CN112757307A - Equipment and method for machining three-dimensional impeller blade welding groove by robot - Google Patents
Equipment and method for machining three-dimensional impeller blade welding groove by robot Download PDFInfo
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- CN112757307A CN112757307A CN201911068179.3A CN201911068179A CN112757307A CN 112757307 A CN112757307 A CN 112757307A CN 201911068179 A CN201911068179 A CN 201911068179A CN 112757307 A CN112757307 A CN 112757307A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
- B25J11/00—Manipulators not otherwise provided for
- B25J11/005—Manipulators for mechanical processing tasks
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23D—PLANING; SLOTTING; SHEARING; BROACHING; SAWING; FILING; SCRAPING; LIKE OPERATIONS FOR WORKING METAL BY REMOVING MATERIAL, NOT OTHERWISE PROVIDED FOR
- B23D69/00—Filing or rasping machines or devices. characterised only by constructional features of particular parts, e.g. guiding arrangements, drives; Accessories for filing or rasping
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
- B25J9/00—Programme-controlled manipulators
- B25J9/16—Programme controls
- B25J9/1628—Programme controls characterised by the control loop
- B25J9/1633—Programme controls characterised by the control loop compliant, force, torque control, e.g. combined with position control
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
- B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
- B25J9/00—Programme-controlled manipulators
- B25J9/16—Programme controls
- B25J9/1656—Programme controls characterised by programming, planning systems for manipulators
- B25J9/1664—Programme controls characterised by programming, planning systems for manipulators characterised by motion, path, trajectory planning
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Abstract
The invention discloses equipment and a method for machining a three-element impeller blade welding groove by a robot, and belongs to the technical field of automatic machining of robots. The equipment comprises an industrial robot, a force control measuring module, a machining tool quick-change module, a machining tool and a workbench. The processing method comprises the following steps: the method comprises the steps of extracting, sequencing and discretizing characteristic curves of impeller blades, generating and extracting a central axis, generating and discretizing a cover plate line, calculating machining allowance, setting and adjusting a frame of a welding groove of the impeller blades, calibrating a cutting tool coordinate system, calibrating a workpiece coordinate system, automatically producing a machining track, measuring in place based on a force control mode, and determining the feed allowance based on online control of machining removal amount. Compared with a five-axis numerical control machining tool, the equipment and the method provided by the invention have the advantages of low cost, good adaptability and very strong flexibility, and the problem of self-adaptive machining of the impeller welding groove is well solved.
Description
Technical Field
The invention relates to the technical field of automatic processing of robots, in particular to equipment and a method for automatically processing a three-element impeller blade welding groove by a robot.
Background
The centrifugal compressor is widely applied to important fields closely related to national economy, such as petroleum and petrochemical industry, natural gas transportation, metal smelting and the like as industrial equipment. The machining quality of the ternary impeller serving as a core component of the centrifugal compressor directly affects the performance and efficiency of the centrifugal compressor, so the ternary impeller is vividly called as the heart of the centrifugal compressor, and how to manufacture the ternary impeller with higher precision and lower manufacturing cost in a short period is a difficult problem to be researched and solved by engineering technicians. Most of impeller blades with free curved surfaces are processed by point contact milling, and a five-axis processing center mainly processes the free curved surface profile and the runner profile of the blade. The processing cost of the method is too high for processing and removing the welding groove of the edge surface of the blade wheel, so that the processing of the welding groove of the integral impeller blade is mainly carried out by manually polishing and polishing by manually holding an electric grinder. By adopting a trial and error processing mode of removing, measuring, removing again and measuring again, the processing quality highly depends on the experience of operators, the processing precision and quality of the welding groove are difficult to ensure, the processing consistency is difficult to control, and the harsh environments such as noise, dust and the like generated in the processing process also have great harm to the health of the operators. The robot processing system can realize the automation of the complex curved surface part processing and removing process, improve the processing quality, greatly shorten the processing time, improve the processing efficiency and ensure the consistency of the processing quality. However, because the robot has low positioning accuracy and large impeller positioning error, the accurate relative machining position of the cutter and the blade rim line is difficult to realize by only depending on the motion accuracy of the robot along the track generated by the impeller model. The width of the edge surface of the blade wheel after finish milling is different, and the dimension and the width of the welded junction process required after welding groove machining are consistent, so that a machining mode of changing the removal allowance is required in the welding groove machining and removing process, and the requirement cannot be met by the existing robot machining and removing method.
