Intelligent upsetting and riveting method of automatic drilling and riveting machine based on force-position hybrid control

Abstract

The invention discloses an intelligent upsetting riveting method of an automatic drilling and riveting machine based on force-position hybrid control, and relates to the field of intelligent riveting control, and the method comprises the following steps: driving a riveting shaft to be fed to a preset approaching area at a first movement speed through a position control mode; based on real-time displacement feedback and dynamic error judgment of a target position, a control mode is triggered to be seamlessly switched to a force control mode; in the force control mode, force signals fed back by a pressure sensor are synchronously collected through a distributed real-time I / O system; when the force signal reaches a dynamically-calibrated preset threshold value, the feeding motion of the riveting shaft is stopped immediately to complete upsetting and riveting forming; and then the riveting shaft is controlled to reversely break away from the riveting area at the second movement speed. According to the scheme, the control precision and stability of riveting force can be remarkably improved, riveting force fluctuation caused by material deformation or external interference is effectively restrained, and therefore the consistency of upset head forming quality and the reliability of a connecting structure are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of intelligent riveting control, and in particular to an intelligent upsetting method for an automatic drilling and riveting machine based on force-position hybrid control. Background Technology

[0002] Drilling and riveting technology, a key mechanical connection process in aircraft panel assembly in the aerospace manufacturing field, has been widely adopted due to its advantages such as light weight and high connection strength. This technology has evolved from manual hammer riveting and pneumatic riveting to CNC automated drilling and riveting methods. With the increasing demands for connection quality in aerospace components, achieving high-precision control of riveting force during the riveting process has become a core challenge for improving the consistency of rivet upsetting and connection reliability. Traditional CNC drilling and riveting systems mostly employ closed-loop position control. While they can achieve high speed and high positioning accuracy, they have significant limitations in force control, often using force signals only as auxiliary monitoring parameters without incorporating them into the core control loop, thus making it difficult to achieve real-time and precise control of the riveting force.

[0003] Existing automatic drilling and riveting methods, primarily based on position control, suffer from several limitations due to the lack of closed-loop force signal control: First, the system cannot dynamically adjust its actions according to the actual riveting force, making it susceptible to deviations from the ideal range due to material deformation, friction, and other factors, leading to quality defects such as over-riveting or insufficient riveting strength. Second, traditional methods lack a force protection mechanism during the rivet contact stage, with the riveting axis often prioritizing displacement, resulting in uncontrollable plastic deformation of the rivet or connector, affecting molding consistency and fatigue performance. Furthermore, the existing control architecture suffers from delays in force detection and response, failing to meet the high real-time and synchronous requirements of aerospace riveting processes, thus limiting its application potential in high-end manufacturing. Therefore, based on these challenges, this invention proposes an intelligent upsetting method for automatic drilling and riveting machines based on force-position hybrid control. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide an intelligent upsetting method for automatic drilling and riveting machines based on force-position hybrid control. This method addresses the issue that existing automatic drilling and riveting machines, due to their single-position control mode, cannot accurately control the riveting force during the riveting process, resulting in unstable riveting quality and poor consistency in upsetting head formation. While ensuring positioning accuracy, the method precisely controls the magnitude and timing of the riveting force, thereby significantly improving the riveting formation quality and connection reliability, and meeting the needs of the aerospace manufacturing industry for high-precision and high-efficiency riveting processes.

[0005] To achieve the above objectives, this invention provides an intelligent upsetting method for an automatic drilling and riveting machine based on force-position hybrid control. This method uses a CNC system as the core control unit, integrating a length detection device and a pressure sensing device to provide high-precision position feedback and real-time force feedback, respectively. Through macro-program logic judgment, during the riveting shaft feed process, a position control mode is first used to quickly position the machine to the rivet area, and then it automatically switches to a force control mode. The riveting force signal collected in real-time is compared with a preset threshold to control the termination and exit of the riveting action. The force signal is transmitted via a high-speed synchronous communication interface to ensure system response speed and control accuracy, thereby completing a high-quality intelligent upsetting process with force-position hybrid control.

