A self-adaptive reconstruction post-processing method for rotation axis stroke overrun of a double-pendulum head five-axis machine tool

Abstract

This invention discloses an adaptive reconstructive post-processing method for overtravel of rotary axes in a dual-swivel-head five-axis machine tool, belonging to the field of CNC machining technology. The method first establishes a rotary axis state observer based on historical cache to monitor the state increment of the rotary axis in real time. By constructing a dewinding and abrupt change feature discrimination model, it determines the graded adaptive tool retraction distance. When a risk of overtravel or abrupt change in posture is detected, it triggers an axis-wise tool retraction based on tool axis isovector constraints, ensuring the tool retracts along the cutting vector line to avoid interference. Subsequently, after physical rewinding, the kinematic solution boundary conditions of the post-processor are corrected through a virtual state injection mechanism. Historical states are used as initial solution constraints for secondary solving, forcibly maintaining consistent head polarity. This invention maximizes continuous machining travel capability through seamless path reconstruction, eliminates tool marks caused by posture flipping, and significantly improves the surface consistency and efficiency of precision layered machining.

Description

Technical Field

[0001] This invention relates to the field of five-axis linkage machining in CNC machine tools, specifically to a post-processing method for five-axis linkage CNC machine tools with a BC double-swivel head structure. It is particularly suitable for adaptive reconstruction of machining paths in scenarios where the rotary axis travel exceeds limits during the deep cavity / spiral milling of complex aerospace structural parts and precision molds. Background Technology

[0002] In five-axis linkage machining of complex aerospace structural components and precision molds, BC double-swivel head machine tools are widely used due to their advantages such as fixed worktable and strong load-bearing capacity. In scenarios such as deep hole spiral milling and circumferential continuous layered machining, the rotary axis needs to achieve continuous rotational motion exceeding 360°. However, the physical travel of the machine tool's rotary axis has a hard limit, and existing post-processing technologies still have unresolved technical defects in handling rotary axis overtravel and attitude switching control. Among existing related technologies, patent CN102175997A discloses a method for handling rotary axis overtravel in five-axis linkage machining by finding the nearest equivalent angle of the C axis by reversing the polarity of the B axis, quickly pulling the overtravel axis back within its travel range; patent CN114254238A discloses a post-processing method for avoiding the limits of five-axis machine tool rotary axes by pre-calculating the rotary axis angles throughout the toolpath and planning the overtravel return point in advance. However, the above-mentioned existing technologies all have the following core defects in engineering applications:

[0003] 1) Fragmented rotary axis travel, resulting in a significant decrease in continuous machining capability: Existing near-circuit strategies only aim to map the overtravel angle to the nearest equivalent point within the travel range. This often leads to the rotary axis being located at the center of the travel range after circumvention, halving the remaining available continuous travel along the current cutting direction. For example, in the C-axis travel [-190°, +190°], when the overtravel reaches +195°, it circumvents to -165°, leaving only about 175° of continuous travel in the same direction. In deep cavity spiral groove and full circumferential machining, frequent overtravel circumvention is very likely to occur, leading to frequent tool breakage and tool retraction, severely reducing machining efficiency and tool life.

[0004] 2) Posture reversal disrupts surface uniformity, failing to meet precision machining requirements: Conventional overtravel return is generally accompanied by a reversal of the B-axis polarity (e.g., abrupt change from +45° to -45°), utilizing the multiple solutions of the BC double-swivel head inverse kinematics to achieve tool axis vector equivalence. However, in precision layer milling, the reversal of the B-axis physical posture leads to abrupt changes in machine tool geometric errors and the projection direction of the cutting force state onto the workpiece surface, resulting in visible tool marks and step differences between different machining layers, failing to meet the surface quality requirements of aerospace-grade parts.

[0005] 3) The retraction path lacks kinematic constraints, posing a serious risk of interference and collision: In Rotation Tool Center Point (RTCP) or fixed-plane machining mode, the physical Z-axis direction of the machine tool is not the actual tool axis direction. Retraction without considering the kinematic constraints of RTCP can easily cause the tool holder or tool to cut into the side wall of the workpiece, resulting in serious interference and collision.

