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Coordinate measuring machines (CMMs) are utilized to acquire coordinate data from manufactured surfaces for inspection reasons. These data are employed to gauge the geometric form errors associated with the surface. An optimization procedure of fitting a substitute surface to the measured points is applied to assess the form error. Since the traditional least-squares approach is susceptible to overestimation, it leads to unreasonable rejections. This paper implements a modified differential evolution (DE) algorithm to estimate the minimum zone femoral head sphericity. In this algorithm, opposition-based learning is considered for population initialization, and an adaptive scheme is enacted for scaling factor and crossover probability. The coefficients of the correlation factor and the uncertainty propagation are also measured so that the result's uncertainty can be determined. Undoubtedly, the credibility and plausibility of inspection outcomes are strengthened by evaluating measurement uncertainty. Several data sets are used to corroborate the outcome of the DE algorithm. CMM validation shows that the modified DE algorithm can measure sphericity with high precision and consistency. This algorithm allows for an adequate initial solution and adaptability to address a wide range of industrial problems. It ensures a proper balance between exploitation and exploration capabilities. Thus, the suggested methodology, based on the computational results, is feasible for the online deployment of the sphericity evaluation. The adopted DE strategy is simple to use, has few controlling variables, and is computationally less expensive. It guarantees a robust solution and can be used to compute different form errors. [ABSTRACT FROM AUTHOR]

Precision glass molding (PGM) is an effective approach to manufacturing infrared chalcogenide glass (ChG) aspherical lens with complex shapes. However, infrared ChG aspherical lens often experiences form error in the designed profile and the final profile obtained by PGM. To reduce the form error of infrared ChG aspherical lens in the PGM process, a form error compensation model based on the random forest (RF) algorithm is proposed. The infrared ChG aspherical lens profile was first machined on an electroless nickel-phosphorus (Ni–P) plating to serve as the mold for PGM. After molding, the profile data of the lens was extracted, and a compensation model based on RF was constructed to optimize the model parameters using the evaluation parameters such as root mean square error (RMSE), coefficient of determination (R2), and out-of-bag (OOB). Finally, the generated compensated profile based on the compensation model was used for the compensation machining of the mold. Through this compensation approach, we have demonstrated a substantial 63.5 % reduction in the form error of the fabricated infrared ChG aspherical lens, decreasing the Peak-to-Valley (PV) value from 1.04 μm to 0.38 μm. • We propose a novel aspherical mold compensation method based on the random forest algorithm, which is applied to precision molding of Infrared Chalcogenide Glass. • Aspherical mold machining is performed on the electroless nickel-phosphorus (Ni–P) surface for precision molding, and the profile data of lens are extracted for construct the mold compensation machining model. • Through this compensation approach, we have demonstrated a substantial 63.5 % reduction in the form error of the fabricated infrared Chalcogenide Glass aspherical lens, decreasing the Peak-to-Valley (PV) value from 1.04 μm to 0.38 μm. [ABSTRACT FROM AUTHOR]

In order to investigated the main influencing factors of the error averaging ability of the orifice-compensated air bearing, an error motion prediction model of a single air pad was established, and the defined averaging coefficient was used to discuss the quantitative relationship among the error motion of the air pad,the form error of the rail and the structural parameters of the air pad. The results show that, for the long waves of the rail form error (with wave number from 0 to 1), when the wave number gradually increases, the averaging coefficient gradually decreases from 1 to close to O. For the short waves of the rail form error (with wave number from 1 to 10), when the wave number is close to or equal to a positive integer, the average coefficient takes the minimum value close to 0. And when the wave number is close to or equal to a positive integer plus 0.5, the average coefficient takes the local maximum value less than 0.25. Among the structural parameters,the width of the air land has a great influence on the error averaging ability,while the air pad gap and the diameter of the orifice restrictor basically have no influence on the error averaging ability. When the moving speed is less than 10 000 mm/s, the moving speed has a very weak influence on the error averaging ability. [ABSTRACT FROM AUTHOR]

