CN108398922B - Robot abrasive belt polishing virtual teaching method based on force feedback - Google Patents

Robot abrasive belt polishing virtual teaching method based on force feedback Download PDF

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CN108398922B
CN108398922B CN201810069280.XA CN201810069280A CN108398922B CN 108398922 B CN108398922 B CN 108398922B CN 201810069280 A CN201810069280 A CN 201810069280A CN 108398922 B CN108398922 B CN 108398922B
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CN108398922A (en
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李静蓉
谢海龙
王清辉
符俊岭
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South China University of Technology SCUT
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B19/00—Programme-control systems
    • G05B19/02—Programme-control systems electric
    • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
    • G05B19/4097—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by using design data to control NC machines, e.g. CAD/CAM
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09B—EDUCATIONAL OR DEMONSTRATION APPLIANCES; APPLIANCES FOR TEACHING, OR COMMUNICATING WITH, THE BLIND, DEAF OR MUTE; MODELS; PLANETARIA; GLOBES; MAPS; DIAGRAMS
    • G09B9/00—Simulators for teaching or training purposes
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/32—Operator till task planning
    • G05B2219/32153—Exchange data between user, cad, caq, nc, capp

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Abstract

The invention discloses a robot abrasive belt polishing virtual teaching method based on force feedback, which comprises the following steps: building a virtual scene; constructing a virtual deformable abrasive belt model; establishing a coordinate mapping relation between the tail end of the force feedback equipment and the virtual workpiece, and reading and updating the posture and the movement speed of the virtual workpiece in the virtual environment in real time; the tail end of the force feedback equipment is held by a hand, and the virtual workpiece is operated to carry out teaching polishing at a contact wheel or a virtual deformable abrasive belt; calculating the abrasive belt polishing force of the virtual workpiece and integrating the output of force feedback equipment; under the guidance of polishing feedback force, a user dynamically adjusts the polishing force and posture parameters of the workpiece according to the geometric information of the workpiece and the deformation of the abrasive belt; and converting the generated track into a robot code to realize automatic processing. The invention integrates the experience of manual polishing, enables a user to select a corresponding polishing mode and dynamically adjusts the polishing force and posture of a workpiece, and provides a more natural and effective interactive programming mode for the abrasive belt polishing of the robot.

Description

Robot abrasive belt polishing virtual teaching method based on force feedback
Technical Field
The invention belongs to the field of robot abrasive belt polishing off-line programming, and particularly relates to a force feedback-based robot abrasive belt polishing virtual teaching method.
Background
With the continuous improvement of the requirements of people on the functions and the aesthetics of products, workpieces consisting of various types of free-form surfaces are more and more common, and the process forms of abrasive belt polishing mainly comprise two types according to the geometric information of the workpieces: one is to polish on a belt supported by a contact wheel in order to obtain a higher material removal rate; the other is to polish curved surfaces with interference problems at the contact wheel support with very large curvature, and the polishing of such curved surfaces is usually realized by elastic deformation of a sanding belt at the abrasive belt without the contact wheel support. Due to a complex material removing mechanism, at present, polishing of complex workpieces is mainly manually completed by experienced workers, so that not only is the efficiency low and the stability and consistency of processing difficult to guarantee, but also noise and dust generated by polishing seriously threaten the physical health of the operators.
