Bolt tightening method and device based on critical gradient

Abstract

The invention discloses a bolt tightening method and device based on critical gradient, and the method comprises the steps: comparing the relative position information between a to-be-tightened bolt and a tightening machine with a set mistake-proof and leakage-proof model, and outputting a position comparison result; wherein when the position comparison result shows that matching succeeds, the to-be-screwed bolt is screwed through a screwing machine; the method comprises the steps that when a tightening machine conducts tightening operation on a to-be-tightened bolt, tightening parameters are collected, the critical gradient in the bolt tightening process is monitored on the basis of the tightening parameters so as to predict the change of pre-tightening force, and a pre-tightening force qualified signal is output when the pre-tightening force meets a set condition. The bolt tightening process and tightening parameters can be monitored in real time, the pre-tightening force of the bolt can be predicted, the tightening strategy required by the technology is monitored in real time, the situation that an operator performs tightening without the strategy specified by the technology is prevented, meanwhile, the situation that the dispersion deviation of the pre-tightening force is too large when the bolt is tightened can be avoided, and therefore the bolt tightening quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of intelligent assembly, and in particular relates to a critical gradient-based bolt tightening method and device. Background Art

[0002] In the prior art, it is usually necessary to use robots to position and tighten bolts. However, in some key special positions, such as in small spaces where tightening mechanisms cannot reach, the method of positioning and tightening bolts by robots is not applicable. In the actual production process, the bolt tightening process of most key and important parts is still assisted by manual operation of power-assisted robotic arms. There are problems such as the tightening process not being tightened according to the process requirements, resulting in large discreteness of the pre-tightening force during tightening, and bolts are easy to loosen. There are hidden dangers in the stability and reliability of bolt connections. Summary of the invention

[0003] In order to address the deficiencies in the prior art, the present invention provides a bolt tightening method and device based on critical gradient, which can monitor the tightening process and tightening parameters of the bolt in real time, and predict the bolt preload, so as to realize real-time monitoring of the tightening strategy required by the process, prevent the operator from tightening the bolt in violation of the strategy specified by the process, and avoid excessive deviation in the discreteness of the preload when tightening the bolt, thereby improving the quality of bolt tightening.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is: In a first aspect, a bolt tightening method based on a critical gradient is provided, comprising: collecting relative position information between a bolt to be tightened and a tightening machine; comparing the relative position information between the bolt to be tightened and the tightening machine with a set error-proofing and leakage-proofing model, and outputting a position comparison result; wherein, when the position comparison result is a successful match, the bolt to be tightened is tightened by the tightening machine; when the tightening machine tightens the bolt to be tightened, tightening parameters are collected, and based on the tightening parameters, the critical gradient in the bolt tightening process is monitored to predict the change in preload force, and a preload force qualified signal is output when the preload force meets the set conditions.

[0005] Furthermore, the error-proofing and leakage-proofing model includes: bolt tightening rules, which are tightening methods formulated according to process requirements, and the tightening methods include: clockwise tightening method and symmetrical cross tightening method; relative position relationship, which is the relative position of the tightening machine and the bolt to be tightened when the tightening machine tightens the bolt to be tightened according to the bolt tightening rules.

[0006] Furthermore, based on the tightening parameters, the critical gradient in the bolt tightening process is monitored to predict the change of the preload force, and when the preload force meets the set conditions, a preload force qualified signal is output, including: Refer to formula (1) when torque is applied to the bolt When the bolt preload Make predictions, (1) in, is the friction coefficient, It is the tooth profile half angle or tooth side angle. is the thread pitch diameter, is the equivalent friction diameter of the bearing surface, is the thread pitch of the bolt; The calculated Substitute into formula (2) to calculate the corresponding rotation angle , (2) in, is the bolt stiffness, is the stiffness of the connected parts; Then refer to formula (1) and change the preset torque of the torque method to Bring it into the calculation to evaluate the target preload after tightening is completed ; Further, the target preload is calculated by formula (3) The relationship between the required torque and the rotation angle, (3) Based on the torque-angle curve, the critical gradient during bolt tightening is evaluated within the yield strength range according to formula (4); (4) The three standard deviations above and below the calculated gradient mean are used as the final critical gradient qualified range, that is, the critical gradient within the plastic range is If it is within the range, the tightening process is qualified, otherwise it is judged as unqualified.