Disclosure of Invention
The invention aims to provide equipment and a method for machining a three-element impeller blade welding groove by a robot, which can realize automatic machining of the blade welding groove in the three-element impeller machining and manufacturing process and replace the conventional manual machining mode. The equipment is taken as a processing technology system, and the variable-allowance processing removal of the three-dimensional impeller blade welding groove can be realized by adopting methods such as processing model characteristic curve extraction and sequencing, curve discretization, central axis extraction and discretization, frame setting and adjustment, cover plate line generation and discretization, track automatic generation, force control mode-based on-site detection, processing track error compensation, variable-allowance processing and the like, so that the welding groove with equal width dimension and equal angle can be obtained.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
an equipment for processing a three-dimensional impeller blade welding groove by a robot comprises an industrial robot, a force control measuring module, a processing tool quick-changing module, a processing tool and a workbench; wherein:
industrial robot: inputting a machining track produced according to the impeller model into a robot controller, controlling the motion track of the robot, driving a machining tool arranged at the tail end of the robot, and machining and removing the blade welding groove;
the force control measurement module: the robot comprises a six-dimensional force/torque sensor, wherein a force control measurement module is arranged on a flange at the tail end of a robot and is used for measuring the magnitude of a machining contact force in real time on line in the machining process and providing measurement data for a force-position control mode;
processing tool quick change module: the device comprises a quick-change head and the like, and is arranged on a connecting flange of a six-dimensional force/torque sensor;
processing a tool: the device comprises a straight grinding machine and a cylindrical rotary file which are connected, wherein the straight grinding machine is connected and installed with a processing tool quick-change module through a clamp, and the straight grinding machine drives the rotary file to rotate during processing;
a workbench: the device is used for installing the impeller workpiece and has the function of realizing the rotation of the impeller workpiece along the Z axis and the X axis during machining;
the equipment further comprises an upper computer, wherein the upper computer is used for finishing the processing of the impeller model, and the processing comprises the extraction and discretization of a rim line, a central axis and a cover plate line, the generation of a processing track, the extraction processing of a processing contact force, the compensation correction control of the processing track and the like.
The equipment further comprises a machining tool library, wherein the machining tool library is used for storing machining tools, the quantity of the machining tools can be set according to the types and the like of the tools required by machining, and the machining tool library is placed at a fixed position and provides different machining tools for machining of the robot.
The method for processing the ternary impeller blade welding groove by using the robot comprises the steps of extracting, sequencing and discretizing impeller blade characteristic curves, generating and extracting a central axis, generating and discretizing a cover plate line and calculating machining allowance, setting and adjusting a calibration frame of the impeller blade welding groove, calibrating a cutting tool coordinate system, calibrating a workpiece coordinate system, automatically producing a machining track, measuring in place based on a force control mode, and determining a feed allowance based on-line control of machining removal amount, and specifically comprises the following steps:
(1) the extraction, sequencing and discretization process of the characteristic curve of the impeller blade comprises the following steps:
extracting a blade rim surface, a pressure surface rim line and a suction surface rim line according to the three-dimensional model of the impeller, if more than one rim curve is available, sequencing all processing curves according to the sequence of end-to-end connection, and discretizing the selected curve according to the processing distance and the precision requirement (when curve discretization is carried out, the number of discrete points of the pressure surface rim line and the suction surface rim line is required to be equal).
(2) The generation and extraction process of the central axis comprises the following steps:
extracting the central axis of the rim surface: firstly, discretizing a rim surface by a method of discretizing the rim surface of a blade into a triangular mesh curved surface, sequentially taking a rim line discrete point of a pressure surface and a rim line discrete point of a suction surface corresponding to the rim line discrete point, and respectively solving a triangular mesh triangle index where the two points are located and a barycentric coordinate system value in the triangle for the two corresponding discrete point pairs; taking the obtained triangle index and the barycentric coordinate system value as input, and applying a triangular mesh discrete geodesic solving algorithm to solve the triangular mesh discrete geodesic between the two points; for all discrete pairs of point pairs of pressure and suction side rim lines, the following is performed: solving the position of a center point of the discrete geodesic line obtained by each discrete point pair, wherein the coordinate of the center point is the center axis point of the rim line pair on the rim surface; carrying out curve fitting on the midpoints of the discrete geodesic lines of all the point pairs to obtain the central axis of the edge surface of the blade wheel;
(3) the generation and discretization process of the cover plate line and the calculation of the machining allowance are as follows:
obtaining a center axis point of a corresponding point according to a relative discrete point pair of a pressure surface rim line and a suction surface rim line, calculating the distance between the discrete point and the center axis in the rim surface as H, setting the residual width of the rim surface after the welding groove is removed in the machining process as D, taking the center axis discrete point as the center, and setting the offset distance of each discrete point along the corresponding rim line in the rim surface as D/2, wherein the two corresponding points are points on the cover disc line of the pressure surface and the suction surface, and the distance from the point to the corresponding point on the corresponding rim line is the machining allowance which is H-D/2; sequentially taking each point on the central axis as a center by adopting the same method to form corresponding points of two cover plate lines on the rim surface; and connecting the points to form a cover plate line, wherein the distance between the cover plate line and the rim line is the size of the total machining allowance, the machining allowances between the cover plate line and the rim line are not the same and are changed along with the change of the machining position point, namely H-D/2 is a variable value.
