A flexible reconfigurable assembly tooling large-size high-precision measurement method

Abstract

The application discloses a flexible reconfigurable assembly tooling large-size high-precision measurement method, and belongs to the technical field of aircraft digitization assembly, which comprises the following steps: a rectangular mounting platform is assembled by using a plurality of unit substrates, and each unit substrate is provided with measurable landmark points; a networking measurement system is constructed by using four laser trackers to perform ring-closed measurement; each laser tracker measures two adjacent unit substrates each time, and two adjacent measurements contain the same unit substrate; one round of measurement is performed around the mounting platform according to the measurement mode until two measurements of each unit substrate are completed; the position coordinates of the landmark points on the unit substrate in each measurement are solved based on the measurement results; and the global optimization algorithm is used to solve the landmark points on all unit substrates. The networking measurement method is adopted, and the ring-closed global optimization algorithm is combined to further reduce the station splicing error, and the global measurement precision in the large-size range is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of digital assembly of aircraft, in particular to a flexible reconfigurable assembly tool large-size high-precision measurement method. BACKGROUND

[0002] The traditional aircraft assembly tool generally adopts the structure form of truss type welded framework, and is directly connected with the foundation through a fastening device. In the tool assembly process, the measurement is completed by setting reference points on the tool body. The specific measurement method is as follows: the tool reference points are used to complete the establishment of the coordinate system, and the measurement is completed under the coordinate system. The number of reference points for station setting is greater than or equal to 6, and the reference points are distributed as much as possible to follow the envelope principle, that is, the space region to be measured can be enveloped, and the reference points are distributed around the space. If single station setting cannot complete the measurement, the measurement is carried out by multiple station setting. The common reference points are set between adjacent station positions, and the number of common reference points that can be measured between adjacent station positions is generally not less than 6.

[0003] This measurement method has two shortcomings. One is that the actual positions of the reference points on the tool will be displaced due to factors such as temperature and vibration, thereby causing large errors in the construction of the measurement field. The other is that when facing large-scale measurement requirements, single or multiple laser trackers are used for multiple station setting measurement, thereby causing large cumulative measurement errors. Therefore, one of the solutions to the large-size high-precision measurement requirement of the flexible reconfigurable assembly tool is to construct a large-size measurement field.

[0004] In the prior art, patent CN109871664B discloses a station setting precision optimization method for large-size multi-station measurement field of aircraft assembly. On the basis of the commonly used TB / ERS points and other station setting reference points for aircraft assembly, a kind of temporary station setting enhancement point without theoretical value is introduced. Two or more measurement stations simultaneously measure such station setting enhancement points, thereby increasing the station setting adjustment constraints between different measurement stations, reducing the station setting parameter variance covariance matrix of the measurement station to the global station, and improving the station setting precision.

[0005] The patent method is the commonly used measurement method at present. It uses a single measurement and obtains a global coordinate system by increasing ERS points and station setting measurement. The station setting reduces the station setting error through station setting adjustment algorithm, but there is still a problem of insufficient precision for large-size range. SUMMARY

[0006] The present application aims to solve the deficiencies of the traditional aircraft assembly tool and measurement method, and proposes a flexible reconfigurable assembly tool large-size high-precision measurement method. The present application adopts a network measurement method, and further reduces the station setting splicing error by combining with a ring-shaped closed global optimization algorithm, thereby improving the global measurement precision of large-size range.

[0007] In order to achieve the above-mentioned purposes, the technical scheme of the present application is as follows:

[0008] A flexible reconfigurable assembly tool large-size high-precision measurement method, characterized by comprising the following steps:

[0009] Step a, a plurality of unit substrates are assembled into a rectangular mounting platform, and each unit substrate has measurable landmark points;

[0010] Step b, a network measurement system is constructed using four laser trackers to perform ring-closed measurement; each laser tracker measures two adjacent unit substrates at a time, and two adjacent measurements include the same unit substrate; one round of measurement is performed around the mounting platform according to this measurement method until each unit substrate is measured twice;

[0011] Step c, based on the measurement result of each time, the landmark point position coordinates on the unit substrate of this measurement are solved;

[0012] Step d, a ring-closed global optimization algorithm is used to solve the landmark points on all unit substrates, a global coordinate system is established, and a large-size measurement field is constructed;

[0013] Step e, tool assembly measurement is carried out in the large-size measurement field, and each laser tracker station is established based on the landmark point coordinates on the unit substrate.