[0007] Furthermore, when the critical gradient drops to The tightening machine stops tightening.

[0008] In a second aspect, a critical gradient bolt tightening device is provided, comprising: a visual camera for collecting relative position information between the bolt to be tightened and the tightening machine; a data processing unit for comparing the relative position information between the bolt to be tightened and the tightening machine with a set error-proofing and leakage-proofing model, and outputting a position comparison result; wherein, when the position comparison result is a successful match, the tightening machine is used to tighten the bolt to be tightened; and it is also used to collect tightening parameters when the tightening machine is tightening the bolt to be tightened, and monitor the critical gradient in the bolt tightening process based on the tightening parameters to predict the change of the preload force, and output a preload force qualified signal when the preload force meets the set conditions.

[0009] Furthermore, it also includes a display unit, which is used to display the data processing results output by the data processing unit and the position of the bolt to be tightened in real time; it is also used to display the process requirements for bolt tightening and the position of the bolt; it is also used to send an alarm signal when the position between the tightening machine and the bolt to be tightened is incorrect.

[0010] Furthermore, it also includes a controller, an MES system and a storage unit; the data processing unit retrieves the relevant parameters of the tightening process of the tightening machine in real time through the MES system; the MES system receives the instructions of the data processing unit and controls the tightening machine through the controller, and uploads the relevant parameters in the controller to the data processing unit; the controller receives the relevant parameters of the tightening machine controlled by the MES system and collects the tightening parameters of the tightening machine and stores them in the storage unit.

[0011] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the present invention compares the relative position information between the bolt to be tightened and the tightening machine with the set error-proofing and leakage-proofing model, and outputs the position comparison result; wherein, when the position comparison result is a successful match, the tightening machine performs a tightening operation on the bolt to be tightened; when the tightening machine performs a tightening operation on the bolt to be tightened, tightening parameters are collected, and based on the tightening parameters, the critical gradient in the bolt tightening process is monitored to predict the change in preload force, and a preload force qualified signal is output when the preload force meets the set conditions; the tightening process of the bolt and the tightening parameters can be monitored in real time, and the preload force of the bolt can be predicted, so as to realize real-time monitoring of the tightening strategy required by the process, prevent the operator from tightening in violation of the strategy specified by the process, and avoid excessive deviation of the preload force discreteness when tightening the bolt, thereby improving the quality of bolt tightening. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The structure of a bolt tightening device based on critical gradient provided by an embodiment of the present invention is schematically shown. Figure 1 ; Figure 2 The structure of a bolt tightening device based on critical gradient provided by an embodiment of the present invention is schematically shown. Figure 2 ; Figure 3 It is a main flow diagram of a bolt tightening method based on critical gradient provided by an embodiment of the present invention; Figure 4 is a torque-angle relationship curve under a critical gradient in an embodiment of the present invention; Figure 5 is a schematic diagram of the bolt tightening sequence used in an embodiment of the present invention, wherein (a) is a clockwise sequence number, and (b) is a symmetrical cross number; Figure 1 , Figure 2In: 1. Power-assisted robotic arm; 2. Tightening machine; 3. Visual camera; 4. Controller; 5. MES system; 6. Data processing unit; 7. Display unit; 8. Bolts to be tightened. DETAILED DESCRIPTION

[0013] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0014] Embodiment 1 A bolt tightening method based on critical gradient comprises: collecting relative position information between a bolt to be tightened and a tightening machine; comparing the relative position information between the bolt to be tightened and the tightening machine with a set error-proofing and leakage-proofing model, and outputting a position comparison result; wherein, when the position comparison result is a successful match, the tightening machine performs a tightening operation on the bolt to be tightened; when the tightening machine performs a tightening operation on the bolt to be tightened, tightening parameters are collected, and based on the tightening parameters, a critical gradient in the bolt tightening process is monitored to predict changes in pre-tightening force, and a pre-tightening force qualified signal is output when the pre-tightening force meets the set conditions.

