An Adaptive Method for the Tool Tip Trajectory of a Robot for Grinding Castings

Abstract

The present invention relates to the field of machining technology, and particularly to a method for adaptively adjusting the tool tip trajectory for a robot to grind castings, which includes: scanning the casting using a 3D sensor, calculating the workpiece coordinate system of the casting in the base coordinate system of the robot, and compensating for the casting error; selecting the working mode of a pressure-type flexible compliant grinding tool assembly, where the working mode includes a rigid mode and a flexible mode; based on the selected working mode, driving the tool mounted on the spindle to rotate and move along the grinding trajectory to perform rigid cutting or flexible grinding on the casting; switching the working mode of the pressure-type flexible compliant grinding tool assembly to complete the grinding of the casting. Adopting the above technical solution can meet the need for adaptive adjustment of the tool tip trajectory of cutting and grinding tools, simplify the requirements for robot teaching programming, reduce the requirements for tooling and fixtures, ensure the grinding effect and the safety of the robot grinding equipment, and improve the mixed-line compatibility of the robot grinding equipment.

Description

Technical Field

[0001] The present invention relates to the field of machining technology, and particularly to a method for adaptively adjusting the trajectory of the tool tip for a robot to grind castings. Background Art

[0002] The process of a robot grinding castings includes cutting and grinding. A disc-shaped grinding wheel is used to cut the riser residue, vent pins, exhaust fins, and excess metal; a cylindrical grinding wheel is used to grind the parting surface flash, burrs, and orifice skins. Among them, the grinding trajectory (cutting) of the disc-shaped grinding wheel is mostly several discrete straight lines; the grinding trajectory (grinding) of the cylindrical grinding wheel is mostly a curve, and profiling machining needs to be realized according to the specific shape of the parting surface. However, the clamping error of the casting, dimensional deformation, and the profiling accuracy of the tool tip trajectory will affect the quality of robot grinding. At the same time, these factors also seriously affect many aspects such as the reliability of the robot grinding equipment, the safety of the grinding process, the tool life, and the mixed-line compatibility ability of the robot grinding equipment.

[0003] Currently, there are corresponding flexible mechanisms on the market to improve the profiling accuracy of the tool tip trajectory of a robot for grinding and achieve a follow-up grinding effect. This type of technology uses compressed air as a power source to provide adjustable radial pressure to the spindle, so that the tool can generate radial floating, and solves the problem of insufficient profiling accuracy of the tool tip trajectory during the process of a robot processing complex curved surfaces. However, it cannot adapt to the cutting requirements of the riser residue, vent pins, exhaust fins, and excess metal of the casting. Moreover, usually, the same spindle is used for both grinding and cutting of the casting, and the corresponding tool is replaced to complete the process, in order to improve the production efficiency of the equipment and reduce the equipment cost. However, there are many problems when using a spindle equipped with a flexible mechanism for cutting, such as unstable grinding quality, low grinding efficiency, tool jamming, tool collision, and low tool life. On the other hand, through the flexible mechanism technology, it is still necessary to design high-precision tooling and fixtures to ensure the safety of the grinding process and the grinding effect, and the problem of robot mixed-line compatibility cannot be fundamentally solved. Summary of the Invention

[0004] (I) Technical Problems to be Solved

[0005] The main purpose of the present invention is to provide a method for adaptively adjusting the trajectory of the tool tip for a robot to grind castings, aiming to solve the problems of insufficient profiling accuracy of the existing tool tip and inability to adapt to the mixed-line compatibility of the robot grinding equipment.

[0006] (II) Technical Solutions

[0007] To achieve the above object, the method for adaptively adjusting the trajectory of the tool tip for a robot to grind castings according to the present invention includes:

[0008] Scan the reference casting to generate a first workpiece coordinate system for the reference casting and save the spatial position of the reference casting within the first workpiece coordinate system;

[0009] Generate a grinding trajectory for the reference casting based on the first workpiece coordinate system;

[0010] Replace the reference casting with the casting to be ground, scan the casting to be ground, and generate a second workpiece coordinate system for the casting to be ground;

[0011] Update the spatial position of the reference casting according to the first workpiece coordinate system and the second workpiece coordinate system, and use the updated spatial position as the spatial position of the casting to be ground to obtain a grinding trajectory with updated coordinates;

[0012] Select the working mode of the pressure - type flexible compliance grinding tool assembly of the robot. The working modes include a rigid mode and a flexible mode;

[0013] Based on the selected working mode, drive the tool installed on the spindle to rotate and move along the grinding trajectory of the casting to be ground, so as to perform rigid cutting or flexible grinding on the casting to be ground and complete the grinding of the casting to be ground.

[0014] (III) Beneficial Effects

[0015] The beneficial effects of the present invention are as follows: First, based on the comparison between the standard casting and the casting to be ground, a workpiece coordinate system and a grinding trajectory that match the positional relationship and dimensional relationship of the casting to be ground are established. In the rigid mode, the spindle and the floating seat are relatively locked; in the flexible mode, the spindle can deflect relative to the floating seat. The working mode is flexibly switched according to the actual situation, and the tool installed on the spindle is driven to rotate and move along the grinding trajectory of the casting to be ground, so as to perform rigid cutting or flexible grinding on the casting, which can meet the need for the adaptive trajectory of the cutting and grinding tool end, simplify the robot teaching programming requirements, reduce the requirements for tooling and fixtures, ensure the grinding effect and the safety of the robot grinding equipment, and improve the mixed - line compatibility of the robot grinding equipment. Description of the Drawings

[0016] Figure 1 It is an application schematic diagram of the pressure - type flexible compliance grinding tool assembly of the present invention;

[0017] Figure 2 It is a semi - sectional structural schematic diagram of the pressure - type flexible compliance grinding tool assembly of the present invention;

[0018] Figure 3 It is a semi - sectional structural schematic diagram of the flexible mode of the pressure - type flexible compliance grinding tool assembly of the present invention;

[0019] Figure 4Schematic diagram of the half-section structure of the rigid mode of the pressure-type flexible compliant grinding tool assembly of the present invention;

[0020] Figure 5 Schematic diagram of the principle of the pneumatic control unit of the pressure-type flexible compliant grinding tool assembly of the present invention;

