CN113714789B - Screw tightening device based on visual positioning and control method - Google Patents

Abstract

The invention discloses a screw tightening device based on visual positioning and a control method, wherein the device comprises the following components: the device comprises a robot, a control system, a feeding mechanism, a vision measuring module and a tightening tool, wherein the control system is respectively in communication connection with the robot and the tightening tool, the feeding mechanism comprises a frame, a conveyor belt, a material tray, a material baffle, a blocking cylinder, a clamping cylinder and a photoelectric sensor, the conveyor belt is arranged on the frame, the material tray is arranged on the conveyor belt, the material baffle is arranged on two sides of the conveyor belt, the blocking cylinder and the clamping cylinder are arranged on the same side of the material baffle, and the photoelectric sensor is arranged on the opposite side of the blocking cylinder; the vision measurement module is installed in the frame, and the tightening tool is installed on the flange of the sixth axis of the robot, and the vision measurement module is located the top of tightening the operation area. The invention can rapidly position a plurality of bolt positions, and can program and control the tightening torque, thereby improving the screw tightening control precision and enabling the screw connection to achieve the expected tightening effect.

Description

Screw tightening device and control method based on vision positioning

technical field

The invention relates to the technical field of thread tightening assembly, in particular to a visual positioning-based thread tightening device and a control method.

Background technique

At present, most production enterprises still use hand-held electric or pneumatic tools to assemble threaded fasteners, or use special locking screw machines to realize semi-automatic screw tightening functions, and a small number of them use fixtures + robots to fasten threads Assembling the parts, that is, preliminarily positioning the workpiece to be assembled through the fixture, and then using the robot equipped with tightening tools to control the trajectory and positioning through teaching and learning, and complete the screw assembly and tightening process, such as Xiao Hai’s "Robot Bolt Tightening" In the article "Application of Technology in Engine Assembly", first insert the guide pin in the jacking mechanism into the corresponding positioning hole of the engine tray, so as to realize the positioning of the engine; Horizontal plane, and finally set the planning robot path program to realize the positioning and tightening of the target bolts. In addition, there are still a few who use machine vision + robots to connect threaded fasteners, that is, realize the positioning of bolts through vision, and then guide the robot to carry out tightening tools to thread the fasteners, such as Tong Zhen's " Research on the key technology of screw lock and SCARA robot based on machine vision" In the article, the vision system and the tightening tool can be installed at the end of the SCARA robot at the same time by designing the fixture, and the trajectory of the robot is designed and planned to take pictures of the threaded holes in different positions. Finally, guide the robot to thread and assemble the LED panel light products.

With the continuous increase of labor costs, the production cost of thread assembly of fasteners using hand-held tools is high, and the tightening accuracy is greatly affected by human factors; the use of special locking screw machine equipment generally cannot flexibly adjust the tightening position, nor can it be adjusted according to It is necessary to flexibly set or change the tightening torque to obtain higher tightening control precision; the use of robot teaching method to thread assembly of fasteners has the disadvantages of complex design of fixtures and high requirements for repeatable positioning accuracy of robots, and adjustment flexibility Poor; the use of SCARA robot vision positioning guidance for thread tightening is only allowed to carry small light-weight tightening tools, and the tightening operations should generally be distributed on a plane, which cannot meet the requirements of multi-directional or attitude thread assembly.

At the same time, during the tightening process of the robot, it is generally equipped with a tightening tool commonly used on the market - an electric screwdriver. Generally, it can only set a certain upper limit torque threshold, and stop rotating when the torque threshold is reached. On the one hand, the torque control accuracy is very low. On the other hand, it is not possible to set different tightening torque values for different threaded fasteners, and plan a more appropriate tightening process to obtain the best assembly effect. At the same time, such tightening tools generally do not have a tightening process data feedback function, and cannot directly judge and warn of abnormalities in the tightening process, nor can further traceability, processing and storage of tightening data.

Contents of the invention

The main purpose of the present invention is to propose a thread tightening device and control method based on visual positioning, aiming at adapting to various thread assembly positions and flexibly setting tightening torque, improving the control precision of thread tightening, and obtaining better assembly and tightening effects.

In order to achieve the above object, the present invention provides a visual positioning-based screw tightening device, including: a robot, a control system, a feeding mechanism for delivering the modules to be tightened, and a visual system for taking pictures of the modules to be tightened. A measurement module and a tightening tool for tightening the module to be tightened according to the shooting results of the visual measurement module, wherein the control system is connected to the robot and the tightening tool in communication, and the feeding mechanism includes a rack , conveyor belt, material tray, material baffle, blocking cylinder, clamping cylinder and photoelectric sensor, the conveyor belt is installed on the frame, the material tray is placed on the conveyor belt, and the material baffle is installed on the The two sides of the conveyor belt, the blocking cylinder and the clamping cylinder are installed on the same side of the material baffle, and are arranged in sequence along the running direction of the conveyor belt, and the photoelectric sensor is installed on the opposite side of the blocking cylinder , located slightly behind the running direction of the conveyor belt; the visual measurement module is installed on the frame, the tightening tool is installed on the robot, and the visual measurement module is located in the tightening work area above.

A further technical solution of the present invention is that the tightening tool includes a tightening shaft connected to the robot, a tightening shaft controller connected to the tightening shaft, the tightening shaft controller is located at the end position of the tightening shaft, and The tightening shafts are connected.

The further technical solution of the present invention is that the screwing shaft includes a screwing bit, an end cover, a coupling, a torque sensor, a reducer, a servo motor and an encoder, wherein the end cover is installed on the front end of the screwing shaft , the couplings are respectively installed between the end cover and the torque sensor, the torque sensor and the reducer, the reducer is connected to the servo motor, and the encoder is installed on the end of the servo motor.