[0015] The error-proofing and leak-proofing model of the present invention includes: formulating the tightening method of the bolts to be tightened according to the process requirements (including tightening methods such as clockwise tightening and symmetrical cross tightening, see Figure 5 ), enter the relative position of the tightening machine and the bolt to be tightened when the tightening conditions are executed, that is, the tightening machine fits the bolt to be tightened according to the tightening method formulated by the process.

[0016] Based on the tightening parameters, the critical gradient in the bolt tightening process is monitored to predict the change of preload force, and a preload qualified signal is output when the preload force meets the set conditions, including: Refer to formula (1) when torque is applied to the bolt When the bolt preload Make predictions, (1) in, is the friction coefficient, is the preload force of the bolt, It is the tooth profile half angle or tooth side angle. is the thread pitch diameter, is the equivalent friction diameter of the bearing surface, is the thread pitch of the bolt, Tightening torque for bolts; The calculated Substitute into formula (2) to calculate the corresponding rotation angle , (2) in, is the bolt stiffness, is the stiffness of the connected parts; Then refer to formula (1) and change the preset torque of the torque method to Bring it into the calculation to evaluate the target preload after tightening is completed ; Further, the target preload is calculated by formula (3) The relationship between the required torque and the rotation angle is (3) Based on the torque-angle curve, the critical gradient during bolt tightening is evaluated within the yield strength range according to formula (4); (4) The three standard deviations above and below the calculated gradient mean are used as the final critical gradient qualified range, that is, the critical gradient within the plastic range is If it is within the range, the tightening process is qualified, otherwise it is judged as unqualified.

[0017] Furthermore, when the critical gradient drops to The tightening machine stops tightening.

[0018] Embodiment 2 Based on the critical gradient bolt tightening method described in Example 1, this embodiment provides a critical gradient bolt tightening device, including: a visual camera, used to collect relative position information between the bolt to be tightened and the tightening machine; a data processing unit, used to compare the relative position information between the bolt to be tightened and the tightening machine with the set error-proofing and leakage-proofing model, and output the position comparison result; wherein, when the position comparison result is a successful match, the tightening operation is performed on the bolt to be tightened by the tightening machine; and it is also used to collect tightening parameters when the tightening machine is tightening the bolt to be tightened, and monitor the critical gradient in the bolt tightening process based on the tightening parameters to predict the change of preload force, and output a preload force qualified signal when the preload force meets the set conditions.

[0019] like Figure 1 , Figure 2 As shown, the bolt tightening device mainly includes an assistive robotic arm 1, a tightening machine 2, a visual camera 3, a controller 4, an MES system (Manufacturing Execution System) 5, a data processing unit 6 and a display unit 7.

[0020] The display unit 7 can display the data results of the data processing unit 6 and the position of the bolt 8 to be tightened in real time, providing guidance for the operator; the data processing unit 6 retrieves the relevant parameters of the tightening process of the tightening machine 2 in real time through the MES system 5 and predicts the preload force through the critical gradient, and at the same time obtains the real-time data of the visual camera 3 to track the tightening position of the bolt; the MES system 5 can receive the instructions of the data processing unit 6 and control the tightening machine 2 through the controller 4, and can also upload the relevant parameters in the controller 4 to the data processing unit 6; the controller 4 receives the relevant parameters of the MES system 5 to control the tightening machine 2 and collects and stores the tightening parameters of the tightening machine 2 in the storage unit; the visual camera 3 obtains the position of the bolt 8 to be tightened and the tightening machine 2 in real time, and uploads the data to the data processing unit 6 through the communication signal; the power-assisted robotic arm 1 mainly adjusts the position of the tightening machine 2 to tighten the bolt 8 to be tightened.