In recent years, the application of a six-degree-of-freedom industrial robot system greatly improves the efficiency and flexibility of abrasive belt polishing. At present, robot abrasive belt polishing is mainly performed automatically by using a field teaching and reproducing mode in China. The online teaching mainly has the following defects: it is difficult to ensure that operators are away from harsh, hazardous machining environments; the accuracy of the teaching is entirely dependent on the experience of the operator. The off-line teaching method corresponds to the on-line teaching, and mainly generates a processing track in a recording mode or algorithm by operating teaching software by workers, so that robot or numerical control machine programming which is far away from an actual processing field and does not need to be synchronous with a processing process is realized. For the shape of a workpiece consisting of various complex curved surfaces, when the polishing track of the workpiece is defined through traditional offline programming, the influence of the deformation of a contact wheel on the position precision of the polishing point is considered, the problem of polishing interference caused by the shape of the workpiece is also considered, particularly for the curved surface which has large curvature and needs to be polished on a deformable abrasive belt without the support of the contact wheel, because of the elastic deformation of the abrasive belt, the ideal polishing track of the workpiece is difficult to obtain through the traditional offline programming, and the method is usually realized by adopting a complex offline programming and online teaching mode, so that a programmer is inevitably in a dangerous and severe machining environment. In addition, among the factors affecting the polishing quality of the abrasive belt, the properties of the abrasive belt, the speed of the abrasive belt and the feeding speed are all determinable before processing, and the processing force must be controlled and adjusted in real time during the processing, which is the factor affecting the polishing quality of the workpiece most and difficult to control. Therefore, in the off-line programming, if the workpiece stress in the abrasive belt polishing process can be really sensed and adjusted in real time like manual polishing, and the deformation of the abrasive belt can be sensed and adjusted in real time, the efficiency and quality of abrasive belt polishing can be greatly improved, however, the traditional on-line programming and off-line programming only define the polishing track through two-dimensional interactive devices such as a teaching box, a keyboard, a mouse and the like, and cannot meet the requirement.
In recent years, more and more scholars have made up for the shortcomings of off-line programming by applying Virtual Reality technology (VR) to robotic teaching. A virtual robot teaching system is constructed based on a VR technology, a force sense feedback technology can be integrated, programming operators can be liberated from a severe and dangerous machining environment by establishing an elastic deformable model of an abrasive belt, and users can adjust polishing parameters such as the polishing force, the polishing posture and the like of a workpiece in real time according to the force sense feedback and the abrasive belt deformation to obtain an ideal track and finally convert the ideal track into a robot code to realize automatic polishing. However, no literature report is found on a virtual teaching method for belt polishing of a robot integrating force feedback.
Disclosure of Invention
Aiming at the defects and improvement requirements in the prior art, the invention provides a robot abrasive belt polishing virtual teaching method based on force feedback. The method aims at polishing of a complex-shaped workpiece, a virtual scene for robot abrasive belt polishing and a virtual deformable abrasive belt model capable of accurately simulating abrasive belt polishing stress deformation in real time are built, then force feedback equipment is integrated, a user can hold the tail end of the force feedback equipment like manual polishing, the workpiece is operated to polish at a contact wheel position or a virtual deformable abrasive belt position in a virtual environment, in the polishing process, the user can dynamically adjust parameters such as the polishing force and the polishing posture of the workpiece according to the geometric information of the workpiece and the deformation of the abrasive belt under the guidance of polishing feedback force to obtain an ideal polishing track, and finally the generated track can be converted into a robot code to realize automatic polishing, so that a more flexible and effective robot abrasive belt polishing teaching method is provided for polishing of the complex workpiece.
In order to achieve the purpose, the invention adopts the following technical scheme.
A robot abrasive belt polishing virtual teaching method based on force feedback comprises the following steps:
step 1: building a virtual scene, wherein the virtual scene comprises a virtual machining tool, a virtual machining object and a virtual environment;
step 2: constructing a virtual deformable abrasive belt model based on the spring mass point model, the mechanical and physical properties of the abrasive belt and the initial tension of the abrasive belt;
and step 3: binding the virtual processing object with the force feedback equipment, establishing a mapping relation between a terminal coordinate system of the force feedback equipment and a virtual processing object coordinate system, enabling the motion of the virtual processing object in a virtual scene to the motion of the terminal of the stress feedback equipment, and reading and updating the posture and the motion speed of the virtual processing object in a virtual environment in real time;
and 4, step 4: the handheld force feedback equipment operates the virtual processing object to carry out polishing in a virtual scene like manual polishing, judges whether the virtual processing object collides with a contact wheel or a virtual deformable abrasive belt supported by the contact wheel, and executes the step 5 if the virtual processing object collides with the contact wheel or the virtual deformable abrasive belt supported by the contact wheel;
and 5: recording the posture and the movement speed of the virtual processing object in the virtual scene, calculating the polishing force according to the collision type, and simultaneously feeding back the calculated polishing force to a user through force feedback equipment;
step 6: dynamically adjusting polishing parameters of the virtual processing object under the guidance of polishing feedback force according to the geometric information of the workpiece and the deformation of the abrasive belt, wherein the polishing parameters comprise force and attitude parameters;
and 7: and generating a polishing track of the virtual processing object according to the posture and the motion speed of the virtual processing object in the virtual scene, and converting the polishing track into a robot code to realize automatic polishing.
