Five-axis numerical control machine tool cutter positioning method and system for machining engine cylinder cover

Abstract

The invention relates to the technical field of five-axis numerical control machining, in particular to a five-axis numerical control machine tool cutter positioning method and system for machining an engine cylinder cover, and the method comprises the steps that a transition machining area is determined according to an engine cylinder cover combustion chamber machining model; a machining point sequence is generated along the transition machining area, and the axis direction of a valve seat, the local normal direction of the top wall of a combustion chamber and the peripheral boundary constraint direction of a spark plug hole are determined at all machining points; a continuous transition relation between the axis direction of the valve seat and the local normal direction of the top wall of the combustion chamber is constructed, the corresponding cutter shaft direction is determined by combining the constraint direction of the peripheral boundary of the spark plug hole, and the cutter pose is determined; the cutter shaft variable quantity and the five-axis numerical control machine tool rotating shaft variable quantity are restrained, and a continuous cutter pose sequence is obtained; and solving control parameters of each motion axis to obtain a tool positioning sequence. According to the method, continuous transition of the cutter shaft direction among different geometric references is achieved, and the smoothness and machining stability of the cutter pose sequence are improved.

Description

Technical Field

[0001] This invention relates to the field of 5-axis CNC machining technology, specifically a 5-axis CNC machine tool tool positioning method and system for machining engine cylinder heads. Background Technology

[0002] The CNC finishing of the engine cylinder head combustion chamber involves the coordinated machining of complex spatial curved surfaces and porous structures, which usually requires determining the tool posture based on the surface normal or the hole axis direction. In a four-valve roof structure, the combustion chamber is composed of the valve seat throat area, the top wall curved surface, and the area around the central spark plug hole. During the machining process, the tool needs to move continuously between different geometric features and complete posture adjustments.

[0003] Existing machining methods typically employ a tool axis determination method based on the local normal direction for curved surfaces, while a method based on the hole axis direction is used for hole systems. When the machining path crosses different regions, the tool axis direction needs to be switched between different references. However, due to the limited space inside the combustion chamber and the short geometric transition region, there is a significant difference between the surface normal direction and the valve seat hole axis direction in the transition zone formed between the valve seat throat, the combustion chamber top wall, and the spark plug hole. Furthermore, the spark plug hole structure imposes spatial constraints on the tool posture. Summary of the Invention

[0004] The purpose of this invention is to provide a 5-axis CNC machine tool positioning method and system for machining engine cylinder heads, so as to solve the problems of abrupt changes in tool axis posture and discontinuous positioning in the short transition area between the valve seat throat, the combustion chamber top wall and the spark plug hole.

[0005] To achieve the above objectives, in one aspect, the present invention provides a 5-axis CNC machine tool tool positioning method for machining engine cylinder heads, the method comprising:

[0006] Obtain the machining model of the engine cylinder head combustion chamber; determine the transition machining area based on the machining model of the engine cylinder head combustion chamber; generate a sequence of machining points along the transition machining area; determine the corresponding valve seat axis direction, the local normal direction of the combustion chamber top wall, and the boundary constraint direction of the spark plug hole at each machining point in the machining point sequence.

[0007] Based on the relative position parameters of the machining points in the transition machining area, a continuous transition relationship is constructed between the valve seat axis direction and the local normal direction of the combustion chamber top wall; based on the continuous transition relationship and the boundary constraint direction of the spark plug hole, the tool axis direction corresponding to each machining point is determined; based on the tool axis direction and spatial coordinates of each machining point in the machining point sequence, the corresponding tool pose is determined.

[0008] Based on the tool poses corresponding to adjacent machining points, the tool axis variation and the 5-axis CNC machine tool rotation axis variation are constrained to obtain a continuous tool pose sequence.

[0009] Based on the continuous tool pose sequence and the kinematic model of the 5-axis CNC machine tool, the control parameters of each motion axis of the 5-axis CNC machine tool are solved to obtain the tool positioning sequence.

[0010] Furthermore, the method for determining the transition machining area based on the engine cylinder head combustion chamber machining model includes:

[0011] Extract the valve seat throat boundary, spark plug orifice boundary, and combustion chamber top wall surface from the engine cylinder head combustion chamber machining model; using the valve seat throat boundary as the starting boundary, extend outward by a first preset width according to the geodesic distance of the combustion chamber top wall surface to obtain the throat transition zone; using the spark plug orifice boundary as the starting boundary, extend outward by a second preset width according to the geodesic distance of the combustion chamber top wall surface to obtain the spark plug transition zone; extract the connected surface sub-region on the combustion chamber top wall surface between the throat transition zone and the spark plug transition zone to obtain the preliminary transition region.

[0012] In the initial transition region, surface units whose distance from the valve seat throat boundary is no greater than a preset first distance threshold and whose distance from the spark plug orifice boundary is no greater than a preset second distance threshold are retained to obtain a constrained transition region; in the constrained transition region, surface units whose normal rate of change exceeds a preset normal rate of change threshold or whose curvature rate of change exceeds a preset curvature rate of change threshold are removed to obtain a filtered transition region; the filtered transition region is then subjected to boundary offset shrinkage according to the tool diameter parameters to obtain a transition machining region.

[0013] Furthermore, the method for determining the corresponding valve seat axis direction, the local normal direction of the combustion chamber top wall, and the boundary constraint direction of the spark plug hole at each processing point in the processing point sequence includes:

[0014] Extract the valve seat hole axis and spark plug hole axis from the engine cylinder head combustion chamber machining model; for each machining point in the machining point sequence, calculate the spatial distance between the machining point and each valve seat hole axis, select the valve seat hole axis with the smallest spatial distance, and determine the valve seat axis direction corresponding to the machining point.

[0015] A spherical neighborhood is constructed with each processing point as the center; surface elements of the combustion chamber top wall surface within the spherical neighborhood are extracted; the unit normal vector of each surface element is calculated; the unit normal vector is weighted and normalized according to the distance between the surface element and the processing point to obtain the initial local normal direction of the combustion chamber top wall corresponding to each processing point.

