Robot path planning method for manufacturing rotary body based on powder DED process

Abstract

The invention discloses a robot path planning method for manufacturing a rotary body based on a powder DED process, and belongs to the technical field of additive manufacturing. The model is divided into a cylinder part and a suspension part, the cylinder part is axially sliced, and the suspension part is radially sliced; and optimizing outer contours and filling line segments of all the slices, and generating a slice filling path as a final execution absolute trajectory. A kinematics coupling model of the six-degree-of-freedom mechanical arm and a double-shaft positioner is established, a mechanical arm base coordinate system, a positioner base coordinate system, a cladding head coordinate system and a workpiece coordinate system are converted into a world coordinate system, and under the constraint that it is ensured that a cladding head nozzle at the tail end of the mechanical arm is perpendicular to a printing curved surface and the ground, absolute tracks are distributed to the mechanical arm and the positioner; and the two are linked and cooperatively operated according to a distribution track. By means of linkage cooperation of the six-degree-of-freedom mechanical arm and the two-axis position changing machine, due to degree-of-freedom redundancy of the eight-axis robot system, optimal robot posture printing is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and particularly to a robot path planning method for manufacturing a rotary body based on a powder DED process. Background Art

[0002] Rotary body parts are important industrial parts, with impellers and propellers being typical representatives, and are widely used in fields such as ships, aerospace, etc. Due to the impact and vibration loads in their operating conditions and the need to meet hydrodynamic requirements, the engineering has high requirements for the blade geometry and structural strength of such parts, resulting in most rotary body parts having complex curved surface structures. With the development of metal additive manufacturing technology, new manufacturing solutions based on the Directed Energy Deposition (DED) process have gradually been applied in engineering. This solution uses a laser, electron beam, or plasma arc device to focus thermal energy to melt materials, and feeds metal raw materials in the form of wires or powders to the molten pool for layer-by-layer deposition, enabling direct forming or repair of parts. Given that the laser has a high energy density, good forming accuracy, and can cover the types of common metal materials for impellers and propellers by changing the powder material type, the laser powder directed energy deposition technology is expected to replace traditional casting and become a better manufacturing solution.

[0003] Currently, when the laser powder directed energy deposition technology is used to manufacture rotary body parts, the application method mainly involves using a single six-degree-of-freedom industrial robotic arm, or although a positioner is equipped, the positioner is only used for positioning and is not linked and coordinated with the robotic arm, and its movement has not been fully exploited. In this mode, the processing process mainly relies on the active movement of the robotic arm.

[0004] However, this technical solution has significant drawbacks. During processing, the direction of the cladding head nozzle often cannot be perpendicular to both the curved surface and the ground simultaneously, seriously affecting the surface forming quality of the deposited layer and the final part. On the one hand, restricted by the principle of laser powder directed energy deposition technology, the cladding head nozzle needs to be as perpendicular to the ground as possible. Whether it is side-axis or coaxial powder feeding, the powder is transported to the molten pool by an inert gas flow. To prevent the powder from sintering and clogging at the nozzle, the powder melting position is usually maintained at 10 - 30 mm from the cladding head nozzle, and the commonly used powder particle size is 15 - 53 microns or 53 - 150 microns. When the cladding head nozzle is perpendicular to the ground, the powder can stably fall into the molten pool; if the deviation angle is large, a large amount of powder cannot reach the molten pool, resulting in the width and height of the deposition track not meeting the expectations, and the deviation accumulating layer by layer, greatly damaging the forming quality. On the other hand, the cladding head nozzle needs to be as perpendicular to the printed curved surface as possible, so that the angle between the orientation of the cladding head nozzle and the normal vector of the curved surface varies within a small range. Because the molten pool is formed by melting the surface with a laser beam, if the angle is too large, the shape of the molten pool changes, and the deposition track does not meet the expectations. Existing robot trajectory planning methods pay insufficient attention to the attitude of the cladding head at the end of the robot, making it difficult to maintain the stability of the cladding process, resulting in poor surface forming quality and serious deviation between the manufactured part and the digital model.