A further technical solution of the present invention is that the visual measurement module includes a visual measurement component and a mounting bracket, the top of the mounting bracket is L-shaped, the bottom of the mounting bracket is installed on the frame, and the visual measurement component It is installed on the top of the mounting bracket through an L-shaped mounting plate.

A further technical solution of the present invention is that the vision component includes a camera, an optical lens and a ring light source arranged coaxially in sequence from top to bottom, wherein the camera is mounted on the L-shaped mounting plate through a camera mounting plate, so The optical lens is screwed to the C interface of the camera, and the ring light source is installed on the L-shaped mounting plate through the ring light source mounting plate.

A further technical solution of the present invention is that the tray includes a support plate and uprights symmetrically installed at both ends of the bottom of the support plate.

A further technical solution of the present invention is that the module to be tightened includes a motor to be screwed, a mounting plate of the motor to be screwed, and mounting bolts, and there are multiple connecting bolts on the motor to be screwed that need to be tightened.

A further technical solution of the present invention is that the control system includes a computer, a switch, a robot control cabinet, and a teaching pendant, wherein the switch is connected to the vision measurement module, the robot control cabinet, and the computer respectively, and the robot control cabinet Connect with the robot.

In order to achieve the above object, the present invention also proposes a visual positioning-based screw tightening device control method, the method is applied to the above-mentioned visual positioning-based screw tightening device, the method includes the following steps:

When the photoelectric sensor detects the tray, the blocking cylinder performs blocking processing on the tray, the clamping cylinder performs clamping processing on the tray, and sends a clamping signal to the Computers in the control system;

The computer in the control system controls the visual measurement module to take pictures and locate the module to be tightened according to the clamping signal, and sends the position information of the bolt on the module to be tightened to the robot;

The robot drives the tightening tool to tighten the bolts, and sends the tightening information to the computer in the control system;

The computer in the control system draws the tightening process curve according to the tightening information, and displays and stores the tightening results.

A further technical solution of the present invention is that the computer in the control system draws the tightening process curve according to the tightening information, and after the step of displaying and storing the tightening result, it also includes:

The computer in the control system judges whether the expected tightening requirements are met according to the tightening information;

If the expected tightening requirements are met, the computer in the control system will count the number of bolts that have been tightened to determine whether to complete the tightening tasks of all the bolts to be tightened this time. If the tightening tasks of all the bolts have been completed, the robot Then carry out the movement of returning to the zero point, the camera measurement module stops taking pictures, and the process ends;

If the expected tightening requirements are not met, judge whether there is a thread tightening defect;

If there is no tightening defect, the computer in the control system controls the tightening tool to realize secondary tightening process to the bolt;

If there is a thread tightening defect, the computer in the control system will display and record the abnormal tightening information.

The beneficial effects of the screw tightening device and method based on visual positioning of the present invention are:

1. Aiming at the problems of high production cost and high influence of human factors on the tightening accuracy of hand-held tightening tools, this invention adopts the method of fastening the bolts with the robot equipped with tightening tools, which is conducive to improving production efficiency and reducing production costs. Improve the automation of thread assembly;

2. In view of the problem that the tightening position cannot be adjusted flexibly during the assembly of the special locking screw machine equipment and the robot teaching method, and the tightening torque cannot be flexibly set or changed according to the needs. And it can accurately set different torque target values, which can obtain higher tightening control accuracy and strong versatility;;

3. Aiming at the problem of SCARA robot tightening assembly orientation and load limitations, the present invention adopts a six-axis industrial robot + vision scheme that matches the load, which solves the limitation of the robot’s activity space due to the robot’s degree of freedom and the robot’s assembly overload problem;

4. Aiming at the problems that the ordinary electric screwdriver carried by the robot cannot set different tightening processes according to different threaded fasteners in the tightening process, the torque control accuracy is low, and there is no data feedback function in the tightening process, the present invention adopts a torque closed-loop control function. Tighten the tool and set the corresponding tightening process according to the material characteristics of different bolts and fasteners according to the torque control-rotation angle monitoring method, so as to achieve a better control effect. At the same time, use the upper software in the computer to communicate with the tightening tool. Real-time collection of tightening data and drawing of tightening curves are beneficial to the analysis of the tightening process and the judgment of the tightening results, and further storage of the tightening process data facilitates the traceability and tracking of assembly data.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings according to the structures shown in these drawings without creative effort.

Fig. 1 is the system composition diagram of the preferred embodiment of the screw tightening device based on vision positioning of the present invention;

Fig. 2 is a schematic structural view of a conveyor belt and a module to be tightened in a preferred embodiment of the visual positioning-based screw tightening device of the present invention;

Fig. 3 is a schematic diagram of the overall structure of the tightening tool;

Fig. 4 is a schematic diagram of the overall structure of another angle of the tightening tool;

Fig. 5 is a schematic diagram of the overall structure of another angle of the tightening tool;

Fig. 6 is a structural schematic diagram of a tightening tool;

Fig. 7 is a schematic structural diagram of a visual measurement module;

Fig. 8 is a schematic flow chart of the control method of the screw tightening device based on visual positioning in the present invention;

Fig. 9 is a schematic diagram of an image processing flow;

Fig. 10 is a schematic diagram of tightening torque-time model;

Figure 11 is a torque-angle-time diagram of the tightening process;

Figure 12 is a partial enlarged view of torque-angle-time in the tightening process;

Fig. 13 is a computer tightening curve interface diagram.