[0016] On the boundary of the spark plug orifice, determine the boundary point with the smallest distance from each processing point, and construct the direction vector of the boundary point pointing to the processing point; project the direction vector onto the tangent plane of the local normal direction of the combustion chamber top wall of the corresponding processing point and normalize it to obtain the initial spark plug orifice peripheral boundary constraint direction corresponding to each processing point.

[0017] Calculate the angle change between the initial local normal directions of the combustion chamber top wall and the angle change between the initial spark plug hole periphery boundary constraint directions corresponding to adjacent processing points; when the angle change is greater than the preset direction change threshold, update the direction of the corresponding processing point according to the weighted average result of the corresponding directions of adjacent processing points, and obtain the local normal direction of the combustion chamber top wall and the spark plug hole periphery boundary constraint direction.

[0018] Furthermore, the method for constructing a continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall based on the relative position parameters of the processing point in the transition processing area includes:

[0019] A transition path is determined along the transition processing area. The geodesic path arc length of each processing point along the transition path is calculated within the transition processing area. The ratio of the geodesic path arc length to the total arc length of the transition path is used as the initial position coefficient corresponding to each processing point. The rate of change of the initial position coefficients corresponding to adjacent processing points is calculated. When the rate of change is greater than a preset rate of change threshold, the initial position coefficients are subjected to nonlinear mapping processing to obtain the corrected position coefficients.

[0020] The rate of curvature change of the local normal direction of the combustion chamber top wall is calculated at each processing point; the normalized value of the rate of curvature change is used as a weighting modulation factor; a first weighting coefficient in the valve seat axis direction is calculated based on the correction position coefficient and the weighting modulation factor; a second weighting coefficient in the local normal direction of the combustion chamber top wall is determined based on the first weighting coefficient, such that the sum of the first weighting coefficient and the second weighting coefficient is 1; the first weighting coefficient and the second weighting coefficient are used as the continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall.

[0021] Furthermore, the method for calculating the first weighting coefficient in the valve seat axis direction based on the corrected position coefficient and the weighting modulation factor includes:

[0022] The correction position coefficient is transformed by a power function to obtain a first position weight term; the weight modulation factor and the correction position coefficient are multiplied and transformed by a power function to obtain a second position weight term; a normalized allocation relationship is constructed based on the first position weight term and the second position weight term to calculate the first weight coefficient in the valve seat axis direction.

[0023] Furthermore, the method for determining the tool axis direction corresponding to each machining point based on the continuous transition relationship and the boundary constraint direction of the spark plug hole includes:

[0024] At each machining point, the initial tool axis direction is obtained by weighted calculation of the valve seat axis direction and the local normal direction of the combustion chamber top wall based on the continuous transition relationship. At each machining point, the minimum clearance between the tool and the spark plug orifice boundary corresponding to the initial tool axis direction is calculated based on the tool geometry parameters and the spark plug orifice boundary. When the minimum clearance is less than the preset safety clearance, the angle between the spark plug orifice peripheral boundary constraint direction and the initial tool axis direction in the tangential plane at the machining point is calculated, and the corrected rotation axis direction corresponding to the angle is determined.

[0025] The correction angle is determined based on the difference between the minimum clearance and the preset safety clearance; the initial tool axis direction is rotated around the correction rotation axis by the correction angle to obtain a candidate tool axis direction; the minimum clearance corresponding to the candidate tool axis direction is updated to obtain the updated minimum clearance; when the updated minimum clearance is not less than the preset safety clearance, the candidate tool axis direction is determined as the tool axis direction corresponding to the machining point; when the updated minimum clearance is still less than the preset safety clearance, the correction angle is incrementally adjusted and the rotation and clearance verification are repeated until the minimum clearance is not less than the preset safety clearance or the preset convergence condition is met, and the final candidate tool axis direction is determined as the tool axis direction corresponding to the machining point.

[0026] Furthermore, the method for obtaining a continuous tool pose sequence by constraining the tool axis variation and the rotation axis variation of the 5-axis CNC machine tool based on the tool poses corresponding to adjacent machining points includes:

[0027] The tool pose corresponding to the first machining point in the machining point sequence is added to the continuous tool pose sequence as the starting pose. For each machining point in the machining point sequence, the inverse kinematics solution is performed on the corresponding tool pose according to the kinematic model of the 5-axis CNC machine tool to obtain the set of rotation axis angle solutions. The set with the smallest change in angle between the previous machining point and the corresponding rotation axis angle solution is selected as the current rotation axis solution.

[0028] Calculate the change in the tool axis angle between the current tool pose and the previous tool pose, as well as the change in the rotation angle between the corresponding rotation axis angle solutions; when the change in the tool axis angle is greater than a preset tool axis angle threshold or the change in the rotation angle is greater than a preset rotation angle threshold, determine the smoothing intensity coefficient based on the correction position coefficient of the current machining point in the transition machining area.

[0029] Using the previous tool pose as a reference, the tool axis direction of the current tool pose is weighted, combined, and normalized to obtain candidate tool poses. Constraint checks are performed on the candidate tool poses. When the updated tool axis angle change and rotation angle change are both no greater than the corresponding threshold, the candidate tool pose is added to the continuous tool pose sequence. If the constraint conditions are not met, the smoothing intensity coefficient is increased, and the tool axis direction adjustment and constraint checks are repeated until the condition that the tool axis angle change and rotation angle change are both no greater than the corresponding threshold is met. The final candidate tool pose is then added to the continuous tool pose sequence.

[0030] Based on the same inventive concept, in another aspect, the present invention also provides a 5-axis CNC machine tool positioning system for machining engine cylinder heads, the system comprising:

[0031] The region definition module is used to obtain the machining model of the engine cylinder head combustion chamber; determine the transition machining region based on the machining model of the engine cylinder head combustion chamber; generate a sequence of machining points along the transition machining region; and determine the corresponding valve seat axis direction, the local normal direction of the combustion chamber top wall, and the boundary constraint direction of the spark plug hole at each machining point in the machining point sequence.

