Algorithm for Detecting Volumetric Geometric Accuracy of NC Machine Tool by Laser Tracker

Quick and accurate detecting the error of NC machine tool and performing the error compensation are important to improve the machining accuracy of NC machine tool. Currently, there are many methods for detecting the geometric accuracy of NC machine tool. However, these methods have deficiencies in detection efficiency and accuracy as well as in versatility. In the paper, a method with laser tracker based on the multi-station and time-sharing measurement principle is proposed, and this method can rapidly and accurately detect the geometric accuracy of NC machine tool. The machine tool is controlled to move in the preset path in a 3D space or 2D plane, and a laser tracker is used to measure the same motion trajectory of the machine tool successively at different base stations. The original algorithm for multi-station and time-sharing measurement is improved. The space coordinates of the measuring point obtained by the laser tracker are taken as parameter values, and the initial position of each base point can be determined. The redundant equation concerning the base point calibration can be established by the distance information of the laser tracker, and the position of each base point is further determined by solving the equation with least squares method, then the space coordinates of each measuring point can be calibrated. The singular matrix does not occur in calculation with the improved algorithm, which overcomes the limitations of the original algorithm, that the motion trajectory of machine tool is in a 3D space and there exits height difference between the base stations. Adopting the improved algorithm can expand the application of multi-station and time-sharing measurement, and can meet the quick and accurate detecting requirements for different types of NC machine tool.

Geometric Accuracy and Energy Absorption Characteristics of 3D Printed Continuous Ramie Fiber Reinforced Thin-Walled Composite Structures

The application of continuous natural fibers as reinforcement in composite thin-walled structures offers a feasible approach to achieve light weight and high strength while remaining environmentally friendly.In addition,additive manufacturing technology provides a favorable process foundation for its realization.In this study,the printability and energy absorption properties of 3D printed continuous fiber reinforced thin-walled structures with different configurations were investigated.The results suggested that a low printing speed and a proper layer thickness would mitigate the printing defects within the structures.The printing geometry accuracy of the structures could be further improved by rounding the sharp corners with appropriate radii.This study successfully fabricated structures with vari-ous configurations characterized by high geometric accuracy through printing parameters optimization and path smoothing.Moreover,the compressive property and energy absorption characteristics of the structures under quasi-static axial compression were evaluated and compared.It was found that all studied thin-walled structures exhibited progressive folding deformation patterns during compression.In particular,energy absorption process was achieved through the combined damage modes of plastic deformation,fiber pullout and delamination.Furthermore,the com-parison results showed that the hexagonal structure exhibited the best energy absorption performance.The study revealed the structure-mechanical property relationship of 3D printed continuous fiber reinforced composite thin-walled structures through the analysis of multiscale failure characteristics and load response,which is valuable for broadening their applications.

Determining Geometric Accuracy in Turning

Mechanical components machined to high levels of ac cu racy are vital to achieve various functional requirements in engineering product s. In particular, the geometric accuracy of turned components play an important role in determining the form, fit and function of mechanical assembly requiremen ts. The geometric accuracy requirements of turned components are usually specifi ed in terms of roundness, straightness, cylindricity and concentricity. In pract ice, the accuracy specifications achievable are influenced by many factors such as component materials, production equipment, environmental factors, and machini ng process variables. While the sources of geometric errors due to materials, ma chinery and environment can be predicted to a large extent, the geometric accura cy due to the machining practice is unpredictable and difficult to determine. Since the fundamental geometric tolerances of work-pieces machined by tur ning a re sensitive to the cutting conditions, optimizing the cutting parameters such a s cutting speed, feed rate, and depth of cut is important for achieving the requ ired accuracy levels. Optimization studies of process variables in turning have not been well documented in the literature. Some experimental studies show the e ffect of process variables like cutting speed, feed rate and depth of cut on sur face roughness, production rate, production cost, etc. However, there have been no in-depth studies of the influence of the process variables on mechanical acc uracy related to the geometrical tolerances. In practice, a mechanical part usually consists of several geometrical features. For many mechanical parts, the geometric tolerances determine their functional characteristics. For example, diameter of a shaft and diameter of a hole decide the clearance of a cylindrical fit. The features of the cylindrical fit depend o n the dimensional tolerances of the size as well as several other geometrical to lerances like, roundness, cylindricity, and concentricity. In the study reported here, the dimensional and geometric tolerances achieved using turning experimen ts over a wide selection of cutting conditions will be used to analyze their inf luence on satisfying the functional requirements. The study will also show a met hodology of optimizing the process variables to achieve dimensional and geom etric tolerances to meet the requirements of specific functional features.

Precision Assessment of UAVRS Based DSM in Disaster Emergency

Ground control point (GCP) is important for georeferencing remotely sensed images and topographic model. However, considering that GCP collection is sometimes a difficult, time-consuming and expensive task with high resolution (HR) data in remote and harsh environments, today unmanned aerial vehicle based remote sensing (UAVRS) is frequently used in geological disaster emergency monitoring and rescuing for its great advantage in collecting timely onsite images. In this paper, for evaluating the feasibility of the UAVRS in disaster emergency and high cut slope safety monitoring, the digital surface model (DSM) without GCPs based on Structure from Motion (SfM) is accessed, and results showed that the geometric accuracy of DSM was smaller than 1 percent, which prove the usefulness of DSM based on UAVRS in emergency. Comparing to normal disaster emergency, the method without GCPs can be more efficient and save the disaster emergency time by neglecting GCPs measurement.