[0021] Figure 6 Flowchart of the tool end trajectory adaptive method for a robot to grind castings according to the present invention;

[0022] Figure 7 Flowchart of a robot obtaining various parameters of a reference casting according to an embodiment of the present invention;

[0023] Figure 8 Flowchart of a robot obtaining various parameters of a casting to be ground according to an embodiment of the present invention;

[0024] Figure 9 Schematic diagram of a robot processing system according to an embodiment of the present invention;

[0025] Figure 10 Schematic diagram of establishing a workpiece coordinate system according to an embodiment of the present invention;

[0026] Figure 11 Flowchart of the pose correction method when a robot processes a casting according to an embodiment of the present invention;

[0027]

Explanation of reference numerals

[0028] 100: Pressure-type flexible compliant grinding tool assembly;

[0029] 1: Spindle; 11: Sliding sleeve; 111: Sliding ring;

[0030] 2: Floating mechanism; 21: Floating seat; 22: Piston cylinder; 23: Fixed ring; 231: Sliding groove; 24: Gas interface; 25: Dynamic sealing ring; 26: Dust cover;

[0031] 3: Locking mechanism; 31: Locking sleeve; 32: Second cylinder; 33: Mounting plate;

[0032] 4: Pneumatic control unit; 41: Air source; 42: Filter pressure reducing valve; 43: Solenoid valve; 44: Electro-hydraulic proportional valve;

[0033] 101: Cylindrical grinding wheel; 102: Disc grinding wheel; 103: Robot;

[0034] 200: Casting; 201: Flash on the parting surface; 202: Gate residue block;

[0035] 300: Tooling fixture; 400: 3D sensor. Detailed Embodiments

[0036] To better explain the present invention for easier understanding, the present invention will be described in detail below in conjunction with the accompanying drawings through specific embodiments.

[0037] As Figures 1 to 4 shown, a pressure - type flexible compliant grinding tool assembly 100 adopted by the present invention includes: a main shaft 1, a floating mechanism 2, and a locking mechanism 3. Among them, the first end of the main shaft 1 is used for installing a cutting tool, and a sliding sleeve 11 is fixedly sleeved outside the main shaft 1. A sliding ring 111 extending radially outward is formed on the sliding sleeve 11. The floating mechanism 2 includes a floating seat 21, a fixed ring 23 fixed on the floating seat 21 and sleeved outside the sliding sleeve 11, and a plurality of piston cylinders 22 arranged in the floating seat 21 and spaced circumferentially along the main shaft 1; each piston cylinder 22 has a predetermined floating holding force and can expand and contract along the axial direction of the main shaft 1. The sliding ring 111 is clamped between the free end of the piston cylinder 22 and the fixed ring 23; wherein, there is a gap between the floating seat 21 and the main shaft 1, and there is a gap between the sliding ring 111 and the floating seat 21, so that the main shaft 1 can deflect relative to the floating seat 21. In addition, the locking mechanism 3 includes a driving unit arranged on the main shaft 1 and a locking sleeve 31 sleeved on the main shaft 1. The driving unit can drive the locking sleeve 31 to reciprocate along the axial direction of the main shaft 1 to lock or release the floating seat 21.

[0038] In the case where the main shaft 1 and the floating seat 21 are released from each other, when the reaction force generated when the cutting tool contacts the casting 200 for grinding is superimposed with gravity, friction, etc. in one direction and is greater than the floating holding force in the corresponding direction, the corresponding piston cylinder 22 in this direction contracts; when the reaction force generated when the cutting tool contacts the casting 200 for grinding is superimposed with gravity, friction, etc. in one direction and is less than the floating holding force in the corresponding direction, the corresponding piston cylinder 22 in this direction expands, and the piston cylinders 22 in each direction always flexibly support the sliding ring 111 without separating from the sliding ring 111, so that the main shaft 1 can maintain a flexible balance effect relative to the floating seat 21. This working mode is the flexible mode. When the piston cylinders 22 on one side of the main shaft 1 contract and the piston cylinders 22 on the other side expand, a deflection effect as Figure 3 shown will be generated, and a deflection angle β is generated between the axial direction of the main shaft 1 and the axial direction of the floating seat 21. Among them, the magnitude of the angle β can be limited according to the gap between the floating seat 21 and the main shaft 1 and the gap between the sliding ring 111 and the floating seat 21. For example, in Figure 3 specifically, the piston cylinders 22 on the upper side of the main shaft 1 expand and the piston cylinders 22 on the lower side contract, so the upper half of the main shaft 1 inclines towards the end where the cutting tool is installed, and the lower half of the main shaft 1 inclines towards the opposite end.

[0039] The further force analysis is as follows: In this flexible mode, the force (floating holding force) between the piston cylinder 22 and the sliding sleeve 11 can completely overcome the gravity of the main shaft 1, the locking mechanism 3, and the tool. During the grinding process, the grinding force is applied to the main shaft 1 in the radial direction. The grinding force and the gravity of each component are defined as the working force. When the working force in one direction exceeds the floating holding force in that direction, the sliding sleeve 11 will deflect (swing) with the main shaft 1 around the sliding groove 231 on the fixed ring 23 until the working force and the floating holding force reach equilibrium; when the working forces in all directions are less than the corresponding floating holding forces (the grinding force is eliminated), the main shaft 1 returns to the initial equilibrium state with the sliding sleeve 11, and the axis of the main shaft 1 coincides or is parallel to the axis of the floating seat 21. To sum up, in this working mode, the floating mechanism 2 can provide radial floating for the tool, that is, the tool follows the main shaft 1 and deflects relative to the axis of the floating seat 21 or achieves the initial equilibrium, and its floating holding force can be adjusted according to actual requirements.

[0040] Relatively, in the case where the main shaft 1 and the floating seat 21 are locked to each other. For example, as Figure 4 shown, the locking sleeve 31 is driven to move axially along the main shaft 1 and is clamped into the gap between the main shaft 1 and the floating seat 21 to keep the main shaft 1 and the floating seat 21 locked, so as to prevent the main shaft 1 from deflecting relative to the floating seat 21, and the main shaft 1 and the floating seat 21 are rigidly connected to facilitate rigid cutting of the redundant casting structure on the casting 200. This working mode is the rigid mode.

