CN103434653B - Aircraft component digitized flexible assembling measuring method based on laser tracking measuring technique - Google Patents

Abstract

A digital flexible assembly measurement method for aircraft components based on laser tracking measurement technology, the assembly measurement method includes the following steps: step 1: assembly measurement preparation; step 2: assembly measurement work; step 3: real-time parallel collaborative measurement. The invention relates to the combination of two technologies of assembly and measurement. It compares the theoretical position information of the digital model of the product in the engineering data set with the coordinates of the reference point of the assembly part obtained by the laser tracker in real time, forms a position deviation, and transmits it to the motion control system. The motion control system generates tooling pose control commands by analyzing the position deviation, and transmits them to the flexible tooling. The flexible tooling drives the workpiece to adjust the pose together. Through the coordinated operation of the three, a closed-loop control system is formed to complete the assembly work. The invention has better practical value and broad application prospect in the fields of laser tracking measurement technology and aircraft digital assembly.

Description

A digital flexible assembly measurement method for aircraft components based on laser tracking measurement technology

technical field

The invention is a digital flexible assembly measurement method for aircraft parts based on laser tracking measurement technology, which belongs to the field of laser tracking measurement technology and aircraft digital assembly.

Background technique

The design of modern aircraft is developing in the direction of structural integration, large-scale parts, and manufacturing precision. This not only increases the difficulty of parts manufacturing, but also increases the requirements for assembly quality. The development of foreign assembly technology is very rapid. Advanced digital technology is used to realize its precise assembly, and a large number of digital definition models and optical measurement and positioning technology and equipment are used. Domestic aircraft manufacturing and assembly are still relatively weak. These advanced technologies have not been systematically researched and applied, and a complete system has not been formed.

Digital assembly measurement technology is one of the key technologies in large-scale aircraft manufacturing, and it runs through the entire process of large-scale aircraft manufacturing. In recent years, laser tracking measurement technology has been widely introduced by major aviation manufacturing enterprises, but it is mainly used in quality inspection, tooling installation, etc., and has failed to achieve new breakthroughs in digital assembly technology, resulting in high aircraft manufacturing costs and leading to advanced Advanced measuring equipment cannot play its due role in aircraft manufacturing.

How to use new assembly technology and adopt reasonable process methods to improve the assembly efficiency of aircraft components, and at the same time, how to minimize design changes, reduce error rework rate, and improve assembly accuracy in terms of benefits have always been the focus of my country's aviation manufacturing production. Issues yet to be studied and resolved.

According to the characteristics of aircraft components, the quality and efficiency of aircraft component assembly can be greatly improved by establishing digital standard workers, using laser trackers to install assembly tools, collecting assembly data in real time during assembly, and simulating assembly effects .

Contents of the invention

1) Purpose: Laser tracking measurement technology is mainly used in precision testing and tooling installation in the field of aviation manufacturing. It is not yet mature for the application in the field of aircraft assembly, especially in the process of digital flexible assembly of aircraft components. Laser tracking measurement technology has great potential. application potential and value. The present invention is a digital flexible assembly measurement method for aircraft parts based on laser tracking measurement technology. It is a new method proposed for flexible assembly, complex process and high precision requirements in large aircraft assembly by using laser tracking measurement technology. The assembly measurement method has strong practicability and feasibility.

The purpose of the assembly measurement method in the present invention is to solve the following problems:

1. Meet the flexible assembly requirements

In the modern aircraft assembly process, due to more frequent aircraft model improvements, there are high requirements for assembly efficiency. The flexibility of assembly tooling has become a development trend, and assembly measurement methods must also meet the requirements of flexibility. Digital flexible assembly uses digital standard work as the basis for size coordination. The assembly measurement method proposed in the invention can perform different assembly tasks according to different digital standard workers to meet the requirements of flexible assembly. The digital flexible assembly measurement method for aircraft components proposed in the invention is one of the core technologies of the invention.

2. Real-time parallel collaborative measurement

During the assembly process of aircraft components, it is necessary to determine the position data of multiple points in real time, and multiple laser trackers work together to complete the measurement work. According to the problem of real-time coordination of multiple laser trackers encountered in actual assembly, the present invention proposes a multi-thread parallel cooperative measurement method, which is one of the core technologies of the present invention.

3. Improve assembly accuracy

Due to the fact that assembly tooling will have certain errors in the process of manufacturing, assembly and installation, in the traditional assembly method, the quality of aircraft assembly will be affected by the manufacturing accuracy of the tooling. The digital assembly measurement method is adopted to directly transfer the assembly dimension data of aircraft components according to the digital standard, so that the assembly accuracy is improved.