[0006] Therefore, there is an urgent need for an adaptive reconfiguration post-processing method that can maintain the B-axis polarity, maximize the continuous rotational stroke in the same direction, and avoid interference risks under the condition of limited rotational axis stroke. Summary of the Invention

[0007] This invention aims to solve the above-mentioned problems by proposing an adaptive reconstructive post-processing method for overtravel of rotary axes in a dual-swivel-head five-axis machine tool. By establishing a rotary axis state observer based on historical cache, when a risk of overtravel or sudden posture change is detected, an axis-wise retraction based on the tool axis vector is triggered. After physical rewinding is completed, the initial solution is obtained by constraining inverse kinematics through virtual state injection, achieving continuous maintenance of machining posture and seamless path reconstruction. This method is integrated into a general-purpose post-processor for CNC programming and includes the following key steps:

[0008] S1: Establish a rotation axis state observer and risk assessment mechanism based on historical cache.

[0009] This invention defines a state observer based on historical cache. It is used to record the tool position coordinates, tool axis vector information, and corresponding machine tool rotary axis status of the previous interpolation cycle. The expression is as follows:

[0010]

[0011] in, This represents the position vector of the tool entry point in the workpiece coordinate system during the previous interpolation cycle. This represents the unit tool axis direction vector in the previous interpolation cycle. The physical rotation angle of the machine tool's B-axis during the previous interpolation cycle. This indicates the physical rotation angle of the machine tool's C-axis during the previous interpolation cycle.

[0012] For the tool position point in the current interpolation cycle, a pre-solution is first performed using the machine tool inverse kinematics model to obtain the theoretical rotation axis angle of the current tool position point, and a pre-solution state observer for the current cycle is then constructed. :

[0013]

[0014] in, The current state of the tool position and tool axis vector is output by the CAM software. The theoretical angle of the rotation axis is pre-solved for the current tool position. Based on the above state observer, the state increment and characteristic parameters of the rotation axis are calculated in real time during the current interpolation cycle, and risk classification is performed. The specific steps are as follows:

[0015] (1) Calculate angular displacement increment and stroke state: Real-time calculation and The absolute angular displacement changes between the rotation axes B and C and :

[0016]

[0017]

[0018] (2) Constructing a dewinding feature discrimination model: setting C-axis travel requirements C-axis overtravel warning threshold B-axis flip tolerance When the C-axis angle is detected to enter the travel limit warning range, and the polarity of the pre-solved B-axis direction is reversed from that of the previous cycle, and the reversal angle is within the tolerance range, it is determined that there is a risk of rotation axis unwinding in the current interpolation cycle. The judgment conditions are as follows:

[0019]

[0020] (3) Constructing a mutation feature discrimination model: setting a threshold for mutation of rotation axis angle. It is used to identify abnormal and drastic angle jumps and abnormal travel, and the discrimination criteria are as follows:

[0021]

[0022] (4) Hierarchical adaptive tool retraction algorithm triggering decision: Based on the above characteristics, the hierarchical decision logic is executed to set the tool retraction distance for stroke unwinding. The retraction distance for a large-angle abrupt change in the rotary axis is Define the graded adaptive retraction distance :

[0023]

[0024] S2: Adaptive out-of-axis retraction based on tool axis iso-vector constraints

[0025] when or When this occurs, it indicates that the current tool position point will cause the rotation axis to exceed the limit or the attitude to change abruptly. The system immediately pauses the current interpolation and triggers the out-of-axis tool retraction logic.

[0026] To avoid nonlinear motion interference in the RTCP state, the tool retraction path of this invention is based solely on tool axis vector planning in the workpiece coordinate system. The rotation axis angle remains constant throughout the entire retraction process, and only the machine tool translation axis is driven to perform linear motion, thus constructing a retraction target state containing six degrees of freedom constraints. The expression is as follows:

[0027]

[0028] use The tool position and tool axis vector are used to introduce a graded adaptive retraction distance. Calculate the tool position in the target retraction state:

[0029]

[0030] Retracting the target status Forced inheritance of tool vectors in The tool position vector, while the rotation axis angle remains unchanged, that is:

[0031]

[0032] The post-processor generates the corresponding linear motion instructions, driving the machine tool from... Exercise to Since the tool position vector remains constant, the rotation axis angle remains constant, and the machine tool moves from... Exercise to During the process, ensure that the tool exits strictly along the hole axis or cutting vector line at the previous interpolation moment to completely avoid sidewall interference.

[0033] S3-based wraparound path reconstruction using virtual state injection

[0034] The blade was safely retracted. Afterwards, rotation axis rewinding needs to be performed. This invention introduces a virtual state injection mechanism, using the rotation axis state before rewinding as the initial constraint condition for inverse kinematics solution, thereby avoiding the multi-solution jump problem that occurs after rewinding. Attitude maintenance is achieved by modifying the solver's boundary conditions. The virtual state injection only applies to the kinematic solution state within the post-processor and does not change the machine tool's physical structure or CNC system parameters.