[0021] The process flow of the error prevention and leakage prevention principle of the bolt tightening device of the present invention is as follows: Figure 3 shown.

[0022] 1. When the product enters the station to be tightened, the power-assisted robotic arm 1 is moved. During this process, the visual camera 3 takes pictures of the bolts to be tightened 8 and the tightening machine 2, and uploads the images to the data processing unit 6 through the factory Wi-Fi.

[0023] 2. The data processing unit 6 generates a three-dimensional image of the position of the tightening machine 2 and the bolt 8 to be tightened in the photograph, and matches and compares it with the posture of the loading system (the error-proofing and leakage-proofing model of the loading system). At the same time, the matching result will be synchronously displayed on the display unit 7 to achieve the purpose of reminding the operator.

[0024] 3. If the matching is unsuccessful, the position of the assisting robot arm 1 is readjusted. When the position matching is successful, the tightening machine 2 is operated to tighten the bolt 8 to be tightened. During the tightening process, the tightening parameters are collected in real time and the critical gradient of the bolt tightening process is monitored through the data processing unit 6 to predict the preload force. At the same time, the real-time data is synchronously displayed on the display unit 7.

[0025] 4. If the tightening is judged to be unqualified, it needs to be re-tightened. If the tightening is qualified, the data processing unit 6 records the current position and jumps to the next bolt to tighten.

[0026] 5 After all bolts are tightened and qualified, the collected data will be stored and retained.

[0027] The present invention also provides a bolt tightening scheme and device based on critical gradient, which includes the following steps.

[0028] Step 1: Plan the best installation position of the visual camera 3 according to the position of the bolt 8 to be tightened and the range of motion of the power-assisted robotic arm 1. This position should ensure that the visual camera 3 can cover the area of ​​the bolt 8 to be tightened, and avoid the collision of the power-assisted robotic arm 1 with the connecting line when it moves. According to the model and size of the visual camera 3, a special bracket or clamp is prepared, and the bracket / clamp is firmly installed on the power-assisted robotic arm 1. The direction and angle of the visual camera 3 are adjusted to ensure that the lens of the visual camera 3 is aimed at the area of ​​the bolt 8 to be tightened, and the cable of the visual camera 3 is connected to the corresponding interface (such as power supply, data transmission, etc.). At the same time, it is ensured that the power-assisted robotic arm 1 will not be disturbed or blocked during the movement and the visual camera 3 can clearly capture the image of the area where the bolt 8 is to be tightened.

[0029] Step 2: Fix the display unit 7 on the power-assisted robot arm 1, and select a suitable communication protocol (common ones are TCP / IP, Modbus, OPC UA, etc.) according to the communication interface of each device (such as Ethernet, RS-232, USB, wireless Wi-Fi, etc.) to connect the display unit 7, data processing unit 6, MES system 5, controller 4, visual camera 3, and tightening machine 2; after completing the independent test of each part, perform the overall joint debugging of the system to test whether the entire system and each functional module work well together.

[0030] Step 3: Import relevant parameters and models of bolt tightening leakage prevention and error prevention into the data processing unit 6 system, and create bolt tightening critical gradient tightening information and tightening process error prevention model information.

[0031] Step 4: When tightening the bolts, the display unit 7 first displays the process requirements for tightening the bolts and reminds the operator of the exact position of the bolts 8 to be tightened. The operator moves the power-assisted robotic arm 1, and the visual camera 3 collects the positions of the tightening machine 2 and the bolts 8 to be tightened in real time, and compares them with the imported error-proofing and leakage-proofing model through the data processing unit 6. If the position is correct, the tightening machine 2 works normally; otherwise, the tightening machine 2 is locked, and the display unit 7 interface issues an alarm and reminds the operator to re-pair.

[0032] Step 5: Corresponding to step 4, during the process of tightening the bolt, relevant parameters of the tightening process are collected in real time, and the relevant tightening parameters are displayed on the display unit 7 at the same time.