[0005] Traditional slicing and filling path planning is mainly applied to commercial gantry three-axis printers. Based on the Fused Deposition Modeling (FDM) technology, the method is to slice at equal layer heights along the z-axis direction and fill at equal intervals by methods such as contour offset or zigzag. The width of the deposition track based on the laser powder directed energy deposition process is relatively large, between 1 - 3 mm. When manufacturing a rotary body curved surface, using the traditional path planning method will result in serious staircase effects and additional support structures, affecting the material utilization rate and surface accuracy. Based on the process characteristics and manufacturing scenarios, the present invention optimizes the paths of slicing and filling, which can achieve support-free printing and improve manufacturing accuracy. Summary of the Invention

[0006] In order to overcome the above problems, the present invention provides a robot path planning method for manufacturing a rotary body based on the powder DED process, which can achieve the manufacturing of high-precision rotary body parts.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In the first aspect, the present invention provides a robot path planning method for manufacturing a rotary body based on the powder DED process, including:

[0009] Mixed slicing of the rotating workpiece model to be manufactured, wherein the rotating workpiece model is divided into a cylindrical part and a hanging part, the cylindrical part is sliced ​​along the axial direction, and the hanging part is sliced ​​along the radial direction; outer contours and filling line segments of all slices are optimized to generate a slice filling path as the final absolute trajectory;

[0010] A kinematic coupling model of a six-degree-of-freedom robot and a two-axis positioner is established. In the kinematic coupling model, the robot base coordinate system, the positioner base coordinate system, the cladding head coordinate system at the end of the robot and the workpiece coordinate system at the positioner table are transformed into the world coordinate system. Under the constraint that the cladding head nozzle at the end of the robot prints both the curved surface and the ground vertically at the same time, the final executed absolute trajectory is assigned to the robot and the positioner, and the robot and the positioner work in coordination according to the assigned trajectory.

[0011] As a preferred embodiment of the present invention, the slicing method of the hanging part of the rotating workpiece model is:

[0012] Along the radial direction of the cylindrical part of the rotating workpiece model, a number of imaginary cylindrical surfaces with increasing diameters are established according to the preset layer thickness, with all the imaginary cylindrical surfaces completely covering the hanging part;

[0013] The imaginary cylindrical surface is regarded as the cutting layer to slice the overhanging part.

[0014] As a preferred embodiment of the present invention, the coordinate points of the slice filling path are described in a polar coordinate system based on an imaginary cylindrical surface.

[0015] As a preferred embodiment of the present invention, when optimizing the outer contour and filling line segments of the slices in the overhanging part of all slices, the slices in the overhanging part located on the same imaginary cylindrical surface are first unfolded into a 2D plane along the generatrix of the imaginary cylindrical surface, and the outer contour and filling line segments are optimized on the 2D plane, and then the results are remapped to the imaginary cylindrical surface.

[0016] As a preferred embodiment of the present invention, the optimization of the outer contour and the filling line segments on the 2D plane includes:

[0017] The outer contour of the slice is marked on the 2D plane, and the path points where the outer contour corners are located are disconnected;

[0018] Taking one long side of the outer contour as the reference, a line segment is offset parallel to the other side to form a line segment covering the 2D plane of the slice. The offset distance is determined according to the width of the printing path, and there is a gap between the two ends of the line segment and the outer contour. The two adjacent slices take the opposite long side of the outer contour as the reference and the offset direction is opposite.

[0019] As a preferred embodiment of the present invention, the slice filling path is generated according to the optimized outer contour and filling line segments, and the paths of two adjacent slice layers have opposite directions.

[0020] As a preferred embodiment of the present invention, under the constraint that the nozzle of the cladding head at the end of the robot arm simultaneously prints the curved surface and the ground vertically, the final absolute trajectory is distributed to the robot arm and the positioner, including:

[0021] The final absolute trajectory is initially assigned to the robot arm according to the unified world coordinate system to obtain the Cartesian coordinates of the path points. , convert Cartesian coordinates to polar coordinates , let the rotation axis angle in the double-axis positioner be ; According to the known angles of the rotation axis and the tilt axis of the dual-axis positioner, the transformation relationship between the workpiece coordinate system and the world coordinate system is obtained, and the Cartesian coordinate system is transformed using this transformation relationship Reconvert to new Cartesian coordinates , as the execution path point of the robot arm, completes the allocation of the absolute trajectory.

[0022] As a preferred embodiment of the present invention, it is also necessary to set the end of the robot arm to reach the coordinate point The posture is as follows:

[0023] The attitude parameters of the cladding head are A, B, and C, which represent the rotation angles of the cladding head coordinate system around the three axes of its own coordinate system. The cladding head orientation satisfies the constraints of the vertical printing surface and the ground at the same time, thereby obtaining the rotation angles around the Y axis and the X axis. In order to avoid the collision between the cladding head structure and the line and the robot body, the rotation angle around the Z axis is directly specified. Since the final position of the cladding head coordinate system is known, the corresponding attitude parameters can be obtained according to the spatial transformation relationship with the original coordinate system.