[0035] (1) Physical wrap-around command output: according to C-axis angle recorded in Calculate the target angle after physical wraparound. :

[0036]

[0037] (Note: If Then reduce Conversely, add )

[0038] The system outputs commands to drive the machine tool's C-axis to physically rotate to Throughout the entire rewind process, the B-axis remains physically stationary, and the RTCP function remains continuously active, ensuring that the tool center point remains stable at all times. Position, no spatial displacement.

[0039] (2) Virtual state injection: Before calculating the final machining coordinates of the current tool position, the state register of the inverse kinematics solver inside the post-processor is forcibly overwritten, and the historical data in the state observer and the C-axis angle after wrapping are injected into the current system state:

[0040]

[0041]

[0042] (3) Quadratic solution and path reconstruction: utilizing the injected virtual state As the initial solution to the inverse kinematics equations, The expression is as follows:

[0043]

[0044] Using the injected virtual state as the initial value, the inverse kinematics solver is called again to calculate the current original overtravel tool position. Tool position data A second solution is performed to obtain the final machine tool axis coordinates. .

[0045]

[0046] in, Solve the inverse kinematics equations for the BC double-swivel head five-axis machine tool.

[0047] Due to the initial solution Having been forcibly constrained within the angular domain after wrapping around, the solution converged by the solver will necessarily maintain the polarity of the B-axis. Consistency is achieved, completely avoiding unnecessary B-axis flipping, while the tool axis vector is completely consistent with the original tool position, realizing a seamless connection from the tool retraction point to the tool re-entry point.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1) Maximizing continuous machining stroke of the rotary axis, significantly improving machining efficiency: For scenarios such as helical milling and continuous circumferential machining, this invention uses virtual state injection to force the C-axis to wrap around to the limit position of its stroke opposite to the current machining direction, rather than the stroke center position of existing technologies. For example, with a C-axis stroke of [-190°, +190°], this invention can achieve a continuous machining stroke of nearly 360° after wrapping, effectively avoiding frequent overtravel wrapping and tool advance / retreat in long-path machining, improving machining efficiency, and significantly extending tool life.

[0050] 2) Ensuring surface consistency in precision layered machining: By injecting virtual states to constrain the convergence direction of the inverse kinematics solution, the B-axis polarity is forced to remain unchanged, ensuring that the cutting posture, machine tool stress state, and geometric error distribution of each layer are completely consistent during layered machining. This completely eliminates tool marks and steps between layers caused by B-axis posture switching, achieving seamless reconstruction of the machining path.

[0051] 3) Adaptive safe retraction: In RTCP mode, a linear retraction method along the tool axis vector is adopted. The rotation axis angle remains unchanged throughout the retraction process, and only the translation axis moves, which completely solves the problem of workpiece sidewall interference when switching between fixed-axis machining and linkage machining. The RTCP function remains active throughout the retraction process, and there is no spatial displacement of the tool center point, which avoids the collision risk during the retraction process from the root.

[0052] 4) High versatility: This invention only operates on the kinematic solution process inside the post-processor, without requiring modification to the physical structure of the machine tool, the parameters of the CNC system, or the core functions of the CAM software. It can be adapted to all five-axis linkage CNC machine tools with BC double-swivel head structure, and has extremely high versatility and engineering applicability. Attached Figure Description

[0053] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0054] Figure 1 is the overall flowchart of the adaptive reconfiguration post-processing method for the excessive travel of the rotary axis of a dual-swivel head five-axis machine tool. Detailed Implementation

[0055] This embodiment uses a five-axis linkage machining center equipped with a BC double-swivel head structure and its supporting post-processing system as an example. The physical travel limit of the C-axis of this machine tool is [-190°, +190°], and the physical travel limit of the B-axis is [-95°, +95°]. The angle range described in this embodiment is only an example, and it can be adjusted according to the specific machine tool parameters in actual applications. Figure 1 The flowchart of an adaptive reconfiguration post-processing method for over-limit travel of the rotary axis of a dual-swivel head five-axis machine tool provided by the present invention is shown.

[0056] Step 1: Establish a rotation axis state observer and risk assessment mechanism based on historical cache.