[0033] Refer to formula (1) when torque is applied to the bolt When the bolt preload Make predictions, (1) in, is the friction coefficient, , is the preload force of the bolt, It is the tooth profile half angle or tooth side angle. is the thread pitch diameter, is the equivalent friction diameter of the bearing surface, is the thread pitch of the bolt, Tightening torque for bolts; The calculated Substitute into formula (2) to calculate the corresponding rotation angle , (2) in, is the bolt stiffness, is the stiffness of the connected parts; Then refer to formula (1) and change the preset torque of the torque method to Bring it into the calculation to evaluate the target preload after tightening is completed ; Further, the target preload is calculated by formula (3) The relationship between the required torque and the rotation angle, (3) According to the torque-angle curve (such as Figure 4 As shown in Figure 4, the critical gradient (the slope of the torque-angle curve) during bolt tightening is evaluated within the yield strength range according to formula (4); (4) According to the statistical principle, the three standard deviations above and below the mean of the calculated gradient can be used as the final critical gradient qualified range, that is, the critical gradient within the plastic range is If the bolt is within the range, the tightening process is qualified, otherwise it is judged as unqualified. After the bolt reaches the yield point, the gradient of the bolt tightening will drop sharply (see Figure 4 ), when the critical gradient drops to The tightening machine stops tightening.

[0034] Step 6: Corresponding to step 4 and step 5, the data collected in real time during the entire tightening process is fed back to the operator through the display unit 7. At the same time, the results of the data processing unit 6 during the tightening process send tightening instructions to the controller 4 through the MES system 5 to control the start and stop of the tightening machine 2.

[0035] The present invention can monitor the tightening strategy required by the process in real time, prevent personnel from not tightening according to the strategy specified by the process, and predict the size of the bolt preload through the critical gradient of the tightening process, avoid excessive discrete deviation of the bolt tightening, and thus improve the quality of bolt tightening. The present invention is simpler than robot automated tightening. For the tightening of large bolts that cannot be tightened by robots at special stations of engineering machinery, the use of this device can effectively avoid improper manual operation and further improve the reliability and stability of the bolt connection. The calculation process of the present invention is simple in principle, can facilitate operators to monitor the tightening process in real time, and is easy to implement.

[0036] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A bolt tightening method based on critical gradient, characterized in that: include: Collect the relative position information between the bolt to be tightened and the tightening machine; Compare the relative position information between the bolt to be tightened and the tightening machine with the set error-proofing and leakage-proofing model, and output the position comparison result; wherein, when the position comparison result is a successful match, the tightening machine performs a tightening operation on the bolt to be tightened; When the tightening machine is tightening the bolt to be tightened, tightening parameters are collected, and the critical gradient in the bolt tightening process is monitored based on the tightening parameters to predict the change of the pre-tightening force, and a pre-tightening force qualified signal is output when the pre-tightening force meets the set conditions.

2. The bolt tightening method based on critical gradient according to claim 1, characterized in that: The error-proofing and leakage-proofing model includes: Bolt tightening rules, which are tightening methods formulated according to process requirements, including: clockwise tightening method and symmetrical cross tightening method; The relative position relationship is the relative position between the tightening machine and the bolt to be tightened when the tightening machine tightens the bolt to be tightened according to the bolt tightening rule.

3. The bolt tightening method based on critical gradient according to claim 1, characterized in that: Based on the tightening parameters, the critical gradient in the bolt tightening process is monitored to predict the change of the pre-tightening force, and when the pre-tightening force meets the set conditions, a pre-tightening force qualified signal is output, including: Refer to formula (1) when torque is applied to the bolt When the bolt preload Make predictions, （1） in, is the friction coefficient, It is the tooth profile half angle or tooth side angle. is the thread pitch diameter, is the equivalent friction diameter of the bearing surface, is the thread pitch of the bolt; The calculated Substitute into formula (2) to calculate the corresponding rotation angle , （2） in, is the bolt stiffness, is the stiffness of the connected parts; Then refer to formula (1) and change the preset torque of the torque method to Bring it into the calculation to evaluate the target preload after tightening is completed ; Further, the target preload is calculated by formula (3) The relationship between the required torque and the rotation angle is （3） Based on the torque-angle curve, the critical gradient during bolt tightening is evaluated within the yield strength range according to formula (4); （4） The three standard deviations above and below the calculated gradient mean are used as the final critical gradient qualified range, that is, the critical gradient within the plastic range is If it is within the range, the tightening process is qualified, otherwise it is judged as unqualified.