[0006] In a first aspect, the present invention provides an intelligent upsetting method for an automatic drilling and riveting machine based on force-position hybrid control, comprising: The riveting shaft is driven by the position control mode to feed to the preset approach area at the first motion speed; Based on real-time displacement feedback and dynamic error determination of target position, the trigger control mode seamlessly switches to force control mode, realizing the synergy of high-speed positioning and precise force control; In force control mode, the force signal fed back by the pressure sensor is synchronously acquired through a distributed real-time I / O system to ensure that the acquisition cycle of the force signal and the position signal are strictly matched. When the force signal reaches the preset threshold of dynamic calibration, the feed motion of the riveting shaft is immediately terminated to complete the upsetting process and suppress the fluctuation of riveting force caused by material deformation or external interference. Then, the riveting shaft is controlled to move in the opposite direction at a second speed away from the riveting area, ensuring the consistency of the upsetting head forming quality and the reliability of the connection.

[0007] Furthermore, the triggering condition for the dynamic error determination is that the displacement error is lower than the critical tolerance threshold, and the mode switching is achieved through pre-compiled real-time interrupt control logic to ensure that the switching action is completed within a single control cycle.

[0008] Furthermore, the distributed real-time I / O system adopts an isochronous synchronization protocol based on industrial Ethernet to ensure that the acquisition cycle of force signals and position signals matches the control cycle of the CNC system.

[0009] Furthermore, the preset threshold for dynamic calibration is generated through the following steps: During the low-speed contact phase, the coordinated response characteristics of the force signal change gradient and micro-displacement are monitored simultaneously. Identify the nonlinear transition points of the force response curve and record the critical force value; A dynamic compensation mechanism based on a safety factor generates a preset threshold to ensure that the rivet is in the elastic deformation stage during switching.

[0010] Furthermore, the nonlinear transition point is identified based on the detection of a force signal change gradient exceeding a preset gradient threshold, accompanied by the detection of micron-level plastic deformation. The threshold calibration is completed before plastic deformation by real-time interruption logic.

[0011] In a second aspect, the present invention also provides an intelligent upsetting and riveting system for an automatic drilling and riveting machine based on force-position hybrid control, the system being based on the method described in the first aspect above, comprising: CNC system, length detection device and pressure sensor integrated into the riveting shaft, distributed real-time I / O system and parameter adaptive module; The distributed real-time I / O system directly connects the position signal output by the length detection device to the dedicated encoder interface of the CNC system, and transmits the force signal of the pressure sensing device through the isochronous real-time communication protocol, thus constructing a dual closed-loop hybrid control architecture of force and position. The parameter adaptive module stores multiple sets of calibration parameters corresponding to rivet specifications and dynamically calls the preset threshold to achieve process adaptability and riveting quality stability.

[0012] Furthermore, the CNC system is equipped with pre-compiled real-time interrupt control logic, which is used to perform dynamic error judgment and mode switching operations to ensure real-time parsing and response of control commands.

[0013] Furthermore, the CNC system is configured collaboratively as follows: Continuously monitor the gradient of force signal changes in force control mode; When the real-time force value reaches the preset threshold, the riveting shaft is triggered to stop urgently within a single control cycle through the real-time interrupt control logic, eliminating over-riveting or under-riveting defects.

[0014] Furthermore, the parameter adaptive module further implements statistical process control of the calibration data, including mean filtering and standard deviation analysis of the critical force value, and triggers an early warning mechanism when the data is abnormal, so as to realize real-time monitoring of rivet material and clamping status.

[0015] Furthermore, the parameter adaptive module performs statistical process control of the calibration data in real time, including: The critical force values ​​of the same specification rivets obtained from multiple calibrations are subjected to mean filtering. The standard deviation of the critical force value was calculated and a historical statistical benchmark was established; When a single calibration value deviates from the historical statistical benchmark and exceeds the preset tolerance range, an abnormal rivet material warning is triggered, forming a closed-loop quality feedback mechanism.

[0016] This invention uses a CNC system as the control center, integrating a length detection device and a pressure sensing device to provide high-precision position feedback and real-time force signal feedback, respectively. During the riveting process, the system first employs a position control mode to achieve rapid and accurate positioning of the riveting shaft. Upon reaching a preset proximity position, it automatically switches to a force control mode. By continuously monitoring the riveting force signal and comparing it in real-time with a set threshold, the system controls the timely termination and exit of the riveting action, ultimately achieving high-precision, adaptive control of the entire riveting process.