Further, in step 1, the virtual scene is a virtual teaching scene for robot belt polishing; the virtual machining tool comprises a virtual robot, a virtual abrasive belt machine and a virtual workpiece clamp; the virtual processing object refers to a workpiece needing virtual teaching; the virtual environment refers to illumination, background and color of a virtual scene; the virtual workpiece clamp is used for clamping a virtual machining object and is arranged at the tail end of the robot.
Further, in step 2, the spring mass model adopts a square spring mass model; the mechanical and physical properties of the abrasive belt comprise a tensile stress-strain relation, a shear stress-strain relation and a bending moment-curvature relation when the abrasive belt is bent; the virtual deformable sanding belt model refers to a virtual deformable sanding belt model of the contact-free wheel support part.
Further, the virtual deformable belt model of the contact-free wheel support part is constructed by the following steps:
(1) dispersing an abrasive belt area of a non-contact wheel supporting part into uniformly distributed quadrilateral grids, and establishing a grid spring mass point model according to the dispersed grid points;
(2) obtaining a tensile stress-strain relationship, a shear stress-strain relationship and a bending moment-curvature relationship of the abrasive belt according to a method for measuring the mechanical property of the fabric;
(3) respectively converting the tensile stress-strain relationship, the shear stress-strain relationship and the bending moment curvature relationship of the abrasive belt obtained by measurement into the stress-deformation relationship of a tension spring, a shear spring and a bending spring in a spring mass point model;
(4) measuring the initial tension of an abrasive belt in an actual abrasive belt machine, and setting the initial tension value of each tension spring in a spring mass point model according to the initial tension of the abrasive belt;
(5) and establishing a spring mass point model capable of simulating abrasive belt polishing stress deformation according to the initial tension and the stress deformation relation of the tension, shear and bending springs.
Furthermore, in the step (5), the stress deformation among the springs of the spring mass point model is nonlinear, and the relations of tensile stress strain, shear stress strain and bending moment curvature of the abrasive belt are integrated, so that the polishing stress deformation of the abrasive belt can be accurately simulated in real time.
Further, in step 4, the step of determining whether the virtual processing object collides with the contact wheel or the virtual deformable abrasive belt supported by the non-contact wheel is specifically implemented by using a collision detection algorithm, wherein the collision detection algorithm includes a hierarchical collision bounding box collision detection algorithm in a binary tree manner.
Further, in step 5, the collision types comprise a collision of a virtual processing object and a contact wheel, and a collision of the virtual processing object and a virtual deformable abrasive belt supported by a non-contact wheel; the calculation of the polishing feedback force comprises the calculation of the polishing force sense of the workpiece when the workpiece is polished at the contact wheel and the calculation of the polishing force sense of the workpiece when the workpiece is polished at the virtual deformable abrasive belt.
Further, the collision of the virtual processing object with the contact wheel is used for collision detection when a higher material removal rate is required to be obtained in polishing on an abrasive belt supported by the contact wheel; the collision between the virtual processing object and the virtual deformable abrasive belt is used for detecting the collision when the curvature of a workpiece is very large and the interference problem exists in the polishing of the contact wheel support position and the polishing is finished by the deformable elastic abrasive belt supported by the non-contact wheel.
