ is the total system delay, vf is the current feed rate, and Ls is the average path length between adjacent tool positions. In the case of non-equally spaced tool positions, the path length between adjacent tool positions can be accumulated along the machining path starting from the current tool position. When the accumulated path length is not less than τ·vf for the first time, the corresponding tool position is determined as the tool position to be compensated.

[0043] The retraction prediction module determines the predicted normal retraction amount of the tool position to be compensated as follows: δpred(q) = Crel(q)·Fn(p); Where δpred(q) is the magnitude of the predicted normal retraction of the tool position to be compensated, Crel(q) is the tool-workpiece relative normal compliance parameter of the tool position to be compensated, and Fn(p) is the magnitude of the normal cutting force component of the current tool position. The feedforward compensation amount can be generated based on the predicted normal retraction amount, for example, it can be taken as the compensation displacement amount that is opposite in direction and corresponds to the magnitude of the predicted normal retraction amount.

[0044] The compensation generation module is used to determine the current machining state and generate the target compensation amount based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction amount of the tool position to be compensated.

[0045] In this embodiment, the compensation generation module can generate different forms of target compensation amounts based on the current machining state. Specifically, when the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction amount of the tool position to be compensated are all less than their respective first thresholds, it is determined that the current machining state belongs to the monitoring mode, and no active compensation is output in the monitoring mode.

[0046] When the tool-workpiece relative normal flexibility parameter of the tool position to be compensated, the forward-looking normal flexibility change index of the current tool position, or the predicted normal retraction amount of the tool position to be compensated is greater than or equal to the corresponding first threshold and all three are less than their respective corresponding second thresholds, it is determined that the current machining state belongs to the pre-activation mode. In the pre-activation mode, the compensation generation module generates a feedforward compensation amount according to the predicted normal retraction amount of the tool position to be compensated and the pre-activation compensation coefficient, and uses the feedforward compensation amount as the target compensation amount.

[0047] When the tool-workpiece relative normal flexibility parameter of the tool position to be compensated, the forward-looking normal flexibility change index of the current tool position, or the predicted normal retraction amount of the tool position to be compensated is greater than or equal to the corresponding second threshold, it is determined that the current machining state belongs to the enhanced compensation mode. In the enhanced compensation mode, the compensation generation module generates an enhanced compensation amount according to the predicted normal retraction amount of the tool position to be compensated and the enhanced compensation coefficient, and uses the enhanced compensation amount as the target compensation amount.

[0048] Specifically, in the pre-activation mode, the target compensation amount can be generated in the following manner: |Δtar(q)| = K1·δpred(q); In the enhanced compensation mode, the target compensation amount can be generated in the following manner: |Δtar(q)| = K2·δpred(q); Where, |Δtar(q)| is the magnitude of the target compensation amount of the tool position to be compensated, δpred(q) is the magnitude of the predicted normal retraction amount of the tool position to be compensated, K1 is the pre-activation compensation coefficient, K2 is the enhanced compensation coefficient, and 0 < K1 < K2. The compensation direction of the target compensation amount is opposite to the predicted normal retraction direction of the tool position to be compensated.

[0049] Among them, the pre-activation mode is used for feedforward compensation when there is a compensation trend in the current machining state but the risk level has not reached a high degree; the enhanced compensation mode is used to increase the compensation response intensity when the tool-workpiece relative normal flexibility parameter is large, the forward-looking normal flexibility change index is large, or the predicted normal retraction amount is large. The enhanced compensation mode increases the feedforward compensation intensity based on the predicted normal retraction amount through an enhanced compensation coefficient greater than the pre-activation compensation coefficient.

[0050] The compensation execution module is used to compensate for the tool's position relative to the workpiece during the basic machining motion according to the target compensation amount, so as to correct the actual cutting position of the tool relative to the workpiece. In this embodiment, the compensation execution module includes a multi-degree-of-freedom micro-displacement execution module disposed between the spindle and the tool holder. The compensation execution module decomposes the target compensation amount into compensation displacement components in each output direction of the multi-degree-of-freedom micro-displacement execution module according to the local surface normal, and drives the multi-degree-of-freedom micro-displacement execution module to output the compensation displacement components corresponding to the local surface normal, so as to correct the actual cutting position of the tool relative to the workpiece.

[0051] When the target compensation amount is less than or equal to the rated stroke of the multi-degree-of-freedom micro-displacement actuator module, the multi-degree-of-freedom micro-displacement actuator module directly completes the compensation. When the target compensation amount is greater than the rated stroke of the multi-degree-of-freedom micro-displacement actuator module, the compensation actuator module converts the compensation amount exceeding the rated stroke into a CNC machine tool feed axis position compensation command and outputs the CNC machine tool feed axis position compensation command to the CNC machining unit, so that the CNC machining unit corrects the position of the basic machining motion and works with the multi-degree-of-freedom micro-displacement actuator module to complete the compensation.