[0014] Further, the solving of the landmark point position coordinates on the unit substrate of this measurement based on the measurement result of each time comprises:

[0015] Step c1. Construct a laser tracker self-calibration residual error model f based on a distance residual error model tj , a measured point accurate estimation model f ij , and a network measurement system parameter initial value estimation model;

[0016] Step c2. Construct four residual error equations of the four laser trackers corresponding to each measured point, and define the minimum sum of residual errors;

[0017] Step c3. An improved LM algorithm is used to solve the optimal solution of the measured point coordinates.

[0018] Further, the improved LM algorithm introduces a non-negative parameter μ k , which ensures global convergence and local quadratic convergence, thereby solving the optimal solution of the system parameters and the measured point coordinates.

[0019] Further, the introduced non-negative parameter μ k is expressed as follows:

[0020]

[0021] Further, the ring-enclosed global optimization algorithm is used to solve the landmark points on all unit substrates, including:

[0022] Step d1. The optimal coordinate system conversion relationship between two adjacent unit substrates is solved by the measured landmark points on the common unit substrate.

[0023] Step d2. The least square function of the coordinate system conversion error of all common unit substrates is constructed to solve the optimal coordinate system conversion parameters between two adjacent unit substrates.

[0024] Step d3. The objective function is constructed, and the set of resection errors caused by the measurement errors of each common unit substrate is obtained to minimize the objective function value.

[0025] Step d4. The conversion relationship between adjacent unit substrates is corrected using the obtained set of resection errors.

[0026] Step d5. The coordinate values in the unified coordinate system are solved for each unit substrate through the corrected conversion relationship.

[0027] Further, the least square function of the coordinate system conversion error of all common unit substrates is:

[0028]

[0029] In the formula, E R is the coordinate system conversion error of all common unit substrates, Δe i is the resection error caused by the measurement error of the i-th common unit substrate, and N is the total number of measured unit substrates.

[0030] Further, the objective function is constructed as:

[0031]

[0032] In the formula, Δe i is the resection error caused by the measurement error of the i-th common unit substrate. represents the coordinate system conversion relationship between the i-th and i+1-th unit substrates, T1 N represents the coordinate system conversion relationship between the N-th unit substrate and the 1st unit substrate; Δe N is the error term of the conversion relationship T1 N .

[0033] Further, the landmark point is the step hole with a manufacturing precision of H7, and a cover is arranged on the landmark point.

[0034] Further, the four laser trackers should have a spatial gradient, and each laser tracker is calibrated by double-sided calibration compensation through a scale before measurement.

[0035] In summary, the present application has the following advantages:

[0036] 1. The patent establishes a laser tracker networking measurement system locally, uses an optimized multi-lateral measurement algorithm to calibrate the unit substrate, improves the overall calibration accuracy of the unit substrate through a ring-closed global optimization algorithm, establishes a global coordinate system for measurement, and thus constructs a large-size measurement field. In the process of tool assembly, a single or multiple laser trackers are used to realize large-size and high-precision assembly of the tool based on the measurement field, and the unit substrate is calibrated regularly to ensure that the measurement field accuracy is within the required range.

[0037] 2. The patent establishes a laser tracker networking measurement system locally, and four trackers can complete the measurement requirement, reducing the number of laser trackers used for large-size and high-precision measurement, and simplifying the laser tracker networking measurement process; the optimized multi-lateral measurement algorithm is used to calibrate the unit substrate, avoiding measurement errors caused by solving the coordinates of the measured points due to the use of angle parameters, and improving the measurement accuracy of the flexible reconfigurable assembly tool.

[0038] 3. The present application improves the overall calibration accuracy of the unit substrate through a ring-closed global optimization algorithm, reduces the cumulative error caused by the laser tracker station transfer, and improves the measurement accuracy of the flexible reconfigurable assembly tool.

[0039] 4. The patent establishes a measurement field by installing a landmark point on the platform, and does not select the reference point on the tool as a reference to participate in the establishment of the measurement field, separates the measurement reference from the tool skeleton assembly, reduces the problem of relative position drift between different types of reference points due to factors such as temperature and vibration, and improves the measurement accuracy of the flexible reconfigurable assembly tool.

