Five-axis machining center and shared axis geometric error hierarchical compensation system and method thereof

Abstract

The invention belongs to the technical field of precision control of numerical control machine tools, particularly relates to a five-axis machining center and a geometric error hierarchical compensation system and method thereof, and solves the problem of compensation interference during concurrent cutting of multiple spindles. The system comprises a physical architecture module, a hierarchy error modeling module and a virtual compensation controller, and a virtual axis control unit of the virtual compensation controller executes the following hierarchy compensation strategies: a common hierarchy: calculating a reference common error based on a shared X axis, and injecting the reference common error into the virtual axis control unit for pre-compensation; the cooperation level is used for collecting real-time cutting force feedback when compensation requirements conflict, dynamically adjusting the weight coefficient of each machining head according to the magnitude of the cutting force, and calculating the optimal common compensation amount by using a WLS algorithm; and the difference level is used for calculating the difference value between the demand of each machining head and the optimal common compensation amount, mapping and decomposing the residual error into independent additional motion instructions of each machining head, and executing compensation by each independent axis servo system. The effect of improving the overall machining precision of the large mold is achieved.

Description

Technical Field

[0001] This invention belongs to the field of CNC machine tool precision control technology, and specifically relates to a five-axis machining center and its shared axis geometric error hierarchical compensation system and method. Background Technology

[0002] In the field of modern ultra-precision manufacturing, especially in the machining of large aerospace components, automotive body panel molds, and thin-walled parts, multi-spindle concurrent cutting (MSSC) technology has become a key means to improve production efficiency and reduce equipment footprint. These machine tools typically employ a large gantry architecture, where multiple independent five-axis linkage machining heads are mounted on the same gantry beam and share the X-axis feed system.

[0003] However, the integration of this physical architecture also brings challenges to precision control. For example, the gantry beam inevitably has nonlinear geometric errors such as straightness, pitch, roll and yaw during its ultra-long stroke. These errors will act on all machining heads at the same time, and will produce complex coupling and amplification effects as the spatial position of the machining heads on the beam changes, affecting machining accuracy and quality. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems in the existing technology by proposing a hierarchical compensation system for shared axis geometric errors in a five-axis machining center.

[0005] The objectives of this invention can be achieved through the following technical solutions: A hierarchical compensation system for shared axis geometric errors in a five-axis machining center includes a physical architecture module, a hierarchical error modeling module, and a virtual compensation controller. The virtual compensation controller is equipped with a virtual axis control unit and executes the following hierarchical compensation strategy: At the common level, the baseline common error based on the shared X-axis is calculated and injected into the virtual axis control unit to pre-compensate the X-axis; In the collaborative layer, when multiple machining heads have conflicting compensation requirements for the X-axis, the real-time cutting force feedback of each machining head is collected, the weight coefficient of each machining head is dynamically adjusted according to the magnitude of the cutting force, and the optimal common compensation amount of the X-axis is calculated using the weighted least squares algorithm. The differential layer is used to calculate the difference between the requirements of each processing head and the optimal common compensation amount. The residual error is then decomposed into additional motion commands for each processing head's independent Y-axis, Z-axis, or rotary axis through inverse kinematic transformation, and the compensation is performed by the servo system of each independent axis.

[0006] This invention proposes a hierarchical compensation mechanism based on "common components + local differences," the core of which lies in spatially decoupling error sources. In the shared axis errors of a five-axis machining center, positioning errors are common, while rotational errors (such as pitch and roll) affect the tool tip point linearly or non-linearly with the offset of the machining head on the crossbeam. This invention constructs a "virtual axis" model using software algorithms, separating the common X-axis displacement from the fine-tuning displacements of each head. It utilizes the five-axis kinematic chains inherent in each head (such as the rotational or vertical axis of the spindle head) to absorb these conflicting errors, thereby achieving optimal accuracy for all machining heads simultaneously.

[0007] Furthermore, at the collaborative level, this invention directly converts the residuals of the weighted least squares algorithm into physical axis commands, which helps to solve accuracy dead zones. It also introduces a physical quantity, namely cutting force, to intervene in the calculation of the geometric quantity of error compensation. This is a cross-level control strategy that enables the machine tool to sense the machining status, easily distinguish between roughing and finishing, and thus intelligently allocate precision resources.

[0008] In the above-mentioned geometric error hierarchical compensation system, the hierarchical error modeling module adopts the following mathematical logic: , Among them, P i Let X be the tip position of i machining heads. shard Real-time feedback coordinates for the shared axis.