Explanation of reference numbers:

Robot 1; module to be tightened 2; visual measurement module 3; tightening tool 4; frame 5; conveyor belt 6; material tray 7; material baffle 8; blocking cylinder 9; clamping cylinder 10; Screwed motor mounting plate 13; computer 14; switch 15; robot control cabinet 16; teach pendant 17; air pump 18; support plate 19; Cover 24; coupling 25; torque sensor 26; reducer 27; servo motor 28; encoder 29; mounting bracket 30; L-shaped mounting plate 31; camera 32; optical lens 33; ring light source 34; camera mounting plate 35; The ring light source mounting plate 36.

The realization, functional characteristics and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts all belong to the protection scope of the present invention.

It should be noted that if there are directional indications (such as up, down, left, right, front, back...) in the embodiment of the present invention, the directional indications are only used to explain the position in a certain posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

In addition, if there are descriptions involving "first", "second" and so on in the embodiments of the present invention, the descriptions of "first", "second" and so on are only for descriptive purposes and should not be interpreted as indicating or implying Its relative importance or implicitly indicates the number of technical features indicated. Thus, features defined as "first" and "second" may explicitly or implicitly include at least one of these features. In addition, the meaning of "and/or" appearing throughout the text includes three parallel schemes, taking "A and/or B" as an example, including scheme A, scheme B, or schemes that both A and B satisfy. In addition, the technical solutions of the various embodiments can be combined with each other, but it must be based on the realization of those skilled in the art. When the combination of technical solutions is contradictory or cannot be realized, it should be considered that the combination of technical solutions does not exist , nor within the scope of protection required by the present invention.

In order to solve the technical problems existing in the prior art, the present invention proposes a thread tightening device based on vision positioning, which uses a vision measurement module to provide the robot with the exact position of the thread to be assembled on the screwed object, thereby guiding the robot to move to the appropriate position. Position and attitude, use the tightening tool to realize the tightening process of the screw by using the torque closed-loop control and angle monitoring method, so as to achieve the purpose of controlling the axial pretightening force of the threaded connection within an appropriate range. Draw the torque-rotation angle-time curve according to the data generated during the tightening process, so as to further analyze and judge the bolt tightening results and ensure that the bolt assembly quality meets the expected requirements. At the same time, using the host software and communication functions, the computer further stores and records the tightening process data, which is convenient for subsequent viewing of the tightening process data and the traceability of problems.

As shown in Figures 1 to 7, the preferred embodiment of the screw tightening device based on visual positioning of the present invention includes: a robot 1, a control system, a feeding mechanism for delivering the module 2 to be tightened, and a camera for the module 2 to be tightened The positioned visual measurement module 3, the tightening tool 4 for tightening the tightening module 2 according to the shooting results of the visual measurement module 3, wherein the control system is connected to the robot 1 and the tightening tool 4 respectively, and the feeding mechanism includes a frame 5. Conveyor belt 6, material tray 7, material baffle 8, blocking cylinder 9, clamping cylinder 10 and photoelectric sensor 11, conveyor belt 6 is installed on frame 5, material tray 7 is placed on conveyor belt 6, material baffle 8 is installed On both sides of the conveyor belt 6, the blocking cylinder 9 and the clamping cylinder 10 are installed on the same side of the material baffle 8, and arranged in sequence along the running direction of the conveyor belt 6. The photoelectric sensor 11 is installed on the opposite side of the blocking cylinder 9, located on the conveyor belt 6 slightly behind the running direction; the visual measurement module 3 is installed on the frame 5, the tightening tool 4 is installed on the robot 1, and the visual measurement module 3 is located above the tightening work area.

Wherein, the module 2 to be tightened may include a screwed motor 12, a screwed motor mounting plate 13 and a plurality of tightening bolts. Control system comprises computer 14, switchboard 15, robot control cabinet 16, teaching pendant 17, wherein, switchboard 15 is connected with visual measurement module 3, robot control cabinet 16, computer 14 respectively, and robot control cabinet 16 is connected with robot 1.

As an implementation, this embodiment also includes an air pump 18, which is connected to the blocking cylinder 9 and the clamping cylinder 10 respectively.

Specifically, the Vision Gige protocol in Ethernet is used for communication between the computer 14 and the visual measurement module 3, and the TCP/IP protocol in Ethernet is used for communication between the robot 1 and the computer 14. The tightening tool 4 Use specific protocol to carry out serial communication with computer 14.

Described charging tray 7 comprises charging tray support plate 19 and the upright column 20 that is symmetrically installed in described support plate 19 bottom two ends. The material tray 7 is mainly used for consignment of the module 2 to be tightened, that is, the screwed motor 12, the screwed motor mounting plate 13 and the mounting bolts.

In this embodiment, the material baffles 8 are installed on both sides of the conveyor belt 6, and play the role of guiding and blocking the material tray 7; Function; the clamping cylinder 10 is installed at a suitable position behind the blocking cylinder 9, mainly to clamp the material tray 7; the photoelectric sensor 11 is installed on the opposite side of the blocking cylinder 9, and is slightly closer to the running direction of the conveyor belt 6. After the appropriate position, it mainly plays a role in detecting the material tray 7, and judging whether there is material passing through.

In this embodiment, the visual measurement module 3 can be used to take pictures of target bolts of different specifications and sizes in a complex environment, and the deviation of the bolt relative to the visual origin can be known by combining the visual origin and the reference point of the tightening position of the robot 1 being the same point on the product. The displacement is equal to the offset of the bolt relative to the reference point of the tightening position of the robot 1, so as to realize the precise positioning of the target bolt, and then guide the robot 1 to quickly tighten the corresponding bolt with the tightening tool 4. At the same time, the control system The computer draws the tightening process curve and displays the tightening results according to the tightening data sent by the tightening tool 4. If necessary, the tightening tool 4 is triggered to repeat the tightening work so as to achieve the expected tightening target. At the same time, the tightening process data is further stored and recorded for convenience. Check the tightening process data and trace the source of the problem later.