4. Build the assembly measurement environment

In the process of digital assembly measurement, in order to facilitate assembly measurement, it is necessary to consider real-time measurement process interaction at the software level, such as the display of assembly position changes, assembly status prompts, and the values of various quality inspection indicators. During the assembly measurement process, the measurement data is sent to the real-time simulation system in a packaged manner, and stored as simulation history data.

2) Technical solution: The specific content of the digital flexible assembly measurement method for aircraft parts based on laser tracking measurement technology is to compare the theoretical position information of the product digital model in the engineering data set with the coordinates of the reference point of the assembly part obtained in real time by the laser tracker to form a position The deviation is transmitted to the motion control system. The motion control system generates tooling pose control commands by analyzing the position deviation, and transmits them to the flexible tooling. The flexible tooling drives the workpiece to adjust the pose together. Through the coordinated operation of the three, a closed-loop control system is formed to complete Assembly work. The invention is a digital flexible assembly measurement method of aircraft parts based on laser tracking measurement technology, which involves two technologies of assembly and measurement, and is a combination of the two, not a simple assembly or a simple measurement method, and is suitable for digital flexible assembly of aircraft parts assembly measurement method. The relationship between the assembly measurement system and the surrounding boundary system is shown in Figure 1, and the overall flow of the assembly measurement method is shown in Figure 2. The assembly measurement method includes the following implementation steps:

Step 1: Preparation for assembly measurement:

The assembly measurement preparation stage mainly completes the preparation of the assembly measurement data model, and establishes the assembly measurement data as the basis for the assembly measurement. Assembly measurement data mainly includes reference point position data, assembly part data, tooling data, assembly quality inspection data, measurement point position data, laser tracker position data, tooling positioning measurement point and other auxiliary coordinate point data.

The independent digital model file import method can meet the flexibility requirements in different assembly tasks. In the whole assembly process, the simplified tooling digital model and assembly parts are the main data in the dynamic assembly simulation, which are used for real-time interaction; the reference point provides the basis for the construction of the assembly environment and assembly coordinate system; the digital standard is the basis for assembly quality inspection; measurement The point is the direct acquisition point of the laser tracker during the assembly process, which is directly related to the execution of the assembly command of the control system and the final assembly quality. The following are the detailed execution steps:

1. Export the tooling data from the engineering data set, simplify the tooling model, and separate the independent motion mechanisms to facilitate assembly measurement simulation.

2. Export the assembly data from the engineering data set to simplify the assembly model.

3. In the process of digital flexible assembly of aircraft components, in the actual assembly measurement environment, according to the accuracy requirements specified in the design, three measurement reference holes are manufactured and target mirrors are installed to establish assembly measurement environment reference points. Select locations with high rigidity and good openness in the environment, such as the edge and corner positions of the tooling frame, and establish more auxiliary benchmark measurement holes. During the assembly of aircraft components, if there is a fixed part, the upper three points can also be selected as the reference points of the aircraft assembly environment.

4. According to the requirements of the assembly quality inspection data, establish a digital standard model for aircraft assembly. In each assembly in the flexible assembly, at least 3 measurement reference points need to be calibrated. The specific position of each measurement reference point can be determined according to the actual situation Sure. When taking points, it should be noted that, starting from the requirements of stable and accurate positioning, the points must be within the measurement range of the laser tracker, and the inner angle of the triangle formed by the three points must be kept within the predetermined range, and obtuse angle relationship should not appear as much as possible.

5. Select Optical Tooling Points (OTP) for the tooling locator to determine the spatial position of the assembly tooling locator. Use the laser tracker to install and adjust the tooling to achieve high-precision installation.

6. Select the location point and transfer station location point for the laser tracker. The occlusion situation, the measurement angle limit and the measurement distance limitation should be considered when selecting the location point. The selection of the position point of the laser tracker transfer station should be considered in conjunction with the selection of the auxiliary reference point, because after the transfer station, the assembly measurement coordinate system needs to be re-established based on the auxiliary reference point, and it is necessary to ensure that at least three reference points or auxiliary reference points can be measured .

7. Establish a coordinate system for assembly measurement. Read the theoretical coordinate value of the reference point, measure the target ball corresponding to the reference point through the laser tracker, obtain the coordinate value of the actual reference point, and solve the matrix transformation relationship between the laser tracker coordinate system and the assembly coordinate system. This operation is performed for each tracker in the collaborative measurement, so that the data measured by the three laser trackers are unified into the assembly coordinate system, and the system coordinate system is established so far.

8. Measure the auxiliary datum point position data and save it to the auxiliary datum point file. Under the assembly coordinate system, the laser tracker is used to measure each auxiliary reference point, and the measurement results are saved with the specified accuracy. In the actual assembly process, if the laser tracker cannot measure the reference point due to reasons such as occlusion, dead angle, and limited range when establishing the assembly measurement coordinate system, the laser tracker can measure at least three Auxiliary datum points, use the measurement values of these auxiliary datum points and the coordinate values of corresponding points in the auxiliary datum point file for matrix conversion, and establish the assembly measurement coordinate system after the transfer station is completed.