[0032] The tool axis generation module is used to construct a continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall based on the relative position parameters of the machining points in the transition machining area; determine the tool axis direction corresponding to each machining point based on the continuous transition relationship and the boundary constraint direction of the spark plug hole; and determine the corresponding tool pose based on the tool axis direction and spatial coordinates of each machining point in the machining point sequence.

[0033] The motion smoothing module is used to constrain the tool axis change and the 5-axis CNC machine tool rotation axis change based on the tool pose corresponding to adjacent machining points, so as to obtain a continuous tool pose sequence.

[0034] The tool positioning module is used to solve the control parameters of each motion axis of the 5-axis CNC machine tool based on the continuous tool pose sequence and the kinematic model of the 5-axis CNC machine tool, and obtain the tool positioning sequence.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. Based on the relative position parameters of the machining point in the transition machining area, a continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall is constructed. Combined with the boundary constraint direction of the spark plug hole, the tool axis direction is constrained in a coordinated manner to realize the continuous change of the tool axis direction between different geometric references. This effectively avoids abrupt changes in tool axis posture in the short transition area between the valve seat throat, the combustion chamber top wall and the spark plug hole, and improves the continuity of tool positioning and the stability of the machining process.

[0037] 2. The inverse kinematics of the tool pose is solved, and a constraint evaluation mechanism is constructed by combining the changes in the rotation axis and the changes in the tool axis angle. At the same time, the smoothing intensity is adaptively adjusted according to the correction position coefficient, and the tool axis direction is iteratively weighted and adjusted to achieve coordinated optimization of tool axis changes and machine tool rotation axis motion, reduce machine tool motion impact and axis fluctuation, and improve the smoothness and executability of the tool pose sequence. Attached Figure Description

[0038] Figure 1 This is a flowchart illustrating a tool positioning method for a 5-axis CNC machine tool used for machining engine cylinder heads, according to the present invention.

[0039] Figure 2 This is a block diagram of a tool positioning system for a 5-axis CNC machine tool used for machining engine cylinder heads, according to the present invention. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Before providing examples, it is necessary to describe the application scenario of this invention. This invention is applicable to the five-axis CNC precision machining scenario of the combustion chamber of a four-valve top-mounted engine cylinder head. In this scenario, the tool needs to move continuously along a narrow transition machining area between the valve seat throat region, the curved surface of the combustion chamber top wall, and the periphery of the central spark plug hole. The machining path is distributed in a strip shape and the space is significantly limited. The tool axis direction is simultaneously constrained by the hole system structure and the curved surface shape, requiring continuous attitude adjustment under multiple reference conditions within a short distance.

[0042] Example 1: As Figure 1 As shown, this embodiment provides a method for positioning a 5-axis CNC machine tool for machining engine cylinder heads, the method comprising:

[0043] Obtain a machining model of the engine cylinder head combustion chamber; determine a transition machining area based on the engine cylinder head combustion chamber machining model; the method for determining the transition machining area based on the engine cylinder head combustion chamber machining model includes:

[0044] Extract the valve seat throat boundary, spark plug orifice boundary, and combustion chamber top wall surface from the engine cylinder head combustion chamber machining model; using the valve seat throat boundary as the starting boundary, extend outward by a first preset width according to the geodesic distance of the combustion chamber top wall surface to obtain the throat transition zone; using the spark plug orifice boundary as the starting boundary, extend outward by a second preset width according to the geodesic distance of the combustion chamber top wall surface to obtain the spark plug transition zone; extract the connected surface sub-region on the combustion chamber top wall surface between the throat transition zone and the spark plug transition zone to obtain the preliminary transition region.

[0045] In the initial transition region, surface units whose distance from the valve seat throat boundary is no greater than a preset first distance threshold and whose distance from the spark plug orifice boundary is no greater than a preset second distance threshold are retained to obtain a constrained transition region; in the constrained transition region, surface units whose normal rate of change exceeds a preset normal rate of change threshold or whose curvature rate of change exceeds a preset curvature rate of change threshold are removed to obtain a filtered transition region; the filtered transition region is then subjected to boundary offset shrinkage according to the tool diameter parameters to obtain a transition machining region.

[0046] For example, the engine cylinder head combustion chamber machining model adopts a STEP format 3D model. The combustion chamber is a four-valve canopy structure, containing two intake valves and two exhaust valves. The valve seat throat boundary is a closed annular curve, the spark plug orifice boundary is a closed circular curve, and the combustion chamber top wall surface is a continuous curved surface with inclined sides. The valve seat throat boundary is obtained by identifying the closed boundary at the junction of the valve seat orifice and the combustion chamber, the spark plug orifice boundary is obtained by identifying the closed boundary at the junction of the spark plug orifice and the combustion chamber, and the combustion chamber top wall surface is obtained by extracting the surface patch connecting the valve seat throat boundary and the spark plug orifice boundary.

[0047] The curved surface of the combustion chamber top wall is discretized into a triangular mesh with an average side length of 0.5 mm. On the curved triangular mesh, the geodesic distance field is calculated using the rapid travel method, starting from the valve seat throat boundary, and then extended by 3 mm along the geodesic distance direction to obtain the throat transition zone. Similarly, the geodesic distance field is calculated using the rapid travel method, starting from the spark plug orifice boundary, and then extended by 2 mm along the geodesic distance direction to obtain the spark plug transition zone.

[0048] In the triangular mesh of the curved surface on the combustion chamber top wall, the surface elements corresponding to the throat transition zone and the spark plug transition zone are marked. The set of surface elements belonging to the connected regions of both is extracted to obtain the preliminary transition region. Within the preliminary transition region, the geodesic distance to the valve seat throat boundary is calculated for each surface element. and geodetic distance to the spark plug orifice boundary , retain satisfaction and The surface elements are used to obtain the constrained transition region.