(4) Setting and adjusting a standard frame of the impeller blade welding groove:
calculating the local frame of each discrete point in the normal evaluation direction of the rim surface according to the discrete points: the discrete point normal vector is used as the Z-axis direction of the discrete point local frame; calculating the tangential vector of each discrete point according to the tangential evaluation method of the discrete point on the rim line, wherein the tangential vector direction is used as the X-axis direction of the local frame of the discrete point; and determining the Y-axis direction of each discrete point local frame according to the right-hand rule: rotating for 45 degrees along the X axis of the local frame to enable the Z axis to be vertical to the welded bevel face after machining;
(5) cutting tool coordinate system (coordinate system T) calibration:
the tool coordinate system of the machining tool is calibrated by adopting the self function of the robot, and the directions of all axes of the established tool coordinate system are defined as follows: the origin of the tool coordinate system is a proper point on the excircle cutting edge of the cylindrical rotary file, the X-axis direction is the tangential direction of a connecting line of the origin and the axis of the rotary file, and the axial direction points to the rotating direction of the origin during processing; the Y axis is parallel to the axis of the rotary file and points to the direction of the robot flange; the Z axis is determined according to the right-hand rule;
(6) calibration process of the workpiece coordinate system (coordinate system B):
establishing a workpiece coordinate system on the workpiece impeller by adopting an indirect method: firstly, selecting four characteristic points in three-dimensional modeling software, and recording coordinate values of the four characteristic points in a workpiece coordinate system; then tool sharp points of a measured tool coordinate system are sequentially close to corresponding feature points on the workpiece, and coordinate values in the corresponding three-dimensional model are output in the robot demonstrator; after the operation is finished, the robot calculates the transformation relation of the established workpiece coordinate system relative to the robot base coordinate system, so as to finish the calibration of the workpiece coordinate system;
(7) automatic production process of machining tracks:
calculating the poses (including positions and postures) of all discrete points on the rim line of the blade by taking an impeller workpiece coordinate system B as a reference system, automatically generating track points processed and removed on the rim line of the processed blade, and then sequentially connecting all the track points to form a processing track;
(8) in-situ measurement process based on force control mode:
an in-situ measurement method based on a force control mode is adopted and used for measuring the difference value between a programming track and an actual track of each discrete position point index in the Z-axis direction of a tool coordinate system when a rotary file is in close contact with a rim line, a robot reads the difference value of each discrete position point index in the Z-axis direction of the tool and compares the difference value with the position value in the Z-axis direction of a corresponding discrete point on a track generated by an impeller model, the deviation (namely correction K) of the actual processing position and the theoretical track position in the Z-axis direction is calculated, and the theoretical position point Z-axis numerical value compensation deviation value is the actual value in the Z-axis direction of the discrete point of the blade profile line, so that the influence of error factors such as the tool coordinate system of the robot, a workpiece coordinate system, the absolute positioning error of the robot and the workpiece manufacturing error of;
adopting a processing track error compensation method, namely compensating and correcting Z-direction deviation K (i) of a position index point when in-place measurement is carried out according to a theoretical discrete point Z-axis direction position point Z (i) on a processing track generated by an impeller model, namely Z (i) -K (i), carrying out secondary curve fitting on each robot theoretical discrete point track point and each corresponding point after correction compensation of the index point, removing the influence of miscellaneous points in the measurement process, and obtaining a smooth removal quantity control curve, wherein the curve is a processing path after compensation and correction are carried out on a workpiece theoretical model track path, namely an actual track point in the processing of a robot, namely W (i), so that the correct relative position relation between a rotary file and a blade welding groove in the processing is realized;
(9) a process of determining a feed margin based on-line control of a machining removal amount:
firstly, calculating the machining allowance H-D/2 of each discrete point on a rim line, and respectively and sequentially marking index names A (1), A (2), A (3), A (4), … … A (i), wherein i is a natural number; the machining allowance with the maximum value being the maximum value is taken from the calculated values, and is also set as A0; when H-D/2 is equal to 0, the edge line and the cover coil line are superposed at the discrete point, and the machining allowance is set to be 0; setting a cutting depth value B of each feed of the selected rotary file, wherein the feed times of one side of the blade is A0/B, and the machining allowance of each feed at each discrete point is A (i) B/A0; when the machine tool is fed for the first time, the Z-direction path position points at the discrete points are W (i) -A (i) B/A0; and during the second feed, the Z-direction path position points at the discrete points are W (i) -2A (i) B/A0, and the rest is repeated until the feed times A0/B are completed, so that the machining of all welding grooves on the pressure surface or the suction surface side is completed.