Further, the polishing force calculation of the workpiece during polishing at the contact wheel is carried out according to the following steps:
(1) analyzing the stress of the workpiece during polishing at the contact wheel;
(2) obtaining the polishing normal force of the workpiece according to the Hertz contact theory and the Huke's law, and multiplying the normal force by a preset coefficient to obtain the polishing tangential force;
(3) and synthesizing the polishing normal force, the polishing tangential force and the gravity of the workpiece to obtain the polishing feedback force of the workpiece at the contact wheel.
Further, the polishing force perception calculation of the workpiece when polished at the virtual deformable abrasive belt is performed according to the following steps:
(1) multiplying the normal distance from the collision particles to the initial plane of the abrasive belt by a preset coefficient to obtain the polishing normal force of each collision particle;
(2) synthesizing the polishing normal forces of all the collision particles to obtain a normal force during workpiece polishing, and multiplying the normal force by a preset friction coefficient to obtain a friction force during workpiece polishing;
(3) and synthesizing the normal force and the friction force to obtain the polishing feedback force of the workpiece at the virtual deformable abrasive belt.
Compared with the prior art, the invention has the following advantages:
(1) the invention enables a user to finish teaching operation of a workpiece in a virtual environment, and can enable workers to be liberated from a severe and dangerous machining environment;
(2) according to the invention, through interaction of the force feedback equipment and the virtual scene, a user can freely control the virtual workpiece to polish and teach in any posture in a virtual environment, and a more natural and effective interactive programming mode is provided for the user;
(2) the virtual deformable abrasive belt model capable of accurately simulating abrasive belt polishing stress deformation in real time is established based on the spring particle model, the real mechanical physical attributes and the initial tension of the abrasive belt, and a user can operate the virtual workpiece to be in contact with the virtual deformable abrasive belt through force feedback equipment like manual polishing aiming at a workpiece area with large curvature and interference in polishing at a contact wheel, and the teaching and polishing of the workpiece are completed by utilizing the elastic deformation of the abrasive belt;
(3) the invention integrates the experience of manual polishing, and enables a user to dynamically adjust parameters such as the polishing force, the polishing attitude and the like of the workpiece under the guidance of the polishing feedback force according to the geometric information of the workpiece and the deformation of the abrasive belt so as to obtain an ideal polishing track.
Drawings
Fig. 1 is a flow chart of a virtual teaching method for robotic belt polishing based on force feedback according to the present invention.
FIG. 2a is a schematic diagram of a spring-mass model.
FIG. 2b is a schematic drawing of an extension spring of the spring mass model.
FIG. 2c is a schematic diagram of a spring showing a spring-mass model of a splice spring.
FIG. 2d is a schematic view of a bending spring of the spring mass model.
FIG. 3 is a schematic view of a force analysis of a workpiece polished at a contact wheel.
Fig. 4 is a schematic view of the contact state of a workpiece when polished at a virtual deformable abrasive belt.
Detailed Description
The practice of the present invention will be further illustrated by the following examples and drawings, but the practice and protection of the present invention is not limited thereto.
Fig. 1 is a flow chart of a virtual teaching method for abrasive belt polishing of a robot based on force feedback, which comprises the following steps:
step 1: and (3) building a virtual scene for polishing the abrasive belt of the robot by using the VC + + and OPENCASDE open source graphic engine, wherein the virtual scene comprises a virtual processing tool, a virtual processing object and a virtual environment. Firstly, three-dimensional modeling of virtual machining tools such as robots, abrasive belt machines, workpiece clamps and the like is completed through modeling software such as SolidWorks, ProE and the like, and the three-dimensional modeling is exported to be a corresponding STL file; then, in order to obtain a virtual processing object, the present embodiment scans a workpiece object to be polished by using a laser scanner, so as to obtain an STL model of the virtual processing object; and finally reading the STL file of the corresponding model through an API (application programming interface) provided by OPENCASDE (open computer architecture), and setting the position, size, color and illumination of the model to complete the construction of the virtual scene.