[0041] The pressure - type flexible compliant grinding tool assembly 100 in the above - mentioned embodiment has two working modes: rigid cutting and flexible grinding. It can meet the technological requirements of both cutting and grinding simultaneously, and through the locking mechanism 3, it can achieve flexible switching between the two working modes, improving the grinding efficiency of the casting 200. When flexible grinding is required, the driving unit on the main shaft 1 drives the locking sleeve 31 away from the floating seat 21 to release the floating seat 21, so that the main shaft 1 can deflect relative to the floating seat 21. At this time, multiple piston cylinders 22 apply corresponding pressures to the sliding ring 111 under the action of a predetermined floating holding force, enabling the main shaft 1 to maintain flexible balance following the sliding ring 111. Furthermore, the working surface of the grinding wheel can perform profiling (compliant) grinding following the shape of the casting 200, making the grinding effect smooth and flat, while reducing the profiling accuracy requirements for the grinding trajectory of the robot 103. When rigid cutting is required, the driving unit on the main shaft 1 can drive the locking sleeve 31 to closely contact the floating seat 21 to lock the floating seat 21. The main shaft 1 and the floating seat 21 are rigidly connected, and the cutting tool on the main shaft 1 can overcome the cutting resistance to meet the cutting requirements for the gate residual block 202, venting pins, exhaust fins, excessive metal growth, etc. on the casting 200. The combination of rigidity and flexibility can improve the grinding quality and efficiency and ensure the tool life. Through this technology, the application and popularization of automatic workpiece grinding can be effectively promoted.

[0042] It should be noted that the piston cylinder 22 of the present invention can be an air cylinder, a hydraulic cylinder, etc., and even a structure that drives the piston by a compression spring, as long as it can provide a predetermined floating holding force. Among them, the predetermined floating holding force can always be a unified value or can be flexibly adjusted to a variable value according to requirements. In a preferred embodiment, the piston cylinder 22 is a first air cylinder, and a gas interface 24 is provided on the first air cylinder. Compressed air with an appropriate pressure can be filled into the piston cylinder 22 through the gas interface 24 to facilitate flexible adjustment of the floating holding force of the piston cylinder 22 according to actual needs. Moreover, for the convenience of controlling the position of the locking sleeve 31, the driving unit can also include a second air cylinder 32 and a mounting plate 33 fixed to the second end of the main shaft 1. One end of the second air cylinder 32 is fixed to the mounting plate 33, and the other end of the second air cylinder 32 is connected to the locking sleeve 31. When the main shaft 1 and the floating mechanism 2 are rigidly connected, the compressed air pressure entering the floating mechanism 2 is adjusted to the maximum system pressure. In this working mode, the radial cutting force borne by the cutting tool during work is transmitted from the main shaft 1 to the locking sleeve 31, and the locking sleeve 31 further transmits it to the floating seat 21. The floating seat 21 and the robot 103 are fixed to overcome the cutting resistance.

[0043] As Figure 5As shown, in order to flexibly adjust the pressures in the first cylinder and the second cylinder 32 according to different working conditions, the floating mechanism 2 further includes a pneumatic control unit 4. The pneumatic control unit 4 includes a gas source 41 (which can be compressed air), a main supply pipe, a first branch pipe for supplying gas to the gas interface 24, an electro-pneumatic proportional valve 44 provided on the first branch pipe, a second branch pipe for supplying gas to the second cylinder 32, and a solenoid valve 43 provided on the second branch pipe. The gas source 41 is connected to the first branch pipe and the second branch pipe respectively through the main supply pipe.

[0044] Among them, the solenoid valve 43 controls the gas pressure in the second cylinder 32, indirectly controls the position of the locking sleeve 31, and thus realizes the locking and release between the main shaft 1 and the floating seat 21. The electro-pneumatic proportional valve 44 is a kind of valve belonging to continuous control. Its characteristic is that the output changes with the change of the input, and there is a certain proportional relationship between the output and the input, and stepless adjustment of pressure and speed can be achieved. By adjusting the gas supply pressure to the piston cylinder 22 through the electro-pneumatic proportional valve 44, the floating holding force of the main shaft 1 is adjusted, and the acting force between the cutting tool and the casting 200 can be indirectly adjusted by adjusting the compressed air pressure for different grinding contents. In addition, increasing the floating holding force of the piston cylinder 22 can also assist the locking mechanism 3 to complete the locking work on the main shaft 1 and the floating seat 21, so that the main shaft 1 can be completely locked with the floating seat 21 in the original state.

[0045] Refer to again Figure 5 , in order to ensure that the first cylinder and the second cylinder 32 can fully exert their respective performances, a filter pressure reducing valve 42 can also be provided on the main supply pipe. The filter pressure reducing valve 42 can dry and lubricate the compressed air and play a role in regulating and stabilizing the outlet pressure. The filter pressure reducing valve 42 applied to compressed air adopts a rolling diaphragm. When the input end pressure fluctuates, the pressure reducing valve diaphragm automatically makes adjustments to output the pressure stably and ensure the pressure stability. In addition, the filter pressure reducing valve 42 can also be a combined filter pressure reducing valve, and a high-precision precision pressure reducing valve can be selected according to the requirements of the output pressure accuracy; during use, after the compressed air passes through a two-stage three-section filter to remove impurities such as oil, water, and dust in the compressed air, the service life of the pressure reducing valve diaphragm and the precision of regulating the pressure are greatly improved; due to the long service life of the filter element, the filter element and the pressure reducing element can be repaired separately during maintenance, and there is no need for overall replacement, which greatly saves costs.

[0046] In addition, refer to again Figure 2 , on the side of the fixed ring 23 in contact with the sliding ring 111, a sliding groove 231 is formed. One end of the sliding ring 111 is adapted to the sliding groove 231. The sliding groove 231 is formed as an annular groove on the fixed ring 23, and the outer side of the sliding ring 111 extends towards the fixed ring 23 and is inserted into the sliding groove 231 so that the sliding ring 111 can deflect (swing) based on the sliding groove 231. Among them, asFigure 3 As shown, the cross-section of the sliding groove 231 can be semi-circular, and the cross-section of the end of the sliding ring 111 adapted to the sliding groove 231 is also semi-circular, so that the deflection of the sliding ring 111 relative to the sliding groove 231 can be smoother. In other embodiments, the cross-section of the sliding groove 231 can also be other shapes, as long as the sliding ring 111 can deflect.