The invention has the following advantages and beneficial effects:
the equipment and the process can realize the automatic robot machining removal of the impeller welding groove, and compared with a five-axis numerical control machining tool, the equipment and the method provided by the invention have the advantages of low cost, good adaptability and very strong flexibility, and the problem of self-adaptive machining of the impeller welding groove is well solved.
Drawings
FIG. 1 is a schematic view of the overall structure of the device of the present invention.
Fig. 2 is a schematic view of the impeller structure.
FIG. 3 is a graph of a vane rim line discrete point extraction.
FIG. 4 is an extraction of discrete points from the central axis of the blade.
Fig. 5 is a graph of a discrete point extraction of the disk line of the blade cover.
Fig. 6 is a disk diagram of the blade cover.
FIG. 7 is a diagram of the positioning of the frame.
Fig. 8 is a machining trajectory correction fitting graph.
Fig. 9 is a diagram showing a variation in the machining allowance.
In the figure: 1-an upper computer; 2-a library of processing tools; 3-an industrial robot; 4-a force control measurement module; 5-machining tool quick-change module; 6-a processing tool; 7-impeller workpiece; 8-a workbench.
Detailed Description
The invention aims to realize automatic processing of a three-element impeller blade welding groove by a robot and replace manual operation processing.
The invention provides equipment for machining a three-element impeller blade welding groove by a robot, which is structurally shown in figure 1. The equipment comprises an industrial robot 3, a force control measuring module 4, a machining tool quick-change module 5, a machining tool 6 and a workbench 8; wherein:
industrial robot: inputting a machining track produced according to the impeller model into a robot controller, controlling the motion track of the robot, driving a machining tool 6 installed at the tail end of the robot, and machining and removing the blade welding groove;
force control measurement module 4: the robot comprises a six-dimensional force/torque sensor, wherein a force control measurement module 4 is arranged on a flange at the tail end of a robot and is used for measuring the magnitude of a machining contact force in real time on line in the machining process and providing measurement data for a force-position control mode;
machining tool quick-change module 5: the device comprises a quick-change head and the like, and is arranged on a connecting flange of a six-dimensional force/torque sensor;
the machining tool 6: the device comprises a straight grinding machine and a cylindrical rotary file which are connected, wherein the straight grinding machine is connected and installed with a processing tool quick-change module 5 through a clamp, and the straight grinding machine drives the rotary file to rotate during processing;
a workbench 8: the device is used for installing the impeller workpiece 7 and has the function of realizing the rotation of the impeller workpiece along the Z axis and the X axis during machining;
the equipment further comprises an upper computer 1 and a processing tool library 2, wherein the upper computer 1 is used for finishing the processing of the impeller model, and comprises the extraction and discretization of a rim line, a central axis and a cover plate line, the generation of a processing track, the extraction processing of a processing contact force, the compensation correction control of the processing track and the like. The machining tool magazine 2 is used for storing machining tools, can be set according to the number of types of tools required by machining, and the like, is placed at a fixed position, and provides different machining tools for machining of the robot.
The equipment is used for processing the ternary impeller blade welding groove by the robot, and the structure of the ternary impeller blade is shown in figure 2. The welding groove processing specifically comprises the following steps:
(1) extracting blade rim surfaces, pressure surface rim lines and suction surface rim lines of the three-dimensional impeller model, and if more than one rim curve is available, sequencing the processing curves in an end-to-end sequence; discretizing the selected curve according to the processing distance and the precision requirement, as shown in fig. 3.
