Design method of self-piercing servo rivet gun controller and self-piercing servo rivet gun controller

Abstract

The present invention belongs to the technical field of self-piercing servo rivet gun controllers, and provides a design method for a self-piercing servo rivet gun controller and a self-piercing servo rivet gun controller. The method automatically plans a rivet force-displacement curve that meets the constraints of riveting quality conditions according to key node information on the riveting force-displacement curve input by a user, and designs a self-piercing servo rivet gun controller by analyzing the force on the rivet gun and designing the self-piercing servo rivet gun controller based on the admittance control strategy of the riveting force closed loop, thereby accurately controlling the riveting force-displacement curve, effectively avoiding secondary processing, improving the riveting quality and efficiency, and realizing flexible riveting operations.

Description

Technical Field

[0001] The invention belongs to the technical field of self-piercing servo rivet gun controllers, and in particular relates to a design method for a self-piercing servo rivet gun controller and a self-piercing servo rivet gun controller. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the continuous improvement of automobile exhaust emission standards, improving the economy and environmental protection of automobile driving is the trend of future automobile production. Studies have shown that many performance of automobiles can be improved by reducing the weight of the whole vehicle, such as fuel economy, CO emissions, braking distance, etc. An important way to lighten the automobile is to use a large amount of light metal and non-metal materials in the car body, such as aluminum alloy, magnesium alloy and reinforced plastic. For the connection between the above materials, the resistance spot welding method cannot meet the performance requirements, especially for non-metallic materials. With more and more composite materials and alloys used in car body manufacturing, self-piercing riveting (SPR) technology has received more and more attention. Compared with traditional connection methods (welding, bonding, etc.), self-piercing riveting (SPR) has the advantages of high energy efficiency, energy saving and environmental protection, and no material restrictions. It has become the main way to connect thin aluminum body plates of new energy vehicles.

[0004] SPR technology is a cold connection technology that uses a riveting gun to press the rivet directly into the plate to be riveted to form a stable connection. Under the action of the riveting force and the die, the plate and the rivet undergo plastic deformation together and form a self-locking structure in the riveting die. After the adaptation of the rivet, the die and the plate to be riveted is completed, the control of the riveting force will directly determine the riveting quality, so the design of the rivet gun controller is of great significance to the development of lightweight vehicles.

[0005] The self-piercing riveting process determines that the riveting quality is affected by factors such as the workpiece plate, rivets, and die, and these influences are ultimately reflected in the trend of the riveting force changing with the rivet displacement, that is, the riveting force-rivet displacement curve. Research and practice have shown that the corresponding relationship between the riveting force and the rivet displacement can be used to preliminarily determine the riveting quality. Therefore, designing and controlling the riveting force-displacement curve is the key to affecting the riveting quality. Summary of the invention

[0006] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a design method of a self-piercing servo rivet gun controller and a self-piercing servo rivet gun controller, which automatically plans a rivet force-displacement curve that meets the riveting quality condition constraints according to the key node information on the riveting force-displacement curve input by the user, and designs the self-piercing servo rivet gun controller by performing force analysis on the rivet gun and adopting an admittance control strategy based on a riveting force closed loop, thereby accurately controlling the riveting force-displacement curve, effectively avoiding secondary processing, improving the riveting quality and efficiency, and realizing flexible riveting operations.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A first aspect of the present invention provides a design method for a self-piercing servo riveting gun controller.

[0009] A design method for a self-piercing servo riveting gun controller, comprising:

[0010] According to the key node information on the input or designed riveting force-displacement curve and the force position information of its neighborhood, a cubic spline function is used to plan a riveting force-displacement curve that meets the riveting quality condition constraints;

[0011] The force analysis of the rivet gun is carried out to obtain the riveting force. The admittance control strategy of the riveting force closed loop is adopted to design the self-piercing servo rivet gun controller so as to control the rivet gun to perform riveting operation according to the riveting force-displacement curve.

[0012] Furthermore, the riveting force is obtained by analyzing the stress conditions of the moving parts of the riveting gun and the rivet during the riveting process according to the mechanical structure of the self-piercing servo riveting gun.