[0052] Please see Figure 2 This embodiment also provides a dynamic compensation method for thin-walled part machining, which can be executed by the aforementioned dynamic compensation system for thin-walled part machining. The method includes the following steps: S1. Read the machining program of the thin-walled part to be machined, discretize the machining path according to the program segment number and tool position number, establish the local surface normal and local remaining wall thickness information of each tool position node, and drive the tool to form a basic machining motion relative to the workpiece according to the machining program.

[0053] Specifically, the CAD model, CAM toolpath, and NC machining program of the thin-walled part to be machined can be read, and the machining path can be discretized according to the program segment number and the tool position number within the segment to obtain the spatial position, local surface normal, and local remaining wall thickness information of each tool position node.

[0054] S2. Based on the local remaining wall thickness information and the current tool clamping status, determine the tool-workpiece relative normal compliance parameters corresponding to each tool position node, and determine the forward normal compliance change index of the current tool position.

[0055] Specifically, the initial value of the local normal compliance on the workpiece side can be determined based on the local remaining wall thickness information, the equivalent normal compliance parameter of the tool end can be determined based on the current tool clamping state, and then the relative normal compliance parameter of the tool-workpiece can be determined; and the forward normal compliance change index can be determined based on the local normal compliance parameters of the workpiece side of multiple tool position nodes after the current tool position.

[0056] S3. During the machining process, acquire the cutting force signal of the current tool position and extract the normal cutting force component along the local surface normal.

[0057] S4. Determine the tool position to be compensated based on the current tool position and the preset number of forward tool positions, and determine the predicted normal retraction amount of the tool position to be compensated based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated and the normal cutting force component of the current tool position.

[0058] The preset number of forward tool positions can be determined based on the total system delay, the current feed rate, and the path length between adjacent tool positions; the tool position to be compensated is the tool position node corresponding to the current tool position after moving forward the preset number of forward tool positions along the machining path.

[0059] S5. Based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction amount of the tool position to be compensated, determine the current machining state, and generate the target compensation amount when the current machining state belongs to the pre-activation mode or the enhanced compensation mode.

[0060] Specifically, when the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction amount of the tool position to be compensated are all less than their respective first thresholds, the current machining state is determined to be in monitoring mode, and no active compensation is output in monitoring mode.

[0061] When the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, or the predicted normal retraction of the tool position to be compensated is greater than or equal to the corresponding first threshold, and all three are less than their respective corresponding second thresholds, the current machining state is determined to be in pre-activation mode. Then, a feedforward compensation amount is generated based on the predicted normal retraction of the tool position to be compensated and the pre-activation compensation coefficient, and the feedforward compensation amount is used as the target compensation amount.

[0062] When the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, or the predicted normal retraction amount of the tool position to be compensated is greater than or equal to the corresponding second threshold, the current machining state is determined to belong to the enhanced compensation mode. An enhanced compensation amount is generated based on the predicted normal retraction amount of the tool position to be compensated and the enhanced compensation coefficient, and this enhanced compensation amount is used as the target compensation amount. The second threshold corresponding to each index is greater than the corresponding first threshold.

[0063] In the pre-activation mode, the target compensation amount can be expressed as: |Δtar(q)|=K1·δpred(q); Under the enhanced compensation mode, the target compensation amount can be expressed as: |Δtar(q)|=K2·δpred(q); Where, |Δtar(q)| is the magnitude of the target compensation amount of the tool position to be compensated, δpred(q) is the magnitude of the predicted normal retraction amount of the tool position to be compensated, K1 is the pre-activated compensation coefficient, K2 is the enhanced compensation coefficient, and 0 < K1 < K2. The compensation direction of the target compensation amount is opposite to the predicted normal retraction direction of the tool position to be compensated.

[0064] S6. Perform compensation according to the current machining state; no active compensation is performed in the monitoring mode, and in the pre-activated mode or the enhanced compensation mode, the relative position of the tool to the workpiece in the basic machining motion is compensated according to the target compensation amount to correct the actual cutting position of the tool relative to the workpiece.

[0065] Specifically, the target compensation amount can be decomposed into compensation displacement components in the output directions of each output of the multi-degree-of-freedom micro-displacement execution module, and the multi-degree-of-freedom micro-displacement execution module is driven to output the compensation displacement component corresponding to the local surface normal to correct the actual cutting position of the tool relative to the workpiece. When the target compensation amount exceeds the rated stroke of the multi-degree-of-freedom micro-displacement execution module, the compensation amount exceeding the rated stroke can be converted into a position compensation command for the CNC machine tool feed axis, so that the CNC machining unit corrects the basic machining motion and cooperates with the multi-degree-of-freedom micro-displacement execution module to complete the compensation.