[0047] Furthermore, referring again to Figure 3 and Figure 4 , the pressure-type flexible compliant grinding tool assembly 100 further includes a dust cover 26 disposed on the floating seat 21. The dust cover 26 covers the second end of the main shaft 1, thereby preventing dust from entering between the main shaft 1 and the floating mechanism 2 to ensure that the main shaft 1, the floating mechanism 2, and the locking mechanism 3 can all maintain good working conditions.

[0048] In a more preferred embodiment, as Figure 2 shown, a dynamic seal ring 25 can be provided between the sliding sleeve 11 and the fixed ring 23, which can achieve the sealing effect without affecting the swing of the main shaft 1. The dynamic seal ring 25 can achieve the seal between relatively moving parts. For example, it can be an O-ring rubber seal or a star-shaped seal, etc.

[0049] Referring again to Figure 1 , Figure 3 and Figure 4 , in the above embodiment, the cutting tool can be a disc-shaped grinding wheel 102 or a cylindrical grinding wheel 101. A tool holder is provided on the cutting tool, and the tool holder can be mounted on the first end of the main shaft 1, and the cutting tool is replaced by replacing the tool holder. The cylindrical grinding wheel 101 is used for grinding the parting surface flash 201 on the casting 200, and the disc-shaped grinding wheel 102 is used for cutting the vent needle or the gate remnant block 202 on the casting 200.

[0050] In addition, in the above embodiments, the main shaft 1 can be an electric main shaft or a mechanical main shaft. Among them, the electric main shaft is a technology that integrates the machine tool main shaft and the main shaft motor in the field of CNC machine tools. The electric main shaft includes the electric main shaft itself and its accessories, specifically including the electric main shaft, high-frequency variable frequency device, oil mist lubricator, cooling device, built-in encoder, tool changing device, etc. The rotor of the main shaft motor directly serves as the main shaft of the machine tool, and the housing of the main shaft unit is the base of the main shaft motor, and it cooperates with other components to realize the integration of the main shaft motor and the machine tool main shaft. When the electric main shaft is used as the main shaft 1 in the present invention, a sliding sleeve 11 is fixedly arranged outside its housing, and the free end of the rotor is used to install the tool. The mechanical main shaft refers to the shaft on the machine tool that drives the workpiece or tool to rotate, and in the machine, the motion and torque are mainly transmitted through transmission parts such as gears and belt pulleys. When the mechanical main shaft is used as the main shaft 1 in the present invention, a belt pulley can be arranged on the mechanical main shaft, and the transmission from the motor to the mechanical main shaft is carried out through the cooperation of the belt pulley and the belt, so that the mechanical main shaft can rotate self and float relative to the floating seat 21.

[0051] Further, referring to Figure 6 , the present invention provides a tool end trajectory adaptive method for a robot to grind castings, which includes:

[0052] S100. Scan the reference casting to generate the first workpiece coordinate system of the reference casting, and save the spatial position of the reference casting in the first workpiece coordinate system. Among them, the first workpiece coordinate system is generated based on the reference casting, and "first" does not limit the quantity.

[0053] S200. Generate the grinding trajectory of the reference casting according to the first workpiece coordinate system; among them, the grinding trajectory can be generated by the common manual teaching method based on the generated coordinate system. The robot simulates the manual action and then completes the operation using the taught action.

[0054] S300. Replace the reference casting with the casting to be ground, scan the casting to be ground, and generate the second workpiece coordinate system of the casting to be ground. Among them, the second workpiece coordinate system is generated based on the casting to be ground, and "second" does not limit the quantity, but is only used to distinguish it from the "first workpiece coordinate system".

[0055] S400. Update the spatial position of the reference casting according to the first workpiece coordinate system and the second workpiece coordinate system, and use the updated spatial position as the spatial position of the casting to be polished, thereby obtaining a polished trajectory with updated coordinates. That is, store the second workpiece coordinate system in the robot control system, and update the spatial positions of all machining points through the update of the coordinate system, so as to use the updated spatial position as the spatial position of the casting to be polished. Thus, the polished trajectory can be adaptively corrected following the position and posture of the casting through coordinate update, which not only has high correction accuracy but also greatly reduces the calculation amount.

[0056] S500. Select the working mode of the pressure - type flexible compliant polishing tool assembly 100 of the robot. The working modes include a rigid mode and a flexible mode. Among them, in the rigid mode, control the locking mechanism 3 to lock the spindle 1 and the floating seat 21; in the flexible mode, control the locking mechanism 3 to release the lock between the spindle 1 and the floating seat 21, and adjust the floating holding force of the piston cylinder 22 to a first preset pressure so that the spindle 1 can deflect relative to the floating seat 21. Among them, before polishing, the robot 103 can arbitrarily select a working mode. For example, it can first perform a cutting process in the rigid mode or first enter the flexible mode, and then switch to another working mode in subsequent steps to continue polishing along the polished trajectory.

[0057] S600. Based on the selected working mode, drive the tool installed on the spindle to rotate and move along the polished trajectory of the casting to be polished, so as to perform rigid cutting or flexible polishing on the casting to be polished. Specifically, the robot 103 can supply electrical energy to the spindle 1 to drive the spindle 1 to rotate. At the same time, the robot 103 drives the entire floating seat 21 and the spindle 1 to move along the polished trajectory of the casting to be polished in three - dimensional space;

[0058] S700. Switch the working mode of the pressure - type flexible compliant polishing tool assembly 100 to complete the polishing of the casting to be polished. Or, for example, if there are only defects that require flexible polishing on the casting to be polished, the working mode can not be switched, and the polishing can be directly completed using the same mode.