[0017] This solution significantly improves the control precision and stability of riveting force through a dual closed-loop hybrid control of force and position. It effectively suppresses riveting force fluctuations caused by material deformation or external interference, thereby ensuring the consistency of upsetting quality and the reliability of the connection structure. The system combines the advantages of high-speed positioning and precise force control, adapting to various riveting process requirements, significantly improving the overall quality and automation level of the riveting process, and meeting the stringent demands for precision connection technology in the high-end equipment manufacturing sector.

[0018] Beneficial effects By implementing the intelligent upsetting method for an automatic drilling and riveting machine based on force-position hybrid control provided by the present invention, the following technical effects are achieved: (1) By organically integrating position control and force control into the same riveting process, the seamless switching between the two control modes not only retains the high speed and high positioning accuracy of position control, but also realizes the precise force value adjustment of force control, thereby fundamentally solving the process problem of large fluctuations in riveting force and inconsistent forming quality under a single control mode.

[0019] (2) By adopting a high-speed isochronous synchronous communication interface to integrate force and position sensing information, the force signal and position signal are collected and processed within a very short system cycle, which greatly reduces the signal transmission and response delay, provides a key hardware foundation for high-precision closed-loop control of the riveting process, and significantly improves the system response speed and control real-time performance.

[0020] (3) A dynamic threshold setting mechanism based on material properties and rivet parameters and combined with low-speed contact calibration experiments is proposed. The force control switching point can be automatically calibrated under different riveting conditions, which can avoid excessive riveting force leading to structural damage and ensure good process adaptability and stability of the riveting process.

[0021] (4) By relying on the macro program of the CNC system, the control command is analyzed in real time and the action decision is made. The entire process of automatic control from rapid feed and force control switching to riveting termination is completed, which significantly improves the intelligence and reliability of riveting action and effectively meets the complex process requirements of high-quality and high-efficiency riveting in aerospace manufacturing. Attached Figure Description

[0022] To make the above-described intelligent upsetting method for an automatic drilling and riveting machine based on force-position hybrid control of the present invention more obvious and understandable, the accompanying drawings used in the specific embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a flowchart illustrating the method described in this application; Figure 2 This is a schematic diagram illustrating the principle of this application. Detailed Implementation

[0024] Example 1: An intelligent upsetting method for an automatic drilling and riveting machine based on force-position hybrid control is provided. The method flow is as follows: Figure 1 As shown, the principle is as follows Figure 2 As shown, the process includes: driving the riveting shaft to feed to a preset approach area at a first motion speed through a position control mode; triggering a seamless switch from control mode to force control mode based on real-time displacement feedback and dynamic error determination of the target position; in force control mode, synchronously acquiring force signals fed back from pressure sensors through a distributed real-time I / O system; when the force signal reaches a dynamically calibrated preset threshold, immediately terminating the feeding motion of the riveting shaft to complete the upsetting process; and then controlling the riveting shaft to reverse and disengage from the riveting area at a second motion speed.

[0025] The details are as follows.

[0026] First, an automatic drilling and riveting machine control system was built. This system uses a high-end CNC system as its core control unit. A length detection device and a pressure sensor are precisely installed on the riveting shaft. A linear encoder, serving as a second measurement system, is directly connected to the dedicated encoder interface of the CNC system to achieve position feedback. The analog output signal from the force sensor is connected to a high-precision signal processing module. This high-precision signal processing module is connected to the CNC system via PROFINET industrial Ethernet and uses the IRT (Isochronous Real-Time) communication protocol to control the jitter of the entire force signal acquisition and transmission cycle to the microsecond level, ensuring strict synchronization with the position control cycle and laying the foundation for hybrid control.

[0027] During the riveting process, the host computer issues riveting commands. The programmable control logic in the CNC system then begins execution. First, the system enters position control mode: the CNC system drives the servo motor, and based on the high-precision position information fed back by the grating ruler, controls the riveting axis to rapidly feed to a preset position very close to the top of the rivet head. This stage fully utilizes the high-gain characteristics of the position loop to achieve high-speed and precise positioning.