(2) The generation and extraction method of the central axis comprises the following steps:
discretizing the rim surface by forming the blade rim surface into a curved surface represented by a triangular mesh, sequentially taking the rim line discrete points of the pressure surface and the corresponding rim line discrete points of the suction surface, and respectively solving triangular mesh triangle indexes where the two points are located and the barycentric coordinate system value in the triangle for the two corresponding discrete point pairs; taking the obtained triangle index and the barycentric coordinate system value as input, and applying a triangular mesh discrete geodesic solving algorithm to solve the triangular mesh discrete geodesic between the two points; performing the above operations for all discrete point pairs of the pressure surface and the suction surface rim lines; solving the position of a center point of the discrete geodesic line obtained by each discrete point pair, wherein the coordinate of the center point is the center axis point of the rim line pair on the rim surface; and (5) carrying out curve fitting on the midpoints of the discrete geodesic lines of all the point pairs to obtain the central axis of the blade rim surface, as shown in figure 4.
(3) The generation and discretization process of the cover plate line and the calculation of the machining allowance are as follows:
obtaining a center axis point of a corresponding point according to the relative discrete point queue of a pressure surface wheel rim line and a suction surface wheel rim line, calculating the distance of the discrete point and the center axis in the wheel rim plane as H, setting the residual width of the wheel rim surface after the welding groove is removed in the machining process as D, taking the center axis discrete point as the center, and setting the offset distance of each discrete point along the corresponding wheel rim line in the wheel rim plane as D/2, wherein the two corresponding points are points on the cover disc line of the pressure surface and the suction surface, and the distance from the point to the corresponding point on the corresponding wheel rim line is the machining allowance which is H-D/2; the corresponding points of the two cover plate lines on the rim surface are formed by sequentially taking each point on the central axis as the center by the same method, as shown in figure 5. And connecting the points to form a cover plate line, wherein the distance between the cover plate line and the rim line is the size of the total machining allowance, the machining allowances between the cover plate line and the rim line are not the same and are changed along with the change of the machining position point, namely H-D/2 is a variable value, as shown in figure 6.
(4) Calculating a normal vector of each discrete point in the normal evaluation direction of the wheel rim surface according to the discrete points by adopting a frame setting and adjusting method, wherein the normal vector is used as the Z-axis direction of the discrete point local frame; calculating the tangential vector of each discrete point according to the tangential evaluation method of the discrete point on the rim line, wherein the tangential vector direction is used as the X-axis direction of the local frame of the discrete point; and determining the Y-axis direction of each discrete point local frame according to the right-hand rule: and then rotating for 45 degrees along the X axis of the local frame to ensure that the Z axis is vertical to the processed welding bevel face, as shown in figure 7.
(5) Performing gravity balancing of the cutting tool: i.e. to eliminate the influence of the cutting tool gravity on the six-dimensional sensor measurement during cutting, the part of the cutting tool gravity included in the sensor measurement is compensated for in the sensor coordinate (coordinate system S) such that the measurement only includes the magnitude of the cutting force during cutting.
(6) Calibration tool coordinate system (coordinate system T): adopting the self function of the robot to establish a tool coordinate method for processing the cutter, and defining the directions of all axes of the established tool coordinate system as follows: the origin of the tool coordinate system is an appropriate point on the excircle cutting edge of the cylindrical rotary file (the point is the outermost point of the rotary file cutting edge, and the distance between the point and the outermost side and the innermost side of the rotary file is greater than the width of a welding groove, so that the cutting edge of the rotary file is ensured to be greater than the width of the welding groove during cutting), the X-axis direction is the tangential direction of the connecting line of the origin and the axis of the rotary file, and the axial direction points to the rotating direction during processing of the origin; the Y axis is parallel to the axis of the rotary file and points to the direction of the robot flange; the Z axis is determined according to the right hand rule.
(7) Calibration of the workpiece coordinate system (coordinate system B):
establishing a workpiece coordinate system on the workpiece impeller by adopting an indirect method: firstly, selecting four characteristic points (as the impeller is composed of a plurality of blades with the same shape, the characteristic points are points which are not on the same blade but have the same relative position on the impeller digital model) in the three-dimensional modeling software, and recording coordinate values of the four characteristic points in a workpiece coordinate system. And then, tool sharp points of the measured tool coordinate system are sequentially close to corresponding feature points on the workpiece, and coordinate values in the corresponding three-dimensional model are output in the robot demonstrator. After the above operations are completed, the robot calculates the transformation relation of the established workpiece coordinate system relative to the robot base coordinate system, thereby completing the calibration of the workpiece coordinate system.
(8) And (3) calculating the poses (three positions and three angles) of each discrete point on the blade rim line by adopting a track automatic production method and taking the impeller workpiece coordinate system B as a reference system, automatically generating the track points processed and removed on the processed blade rim line, and sequentially connecting each track point to form the processing track.