[0066] S7. When the machining path to be processed is not completed, take the next tool position as the new current tool position, and loop to execute steps S3 to S6 until the machining path to be processed is completed.

[0067] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of this invention.

Claims

1. A dynamic compensation system for thin-walled part processing, characterized in that, include: The CNC machining unit is used to drive the cutting tool to form a basic machining motion relative to the workpiece according to the machining program of the thin-walled part to be machined; The node establishment module is used to read the machining program and discretize the machining path according to the program segment number and tool position number to establish the local surface normal and local remaining wall thickness information of each tool position node. The relative compliance determination module is used to determine the tool-workpiece relative normal compliance parameters corresponding to each tool position node based on the local remaining wall thickness information and the current tool clamping state, and to determine the forward normal compliance change index of the current tool position. The cutting force acquisition module is used to acquire the cutting force signal of the current tool position during the machining process and extract the normal cutting force component along the local surface normal. The retraction prediction module is used to determine the tool position to be compensated based on the current tool position and the preset number of forward tool positions, and to determine the predicted normal retraction amount of the tool position to be compensated based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated and the normal cutting force component of the current tool position. The compensation generation module is used to determine the current machining state based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction amount of the tool position to be compensated, and to generate the target compensation amount when the current machining state belongs to the pre-activation mode or the enhanced compensation mode. The compensation execution module is used to compensate the tool position relative to the workpiece in the basic machining motion according to the target compensation amount, so as to correct the actual cutting position of the tool relative to the workpiece.

2. The dynamic compensation system for thin-walled part processing according to claim 1, characterized in that, The preset number of forward tool positions is determined based on the total system delay, the current feed rate, and the path length between adjacent tool positions. The preset number of forward tool positions is the minimum number of tool positions required to ensure that the cumulative path length along the machining path from the current tool position is not less than the distance the tool moves along the machining path within the total system delay.

3. The dynamic compensation system for thin-walled part processing according to claim 1, characterized in that, The relative compliance determination module is configured to determine the initial value of the local normal compliance on the workpiece side based on the local remaining wall thickness information of the i-th tool position node, determine the equivalent normal compliance parameter of the tool end based on the current tool clamping state, and determine the local normal compliance parameter of the workpiece side and the tool-workpiece relative normal compliance parameter of the i-th tool position node in the following manner: Cw(i) = μ(i)·Cw0(i); Crel(i) = Cw(i) + Ct(k); Wherein, Cw(i) is the workpiece-side local normal compliance parameter of the i-th tool position node, Crel(i) is the tool-workpiece relative normal compliance parameter of the i-th tool position node, μ(i) is the node correction coefficient of the i-th tool position node, Cw0(i) is the initial value of the workpiece-side local normal compliance of the i-th tool position node, and Ct(k) is the equivalent normal compliance parameter of the tool end under the current tool clamping state k.

4. The dynamic compensation system for thin-walled part processing according to claim 3, characterized in that, The relative compliance determination module is also configured to determine the forward normal compliance change index of the i-th tool position node based on the workpiece-side local normal compliance parameters of multiple tool position nodes following the current tool position, in the following manner: H(i)=w1·Cw(i+1)+w2·Cw(i+2)+w3·Cw(i+3)-Cw(i); Where H(i) is the forward normal compliance change index of the i-th tool position node, Cw(i) is the workpiece-side local normal compliance parameter of the i-th tool position node, and w1, w2, and w3 are preset weights, satisfying w1>w2>w3.

5. The dynamic compensation system for thin-walled part processing according to claim 1, characterized in that, The retraction prediction module determines the predicted normal retraction amount of the tool position to be compensated in the following manner: δpred(q) = Crel(q)·Fn(p); Where δpred(q) is the magnitude of the predicted normal retraction of the tool position to be compensated, Crel(q) is the tool-workpiece relative normal compliance parameter of the tool position to be compensated, and Fn(p) is the magnitude of the normal cutting force component of the current tool position.

6. The dynamic compensation system for thin-walled part processing according to claim 1, characterized in that, The compensation generation module is configured as follows: When the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction of the tool position to be compensated are all less than their respective first thresholds, the current machining state is determined to be in monitoring mode, and no active compensation is output in the monitoring mode. When the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, or the predicted normal retraction of the tool position to be compensated is greater than or equal to the corresponding first threshold, and all three are less than their respective corresponding second thresholds, the current machining state is determined to be in the pre-activation mode, and a feedforward compensation amount is generated based on the predicted normal retraction amount and the pre-activation compensation coefficient, and the feedforward compensation amount is used as the target compensation amount. When the relative normal compliance parameter of the tool-workpiece of the tool position to be compensated, the forward normal compliance change index of the current tool position, or the predicted normal retraction of the tool position to be compensated is greater than or equal to the corresponding second threshold, the current machining state is determined to be in the enhanced compensation mode, and the enhanced compensation amount is generated according to the predicted normal retraction amount and the enhanced compensation coefficient, and the enhanced compensation amount is used as the target compensation amount. Wherein, the enhancement compensation coefficient is greater than the pre-activation compensation coefficient, and the second threshold corresponding to each index is greater than the corresponding first threshold.

