A robot grinding and polishing trajectory correction method and system based on coordinate system integration

Abstract

The present invention relates to a robot grinding and polishing trajectory correction method and system based on coordinate system integration, which is applied to the adaptive grinding and polishing process of the inner and outer boundaries of characteristic surfaces with variable processing directions such as circles and broken lines, such as aircraft thin-walled plates. The method adopts an offline trajectory planning method to calculate the processing path, and can generate a robot-executable processing program after post-processing. During the processing, in order to adapt to the deformation of the thin-walled parts, the planned trajectory is corrected in real time according to the contact force value between the tool and the workpiece. During the correction, the correction coordinate system of the current processing point is set according to the movement direction of the processing point, and the robot posture is adjusted on the basis of the correction coordinate system. Reasonable setting of the correction coordinate system direction can ensure that the robot grinding tool moves away from or close to the grinding position along a fixed direction of the correction coordinate system, and realizes the parallel movement of the grinding tool center and the grinding feature boundary, while avoiding the problems of large-scale changes in the robot posture and uneven processing line speed, so as to achieve the purpose of continuous and uniform adaptive processing of variable boundary paths.

Description

Technical Field

[0001] The invention relates to a robot grinding and polishing trajectory correction method and system based on coordinate system integration, belonging to the technical field of intelligent processing and grinding and polishing. Background Art

[0002] At present, the boundary polishing of complex thin-walled structural parts such as aircraft wall panels is mainly carried out by traditional manual polishing. The polishing process is labor-intensive and inefficient. Since the polishing quality is determined by the operator's proficiency and operating skills, it leads to human errors in key indicators such as component surface accuracy and surface quality, affecting the performance of the component. Manual polishing also generates a large amount of dust, which seriously affects the health of the operator.

[0003] At present, the use of robot compliant control for grinding and polishing is a common polishing method and effective way. The patent named "Automatic grinding and polishing system and processing method of complex curved surfaces based on compliant control" (CN105643399A) plans the processing trajectory before grinding and polishing of complex curved surface workpieces. The robot drives the robot movement according to the processing trajectory planning program file, driving the grinding and polishing tool installed on the robot end effector to contact the processing surface for processing. The patent named "Robot grinding method with constant removal rate of complex surfaces based on real-time force control" (CN110524371B) uses a host computer to calculate the tool path trajectory, based on the gravity compensation method of the standard position, and adjusts the position of the tool in real time through an adaptive impedance control algorithm to achieve a constant removal rate of the workpiece grinding pressure.

[0004] The above methods are mainly targeted at machining surfaces with relatively slow curvature changes, such as curved surfaces, and all use a fixed coordinate system for machining trajectory planning and adaptive adjustment. They are not suitable for situations where large curvature changes, such as broken lines and circles, can cause robot limitations or forced segmented machining. Furthermore, large changes in the robot's curvature can easily lead to abnormal machining conditions such as local tool interference. Therefore, a more effective robot grinding and polishing trajectory correction method is urgently needed to effectively address the above issues. Summary of the Invention

[0005] In order to realize the grinding and polishing system for the boundaries of the above-mentioned complex structural parts, the present invention proposes a robot grinding and polishing trajectory correction method and system based on coordinate system integration, which achieves the purpose of automatic grinding and polishing of workpieces by combining theoretical calculation analysis with automatic control.

[0006] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0007] A robot grinding and polishing trajectory correction method based on coordinate system integration is proposed. In the process of robot machining the inner and outer boundaries of the feature surface with variable direction, a time-varying robot integrated coordinate system T is defined.Adjust The system calculates and updates in real time, and corrects the machining posture based on force feedback to achieve adaptive grinding and polishing. The system includes the following steps:

[0008] Offline path generation: load the workpiece 3D model, select the boundary curve feature to be processed, set the processing parameters, and generate the workpiece base coordinate system T of the current curve feature to be processed Base The processing path below;

[0009] Post-processing: Process the machining path into a machining program, which is then called during machining.

[0010] Coordinate system calculation: Define the robot integrated coordinate system T that varies with time Adjust , used to characterize the characteristics of the current curve to be processed; control the robot to execute the processing program, and during the processing, according to the trajectory processing direction and tool coordinate system T Tool Direction calculation updates the time-varying coordinate system T of the current processing position Adjust ;

[0011] Trajectory correction: Based on force sensor feedback, in the time-varying coordinate system T Adjust The robot posture is corrected and the industrial robot processing posture is adjusted to adapt to the deformation of thin-walled parts, thereby continuously processing the boundary path.