Step 2: in order to perform virtual polishing teaching on a workpiece area with large curvature and interference in polishing at a contact wheel in a virtual teaching process, a virtual deformable abrasive belt model capable of accurately simulating a support position of a non-contact wheel in real time needs to be established so as to complete virtual teaching on the large curvature area of the workpiece in a virtual scene by using elastic deformation of an abrasive belt, wherein the virtual deformable abrasive belt model is established in the following process:
(1) dispersing the abrasive belt area of the non-contact wheel supporting part into uniformly distributed quadrilateral grids, and establishing a grid spring mass point model according to the dispersed grid points, wherein the spring mass point model can be seen as being composed of an extension spring resisting tensile deformation, a splicing spring resisting shear deformation and a bending spring resisting bending deformation as shown in FIGS. 2 a-2 b; the spring force of each mass point can be obtained by the following formula:
Figure BDA0001557659540000091
wherein, FLIs the spring force experienced by the ith mass point,/ijIs the vector of dot i to adjacent dot j, KmIs the spring rate, rijIs the original length of the spring;
(2) according to the stress formula of the mass points in the spring mass point model, the mechanical behavior of each spring is linear, and the stress deformation of the abrasive belt during polishing is nonlinear, so that if the mechanical properties of the abrasive belt, such as stretching, shearing, bending and the like, are simulated by using a pure linear spring mass point model, the stress deformation of the abrasive belt during polishing cannot be accurately simulated, and in order to make up for the defects of the spring mass point model, the mechanical and physical properties of the abrasive belt, including a tensile stress-strain curve, a shearing stress-strain curve and a bending moment curvature curve of the abrasive belt in a bending state, are obtained according to a fabric mechanical property measurement method, wherein the fabric mechanical and physical properties are obtained by using a KES fabric mechanical property measurement instrument;
(3) and then respectively converting the tensile stress-strain curve, the shear stress-strain curve and the bending moment curvature curve of the abrasive belt obtained by measurement into stress-deformation curves of an extension spring, a shear spring and a bending spring in a spring mass point model, wherein the tensile stress-strain relation of the abrasive belt is converted into the tensile force-deformation relation of the extension spring by adopting the following formula:
Figure BDA0001557659540000092
Figure BDA0001557659540000093
wherein σKES_SMeasuring the tensile stress of the unit width of the sand belt in the KES; epsilonSIs at sigmaKES_SStrain per unit length direction under the action of (2); fSThe stress of each extension spring in the spring mass point model is measured; deltaSIs at FSUnder the action, the deformation of the spring is stretched; l is the side length of the square abrasive belt sample when the KES is used for testing; n is the node number of the spring mass point within the range of the length of the sample; according to the conversion formula, the tensile stress-strain relationship of the abrasive belt can be converted into the relationship between the tensile force and the deformation of each tensile spring in a spring mass point model; similarly, the shearing stress-strain relationship of the abrasive belt can be converted into the relationship between the shearing force and the deformation of each shearing spring by using the following formula;
Figure BDA0001557659540000101
Figure BDA0001557659540000102
wherein σKES_SHMeasuring the shear stress of the unit width of the sand belt in the KES; epsilonSHIs at sigmaKES_SHStrain per unit length direction under the action of (2); fSHThe stress of each shear spring in the spring mass point model is measured; deltaSIs at FSHShearing the deformation of the spring under the action of the elastic force; similarly, the bending moment-curvature relation of the abrasive belt can be converted into the stress deformation relation of each bending spring by using the following formula;
Figure BDA0001557659540000103
Figure BDA0001557659540000104
wherein M isKEs_BAnd K is the bending moment and curvature of the abrasive belt per unit width when the abrasive belt is bent, obtained by KES test, FBAnd ΔBThe stress and deformation of each bending spring;
(4) measuring actual abrasive beltBelt tensioning force F in machineTSetting an initial tension value of each tension spring in the spring mass point model according to the following formula;
Figure BDA0001557659540000105
wherein, FS_0The initial tension of each extension spring in the spring mass point model; n is the number of spring mass point nodes bearing the tension;
(5) and establishing a spring mass point model representing the abrasive belt according to the stress deformation curves of the extension spring, the shearing spring and the bending spring, so as to obtain a virtual deformable abrasive belt model capable of accurately simulating abrasive belt polishing stress deformation in real time.