[0040] 5. The patent uses a single or multiple laser trackers to simultaneously carry out tool assembly measurement in the constructed large-size measurement field during tool assembly, improves tool assembly efficiency, avoids the inconvenience caused by using multiple laser trackers for networking measurement to improve measurement accuracy during tool assembly; at the same time, regular landmark calibration is used to realize rapid tool inspection, improve tool inspection efficiency, and shorten tool inspection cycle. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 FIG. 1 is a structural schematic diagram of the flexible reconfigurable assembly tool of the present application;

[0042] Figure 2 FIG. 4 is an implementation flowchart of the measurement method of the present application;

[0043] Figure 3 A schematic diagram of the structure of a measurement unit substrate;

[0044] Figure 4 A schematic diagram of a unit substrate module;

[0045] Figure 5 A schematic diagram of a single unit substrate and the distribution of landmark points;

[0046] Figure 6 A schematic diagram of the arrangement of a measurement unit. DETAILED DESCRIPTION

[0047] In order to more clearly illustrate the present application, the present application will be further described below in conjunction with preferred embodiments and the accompanying drawings. Those skilled in the art should understand that the specific description below is illustrative rather than limiting, and should not limit the scope of protection of the present application.

[0048] With the development of the aircraft manufacturing industry, aircraft parts are increasingly tending to be integrated, large in size, high in precision during assembly. Based on this, the present application proposes a flexible reconfigurable assembly tool, i.e., a "building block type" manufacturing method is adopted to realize assembly tool assembly, which can realize the integrated assembly of the front fuselage, middle fuselage and rear fuselage of an aircraft. The characteristics of the assembly tool are large size and high manufacturing precision. The precision of the aircraft assembly tool depends on the measurement precision and measurement method of the digital measurement equipment.

[0049] At present, for the measurement requirements of large-size high-precision assembly tools, large-range high-precision measurement equipment (such as laser trackers, laser radars, iGPS, scanning equipment, etc.) is often used for measurement. The laser tracker has the characteristics of high precision and large measurement range, and is often used as a measurement instrument for assisting assembly of aircraft assembly tools.

[0050] The present application provides a flexible reconfigurable assembly tool large-size high-precision measurement method. The flexible reconfigurable assembly tool mainly consists of an installation platform and a skeleton assembly. Both the installation platform and the skeleton assembly can be modularized, disassembled and reconfigured.

[0051] As shown in Figure 1 , the installation platform is installed on the ground after being spliced by a plurality of unit substrates. The skeleton assembly is fixedly connected to the spliced installation platform through a fastening device, and finally realizes the assembly of the aircraft parts on the skeleton assembly.

[0052] The measurement method of the present application is implemented according to the following steps:

[0053] Step one, according to the size range of the assembled installation platform, select the unit substrate on the installation platform as the measurement object.

[0054] In this embodiment, a plurality of unit substrates of uniform size are spliced ​​together to form a Figure 3 The rectangular mounting platform shown. Figure 5 As shown, each unit substrate is designed with landmark points at the four corners, each landmark point is The step hole is manufactured with an accuracy of H7. The landmark points are designed with covers to prevent dust, iron filings and other impurities from wearing the step hole.

[0055] Go around the installation platform and determine that every m (m ≥ 1) unit substrates constitute a unit substrate module according to the size of the installation platform. For example, Figure 4 As shown, in this embodiment, three unit substrates can be selected around the mounting platform to form a unit substrate module, and the middle unit substrate of the unit substrate module is used as the measurement object. The selected middle unit substrates are sorted in order of 1, 2, 3, ..., N, as shown in FIG. Figure 3 The landmark points in each unit substrate are grouped and numbered in the form of unit substrate-serial number, and the landmark points on the same unit substrate will not move relative to each other.

[0056] Step 2: Use four laser trackers to build a network measurement system and perform closed-loop measurement in a clockwise or counterclockwise direction around the installation platform. Figure 6 shown.

[0057] In this embodiment, the layout of the four laser trackers should have a spatial gradient, and each laser tracker is subjected to double-sided calibration compensation using a ruler before measurement.