[0012] The processing boundary curve feature is to select a preset basic processing trajectory for the current boundary curve to be processed: a graphic, a straight line segment, a plane or a space curve.

[0013] The processing parameters are set according to the processing tools and processing requirements; the processing parameters include line spacing, processing step length, processing speed, tool feed direction, and tool normal direction.

[0014] The T Adjust The coordinate axes are defined as follows:

[0015] X Adjust : Workpiece base coordinate system T Base The tangent direction of the lower machining path curve at the current machining point;

[0016] Y Adjust :From the workpiece base coordinate system T Base Trajectory tangent and tool coordinate system T Tool The plane normal vector formed by the X+ direction;

[0017] Z Adjust :By X Adjust and Y Adjust The vectors that form the rectangular coordinate system.

[0018] The robot integrated coordinate system T AdjustIt is updated during the movement and is calculated when performing linear or circular motion;

[0019] The tangent direction of the trajectory is not parallel to the X+ direction of the tool coordinate system, otherwise T cannot be calculated. Adjust ;

[0020] Adjust the coordinate system T during processing Adjust The origin is always located on the TCP of the workpiece to be processed. Adjust The posture makes the robot position parallel to the trajectory, and T Adjust The Y-axis or Z-axis direction is always consistent with the vertical direction of the trajectory;

[0021] When the trajectory is corrected, T Adjust Correction is performed based on the Y-axis or Z-axis.

[0022] The robot posture correction is to adjust the posture of the robot offline path according to the force of the tool after gravity compensation, thereby controlling the contact between the grinding tool and the workpiece to achieve adaptive processing.

[0023] The robot posture is corrected as follows: the adjustment direction is from the vertical direction of the processing point to the integrated coordinate system T Adjust The contact force is calculated by the tool coordinate system T Tool The direction of the resultant force is at T Adjust For absolute correction, the sensor correction is calculated using the current nominal position of the robot or each axis in the form of an absolute value, and the new position is the sum of the distance between the current nominal position and the correction value.

[0024] The post-processing processes the trajectory into a control node signal for starting and stopping the integrated grinding tool and starting and ending the trajectory correction.

[0025] A robot adaptive grinding and polishing control system based on coordinate system correction includes: a host computer, a robot controller, and an end force sensor; the host computer stores a program, and when the program is loaded, the method steps described above are executed to achieve adaptive grinding and polishing; the robot controller is used to execute the execution program sent by the host computer and feedback execution data; the end force sensor is used to detect and feedback contact force values in real time.

[0026] The host computer transmits data to the robot controller and the end force sensor respectively via Ethernet UDP / IP protocol.

[0027] The present invention has the following advantages:

[0028] 1. The present invention is mainly used in the adaptive grinding and polishing process of the inner and outer boundaries of characteristic surfaces with variable processing directions such as circles and broken lines, such as aircraft thin-walled plates.

[0029] 2. During the processing of the present invention, in order to adapt to the deformation of thin-walled parts, the planned trajectory is corrected in real time according to the contact force value between the tool and the workpiece. During the correction, the corrected coordinate system of the current processing point is set according to the movement direction of the processing point, and the robot posture is adjusted on the basis of the corrected coordinate system.

[0030] 3. During the processing of the present invention, the direction of the corrected coordinate system is reasonably set to ensure that the robot grinding tool moves away from or close to the grinding position along a fixed direction of the corrected coordinate system, thereby achieving parallel movement between the center of the grinding tool and the grinding feature boundary. At the same time, it avoids the problems of large-scale changes in the robot posture and uneven processing line speed, and achieves the purpose of continuous and uniform adaptive processing of the boundary path with changing directions.

[0031] 4. The present invention realizes the boundary trajectory planning and the adaptive grinding and polishing adjustment process.