[0049] Within the constrained transition region, calculate the unit normal vector for each surface element; calculate the rate of change of normal vector based on adjacent surface elements. ;in, and The unit normal vector of the adjacent surface element. This represents the side length of the common edge of adjacent surface elements. Calculate the Gaussian curvature of each surface element. In the spherical neighborhood radius Calculate the rate of change of curvature within the range ;in, Let be the average Gaussian curvature of all surface elements within the spherical neighborhood of a surface element. Elements satisfying are excluded. or The curved surface unit is used to obtain the transition region after screening. The tool diameter is 10 mm, corresponding to a tool radius of 5 mm. The boundary of the transition region after screening is reduced by geodesic distance on the curved surface of the combustion chamber top wall. The reduction distance is 1.5 mm to reserve sufficient tool contact area and avoid overcutting caused by sudden changes in boundary curvature, thus obtaining the transition machining region.

[0050] A sequence of machining points is generated along the transition machining region; at each machining point in the sequence, the corresponding valve seat axis direction, the local normal direction of the combustion chamber top wall, and the boundary constraint direction of the spark plug hole are determined; the method for determining the corresponding valve seat axis direction, the local normal direction of the combustion chamber top wall, and the boundary constraint direction of the spark plug hole at each machining point in the sequence includes:

[0051] Extract the valve seat hole axis and spark plug hole axis from the engine cylinder head combustion chamber machining model; for each machining point in the machining point sequence, calculate the spatial distance between the machining point and each valve seat hole axis, select the valve seat hole axis with the smallest spatial distance, and determine the valve seat axis direction corresponding to the machining point.

[0052] A spherical neighborhood is constructed with each processing point as the center; surface elements of the combustion chamber top wall surface within the spherical neighborhood are extracted; the unit normal vector of each surface element is calculated; the unit normal vector is weighted and normalized according to the distance between the surface element and the processing point to obtain the initial local normal direction of the combustion chamber top wall corresponding to each processing point.

[0053] On the boundary of the spark plug orifice, determine the boundary point with the smallest distance from each processing point, and construct the direction vector of the boundary point pointing to the processing point; project the direction vector onto the tangent plane of the local normal direction of the combustion chamber top wall of the corresponding processing point and normalize it to obtain the initial spark plug orifice peripheral boundary constraint direction corresponding to each processing point.

[0054] Calculate the angle change between the initial local normal directions of the combustion chamber top wall and the angle change between the initial spark plug hole periphery boundary constraint directions corresponding to adjacent processing points; when the angle change is greater than the preset direction change threshold, update the direction of the corresponding processing point according to the weighted average result of the corresponding directions of adjacent processing points, and obtain the local normal direction of the combustion chamber top wall and the spark plug hole periphery boundary constraint direction.

[0055] For example, a sequence of processing points is generated by sampling along a geodesic path in the transition processing area with equal arc lengths, and the arc length spacing between adjacent processing points is 0.2 mm. The length of the transition processing area is 35 mm, and 176 processing points are generated. The processing point sequence is denoted as... ,in For processing point index, The axes of four valve seat holes and spark plug holes are extracted from the machining model of the engine cylinder head combustion chamber. The direction vector of the valve seat hole axis is denoted as... ,in For valve seat bore index, The direction vector of the spark plug hole axis is denoted as... The four valve seat bore axes are arranged in a V-shape, with the included angle between adjacent axes being [missing information]. .

[0056] For each processing point in the processing point sequence Calculate processing points To the Spatial distance between the axes of the valve seat holes: ;in, For the first Reference point on the axis of the valve seat bore. At the first... At each processing point, the following calculations were obtained: ; ; ; .

[0057] Select the valve seat bore axis direction corresponding to the minimum value As a processing point The corresponding valve seat axis direction is denoted as Processing point A spherical neighborhood is constructed centered at the center, with a radius of 0.3 mm. A set of surface elements located within the spherical neighborhood is extracted from the triangular mesh of the combustion chamber top wall surface. The surface element index is denoted as... For each surface element Calculate the unit normal vector at the center point of the cell. And calculate the distance from the unit center point to the machining point. spatial distance .

[0058] The initial local normal direction of the combustion chamber top wall is obtained by weighting the distance and normalizing the average. ; in the At each processing point, the spherical neighborhood contains 15 surface elements, with the nearest element being at a distance of... normal vector Farthest unit distance normal vector Substituting into the calculation yields... Establish a discrete point set on the spark plug orifice boundary. ,in For boundary point indexing, the discrete spacing is 0.1 mm. For machining points... Calculate to each boundary point spatial distance Select the boundary point with the smallest distance as .

[0059] Direction vector ; in the At each processing point ;Will Projected onto processing point Local normal direction of the initial combustion chamber top wall In the tangent plane Substitute the data from the 32nd processing point. ;right Normalization get The change in the angle between the initial combustion chamber top wall local normal direction and adjacent processing points. The change in the angle between the initial spark plug hole perimeter boundary constraint directions The changes in the two included angles mentioned above exceed the directional change threshold. The need to update, for example, in the first... At each processing point, , Update the direction corresponding to the 23rd processing point. ; ;get correspond Down to , Down to The changes in the two included angles mentioned above do not exceed the directional change threshold. hour, , This allows us to obtain the local normal direction of the combustion chamber top wall corresponding to each processing point in the processing point sequence. and the direction of the boundary constraint around the spark plug hole .

[0060] Based on the relative position parameters of the machining points in the transition machining region, a continuous transition relationship is constructed between the valve seat axis direction and the local normal direction of the combustion chamber top wall; the method for constructing the continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall based on the relative position parameters of the machining points in the transition machining region includes:

[0061] A transition path is determined along the transition processing area. The geodesic path arc length of each processing point along the transition path is calculated within the transition processing area. The ratio of the geodesic path arc length to the total arc length of the transition path is used as the initial position coefficient corresponding to each processing point. The rate of change of the initial position coefficients corresponding to adjacent processing points is calculated. When the rate of change is greater than a preset rate of change threshold, the initial position coefficients are subjected to nonlinear mapping processing to obtain the corrected position coefficients.