(9) And (3) controlling the position of the rotary file by adopting a force/position control mode, realizing the close fit feeding of the rotary file and a processing point, guiding the calculated processing track of the edge line of the blade wheel into a robot controller, and controlling the robot to drive the rotary file to move according to the track. Adopting a force control method in the Z direction of the machining track along a tool coordinate system, setting the target force in the contact force Z direction to be 3N, and when the measured contact force is smaller than the target force, performing small compensation motion in the reverse direction of the robot to the Z axis of the machining track; when the contact force is larger than the target force, the robot performs small compensation motion towards the Z axis of the processing track, so that the rotary file is tightly attached to the edge line of the blade wheel.
(10) An in-situ measurement method based on a force control mode is adopted and used for measuring the actual position of each discrete position point index in the Z-axis direction when a rotary file is in close contact with a rim line, a robot reads the actual position of each discrete position point in the Z-axis direction of a tool coordinate system, compares the actual position with the position value in the Z-axis direction of the corresponding discrete point on a track generated by an impeller model, calculates the deviation (namely correction K) of the actual processing position and the theoretical track position in the Z-axis direction, and the theoretical position point Z-axis numerical value compensation deviation value is the actual value in the Z-axis direction of the discrete point of the blade profile line, so that the influence of error factors such as the tool coordinate system of the robot, a workpiece coordinate system, the absolute positioning error of the robot and the workpiece manufacturing error of the robot can be eliminated.
(11) The machining track error compensation method is adopted, namely, according to a theoretical discrete point Z-axis direction position point Z (i) on a machining track generated by an impeller model, Z-direction deviation K (i) of a position index point during in-place measurement is compensated and corrected, namely Z (i) -K (i), secondary curve fitting is carried out on each theoretical discrete point track point of each robot and each corresponding point after correction quantity compensation of the index point, the influence of miscellaneous points in the measurement process is removed, a smooth removal quantity control curve is obtained, the curve is a machining path after compensation and correction are carried out on a theoretical model track path of a workpiece, namely an actual track point during robot machining, namely W (i), so that the correct relative position relation between a rotary file and a blade welding groove during machining is realized, vibration in the machining process is reduced, and the operation process is shown as figure 8.
(12) The method for determining the feed allowance comprises the steps of firstly calculating the machining allowance H-D/2 at each discrete point on a rim line, and respectively and sequentially marking indexes of A (1), A (2), A (3), A (4), … … A (i) … … (i is a natural number); the machining allowance with the maximum value being the maximum value is taken from the calculated values, and is also set as A0; when H-D/2 is 0, which represents that the rim line and the lid panel line coincide at the discrete point, the machining allowance is set to 0. And setting the cutting depth value B of each feed of the selected rotary file, wherein the feed times of one side of the blade is A0/B, and the machining allowance of each feed at each discrete point is A (i) B/A0. When the machine tool is fed for the first time, the Z-direction path position points at the discrete points are W (i) -A (i) B/A0; during the second feed, the path position points in the Z direction at each discrete point are w (i) -2a (i) B/a0, and so on until the feed times a0/B are completed, the machining of all welding grooves on the pressure surface or the suction surface side is completed, and the method for determining the feed cutting allowance is shown in fig. 9.
Claims (5)
1. The utility model provides an equipment of three way impeller blade welding grooves of robot processing which characterized in that: the equipment comprises an industrial robot, a force control measuring module, a machining tool quick-changing module, a machining tool and a workbench; wherein:
industrial robot: inputting a machining track produced according to the impeller model into a robot controller, controlling the motion track of the robot, driving a machining tool arranged at the tail end of the robot, and machining and removing the blade welding groove;
the force control measurement module: the robot comprises a six-dimensional force/torque sensor, wherein a force control measurement module is arranged on a flange at the tail end of a robot and is used for measuring the magnitude of a machining contact force in real time on line in the machining process and providing measurement data for a force-position control mode;
processing tool quick change module: the device comprises a quick-change head, wherein the quick-change head is arranged on a connecting flange of a six-dimensional force/torque sensor;
processing a tool: the device comprises a straight grinding machine and a cylindrical rotary file which are connected, wherein the straight grinding machine is connected and installed with a processing tool quick-change module through a clamp, and the straight grinding machine drives the rotary file to rotate during processing;
a workbench: the device is used for installing the impeller workpiece and has the function of realizing the rotation of the impeller workpiece along the Z axis and the X axis during machining.
2. The equipment for machining the ternary impeller blade welding groove by the robot according to claim 1, characterized in that: the equipment further comprises an upper computer, wherein the upper computer is used for finishing the processing of the impeller model, and the processing comprises the extraction and discretization of a rim line, a central axis and a cover plate line, the generation of a processing track, the extraction processing of a processing contact force, the compensation correction control of the processing track and the like.