[0013] Furthermore, the riveting force is the thrust exerted on the rivet by the rivet rod.

[0014] Furthermore, the riveting quality condition constraint is: according to the key node information and the force position information of its neighborhood, the slope of the riveting force-displacement curve is determined, and when the slope meets the limited condition, the riveting quality is qualified.

[0015] Furthermore, the process of adopting the cubic spline function includes:

[0016] According to the definition of cubic spline function, the function , is the rivet height, where ; The spline curve is actually composed of cubic curves between nodes, and the second-order derivative continuity is guaranteed at the nodes, and two-point cubic polynomial curve interpolation is used between the nodes;

[0017] Let the spline function The second-order derivative at the node is , select the interpolation node and , then in the interval superior, is a linear function, expressed as:

[0018]

[0019] The known key nodes and their derivative information are expressed as:

[0020]

[0021] right Integrate and use the above condition (1) to calculate the interval Upper cubic spline function The expression is:

[0022]

[0023] Taking the derivative of the above formula, we get The expression is:

[0024]

[0025] Similarly, calculate In the interval The expression on:

[0026]

[0027] According to the above condition (2), we can get:

[0028]

[0029] The coefficient , ,parameter and The expression is:

[0030]

[0031] in for About Dot and The first-order mean difference of , ,but Written in matrix form:

[0032]

[0033] Solving the above matrix gives the vector , substitute into the above cubic spline function In the expression of , we get the interpolation function The piecewise expression of ;

[0034] in, is the location information of the key nodes, For riveting force information, is the riveting force derivative information, and the above parameters are all input parameters.

[0035] Furthermore, the rivet feed rate measured in real time by the position sensor on the self-piercing servo riveting gun is input into the interpolation function The real-time setting value of the riveting force is obtained by using the piecewise expression of

[0036] Furthermore, the principle of the admittance control strategy is: according to the deviation of the riveting force, the movement of the rivet gun actuator-servo motor is calculated to obtain the actual displacement at a certain moment to control the corresponding riveting force on the riveting force-displacement curve.

[0037] Furthermore, the process of designing the self-piercing servo riveting gun controller includes:

[0038] Adopting the admittance control algorithm:

[0039]

[0040] Self-piercing servo riveting gun controller design method:

[0041]

[0042] Combining the above two formulas and performing Laplace transform, we can get the transfer function of the admittance controller:

[0043]

[0044] in is the actuator end force deviation, is the force deviation threshold, is the position increment of the actuator.

[0045] Furthermore, the process of designing the self-piercing servo riveting gun controller also includes: introducing the riveting force into the closed-loop control of the riveting gun, changing the given value of the riveting speed according to the riveting force deviation and based on the admittance control algorithm, and indirectly controlling the torque of the servo motor to achieve the set riveting force;

[0046] The speed increment output by the admittance controller is added to the initial speed value, which is the target speed command received by the servo drive.

[0047] A second aspect of the present invention provides a self-piercing servo riveter controller.

[0048] A self-piercing servo rivet gun controller adopts the design method of the self-piercing servo rivet gun controller described in the first aspect.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention can automatically plan a riveting force-displacement curve that meets the riveting quality condition constraints according to the key node information of the riveting process designed by the user, and at the same time design a riveting gun controller to perform riveting strictly according to the above riveting curve.

[0051] The present invention can effectively avoid secondary riveting, improve the quality and efficiency of riveting, and at the same time save the riveting quality monitoring system, reduce costs and improve the utilization rate of computing resources, thereby realizing flexible riveting operations. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0053] Figure 1 It is a schematic diagram of the self-piercing riveting process shown in the present invention;

[0054] FIG2 (a) is a schematic diagram of the force analysis of each part during the riveting process shown in the present invention. Figure 1 ;

[0055] FIG2 (b) is a second schematic diagram of force analysis of various parts during the riveting process shown in the present invention;

[0056] Figure 3 It is a schematic diagram of the riveting force-displacement curve and its node information shown in the present invention;