[0024] As a preferred embodiment of the present invention, when the robot arm and the positioner work in coordination according to the assigned trajectory, according to the path coordinate point The forward and inverse kinematic solutions of the robot arm are solved based on its posture, the angles of each joint of the robot arm are obtained, and the rotation axis angle of the combined positioner is used to realize the coordinated work of the robot arm and the positioner.

[0025] In a second aspect, the present invention also provides a robot for manufacturing a rotating body based on a powder DED process, comprising a six-degree-of-freedom robotic arm and a two-axis positioner. The six-degree-of-freedom robotic arm and the two-axis positioner adopt the above-mentioned path planning method to collaboratively manufacture a rotating body workpiece.

[0026] The beneficial effects of the present invention are:

[0027] The present invention proposes a robot path planning method for manufacturing a rotating body based on a powder DED process, which achieves optimal robot posture printing by means of the linkage coordination of a six-degree-of-freedom robotic arm and a two-axis positioner and benefits from the redundancy of the degrees of freedom of an eight-axis robot system.

[0028] (1) Expand the machining capabilities of the six-degree-of-freedom robotic arm: Integrate the two-axis positioner as an additional axis into the robotic system. The introduction of the tilting axis and the rotating axis greatly expands the reach and machining range of the robotic arm, meeting the machining requirements of various rotating workpieces. Even in the same machining area, in cooperation with the movement of the positioner, the robotic arm can select a better pose and optimize the overall trajectory of the robotic system.

[0029] (2) Ensure the forming quality of parts: By controlling the nozzle of the cladding head at the end of the robotic arm to maintain an optimal printing pose basically throughout the printing process, that is, perpendicular to the ground and the printing surface simultaneously, the morphology of the molten pool can be stabilized, and the metal powder can fall into the molten pool evenly, ensuring a better part forming effect. In addition, the model of the rotating workpiece to be manufactured is sliced in a hybrid manner. The model of the rotating workpiece is divided into a cylindrical part and a hanging part. The cylindrical part is sliced axially, and the hanging part is sliced radially, laying a foundation for generating accurate slice filling paths.

[0030] (3) Expand the scope of process application: When maintaining the optimal printing pose, the area where the molten pool is located is a relatively flat surface, the deposition trajectory is stable, accidental flow is not likely to occur, and the stacking error of each layer is reduced. Furthermore, complex structures with a higher number of printable manufacturing layers or a larger overhang angle can be printed, broadening the scope of process application.

[0031] In summary, the present invention shows good application prospects in various high-precision manufacturing scenarios based on the directed energy deposition process. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of an eight-degree-of-freedom robotic system.

[0033] In the figure: 1 - six-degree-of-freedom robotic arm, 2 - cladding head module, 3 - two-axis positioner.

[0034] Figure 2 It is a schematic diagram of the structure of a simple propeller workpiece.

[0035] Figure 3 It is a schematic diagram of the hybrid slicing of a simple propeller workpiece model.

[0036] Figure 4 It is a schematic diagram of the transformation between the Cartesian coordinate system and the cylindrical coordinate system.

[0037] Figure 5 It is the process in which the overhanging part of the rotating body undergoes surface mapping to a plane and then remapping to a surface.

[0038] Figure 6 It is a schematic diagram of the path direction change of the odd and even layers of the overhanging part of the rotating body.

[0039] Figure 7 It is a schematic diagram of the coordinate system of the six-degree-of-freedom robotic arm in the eight-degree-of-freedom robotic system.

[0040] Figure 8 It is a schematic diagram of the coordinate system of a two-axis positioner in an eight-degree-of-freedom robot system.

[0041] Figure 9 It is a schematic diagram of the orientation of the cladding head in the workpiece coordinate system.

[0042] Figure 10 It is a schematic diagram of the orientation of the cladding head in the world coordinate system.

[0043] Figure 11 It is the angle with the gravity direction when the positioner's tilt axis rotates -90 degrees and the cladding head is oriented perpendicular to the printing surface.

[0044] Figure 12 It is a schematic diagram of obtaining the attitude parameters of the cladding head through the spatial coordinate transformation relationship.

[0045] Figure 13 It is the motion trajectory diagram of the manipulator moving only vertically to the ground with the positioner stationary.