Further, in this embodiment, the tightening tool 4 includes a tightening shaft 21 connected to the robot 1, a tightening shaft controller 22 connected to the tightening shaft 21, the tightening shaft controller 22 is located at the end position of the tightening shaft 21, and connected to the tightening shaft 21 connected.

The tightening shaft 21 includes a tightening bit 23, an end cap 24, a shaft coupling 25, a torque sensor 26, a reducer 27, a servo motor 28 and an encoder 29, wherein the end cap 24 is installed on the front end of the tightening shaft 21, and the shaft coupling 25 are respectively installed between the end cover 24 and the torque sensor 26, the torque sensor 26 and the reducer 27, the reducer 27 is connected with the servo motor 28, and the encoder 29 is installed at the end of the servo motor.

In this embodiment, the tightening shaft 21 control driver of the tightening tool 4 is installed at the end of the tightening shaft 21 and is connected with the tightening shaft 21, mainly playing the role of driving control and signal transmission for the tightening shaft 21.

In this embodiment, the visual measurement module 3 mainly obtains the accurate position of the target bolt by taking pictures of the screwed motor 12 and the supporting fastening device.

This visual measuring module 3 comprises visual measuring assembly and mounting bracket 30, and the top of mounting bracket 30 is L-shaped, and the bottom of mounting bracket 30 is installed on the frame 5, and visual measuring assembly is installed on the mounting bracket 30 by L-shaped mounting plate 31 top.

Wherein, the visual assembly includes a camera 32, an optical lens 33 and a ring light source 34 coaxially arranged in sequence from top to bottom, wherein the camera 32 is installed on the L-shaped mounting plate 31 by a camera mounting plate 35, and the optical lens 33 and the camera 32 The C interface is threaded, and the ring light source 34 is installed on the L-shaped mounting plate 31 through the ring light source mounting plate 36 .

The overall working process of the screw tightening device based on visual positioning of the present invention is:

After the system starts running, use the photoelectric sensor 11 installed on the conveyor belt 6 and under the field of view of the camera 32 to detect the tray 7 carrying the screwed motor 12 and the supporting fastening device. When the tray 7 triggers the photoelectric sensor 11, Block the action of the cylinder 9 and stretch out to block the material tray 7, stop the conveyor belt 6 and trigger the action of the clamping cylinder 10, and clamp the material tray 7. At this time, there are 32 pairs of cameras installed on the side bracket of the conveyor belt 6. The screwed motor 12 below the camera 32, the screwed motor mounting plate and the mounting bolts are photographed, and the result after taking pictures is the distance between the screwed motor and the screwed motor mounting plate with respect to the visual origin of the fastening bolts. The offset is transmitted to the computer in the control system. After receiving the offset of the tightening bolt of the tightened motor relative to the origin of vision, the computer in the control system will use the TCP/IP protocol to transfer the tightening bolt of the tightened motor relative to the The offset of the visual origin is sent to robot 1, and then robot 1 moves to the position of the corresponding bolt with tightening tool 4 for tightening processing, and sends the tightening data to the control system through serial communication, and finally the control system draws Tighten the curve and display the results, and at the same time perform secondary tightening or move to the next bolt position for tightening processing according to the tightening results, until all the bolts to be tightened are tightened, the device exits the control process and enters the waiting execution state.

The beneficial effects of the screw tightening device based on visual positioning of the present invention are:

1. Aiming at the problems of high production cost and high influence of human factors on the tightening accuracy of hand-held tightening tools, this invention adopts the method of fastening the bolts with the robot equipped with tightening tools, which is conducive to improving production efficiency and reducing production costs. Improve the automation of thread assembly;

2. In view of the problem that the tightening position cannot be adjusted flexibly during the assembly of the special locking screw machine equipment and the robot teaching method, and the tightening torque cannot be flexibly set or changed according to the needs. And it can accurately set different torque target values, which can obtain higher tightening control accuracy and strong versatility;;

3. Aiming at the problem of SCARA robot tightening assembly orientation and load limitations, the present invention adopts a six-axis industrial robot + vision scheme that matches the load, which solves the limitation of the robot’s activity space due to the robot’s degree of freedom and the robot’s assembly overload problem;

4. Aiming at the problems that the ordinary electric screwdriver carried by the robot cannot set different tightening processes according to different threaded fasteners in the tightening process, the torque control accuracy is low, and there is no data feedback function in the tightening process, the present invention adopts a torque closed-loop control function. Tighten the tool and set the corresponding tightening process according to the material characteristics of different bolts and fasteners according to the torque control-rotation angle monitoring method, so as to achieve a better control effect. At the same time, use the upper software in the computer to communicate with the tightening tool. Real-time collection of tightening data and drawing of tightening curves are beneficial to the analysis of the tightening process and the judgment of the tightening results, and further storage of the tightening process data facilitates the traceability and tracking of assembly data.

In order to achieve the above object, the present invention also proposes a visual positioning-based screw tightening device control method, the method is applied to the above-mentioned visual positioning-based screw tightening device, the method includes the following steps:

When the photoelectric sensor detects the tray, the blocking cylinder performs blocking processing on the tray, the clamping cylinder performs clamping processing on the tray, and sends a clamping signal to the Computers in the control system;

The computer in the control system controls the visual measurement module to take pictures and locate the module to be tightened according to the clamping signal, and sends the position information of the module to be tightened to the robot;

The robot drives the tightening tool to tighten the bolts, and sends the tightening information to the computer in the control system;

The computer in the control system draws the tightening process curve according to the tightening information, and displays and stores the tightening results.