4. The bolt tightening method based on critical gradient according to claim 3, characterized in that: When the critical gradient drops to The tightening machine stops tightening.

5. A bolt tightening device based on critical gradient, characterized in that: include: A visual camera is used to collect the relative position information between the bolt to be tightened and the tightening machine; A data processing unit is used to compare the relative position information between the bolt to be tightened and the tightening machine with the set error-proofing and leakage-proofing model, and output the position comparison result; wherein, when the position comparison result is a successful match, the tightening machine performs a tightening operation on the bolt to be tightened; It is also used to collect tightening parameters when the tightening machine is tightening the bolt to be tightened, and monitor the critical gradient during the bolt tightening process based on the tightening parameters to predict the change of the pre-tightening force, and output a pre-tightening force qualification signal when the pre-tightening force meets the set conditions.

6. The bolt tightening device based on critical gradient according to claim 5, characterized in that: The error-proofing and leakage-proofing model includes: Bolt tightening rules, which are tightening methods formulated according to process requirements, including: clockwise tightening method and symmetrical cross tightening method; The relative position relationship is the relative position between the tightening machine and the bolt to be tightened when the tightening machine tightens the bolt to be tightened according to the bolt tightening rule.

7. The bolt tightening device based on critical gradient according to claim 5, characterized in that: Based on the tightening parameters, the critical gradient in the bolt tightening process is monitored to predict the change of the pre-tightening force, and when the pre-tightening force meets the set conditions, a pre-tightening force qualified signal is output, including: Refer to formula (1) when torque is applied to the bolt When the bolt preload Make predictions, （1） in, is the friction coefficient, It is the tooth profile half angle or tooth side angle. is the thread pitch diameter, is the equivalent friction diameter of the bearing surface, is the thread pitch of the bolt; The calculated Substitute into formula (2) to calculate the corresponding rotation angle , （2） in, is the bolt stiffness, is the stiffness of the connected parts; Then refer to formula (1) and change the preset torque of the torque method to Bring it into the calculation to evaluate the target preload after tightening is completed ; Further, the target preload is calculated by formula (3) The relationship between the required torque and the rotation angle is （3） Based on the torque-angle curve, the critical gradient during bolt tightening is evaluated within the yield strength range according to formula (4); （4） The three standard deviations above and below the calculated gradient mean are used as the final critical gradient qualified range, that is, the critical gradient within the plastic range is If it is within the range, the tightening process is qualified, otherwise it is judged as unqualified.

8. The bolt tightening device based on critical gradient according to claim 7, characterized in that: When the critical gradient drops to The tightening machine stops tightening.

9. The bolt tightening device according to claim 5, characterized in that: It also includes a display unit, which is used to display the data processing results output by the data processing unit and the position of the bolt to be tightened in real time; it is also used to display the process requirements for bolt tightening and the position of the bolt; and it is also used to send an alarm signal when the position between the tightening machine and the bolt to be tightened is incorrect.

10. The bolt tightening device according to claim 9, characterized in that: It also includes a controller, an MES system and a storage unit; the data processing unit retrieves the relevant parameters of the tightening process of the tightening machine in real time through the MES system; the MES system receives the instructions of the data processing unit and controls the tightening machine through the controller, and uploads the relevant parameters in the controller to the data processing unit; the controller receives the relevant parameters of the tightening machine controlled by the MES system and collects the tightening parameters of the tightening machine and stores them in the storage unit.

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