[0046] Figure 14 It is the motion trajectory diagram of the manipulator moving only perpendicular to the printing surface with the positioner stationary.

[0047] Figure 15 It is the motion trajectory diagram of the positioner and the manipulator moving in tandem to print a hanging structure.

[0048] Figure 16 It is the flowchart of a robot path planning method for manufacturing a revolving body based on the powder DED process. Detailed implementation manners

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present disclosure. Obviously, the described embodiments are some, but not all, of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present disclosure without creative efforts shall fall within the scope of protection of the present disclosure.

[0050] Unless otherwise defined, the technical terms or scientific terms used in this disclosure shall have the ordinary meanings understood by those of ordinary skill in the field to which this disclosure pertains. The use of words such as "a", "an", or "the" in this disclosure does not denote a limitation of quantity, but rather means that there is at least one. Words such as "comprising" or "including" mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects. Words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Upper", "lower", "left", "right", etc. are only used to represent relative position relationships, and when the absolute position of the object being described changes, the relative position relationship may also change accordingly.

[0051] The robot path planning method for manufacturing a revolving body based on the powder DED process proposed by the present invention is implemented based on an eight-axis robot system. As Figure 1 shown, it mainly includes a six-degree-of-freedom robotic arm 1, a cladding head module 2, and a two-axis positioner 3. Among them, the two-axis positioner 3 includes a tilt axis E1 and a rotation axis E2. When manufacturing the overhanging structure of the revolving body, first rotate the tilt axis E1 by -90 degrees to make the positioner workbench surface perpendicular to the ground, and then continuously rotate the rotation axis E2 to compensate for the tilt angle of the laser nozzle. The cladding head module 2 integrates a laser fiber, a cooling circuit, a powder feeding pipeline, etc., and is the core equipment for laser directed energy deposition. The present invention focuses on using the degree-of-freedom redundancy of the 8-axis robot system for trajectory planning to keep the cladding head nozzle in the optimal posture during the printing process and obtain better forming quality.

[0052] For various revolving body workpieces, based on their own geometric characteristics, they can be divided into a cylindrical part and an overhanging part. To better explain the present invention, take Figure 2 the simple propeller workpiece shown as an example. According to the geometric characteristics of this part, hybrid slicing is performed, where the cylindrical part is sliced along the axial direction (i.e., the height direction of the cylinder), and the overhanging part is sliced along the radial direction (i.e., the radius direction of the cylinder surface); as Figure 3 shown, along the radial direction of the cylindrical part of the revolving body workpiece model, a number of imaginary cylindrical surfaces with increasing diameters are established according to a preset layer thickness. Taking that all the imaginary cylindrical surfaces completely cover the overhanging part as the criterion, the imaginary cylindrical surfaces are regarded as cutting layers to realize the slicing of the overhanging part. Here, the overhanging blade of the propeller is a difficult point in processing. As Figure 4 shown, for any coordinate point of the revolving body part, it can be described in the Cartesian coordinate system and can also be converted to the cylindrical coordinate system for description, where It can be used to adjust the rotation angle of the positioner, and through the linkage of the positioner, the nozzle at the end of the robotic arm can be kept in the optimal printing posture. Since the outer contour is obtained by slicing radially along the core cylinder, and since the revolving body usually has a certain thickness, filling treatment is required. When optimizing the outer contour and filling line segments for all slices, the cylindrical part is a regular body, and the contour line filling technology for it is relatively mature and can be realized by existing technologies, which will not be elaborated here. To facilitate the processing path of the overhanging part, each layer of the overhanging part is mapped to a 2D plane, as Figure 5 shown. Each layer in the overhanging part can be imagined to be on the surface of a hypothetical cylinder. First, the slices in the overhanging part located on the same hypothetical cylindrical surface are unfolded along the generatrix to a 2D plane, and the coordinate points therein can be described in polar coordinates. The outer contour and filling line segments are optimized on the 2D plane, and then the results are remapped to the hypothetical cylindrical surface.