And step 3: after the virtual deformable sanding belt model was constructed, the embodiment adopted Phantom of Sensable corporation, USA
Figure BDA0001557659540000111
As a force feedback device, a position input of 6 degrees of freedom and a force sense output of 3 degrees of freedom can be provided; firstly, connecting a force feedback device with a virtual workpiece in a virtual scene through an interface, and establishing a coordinate mapping relation between the virtual workpiece and the tail end of the force feedback device to enable the motion of the virtual workpiece in the virtual scene to the motion of the tail end of the stress feedback device; meanwhile, the posture and the movement speed of the virtual workpiece in the virtual environment are read and updated in real time.
And 4, step 4: the user holds Phantom with hand
Figure BDA0001557659540000112
And the tail end of the force feedback equipment selects a workpiece polishing mode according to the geometric information of the workpiece like manual polishing of the workpiece: for the area of the workpiece with large curvature and interference in polishing at the contact wheel, the operation workpiece is at the virtual deformable abrasive belt, teaching polishing is carried out by using elastic deformation of the abrasive belt, and for the area of the workpiece needing to obtain higher material removal rate, the operation workpiece is in contact with the contact wheel to carry out teaching polishing. During the virtual teaching process, the collision detection calculation is carried outAnd (5) judging whether the virtual workpiece collides with the contact wheel or the deformable abrasive belt at the support part without the contact wheel, if so, executing the step.
And 5: when the collision of the virtual workpiece and the contact wheel or the deformable abrasive belt is detected, recording the posture and the movement speed of the workpiece in a virtual scene, calculating the polishing force according to the collision type, and simultaneously feeding back the calculated polishing force to a user through a force feedback device, wherein when the collision of the virtual workpiece and the contact wheel is detected, the polishing feedback force of the workpiece at the contact wheel is calculated according to the following processes:
as shown in fig. 3, the workpiece and the contact wheel are in polishing contact at the point O, and the stress analysis of the workpiece shows that: during polishing, the workpiece is subjected to a gravitational force FgPolishing normal force FnPolishing tangential force Ft(ii) a The polishing normal force is proportional to the amount of deflection of the contact wheel according to Hertz's theory of contact and Hooke's law, and
Figure BDA0001557659540000121
wherein δ is the amount of deformation of the contact wheel, approximately equal to the maximum depth of collision of the virtual workpiece with the contact wheel; l is the collision contact length of the virtual workpiece and the contact wheel;
Figure BDA0001557659540000122
is the relative modulus of elasticity of the workpiece and the contact wheel, wherein E1、E2Modulus of elasticity, v, of the workpiece and of the contact wheel, respectively1、v2The Poisson ratio of the workpiece to the contact wheel; f can be obtained according to the proportional relation between the tangential force and the normal force of the abrasive belt polishingt＝κ1Fn(ii) a And finally, synthesizing the normal force, the tangential force and the gravity to obtain a polishing feedback force:
Figure BDA0001557659540000123
wherein, FuFeeding back force for polishing; theta is an included angle between the polishing normal force and a horizontal plane where the polishing contact point is located;
when the virtual workpiece is detected to collide with the virtual deformable abrasive belt, calculating the polishing feedback force of the workpiece at the virtual deformable abrasive belt according to the following process:
as shown in FIG. 4, the polishing contact state of the workpiece and the virtual deformable abrasive belt is shown, and mass points 1, 2, 3 and 4 are spring mass points colliding with the virtual workpiece, at this time, the polishing feedback force of the workpiece is mainly formed by the contact normal force F of the abrasive belt and the workpiecenFriction force F between work and abrasive belttAnd (4) forming. For normal force FnCan be represented by formula
Figure BDA0001557659540000124
Obtaining n, wherein n is the number of particles colliding with the virtual workpiece; x is the number ofiThe distance between the collision mass point and the initial plane of the abrasive belt along the normal direction of the collision point of the workpiece,
Figure BDA0001557659540000125
is a unit normal vector of the workpiece at the collision mass point; the friction force for the workpiece can be represented by Ft＝μ·FnAnd (4) obtaining.