[0062] Calculate the rate of curvature change of the local normal direction of the combustion chamber top wall at each processing point; use the normalized value of the rate of curvature change as a weighting modulation factor; calculate the first weighting coefficient in the valve seat axis direction based on the corrected position coefficient and the weighting modulation factor; the method for calculating the first weighting coefficient in the valve seat axis direction based on the corrected position coefficient and the weighting modulation factor includes:

[0063] A power function transformation is performed on the correction position coefficient to obtain a first position weight term; the product of the weight modulation factor and the correction position coefficient is performed and then a power function transformation is performed to obtain a second position weight term; a normalized allocation relationship is constructed based on the first and second position weight terms to calculate a first weight coefficient in the valve seat axis direction. A second weight coefficient in the local normal direction of the combustion chamber top wall is determined based on the first weight coefficient, such that the sum of the first and second weight coefficients is 1; the first and second weight coefficients are used as a continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall.

[0064] For example, a transition path is extracted within the transition processing region. The transition path is taken as the centerline of the transition processing region on the curved surface, obtained by interpolating the two boundaries of the transition processing region at equal intervals and connecting the corresponding midpoints. Let the starting point of the transition path be... The destination is Calculate processing points Geodesic path arc length along the transition path ,in This indicates the path from the starting point of the transition path to the processing point. The length of the surface path. The total arc length of the transition path is denoted as... In this embodiment .

[0065] Initial position coefficients For example, in the first At each processing point, ,get At the 100th processing point, ,get ; in the At each processing point, ,get The geodetic path arc length between adjacent processing points is denoted as... In this embodiment Rate of change of initial position coefficient The preset rate of change threshold is taken as follows: The initial position coefficients are nonlinearly mapped to obtain the corrected position coefficients. ;in Let be the compression factor, and take . .

[0066] In the At each processing point, Calculations yielded ; in the At each processing point, Calculations yielded .

[0067] The processing point is obtained by interpolating the Gaussian curvature of the adjacent surface elements. Gaussian curvature of the top wall surface of the combustion chamber And calculate the rate of change of curvature. Construct a normalization factor for the rate of change of curvature, and set... Define the weighted modulation factor ; in the At each processing point, , ,get ; in the At each processing point, ,get .

[0068] According to the correction position coefficient and weighted modulation factor Calculate the first weighting coefficient along the valve seat axis. Perform a power function transformation on the correction position coefficient to obtain the first position weighting term. A power function transformation is performed on the product of the weight modulation factor and the correction position coefficient to obtain the second position weight term. Construct a normalized allocation relationship to obtain the first weight coefficient. For example, in the first At each processing point, Obtained through nonlinear mapping , Calculations yielded ; in the At each processing point, , Calculations yielded ; in the At each processing point, , Calculations yielded The second weighting coefficient in the local normal direction of the combustion chamber top wall .by and This represents a continuous transition between the valve seat axis direction and the local normal direction of the combustion chamber top wall.

[0069] Based on the continuous transition relationship and the boundary constraint direction around the spark plug hole, the tool axis direction corresponding to each machining point is determined; based on the tool axis direction and spatial coordinates of each machining point in the machining point sequence, the corresponding tool pose is determined; the method for determining the tool axis direction corresponding to each machining point based on the continuous transition relationship and the boundary constraint direction around the spark plug hole includes:

[0070] At each machining point, the initial tool axis direction is obtained by weighted calculation of the valve seat axis direction and the local normal direction of the combustion chamber top wall based on the continuous transition relationship. At each machining point, the minimum clearance between the tool and the spark plug orifice boundary corresponding to the initial tool axis direction is calculated based on the tool geometry parameters and the spark plug orifice boundary. When the minimum clearance is less than the preset safety clearance, the angle between the spark plug orifice peripheral boundary constraint direction and the initial tool axis direction in the tangential plane at the machining point is calculated, and the corrected rotation axis direction corresponding to the angle is determined.

[0071] The correction angle is determined based on the difference between the minimum clearance and the preset safety clearance; the initial tool axis direction is rotated around the correction rotation axis direction by the correction angle to obtain the candidate tool axis direction.

[0072] The minimum clearance corresponding to the candidate tool axis direction is updated and calculated to obtain the updated minimum clearance. When the updated minimum clearance is not less than the preset safety clearance, the candidate tool axis direction is determined as the tool axis direction corresponding to the machining point. When the updated minimum clearance is still less than the preset safety clearance, the correction angle is adjusted incrementally and the rotation and clearance verification are repeated until the minimum clearance is not less than the preset safety clearance or the preset convergence condition is met. The final candidate tool axis direction is then determined as the tool axis direction corresponding to the machining point.

[0073] For example, the valve seat axis direction is determined according to the continuous transition relationship. and the local normal direction of the combustion chamber top wall The initial tool axis direction is obtained by performing weighted calculations. For example, in the first At each processing point, , , , ,but .

[0074] tool radius A local envelope approximation model of the ball-end tool is constructed at the corresponding machining point, and the tool is equivalent to a sphere with the tool's center point as the center and a radius of... A sphere. Tool center point. The spark plug orifice boundary uses a circular discrete point set. The discrete spacing is set to 0.1 mm. Calculate the minimum clearance between the tool spherical surface and the boundary points. In the first At each processing point, Calculations yielded The minimum gap is .

[0075] The preset safety clearance is denoted as , Correction is needed. Calculate the spark plug constraint direction within the tangential plane. and initial tool axis direction The included angle Correct the direction of rotation axis to Gap difference , Correcting the angle .in , therefore . Direction about the correction axis of rotation The direction of the candidate tool axis is obtained after rotation. Recalculate the gap Therefore, take Obtain the tool center point. .