As one of key enabling technologies in digital twin-based assembly precision analysis, three dimensional (3D) assembly tolerance analysis technology has increasingly become an important means for predicting the assembly accuracy and verifying the assembly quality of mechanical assemblies. However, current methods exist some deficiencies that (i) the traditional model mostly cannot cover geometric tolerances or form errors in 3D assembly tolerance analysis, and (ii) a loss of assembly accuracy can be caused by ignoring these parallel connections in the assembly deviation propagation. To address these issues, this study proposes a novel assembly tolerance analysis method considering form errors and partial parallel connections with assembly accuracy and reliability guarantees in mechanical assemblies. First of all, through the integration of the unified Jacobian-Torsor model and skin model shapes, the resulting integrated Jacobian-skin model shapes model is presented, which contains the two advantages of easy-to-use tolerance propagation and geometric tolerance representation. Secondly, a novel improved approach combined with progressive contact method and algebraic operation is introduced into the assembly deviation propagation, which can realize the calculation of assembly relative positioning errors in both serial and partial parallel connections. Meanwhile, an overall calculation scheme of the proposed method is elaborated for assembly tolerance analysis with a statistical way, which is used to obtain the final deviation results of the assembly functional requirements (AFRs). At last, a typical mechanical assembly involving three parts is used as a case study to illustrate the effectiveness and feasibility of this solution. [ABSTRACT FROM AUTHOR]

During milling operations, regenerative and periodic forces are generated from the interactions of cutting tools and workpieces. While the regenerative forces can be preempted by proper choice of process parameters, the periodic forces cannot. The latter induce forced responses which leave behind imprints on machined parts causing, for example, tolerance concerns. Fortunately, the responses and thus the imprints can be mitigated by proper choice of parameters. In the published literature, the imprints seem to be predominantly named according to the type of analytical treatment of the problem. They are mostly called (surface) form error (SFE) when deemed to result from static deflections at instants of periodic forces while they are mostly called surface location error (SLE) when deemed to result from dynamic responses to the periodic forces. Both SFE and SLE are referred to as periodic force induced surface error (PFISE) here. This work presents a comprehensive literature review of the available PFISE modeling methods, including concise generic explanations of the analytical formulations and the solution algorithms. The review contains more than 340 literature references which also cover data-driven methods for which measurements/images of machined surface are used to generate point cloud of surface topography from which patterns of PFISE can be identified or empirical/black box models of surface errors (which include PFISE) can be calibrated. The results of PFISE modeling is usually applied in error compensation algorithms and, hence, works on such applications are also reviewed. This literature review unveils the trends of over 6 decades and still continuing research and recommends avenues to further the research in the future. [ABSTRACT FROM AUTHOR]

Coordinate measuring machines (CMMs) are utilized to acquire coordinate data from manufactured surfaces for inspection reasons. These data are employed to gauge the geometric form errors associated with the surface. An optimization procedure of fitting a substitute surface to the measured points is applied to assess the form error. Since the traditional least-squares approach is susceptible to overestimation, it leads to unreasonable rejections. This paper implements a modified differential evolution (DE) algorithm to estimate the minimum zone femoral head sphericity. In this algorithm, opposition-based learning is considered for population initialization, and an adaptive scheme is enacted for scaling factor and crossover probability. The coefficients of the correlation factor and the uncertainty propagation are also measured so that the result’s uncertainty can be determined. Undoubtedly, the credibility and plausibility of inspection outcomes are strengthened by evaluating measurement uncertainty. Several data sets are used to corroborate the outcome of the DE algorithm. CMM validation shows that the modified DE algorithm can measure sphericity with high precision and consistency. This algorithm allows for an adequate initial solution and adaptability to address a wide range of industrial problems. It ensures a proper balance between exploitation and exploration capabilities. Thus, the suggested methodology, based on the computational results, is feasible for the online deployment of the sphericity evaluation. The adopted DE strategy is simple to use, has few controlling variables, and is computationally less expensive. It guarantees a robust solution and can be used to compute different form errors.