Step 6: under the guidance of the real-time polishing feedback force, a user dynamically adjusts parameters such as the polishing position, angle, force and the like of the virtual workpiece according to the geometric information of the workpiece so as to obtain a better polishing track; when the virtual deformable abrasive belt is polished, the deformation of the abrasive belt can be adjusted in real time to adapt to the polishing of different curvatures of the workpiece.
And 7: and finally, generating a polishing track of the virtual workpiece according to the posture and the motion speed of the virtual workpiece in the virtual scene, and converting the polishing track into a robot code to realize automatic polishing.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (9)

1. A robot abrasive belt polishing virtual teaching method based on force feedback is characterized by comprising the following steps:
step 1: building a virtual scene, wherein the virtual scene comprises a virtual machining tool, a virtual machining object and a virtual environment;
step 2: constructing a virtual deformable abrasive belt model based on the spring mass point model, the mechanical and physical properties of the abrasive belt and the initial tension of the abrasive belt; the spring mass point model adopts a square spring mass point model; the mechanical and physical properties of the abrasive belt comprise a tensile stress-strain relation, a shear stress-strain relation and a bending moment-curvature relation when the abrasive belt is bent; the virtual deformable abrasive belt model refers to a virtual deformable abrasive belt model of a non-contact wheel supporting part;
and step 3: binding the virtual processing object with the force feedback equipment, establishing a mapping relation between a terminal coordinate system of the force feedback equipment and a virtual processing object coordinate system, enabling the motion of the virtual processing object in a virtual scene to the motion of the terminal of the stress feedback equipment, and reading and updating the posture and the motion speed of the virtual processing object in a virtual environment in real time;
and 4, step 4: the handheld force feedback equipment operates the virtual processing object to carry out polishing in a virtual scene like manual polishing, judges whether the virtual processing object collides with a contact wheel or a virtual deformable abrasive belt supported by the contact wheel, and executes the step 5 if the virtual processing object collides with the contact wheel or the virtual deformable abrasive belt supported by the contact wheel;
and 5: recording the posture and the movement speed of the virtual processing object in the virtual scene, calculating the polishing force according to the collision type, and simultaneously feeding back the calculated polishing force to a user through force feedback equipment;
step 6: dynamically adjusting polishing parameters of the virtual processing object under the guidance of polishing feedback force according to the geometric information of the workpiece and the deformation of the abrasive belt, wherein the polishing parameters comprise force and attitude parameters;
and 7: and generating a polishing track of the virtual processing object according to the posture and the motion speed of the virtual processing object in the virtual scene, and converting the polishing track into a robot code to realize automatic polishing.
2. The virtual teaching method for robot belt polishing based on force feedback as claimed in claim 1, wherein: in the step 1, the virtual scene is a virtual teaching scene for robot abrasive belt polishing; the virtual machining tool comprises a virtual robot, a virtual abrasive belt machine and a virtual workpiece clamp; the virtual processing object refers to a workpiece needing virtual teaching; the virtual environment refers to illumination, background and color of a virtual scene; the virtual workpiece clamp is used for clamping a virtual machining object and is arranged at the tail end of the robot.