9. After the coordinate system is established, use the laser tracker to install the tooling locator. When the tooling locator is assembled, use the laser tracker to measure the OTP point while adjusting the position of the tooling locator until the key position parameters meet the tolerance requirements.

Step 2: Assembly measurement work

After the assembly measurement preparation work is completed, the assembly measurement work on aircraft components is started. In the process of assembly measurement, it is not only necessary to provide measurement data for the control system, but also to monitor the entire assembly process and save and manage the measurement data. The entire assembly process requires multi-laser trackers to perform real-time parallel collaborative measurement, which not only ensures high precision of data, but also meets real-time requirements. The specific implementation process of assembly measurement is as follows:

1. Assembly parts in place. After the position of the tooling is adjusted, use the hoisting equipment to complete the assembly.

2. Import assembly digital models, such as assembly digital models, tooling digital models, laser tracker models, assembly digital standard workers, etc.

3. Preheating, IP setting, network construction, etc. for each laser tracker before the start of assembly measurement, establish communication connection, initialize, and check the working status of the tracker.

4. The hardware part of the control system is in place, the initialization of each software system is completed, and the operator issues an assembly command through the main interface of the assembly system. After the assembly measurement system receives the assembly execution command, it starts the dynamic measurement work of multiple trackers.

5. When the assembly starts, the assembly measurement system sends the initial position data of each assembly measurement point and the theoretical position data of the assembly measurement point to the control system, and issues a command to execute the assembly action. The control system calculates the step length of the control mechanism according to the deviation of the position, and then executes the assembly action.

6. In the process of executing the assembly action of the actuator, the laser tracker collects the measurement point data according to a certain frequency, and performs a difference operation between the data collected each time and the data point collected last time. If the difference is small If it is within the range and lasts for a long time, it is determined that the assembly action of the actuator is over; otherwise, continue to collect measurement point data at a fixed frequency.

7. After the assembly action of the actuator is completed, compare the current position point with the theoretical position point. If the difference between the two meets the assembly tolerance requirements, the assembly is completed and the assembly measurement work is completed; if the difference is large, return to step 5. During the assembly process, if an assembly accident occurs, the operator can issue a stop assembly command through the main interface of the assembly system.

8. After the assembly work is completed, the operator issues a resume assembly command through the main interface of the assembly system to restore the software system and execution hardware to the initial assembly state and wait for the next assembly task.

Step 3: Real-time parallel collaborative measurement

The real-time simulation of dynamic assembly requires multiple laser trackers to measure the position information of the assembly parts and analyze the assembly status during the assembly process. The entire assembly process does not require manual intervention. In order to meet the requirements of real-time synchronization of measurement data, parallel cooperative measurement of each laser tracker, and convenient management of measurement data, the present invention proposes a real-time parallel cooperative measurement method based on multi-thread technology. This method is also applicable to other measurement devices other than laser trackers, and is suitable for mixed parallel collaborative measurement of multiple types of measurement devices. Real-time parallel measurement is the core of the entire measurement and assembly work. It is mainly based on the TCP/IP protocol to establish a LAN communication connection between the laser tracker group and the host. The flow chart is shown in Figure 4. The specific process is as follows:

1. Establish a local area network

The establishment method can be wired routing or wireless connection. Set the laser tracker group and the client computer to be in the same network segment.

2. Multi-thread parallel measurement

When measuring with a single laser tracker, it does not involve system measurement issues. The method of establishing measurement connections sequentially in a separate process will increase time overhead and make data management inconvenient. If a multi-threaded approach is adopted, the control rights of each laser tracker can be handed over to several measurement threads, and the measurement threads are only responsible for measurement and value transmission. Through the management of the operating system, the parallel collaborative acquisition of measurement data can be well guaranteed.

The present invention proposes a multi-thread communication connection mode. According to the number of laser tracker devices, the client dynamically allocates threads, and each thread is responsible for the measurement work of a separate laser tracker. The main thread of the client is responsible for controlling each laser tracker thread, and is responsible for communicating with For the communication of the control system, the measurement mode of the laser tracker is set to the dynamic measurement mode. The specific implementation process is as follows:

2.1. After the assembly measurement starts, the process dynamically allocates each measurement thread, and each thread establishes a set of laser tracker communication connections, and sets the measurement mode to dynamic measurement mode.

2.2. Set the measurement thread to the assembly measurement state. In this state, each measurement thread immediately sends a measurement command to the laser tracker server.