[0059] In the above embodiments of the present invention, first, based on the comparison between the standard casting and the casting to be polished, a workpiece coordinate system and a polishing trajectory that match the positional relationship and dimensional relationship of the casting to be polished are established. In the rigid mode, the main shaft and the floating seat are relatively locked; in the flexible mode, the main shaft can deflect relative to the floating seat. According to the actual situation (the type of defect to be polished on the casting), the working mode is flexibly switched, and the tool mounted on the main shaft is driven to rotate and move along the polishing trajectory of the casting to be polished, so as to perform rigid cutting or flexible polishing on the casting, which can meet the need for the end trajectory of the cutting and polishing tool to be adaptive, simplify the requirements for robot teaching programming, reduce the requirements for tooling and fixtures, ensure the polishing effect and the safety of the robot polishing equipment, and improve the mixed-line compatibility of the robot polishing equipment. Among them, in the rigid mode, the tool can be a disc-shaped grinding wheel; in the flexible mode, the tool can be a cylindrical grinding wheel.

[0060] Specifically, in one embodiment of the present invention, as Figure 9 shown, the robot processing system may include a robot 103 (which includes a pressure-type flexible compliance polishing tool assembly 100), tooling fixtures 300 and 3D sensors 400, and other auxiliary devices. Among them, the 3D sensor can be, but is not limited to, a binocular 3D camera, a 3D camera composed of a monocular and structured light; the 3D sensor can be mounted at the end of the robot or can be independently mounted away from the robot; the tooling fixture can be mounted at the end of the robot or can be independently mounted away from the robot.

[0061] In order to be able to generate a polishing trajectory corresponding to the polishing requirements of different castings 200, the casting 200 is scanned to generate a workpiece coordinate system of the casting 200; a polishing trajectory is generated according to the workpiece coordinate system. The polishing trajectory is designed for the position to be polished, and the robot 103 operates according to the polishing trajectory, and can polish off the riser residue or burrs that need to be polished off on the casting 200. Specifically, it includes: 1) Before the robot 103 operates, scan the workpiece (sample) to obtain the sample features; 2) Establish a sample coordinate system using the sample features; 3) Convert the sample coordinate system into the world coordinate system of the robot 103 to obtain the position of the workpiece relative to the robot coordinate system and generate a workpiece coordinate system; 4) Establish the polishing trajectory of the robot with the workpiece coordinate system as the reference coordinate system; 5) During the automated polishing process of the robot, scan the casting to be polished to extract the features of the casting to be polished; 6) Calculate a new workpiece coordinate system using the feature information of the casting to be polished; 7) Update the original workpiece coordinate system to generate a new polishing trajectory, which can solve the error caused by clamping of the casting (by this method, the positioning requirements for tooling and fixtures can be effectively reduced, and the mixed-line compatibility of the robot polishing equipment can be improved).

[0062] In order to further improve the stability of the spindle 1 in the rigid mode, increasing the floating holding force of the piston cylinder 22 can also assist the locking mechanism 3 to complete the locking work on the spindle 1 and the floating seat 21, so that the spindle 1 can be completely locked with the floating seat 21 in the original state. That is, adjust the floating holding force of the piston cylinder 22 to the second preset pressure, and the second preset pressure is greater than the first preset pressure. Among them, the first preset pressure can be 0.2 MPA to 0.4 MPA, and the second preset pressure can be 0.6 MPA to 0.8 MPA. In the actual production process, the floating holding force of the piston cylinder can be adjusted from the first preset pressure to the second preset pressure or from the second preset pressure to the first preset pressure according to the needs through the electro-hydraulic proportional valve 44.

[0063] In a more preferred embodiment, as Figure 7 shown, step S100 specifically includes:

[0064] S110. Obtain the coordinate transformation matrix through robot hand-eye calibration; obtain the position relationship of the 3D sensor relative to the flange center of the robot or the base coordinate system of the robot through robot hand-eye calibration.

[0065] In the embodiment of the present invention, robot hand-eye calibration is to calibrate the 3D sensor, so as to obtain the position and attitude conversion relationship of the 3D sensor relative to the end flange center of the robot (when the 3D sensor is installed on the robot), or the relationship between the 3D sensor and the base coordinate system of the robot (when the 3D sensor is installed outside the robot), which is represented by the coordinate transformation matrix Xs.

[0066] S120. Obtain the point cloud data of the reference casting and obtain the first pose coordinates of the robot.

[0067] Optionally, according to an embodiment of the present invention, the point cloud data of the reference casting is obtained through a 3D sensor. That is to say, the 3D sensor is used to scan the reference casting or directly photograph to collect the 3D point cloud of the reference casting, and record the position and attitude of the robot when the 3D sensor collects the point cloud data, that is, the first pose coordinates Xr of the robot.

[0068] Among them, the scanning or photographing of the reference casting by the 3D sensor can be single-time or multiple times for processing multiple regions; the obtained point cloud can be a single point cloud set or multiple point cloud sets of different regions. Whether it is a single point cloud set or multiple point cloud sets of different regions, it is for establishing the workpiece coordinate system later.

[0069] S130. Establish the workpiece coordinate system of the reference casting based on the point cloud data of the reference casting, and convert the workpiece coordinate system of the reference casting to the base coordinate system of the robot according to the coordinate transformation matrix and the first pose coordinate of the robot to obtain the first workpiece coordinate system.

[0070] Among them, the workpiece coordinate system of the reference casting contains 6 degrees-of-freedom components, denoted as Xi. And for a single point cloud set, the centroid of the point cloud set can be directly extracted, or a method of extracting multiple point cloud features from a single point cloud set can be used to establish the workpiece coordinate system of the reference casting; for point cloud sets in multiple different regions, a method of extracting each point cloud feature can be used to establish the workpiece coordinate system of the reference casting.

[0071] Specifically, in an embodiment of the present invention, when extracting point cloud features based on the workpiece point cloud set, n≥3 original feature point positions can be obtained. Each feature point contains three components x, y, and z, which are respectively denoted as Xi1, Xi2, …, Xin. Among them, the selected feature points are ideally the reference points of the casting.

[0072] Furthermore, the original feature points are processed by an algorithm to establish the workpiece coordinate system of the reference casting by constructing three new feature points.

[0073] Among them, when the number n of original feature points = 3, the following method is used to construct three new feature points.

[0074] The first method is to directly select one of the 3 original feature points as the establishment of the first point P1; among the remaining 2 original feature points, select one as the establishment of the second point P2; and use the remaining one original feature point as the establishment of the third point P3. Among them, P1, P2, and P3 cannot be collinear in space.