[0032] 5. The present invention realizes the automated process of adaptive grinding and polishing of polygonal boundaries of complex structural parts, greatly improving processing efficiency and workpiece processing quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Flow chart of the method of the present invention;

[0034] FIG2( a ) is an illustration of the position 0° of the tool coordinate circle of the system of the present invention;

[0035] FIG2( b ) is an illustration of the 90° position of the tool coordinate circle of the system of the present invention;

[0036] FIG2( c ) is an illustration of the position of the tool coordinate circle 180° of the system of the present invention;

[0037] FIG2( d ) is an illustration of the position of the tool coordinate circle 270° of the system of the present invention;

[0038] Figure 3 This is an illustration of the corresponding definitions of the system integration coordinate system of the present invention at 0°, 90°, 180°, and 270°;

[0039] FIG4( a ) is a feature diagram of a processing object model according to the present invention;

[0040] FIG4( b ) is a diagram showing the offline trajectory generation of a circular feature of a processing object according to the present invention;

[0041] FIG4( c ) is a diagram showing offline trajectory generation of the broken line features of the processing object according to the present invention;

[0042] Figure 5 Generate a processing trajectory program diagram for the post-processing of the present invention;

[0043] Figure 6This is the trajectory correction control logic diagram of the present invention; DETAILED DESCRIPTION

[0044] To make the above-mentioned objects, features, and advantages of the present invention more readily apparent, the specific implementation methods of the present invention are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art may make similar modifications without departing from the scope of the invention. Therefore, the present invention is not limited to the specific implementation methods disclosed below.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art of the art to which the present invention pertains. The terms used in the specification of the invention herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention.

[0046] like Figure 1 As shown, a robot grinding and polishing trajectory correction method based on coordinate system integration includes offline path generation, post-processing, follow-up time-varying coordinate system calculation and robot grinding and polishing trajectory correction steps.

[0047] Specifically:

[0048] As shown in Figure 2, in actual processing we are accustomed to the tool coordinate system T Tool With force sensor T Force The coordinate system direction is consistent. Taking the circular trajectory as an example, the traditional trajectory correction method is to use the normal direction of the trajectory and T Tool The Z axis coincides with the Z axis. During the entire circular trajectory processing, the tool is required to rotate 360 degrees while keeping the contact point position consistent. For example, in the robot processing states of 90° and 270°, if T Tool The Z positive vertical trajectory is inward, and the robot needs to go around T Tool When the X-axis rotates 180°, the robot often encounters singular points or axis limits during the process, affecting the continuity of processing.

[0049] and Figure 3 T Adjust As the reference coordinate system, the center point of the grinding tool is set as the center of the tool coordinate system T Tool , the trajectory is offset by the tool radius value, and the machining direction is along T Adjust For X-direction machining, the machining tool moves along T Adjust The Y-axis adjustment is sufficient, and the robot can process the entire circumferential trajectory with a slight attitude fluctuation. Adjust The basis for Y-axis adjustment is the force value after tool gravity compensation at T Adjust The Y vector of .

[0050] T Adjust The calculation of is as follows:

[0051] The position of the robot in the base coordinate system at the last moment during the processing is P last =(x0, y0, z0), the current position of the robot in the base coordinate system is P now =(x1, y1, z1), then the tangent vector is

[0052] (D x , D y , D z )=((x1-x0), (y1-y0), (z1-z0))

[0053] The posture of the tool coordinate system in the base coordinate system can be expressed as (0, 0, 0, a, b, c), which is converted into the posture matrix:

[0054] Then the X-axis direction of the tool coordinate system can be expressed as: (n x , n y , n z )

[0055] T Adjust The X-axis direction is: (D x , D y , D z )

[0056] T Adjust The Y-axis direction is: (D x , D y , D z ) and (n x , n y , n z ) to perform cross product:

[0057]

[0058] Among them, i, j, k are T Adjust Three axes;

[0059] T Adjust The Y-axis can be expressed as:

[0060] T Adjust_y =((D y n z -n y D z ), -(D x n z -n x D z ), (D x ny -n x D y ))

[0061] Z Adjust Because of T Adjust X-axis and T Adjust The Y axis of the rectangular coordinate system forms a vector. So far, T Adjust It can be confirmed.