3. The equipment for machining the ternary impeller blade welding groove by the robot according to claim 1, characterized in that: the equipment further comprises a machining tool library, wherein the machining tool library is used for storing machining tools, the quantity of the machining tools can be set according to the types and the like of the tools required by machining, and the machining tool library is placed at a fixed position and provides different machining tools for machining of the robot.
4. A method for machining a three-dimensional impeller blade welding groove by using the robot of the device in claim 1, which is characterized by comprising the following steps: the method comprises the steps of extracting, sequencing and discretizing the characteristic curve of the impeller blade, generating and extracting a central axis, generating and discretizing a cover plate line and calculating machining allowance, setting and adjusting a standard frame of a welding groove of the impeller blade, balancing the gravity of a cutting tool, calibrating a coordinate system of the cutting tool, calibrating a coordinate system of a workpiece, automatically producing a machining track, controlling a close fit feed of a rotary file and a machining point, adopting a machining track error compensation method based on an in-situ measurement process of a force control mode, and determining the machining allowance based on the online control of machining removal, and specifically comprises the following steps:
(1) the extraction, sequencing and discretization process of the characteristic curve of the impeller blade comprises the following steps:
extracting a blade rim surface, a pressure surface rim line and a suction surface rim line according to the three-dimensional model of the impeller, if more than one rim curve is available, sequencing all processing curves according to the sequence of end-to-end connection, and discretizing the selected curve according to the processing distance and the precision requirement;
(2) the generation and extraction process of the central axis comprises the following steps:
extracting the central axis of the rim surface: firstly, discretizing a rim surface by a method of discretizing the rim surface of a blade into a triangular mesh curved surface, sequentially taking a rim line discrete point of a pressure surface and a rim line discrete point of a suction surface corresponding to the rim line discrete point, and respectively solving a triangular mesh triangle index where the two points are located and a barycentric coordinate system value in the triangle for the two corresponding discrete point pairs; taking the obtained triangle index and the barycentric coordinate system value as input, and applying a triangular mesh discrete geodesic solving algorithm to solve the triangular mesh discrete geodesic between the two points; for all discrete pairs of point pairs of pressure and suction side rim lines, the following is performed: solving the position of a center point of the discrete geodesic line obtained by each discrete point pair, wherein the coordinate of the center point is the center axis point of the rim line pair on the rim surface; carrying out curve fitting on the midpoints of the discrete geodesic lines of all the point pairs to obtain the central axis of the edge surface of the blade wheel;
(3) the generation and discretization process of the cover plate line and the calculation of the machining allowance are as follows:
obtaining a center axis point of a corresponding point according to a relative discrete point pair of a pressure surface rim line and a suction surface rim line, calculating the distance between the discrete point and the center axis in the rim surface as H, setting the residual width of the rim surface after the welding groove is removed in the machining process as D, taking the center axis discrete point as the center, and setting the offset distance of each discrete point along the corresponding rim line in the rim surface as D/2, wherein the two corresponding points are points on the cover disc line of the pressure surface and the suction surface, and the distance from the point to the corresponding point on the corresponding rim line is the machining allowance which is H-D/2; sequentially taking each point on the central axis as a center by adopting the same method to form corresponding points of two cover plate lines on the rim surface; connecting the points to form a cover plate line, wherein the distance between the cover plate line and the rim line is the size of the total machining allowance, the machining allowances between the cover plate line and the rim line are not the same and change along with the change of machining position points, namely H-D/2 is a variable value;
(4) setting and adjusting a standard frame of the impeller blade welding groove:
calculating the local frame of each discrete point in the normal evaluation direction of the rim surface according to the discrete points: the discrete point normal vector is used as the Z-axis direction of the discrete point local frame; calculating the tangential vector of each discrete point according to the tangential evaluation method of the discrete point on the rim line, wherein the tangential vector direction is used as the X-axis direction of the local frame of the discrete point; and determining the Y-axis direction of each discrete point local frame according to the right-hand rule: rotating for 45 degrees along the X axis of the local frame to enable the Z axis to be vertical to the welded bevel face after machining;
(5) gravity balancing of the cutting tool:
compensating the part of the gravity of the cutting tool included in the measurement value of the sensor under the sensor coordinate, so that the measurement value only comprises the cutting force during the cutting process;
(6) cutting tool coordinate system (coordinate system T) calibration:
the tool coordinate system of the machining tool is calibrated by adopting the self function of the robot, and the directions of all axes of the established tool coordinate system are defined as follows: the origin of the tool coordinate system is a proper point on the excircle cutting edge of the cylindrical rotary file, the X-axis direction is the tangential direction of a connecting line of the origin and the axis of the rotary file, and the axial direction points to the rotating direction of the origin during processing; the Y axis is parallel to the axis of the rotary file and points to the direction of the robot flange; the Z axis is determined according to the right-hand rule;
(7) calibration process of the workpiece coordinate system (coordinate system B):
establishing a workpiece coordinate system on the workpiece impeller by adopting an indirect method: firstly, selecting four characteristic points in three-dimensional modeling software, and recording coordinate values of the four characteristic points in a workpiece coordinate system; then tool sharp points of a measured tool coordinate system are sequentially close to corresponding feature points on the workpiece, and coordinate values in the corresponding three-dimensional model are output in the robot demonstrator; after the operation is finished, the robot calculates the transformation relation of the established workpiece coordinate system relative to the robot base coordinate system, so as to finish the calibration of the workpiece coordinate system;
(8) automatic production process of machining tracks:
calculating the poses (including positions and postures) of all discrete points on the rim line of the blade by taking an impeller workpiece coordinate system B as a reference system, automatically generating track points processed and removed on the rim line of the processed blade, and then sequentially connecting all the track points to form a processing track;
(9) controlling the close fitting feed of the rotary file and the processing point:
guiding the calculated machining track of the blade wheel rim line into a robot controller, and controlling a robot to drive a rotary file to move according to the track; adopting a force control method in the Z direction of the machining track along a tool coordinate system, setting the target force in the contact force Z direction to be 3N, and when the measured contact force is smaller than the target force, performing small compensation motion in the reverse direction of the robot to the Z axis of the machining track; when the contact force is larger than the target force, the robot performs micro compensation motion to the Z axis of the processing track in the positive direction, so that the rotary file is tightly attached to the edge line of the blade wheel;
(10) in-situ measurement process based on force control mode:
an in-situ measurement method based on a force control mode is adopted and used for measuring the difference value between a programming track and an actual track of each discrete position point index in the Z-axis direction of a tool coordinate system when a rotary file is in close contact with a rim line, a robot reads the difference value of each discrete position point index in the Z-axis direction of the tool and compares the difference value with the position value in the Z-axis direction of a corresponding discrete point on a track generated by an impeller model, the deviation (namely correction K) of the actual processing position and the theoretical track position in the Z-axis direction is calculated, and the theoretical position point Z-axis numerical value compensation deviation value is the actual value in the Z-axis direction of the discrete point of the blade profile line, so that the influence of error factors such as the tool coordinate system of the robot, a workpiece coordinate system, the absolute positioning error of the robot and the workpiece manufacturing error of;
(11) adopting a processing track error compensation method:
performing compensation correction on a theoretical discrete point Z-axis direction position point Z (i) on a machining track generated by an impeller model to correct Z-direction deviation K (i) of a position index point during in-place measurement, namely Z (i) -K (i), performing secondary curve fitting on each robot theoretical discrete point track point and each corresponding point after correction compensation of the index point, removing the influence of miscellaneous points in the measurement process, and obtaining a smooth removal amount control curve, wherein the curve is a machining path after compensation correction is performed on a workpiece theoretical model track path, namely an actual track point during robot machining, namely W (i), so that the correct relative position relation between a rotary file and a blade welding groove during machining is realized;
(12) a process of determining a feed margin based on-line control of a machining removal amount:
firstly, calculating the machining allowance H-D/2 of each discrete point on a rim line, and respectively and sequentially marking index names A (1), A (2), A (3), A (4), … … A (i), wherein i is a natural number; the machining allowance with the maximum value being the maximum value is taken from the calculated values, and is also set as A0; when H-D/2 is equal to 0, the edge line and the cover coil line are superposed at the discrete point, and the machining allowance is set to be 0; setting a cutting depth value B of each feed of the selected rotary file, wherein the feed times of one side of the blade is A0/B, and the machining allowance of each feed at each discrete point is A (i) B/A0; when the machine tool is fed for the first time, the Z-direction path position points at the discrete points are W (i) -A (i) B/A0; and during the second feed, the Z-direction path position points at the discrete points are W (i) -2A (i) B/A0, and the rest is repeated until the feed times A0/B are completed, so that the machining of all welding grooves on the pressure surface or the suction surface side is completed.
5. The method for machining the three-element impeller blade welding groove by the robot according to claim 4, wherein the method comprises the following steps: in the step (1), when the curve discretization is carried out, the number of discrete points of the pressure surface rim line and the suction surface rim line is required to be equal.
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