[0075] The second method is to calculate the centroid of the 3 original feature points as the establishment of the first point P1; among the 3 original feature points, select one as the establishment of the second point P2; and select one from the remaining 2 feature points as the establishment of the third point P3. Among them, the 3 original feature points cannot be collinear in space.

[0076] When the number n of original feature points > 3, generally, the centroid of all original feature points is obtained, or a certain original feature point can be directly selected as the establishment of the first point P1, and the centroid of some original feature points or a certain original feature point is directly selected as the establishment of the second point P2; the centroid of some original feature points or a certain original feature point is selected as the establishment of the third point P3.

[0077] Then, based on the three new feature points constructed, the workpiece coordinate system of the reference casting is established as follows:

[0078] After obtaining P1, P2, and P3, start to establish a coordinate system. First, select P1 as the origin of the coordinate system, and then calculate the X, Y, and Z axes of the coordinate system, as Figure 10 shown.

[0079] Among them, the calculation processes of the X, Y, and Z axes of the coordinate system are as follows:

[0080] In the first step, construct a space vector with points P1 and P2,

[0081] In the second step, construct a space vector with points P1 and P3,

[0082] In the third step, normalize the vectors,

[0083] In the fourth step, calculate the X axis as

[0084] In the fifth step, take the and vector cross product to obtain the Z axis of the coordinate system, that is Among them, and the cross product order of the vectors should satisfy the right-hand rule;

[0085] In the sixth step, the Y axis of the coordinate system is Y = Z × X.

[0086] In this way, the coordinate system is constituted by the origin of the coordinate system and the X, Y, and Z axes, as Figure 10 shown.

[0087] In this embodiment, the centroid calculation method is as follows: taking the centroid of m points as an example, the points are C1, C2... Cm, then the centroid M = (C1 + C2 +... + Cm) / m.

[0088] Therefore, by establishing the workpiece coordinate system of the reference casting through the above method, the coordinate system error caused by poor workpiece consistency can be reduced to a certain extent, and the accuracy of the robot in processing such castings can be improved.

[0089] Optionally, in an embodiment of the present invention, when converting the workpiece coordinate system of the reference casting to the first workpiece coordinate system of the robot, when the 3D sensor is installed on the robot, the workpiece coordinate system of the reference casting is converted to the base coordinate system of the robot according to the formula Xb = Xr * Xs * Xi to obtain the first workpiece coordinate system, where Xb is the first workpiece coordinate system, Xr is the first pose coordinate of the robot, Xs is the coordinate transformation matrix, and Xi is the workpiece coordinate system of the reference casting.

[0090] Among them, for the equation Xb = Xr * Xs * Xi, each variable in the equation can be a 4×4 homogeneous transformation matrix, which can be specifically expressed as:

[0091]

[0092] In the above formula, the upper left 3×3 sub-matrix of each matrix is the rotational component of the pose, and the last column of each matrix is the position component of the pose.

[0093] When the 3D sensor is installed outside the robot, the workpiece coordinate system of the reference casting is converted to the base coordinate system of the robot according to the formula Xb = Xs * Xi to obtain the first workpiece coordinate system, where Xb is the first workpiece coordinate system, Xs is the coordinate transformation matrix, and Xi is the workpiece coordinate system of the reference casting.

[0094] For the equation Xb = Xs * Xi, each variable in the equation can be a 4×4 homogeneous transformation matrix, which can be specifically expressed as:

[0095]

[0096] Similarly, the upper left 3×3 sub-matrix of each matrix in the above formula is the rotational component of the pose, and the last column of each matrix is the position component of the pose.

[0097] In an embodiment of the present invention, after the first workpiece coordinate system Xb is established, it is stored in the robot control system, and within the first workpiece coordinate system Xb, manual teaching is started. The spatial point coordinates of the grinding trajectories of all reference castings are saved in the Xb coordinate system, so that the spatial position of the reference casting can be obtained and saved in the Xb coordinate system. Then, the taught machining program is run. After the machining of the reference casting is completed, the casting can be replaced.

[0098] Optionally, according to an embodiment of the present invention, as Figure 8 shown, step S300 includes:

[0099] S310. Obtain the point cloud data of the casting to be ground and obtain the second pose coordinate of the robot.

[0100] Optionally, according to an embodiment of the present invention, the point cloud data of the casting to be ground is obtained by a 3D sensor. That is to say, the 3D sensor is used to scan or directly photograph the casting to be ground to collect the 3D point cloud of the casting to be ground, and the position and pose of the robot when the 3D sensor collects the point cloud data, that is, the second pose coordinate Xrnew of the robot, are recorded.

[0101] It can be understood that in the embodiments of the present invention, the second pose coordinate Xrnew may be the same as the first pose coordinate Xr, that is, when collecting point cloud data through the 3D sensor, the position and pose of the robot may remain unchanged.

[0102] Similarly, the scanning or shooting of the casting to be polished by the 3D sensor can be single-time or multiple times for processing multiple regions; the obtained point cloud can be a single point cloud set or point cloud sets of multiple different regions. Whether it is a single point cloud set or point cloud sets of multiple different regions, it is for establishing the workpiece coordinate system subsequently.

[0103] S320. Establish the workpiece coordinate system of the casting to be polished according to the point cloud data of the casting to be polished, and convert the workpiece coordinate system of the casting to be polished to the base coordinate system of the robot according to the coordinate transformation matrix and the second pose coordinate of the robot to obtain the second workpiece coordinate system.

[0104] Among them, the workpiece coordinate system of the casting to be polished includes 6 degrees-of-freedom components, denoted as Xinew.

[0105] It should be noted that the establishment process of the workpiece coordinate system of the casting to be polished may be the same as that of the workpiece coordinate system of the reference casting, and will not be elaborated here.

[0106] Optionally, as an embodiment, when converting the workpiece coordinate system of the casting to be polished to the base coordinate system of the robot, when the 3D sensor is installed on the robot, convert the workpiece coordinate system of the casting to be polished to the base coordinate system of the robot according to the formula Xbnew = Xrnew * Xs * Xinew to obtain the second workpiece coordinate system, where Xbnew is the second workpiece coordinate system, Xrnew is the second pose coordinate of the robot, Xs is the coordinate transformation matrix, and Xinew is the workpiece coordinate system of the casting to be polished; when the 3D sensor is installed outside the robot, convert the workpiece coordinate system of the casting to be polished to the base coordinate system of the robot according to the formula Xbnew = Xs * Xinew to obtain the second workpiece coordinate system, where Xbnew is the second workpiece coordinate system, Xs is the coordinate transformation matrix, and Xinew is the workpiece coordinate system of the casting to be polished.