[0062] Robot integrated coordinate system T Adjust It is a coordinate system synchronized with the trajectory, and it is calculated when performing linear or circular motion. Adjust From the definition, it can be seen that the trajectory tangent direction is not allowed to be parallel to the X+ direction of the tool coordinate system, otherwise T cannot be calculated. Adjust . Adjust the coordinate system T Adjust The origin of the tool is always located on the TCP of the activated tool. For circular or other broken line trajectories, the robot processing posture can be determined by T Adjust Take over, change T Adjust The posture ensures that the robot position is parallel to the trajectory, and T Adjust The Y-axis or Z-axis direction of the track is always consistent with the vertical direction of the track. When the track is corrected, directly use T Adjust The Y-axis or Z-axis can be used as the reference for correction.

[0063] As shown in Figure 4, we selected a thin-walled workpiece containing multiple boundary features, such as circles, ellipses, and polylines, and performed path planning for the typical features that needed to be machined. First, the 3D workpiece model was input into the host computer's offline programming software. After loading, the boundary curve feature to be machined was selected. Based on the machining tool and process requirements, machining parameters such as line spacing, machining step length, machining speed, tool feed direction, and tool normal direction were set to generate a machining path for the current feature in the base coordinate system.

[0064] like Figure 5 As shown in the figure, after post-processing, a robot-executable machining program is generated. Using a KUKA robot system as an example, we generate a machining program recognizable by the robot. Post-processing integrates control node signals such as the start and stop of the grinding tool and the start and end of trajectory correction. The control system communicates with the robot via Ethernet UDP / IP protocol, and with the force sensor via Ethernet TCP / IP protocol. During motion, force sensor corrections directly affect the robot's movement. The industrial robot's motion, based on the normal trajectory, will be altered based on the force sensor measurements.

[0065] The host computer control system controls the robot to execute the processing program. During the processing, the robot integrated coordinate system T of the current processing position is calculated according to the trajectory processing direction and the tool coordinate system direction. Adjust, the path correction is based on force sensing feedback, according to the contact force value between the tool and the workpiece, in the integrated coordinate system T Adjust The robot posture is corrected on the basis to achieve the effect of adjusting the processing posture of the industrial robot and achieve the purpose of continuous processing boundary path.

[0066] The robot grinding and polishing trajectory correction method adjusts the robot's offline path posture according to the tool force after gravity compensation, and then controls the contact between the grinding tool and the workpiece to achieve the effect of adaptive processing. Among them, the adjustment direction of the robot posture is from the vertical direction of the processing point in the integrated coordinate system T Adjust The contact force is calculated by the tool coordinate system T Tool The direction of the resultant force is at T Adjust For absolute correction, the sensor correction is calculated using the current setpoint position of the robot or each axis in the form of an absolute value. The new position is obtained by shifting the programmed setpoint position by the current correction value.

[0067] like Figure 6 As shown in the figure, the trajectory correction process is performed. The host computer control system controls the robot to execute the processing program. During the processing, the robot integrated coordinate system T of the current processing position is calculated according to the trajectory processing direction and the tool coordinate system direction. Adjust , the path correction is based on force sensing feedback, according to the contact force value between the tool and the workpiece, in the integrated coordinate system T Adjust The robot posture is corrected on the basis to achieve the effect of adjusting the processing posture of the industrial robot. Among them, the adjustment direction of the robot posture is from the vertical direction of the processing point in the integrated coordinate system T Adjust The calculation is done by expressing T, while the calculation of contact force is done by first finding T Tool To T Adjust The transformation matrix of F is calculated according to the transformation relationship. y .

[0068] The specific calculation process is:

[0069] The contact force after gravity compensation is expressed in the base coordinates as:

[0070] B_Force=(B_Force x , B_Force y , B_Force z )

[0071] Then the contact force under the y-axis of the integrated coordinate system is expressed as:

[0072] B_Force to T Adjust_y Projection calculation:

[0073]

[0074] but

[0075] If T Adjust_y If the angle between the direction and the B_Force direction is greater than 90°, then F y Take the negative.

[0076] From the example, we can calculate F y The size and direction of the Adjust By adjusting the position in the y direction, the motion process of the trajectory can be corrected, and the effect of continuously adjusting the processing posture of the industrial robot can be achieved, so as to achieve the purpose of continuously processing the boundary path with changing directions.