[0009] In the aforementioned geometric error hierarchical compensation system, the hierarchical error modeling module establishes the full error vector equation of machining head i through homogeneous coordinate transformation, and uses a spatial decoupling operator to define the rigid body displacement component that does not change with the Y / Z coordinates of the machining head among the 21 geometric errors generated by the shared axis as the reference common error E. base The shared axis rotation error term ε will be used to explain this error. xx ε yx ε zx The Abbe error component, which is generated by interference with the instantaneous offset of the processing head, is mapped to the independent fine-tuning axis of each channel for local differential compensation.

[0010] Reference common error E base This is obtained by "principal component extraction" of the total error requirement of all active processing heads. Specifically, this can be achieved using spatial decoupling operators, such as the Jacobian matrix or error propagation matrix based on Hidden Tense Motion (HTM). This is existing technology and will not be elaborated further. In the aforementioned geometric error hierarchical compensation system, after receiving the multi-channel interpolation command stream, the virtual compensation controller pre-calculates the error trend within a preset time window in the virtual axis control unit. When the rate of change dδ of the compensation demand for the shared axis from each channel is detected... reqWhen / dt exceeds the acceleration limit of the physical axis, the controller automatically reduces the common compensation amount of each channel according to the weight ratio, and feeds back the undigested residual error to the residual error prediction model of each channel, so that each independent axis can perform feedforward compensation.

[0011] The virtual axis control unit is not just a storage unit, but also has the ability to "predictively" process multi-channel commands, which can solve the dynamic response problem during high-speed cutting and demonstrate the robustness of the algorithm under extreme working conditions.

[0012] Another objective of this invention is to address the aforementioned problems in the prior art by proposing a hierarchical compensation method for shared axis geometric errors in a five-axis machining center.

[0013] To achieve this objective of the present invention, the following technical solutions can be used: A method for hierarchical compensation of shared axis geometric errors in a five-axis machining center, applicable to the aforementioned hierarchical compensation system for geometric errors, includes the following steps: S1. Initialize error mapping: Obtain 6 geometric error data of the shared axis throughout its full stroke through external measuring equipment, and generate a reference common error mapping table; S2. Spatial coordinate synchronous analysis: The CNC system reads the interpolation position in multiple channels in real time and identifies the relative position distribution of each machining head on the crossbeam; S3, Execution level compensation strategy: (1) Extract the reference common error components and feed them directly back to the X-axis servo drive for global pre-compensation; (2) Calculate the residual offset of each machining head at its respective tool tip point due to yaw and tumbling, and perform differential fine adjustment through the independent Y-axis or Z-axis of each machining head; S4: Conflict Coordination Optimization: When multiple processing heads have opposite directions or inconsistent values ​​for compensation requirements on a shared axis, the weighted least squares algorithm is called to calculate the optimal median compensation displacement.

[0014] In the above-described geometric error hierarchical compensation method, the least squares algorithm formula in step S4 is specifically as follows: , in, This is the common compensation amount that is ultimately sent to the X-axis driver. Let represent the X-axis requirement of the i-th channel.

[0015] In the geometric error hierarchy compensation method described above, the weighted least squares optimization process in step S4 assigns different weight coefficients according to the current accuracy level of the workpiece surface. This is to ensure priority compensation for high-precision mission areas.

[0016] Weighting coefficient Changing from a static constant to a dynamically evolving function helps solve the problem of striped texture on the surface of the workpiece.

[0017] In the above-mentioned geometric error hierarchical compensation method, the aforementioned The dynamic evolution function satisfies the following formula: Among them, Rank i As a task priority, For real-time cutting force feedback, Smooth is a position-dependent smoothing function.

[0018] Weight With real-time cutting force Inversely proportional; in other words, this method can sense the processing state, and the specific correspondence is as follows: Heavy cutting (large F) – roughing – low precision requirements – reduce weight ; Light cutting (small F) – finishing – high precision requirements – increased weighting .

[0019] This "process-aware" compensation strategy innovatively integrates cutting force with geometric compensation.

[0020] In the above-described geometric error hierarchical compensation method, step S1, specifically the acquisition of geometric error data, includes: A. Full-range measurement, using a laser interferometer to identify the 6 basic geometric errors sharing the X-axis; B. Spatial grid scanning, using a laser tracker to identify the displacement error of the tool tip at different positions on the crossbeam; C. Differential error identification: Local errors of the linkage Y / Z / A / C of each processing head are extracted using a double ballbar.