[0028] When the error between the actual position fed back by the grating ruler and the target position falls within a very small range, the macro program immediately triggers a mode switch. The system seamlessly transitions to force control mode. In this mode, the CNC system continuously reads and samples the real-time force signal at high speed through a high-precision signal processing module, and compares it with a preset force threshold. This threshold is pre-calibrated through offline experiments and stored in the system parameters based on the rivet material, diameter, and target upsetting head size.

[0029] Once the real-time force value is detected to reach or exceed the preset threshold, the macro program immediately issues an "emergency stop" command in the next control cycle, halting all feed movements of the servo motor. At this point, the rivet head has been precisely formed. Subsequently, the control logic commands the riveting shaft to retract rapidly in the opposite direction at a predetermined speed, detaching it from the workpiece and completing the entire riveting cycle. Through the precise intervention of the force control mode, the system completely avoids defects such as over-riveting or under-riveting that may occur due to relying solely on the displacement endpoint, ensuring a high degree of consistency in riveting quality.

[0030] The same equipment uses only the traditional position control mode, the target riveting force is set to 20kN, and 500 rivets are continuously riveted under each control mode. The comparison results of the force-position hybrid control method with the traditional position control method in terms of riveting accuracy, quality consistency and stability are shown in Table 1.

[0031] Table 1. Comparison results of riveting accuracy, quality consistency, and stability.

[0032] Verification shows that, while achieving a similar average error to the above embodiments, this method offers orders of magnitude improvements in riveting force control accuracy, upsetting head forming quality consistency, and process reliability compared to traditional position control schemes. Although the single-point riveting cycle is slightly extended due to the addition of a force control step, the overall improvement in quality and efficiency makes it fully applicable to the demanding aerospace manufacturing field. Experimental results demonstrate that, compared to traditional position control schemes, this method exhibits significant advantages in riveting force control accuracy, upsetting head forming quality consistency, and process stability. It effectively suppresses riveting force fluctuations, improves forming size uniformity, significantly reduces scrap rates, and achieves precise closed-loop control of the riveting process through high real-time system response capabilities. This comprehensively improves the reliability, consistency, and overall performance of the riveting process, meeting the stringent requirements of precision connection technology in the high-end equipment manufacturing field.

[0033] Example 2: Based on the aforementioned embodiments, this paper focuses on how to adaptively determine and optimize key force control thresholds through a dynamic calibration process to adapt to different rivet specifications and working conditions, thereby further enhancing the versatility and reliability of the system.

[0034] Upon initial equipment use, or after changing rivet batches or specifications, the system initiates a built-in parameter calibration program. This program guides the operator to move the riveting shaft over the workpiece with the new rivet already clamped.

[0035] At the start of calibration, the system controls the riveting shaft to slowly feed towards the rivet at an extremely low speed. During this process, the macro program monitors the gradient changes of the force sensor signal in real time at the highest sampling rate. Simultaneously, the system integrates the position information from the grating ruler to accurately calculate the micro-displacement of the riveting shaft.

[0036] When the pressure value detected by the force sensor shows a non-linear jump, and simultaneously a micron-level plastic deformation is detected on the riveting shaft under continuous feed conditions, the macro program determines that the rivet has entered the initial plastic deformation stage from elastic deformation. The program immediately records the instantaneous force value at this critical point and calculates it according to the formula:

[0037] In the formula, This is the material deformation coefficient, used to compensate for nonlinear factors such as sheet metal constraint forces and frictional losses. The value is dynamically adjusted according to the rivet specifications, sheet material and surface treatment, with a typical range of 0.85 to 1.15. This represents the instantaneous force value during plastic deformation. The yield strength of the rivet material; Let be the cross-sectional area of ​​the rivet.

[0038] Therefore, the relationship between the instantaneous force value and the yield strength of the rivet material, the rivet diameter, and the target upset head forming size is as follows:

[0039] In the formula, This represents the instantaneous force value.

[0040] Subsequently, the system automatically calculates the force control switching threshold based on a pre-stored algorithm:

[0041] In the formula, Force control switching threshold; This represents the instantaneous force value.