3. The virtual teaching method for robot belt polishing based on force feedback as claimed in claim 2, characterized in that: the virtual deformable abrasive belt model of the contact-free wheel supporting part is constructed by the following steps:
(1) dispersing an abrasive belt area of a non-contact wheel supporting part into uniformly distributed quadrilateral grids, and establishing a grid spring mass point model according to the dispersed grid points;
(2) obtaining a tensile stress-strain relationship, a shear stress-strain relationship and a bending moment-curvature relationship of the abrasive belt according to a method for measuring the mechanical property of the fabric;
(3) respectively converting the tensile stress-strain relationship, the shear stress-strain relationship and the bending moment curvature relationship of the abrasive belt obtained by measurement into the stress-deformation relationship of a tension spring, a shear spring and a bending spring in a spring mass point model;
(4) measuring the initial tension of an abrasive belt in an actual abrasive belt machine, and setting the initial tension value of each tension spring in a spring mass point model according to the initial tension of the abrasive belt;
(5) and establishing a spring mass point model capable of simulating abrasive belt polishing stress deformation according to the initial tension and the stress deformation relation of the tension, shear and bending springs.
4. The virtual teaching method for robot belt polishing based on force feedback as claimed in claim 3, characterized in that: in the step (5), the stress deformation among the springs of the spring mass point model is nonlinear, the relation among the tensile stress strain, the shearing stress strain and the bending moment curvature of the abrasive belt is integrated, and the polishing stress deformation of the abrasive belt can be accurately simulated in real time.
5. The virtual teaching method for robot belt polishing based on force feedback as claimed in claim 1, wherein: in step 4, the step of judging whether the virtual processing object collides with the contact wheel or the virtual deformable abrasive belt supported by the non-contact wheel is specifically realized by adopting a collision detection algorithm, wherein the collision detection algorithm comprises a hierarchical collision bounding box collision detection algorithm in a binary tree mode.
6. The virtual teaching method for robot belt polishing based on force feedback as claimed in claim 1, wherein: in step 5, the collision types comprise the collision of a virtual processing object and a contact wheel and the collision of the virtual processing object and a virtual deformable abrasive belt supported by the non-contact wheel; the calculation of the polishing feedback force comprises the calculation of the polishing force sense of the workpiece when the workpiece is polished at the contact wheel and the calculation of the polishing force sense of the workpiece when the workpiece is polished at the virtual deformable abrasive belt.
7. The virtual teaching method for robot belt polishing based on force feedback as claimed in claim 6, wherein: the collision of the virtual processing object and the contact wheel is used for collision detection when a higher material removal rate is required to be obtained during polishing on an abrasive belt supported by the contact wheel; the collision between the virtual processing object and the virtual deformable abrasive belt is used for detecting the collision when the curvature of a workpiece is very large and the interference problem exists in the polishing of the contact wheel support position and the polishing is finished by the deformable elastic abrasive belt supported by the non-contact wheel.
8. The virtual teaching method for robot belt polishing based on force feedback as claimed in claim 6, wherein: the polishing force sense calculation of the workpiece during polishing at the contact wheel is carried out according to the following steps:
(1) analyzing the stress of the workpiece during polishing at the contact wheel;
(2) obtaining the polishing normal force of the workpiece according to the Hertz contact theory and the Huke's law, and multiplying the normal force by a preset coefficient to obtain the polishing tangential force;
(3) and synthesizing the polishing normal force, the polishing tangential force and the gravity of the workpiece to obtain the polishing feedback force of the workpiece at the contact wheel.
9. The virtual teaching method for robot belt polishing based on force feedback as claimed in claim 6, wherein: the polishing force sense calculation of the workpiece during polishing at the virtual deformable abrasive belt is carried out according to the following steps:
(1) multiplying the normal distance from the collision particles to the initial plane of the abrasive belt by a preset coefficient to obtain the polishing normal force of each collision particle;
(2) synthesizing the polishing normal forces of all the collision particles to obtain a normal force during workpiece polishing, and multiplying the normal force by a preset friction coefficient to obtain a friction force during workpiece polishing;
(3) and synthesizing the normal force and the friction force to obtain the polishing feedback force of the workpiece at the virtual deformable abrasive belt.
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