[0021] Separating the errors of each axis can be achieved using the "nine-line method" or the "twenty-one-line method". For a shared axis system, it is necessary to test under different counterweight loads on all main axes to compensate for the nonlinear elastic deformation of the crossbeam caused by uneven load distribution.

[0022] Another objective of this invention is to address the aforementioned problems in the prior art by proposing a five-axis machining center.

[0023] To achieve this objective of the present invention, the following technical solutions can be used: A five-axis machining center, applicable to the aforementioned geometric error level compensation system or method, includes a gantry beam and at least two machining head mounting seats disposed on the gantry beam. Machining heads are mounted on the machining head mounting seats via a lifting structure. Both ends of the gantry beam are disposed on a Y-axis bottom beam. An X-axis feed system is provided between the gantry beam and the Y-axis bottom beam. A Y-axis feed system is provided between the machining head mounting seats and the gantry beam. A machining station located below the machining head is provided between the gantry beam and the Y-axis bottom beam.

[0024] The gantry beam serves as a shared beam, with the Y-axis bottom beam perpendicular to it, used to mount and support both ends of the gantry beam. The machining head is slidably connected to the gantry beam via a machining head mounting seat. The X-axis feed system controls the translational movement of the gantry beam on the Y-axis bottom beam, and the Y-axis feed system controls the translational movement of the machining head mounting seat along the gantry beam. The lifting structure controls the lifting action of the machining head. The machining station is used to place and fix the product to be processed. This machining center achieves precise displacement of the machining head through a shared axis geometric error hierarchical compensation system and method, thereby improving machining quality. For illustrative purposes, the specific structures and operating principles of the lifting structure, machining head, X-axis feed system, Y-axis feed system, and machining station, as well as the installation structure between the gantry beam, machining head mounting seat, machining head, and Y-axis bottom beam, are all existing technologies and will not be elaborated further here.

[0025] Compared with the prior art, the present invention has the following main advantages: This invention proposes a hierarchical compensation mechanism based on "common components + local differences," the core of which lies in spatially decoupling error sources. In the shared axis errors of a five-axis machining center, positioning errors are common, while the influence of rotational errors on the tool tip varies linearly or non-linearly with the offset of the machining head on the crossbeam. This invention constructs a "virtual axis" model through software algorithms, separating the common displacement of the X-axis from the fine-tuning displacement of each head. It utilizes the five-axis kinematic chains inherent in each head (such as the rotational or vertical axis of the spindle head) to absorb these conflicting error quantities, thereby achieving optimal precision for all machining heads simultaneously. Furthermore, at the collaborative level, this invention directly converts the residuals of the weighted least squares algorithm into physical axis commands, helping to resolve precision blind spots. It also introduces a physical quantity, namely cutting force, to intervene in the calculation of the geometric quantity of error compensation. This is a cross-level control strategy that enables the machine tool to perceive the machining status, facilitating roughing and finishing, and thus intelligently allocating precision resources. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the geometric error hierarchical compensation system provided by the present invention; Figure 2 This is a flowchart illustrating the geometric error hierarchical compensation method provided by the present invention; Figure 3 This is a schematic diagram of the overall structure of the five-axis machining center provided by the present invention.

[0027] In the diagram, 1 is the gantry beam, 2 is the machining head mounting base, 3 is the lifting structure, 4 is the machining head, 5 is the Y-axis bottom beam, 6 is the X-axis feed system, 7 is the Y-axis feed system, and 8 is the machining station. Detailed Implementation

[0028] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings to further illustrate the technical solutions of the present invention. However, the present invention is not limited to these embodiments.

[0029] Specific implementation examples Figure 3 As shown, this five-axis machining center is applicable to a geometric error level compensation system or method, including a gantry beam 1 and two machining head mounting seats 2 set on the gantry beam 1. Machining heads 4 are set on the machining head mounting seats 2 through a lifting structure 3. The two ends of the gantry beam 1 are set on the Y-axis bottom beam 5. An X-axis feed system 6 is provided between the gantry beam 1 and the Y-axis bottom beam 5. A Y-axis feed system 7 is provided between the machining head mounting seats 2 and the gantry beam 1. A machining station 8 located below the machining head 4 is provided between the gantry beam 1 and the Y-axis bottom beam 5.