[0057] Figure 4 It is a control block diagram of the self-piercing servo riveting gun shown in the present invention;

[0058] Figure 5 It is a mechanical structure diagram of a self-piercing servo riveting gun shown in the present invention;

[0059] Figure 6 The present invention is a flow chart of a design method of a self-piercing servo riveting gun controller. DETAILED DESCRIPTION

[0060] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0061] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0062] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0063] It should be noted that the flowcharts and block diagrams in the accompanying drawings illustrate the possible implementation architecture, functions and operations of the methods and systems according to various embodiments of the present disclosure. It should be noted that each box in the flowchart or block diagram can represent a module, a program segment, or a part of a code, and the module, program segment, or a part of a code may include one or more executable instructions for implementing the logical functions specified in each embodiment. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the flowchart and / or block diagram, and the combination of boxes in the flowchart and / or block diagram can be implemented using a dedicated hardware-based system that performs a specified function or operation, or can be implemented using a combination of dedicated hardware and computer instructions.

[0064] Embodiment 1

[0065] like Figure 6 As shown, this embodiment provides a design method for a self-piercing servo rivet gun controller, including:

[0066] According to the key node information on the input or designed riveting force-displacement curve and the force position information of its neighborhood, a cubic spline function is used to plan a riveting force-displacement curve that meets the riveting quality condition constraints;

[0067] The force analysis of the rivet gun is carried out to obtain the riveting force. The admittance control strategy of the riveting force closed loop is adopted to design the self-piercing servo rivet gun controller so as to control the rivet gun to perform riveting operation according to the riveting force-displacement curve.

[0068] The SPR process is roughly divided into four stages (such as Figure 1 As shown in the figure: clamping stage (the rivet presses the sheet under the drive of the rivet rod), self-piercing stage (the rivet rod moves downward according to the set rules, pushing the rivet to pierce the upper sheet), expansion stage (the rivet leg enters the lower sheet and gradually expands to the surrounding), interlocking stage (an interlocking structure is gradually formed between the rivet leg and the sheet).

[0069] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0070] The design method of this embodiment includes:

[0071] Step 1: Combined with the mechanical structure of the riveting gun, the force conditions of the moving parts of the riveting gun and the rivet during the riveting process are analyzed (as shown in Figure 2 (a)-Figure 2 (b)), and the physical definition of the riveting force is given;

[0072] Step 2: According to the detection rules of riveting quality, extract the force and position information of key nodes and their neighborhoods in the self-piercing riveting process (such as Figure 3 ), and use cubic spline to quickly fit the riveting force-displacement curve;

[0073] Step 3: For the planned riveting force-displacement curve, design the riveting gun controller based on the admittance control strategy (such as Figure 4 ), to achieve precise control of the riveting force-displacement curve.

[0074] In the first step, in order to accurately control the servo motor during the riveting process, force analysis is essential. According to the mechanical structure of the self-piercing servo riveting gun (such as Figure 5 As shown in Figure 1), the force analysis of the moving parts of the rivet and the riveter is carried out respectively (as shown in Figure 2 (a) and Figure 2 (b)). In Figure 2 (a), The rivet is subjected to a thrust from the rivet rod (i.e. the riveting force referred to in the present invention, which is measured by the force sensor 1 and constitutes a full closed-loop control of the riveting gun system force, and can be flexibly designed according to the workpiece material and the riveting process). is the weight of the rivet itself, is the resistance of the riveted sheet to the rivet. In Figure 2 (b), It is the force applied by the servo motor to the moving part of the rivet gun through the reducer and roller screw. is the equivalent gravity of the moving part as a whole, is the elastic force generated by the elastic element, is the sliding friction force on the moving part as a whole. From Figure 2 (a) - Figure 2 (b), the following relationship can be obtained:

[0075] (1)

[0076] in, is the motion acceleration. It should be pointed out that Figure 2 (a)-Figure 2 (b) are schematic diagrams of force analysis when the rivet gun is placed vertically. In actual riveting, the rivet gun is carried by a robot and its posture changes continuously with the change of the riveting position. When the posture of the rivet gun changes, the equivalent gravity of the moving part and sliding friction will change, the other forces remaining constant.

