Invention Relates to an Automatic Coordinate System Calibration Method Applied to a Large Size Measurement System
The large-scale measurement technology is widely used in aerospace equipment assembly,precision measurement of geometric quantities,mobile robot positioning,and navigation in the field of industrial manufacturing.As the measurement objects become more complex,refined,large-scale,and multi-target,the single-station measurement mode has become difficult to complete the corresponding measurement tasks.Compared to single-station systems,distributed measurement systems can control the measurement range by adding or removing measurement units,and flexibly adjust the measurement scheme according to the measurement requirements,fully leveraging the advantages of each measurement unit.These characteristics make distributed measurement systems have higher measurement accuracy and a wider measurement range compared to single-station systems.Accurate Laser Positioning Systems(ALPS)for large-scale measurement are typical distributed measurement systems.During measurement,each measurement unit of the accurate laser positioning system obtains measurement data in its independent local coordinate system.To achieve networked measurement of multiple measurement units,it is necessary to calibrate the local coordinate systems of each measurement unit in advance.When using the method based on a standard ruler to unify the coordinate systems of measurement units,it is necessary to manually move the standard ruler to different positions in the measurement space for measurement,in order to cover the entire measurement space.The application scenarios of distributed measurement systems usually have a large measurement range,high accuracy requirements,and a complex measurement environment.In order to adapt to the measurement task,the more positions the standard instrument is moved,the higher the calibration accuracy.However,each movement of the standard ruler inevitably increases the time cost of calibration,sacrificing efficiency to obtain higher accuracy.Moreover,the coordinate system based on a standard ruler limits the flexibility of adding measurement units or mobile stations to the distributed measurement system.In response to the low efficiency of the coordinate system based on a standard instrument during the calibration process,this paper proposes a fully automatic coordinate system calibration method for large-scale measurement systems.This method uses two measurement nodes with known coordinates in the local coordinate system of each measurement unit as mark targets.The measurement units measure the mark targets of each other to obtain the coordinates of the mark points in different coordinate systems,and uses these coordinates to establish three-dimensional geometric constraints,thereby automatically calibrating the coordinate transformation relationship between different coordinate systems.In addition,when a measurement unit moves or new measurement units are added to the original measurement network,the method proposed in this paper can naturally realize the automatic networking between measurement units without the need to recalibrate the measurement field.This method greatly improves the calibration efficiency of the system compared to the traditional standard ruler method.Moreover,compared with existing automatic calibration models,the method proposed in this paper can automatically calibrate multiple measurement units in actual measurement scenarios,solving the problem of existing automatic calibration models that can only calibrate two measurement units.Additionally,the manufacturing process of the marker targets is simple,which provides a new theoretical basis for the industrialization of distributed measurement equipment with automatic calibration function.Finally,this paper verifies the proposed method using the precision laser positioning system.In a measurement space with a distance of about 2 m from the measurement unit deployment area and a size of 5 000 mm×5 000 mm×500 mm,length data of a standard ruler(1 156.704 mm)is sequentially measured at 12 different positions.The deviation of the measurement results relative to their reference length is recorded,and the experimental results show that the accuracy of length measurement is within 0.46 mm/m.In addition,this paper uses a target ball to perform a comparative test of measurement points between the precision laser positioning system and the laser tracker.The experimental results show that the standard deviation of three-dimensional coordinate measurement is within 0.026 mm after using the method proposed in this paper to calibrate the coordinate system of the accurate laser positioning system.The maximum errors in coordinate measurement in the x,y,and z directions are 0.5 mm,0.55 mm,and 0.5 mm,respectively,which can meet the needs of the majority of industrial measurement.Furthermore,this paper's method achieves automatic calibration of local coordinate systems between measurement units,greatly reducing the manual cost during the coordinate system calibration process.Compared to traditional standard ruler calibration methods,this method improves the calibration efficiency by more than 10 times and solves the problem of the inability of existing automatic calibration models to automatically network multiple measurement units.
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