[0107] Moreover, the coordinate transformation process of converting the workpiece coordinate system of the casting to be polished to the base coordinate system of the robot is the same as the process of converting the workpiece coordinate system of the above-mentioned reference casting to the base coordinate system of the robot, and will not be elaborated here either.

[0108] It should be noted that in the embodiments of the present invention, when debugging the reference casting, all the robot machining spatial position points are saved in the first workpiece coordinate system, and the first workpiece coordinate system is described relative to the robot's base coordinate system. After updating the first workpiece coordinate system according to the second workpiece coordinate system, it is necessary to ensure that the robot machining spatial position points remain unchanged in the workpiece coordinate system, that is, the position of the machining tool relative to the casting to be polished remains unchanged. After the position of the casting changes, the position of the robot machining spatial position relative to the robot's base coordinate system must change to follow the position of the casting for machining. Among them, the kinematic conversion process can be independently completed by the robot control system, which can not only achieve accurate correction of the position and posture of the casting, but also does not require too many calculation processes, reducing the calculation amount while providing a basis for ensuring the consistency of casting machining.

[0109] According to the error compensation method for a robot to machine a casting proposed in the embodiments of the present invention, first, a coordinate transformation matrix is obtained through robot hand-eye calibration. Then, when the reference casting is placed in the fixture, the point cloud data of the reference casting is obtained, and the first pose coordinate of the robot at this time is obtained. Next, the workpiece coordinate system of the reference casting is established based on the point cloud data of the reference casting, and the workpiece coordinate system of the reference casting is transformed to the robot's base coordinate system according to the coordinate transformation matrix and the first pose coordinate of the robot to obtain the first workpiece coordinate system. Then, after replacing the casting, the point cloud data of the casting to be polished is obtained, and the second pose coordinate of the robot at this time is obtained. Then, the workpiece coordinate system of the casting to be polished is established based on the point cloud data of the casting to be polished, and the workpiece coordinate system of the casting to be polished is transformed to the robot's base coordinate system according to the coordinate transformation matrix and the second pose coordinate of the robot to obtain the second workpiece coordinate system. Finally, the spatial position of the reference casting is updated according to the first workpiece coordinate system and the second workpiece coordinate system, and the updated spatial position is used as the spatial position of the casting to be polished to achieve the pose correction of the casting. Therefore, the present invention realizes the adaptive correction of the grinding trajectory following the position and posture of the casting through coordinate update, thus eliminating the need to optimize the fixture design, improving the universality of the fixture, simplifying the design of the workpiece fixture, and only requiring the fixture to ensure that the workpiece does not loosen during machining and allowing the position and posture of the workpiece after clamping to change, reducing the fixture design difficulty and workload, ensuring the consistency of casting machining, effectively solving the workpiece machining error problem, and guaranteeing the machining quality.

[0110] In an embodiment of the present invention, as Figure 11 shown, the pose correction method for a robot to machine a casting includes the following steps:

[0111] S11. Calibrate the 3D sensor to obtain the position and attitude transformation relationship of the 3D sensor relative to the robot end flange (the 3D sensor is installed on the robot), or the relationship of the 3D sensor relative to the robot's base coordinate system (the 3D sensor is installed outside the robot), and denote it as Xs.

[0112] S12. Use the 3D sensor to scan the reference casting or directly take pictures to collect the 3D point cloud of the reference casting, and record the position and attitude of the robot when the 3D sensor collects data, denoted as Xr. Among them, the scanning or photographing of the reference casting by the 3D sensor can be single-time or multiple times for processing multiple regions; the obtained point cloud can be a single point cloud set or point cloud sets of multiple different regions.

[0113] S13. Use the point cloud collected in step S12 to establish the workpiece coordinate system of the reference casting. The workpiece coordinate system contains 6 degrees-of-freedom components, denoted as Xi. And, for a single point cloud set, the centroid of the point cloud set can be directly extracted, or a method of extracting multiple point cloud features from a single point cloud set can be used to establish the workpiece coordinate system of the reference casting; for point cloud sets of multiple different regions, a method of extracting the features of each point cloud can be used to establish the workpiece coordinate system of the reference casting.

[0114] The specific process of establishing the workpiece coordinate system is as described above and will not be elaborated here.

[0115] S14. Convert the workpiece coordinate system established in step S13 to the robot's base coordinate system to obtain the first workpiece coordinate system, denoted as Xb. Among them, Xb = Xr * Xs * Xi (the 3D sensor is installed on the robot); Xb = Xs * Xi (the 3D sensor is installed outside the robot).

[0116] Among them, for the equation Xb = Xr * Xs * Xi, each variable in the equation is a 4×4 homogeneous transformation matrix, which can be specifically expressed as:

[0117]

[0118] In the above formula, the upper left 3×3 sub-matrix of each matrix is the rotation component of the pose, and the last column of each matrix is the position component of the pose.

[0119] For the equation Xb = Xs * Xi, each variable in the equation is a 4×4 homogeneous transformation matrix, which can be specifically expressed as:

[0120]

[0121] Similarly, the upper left 3×3 sub-matrix of each matrix in the above formula is the rotation component of the pose, and the last column of each matrix is the position component of the pose.

[0122] S15. Store the Xb coordinate system in the robot control system, and start manual teaching. The spatial point coordinates of all grinding trajectories are saved in the Xb coordinate system.

[0123] S16. Run the program of manual teaching to complete the machining of the reference casting (debugging sample), and perform casting replacement.

[0124] S17. Use the 3D sensor to scan or photograph the replaced casting again to obtain the new 3D point cloud of the current casting. The acquisition method is the same as that in step S12 above. Among them, when the 3D sensor collects data, the position and pose of the robot are still Xr.

[0125] S18. Use the point cloud collected in step S17 to establish a workpiece coordinate system for the current casting. The coordinate system also includes 6 degrees-of-freedom components, denoted as Xinew.

[0126] Among them, the method for establishing the workpiece coordinate system is as described above.