2.3. After receiving the measurement command, the laser tracker server returns the measurement value.

2.4. In the assembly measurement state, the measurement thread needs to perform multiple measurements to obtain the average value of the measurement point position. This value is called assembly measurement data.

2.5. The measurement thread sends the mean value to the main thread, and sets the measurement thread to monitor the measurement state.

2.6. After the main thread obtains the measurement data of multiple points, it converts the measurement data matrix into the assembly measurement coordinate system, and sends it to the control system in a package.

2.7. The control system gives feedback according to the measurement data and executes assembly actions.

2.8. The measurement thread is always in the state of monitoring and measuring during the assembly action of the control system. In this state, the main thread of the assembly measurement system sends a monitoring measurement command to each measurement thread at regular intervals, and the measurement thread immediately obtains the current position data information and directly returns this value, which is called the simulation measurement data.

2.9. After the main thread obtains the simulation measurement data, it forwards the data to the real-time simulation system and the assembly history engineering system.

2.10. After the assembly execution action is completed, if you need to obtain the assembly position data again, return to step 2.

2.11. During the assembly process, if the laser tracker is out of light, if the current thread status is the assembly measurement state, the assembly will stop and a light outage warning will pop up. After the operator checks the cause of the light outage, choose to continue the assembly command to complete Subsequent assembly; if the current state is the monitoring measurement state, discard the current measurement point data package and continue the assembly.

3. Measured data collation

After an assembly work is completed, disconnect each laser tracker, close each measurement thread, take out the real-time parallel measurement data during the assembly process, and save it in the form of a file.

3) advantages and effects: advantages and positive effects of the present invention

The digital flexible assembly measurement technology of aircraft components is a set of methods that use digital equipment and technology to complete automatic, fast and accurate measurement purposes, tasks and work with computer control. Its functions and advantages mainly include the following points:

(1) It has the ability to automatically complete large-scale assembly measurement tasks with high precision. During the entire assembly process, the operator presses the button to start the assembly task, and the remaining tasks such as point collection, assembly, and data processing are automatically completed by the system.

(2) Since the assembly measurement task can be adapted to different digital standard workers and different assembly digital models, the entire assembly measurement method is very suitable for digital flexible assembly work and meets the flexibility requirements.

(3) The multi-thread parallel cooperative measurement method of the laser tracker can avoid the real-time distortion problem caused by the asynchronous triggering of the measurement commands of multiple laser trackers, and adopts the method of separately managing a measurement device by each measurement thread, which is convenient for measurement Data management and overall coordination.

Description of drawings

Figure 1 Schematic diagram of the relationship between the assembly measurement system and the boundary system

Figure 2 Flow chart of measurement process for digital flexible assembly of aircraft components

Figure 3 Schematic diagram of assembly measurement simulation environment

Figure 4 Flow chart of multi-thread measurement method

Detailed ways

The specific implementation of the assembly measurement method will be introduced in detail below in conjunction with the digital flexible assembly of aircraft components. In the digital flexible assembly system, the software platform of the entire assembly measurement system is a software system with Opencascade as the geometric core, and C++ as the development language. The entire assembly measurement method is realized in this software environment, and the working object is the side of a certain type of aircraft. Wall board and bottom board, the size of the wall board (height x length x thickness) is about 4m x 4m x 2mm, the size is large and the thickness is small, the rigidity is poor, the assembly tolerance requirement is 0.5mm, and the bottom plate is a fixed part. The relationship between the assembly measurement system and the surrounding boundary system is shown in Figure 1.

See Fig. 2, the present invention is a digital flexible assembly measurement method for aircraft parts based on laser tracking measurement technology, the detailed execution steps of the assembly measurement are as follows:

Step 1: Preparation for assembly measurement:

The preparation work for digital flexible assembly measurement of aircraft components mainly includes digital and analog processing, establishment of digital standard, reference point selection, laser tracker position layout, etc. These tasks are the basis of digital assembly measurement. The following are the detailed execution steps:

1. Simplification of tooling digital model

The tooling digital model includes frame, locator, etc. For static parts such as frame, dynamic parts such as independent positioning arms, connectors, sliders, etc. are separately simplified into STEP format, which is mainly to facilitate the simulation of each model in the assembly process.

2. Simplified assembly

Taking aircraft fuselage components as an example, the assembly includes the bottom plate, side wall panels, bulkheads, etc. Since the data comes from the product engineering data set, and the assembly model has a huge amount of data, it is not convenient for simulation calculation, so it needs to be simplified into STEP format.