[0057] A state observer based on a history cache is defined. It is used to record the tool position coordinates, tool axis vector information, and corresponding machine tool rotary axis status of the previous interpolation cycle. For example, it can be expressed as follows:

[0058]

[0059] get:

[0060]

[0061]

[0062] In the current interpolation cycle, if the C-axis has no travel limit, the obtained value will be... as follows:

[0063]

[0064] From the results = This clearly exceeds the physical travel limit of the C-axis [-190°, +190°]. Therefore, conventional post-processing will perform C-axis wrap-around calculations, resulting in the obtained... as follows:

[0065]

[0066] get:

[0067]

[0068]

[0069] The results show that the B-axis changed from -90° to 90°, and the C-axis changed from -190.556° to -10.556°. Although this solution satisfies the rotation axis travel constraint, the polarity reversal of the tool axis direction will cause the tool to cut into the workpiece sidewall unexpectedly, posing a serious risk of interference.

[0070] Under these conditions, and within the current interpolation cycle, the state increment and characteristic parameters of the rotation axis are calculated in real time. The specific steps are as follows:

[0071] Step 1.1 Calculate the angular displacement increment and stroke state

[0072] Real-time calculation under the current interpolation period and The absolute angular displacement changes between the rotation axes B and C and :

[0073]

[0074]

[0075] Step 1.2 Constructing a dewinding feature discrimination model

[0076] C-axis overtravel warning threshold B-axis flip tolerance Deconstruction feature discrimination condition :

[0077]

[0078] If all the above conditions are met, then:

[0079]

[0080] Step 1.3 Constructing a mutation feature discrimination model

[0081] Set the threshold for sudden changes in rotation axis angle Mutation feature discrimination conditions :

[0082]

[0083] get:

[0084]

[0085] Step 1.4: Hierarchical Adaptive Tool Retraction Algorithm Triggers Decision

[0086] Based on the above characteristics, a hierarchical decision-making logic is executed. Under the requirements of unwinding and sudden change, the distance of tool retraction along the axis is different, and the retraction distance for stroke unwinding is set accordingly. The retraction distance for a large-angle abrupt change in the rotary axis is Define the graded adaptive retraction distance :

[0087]

[0088] get:

[0089]

[0090] Step 2: Adaptive Extended-Axis Tool Retraction Based on Tool Axis Iso-Vector Constraints

[0091] when or When, it indicates that the state observer is in the current interpolation period. This could lead to the rotary axis exceeding its limits or a sudden change in posture, causing the system to immediately pause the current interpolation and trigger the along-axis retraction logic. To avoid nonlinear motion interference in the RTCP state, this invention does not move the physical axes of the machine tool, but instead constructs a retraction target state with six degrees of freedom constraints in the workpiece coordinate system. The expression is as follows:

[0092]

[0093] use The tool position and tool axis vector are used to introduce the graded adaptive retraction distance. Then the target state of the retraction tool. The tool position is calculated as follows:

[0094]

[0095] Retracting the target status Forced inheritance of tool vectors in The tool position vector, while the rotation axis angle remains unchanged, that is:

[0096]

[0097] In the current case state, we get:

[0098]

[0099] Subsequently, the post-processor generates the corresponding linear motion instructions, driving the machine tool from... Exercise to Since the tool position vector remains constant, the rotation axis angle remains constant, and the machine tool moves from... Exercise to During the process, ensure that the tool exits strictly along the hole axis or cutting vector line at the previous interpolation moment to completely avoid sidewall interference.

[0100] Step 3: Reconstructing the wraparound path based on virtual state injection

[0101] The blade was safely retracted. Subsequently, rotation axis rewinding needs to be performed. This invention proposes a virtual state injection mechanism, which achieves attitude maintenance by modifying the solver's boundary conditions:

[0102] Step 3.1 Physical wrap command output

[0103] according to C-axis angle recorded in Calculate the target angle after physical wraparound. :

[0104]

[0105] (Note: If Then reduce Conversely, add )

[0106] The system outputs commands to drive the machine tool's C-axis to physically rotate to At this time, the B-axis of the machine tool remains physically stationary.

[0107] Step 3.2 Virtual State Injection

[0108] Before calculating the entry point of the cutting edge, the internal status register of the post-processor is forcibly overwritten, and historical data from the status observer is injected into the current system state:

[0109]

[0110]

[0111] Step 3.3 Quadratic Solution and Path Reconstruction

[0112] Utilizing the injected virtual state As the initial solution to the inverse kinematics equations, The expression is as follows:

[0113]

[0114] Call the solver again to calculate the current interpolation point. The physical coordinates.