[0077] In the second step, a large number of experiments are conducted to summarize the criteria for determining good riveting quality, and the riveting force information of the key nodes and their neighborhoods that determine the riveting quality is analyzed and extracted. Assuming that the workpiece plate, rivet, and die have been determined and successfully matched, the position information of the key nodes is , the riveting force information is , the riveting force derivative information is .like Figure 3 The dotted window in the middle is the quality monitoring window. In this window, the overall slope of the riveting curve must meet the specified conditions to be considered as qualified riveting quality. According to the definition of the cubic spline function, the function , is the rivet height, where The spline curve is actually composed of cubic curves between nodes, and the second-order derivative continuity is guaranteed at the nodes, and two-point cubic polynomial curve interpolation is used between the nodes.

[0078] Let the spline function The second-order derivative at the node is , select the interpolation node and , then in the interval superior, is a linear function and can be expressed as:

[0079] (2)

[0080] The known key nodes and their derivative information can be expressed as:

[0081]

[0082] right Integrate and use the above condition 1 to calculate the interval Upper cubic spline function The expression is:

[0083] (3)

[0084] Taking the derivative of the above formula, we get The expression is:

[0085] (4)

[0086] Similarly, we can calculate In the interval The expression on:

[0087] (5)

[0088] According to the above condition 2, we can get:

[0089] (6)

[0090] The coefficient , ,parameter and The expression is:

[0091] (7)

[0092] in for About Dot and The first-order mean difference of , , then the above formula 2 is written in matrix form as:

[0093] (8)

[0094] Solving the above matrix gives the vector , substituting into the above formula 3, we can get the interpolation function By substituting the rivet feed amount measured by the position sensor in real time into the segmented expression, the real-time setting value of the riveting force can be obtained.

[0095] In the third step, the power source of the self-piercing servo riveting gun is a permanent magnet synchronous motor (PMSM), the working mode of the servo driver is speed control (ISMC), and the admittance control strategy is used to design the riveting gun controller. The control block diagram is shown in the figure. Figure 4 The basic principle of admittance control is to calculate the movement of the rivet gun actuator-servo motor according to the deviation of the riveting force, and then achieve the control target of the riveting force-displacement curve. The general expression of the admittance control algorithm is:

[0096] (9)

[0097] in is the actuator end force deviation, is the force deviation threshold, is the position increment of the actuator. In the design method of the self-piercing servo riveting gun controller proposed in the present invention:

[0098] (10)

[0099] Substituting equation 10 into equation 9 and performing Laplace transform, the transfer function of the admittance controller can be obtained:

[0100] (11)

[0101] The control block diagram of the self-piercing servo riveting gun disclosed in the present invention is as follows: Figure 4 As shown in the figure, during the riveting process, the riveting force is introduced into the closed-loop control of the riveting gun. According to the riveting force deviation and based on the admittance control algorithm, the given value of the riveting speed is changed, and the torque of the servo motor is indirectly controlled to achieve the set riveting force. Applied to the initial value of velocity The target speed command received by the servo drive is By adjusting the control parameters , , , a good system response can be obtained.

[0102] Embodiment 2

[0103] This embodiment provides a self-piercing servo rivet gun controller.