3. Establish benchmarks

In the assembly environment, select P1 (0,0,0), P2 (2000,0,0), P3 (0,2000,0) as the reference point for assembly measurement, manufacture the target position according to this data, and fix the target Mirror, the three-point theoretical position model is the digital standard of the coordinate system. According to the actual layout of the tooling, select a location with high openness and stability to make an auxiliary reference point for assembly measurement. Use the laser tracker to measure three reference points. The value of the measurement result is the value in the laser tracker's own coordinate system, not the value in the assembly coordinate system. It is necessary to solve the transformation matrix of the two sets of coordinate systems. The transformation matrix solution method is relatively common, and will not be introduced in the present invention.

4. Establish Auxiliary Datum Points

After solving the transformation matrix, the corresponding relationship between the measurement data of the laser tracker and the position data in the assembly environment can be established. Use the laser tracker to measure the auxiliary reference points of each assembly measurement, and save the measurement results as xml files. Part of the measurement point data is shown in Table 1:

Table 1 Coordinate values of auxiliary reference point

serial number X coordinate (mm) Y coordinate (mm) Z coordinate (mm) 1 11312.196 3999.617 20.395 2 11332.389 7071.520 20.398 3 5312.765 7721.718 20.401 4 5352.319 4649.918 20.398 5 6980.675 2045.876 0.655

5. Establish a digital standard for assembly parts

According to the requirements of assembly quality inspection data, a digital standard model of aircraft assembly is established. In each assembly in the flexible assembly, at least three measurement reference points need to be calibrated. The specific position of each measurement reference point can be determined according to the actual situation. When taking points, it should be noted that, starting from the requirements of stable and accurate positioning, the points must be within the measurement range of the laser tracker, and the inner angle of the triangle formed by the three points must be kept within a certain range. Taking the wall panel assembly in the fuselage component as an example to establish the digital standard model, the digital standard model of other wall panels is established in the same way. The specific method is to construct three points on the CATIA model of the wall panel according to the actual needs, and save these three points as the theoretical reference point of the wall panel. The theoretical values of the three points are:

P1 (9023.247, 2765.613, 2321.321)

P2(6680.342, 2356.753, 2281.589)

P3(6680.254, 1820.295, 453.997)

6. Select the optical tool ball point

Select Optical Tooling Points (OTP) for the tooling to determine the spatial position of the locator of the assembly tooling, and the theoretical position and tolerance requirements are designed by the tooling design department. Installed using a laser tracker for high precision installation tooling.

7. Select the location point and transfer station location point for the laser tracker

The occlusion situation, the measurement angle limit and the measurement distance limitation should be considered when selecting the location point. The selection of the position point of the laser tracker transfer station should be considered in conjunction with the selection of the auxiliary reference point, because after the transfer station, the assembly measurement coordinate system needs to be re-established based on the auxiliary reference point, and it is necessary to ensure that at least three reference points or auxiliary reference points can be measured .

8. Establish a coordinate system for assembly measurement

Read the theoretical coordinate value of the reference point, measure the target ball corresponding to the reference point through the laser tracker, obtain the coordinate value of the actual reference point, and solve the matrix transformation relationship between the laser tracker coordinate system and the assembly coordinate system. This operation is performed for each tracker in the collaborative measurement, so that the data measured by the three laser trackers are unified into the assembly coordinate system, and the assembly measurement system coordinate system is established so far.

9. Reconstruction of the assembly measurement coordinate system after the transfer station

In the actual assembly process, if the laser tracker cannot measure the reference point due to reasons such as occlusion, dead angle, and limited range when establishing the assembly measurement coordinate system, the laser tracker can at least meet the three auxiliary points. Datum points, the measured values of these auxiliary datum points and the coordinate values of the corresponding points in the auxiliary datum point file are used for matrix transformation, and the assembly measurement coordinate system is established after the transfer station is completed.

10. Tooling installation and debugging

After the coordinate system is established, the tooling locator is installed in the laser tracker. When the tooling locator is assembled, use the laser tracker to measure the OTP point while adjusting the position of the tooling locator until the key position parameters meet the tolerance requirements.

Step 2: Assembly measurement work

After the construction of the measurement environment is completed, the assembly measurement of the aircraft components is started. The measurement equipment is three Leica901 laser trackers, and the measurement objects are three measurement points on the right wall. During the assembly measurement process, it is not only necessary to provide measurement data for the control system, but also to monitor the entire assembly process. The whole assembly process requires three laser trackers to adopt a real-time parallel method for measuring points, which must not only ensure the high precision of the data, but also meet the real-time requirements. The overall assembly environment is shown in Figure 3. The specific implementation process of assembly is as follows:

1. Assembly parts in place

During the assembly process, the right wall panel is hoisted to the flexible tooling first. The connection between the wall panel and the tooling is a ball hinge connection. According to the connection characteristics of the assembly parts and the tooling, the assembly parts are put in place, and the tooling is properly adjusted to avoid assembly stress.

2. Import the assembly digital model, including the base plate and assembly frame digital model, the tooling digital model, the laser tracker model, the right wall panel digital standard, etc.