Further, the computer in the control system draws the tightening process curve according to the tightening information, and after the step of displaying and storing the tightening results, it also includes:

The computer in the control system judges whether the expected tightening requirements are met according to the tightening information;

If the expected tightening requirements are met, the computer in the control system will count the number of bolts that have been tightened to determine whether all the bolt tightening tasks have been completed. If all the bolt tightening tasks have been completed, the robot will return Zero point movement, the camera measurement module stops taking pictures, and the process ends;

If the expected tightening requirements are not met, judge whether there is a thread tightening defect;

If there is no tightening defect, the computer in the control system controls the tightening tool to realize secondary tightening process to the bolt;

If there is a thread tightening defect, the control system will display and record tightening abnormality information.

The visual positioning-based screw tightening device control method of the present invention will be further described below in conjunction with Fig. 8 to Fig. 13 .

As shown in Figure 8, the specific process of the control method of the screw tightening device based on visual positioning in the present invention is as follows:

Step 1: Carry out the following preparations before the system enters initialization:

1) Complete the selection of cameras, robots, experimental objects, etc. according to the requirements of the system plan, and finally determine the Hikvision 6-megapixel black and white industrial camera, ordinary optical lens, ring light source and controller, tightening tools and models The six-axis robot of ABB-1410 is used as the experimental object;

2) Install a calibration pin at the screwdriver head installed at the end of the robot to complete the establishment of the tool coordinate system;

3) Complete the programming of the robot motion control program and the design of the tightening process of the tightening tool;

4) Connect the computer, camera, and robot controller cabinet through the Gigabit network card switch with network cables, and set the network addresses of the above three in the same network segment;

5) Complete the writing of the visual image processing program, including calibration of the camera, hand-eye calibration, template matching, establishment of a template coordinate system, etc., and the use of circle finding tools to fit the circle of the nut of the bolt so as to confirm the position of the center of the circle;

6) Complete the writing of the host software, the functions of the host software include:

a) The communication function between the computer and the robot, which is used for the computer to receive the robot ready signal from the robot and send the computer to the robot the position information of the nut center point of the bolt and the signal of the completion of tightening of the tightening tool;

b) The communication function between the computer and the camera, which is used for the computer to send operation instructions to the camera in real time and the computer to receive real-time images or single images fed back by the camera in real time for subsequent image processing;

c) The communication function between the computer and the tightening tool, which is used for the computer to send operating instructions and tightening process parameters to the tightening tool in real time, and the computer receives real-time tightening data fed back by the tightening tool in real time for subsequent curve drawing;

d) The function of displaying the camera shooting picture in real time, which is used to display the image of the camera shooting picture in real time, so as to have a more intuitive understanding of the camera shooting picture;

E) call the function of image processing program, this function is used to call the image that camera takes to process, and output the coordinate value of the nut center point of bolt in the image after processing by image processing program;

f) The display function of the coordinates of the nut center point of the bolt, which is used to display the coordinate value of the nut center point of the bolt in the robot tool coordinate system;

g) The function of drawing the torque-rotation angle-time curve in real time according to the tightening data, which can intuitively understand the torque change trend during the tightening process;

h) The function of saving and viewing tightening data, which can save real-time tightening data and view historical tightening data as needed.

Step 2: After completing the above preparations before initialization, the system enters the initialization state, which includes: the robot performs a return to the original movement, checks whether the functions of each component are normal, confirms whether the circuit and communication are normal, and sends corresponding tightening according to the type of bolts. Process parameters;

Step 3: Put the tray with the screwed motor, its mounting plate and fastening bolts on the conveyor belt and start the conveyor belt. The motor and fastening device above the tray move together with the conveyor belt; at the same time, start the photoelectric sensor to The tray is inspected;

Step 4: When the material tray triggers the photoelectric sensor, the blocking cylinder moves and stretches out to block the material tray, and at the same time stops the conveyor belt and triggers the action of the clamping cylinder to clamp the material tray;

Step 5: After receiving the signal from the robot that the clamping cylinder is in place, the computer triggers the camera to take pictures of the screwed motor on the conveyor belt, its mounting plate and fastening bolts, and calls the image processing program to process the captured images. Finally, the computer sends the processing result, that is, the position of the center point of the bolt to be tightened, to the robot;

Step 6: The robot moves to the corresponding bolt with the tightening tool for tightening processing and sends the tightening process data to the computer through serial communication;

Step 7: The computer draws the tightening process curve and displays the tightening results according to the tightening data;

Step 8: Determine whether the tightening task meets the expected tightening requirements according to the tightening data. If the expected tightening requirements are met, the process jumps to step 13 to determine whether the tightening task is completed; if the expected tightening requirements are not met, Then the process jumps to step 9 to determine whether there is a thread tightening defect;

Step 9: Determine whether there is a thread tightening defect according to the torque variation trend in the tightening data. If there is a thread tightening defect, the process jumps to step 12, and the tightening abnormal information is displayed and recorded; if there is no thread tightening defect, the process jumps Go to step 10, the tightening tool performs secondary tightening process on the bolt;

Step 10: The computer sends a re-tightening signal, and the tightening tool performs a second tightening process on the bolt;

Step 11: Determine whether the number of tightening times exceeds 3 times. If the number of tightening times exceeds 3 times, it is considered to be abnormal tightening, and jump to step 12 to display and record the abnormal tightening information; if the number of tightening times does not exceed 3 times, the process jumps to step 8 , re-judging whether the expected tightening requirements are met;

Step 12: Display abnormal tightening results and record corresponding abnormal tightening information;

Step 13: According to the statistics of the number of bolts that have been tightened by the computer, it is judged whether all the bolt tightening tasks have been completed this time. If all the bolt tightening tasks have been completed, the process will jump to step 14; if the tightening tasks of all bolts have not been completed , the process jumps to step 3 and restarts the conveyor belt;

Step 14: This tightening task has been completed, the robot performs the movement of returning to the zero point, the camera stops taking pictures, and the process ends.