[0076] Based on the tool poses corresponding to adjacent machining points, and constraining the changes in the tool axis and the rotational axis of the 5-axis CNC machine tool, a continuous tool pose sequence is obtained; the method for obtaining the continuous tool pose sequence based on the tool poses corresponding to adjacent machining points and constraining the changes in the tool axis and the rotational axis of the 5-axis CNC machine tool includes:

[0077] The tool pose corresponding to the first machining point in the machining point sequence is added to the continuous tool pose sequence as the starting pose. For each machining point in the machining point sequence, the inverse kinematics solution is performed on the corresponding tool pose according to the kinematic model of the 5-axis CNC machine tool to obtain the set of rotation axis angle solutions. The set with the smallest change in angle between the previous machining point and the corresponding rotation axis angle solution is selected as the current rotation axis solution.

[0078] Calculate the change in the tool axis angle between the current tool pose and the previous tool pose, as well as the change in the rotation angle between the corresponding rotation axis angle solutions; when the change in the tool axis angle is greater than a preset tool axis angle threshold or the change in the rotation angle is greater than a preset rotation angle threshold, determine the smoothing intensity coefficient based on the correction position coefficient of the current machining point in the transition machining area.

[0079] Using the previous tool pose as a reference, the tool axis direction of the current tool pose is weighted, combined, and normalized to obtain candidate tool poses. Constraint checks are performed on the candidate tool poses. When the updated tool axis angle change and rotation angle change are both no greater than the corresponding threshold, the candidate tool pose is added to the continuous tool pose sequence. If the constraint conditions are not met, the smoothing intensity coefficient is increased, and the tool axis direction adjustment and constraint checks are repeated until the condition that the tool axis angle change and rotation angle change are both no greater than the corresponding threshold is met. The final candidate tool pose is then added to the continuous tool pose sequence.

[0080] For example, the tool pose corresponding to the first machining point in the machining point sequence is recorded as the starting pose in the continuous tool pose sequence. The tool pose uses the coordinates of the tool center point. relative to the direction of the tool axis The 5-axis CNC machine tool adopts an AC double-swivel head structure, and the A-axis rotation angle is denoted as... The C-axis rotation angle is denoted as Tool axis direction The angle between the rotation axis and the rotation axis satisfies , .

[0081] For the first Inverse kinematics is performed on the tool pose corresponding to each machining point to obtain the solution set of rotation axis angles. For the AC double-swivel head structure, when At that time, the solution set of rotation axis angles contains two sets of rotation axis angle solutions. , ; , .

[0082] For the first For each machining point, calculate the change in rotation angle between each set of rotation axis angle solutions in the solution set and the corresponding rotation axis angle solution of the previous machining point. The change in axis A is... The change in the C-axis is .

[0083] The evaluation function for the change in rotation angle is: The weight of axis A C-axis weight Select The minimum corresponding rotation axis angle solution is taken as the first The current rotation axis solution corresponding to the machining point. In the... At each machining point, the tool axis direction Two sets of rotation axis angle solutions were calculated. , The previous processing point corresponds to Calculations yielded , , ; , , Therefore, select This is the rotary axis solution corresponding to the 30th machining point.

[0084] Change in the tool axis angle between the current tool pose and the previous tool pose The change in rotation angle between the current rotation axis solution and the previous rotation axis solution. ,in Tool axis included angle threshold Corner threshold .when or At that time, the correction position coefficient of the current processing point in the transition processing area is used. Determine the smoothing strength coefficient .when hour, ;when hour, ;when hour, In this embodiment, in the first... At each processing point, Calculations yielded .

[0085] Using the tool pose of the previous machining point as a reference, the tool axis directions corresponding to the current machining point are weighted, combined, and normalized to obtain candidate tool axis directions. Based on the candidate tool axis direction and the coordinates of the current processing point Recalculate the coordinates of the candidate tool center point. ,by and Form the candidate tool pose.

[0086] In the At each machining point, the original tool axis direction , , Calculations yielded After normalization, we get Based on the coordinates of the processing point and tool radius Recalculate the center point of the candidate tool. For candidate tool pose The change in the cutter axis angle after inverse kinematics solution Updated angle change .satisfy and The candidate tool pose is added to the continuous tool pose sequence. For example, the first... The change in the original cutter axis angle at each machining point. The original change in angle Initial smoothing strength coefficient The first iteration of weighted combination yields the candidate tool axis direction, and the center point of the candidate tool is recalculated to obtain... , The second iteration increases the smoothing intensity coefficient to... The candidate tool axis direction and candidate tool center point are recalculated to obtain , If the conditions are met, the corresponding candidate tool pose is added to the sequence. The continuous tool pose sequence is obtained by sequentially calculating the poses of each machining point in the machining point sequence.

[0087] Based on the continuous tool pose sequence and the kinematic model of the 5-axis CNC machine tool, the control parameters of each motion axis of the 5-axis CNC machine tool are solved to obtain the tool positioning sequence.

[0088] For example, in the AC double-swivel head structure, the structural offset distance from the spindle end face reference point to the tool center point along the tool axis direction is denoted as... In this embodiment, Based on the coordinates of the tool center point and rotation axis control parameters , Calculate linear axis control parameters , , .

[0089] At the 150th machining point, the coordinates of the tool center point are: The direction of the cutter axis is Substituting into the calculation yields... , Substituting, we get , , The corresponding control parameters are .

[0090] At the first machining point, the coordinates of the tool center point are: , Calculations yielded , Substituting into the calculation yields... , , The control parameters corresponding to the first processing point are: The control parameter sequence is obtained by sequentially calculating all 176 machining points in the continuous tool pose sequence. Arrange the machining point indices in order to obtain the tool positioning sequence.