3. Laser tracker measurement preparation

Preheat each laser tracker for about 10 minutes before the start of assembly measurement, set the host IP to 192.168. The instrument completes the communication and initialization, and detects the working status.

4. The hardware part of the control system is in place, the initialization of each software system is completed, and the operator issues an assembly command through the main interface of the assembly system. After the assembly measurement system receives the command to start the assembly, it starts the dynamic measurement work of the three trackers. In the assembly system, set the system assembly measurement state variable to identify the current operation state of the assembly measurement work. There are five operation states, namely, the initial state of assembly, the state of execution of assembly action, the state of stop of assembly action, the state of assembly completion, and the state of assembly failure state.

5. When the assembly starts, the assembly state variable is set to the initial state of the assembly. The assembly measurement system sends the initial position data of the measurement point of the right wall panel and the theoretical position data of the measurement point of the right wall panel to the control system, and issues a command to execute the assembly action, and sets the current assembly state as the execution state of the assembly action.

6. After the control system receives the data, it calculates the step length of the control mechanism according to the position deviation, and then executes the assembly action.

7. During the process of executing the assembly action of the actuator, the laser tracker collects measurement point data every 0.5 seconds, and performs a difference operation between the data collected each time and the data point collected last time. If the difference is 0.01mm If it is within 10 seconds and the duration exceeds 10 seconds, it is determined that the assembly action of the actuator is completed, and the current assembly state is set as the stop state of the assembly action; otherwise, continue to collect measurement point data with a fixed period of 0.5 seconds, and collect the collected data every 5 seconds. Save once.

8. After the assembly action of the actuator is completed, compare the current position point with the theoretical position point. If the difference between the two meets the assembly tolerance requirements, the assembly is completed, and the current assembly state is set as the assembly completion state; if the difference is large, return Step 5. During the assembly process, if an assembly accident occurs, the operator can issue a stop assembly command through the main interface of the assembly system.

9. After the assembly work is completed, the operator issues a resume assembly command through the main interface of the assembly system to restore the software system and execution hardware to the initial assembly state and wait for the next assembly task.

Step 3: Real-time Parallel Measurement Method

The real-time simulation of dynamic assembly requires that the three laser trackers need to cooperate in real-time to complete the measurement work during the assembly process. In the laser tracker TPI of the Leica901 model, the measurement work of a single unit needs to be completed jointly by the socket class CESSocket, the information sending class CESAPICommand, and the information receiving class CESAPIReceive. Concentration of measurement commands into one process will cause confusion of measurement data, and the synchronization of data will also be affected. Using multi-threading, creating a separate thread to manage the measurement work of a single laser tracker can solve the above problems very well, and the program is relatively simple and well-structured. Figure 4 is a flow chart of the multi-thread measurement method. The overall flow of multi-thread measurement is as in Step 3 of the technical solution. The detailed flow of single measurement data is as follows:

1. Establish the connection between 3 laser trackers and the client computer by wired connection, and set the IP to be in the same network segment.

2. The integrated socket class, information sending class, and information receiving class are the laser tracker communication class, and the laser tracker class members are added to the thread class.

3. After the assembly measurement system receives the start assembly measurement command, the system process dynamically creates each measurement thread, and each thread establishes a set of laser tracker communication connections, and the laser tracker members in the thread provide all kinds of laser tracker measurement processes. Required functional interface.

4. The system main thread sends measurement commands to the measurement thread.

5. After the measurement thread receives the measurement command, it sends the measurement point command to the laser tracker device through its internal socket and other logical communication interfaces, and returns immediately without waiting for the laser tracker to finish measuring the data. In this way, the triggering of measurement commands of each laser tracker can be guaranteed to have high synchronization.

6. After receiving the measurement command, the laser tracker completes the measurement work, and sends the measurement point data to the corresponding thread.

7. The communication reception response function inside the measurement thread is triggered, the data reception is completed, and the measurement result data is sent to the main thread of the measurement system. Since the threads are independent, the measurement processes of each other do not interfere with each other.

8. The main thread of the assembly measurement system performs coordinate transformation on the data measured by each tracking laser tracker, so that the data is transformed into a unified assembly coordinate system. After the data is packaged, it is sent to the control system or simulation system, and Save some data as measured assembly history information.