As shown in Figure 9, it is the image processing flow. Camera calibration, hand-eye calibration and other work need to be carried out before the image processing flow to ensure that the visual measurement system can be directly applied to the experiment of the present invention, wherein the image processing flow includes image acquisition, template Matching, establishment of template coordinate system, image filtering processing, image dynamic threshold segmentation processing, expansion and corrosion processing, and the process of determining the position of the center point of the bolt by using the circle-finding tool. The upper software performs image processing; template matching is to establish a matching template based on the shape characteristics of the tail of the twisted motor, which is used to confirm the camera’s photographing processing object; establishing a template coordinate system is to establish a coordinate system based on the characteristics of template matching, mainly used to determine and reduce Image processing area; image filtering processing is mainly to suppress the noise of the target image, and selectively enhance or suppress it, so as to highlight the required image features and enhance the visual recognition effect; dynamic threshold segmentation processing is mainly to obtain images that can reflect the overall and Local binarization of images improves the contour contrast of captured features and reduces the complexity of post-image processing; dilation and corrosion processing mainly highlights the characteristics of nuts, while reducing background interference factors, making the shape of nuts It is clearer in the image; the main purpose of using the find circle tool is to find the circle of the nut head and determine its center point position.

As shown in Figure 10, it is a torque control model diagram of the tightening process, wherein the tightening process includes the following stages: cap search stage, thread defect detection stage, tightening stage, tightening maintenance stage, reverse screwing stage, the specific process is as follows:

1. Cap-seeking stage (0–t ₁ ): the bit or sleeve rotates one circle at a slow speed, so that the bit or sleeve is combined with the bolt;

2. Thread defect detection stage (t ₁ - _{t 2} ): the electric screwdriver rotates to make the bolts spin down, and check whether the torque increases abnormally during this period. If there is an abnormal increase, it indicates that the thread is defective;

3. Fitting point detection stage (t ₂ -t ₃ ): In this stage, the fitting torque is detected, and the lower end of the bolt and nut fits with the joint body at t ₃ , and t ₃ is called the fitting moment, and the corresponding point is the fitting point;

4. Tightening stage (t ₃ -t ₄ ): This stage starts from the fitting point and uses the torque method to tighten according to the set target torque, and switches to the next stage when the set torque value is reached. This stage can be set for different bolts different target torques;

5. Tightening and holding stage (t ₄ -t ₅ ): this stage starts from reaching the set torque, and keeps the tightening torque for a period of time. This holding time can be set according to needs;

6. Anti-tightening stage (t ₅ -t ₆ ): In this stage, the proper reverse control of the tightening bit is not performed on the bolts in the actual sense. The friction between the small bit and the bolt facilitates the extraction of the bit without affecting the original tightening effect. The anti-tightening angle ranges from 1 to 10 degrees, which can be set according to the actual situation on site.

In order to make the purpose, technical solution and advantages of the control model clearer, the model will be further described below in conjunction with the accompanying drawings.

As shown in Figure 11, this figure is based on the actual application effect diagram of the above control model, in which the triangle mark is the angle curve during the tightening process, and the circle mark is the torque curve during the tightening process. These two curves are respectively Corresponding to the angle scale line on the left and the torque scale line on the right, the horizontal axis is the time axis, and the average acquisition interval of each data point is 50ms.

It can be seen from Figure 11 that the tightening tool successfully finds the cap when it turns roughly half a circle from the beginning, and the torque measured by the torque sensor rises slowly from zero to a certain value at this stage, and switches to the thread defect detection stage; The tool rotates quickly to make the bolts spin down, and the torque value is monitored in real time. When the torque reaches the set point torque value, it switches to the tightening stage; in the tightening stage, the tightening tool controls the electric batch according to the torque method, so that the tightening torque gradually rises to Set value, when the torque setting value is reached, switch to the tightening and holding stage; in the tightening and holding stage, the tightening tool will maintain the target torque of the previous stage for a period of time according to the set holding time, and switch to the reverse screwing stage when the holding time is reached ;In the anti-tightening stage, the tightening tool performs appropriate reverse control according to the position mode, removes the holding torque and reduces the friction between the bit and the bolt, but at the same time does not affect the previous tightening effect. The anti-tightening at this stage in Figure 11 The angle is 8 degrees, and the partially enlarged view of the anti-twist stage in Fig. 11 is shown in Fig. 12 .

As shown in Figure 13, it is the tightening curve display interface in the upper software developed by the present invention. The upper software is developed in Visual Studio based on the .Net language, which includes communication, image display, image processing, tightening curve display, and tightening process settings. and other functions. Wherein the image processing function is to call the image processing file generated by the VisionPro software of the U.S. Cognex company to process the captured image.