[0030] Specifically, the gantry beam 1 serves as a shared beam, and the Y-axis bottom beam 5 is perpendicular to the gantry beam 1, used to install and support both ends of the gantry beam 1. The machining head 4 is slidably connected to the gantry beam 1 via the machining head mounting seat 2. The X-axis feed system 6 is used to control the translational movement of the gantry beam 1 on the Y-axis bottom beam 5, and the Y-axis feed system 7 is used to control the translational movement of the machining head mounting seat 2 along the gantry beam 1. The lifting structure 3 is used to control the lifting action of the machining head 4. The machining station 8 is used to place and fix the product to be processed. This machining center achieves precise displacement control of the machining head 4 through a shared axis geometric error level compensation system and method, ensuring processing quality.

[0031] like Figure 1 As shown, the shared axis geometric error hierarchical compensation system for a five-axis machining center in this embodiment includes a physical architecture module, a hierarchical error modeling module, and a virtual compensation controller. The virtual compensation controller is equipped with a virtual axis control unit and executes the following hierarchical compensation strategy: At the common level, the baseline common error based on the shared X-axis is calculated and injected into the virtual axis control unit to pre-compensate the X-axis; In the collaborative layer, when multiple machining heads have conflicting compensation requirements for the X-axis, the real-time cutting force feedback of each machining head is collected, the weight coefficient of each machining head is dynamically adjusted according to the magnitude of the cutting force, and the optimal common compensation amount of the X-axis is calculated using the weighted least squares algorithm. The differential layer is used to calculate the difference between the requirements of each processing head and the optimal common compensation amount. The residual error is decomposed into additional motion commands for each processing head's independent Y-axis, Z-axis or rotary axis through inverse kinematic transformation, and the compensation is performed by the servo system of each independent axis.

[0032] Furthermore, the hierarchical error modeling module establishes the full error vector equation of machining head i through homogeneous coordinate transformation, and uses the spatial decoupling operator to define the rigid body displacement component that does not change with the Y / Z coordinates of the machining head among the 21 geometric errors generated by the shared axis as the reference common error E. base The shared axis rotation error term ε will be used to explain this error. xx ε yx ε zx The Abbe error component, generated by interference with the instantaneous offset of the machining head, is mapped to the independent fine-tuning axes of each channel for local differential compensation. The specific mathematical logic employed is as follows: , Among them, P i Let X be the tip position of i machining heads. shard Real-time feedback coordinates for the shared axis.

[0033] Furthermore, after receiving the multi-channel interpolation command stream, the virtual compensation controller pre-calculates the error trend within a preset time window in the virtual axis control unit. When it detects the rate of change dδ of the compensation demand for the shared axis from each channel... req When / dt exceeds the acceleration limit of the physical axis, the controller automatically reduces the common compensation amount of each channel according to the weight ratio, and feeds back the undigested residual error to the residual error prediction model of each channel, so that each independent axis can perform feedforward compensation.

[0034] Specific working principle: 1. Reference error acquisition: 21 error tests were performed on the shared X-axis using a laser interferometer.

[0035] 2. Constructing a virtual axis control unit: In the control system, the command coordinate of the X-axis is X... cmd Instead of being sent directly to the motor, the signal enters the virtual axis control unit.

[0036] 3. Layered compensation solution: (1) Calculate the average error caused by the common deflection of the beam and inject it into the X-axis motor.

[0037] (2) Calculate the Z-axis deviation of head 1 caused by the torsion of the crossbeam and compensate it independently through the Z-axis of head 1.

[0038] (3) Calculate the Y-axis deviation of head 2 caused by the horizontal straightness of the crossbeam, and compensate independently through the Y-axis of head 2.

[0039] 4. Dynamic refresh: As the compensation amount changes with position, the interpolation frequency is kept within 500µs to ensure smooth motion.

[0040] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A hierarchical compensation system for shared axis geometric errors in a five-axis machining center, characterized in that, It includes a physical architecture module, a hierarchical error modeling module, and a virtual compensation controller. The virtual compensation controller is configured with a virtual axis control unit and executes the following hierarchical compensation strategy: At the common level, the baseline common error based on the shared X-axis is calculated and injected into the virtual axis control unit to pre-compensate the X-axis; In the collaborative layer, when multiple machining heads have conflicting compensation requirements for the X-axis, the real-time cutting force feedback of each machining head is collected, the weight coefficient of each machining head is dynamically adjusted according to the magnitude of the cutting force, and the optimal common compensation amount of the X-axis is calculated using the weighted least squares algorithm. The differential layer is used to calculate the difference between the requirements of each processing head and the optimal common compensation amount. The residual error is then decomposed into additional motion commands for each processing head's independent Y-axis, Z-axis, or rotary axis through inverse kinematic transformation, and the compensation is performed by the servo system of each independent axis.