9. After a measurement job is completed, wait for the next measurement command from the main thread.

Claims (1)

1. A digital flexible assembly measurement method for aircraft parts based on laser tracking measurement technology, characterized in that: the assembly measurement method comprises the following steps: Step 1: Preparation for assembly measurement: In the assembly measurement preparation stage, the preparation of the assembly measurement data model is completed, and the assembly measurement data is established as the basis for assembly measurement; the assembly measurement data includes reference point position data, assembly part data, tooling data, assembly quality inspection data, and measurement point positions data, laser tracker position data, tool positioning measurement points and other auxiliary coordinate point data; The independent digital model file import method is adopted to meet the flexibility requirements of different assembly tasks; in the whole assembly process, the simplified tooling digital model and assembly parts are the main data in the dynamic assembly simulation, which are used for real-time interaction; the reference point is the assembly environment, The construction of the assembly coordinate system provides the basis; the digital standard is the basis for the assembly quality inspection; the measurement point is the direct collection point of the laser tracker during the assembly process, which is directly related to the execution of the assembly command of the control system and the final assembly quality; the following are the detailed execution steps : Step 1.1. Export the tooling data from the engineering data set, simplify the tooling model, and separate the independent motion mechanisms to facilitate assembly measurement simulation; Step 1.2. Export the assembly data from the engineering data set to simplify the assembly model; Step 1.3. In the process of digital flexible assembly of aircraft components, in the actual assembly measurement environment, according to the accuracy requirements specified in the design, manufacture three measurement reference holes and install target mirrors to establish assembly measurement environment reference points; For positions with good openness, such as the edge and corner positions of the tooling frame, establish more auxiliary reference measurement holes; when assembling aircraft components, if there is a fixed part, select the upper three points as the reference points for the aircraft assembly environment; Step 1.4. According to the requirements of the assembly quality inspection data, establish an aircraft assembly digital standard model. In each assembly in the flexible assembly, at least 3 measurement reference points need to be calibrated. The specific position of each measurement reference point depends on the actual situation. Make sure; pay attention when taking points, starting from the requirements of stable and accurate positioning, the points must be within the measurement range of the laser tracker, and the inner angle of the triangle formed by the 3 points must be kept within the predetermined range, and obtuse angle relationship should not appear as far as possible ; Step 1.5. Select the optical tool ball point OTP for the tooling locator to determine the spatial position of the assembly tooling locator; use the laser tracker to install and adjust the tooling to achieve high-precision installation; Step 1.6. Select the location point and transfer station location point for the laser tracker. When selecting the location point, the occlusion situation, measurement angle limit and measurement distance limit should be considered; the selection of the laser tracker transfer station location point should be combined with the selection of the auxiliary reference point Consider, because the assembly measurement coordinate system needs to be re-established based on the auxiliary datum points after the station transfer, it is necessary to ensure that at least three datum points or auxiliary datum points can be measured; Step 1.7. Establish the coordinate system of assembly measurement, read the theoretical coordinate value of the reference point, measure the target ball corresponding to the reference point through the laser tracker, obtain the coordinate value of the actual reference point, and solve the coordinate system of the laser tracker and the assembly coordinate system The matrix transformation relationship among them; this operation is performed for each tracker in the collaborative measurement, so that the data measured by the three laser trackers are unified into the assembly coordinate system, and the system coordinate system is established so far; Step 1.8. Measure the auxiliary reference point position data and save it in the auxiliary reference point file; under the assembly coordinate system, use the laser tracker to measure each auxiliary reference point, and the measurement results are saved with the specified accuracy; in the actual assembly process If the laser tracker cannot measure the reference point due to occlusion, dead angle, and limited range when establishing the assembly measurement coordinate system, the laser tracker can measure at least three auxiliary reference points. The measurement value of the auxiliary datum point and the coordinate value of the corresponding point in the auxiliary datum point file are transformed into a matrix, and the assembly measurement coordinate system is established after the transfer station is completed; Step 1.9. After the coordinate system is established, use the laser tracker to install the tooling locator; when assembling the tooling locator, use the laser tracker to measure the OTP point while adjusting the position of the tooling locator until the key position parameters reach Tolerance requirements; Step 2: Assembly measurement work: After the assembly measurement preparation work is completed, the assembly measurement work of aircraft components is started; during the assembly measurement process, not only the measurement data needs to be provided for the control system, but also the entire assembly process must be monitored and the measurement data should be saved and managed; the entire assembly process needs Multi-laser trackers perform real-time parallel collaborative measurement, which must not only ensure the high precision of the data, but also meet the real-time requirements; the specific implementation process of the assembly measurement is as follows: Step 2.1. Assembling parts are in place, after the position of tooling is adjusted, use hoisting equipment to complete the fitting; Step 2.2. Import assembly digital models, such as assembly digital models, tooling digital models, laser tracker models, and assembly digital standard workers; Step 2.3. Preheat each laser tracker, set IP, set up network, establish communication connection, initialize, and check the working status of the tracker before the start of assembly