[0058] In this step, every four laser trackers form a measurement unit. Each laser tracker in each measurement unit measures all landmark points on two adjacent target unit substrates in a single measurement. This means that two consecutive measurements encompass all landmark points on the same unit substrate, and the last unit substrate measured includes the penultimate unit substrate and the starting unit substrate. In other words, the first measurement involves unit substrates numbered 1 and 2, the second measurement involves unit substrates numbered 2 and 3, and so on, until the final measurement involves unit substrates numbered N and 1.

[0059] Step 3: Establish a global measurement coordinate system and construct a large-scale measurement field.

[0060] This step uses an optimized multilateral measurement algorithm based on each measurement result to solve the position coordinates of the landmark points on the unit substrate measured this time.

[0061] The optimized multilateration algorithm is as follows:

[0062] First, three models of the laser tracker network measurement multilateral method are constructed: the laser tracker self-calibration residual model f is constructed based on the distance residual model tj, the precise estimation model of the measured point f ij And four laser tracker measurement system parameter initial value estimation model, the three models belong to the prior art, not here.

[0063] Each measured point can be established to correspond to four laser tracker four residual equation, define the residual sum of minimum:

[0064] Then, using the improved LM algorithm to solve the measured point optimal solution: that is, the introduction of non-negative parameters μ k , to ensure global convergence, local quadratic convergence, so as to solve the system parameters and the measured point coordinates of the optimal solution.

[0065] Where the non-negative parameter System parameters include distance, angle, etc.

[0066] Finally, based on the measurement unit of the ring closed type measurement results, using ring closed type global optimization algorithm to complete all unit substrate on the landmark point coordinate solving, measurement global coordinate system is established, and large size measurement field is constructed. The specific operation of ring closed type global optimization algorithm is:

[0067] a. Through the measurement of the landmark point on the common unit substrate to solve the best coordinate system conversion relationship between adjacent two unit substrates. The coordinate system conversion relationship between unit substrate 1 and unit substrate 2 The coordinate system conversion relationship between unit substrate 2 and unit substrate 3 ……The coordinate system conversion relationship between unit substrate N and unit substrate 1 T1 N .

[0068] b. In order to solve the best coordinate system conversion parameters between adjacent two unit substrates, the least square function of coordinate system conversion error (E R ) of all common unit substrates is constructed: SVD decomposition method can be used to solve the coordinate system conversion parameters, Δe i is the stationing error caused by the measurement error of the i th common unit substrate.

[0069] c. At the same time, the objective function The ideal value of the objective function is the unit rotation translation matrix, that is, the unit substrate 1 coordinate system is finally returned to itself after continuous rotation translation transformation, Δe N is the error term of the conversion relationship T1 N , the minimum set {Δe i} is solved.

[0070] d. Through the minimum set solved above, the conversion relationship between adjacent unit substrates is corrected The four ground marks on each unit substrate are connected by a conversion relationship The coordinate values in the unified coordinate system are solved, the global coordinate system is established, and the large-size measurement field is constructed by the ground marks on each unit substrate.

[0071] In the unit substrate calibration process, only four laser trackers are needed to complete the measurement requirement, i.e., the laser trackers can be time multiplexed, such as the first one can be moved to the position of the fifth one to continue to measure and calibrate, which can reduce the use of laser trackers.

[0072] Step four, a single or multiple laser trackers are used to carry out tool assembly measurement in the measurement field, and the ground mark coordinates on the unit substrate of the measurement field are used as the basis for station measurement each time the laser tracker is transferred.

[0073] After the laser tracker transfer position is determined, 3-4 ground marks on the nearby unit substrate are selected as the station reference. This method can realize the simultaneous tool assembly of multiple stations in the large-size tool assembly process, and the laser tracker of each station is built on the basis of the ground mark coordinates on the unit substrate, which can ensure the overall accuracy and improve the tool assembly efficiency.

[0074] When the aircraft product is removed, the above step three method is used to complete the re-calibration of the ground mark, and if the calibration result is within the error range, the tool positioner does not need to be re-measured, otherwise it needs to be re-measured. Because the tool is affected by environmental factors such as temperature, humidity, vibration, etc. during use, it may cause deformation of the unit substrate of the installation platform, etc., so periodic calibration of the unit substrate can reduce the measurement field accuracy caused by other factors that cannot meet the use requirements.