[0042] This measure aims to ensure that the system switches to force control mode before significant plastic deformation of the rivet occurs during subsequent formal riveting, thereby absolutely avoiding any pre-damage to the rivet or workpiece. The calculated threshold is automatically written into the system parameter library and bound to the rivet specification for use in subsequent batch riveting.

[0043] Furthermore, the system can perform mean filtering on the instantaneous force values ​​of rivets of the same specification obtained from multiple calibrations and record their standard deviation. This not only allows for adaptive threshold setting but also enables process monitoring of the rivet quality consistency. If abnormal fluctuations in instantaneous force values ​​are detected during calibration, the system can issue an alarm to the operator, indicating potential abnormalities in rivet material or clamping.

[0044] By introducing this dynamic calibration and adaptive mechanism, the system described in this invention no longer relies on a fixed force threshold, but can learn and adjust its core parameters to intelligently adapt to changes in the production process, thus achieving truly intelligent and highly reliable riveting.

Claims

1. An intelligent upsetting and riveting method of a force-position hybrid control-based automatic drilling and riveting machine, characterized in that, Comprising: Driving the riveting shaft to feed into a preset approaching area at a first motion speed through a position control mode; Triggering a seamless switch to a force control mode based on a dynamic error determination of real-time displacement feedback and target position; In the force control mode, synchronously collecting force signals fed back by pressure sensors through a distributed real-time I / O system; When the force signal reaches a preset threshold value of dynamic calibration, immediately terminating the feeding motion of the riveting shaft to complete the rivet forming; Subsequently, controlling the riveting shaft to reverse away from the riveting area at a second motion speed.

2. The method according to claim 1, wherein: The trigger condition of the dynamic error determination is that the displacement error is lower than a critical tolerance threshold, and the mode switching is realized through pre-compiled real-time interrupt control logic.

3. The method according to claim 1, wherein: The distributed real-time I / O system adopts an isochronous synchronization protocol based on industrial Ethernet to ensure that the collection period of the force signal and the position signal matches the control period of the numerical control system.

4. The method of claim 1, wherein, The preset threshold value of dynamic calibration is generated by the following steps: In the low-speed contact stage, the cooperative response characteristics of the force signal change gradient and the micro displacement are synchronously monitored; The nonlinear transition point of the force-position response curve is identified, and the critical force value is recorded; The preset threshold value is generated based on a dynamic compensation mechanism of a safety factor to ensure that the rivet is in the elastic deformation stage when switching.

5. The method according to claim 4, wherein: The identification basis of the nonlinear transition point is that the force signal change gradient exceeds a preset gradient threshold value, accompanied by the detection of micron-level plastic deformation.

6. A force-position hybrid control based intelligent upsetting and riveting system of an automatic drilling and riveting machine, characterized in that: The system executes the method of any one of claims 1-5 when in operation, comprising: A numerical control system, a length detection device and a pressure sensing device integrated in the riveting shaft, a distributed real-time I / O system, and a parameter adaptive module; The distributed real-time I / O system directly connects the position signal output by the length detection device to the special encoder interface of the numerical control system, and transmits the force signal of the pressure sensing device through an isochronous synchronization real-time communication protocol; The parameter adaptive module stores multiple sets of calibration parameters corresponding to rivet specifications, and dynamically calls the preset threshold value.

7. The system according to claim 6, wherein: The numerical control system is configured with pre-compiled real-time interrupt control logic for performing dynamic error determination and mode switching operations.

8. The system of claim 7, wherein, The numerical control system is configured to: Continuously monitor the force signal change gradient in the force control mode; When the real-time force value reaches the preset threshold value, the riveting shaft is triggered to stop urgently within a single control period through real-time interrupt control logic.

9. The system according to claim 6, wherein: The parameter adaptive module further implements statistical process control of calibration data, including mean filtering processing and standard deviation analysis of the critical force value, and triggers a warning mechanism when the data is abnormal.

10. The system of claim 9, wherein, The parameter adaptive module performs real-time statistical process control of calibration data, including: Mean filtering processing of the critical force value of the same specification rivet obtained through multiple calibrations; Calculating the standard deviation of the critical force value and establishing a historical statistical benchmark; When the single calibration value deviates from the historical statistical benchmark and exceeds the preset tolerance range, a rivet material abnormality early warning is triggered.

Images