[0115]

[0116] Finally, we obtained:

[0117]

[0118] Due to the initial solution Having been forcibly constrained within the angular domain after wrapping around, the solution converged by the solver will necessarily maintain the polarity of the B-axis. This consistency avoids unnecessary B-axis flipping and achieves a seamless connection from the tool retraction point to the tool re-entry point. Furthermore, the C-axis angle, after virtual state injection and path reconstruction, changes from the previous... It became As the C-axis angle continues to decrease, the range of motion of the C-axis will be greatly increased, reducing the risk of continuous overtravel of the C-axis.

Claims

1. An adaptive reconfiguration post-processing method for excessive travel of rotary axes in a dual-swivel-head five-axis machine tool, characterized in that, Includes the following steps: S1: Establish a rotary axis state observer and risk assessment mechanism based on historical cache: Use the state observer to record the tool position coordinates, tool axis vector, and rotary axis state of the previous interpolation cycle. And obtain the status of the current interpolation cycle in real time. ; Calculate the angular displacement increment of the rotation axis and use the unwinding feature discrimination model. Mutation feature discrimination model Perform hierarchical decision-making to determine the adaptive retraction distance. ; S2: Perform adaptive long-axis retraction based on tool axis iso-vector constraints: When an over-limit or abrupt change risk is detected, construct the retraction target state in the workpiece coordinate system. ;make The tool position vector and rotation axis angle are forcibly inherited from and cause the tool to retract a distance along the current tool axis vector direction. Generate linear motion commands to drive the machine tool to complete the tool retraction; S3: Perform path reconstruction after wraparound based on virtual state injection: After performing physical wraparound of the rotation axis at the tool retraction point, the register state of the inverse kinematics solver inside the post-processor is forcibly overwritten through the virtual state injection mechanism; the injected virtual state is then reconstructed. The initial solution constraint conditions of the inverse kinematics solver are used to solve the tool position point of the current interpolation cycle for the second time to obtain the physical coordinates of the machine tool for re-entry, and the polarity of the machine tool head is kept consistent with that of the previous interpolation cycle throughout the process.

2. The method according to claim 1, characterized in that, In step S1, the unwinding feature discrimination model The criteria for discrimination are: ； in, This is the limit of the travel of the rotating shaft. The over-range warning threshold, For flip tolerance, The C-axis angle of the previous interpolation cycle. The B-axis angle is to be pre-solved for the current interpolation cycle. This is the B-axis angle of the previous interpolation cycle.

3. The method according to claim 1, characterized in that, In step S1, the mutation feature discrimination model The criteria for discrimination are: ； in, This represents the absolute angular displacement change along the B-axis between adjacent interpolation periods. This represents the absolute angular displacement change along the C-axis between adjacent interpolation periods. This is the threshold for sudden changes in the rotation axis angle.

4. The method according to claim 1, characterized in that, In step S1, the graded adaptive tool retraction distance The decision-making logic is as follows: ； in, The retraction distance for unwinding the travel. For retraction distances caused by large angle changes in the rotation axis, otherwise... .

5. The method according to claim 1, characterized in that, In step S2, the rotation axis state observer based on historical cache State observer with the current interpolation period The expression is: ； ； in, This represents the position vector of the tool entry point in the workpiece coordinate system during the previous interpolation cycle. This represents the unit tool axis direction vector in the previous interpolation cycle. The physical rotation angle of the machine tool's B-axis during the previous interpolation cycle. This indicates the physical rotation angle of the machine tool's C-axis during the previous interpolation cycle. The current state of the tool position and tool axis vector is output by the CAM software. The theoretical angle of the rotation axis is obtained by pre-solving for the current tool position.

6. The method according to claim 1, characterized in that, In step S2, the target state of tool retraction The expression is as follows: ； ； ； in, The coordinates of the target point for tool retraction. The tool axis vector for the target retraction state. This refers to the rotation axis angle maintained during the tool retraction process.

7. The method according to claim 1, characterized in that, In step S3, the target angle of the physical rotation of the rotating axis is determined. The calculation formula is: ； like Then reduce Conversely, add .

8. The method according to claim 1, characterized in that, In step S3, the specific implementation method of the virtual state injection is as follows: The machine tool's C-axis physically rotates to the target rotation angle. Then, the internal status register of the post-processor is forcibly overwritten: ； ； By injecting historical sway angles As an initial solution constraint, the inverse kinematics solver is forced to converge in the angular domain after wrapping around, thus avoiding B-axis polarity reversal.

9. The method according to claim 1, characterized in that, In step S3, the injected virtual state The expression is: ； The expression for the quadratic solution is: ； in, The machine tool axis coordinates are obtained from the second solution in the current interpolation cycle. Solve the inverse kinematics equations for the BC double-swivel head five-axis machine tool.

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