[0053] In a specific implementation of the present invention, when optimizing the outer contour and filling line segments on the 2D plane, the outer contour is marked on the 2D plane for the slice, and the path points at the corners of the outer contour are disconnected. The corners of the outer contour represent a large change in the direction of the velocity vector, which involves the direction change of the positioner and there is an obvious deceleration and then acceleration stage. If it is not disconnected here, it will inevitably cause serious accumulation at the corners and reduce the surface accuracy; taking one long side of the outer contour as a reference, a line segment covering the 2D plane of the slice is formed by parallel offset to the other side, and the offset distance is determined according to the printing track width. There is a gap between the two ends of the line segment and the outer contour; for adjacent two-layer slices, the opposite long sides of the outer contour are taken as references and the offset directions are opposite. Since the design of the overhanging blade is based on aerodynamics, etc., there are actually certain differences between the two long sides on both sides of the outer contour. If only one long side is used as a reference for offset, it is easier to cause filling gaps at the relative boundary positions. By using the two long sides of the outer contour for offset respectively, due to the fluidity of the molten pool, the latter layer can appropriately compensate for the filling gap of the previous layer to make the filling as uniform and dense as possible and improve the mechanical properties. The slice filling path is generated according to the optimized outer contour and filling line segments. By adjusting the path directions of adjacent layers, as Figure 6 shown, the path directions of the filling of adjacent two-layer slices are opposite. This is because of the typical trapezoidal velocity curve, which has an acceleration stage at the start and a deceleration stage at the end. The acceleration and deceleration stages will inevitably cause poor deposition at the starting point and the ending point of the deposition track, and the deposition states are different. Changing the path directions of adjacent two layers can make the deposition tracks on both sides relatively uniform and ensure the deposition consistency as much as possible. In addition, since the deposition track width of laser powder DED is between 1-3 mm, the design of the overhanging structure cannot ensure that the filling can be exactly completed with an integer number of track lines, and the outer contour changes after the unfolding of each curved surface layer. Therefore, it is necessary to adaptively generate an appropriate number of track lines. Assuming that at the i-th layer, the appropriate overlap rate requires the track spacing to be and the distance between the two long sides on both sides of the outer contour is , the number of adaptive deposition trajectory passes is and rounded down, which slightly changes the overlap rate but avoids filling gaps or accumulations at the boundaries.

[0054]

[0055] The slicing filling path of the workpiece is the absolute trajectory finally executed.

[0056] The present invention relies on the degree-of-freedom redundancy of the eight-axis robot system to distribute the absolute trajectory obtained from the above design to the robotic arm and the positioner, ensuring the optimal printing posture under the constraint conditions such as joint axis limits. After the trajectory distribution, the trajectories to be executed by both the robotic arm and the positioner are obtained. To achieve this goal, it is necessary to first establish a kinematic coupling model of the six-degree-of-freedom robotic arm and the two-axis positioner. In the kinematic coupling model, the base coordinate system of the robotic arm, the base coordinate system of the positioner, the cladding head coordinate system located at the end of the robotic arm, and the workpiece coordinate system located on the positioner table are transformed into the world coordinate system.

[0057] Taking Figure 1 the six-degree-of-freedom robotic arm shown as an example, its coordinate system is constructed as Figure 7 shown, and the DH parameter table describing the coordinate system transformation relationship is shown in Table 1.

[0058] Table 1

[0059]

[0060] For the convenience of formula expression, use to represent the joint angle of rotation of the th joint axis of the robot, to represent the transformation matrix between the link and the link, which is composed of the rotation matrix Rot and the translation matrix Trans:

[0061]

[0062]

[0063] Among them, represents the rod length, which is the distance from the z-axis direction of the coordinate system corresponding to the th joint to the z-axis direction of the coordinate system corresponding to the th joint; represents the rod twist angle, which is the rotation angle from the z-axis direction of the coordinate system corresponding to the th joint to the z-axis direction of the coordinate system corresponding to the th joint; represents the joint distance, which is the distance from the x-axis direction of the coordinate system corresponding to the th joint to the Distance in the x-axis direction of the corresponding coordinate system; Represents the joint rotation angle, which is from the joint To the x-axis direction of the corresponding coordinate system of the joint Rotation angle in the x-axis direction of the corresponding coordinate system.

[0064] The pose of the cladding head can be described in the world coordinate system:

[0065]

[0066] Among them, Can be calculated according to the formula, while And Respectively represent the transformation between the world coordinate system and the robot base coordinate system, and the transformation between the flange coordinate system and the cladding head coordinate system. Both are constant and depend on the base and tool positions. They are calculated separately according to the coordinate system transformation matrix. Here, the flange refers to the connecting flange between the cladding head and the end of the robotic arm. The Obtained according to the above formula, that is, the transformation relationship between the world coordinate system and the cladding head coordinate system, represents the description of the cladding head coordinate system in the world coordinate system.