7. The dynamic compensation system for thin-walled part processing according to claim 1, characterized in that, The compensation execution module includes a multi-degree-of-freedom micro-displacement execution module disposed between the spindle and the tool holder. The compensation execution module is used to decompose the target compensation amount into compensation displacement components in each output direction of the multi-degree-of-freedom micro-displacement execution module, and drive the multi-degree-of-freedom micro-displacement execution module to output compensation displacement components corresponding to the local surface normal, so as to correct the actual cutting position of the tool relative to the workpiece. When the target compensation amount exceeds the rated stroke of the multi-degree-of-freedom micro-displacement execution module, the compensation execution module converts the compensation amount exceeding the rated stroke into a CNC machine tool feed axis position compensation command, and outputs the CNC machine tool feed axis position compensation command to the CNC machining unit, so that the CNC machining unit performs position correction on the basic machining motion and works in conjunction with the multi-degree-of-freedom micro-displacement execution module to complete the compensation.

8. A method for dynamic compensation in the machining of thin-walled parts, characterized in that, Includes the following steps: S1. Read the machining program of the thin-walled part to be machined, discretize the machining path according to the program segment number and tool position number, establish the local surface normal and local remaining wall thickness information of each tool position node, and drive the tool to form a basic machining motion relative to the workpiece according to the machining program. S2. Based on the local remaining wall thickness information and the current tool clamping state, determine the tool-workpiece relative normal compliance parameter corresponding to each tool position node, and determine the forward normal compliance change index of the current tool position. S3. During the machining process, acquire the cutting force signal of the current tool position and extract the normal cutting force component along the local surface normal. S4. Determine the tool position to be compensated based on the current tool position and the preset number of forward tool positions, and determine the predicted normal retraction amount of the tool position to be compensated based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated and the normal cutting force component of the current tool position. S5. Based on the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction amount of the tool position to be compensated, determine the current machining state, and generate the target compensation amount when the current machining state belongs to the pre-activation mode or the enhanced compensation mode. S6. Perform compensation according to the current machining state; in monitoring mode, do not perform active compensation; in pre-activation mode or enhanced compensation mode, compensate the tool position relative to the workpiece in the basic machining motion according to the target compensation amount to correct the actual cutting position of the tool relative to the workpiece. S7. If the processing path is not completed, take the next tool position as the new current tool position and repeat steps S3 to S6 until the processing path is completed.

9. The dynamic compensation method for thin-walled part processing according to claim 8, characterized in that, Step S5 specifically includes: When the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, and the predicted normal retraction of the tool position to be compensated are all less than their respective first thresholds, the current machining state is determined to be in monitoring mode, and no active compensation is output in the monitoring mode. When the tool-workpiece relative normal compliance parameter of the tool position to be compensated, the forward normal compliance change index of the current tool position, or the predicted normal retraction of the tool position to be compensated is greater than or equal to the corresponding first threshold, and all three are less than their respective corresponding second thresholds, the current machining state is determined to be in the pre-activation mode, and a feedforward compensation amount is generated based on the predicted normal retraction amount and the pre-activation compensation coefficient, and the feedforward compensation amount is used as the target compensation amount. When the relative normal compliance parameter of the tool-workpiece of the tool position to be compensated, the forward normal compliance change index of the current tool position, or the predicted normal retraction of the tool position to be compensated is greater than or equal to the corresponding second threshold, the current machining state is determined to be in the enhanced compensation mode, and the enhanced compensation amount is generated according to the predicted normal retraction amount and the enhanced compensation coefficient, and the enhanced compensation amount is used as the target compensation amount. Wherein, the enhancement compensation coefficient is greater than the pre-activation compensation coefficient, and the second threshold corresponding to each index is greater than the corresponding first threshold.

10. The dynamic compensation method for thin-walled part processing according to claim 9, characterized in that, In pre-activation mode, the target compensation amount is generated as follows: |Δtar(q)|=K1·δpred(q); In the enhanced compensation mode, the target compensation amount is generated as follows: |Δtar(q)|=K2·δpred(q); Where, |Δtar(q)| is the magnitude of the target compensation amount of the tool position to be compensated, δpred(q) is the magnitude of the predicted normal retraction amount of the tool position to be compensated, K1 is the pre-activated compensation coefficient, K2 is the enhanced compensation coefficient, and 0 < K1 < K2; the compensation direction of the target compensation amount is opposite to the predicted normal retraction direction of the tool position to be compensated.

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