[0075] The above is only the preferred embodiment of the present application, and does not limit the present application in any form. Any simple modification or equivalent change based on the technical essence of the present application to the above embodiment falls within the protection scope of the present application.

Claims

1. A large-scale, high-precision measurement method for flexible and reconfigurable assembly tooling, characterized in that: The steps include: Step a: assemble a plurality of unit substrates into a rectangular mounting platform, each unit substrate having a measurable landmark point; Step b: Using four laser trackers to construct a networked measurement system and perform a circular closed measurement; each laser tracker measures two adjacent unit substrates at a time, and the two adjacent measurements include the same unit substrate; this measurement method is repeated around the mounting platform until each unit substrate is measured twice; Step c, solving the coordinates of the landmark points on the unit substrate measured each time based on the measurement results; Step d: using a circular closed-form global optimization algorithm to solve the landmark points on all unit substrates, establish a global measurement coordinate system, and construct a large-scale measurement field; Step e: Conduct tooling assembly measurement simultaneously in the large-scale measurement field. Each time the laser tracker transfers to a new station, the coordinates of the landmark points on the unit substrate are used as the basis for station measurement. The circular closed-form global optimization algorithm is used to solve the landmark points on all unit substrates, including: Step d1. Determine the optimal coordinate system transformation relationship between two adjacent unit substrates by measuring landmark points on the common unit substrate; Step d2. Constructing a least square function of the coordinate system conversion errors of all common unit substrates to solve the optimal coordinate system conversion parameters between two adjacent unit substrates; Step d3. Construct an objective function and find the set of transfer errors caused by the measurement errors of each common unit substrate that minimizes the objective function value; Step d4. Using the obtained transfer error set, correct the conversion relationship between adjacent unit substrates; Step d5. The coordinate values ​​of each unit substrate in the unified coordinate system are solved by using the corrected conversion relationship.

2. A method for measuring large sizes and high precision of a flexible reconfigurable assembly tool as claimed in claim 1, characterized in that: The method of solving the coordinates of the landmark points on the unit substrate measured each time based on the measurement results includes: Step c1. Construct the laser tracker self-calibration residual model based on the distance residual model , accurate estimation model of the test point and the initial value estimation model of network measurement system parameters; Step c2. Construct four residual equations for each measured point corresponding to the four laser trackers and define the minimum sum of the residuals; Step c3. Use the improved LM algorithm to find the optimal solution for the coordinates of the measured point.

3. A method for measuring large sizes and high precision of a flexible reconfigurable assembly tool as claimed in claim 2, characterized in that: Improved LM algorithm introduces non-negative parameters , ensuring global convergence and local quadratic convergence, thereby solving the optimal solution of system parameters and measured point coordinates.

4. A method for measuring large sizes and high precision of a flexible reconfigurable assembly tool as claimed in claim 3, characterized in that: The non-negative parameters introduced The expression is as follows: 。 5. A method for measuring large size and high precision of a flexible reconfigurable assembly tool as claimed in claim 1, characterized in that: The least square function of the coordinate system conversion error of all common unit substrates is constructed as: ； Where, is the coordinate system conversion error of all common unit substrates, is the transfer error caused by the measurement error of the i-th common unit substrate, and N is the total number of unit substrates measured.

6. A method for measuring large sizes and high precision of flexible reconfigurable assembly tooling according to claim 1, characterized in that: The constructed objective function is: ； Where, is the transfer error caused by the measurement error of the i-th common unit substrate; Represents the coordinate system transformation relationship between the i-th and i+1-th unit substrates, Indicates the coordinate system transformation relationship between the Nth unit substrate and the 1st unit substrate; For conversion relationship The error term.

7. A method for measuring large sizes and high precision of flexible reconfigurable assembly tooling according to claim 1, characterized in that: The landmark point is a stepped hole of φ6.35 mm with a manufacturing accuracy of H7, and a cover is provided on the landmark point.

8. The method for measuring large size and high precision of flexible reconfigurable assembly tooling according to claim 1, characterized in that: The layout of the four laser trackers should have a spatial gradient, and each laser tracker should be double-sided calibrated and compensated using a ruler before measurement.

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