The beneficial effects of the screw tightening method based on visual positioning of the present invention are:

1. Aiming at the problems of high production cost and high influence of human factors on the tightening accuracy of hand-held tightening tools, this invention adopts the method of fastening the bolts with the robot equipped with tightening tools, which is conducive to improving production efficiency and reducing production costs. Improve the automation of thread assembly;

2. In view of the problem that the tightening position cannot be adjusted flexibly during the assembly of the special locking screw machine equipment and the robot teaching method, and the tightening torque cannot be flexibly set or changed according to the needs. And it can accurately set different torque target values, which can obtain higher tightening control accuracy and strong versatility;;

3. Aiming at the problem of SCARA robot tightening assembly orientation and load limitations, the present invention adopts a six-axis industrial robot + vision scheme that matches the load, which solves the limitation of the robot’s activity space due to the robot’s degree of freedom and the robot’s assembly overload problem;

4. Aiming at the problems that the ordinary electric screwdriver carried by the robot cannot set different tightening processes according to different threaded fasteners in the tightening process, the torque control accuracy is low, and there is no data feedback function in the tightening process, the present invention adopts a torque closed-loop control function. Tighten the tool and set the corresponding tightening process according to the material characteristics of different bolts and fasteners according to the torque control-rotation angle monitoring method, so as to achieve a better control effect. At the same time, use the upper software in the computer to communicate with the tightening tool. Real-time collection of tightening data and drawing of tightening curves are beneficial to the analysis of the tightening process and the judgment of the tightening results, and further storage of the tightening process data facilitates the traceability and tracking of assembly data.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Under the conception of the present invention, the equivalent structural transformation made by using the description of the present invention and the contents of the accompanying drawings, or directly/indirectly used in Other relevant technical fields are all included in the patent protection scope of the present invention.

Claims (7)

1. A visual positioning-based screw tightening device, comprising: the device comprises a six-axis industrial robot, a control system, a feeding mechanism for conveying a module to be screwed down, a vision measurement module for photographing and positioning threaded holes of various shapes and layouts of the module to be screwed down and target bolts of different specifications and guiding the six-axis industrial robot to move to a proper position and posture, and a screwing tool for screwing down the module to be screwed down according to the photographing result of the vision measurement module, wherein the control system is respectively in communication connection with the robot and the screwing tool, the feeding mechanism comprises a frame, a conveyor belt, a material tray, a material baffle, a blocking cylinder, a clamping cylinder and a photoelectric sensor, the conveyor belt is mounted on the frame, the material tray is placed on the conveyor belt, the material baffle is mounted on two sides of the conveyor belt, the blocking cylinder and the clamping cylinder are mounted on the same side of the material baffle, and are sequentially arranged front and back along the running direction of the conveyor belt, and the photoelectric sensor is mounted on the opposite side of the blocking cylinder and is positioned at a position later than the running direction of the conveyor belt. The visual measurement module is arranged on the frame, the tightening tool is arranged on a flange of a sixth shaft of the robot, and the visual measurement module is positioned above a tightening operation area;

The visual measurement module comprises a visual measurement assembly and a mounting bracket, wherein the top of the mounting bracket is L-shaped, the bottom of the mounting bracket is mounted on the frame, and the visual measurement assembly is mounted on the top of the mounting bracket through an L-shaped mounting plate;

the vision measurement assembly comprises a camera, an optical lens and an annular light source which are sequentially and coaxially arranged from top to bottom, wherein the camera is arranged on the L-shaped mounting plate through a camera mounting plate, the optical lens is in threaded connection with a C interface of the camera, and the annular light source is arranged on the L-shaped mounting plate through an annular light source mounting plate;

the tightening tool comprises a tightening shaft connected with the robot and a tightening shaft controller connected with the tightening shaft, wherein the tightening shaft controller is positioned at the tail end of the tightening shaft and is connected with the tightening shaft; the tightening shaft comprises a tightening head, an end cover, a coupler, a torque sensor, a speed reducer, a servo motor and an encoder, wherein the end cover is arranged at the front end of the tightening shaft, the coupler is respectively arranged between the end cover and the torque sensor as well as between the torque sensor and the speed reducer, the speed reducer is connected with the servo motor, and the encoder is arranged at the tail end of the servo motor;

The module to be screwed comprises a screwed motor, a screwed motor mounting plate and mounting bolts, wherein a plurality of screwed bolts are arranged on the screwed motor to be screwed;

the vision measurement module photographs the module to be screwed up, and the processing flow of photographed pictures is as follows: the method comprises the steps of image acquisition, template matching, template coordinate system establishment, image filtering processing, image dynamic threshold segmentation processing, expansion corrosion processing and bolt center point position determination by using a circle finding tool, wherein the image acquisition is to trigger a camera to take a picture through upper software; the template matching is to establish a matching template according to the shape characteristics of the tail part of the twisted motor and is used for confirming a photographic processing object of a camera; establishing a template coordinate system is to establish the coordinate system according to the characteristics of template matching and is used for determining and shrinking the image processing area; the image filtering processing is to inhibit the noise of the target image, selectively enhance or inhibit the noise, thereby highlighting the required image characteristics and enhancing the visual recognition effect; the dynamic threshold segmentation processing is to obtain a binary image capable of reflecting the whole and part of the image, so that the contour contrast of the captured features is improved, and the complexity of the later image processing is reduced; the expansion corrosion treatment is characterized by highlighting the nut, and simultaneously reduces interference factors of the background, so that the shape of the nut is clearer in the image; the round finding tool is used for finding the circle of the head of the nut and determining the position of the center point of the circle;