[0091] Example 2: Based on the same inventive concept, such as Figure 2 As shown, this embodiment also provides a 5-axis CNC machine tool positioning system for machining engine cylinder heads, the system comprising:

[0092] The region definition module is used to obtain the machining model of the engine cylinder head combustion chamber; determine the transition machining region based on the machining model of the engine cylinder head combustion chamber; generate a sequence of machining points along the transition machining region; and determine the corresponding valve seat axis direction, the local normal direction of the combustion chamber top wall, and the boundary constraint direction of the spark plug hole at each machining point in the machining point sequence.

[0093] The tool axis generation module is used to construct a continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall based on the relative position parameters of the machining points in the transition machining area; determine the tool axis direction corresponding to each machining point based on the continuous transition relationship and the boundary constraint direction of the spark plug hole; and determine the corresponding tool pose based on the tool axis direction and spatial coordinates of each machining point in the machining point sequence.

[0094] The motion smoothing module is used to constrain the tool axis change and the 5-axis CNC machine tool rotation axis change based on the tool pose corresponding to adjacent machining points, so as to obtain a continuous tool pose sequence.

[0095] The tool positioning module is used to solve the control parameters of each motion axis of the 5-axis CNC machine tool based on the continuous tool pose sequence and the kinematic model of the 5-axis CNC machine tool, and obtain the tool positioning sequence.

[0096] It should be noted that the specific methods by which each module performs operations in the system described in the above embodiments have been described in detail in the embodiments related to the method, and will not be elaborated here.

[0097] Finally, it should be noted that although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for positioning cutting tools on a 5-axis CNC machine tool for machining engine cylinder heads, characterized in that, The method includes: Obtain the machining model of the engine cylinder head combustion chamber; determine the transition machining area based on the machining model of the engine cylinder head combustion chamber; generate a sequence of machining points along the transition machining area; determine the corresponding valve seat axis direction, the local normal direction of the combustion chamber top wall, and the boundary constraint direction of the spark plug hole at each machining point in the machining point sequence; Based on the relative position parameters of the machining points in the transition machining area, a continuous transition relationship is constructed between the valve seat axis direction and the local normal direction of the combustion chamber top wall; based on the continuous transition relationship and the boundary constraint direction of the spark plug hole, the tool axis direction corresponding to each machining point is determined; based on the tool axis direction and spatial coordinates of each machining point in the machining point sequence, the corresponding tool pose is determined. Based on the tool poses corresponding to adjacent machining points, constrain the tool axis variation and the rotary axis variation of the 5-axis CNC machine tool to obtain a continuous tool pose sequence; Based on the continuous tool pose sequence and the kinematic model of the 5-axis CNC machine tool, the control parameters of each motion axis of the 5-axis CNC machine tool are solved to obtain the tool positioning sequence.

2. The method for positioning a 5-axis CNC machine tool for machining an engine cylinder head according to claim 1, characterized in that, The method for determining the transition machining area based on the engine cylinder head combustion chamber machining model includes: Extract the valve seat throat boundary, spark plug orifice boundary, and combustion chamber top wall surface from the engine cylinder head combustion chamber machining model; using the valve seat throat boundary as the starting boundary, extend outward by a first preset width according to the geodesic distance of the combustion chamber top wall surface to obtain the throat transition zone; using the spark plug orifice boundary as the starting boundary, extend outward by a second preset width according to the geodesic distance of the combustion chamber top wall surface to obtain the spark plug transition zone; extract the connected surface sub-region on the combustion chamber top wall surface between the throat transition zone and the spark plug transition zone to obtain the preliminary transition region; In the initial transition region, surface units whose distance from the valve seat throat boundary is no greater than a preset first distance threshold and whose distance from the spark plug orifice boundary is no greater than a preset second distance threshold are retained to obtain a constrained transition region; in the constrained transition region, surface units whose normal rate of change exceeds a preset normal rate of change threshold or whose curvature rate of change exceeds a preset curvature rate of change threshold are removed to obtain a filtered transition region; the filtered transition region is then subjected to boundary offset shrinkage according to the tool diameter parameters to obtain a transition machining region.

3. The method for positioning a 5-axis CNC machine tool for machining an engine cylinder head according to claim 2, characterized in that, The method for determining the corresponding valve seat axis direction, the local normal direction of the combustion chamber top wall, and the boundary constraint direction of the spark plug hole at each processing point in the processing point sequence includes: Extract the valve seat hole axis and spark plug hole axis from the engine cylinder head combustion chamber machining model; calculate the spatial distance between each machining point in the machining point sequence and each valve seat hole axis, select the valve seat hole axis with the smallest spatial distance, and determine the valve seat axis direction corresponding to the machining point; A spherical neighborhood is constructed with each processing point as the center; surface elements of the combustion chamber top wall surface within the spherical neighborhood are extracted; the unit normal vector of each surface element is calculated; the unit normal vector is weighted and normalized according to the distance between the surface element and the processing point to obtain the initial local normal direction of the combustion chamber top wall corresponding to each processing point. On the boundary of the spark plug orifice, determine the boundary point with the smallest distance from each processing point, and construct the direction vector of the boundary point pointing to the processing point; project the direction vector onto the tangent plane of the local normal direction of the combustion chamber top wall of the corresponding processing point and normalize it to obtain the initial spark plug orifice peripheral boundary constraint direction corresponding to each processing point; Calculate the angle change between the initial local normal directions of the combustion chamber top wall and the angle change between the initial spark plug hole periphery boundary constraint directions corresponding to adjacent processing points; when the angle change is greater than the preset direction change threshold, update the direction of the corresponding processing point according to the weighted average result of the corresponding directions of adjacent processing points, and obtain the local normal direction of the combustion chamber top wall and the spark plug hole periphery boundary constraint direction.