2. The geometric error hierarchical compensation system according to claim 1, characterized in that, The hierarchical error modeling module adopts the following mathematical logic: ， Among them, P i Let X be the tip position of i machining heads. shard Real-time feedback coordinates for the shared axis.

3. The geometric error hierarchical compensation system according to claim 1, characterized in that, The hierarchical error modeling module establishes the full error vector equation of machining head i through homogeneous coordinate transformation, and uses a spatial decoupling operator to define the rigid body displacement component that does not change with the Y / Z coordinates of the machining head among the 21 geometric errors generated by the shared axis as the reference common error E. base The shared axis rotation error term ε will be used to explain this error. xx ε yx ε zx The Abbe error component, which is generated by interference with the instantaneous offset of the processing head, is mapped to the independent fine-tuning axis of each channel for local differential compensation.

4. The geometric error hierarchical compensation system according to claim 1, characterized in that, After receiving the multi-channel interpolation command stream, the virtual compensation controller pre-calculates the error trend within a preset time window in the virtual axis control unit. When it detects the rate of change dδ of the compensation demand of each channel on the shared axis... req When / dt exceeds the acceleration limit of the physical axis, the controller automatically reduces the common compensation amount of each channel according to the weight ratio, and feeds back the undigested residual error to the residual error prediction model of each channel, so that each independent axis can perform feedforward compensation.

5. A method for hierarchical compensation of geometric errors of a shared axis in a five-axis machining center, applicable to the hierarchical compensation system of geometric errors as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Initialize error mapping: Obtain 6 geometric error data of the shared axis throughout its full stroke through external measuring equipment, and generate a reference common error mapping table; S2. Spatial coordinate synchronous analysis: The CNC system reads the interpolation position in multiple channels in real time and identifies the relative position distribution of each machining head on the crossbeam; S3, Execution level compensation strategy: (1) Extract the reference common error components and feed them directly back to the X-axis servo drive for global pre-compensation; (2) Calculate the residual offset of each machining head at its respective tool tip point due to yaw and tumbling, and perform differential fine adjustment through the independent Y-axis or Z-axis of each machining head; S4: Conflict Coordination Optimization: When multiple processing heads have opposite directions or inconsistent values ​​for compensation requirements on a shared axis, the weighted least squares algorithm is called to calculate the optimal median compensation displacement.

6. The geometric error hierarchical compensation method according to claim 5, characterized in that, In step S4, the weighted least squares algorithm formula for the optimal median compensation displacement is as follows: ， in, This is the common compensation amount that is ultimately sent to the X-axis driver. Let represent the X-axis requirement of the i-th channel.

7. The geometric error hierarchical compensation method according to claim 6, characterized in that, The weighted least squares optimization process in step S4 assigns different weight coefficients based on the current precision level of the workpiece surface. This is to ensure priority compensation for high-precision mission areas.

8. The geometric error hierarchical compensation method according to claim 7, characterized in that, The aforementioned The dynamic evolution function satisfies the following formula: Among them, Rank i As a task priority, For real-time cutting force feedback, Smooth is a position-dependent smoothing function.

9. The geometric error hierarchical compensation method according to claim 5, characterized in that, In step S1, the acquisition of geometric error data specifically includes: A. Full-range measurement, using a laser interferometer to identify the 6 basic geometric errors sharing the X-axis; B. Spatial grid scanning, using a laser tracker to identify the displacement error of the tool tip at different positions on the crossbeam; C. Differential error identification: Local errors of the linkage Y / Z / A / C of each processing head are extracted using a double ballbar.

10. A five-axis machining center, characterized in that, The geometric error hierarchical compensation system or method applicable to any one of claims 1-8 includes a gantry beam (1) and at least two machining head mounting seats (2) disposed on the gantry beam (1). The machining head mounting seats (2) are provided with machining heads (4) through a lifting structure (3). The two ends of the gantry beam (1) are disposed on the Y-axis bottom beam (5). An X-axis feed system (6) is provided between the gantry beam (1) and the Y-axis bottom beam (5). A Y-axis feed system (7) is provided between the machining head mounting seats (2) and the gantry beam (1). A machining station (8) located below the machining head (4) is provided between the gantry beam (1) and the Y-axis bottom beam (5).

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