[0067] Taking Figure 1 The shown two-axis positioner as an example, similar to the modeling process of a six-degree-of-freedom robotic arm, its coordinate system construction is as Figure 8 Shown. In the case of only using a six-degree-of-freedom robotic arm, the position and orientation of the workpiece coordinate system in the world coordinate system are fixed. In this embodiment, the workpiece coordinate system is fixed at the center of the table of the positioner, which can adapt to various workpiece processing scenarios. After planning the path through modeling and simulation, there is no need to repeatedly establish the workpiece coordinate system.

[0068] The transformation relationship between the workpiece coordinate system and the world coordinate system can be described by the following formula:

[0069]

[0070]

[0071]

[0072] Among them, The transformation between the world coordinate system and the positioner base coordinate system represented is constant, while And It will change with the rotation of the joint axes E1 and E2; a represents the distance from the z-axis direction of the base coordinate system of the positioner to the z-axis direction of the coordinate system corresponding to the joint axis E1, b represents the distance from the x-axis direction of the base coordinate system of the positioner to the x-axis direction of the coordinate system corresponding to the joint axis E1, c represents the distance from the x-axis direction of the coordinate system corresponding to the joint axis E1 to the x-axis direction of the workpiece coordinate system, and d represents the distance from the z-axis direction of the coordinate system corresponding to the joint axis E1 to the z-axis direction of the workpiece coordinate system. and respectively represent the rotation angles of the joint axis E1 and the joint axis E2.

[0073] Therefore, through the above modeling, the positioner and the robotic arm can be unified in the world coordinate system. However, what actually determines the printing trajectory is the movement of the cladding head nozzle in the workpiece coordinate system. Based on the above calculations of and , taking the world coordinate system as an intermediary, the description of the cladding head in the workpiece coordinate system can be obtained:

[0074]

[0075] The cladding head needs to meet two constraint conditions to reach the optimal deposition posture, being perpendicular to the printing surface and the ground simultaneously. The orientation of the cladding head perpendicular to the printing surface is described in the workpiece coordinate system. As Figure 9 shown, the cylindrical part indicates that the vector of the cladding head orientation is along the negative z-axis direction, and the overhang structure part indicates that the vector of the cladding head orientation is perpendicular to the axis. The constraint condition of being perpendicular to the ground is described in the world coordinate system. As Figure 10 shown, it is required that the vector representing the cladding head orientation is the same as the gravity direction.

[0076] Under the constraint condition that the cladding head nozzle at the end of the robotic arm is perpendicular to the printing surface and the ground simultaneously, the final executed absolute trajectory is allocated to the robotic arm and the positioner. To ensure meeting the constraint condition that the cladding head nozzle is perpendicular to the ground, when printing the overhang structure, first rotate the tilting axis of the positioner by -90 degrees, then the orientation of the cladding head can be kept downward. However, if it is necessary to meet the perpendicularity to the printing surface, it is inevitable to rotate around the axis of the cylinder, which destroys the constraint condition of being perpendicular to the ground. By calculating the rotation angle of the rotating axis of the positioner and actively rotating by the printing surface, the constraint that the cladding head is perpendicular to the printing surface can be achieved. Assume that a path point on the overhang structure is described as in the workpiece coordinate system, and converting the Cartesian coordinates to polar coordinates gives . That is, when the orientation of the cladding head is perpendicular to the printing surface, it will form an angle of magnitude with the gravity direction, as Figure 11 . It shows that if the rotating axis of the two-axis positioner rotates by , the constraint conditions that the orientation of the cladding head is perpendicular to the printing surface and the ground can be met simultaneously. Therefore, the angles of the tilting axis and the rotating axis of the positioner are According to the robot model, the transformation relationship between the workpiece coordinate system and the world coordinate system can be calculated. According to it is possible to convert into the path points that the robot needs to execute in the world coordinate system. Thus, the robotic arm and the turntable are enabled to work in linkage according to the assigned trajectory.