measurement; Step 2.4. The hardware part of the control system is in place, and the initialization of each software system is completed. The operator issues an execution assembly command through the main interface of the assembly system. After receiving the execution assembly command, the assembly measurement system starts the dynamic measurement work of multiple trackers; Step 2.5. When the assembly starts, the assembly measurement system sends the initial position data of each assembly measurement point and the theoretical position data of the assembly measurement point to the control system, and issues a command to execute the assembly action; the control system calculates the step size of the control mechanism according to the position deviation , and then execute the assembly action; Step 2.6. In the process of executing the assembly action of the actuator, the laser tracker collects the measurement point data according to a certain frequency, and performs a difference operation between the data collected each time and the data point collected last time. If the difference is small If it is within the range and lasts for a long time, it is determined that the assembly action of the actuator is over; otherwise, continue to collect measurement point data at a fixed frequency; Step 2.7. After the assembly action of the actuator is completed, compare the current position point with the theoretical position point. If the difference between the two meets the assembly tolerance requirements, the assembly is completed and the assembly measurement work is completed; if the difference is large, return to step 2.5; During the assembly process, if there is an assembly accident, the operator will issue a command to stop the assembly through the main interface of the assembly system; Step 2.8. After the assembly work is completed, the operator issues a resume assembly command through the main interface of the assembly system to restore the software system and execution hardware to the initial state of assembly, and wait for the next assembly task; Step 3: Real-time parallel collaborative measurement: The real-time simulation of dynamic assembly requires multiple laser trackers to measure the position information of the assembly parts and analyze the assembly status during the assembly process. The entire assembly process does not require manual intervention; To meet the requirements of convenient management, a real-time parallel collaborative measurement method based on multi-thread technology is proposed; this method is also applicable to other measurement equipment other than laser trackers, and is suitable for mixed parallel collaborative measurement of multiple types of measurement equipment; real-time parallel measurement is the whole measurement The core of the assembly work is based on the TCP/IP protocol to establish a LAN communication connection between the laser tracker group and the host computer. The specific process is as follows: Step 3.1. Establish LAN The establishment method is wired routing or wireless connection; set the laser tracker group and the client computer to be on the same network segment; Step 3.2. Multi-thread parallel measurement When measuring with a single laser tracker, it does not involve system measurement issues; adopting the method of establishing measurement connections sequentially in a separate process will increase time overhead and data management is inconvenient; if multi-threading is used, each laser tracker The control right of the instrument is handed over to several measurement threads, and the measurement thread is only responsible for measurement and value transmission. Through the management of the operating system, the parallel collaborative acquisition of measurement data can be well guaranteed; Multi-thread communication connection mode, according to the number of laser tracker devices, the client dynamically allocates threads, each thread is responsible for the measurement of a separate laser tracker, the main thread of the client is responsible for controlling each laser tracker thread, and is responsible for the communication with the control system For communication, the laser tracker measurement mode is set to dynamic measurement mode; the specific execution process is as follows: Step 3.2.1. After the assembly measurement starts, the process dynamically allocates each measurement thread, and each thread establishes a set of laser tracker communication connections, and sets the measurement mode to dynamic measurement mode; Step 3.2.2. Set the measurement thread to the assembly measurement state. In this state, each measurement thread immediately sends a measurement command to the laser tracker server; Step 3.2.3. After receiving the measurement command, the laser tracker server returns the measurement value; Step 3.2.4. In the assembly measurement state, the measurement thread needs to perform multiple measurements to obtain the average value of the measurement point position. This value is called assembly measurement data; Step 3.2.5. The measurement thread sends the mean value to the main thread, and sets the measurement thread to monitor the measurement state; Step 3.2.6. After the main thread obtains the measurement data of multiple points, it converts the measurement data matrix into the assembly measurement coordinate system, and sends it to the control system in a package; Step 3.2.7. The control system gives feedback according to the measurement data and executes the assembly action; Step 3.2.8. The measurement thread is always in the state of monitoring and measuring during the assembly action of the control system; in this state, the main thread of the assembly and measuring system sends a monitoring and measuring command to each measurement thread at regular intervals, and the measurement thread immediately obtains Current position data information, directly return this value, this value is called simulation measurement data; Step 3.2.9. After the main thread obtains the simulation measurement data, it forwards the data to the real-time simulation system and the assembly history engineering system; Step 3.2.10. After the assembly execution action is completed, if you need to obtain the assembly position data again, return to step 2; Step 3.2.11. During the assembly process, if the laser tracker is out of light, if the current thread status is the assembly measurement state, the assembly will be stopped and a light outage warning will pop up. After the operator checks the cause of the light outage, choose to continue The assembly command completes the subsequent assembly; if the current state is the monitoring measurement state, discard the current measurement point data packet and continue the assembly; Step 3.3. Measured data collation After an assembly work is completed, disconnect each laser tracker, close each measurement thread, take out the real-time parallel measurement data during the assembly process, and save it in the form of a file.