[0127] S19. Convert the workpiece coordinate system of the current casting to the base coordinate system of the robot to obtain the second workpiece coordinate system, denoted as Xbnew. Xbnew = Xr * Xs * Xinew (the 3D sensor is installed on the robot); Xbnew = Xs * Xinew (the 3D sensor is installed outside the robot). Among them, the coordinate conversion process is the same as that in step S14 and will not be elaborated here.

[0128] S20. Transmit the Xbnew coordinate system to the robot control system, and the control system automatically updates all machining positions to achieve pose correction when the robot machines the casting.

[0129] The method for pose correction when the robot machines the casting in the embodiment of the present invention updates the spatial positions of all machining points by updating the coordinate system, so as to realize taking the updated spatial position as the spatial position of the current casting. Thus, the grinding trajectory can be adaptively corrected following the position and pose of the casting through coordinate update, which not only has high correction accuracy but also can greatly reduce the calculation amount.

[0130] It should be understood that the above description of the specific embodiments of the present invention is only for explaining the technical route and features of the present invention, and its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. However, the present invention is not limited to the above specific embodiments.

Claims

1. A tool tip trajectory self - adaptation method for a robot to grind castings, characterized in that, It includes: Scanning a reference casting to generate a first workpiece coordinate system of the reference casting, and saving the spatial position of the reference casting within the first workpiece coordinate system; Generating a grinding trajectory of the reference casting according to the first workpiece coordinate system; Replacing the reference casting with a casting to be ground, scanning the casting to be ground, and generating a second workpiece coordinate system of the casting to be ground; Updating the spatial position of the reference casting according to the first workpiece coordinate system and the second workpiece coordinate system, and using the updated spatial position as the spatial position of the casting to be ground to obtain a grinding trajectory with updated coordinates; Selecting a working mode of a pressure - type flexible compliant grinding tool assembly of a robot, where the working mode includes a rigid mode and a flexible mode; Based on the selected working mode, driving a tool installed on the spindle to rotate and move along the grinding trajectory of the casting to be ground, so as to perform rigid cutting or flexible grinding on the casting to be ground and complete the grinding of the casting to be ground; This method uses a pressure - type flexible compliant grinding tool assembly, which includes: a spindle, a floating mechanism, and a locking mechanism; wherein, the first end of the spindle is used for installing a tool, and a sliding sleeve is fixedly sleeved outside the spindle, and a sliding ring extending radially outward is formed on the sliding sleeve; the floating mechanism includes a floating seat, a fixed ring fixed on the floating seat and sleeved outside the sliding sleeve, and a plurality of piston cylinders arranged at intervals along the circumferential direction of the spindle and arranged inside the floating seat; each piston cylinder has a predetermined floating holding force and can expand and contract along the axial direction of the spindle, and the sliding ring is clamped between the free end of the piston cylinder and the fixed ring; there is a gap between the floating seat and the spindle, and there is a gap between the sliding ring and the floating seat, so that the spindle can deflect relative to the floating seat; the locking mechanism includes a driving unit arranged on the spindle and a locking sleeve sleeved on the spindle, and the driving unit can drive the locking sleeve to reciprocate along the axial direction of the spindle to lock or release the floating seat; In the rigid mode, controlling the locking mechanism to lock the spindle and the floating seat; in the flexible mode, controlling the locking mechanism to release the lock between the spindle and the floating seat, and adjusting the floating holding force of the piston cylinder to a first preset pressure so that the spindle can deflect relative to the floating seat.

2. The tool tip trajectory self - adaptation method for robot grinding castings according to claim 1, characterized in that, The steps of scanning a reference casting to generate a first workpiece coordinate system of the reference casting, and saving the spatial position of the reference casting within the first workpiece coordinate system include: Obtaining a coordinate transformation matrix through robot hand - eye calibration; Obtaining the point cloud data of the reference casting and the first - pose coordinates of the robot; Establishing a workpiece coordinate system of the reference casting according to the point cloud data of the reference casting, and converting the workpiece coordinate system of the reference casting to the base coordinate system of the robot according to the coordinate transformation matrix and the first - pose coordinates of the robot to obtain a first workpiece coordinate system.

3. The tool tip trajectory self-adaptive method for a robot to grind a casting according to claim 2, characterized in that, The steps of scanning a casting to be ground to generate a second workpiece coordinate system of the casting to be ground include: Obtaining the point cloud data of the casting to be ground and the second - pose coordinates of the robot; Establish the workpiece coordinate system of the casting to be polished according to the point cloud data of the casting to be polished, and convert the workpiece coordinate system of the casting to be polished to the base coordinate system of the robot according to the coordinate transformation matrix and the second pose coordinate of the robot to obtain the second workpiece coordinate system.

4. The tool tip trajectory self - adaptation method for robot grinding castings according to claim 3, characterized in that, Obtain the point cloud data of the reference casting and the point cloud data of the casting to be polished through a 3D sensor respectively.

5. The tool tip trajectory self-adaptive method for robot grinding castings according to claim 1, characterized in that, In the rigid mode, adjust the floating holding force of the piston cylinder to a second preset pressure, and the second preset pressure is greater than the first preset pressure.

6. The tool tip trajectory self-adaptive method for a robot to grind a casting according to claim 5, characterized in that, The first preset pressure is 0.2 MPA to 0.4 MPA, and the second preset pressure is 0.6 MPA to 0.8 MPA.

7. The tool tip trajectory self - adaptation method for a robot to grind castings according to claim 5, characterized in that, The piston cylinder is a first cylinder connected to a compressed air source; the compressed air source is connected to the first cylinder through an electro-pneumatic proportional valve; The floating holding force of the piston cylinder can be adjusted from the first preset pressure to the second preset pressure or from the second preset pressure to the first preset pressure through the electro-pneumatic proportional valve.

8. The tool tip trajectory self - adaptation method for a robot to grind a casting as described in claim 7, characterized in that, The driving unit of the locking mechanism is a second cylinder connected to a compressed air source, and the compressed air source is connected to the second cylinder through a solenoid valve.

9. The tool tip trajectory self - adapting method for robot - grinding castings according to claim 1, characterized in that, In the rigid mode, the tool is a disc-shaped grinding wheel; in the flexible mode, the tool is a cylindrical grinding wheel.

Images