Improving georeferencing accuracy of Very High Resolution satellite imagery using freely available ancillary data at global coverage

While impressive direct geolocation accuracies better than 5.0 m CE90(90%of circular error)can be achieved from the last DigitalGlobe’s Very High Resolution(VHR)satellites(i.e.GeoEye-1 and WorldView-1/2/3/4),it is insufficient for many precise geodetic applications.For these sensors,the best horizontal geopositioning accuracies(around 0.55 m CE90)can be attained by using third-order 3D rational functions with vendor’s rational polynomial coefficients data refined by a zero-order polynomial adjustment obtained from a small number of very accurate ground control points(GCPs).However,these high-quality GCPs are not always available.In this work,two different approaches for improving the initial direct geolocation accuracy of VHR satellite imagery are proposed.Both of them are based on the extraction of three-dimensional GCPs from freely available ancillary data at global coverage such as multi-temporal information of Google Earth and the Shuttle Radar Topography Mission 30 m digital elevation model.The application of these approaches on WorldView-2 and GeoEye-1 stereo pairs over two different study sites proved to improve the horizontal direct geolocation accuracy values around of 75%.

A toolpath strategy for improving geometric accuracy in double-sided incremental sheet forming

The double-sided incremental forming(DSIF)improved the process flexibility compared to other incremental sheet forming(ISF)processes.Despite the flexible nature,it faces the challenge of low geometric precision like ISF variants.In this work,two strategies are used to overcome this.First,a novel method is employed to determine the optimal support tool location for improving geometric precision.In this method,the toolpath oriented the tools to each other systematically in the circumferential direction.Besides,it squeezed the sheet by the same amount at the point of interest.The impacts of various support tool positions in the circumferential direction are evaluated for geometric precision.The results demonstrate that the support tool should support the master tool within 10°to its local normal in the circumferential direction to improve the geometric accuracy.Second,a two-stage process reduced the geometric error of the part by incrementally accommodating the springback error by artificially increasing the step size for the second stage.With the optimal support tool position and two-stage DSIF,the geometric precision of the part has improved significantly.The proposed method is compared to the best DSIF toolpath strategies for geometric accuracy,surface roughness,forming time,and sheet thickness fluctuations using grey relational analysis(GRA).It outperforms the other toolpath strategies including single-stage DSIF,accumulative double-sided incremental forming(ADSIF),and two-stage mixed double sided incre-mental forming(MDSIF).Our approach can improve geometric precision in complex parts by successfully employing the support tool and managing the springback incrementally.

Analysis and Suppression of End Flare in AHSS Roll‑Formed Seat Rail

Roll forming has been widely used to manufacture long channels with complex cross-sections.End flare,one of the typical shape errors,seriously affects the forming accuracy of roll-formed parts,especially using advanced high-strength steel.In this paper,the mechanism of end flare during the roll forming process of a high-strength automobile seat rail is analyzed.The roll forming process of an actual seat rail is designed.The finite element models of the roll forming process and cut-off springback are established to predict the deformation process and occurrence of end flare.Simulation results indicate that the uneven distribution of longitudinal and shear residual stress along the length of the part is the main reason for the end flare.Based on the simulation,two strategies are proposed to mitigate the end flare.Employing multiple bending processes in the transverse direction effectively balances the longitudinal and shear residual stress.Additionally,the longitudinal bending process can make the longitudinal residual stress in the roll-formed parts more homogenised.Finally,verification experiments are carried out,and the forming accuracy of the seat rail is significantly improved.

An improved approach for the production of satellite-based geospatialreference imagery

An innovative and practical satellite image product is described that is ideal for applications in Northern Canada because of its wide area coverage and mappingquality features.This product is generated from a new procedure developed at the Canada Centre for Remote Sensing(CCRS)for processing Landsat 7 imagery,and by extension,imagery from other Earth Observation satellites.By working with multiple satellite passes,each containing the equivalent of multiple scenes,the new procedure could dramatically reduce the turn-around time for generating georeferenced image products,and also increase their geometric and radiometric accuracy compared to those produced by the current methods.The objective of the process has been to generate satellite image mosaics covering large areas(e.g.>500000 km^(2))with uniformly distributed errors at sub-pixel resolution.The paper discusses the theoretical basis of a photogrammetric adjustment for satellite imagery and the results obtained from several tests.The process is generic,involving a sensor model,a satellite orbit model and ground control information;thus it may be easily adapted to any satellite that allows for repeat coverage with overlapping paths.By performing an adjustment to correct the satellite position and attitude data prior to the production of orthoimage products,it is possible to create a mosaic with a single resampling process which minimises both the radiometric and geometric resampling artifacts.The results from three separate tests are presented,along with a discussion of the procedures that were followed in each case.All three tests have successfully demonstrated that sub-pixel sample size errors may be consistently obtained over large areas.A by-product process developed to support the measurement of ground control point coordinates for the satellite adjustment was the automatic matching of geographic features such as lakes and islands in vector data format.This has been a significant development in that it has eliminated manual intervention in the measurement of these features in the imagery,allowing the ground control for entire passes containing several scenes to be obtained in minutes instead of hours.