[0104] A self-piercing servo rivet gun controller adopts the design method of the self-piercing servo rivet gun controller described in the first embodiment.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. The design method of the self-piercing servo riveting gun controller is characterized in that: include: According to the key node information on the input or designed riveting force-displacement curve and the force position information of its neighborhood, a cubic spline function is used to plan a riveting force-displacement curve that meets the riveting quality condition constraints; The force analysis of the riveting gun is carried out to obtain the riveting force, and the self-piercing servo riveting gun controller is designed by adopting the admittance control strategy of the riveting force closed loop to control the riveting gun to perform riveting operations according to the riveting force-displacement curve; The riveting force is obtained by analyzing the force conditions of the moving part of the riveting gun and the rivet during the riveting process according to the mechanical structure of the self-piercing servo riveting gun, specifically: The riveting force is , measured by force sensors, forming a full closed-loop control of the riveting gun system force, and flexibly designed according to the workpiece material and riveting process. is the weight of the rivet itself, is the resistance of the riveted sheet to the rivet, It is the force applied by the servo motor to the moving part of the rivet gun through the reducer and roller screw. is the equivalent gravity of the moving part as a whole, is the elastic force generated by the elastic element, The sliding friction force on the moving part as a whole is analyzed by combining the mechanical structure of the riveting gun to analyze the force on the moving part of the riveting gun and the rivet during the riveting process, and the following relationship is obtained: （1） in, It is the motion acceleration. It should be pointed out that in actual riveting, the rivet gun is carried by the robot and its posture changes with the change of the riveting position. When the posture of the rivet gun changes, the equivalent gravity of the moving part and sliding friction will change, the other forces remaining constant.

2. The design method of the self-piercing servo riveter controller according to claim 1 is characterized in that: The riveting force is the thrust exerted on the rivet by the rivet rod.

3. The design method of the self-piercing servo riveting gun controller according to claim 1 is characterized in that: The riveting quality condition constraint is: according to the key node information and the force position information of its neighborhood, the slope of the riveting force-displacement curve is determined, and when the slope meets the limited condition, the riveting quality is qualified.

4. The design method of the self-piercing servo riveting gun controller according to claim 1 is characterized in that: The process of adopting the cubic spline function comprises: According to the definition of cubic spline function, the function , is the rivet height, where ; The spline curve is actually composed of cubic curves between nodes, and the second-order derivative continuity is guaranteed at the nodes, and two-point cubic polynomial curve interpolation is used between the nodes; Let the spline function The second-order derivative at the node is , select the interpolation node and , then in the interval superior, is a linear function, expressed as: The known key nodes and their derivative information are expressed as: right Integrate and use the above condition (1) to calculate the interval Upper cubic spline function The expression is: Taking the derivative of the above formula, we get The expression is: Similarly, calculate In the interval The expression on: According to the above condition (2), we can get: The coefficient , ,parameter and The expression is: in for About Dot and The first-order mean difference of , ,but Written in matrix form: Solving the above matrix gives the vector , substitute into the above cubic spline function In the expression of , we get the interpolation function The piecewise expression of ; in, is the location information of the key nodes, For riveting force information, It is the riveting force derivative information.

5. The design method of the self-piercing servo riveting gun controller according to claim 4 is characterized in that: The rivet feed rate measured in real time by the position sensor on the self-piercing servo riveting gun is input into the interpolation function The real-time setting value of the riveting force is obtained by using the piecewise expression of 6. The design method of the self-piercing servo riveting gun controller according to claim 1 is characterized in that: The principle of the admittance control strategy is: according to the deviation of the riveting force, the movement of the rivet gun actuator-servo motor is calculated to obtain the actual displacement at a certain moment to control the corresponding riveting force on the riveting force-displacement curve.

7. The design method of the self-piercing servo riveting gun controller according to claim 1 is characterized in that: The process of designing a self-piercing servo riveter controller includes: Adopting the admittance control algorithm: Self-piercing servo riveting gun controller design method: Combining the above two formulas and performing Laplace transform, we can get the transfer function of the admittance controller: in is the actuator end force deviation, is the force deviation threshold, is the position increment of the actuator, is the initial angular velocity of the servo motor.

8. The design method of the self-piercing servo riveting gun controller according to claim 7 is characterized in that: The process of designing the self-piercing servo riveting gun controller also includes: introducing the riveting force into the closed-loop control of the riveting gun, changing the given value of the riveting speed according to the riveting force deviation and based on the admittance control algorithm, and indirectly controlling the torque of the servo motor to achieve the set riveting force; The speed increment output by the admittance controller is added to the initial speed value, which is the target speed command received by the servo drive.

9. Self-piercing servo riveting gun controller, characterized in that: The design method of the self-piercing servo riveting gun controller according to any one of claims 1 to 8 is adopted.

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