Claims

1. A robot grinding and polishing trajectory correction method based on coordinate system integration, characterized in that: In the process of robot machining the inner and outer boundaries of the characteristic surface with changing directions, a time-varying robot integrated coordinate system T is defined. Adjust The system calculates and updates in real time, and corrects the machining posture based on force feedback to achieve adaptive grinding and polishing. The system includes the following steps: Offline path generation: load the workpiece 3D model, select the boundary curve feature to be processed, set the processing parameters, and generate the workpiece base coordinate system T of the current curve feature to be processed Base The processing path below; Post-processing: Process the machining path into a machining program, which is then called during machining. Coordinate system calculation: Define the robot integrated coordinate system T that varies with time Adjust , used to characterize the characteristics of the current curve to be processed; control the robot to execute the processing program, and during the processing, according to the trajectory processing direction and tool coordinate system T Tool Direction calculation updates the time-varying coordinate system T of the current processing position Adjust ; Trajectory correction: Based on force sensor feedback, in the time-varying coordinate system T Adjust The robot posture is corrected to adjust the processing posture of the industrial robot to adapt to the deformation of thin-walled parts, thereby continuously processing the boundary path.

2. The robot grinding and polishing trajectory correction method based on coordinate system integration according to claim 1 is characterized in that ,The processing boundary curve feature is to select a preset basic processing trajectory for the ,currently processed boundary curve: a graphic, a straight line segment, a plane or a ,space curve.

3. The robot grinding and polishing trajectory correction method based on coordinate system integration according to claim 1 is characterized in that , is to set the processing parameters according to the processing tools and processing technology requirements; the processing parameters include line spacing, processing step length, processing speed, tool feed direction, and tool normal direction.

4. The robot grinding and polishing trajectory correction method based on coordinate system integration according to claim 1 is characterized in that , the T Adjust The coordinate axes are defined as follows: X Adjust : Workpiece base coordinate system T Base The tangent direction of the lower machining path curve at the current machining point; Y Adjust :From the workpiece base coordinate system T Base Trajectory tangent and tool coordinate system T Tool The plane normal vector formed by the X+ direction; Z Adjust :By X Adjust and Y Adjust The vectors that form the rectangular coordinate system.

5. The robot grinding and polishing trajectory correction method based on coordinate system integration according to claim 4 is characterized in that: The robot integrated coordinate system T Adjust It is updated during the movement and is calculated when performing linear or circular motion; The tangent direction of the trajectory is not parallel to the X+ direction of the tool coordinate system, otherwise T cannot be calculated. Adjust ; Adjust the coordinate system T during processing Adjust The origin is always located on the TCP of the workpiece to be processed. Adjust The posture makes the robot position parallel to the trajectory, and T Adjust The Y-axis or Z-axis direction is always consistent with the vertical direction of the trajectory; When the trajectory is corrected, T Adjust Correction is performed based on the Y-axis or Z-axis.

6. The robot grinding and polishing trajectory correction method based on coordinate system integration according to claim 1 is characterized in that: The robot posture correction is to adjust the posture of the robot offline path according to the force of the tool after gravity compensation, thereby controlling the contact between the grinding tool and the workpiece to achieve adaptive processing.

7. The robot grinding and polishing trajectory correction method based on coordinate system integration according to claim 1 is characterized in that: The robot posture is corrected as follows: the adjustment direction is from the vertical direction of the processing point to the integrated coordinate system T Adjust The contact force is calculated by the tool coordinate system T Tool The direction of the resultant force is at T Adjust For absolute correction, the sensor correction is calculated using the current nominal position of the robot or each axis in the form of an absolute value, and the new position is the sum of the distance between the current nominal position and the correction value.

8. The robot grinding and polishing trajectory correction method based on coordinate system integration according to claim 1 is characterized in that: The post-processing processes the trajectory into a control node signal for starting and stopping the integrated grinding tool and starting and ending the trajectory correction.

9. A robot adaptive grinding and polishing control system based on coordinate system correction, characterized in that: include: A host computer, a robot controller and an end force sensor; the host computer stores a program, and when the program is loaded, the method steps described in any one of claims 1 to 8 are executed to achieve adaptive grinding and polishing; the robot controller is used to execute the execution program sent by the host computer and feedback the execution data; the end force sensor is used to detect and feedback the contact force value in real time.

10. The robot grinding and polishing trajectory correction system based on coordinate system integration according to claim 9, characterized in that: The host computer transmits data to the robot controller and the end force sensor respectively via Ethernet UDP / IP protocol.

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