[0077] Since the trajectory can be regarded as composed of a series of path points, but at this time the path points only contain three-dimensional space coordinates. For the robotic arm, it is also necessary to consider in what pose to reach the target point. Taking the KUKA robotic arm as an example, the pose data format is , where A, B, and C represent the pose, that is, the angles of rotation of the cladding head coordinate system around the Z, Y, and X axes of its own coordinate system respectively. The constraint condition that the cladding head is perpendicular to both the printing surface and the ground at the same time specifies the orientation of the cladding head, corresponding to the rotation angles around the Y-axis and X-axis in the original coordinate system. Although theoretically the cladding head can rotate infinitely around the Z-axis without breaking the constraint condition. In practice, due to the structural size and pipeline limitations of the cladding head, the rotation angle of the cladding head around the Z-axis is limited. To avoid collisions and for calculation convenience, the rotation angle around the Z-axis is directly specified. Therefore, the final position of the cladding head coordinate system is determined. Through the spatial transformation relationship of the coordinate system, the pose parameters of the cladding head can be obtained, such as Figure 12 . Therefore, pose angle parameters can be specified for each path point, which forms different robot trajectories. For the directed energy deposition process, different printing effects will also be produced. The forward and inverse kinematic solutions of the robot can be solved by means of a robot toolbox, etc. to obtain the joint angles of the robotic arm. Combining with the rotation axis angle of the turntable realizes the collaborative work of the robotic arm and the turntable. The process of solving the joint angles of the robotic arm belongs to the common knowledge in the art and will not be elaborated here.

[0078] Figures 13 - 15 shows the printing schematic diagrams of the robotic arm and the turntable in different states. As Figure 13 shown, when the turntable is stationary and the robotic arm only moves vertically with respect to the ground, at this time the nozzle of the cladding head cannot be perpendicular to the printing surface, so the morphology of the molten pool may be deformed; as Figure 14 shown, when the turntable is stationary and the robotic arm only moves perpendicular to the printing surface, at this time the nozzle of the cladding head cannot be perpendicular to the ground, so some powder may deviate from the molten pool under the action of gravity, and the morphology of the molten pool may be deformed. Therefore, the nozzle of the cladding head should be perpendicular to both the ground and the surface as much as possible. In the present invention, a turntable is introduced as an additional axis, and the complete path can be decomposed into the axial movement of the robotic arm and the radial movement of the turntable. As Figure 15 shown, the trajectory of the nozzle of the cladding head is a reciprocating straight line segment, and the turntable only has a change in the angle of the rotation axis.

[0079] AsFigure 16 As shown, the path planning method of the present invention is summarized as follows:

[0080] S1, slice filling, generate absolute trajectory:

[0081] Mixed slicing of the rotating workpiece model to be manufactured, wherein the rotating workpiece model is divided into a cylindrical part and a hanging part, the cylindrical part is sliced ​​along the axial direction, and the hanging part is sliced ​​along the radial direction; outer contours and filling line segments of all slices are optimized to generate a slice filling path as the final absolute trajectory;

[0082] S2, Modeling kinematic coupling model:

[0083] A kinematic coupling model of a six-degree-of-freedom manipulator and a dual-axis positioner is established, in which the manipulator base coordinate system, the positioner base coordinate system, the cladding head coordinate system at the end of the manipulator and the workpiece coordinate system on the positioner table are transformed into the world coordinate system.

[0084] S3, trajectory allocation:

[0085] Under the constraint that the nozzle of the cladding head at the end of the robot arm prints the curved surface and the ground vertically at the same time, the final executed absolute trajectory is assigned to the robot arm and the positioner, and the robot arm and the positioner work in coordination according to the assigned trajectory.

[0086] In view of the characteristics of the rotating workpiece, the present invention uses imaginary cylindrical surface slicing as an effective slicing scheme, and uses coordinate system transformation to transform each coordinate system to the world coordinate system. On the basis of cylindrical surface slicing of the rotating body and filling the obtained path, considering that the cladding head nozzle simultaneously prints the curved surface and the ground vertically is the theoretically optimal printing posture, under the constraint condition of limiting this posture, a relative motion trajectory can be allocated to the six-degree-of-freedom robot arm and the two-axis positioner, and the absolute motion after the synthesis of the two conforms to the slicing filling path.

[0087] The preferred embodiments of the present invention are described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0088] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0089] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A robot path planning method for manufacturing a rotating body based on a powder DED process, characterized in that: include: Mixed slicing of a rotating workpiece model to be manufactured, wherein the rotating workpiece model is divided into a cylindrical part and a hanging part, the cylindrical part is sliced ​​along the axial direction, and the hanging part is sliced ​​along the radial direction; Optimize the outer contour and filling line segments of all slices to generate slice filling paths as the absolute trajectory for final execution; A kinematic coupling model of a six-degree-of-freedom robot and a two-axis positioner is established. In the kinematic coupling model, the robot base coordinate system, the positioner base coordinate system, the cladding head coordinate system at the end of the robot and the workpiece coordinate system at the positioner table are transformed into the world coordinate system. Under the constraint that the cladding head nozzle at the end of the robot prints both the curved surface and the ground vertically at the same time, the final executed absolute trajectory is assigned to the robot and the positioner, and the robot and the positioner work in coordination according to the assigned trajectory.

