Robot Path Planning Method for Manufacturing Rotating Bodies Based on Powder DED Process

Abstract

The invention discloses a robot path planning method for manufacturing a revolving body based on the powder DED process, belonging to the technical field of additive manufacturing. The revolving body workpiece model is mixed sliced, and the model is divided into a cylindrical part and a hanging part. The former is axially sliced, and the latter is radially sliced. The outer contours and filling line segments of all slices are optimized to generate a slice filling path as the absolute trajectory for final execution. A kinematic coupling model of a six-degree-of-freedom robotic arm and a two-axis positioner is established. The base coordinate system of the robotic arm, the base coordinate system of the positioner, the cladding head coordinate system, and the workpiece coordinate system are converted to the world coordinate system. Under the constraint of ensuring that the cladding head nozzle at the end of the robotic arm is perpendicular to the printing surface and the ground, the absolute trajectory is assigned to the robotic arm and the positioner, and the two cooperate in a linkage manner according to the assigned trajectory. With the aid of the linkage and cooperation of the six-degree-of-freedom robotic arm and the two-axis positioner, and benefiting from the degree-of-freedom redundancy of the eight-axis robot system, the invention achieves printing with the optimal robot posture.

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 rotating body based on a powder DED process. Background Art

[0002] Rotating 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 them, resulting in most rotating body parts having complex curved surface structures. With the development of metal additive manufacturing technology, a new manufacturing solution based on the Directed Energy Deposition (DED) process has gradually been applied in engineering. This solution uses a laser, electron beam or plasma arc device to focus thermal energy to melt materials, and sends metal raw materials in the form of wire or powder to the molten pool for layer-by-layer deposition, which can directly form or repair 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 rotating body parts, the application method mainly uses a single six-degree-of-freedom industrial robot arm, or although a positioner is equipped, the positioner is only used for positioning and is not linked and coordinated with the robot arm, and its movement is not fully exploited. In this mode, the processing process mainly relies on the active movement of the robot 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 deposition 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 the 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 trajectory 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 trajectory does not meet the expectations. Existing robot trajectory planning methods pay insufficient attention to the posture 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 trajectory based on the laser powder directed energy deposition process is relatively large, between 1 - 3 mm. When manufacturing a rotary body curved surface, using traditional path planning methods will result in serious staircase effects and additional support structures, affecting material utilization 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] 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 rotary workpieces. Even in the same machining area, in cooperation with the movement of the positioner, the robotic arm can select a better pose to 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. In this way, the morphology of the molten pool can be stabilized, and the metal powder can fall evenly into the molten pool, ensuring a better part forming effect. In addition, the model of the rotary workpiece to be manufactured is sliced in a hybrid manner. The model of the rotary 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 an accurate sliced filling path.

[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, and accidental flow is not likely to occur. The stacking error of each layer is reduced, and thus 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. Brief 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 of the overhanging part of the rotary body experiencing 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 rotary 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

[0043] Figure 11 It is the angle between the direction of gravity and the orientation of the cladding head when the positioner's tilt axis rotates -90 degrees and the cladding head is 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 a trajectory diagram of the manipulator moving only vertically to the ground when the positioner is stationary.

[0046] Figure 14 It is a trajectory diagram of the manipulator moving only vertically to the printing surface when the positioner is stationary.

[0047] Figure 15

[0048] Figure 16 It is a trajectory diagram of the positioner and the manipulator moving together to print a hanging structure.

[0049] Specific embodiments

[0050] 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 art 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 "including" or "comprising" 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. "Up", "down", "left", "right", etc. are only used to represent relative positional relationships, and when the absolute position of the object being described changes, the relative positional 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 an overhanging structure of a revolving body, first, the tilt axis E1 rotates -90 degrees to make the positioner workbench surface perpendicular to the ground, and then the rotation axis E2 continuously rotates 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 eight-axis robot system for trajectory planning to keep the cladding head nozzle in an optimal posture during the printing process and obtain better forming quality.