4. The method for positioning a 5-axis CNC machine tool for machining an engine cylinder head according to claim 3, characterized in that, The method for constructing a continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall based on the relative position parameters of the processing point in the transition processing area includes: A transition path is determined along the transition processing area. The geodesic path arc length of each processing point along the transition path is calculated within the transition processing area. The ratio of the geodesic path arc length to the total arc length of the transition path is used as the initial position coefficient corresponding to each processing point. The rate of change of the initial position coefficients corresponding to adjacent processing points is calculated. When the rate of change is greater than a preset rate of change threshold, the initial position coefficients are subjected to nonlinear mapping processing to obtain the corrected position coefficients. The rate of curvature change of the local normal direction of the combustion chamber top wall is calculated at each processing point; the normalized value of the rate of curvature change is used as a weighting modulation factor; a first weighting coefficient in the valve seat axis direction is calculated based on the correction position coefficient and the weighting modulation factor; a second weighting coefficient in the local normal direction of the combustion chamber top wall is determined based on the first weighting coefficient, such that the sum of the first weighting coefficient and the second weighting coefficient is 1; the first weighting coefficient and the second weighting coefficient are used as the continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall.

5. The method for positioning a 5-axis CNC machine tool for machining an engine cylinder head according to claim 4, characterized in that, The method for calculating the first weighting coefficient in the valve seat axis direction based on the correction position coefficient and the weighting modulation factor includes: The correction position coefficient is transformed by a power function to obtain a first position weight term; the weight modulation factor and the correction position coefficient are multiplied and transformed by a power function to obtain a second position weight term; a normalized allocation relationship is constructed based on the first position weight term and the second position weight term to calculate the first weight coefficient in the valve seat axis direction.

6. The method for positioning a 5-axis CNC machine tool for machining an engine cylinder head according to claim 5, characterized in that, The method for determining the tool axis direction corresponding to each machining point based on the continuous transition relationship and the boundary constraint direction of the spark plug hole includes: At each machining point, the initial tool axis direction is obtained by weighted calculation of the valve seat axis direction and the local normal direction of the combustion chamber top wall based on the continuous transition relationship. At each machining point, the minimum clearance between the tool and the spark plug orifice boundary corresponding to the initial tool axis direction is calculated based on the tool geometry parameters and the spark plug orifice boundary. When the minimum clearance is less than the preset safety clearance, the angle between the spark plug orifice peripheral boundary constraint direction and the initial tool axis direction in the tangential plane at the machining point is calculated, and the corrected rotation axis direction corresponding to the angle is determined. The correction angle is determined based on the difference between the minimum clearance and the preset safety clearance; the initial tool axis direction is rotated around the correction rotation axis by the correction angle to obtain a candidate tool axis direction; the minimum clearance corresponding to the candidate tool axis direction is updated to obtain the updated minimum clearance; when the updated minimum clearance is not less than the preset safety clearance, the candidate tool axis direction is determined as the tool axis direction corresponding to the machining point; when the updated minimum clearance is still less than the preset safety clearance, the correction angle is incrementally adjusted and the rotation and clearance verification are repeated until the minimum clearance is not less than the preset safety clearance or the preset convergence condition is met, and the final candidate tool axis direction is determined as the tool axis direction corresponding to the machining point.

7. A method for positioning a 5-axis CNC machine tool for machining an engine cylinder head according to claim 6, characterized in that, The method for obtaining a continuous tool pose sequence by constraining the tool axis variation and the rotary axis variation of a 5-axis CNC machine tool based on the tool poses corresponding to adjacent machining points includes: The tool pose corresponding to the first machining point in the machining point sequence is added to the continuous tool pose sequence as the starting pose. For each machining point in the machining point sequence, the inverse kinematics solution of the corresponding tool pose is performed according to the kinematic model of the 5-axis CNC machine tool to obtain the set of rotation axis angle solutions. The set with the smallest change in angle between the previous machining point and the corresponding rotation axis angle solution is selected as the current rotation axis solution. Calculate the change in the tool axis angle between the current tool pose and the previous tool pose, as well as the change in the rotation angle between the corresponding rotation axis angle solutions; when the change in the tool axis angle is greater than a preset tool axis angle threshold or the change in the rotation angle is greater than a preset rotation angle threshold, determine the smoothing intensity coefficient based on the correction position coefficient of the current machining point in the transition machining area; Using the previous tool pose as a reference, the tool axis direction of the current tool pose is weighted, combined, and normalized to obtain candidate tool poses. Constraint checks are performed on the candidate tool poses. When the updated tool axis angle change and rotation angle change are both no greater than the corresponding threshold, the candidate tool pose is added to the continuous tool pose sequence. If the constraint conditions are not met, the smoothing intensity coefficient is increased, and the tool axis direction adjustment and constraint checks are repeated until the condition that the tool axis angle change and rotation angle change are both no greater than the corresponding threshold is met. The final candidate tool pose is then added to the continuous tool pose sequence.

8. A 5-axis CNC machine tool positioning system for machining engine cylinder heads, characterized in that, The system includes: The region definition module is used to obtain the machining model of the engine cylinder head combustion chamber; determine the transition machining region based on the machining model of the engine cylinder head combustion chamber; generate a sequence of machining points along the transition machining region; and determine the corresponding valve seat axis direction, the local normal direction of the combustion chamber top wall, and the boundary constraint direction of the spark plug hole at each machining point in the machining point sequence. The tool axis generation module is used to construct a continuous transition relationship between the valve seat axis direction and the local normal direction of the combustion chamber top wall based on the relative position parameters of the machining points in the transition machining area; determine the tool axis direction corresponding to each machining point based on the continuous transition relationship and the boundary constraint direction of the spark plug hole; and determine the corresponding tool pose based on the tool axis direction and spatial coordinates of each machining point in the machining point sequence. The motion smoothing module is used to constrain the tool axis change and the rotary axis change of the 5-axis CNC machine tool based on the tool pose corresponding to adjacent machining points to obtain a continuous tool pose sequence; The tool positioning module is used to solve the control parameters of each motion axis of the 5-axis CNC machine tool based on the continuous tool pose sequence and the kinematic model of the 5-axis CNC machine tool, and obtain the tool positioning sequence.

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