2. The robot path planning method for manufacturing a rotating body based on a powder DED process according to claim 1 is characterized in that: The slicing method of the overhanging part of the rotating workpiece model is: Along the radial direction of the cylindrical part of the rotating workpiece model, a number of imaginary cylindrical surfaces with increasing diameters are established according to the preset layer thickness, with all the imaginary cylindrical surfaces completely covering the hanging part; The imaginary cylindrical surface is regarded as the cutting layer to slice the overhanging part.

3. The robot path planning method for manufacturing a rotating body based on a powder DED process according to claim 2 is characterized in that: The coordinate points of the slice filling path are described in a polar coordinate system based on an imaginary cylindrical surface.

4. The robot path planning method for manufacturing a rotating body based on a powder DED process according to claim 2 is characterized in that: When optimizing the outer contour and filling line segments of the overhanging part of all slices, first unfold the slices in the overhanging part located on the same imaginary cylindrical surface into a 2D plane along the generatrix, optimize the outer contour and filling line segments on the 2D plane, and then remap the results to the imaginary cylindrical surface.

5. The robot path planning method for manufacturing a rotating body based on a powder DED process according to claim 4 is characterized in that: The optimization of the outer contour and the filled line segments on the 2D plane includes: The outer contour of the slice is marked on the 2D plane, and the path points where the outer contour corners are located are disconnected; Taking one long side of the outer contour as the reference, a line segment is offset parallel to the other side to form a line segment covering the 2D plane of the slice. The offset distance is determined according to the width of the printing path, and there is a gap between the two ends of the line segment and the outer contour. The two adjacent slices take the opposite long side of the outer contour as the reference and the offset direction is opposite.

6. The robot path planning method for manufacturing a rotating body based on a powder DED process according to claim 5, characterized in that: The slice filling path is generated according to the optimized outer contour and filling line segments, and the paths of two adjacent slices are in opposite directions.

7. The robot path planning method for manufacturing a rotating body based on a powder DED process according to claim 1, characterized in that: The method of allocating the final executed absolute trajectory to the robot arm and the positioner under the constraint that the nozzle of the cladding head at the end of the robot arm simultaneously prints the curved surface and the ground vertically includes: The final absolute trajectory is initially assigned to the robot arm according to the unified world coordinate system to obtain the Cartesian coordinates of the path points. , convert Cartesian coordinates to polar coordinates , let the rotation axis angle of the double-axis positioner be ; According to the known angles of the rotation axis and the tilt axis of the dual-axis positioner, the transformation relationship between the workpiece coordinate system and the world coordinate system is obtained, and the Cartesian coordinate system is transformed using this transformation relationship Reconvert to new Cartesian coordinates , as the execution path point of the robot arm, completes the allocation of the absolute trajectory.

8. The robot path planning method for manufacturing a rotating body based on a powder DED process according to claim 7, characterized in that: It is also necessary to set the coordinate point where the cladding head at the end of the robot arm reaches The posture is as follows: The attitude parameters of the cladding head are A, B, and C, which represent the rotation angles of the cladding head coordinate system around the three axes of its own coordinate system. The cladding head orientation satisfies the constraints of being perpendicular to the printed surface and the ground at the same time, thereby obtaining the rotation angles around the Y-axis and the X-axis, and directly specifying the rotation angle around the Z-axis.

9. The robot path planning method for manufacturing a rotating body based on a powder DED process according to claim 8, characterized in that: When the robot arm and positioner work together according to the assigned trajectory, according to the path coordinate points The forward and inverse kinematic solutions of the robot arm are solved based on its posture, the angles of each joint of the robot arm are obtained, and the rotation axis angle of the combined positioner is used to realize the coordinated work of the robot arm and the positioner.

10. A robot for manufacturing a rotating body based on a powder DED process, comprising a six-degree-of-freedom robot arm and a two-axis positioner, characterized in that: The six-degree-of-freedom robot arm and the two-axis positioner adopt the path planning method described in any one of claims 1 to 9 to collaboratively manufacture a rotating workpiece.

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