[0052] For various revolving body workpieces, based on their own geometric features, 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 features 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 achieve 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 maintain the optimal printing posture. Since the outer contour is obtained by slicing radially along the core cylinder, and since the rotary 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, as a regular body, has a relatively mature contour line filling technology and can be realized by existing technologies, which will not be elaborated here. To facilitate the processing path of the overhang part, each layer of the overhang part is mapped to a 2D plane. As Figure 5 shown, each layer in the overhang part can be imagined as being on the surface of a hypothetical cylinder. First, the slices in the overhang 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 of 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 overhang 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 opposite boundary positions. 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 trajectory, and the deposition states are different. Changing the path directions of adjacent two layers can make the deposition trajectories on both sides relatively uniform and ensure the deposition consistency as much as possible. In addition, since the deposition trajectory track width of laser powder DED is between 1-3 mm, the design of the overhang structure cannot ensure that the filling can be exactly completed with an integer number of track trajectories, 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 trajectories. Assuming that at the i-th layer, the appropriate overlap rate requires the track spacing to be , and the spacing 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 final executed absolute trajectory.

[0056] The present invention relies on the degree - of - freedom redundancy of the eight - axis robot system to allocate the absolute trajectory obtained from the above design to the robotic arm and the positioner, ensuring the optimal printing posture under constraints such as joint - axis limits. After trajectory allocation, 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 a six - degree - of - freedom robotic arm and a 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 links, which is composed of a rotation matrix Rot and a translation matrix Trans:

[0061]

[0062]

[0063] Among them, represents the link length, which is the distance from the z - axis direction of the coordinate system corresponding to joint to the z - axis direction of the coordinate system corresponding to joint ; represents the link twist angle, which is the rotation angle from the z - axis direction of the coordinate system corresponding to joint to the z - axis direction of the coordinate system corresponding to joint ; represents the joint distance, which is the distance from the x - axis direction of the coordinate system corresponding to joint to the x - axis direction of the coordinate system corresponding to joint The distance in the x-axis direction of the corresponding coordinate system; Indicates the joint rotation angle, which is from the joint To the x-axis direction of the corresponding coordinate system of the joint The rotation angle of 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, and 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] Take 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, and And It will change with the rotation of joint axes E1 and E2; a represents the distance from the z-axis direction of the positioner base coordinate system 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 positioner base coordinate system 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, 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 Represent the rotation angles of joint axis E1 and joint axis E2 respectively.

[0073] Therefore, through the above modeling, the positioner and the robot arm can be unified in the world coordinate system, but the actual printing trajectory is determined by the movement of the cladding head nozzle in the workpiece coordinate system. and , using the world coordinate system as the medium, the description of the cladding head in the workpiece coordinate system can be obtained:

[0074]

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

[0076] Under the constraint that the nozzle of the cladding head at the end of the robot arm is perpendicular to the printing surface and the ground at the same time, the final executed absolute trajectory is assigned to the robot arm and the positioner. In order to ensure that the constraint condition of the cladding head nozzle being perpendicular to the ground is met, when printing the overhanging structure, the tilt axis of the positioner is first rotated -90 degrees, so that the cladding head can be kept facing downward, but if the vertical printing surface is to be satisfied, it must be rotated around the axis of the cylinder, which destroys the constraint condition of being perpendicular to the ground. By calculating the rotation angle of the rotation axis of the positioner and actively rotating the printing surface, the constraint of the cladding head being perpendicular to the printing surface can be achieved. Assume that a path point on the overhanging structure is described in the workpiece coordinate system as , converting Cartesian coordinates into polar coordinates is That is, when the cladding head is facing vertically to the printed surface, it will form a distance of The angle of Figure 11 . Explain that the rotating axis of the double-axis positioner rotates again , the constraints of the cladding head facing the vertical printing surface and the ground can be satisfied at the same time. Therefore, the angles of the tilt axis and the rotation 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 positioner are enabled to work in linkage and coordination according to the assigned trajectory.