The blocking cylinder is used for blocking the material tray when the photoelectric sensor detects the material tray, and the clamping cylinder is used for clamping the material tray and sending a clamping signal to the control system;

the robot is used for driving the tightening tool to tighten the bolt and sending tightening information to the control system;

the control system is used for controlling the vision measurement module to take a picture of the module to be screwed according to the clamping signal, and sending the position information of the connecting bolt of the screwed motor on the module to be screwed to the robot; and then guiding the robot to carry a tightening tool to quickly tighten the corresponding bolt;

the control system is also used for sending corresponding tightening process parameters according to the types of the bolts, drawing a tightening process curve according to the tightening information, setting corresponding tightening processes according to the material characteristics of different bolts and fasteners by adopting a torque control-rotation angle monitoring method, displaying and storing tightening results, and triggering a tightening tool to perform repeated tightening work when necessary so as to achieve the preset tightening target;

The control system is also used for judging whether the expected tightening requirement is met according to the tightening information;

if the expected tightening requirement is met, the computer in the control system counts the number of the bolts which are subjected to tightening processing to judge whether all the tightening tasks of the bolts to be tightened are completed, if the tightening tasks of all the bolts are completed, the robot performs zero-return movement, the camera measurement module stops photographing, and the process is finished;

if the expected tightening requirement is not met, judging whether a screw tightening defect exists or not;

if the tightening defect does not exist, a computer in the control system controls the tightening tool to realize secondary tightening treatment on the bolt;

if the screw tightening defect exists, the computer in the control system displays and records abnormal tightening information.

2. The visual positioning-based screw-on device of claim 1, wherein camera calibration, hand-eye calibration is required.

3. The visual positioning-based screw-on device of claim 2, wherein the photo is captured by a host software for image processing.

4. The visual positioning-based screw-on device of claim 1, wherein the tray comprises a support plate and posts symmetrically mounted at both ends of the bottom of the support plate.

5. The visual positioning-based screw tightening device according to any one of claims 1 to 4, wherein the control system comprises a computer, a switch, a robotic control cabinet, and a teach pendant, wherein the switch is connected to the visual measurement module, the robotic control cabinet, and the computer, respectively, and the robotic control cabinet is connected to the robot.

6. A method of controlling a visual positioning-based screw tightening device, characterized in that the method is applied to the visual positioning-based screw tightening device according to any one of claims 1 to 5, the method comprising the steps of:

step 1: the system enters an initialization state, which includes: the robot performs the original return movement, detects whether the functions of all the parts are normal, confirms whether the circuits and the communication are normal, and sends corresponding tightening technological parameters according to the types of the bolts;

step 2: placing a tray provided with a screwed motor, a mounting plate and a fastening bolt of the screwed motor on a conveyor belt, starting the conveyor belt to run, and enabling the motor and the fastening device above the tray to move along with the conveyor belt; simultaneously, a photoelectric sensor is started to detect the material tray;

step 3: when the charging tray triggers the photoelectric sensor, the blocking cylinder acts and extends out to block the charging tray, meanwhile, the operation of the conveyor belt is stopped, the action of the clamping cylinder is triggered, and the charging tray is clamped;

Step 4: after receiving a signal from a robot that a clamping cylinder acts in place, a computer triggers a camera to photograph a screwed motor, a mounting plate and a fastening bolt of the screwed motor on a conveyor belt, invokes an image processing program to process a photographed image, and finally, the computer sends a processing result, namely a central point position of the bolt to be screwed to the robot;

step 5: the robot moves to the corresponding bolt with the tightening tool to carry out tightening treatment and sends tightening process data to the computer in a serial port communication mode;

step 6: the computer draws a tightening process curve according to the tightening data and displays the tightening result;

step 7: judging whether the tightening task reaches the expected tightening requirement according to the tightening data, if so, jumping to a step 12, and judging whether the tightening task is completed; if the expected tightening requirement is not met, the flow jumps to step 8, and whether the screw tightening defect exists is judged;

step 8: judging whether a screw tightening defect exists according to the torque variation trend in the tightening data, if so, jumping to a step 11, and displaying and recording abnormal tightening information; if the screw tightening defect does not exist, the flow jumps to step 9, and the tightening tool performs secondary tightening treatment on the bolt;

Step 9: the computer sends a re-tightening signal, and the tightening tool performs secondary tightening treatment on the bolt;

step 10: judging whether the tightening times exceeds 3 times, if so, judging that the tightening is abnormal, jumping to the step 11 to display and record abnormal tightening information; if the tightening times are not more than 3 times, the flow jumps to step 6, and whether the expected tightening requirement is met is judged again;

step 11: displaying the abnormal tightening result and recording corresponding abnormal tightening information;

step 12: judging whether all the bolt tightening tasks are completed according to the statistics of the number of the bolts which are subjected to tightening processing by the computer, and if all the bolt tightening tasks are completed, jumping the flow to the step 13; if the tightening tasks of all the bolts are not completed, the flow jumps to step 2, and the conveyor belt is restarted;

step 13: the tightening task is completed, the robot performs zero-point motion, the camera stops photographing, and the process is finished.

7. The method for controlling a screw tightening device based on visual positioning according to claim 6, wherein the step of the control system drawing a tightening process curve based on the tightening information and displaying and storing the tightening result further comprises:

The computer in the control system judges whether the expected tightening requirement is met according to the tightening information;

if the expected tightening requirement is met, the computer in the control system counts the number of the bolts which are subjected to tightening processing to judge whether all the tightening tasks of the bolts to be tightened are completed, if the tightening tasks of all the bolts are completed, the robot performs zero-return movement, the camera measurement module stops photographing, and the process is finished;

if the expected tightening requirement is not met, judging whether a screw tightening defect exists or not;

if the tightening defect does not exist, a computer in the control system controls the tightening tool to realize secondary tightening treatment on the bolt;

if the screw tightening defect exists, the computer in the control system displays and records abnormal tightening information.