[0077] Since the trajectory can be regarded as being 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 posture 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 posture, 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 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 posture parameters of the cladding head can be obtained, such as Figure 12 . Therefore, attitude 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 and other methods to obtain the joint angles of the robotic arm, and the rotation axis angles of the positioner are combined to enable the robotic arm and the positioner to work in coordination. 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 positioner in different states. As Figure 13 shown, when the positioner does not move and the robotic arm only moves vertically to the ground, at this time the cladding head nozzle cannot be perpendicular to the printing surface, so the molten pool morphology may be deformed; as Figure 14 shown, when the positioner does not move and the robotic arm only moves perpendicular to the printing surface, at this time the cladding head nozzle cannot be perpendicular to the ground, so part of the powder may deviate from the molten pool under the action of gravity, and the molten pool morphology may be deformed. Therefore, the cladding head nozzle should be made perpendicular to the ground and the surface as much as possible. The present invention introduces a positioner as an additional axis, which can decompose the complete path into the axial movement of the robotic arm and the radial movement of the positioner. As Figure 15 shown, the trajectory of the cladding head nozzle is a reciprocating straight line segment, and the positioner 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 revolving body based on powder DED process, characterized in that, Including: Mixing and slicing the model of the revolving body workpiece to be manufactured, wherein the model of the revolving body workpiece 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; Optimizing the outer contour and filling line segments of all the slices to generate a slice filling path as the absolute trajectory finally executed; Establishing a kinematic coupling model of a six-degree-of-freedom robotic arm and a two-axis positioner. In the kinematic coupling model, transforming the robotic arm base coordinate system, the positioner base coordinate system, the cladding head coordinate system located at the end of the robotic arm, and the workpiece coordinate system located on the positioner tabletop to the world coordinate system. Under the constraint condition that the nozzle of the cladding head at the end of the robotic arm is perpendicular to the printing surface and the ground simultaneously, distributing the finally executed absolute trajectory to the robotic arm and the positioner, and the robotic arm and the positioner work in linkage and coordination according to the distributed trajectory; The slicing method for the hanging part of the revolving body workpiece model is as follows: 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, so that all the imaginary cylindrical surfaces completely cover the hanging part; Regarding the imaginary cylindrical surface as a cutting layer to realize the slicing of the hanging part; When optimizing the outer contour and filling line segments of the slices of the hanging part in all the slices, first unfold the slices located on the same imaginary cylindrical surface in the hanging part along the generatrix to a 2D plane, optimize the outer contour and filling line segments on the 2D plane, and then remap the result to the imaginary cylindrical surface; The optimization of the outer contour and filling line segments on the 2D plane mentioned above includes: Marking the outer contour of the slice on the 2D plane, and disconnecting the path points at the corners of the outer contour; Taking one long side of the outer contour as a reference, parallelly offsetting to the other side to form a line segment covering the 2D plane of the slice, the offset distance is determined according to the printing track width, and there is a gap between the two ends of the line segment and the outer contour; for adjacent two layers of slices, take the opposite long sides of the outer contour as references and the offset directions are opposite.

2. The robot path planning method for manufacturing a solid of revolution based on the powder DED process according to claim 1, wherein The coordinate points of the slice filling path are described in the polar coordinate system based on the imaginary cylindrical surface.

3. The robot path planning method for manufacturing a rotating body based on the powder DED process according to claim 1, wherein, The slice filling path is generated according to the optimized outer contour and filling line segments, and the path directions of adjacent two layers of slices are opposite.

4. The robot path planning method for manufacturing a rotating body based on the powder DED process according to claim 1, wherein, The distributing the finally executed absolute trajectory to the robotic arm and the positioner under the constraint condition that the nozzle of the cladding head at the end of the robotic arm is perpendicular to the printing surface and the ground simultaneously includes: The absolute trajectory to be finally executed is initially assigned to the robotic arm according to the unified world coordinate system to obtain the Cartesian coordinates of the path points , and the Cartesian coordinates are converted into polar coordinates , and the angle of the rotating axis in the two-axis positioner is set to ; according to the known angles of the rotating axis and tilting axis of the two-axis positioner, the transformation relationship between the workpiece coordinate system and the world coordinate system is obtained, and the Cartesian coordinates are re-converted into new Cartesian coordinates , which are used as the execution path points of the robotic arm to complete the assignment of the absolute trajectory.

5. The robot path planning method for manufacturing a rotating body based on the powder DED process according to claim 4, wherein, It is also necessary to set the attitude of the cladding head at the end of the robotic arm when it reaches the coordinate point which is specifically as follows: The attitude parameters of the cladding head are A, B, and C, which respectively represent the angles of rotation of the cladding head coordinate system around its own coordinate system's three axes. The orientation of the cladding head simultaneously satisfies the constraint conditions of being perpendicular to the printing surface and the ground, thereby obtaining the rotation angles around the Y-axis and the X-axis, and directly specifying the rotation angle around the Z-axis.

6. The robot path planning method for manufacturing a solid of revolution based on the powder DED process according to claim 5, 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.

7. A robot for manufacturing a solid of revolution based on the powder DED process, comprising a six-degree-of-freedom robotic arm and a two-axis positioner, characterized in that, The six-degree-of-freedom robotic arm and the two-axis positioner adopt the path planning method described in any one of claims 1 to 6 to work in linkage and coordination to manufacture the revolving body workpiece.

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