In ultra-precision machining (UPM), position-independent geometric errors (PIGEs), i.e., squareness errors, have a crucial impact upon the form accuracy of a machined surface. Accordingly, more research work has been conducted in PIGE identification, to improve the form accuracy. However, the general identification methods were developed without consideration of the specific squareness errors for crucial PIGEs under the form errors of the machining process. Therefore, a new method with featured structures was proposed, to identify crucial PIGEs in UPM. Firstly, a volumetric error model was developed for PIGEs, to discuss the relationship between squareness errors and their resulting machining form errors. Secondly, following the developed model, some featured structures have been proposed with their machining form errors, to significantly indicate crucial PIGEs. Finally, a series of UPM and measuring experiments were conducted for the featured structures, and then their machining form errors were measured and extracted with specific squareness errors for the identification of crucial PIGEs. The theoretical and experimental results revealed that the proposed method is simple and efficient with the featured structures to accurately identify crucial PIGEs in UPM. Significantly, the study offers a deep insight into high-quality fabrication in UPM. [ABSTRACT FROM AUTHOR]

Evaluation of the deviation zone based on discrete measured points is crucial for quality control in manufacturing and metrology. However, deviation-zone evaluation is a highly nonlinear problem that is difficult to solve using traditional numerical optimization methods. Swarm intelligence has many advantages in solving this problem: it produces gradient-free, high-quality solutions and is characterized by its ease of implementation. Therefore, this study applies an improved Harris hawks algorithm (HHO) to tackle the problem. The average fitness is applied to replace the random operator in the exploration phase to solve the problem of conflicting exploration strategies due to randomness. In addition, the salp swarm algorithm (SSA) with a nonlinear inertia weight is embedded into the HHO, such that the superior explorative ability of SSA can fill the gap in the exploration of HHO. Finally, the optimal solution is greedily selected between SSA-based individuals and HHO-based individuals. The effectiveness of the proposed improved HHO optimizer is checked through a comparison with other swarm intelligence methods in typical benchmark problems. Moreover, the experimental results of form deviation-zone evaluation on primitive geometries show that the improved method can accurately solve various form deviations, providing an effective general solution for primitive geometries in the manufacturing and metrology fields. [ABSTRACT FROM AUTHOR]

Abstract Precision grinding is a key process for realizing the use of large-aperture aspherical optical elements in laser nuclear fusion devices, large-aperture astronomical telescopes, and high-resolution space cameras. In this study, the arc envelope grinding process of large-aperture aspherical optics is investigated using a CM1500 precision grinding machine with a maximum machinable diameter of Φ1500 mm. The form error of the aspherical workpiece induced by wheel setting errors is analytically modeled for both parallel and cross grinding. Results show that the form error is more sensitive to the wheel setting error along the feed direction than that along the lateral direction. It is a bilinear function of the feed-direction wheel setting error and the distance to the optical axis. Based on the error function above, a method to determine the wheel setting error is proposed. Subsequently, grinding tests are performed with the wheels aligned accurately. Using a newly proposed partial error compensation method with an appropriate compensation factor, a form error of 3.4 μm peak-to-valley (PV) for a Φ400 mm elliptical K9 glass surface is achieved.

Micro-lens array (MLA) has been widely used for 3D imaging, etc., due to its excellent functional performances. Ultra-precision diamond turning (UPDT) offers a satisfying solution to the high-quality fabrication of MLA with sub-micrometric form accuracy and nanometric surface roughness. However, in UPDT tool setting, errors would deteriorate form accuracy as a crucial factor. This study focuses on discussing the tool setting effect on form error of MLA and proposes a new two-step tool setting method for UPDT. Firstly, a theoretical model was established for form error of MLA under tool setting errors. Moreover, a new two-step tool setting method was developed with high accuracy to control the tool setting errors. Finally, a series of experiments were carried out with different tool setting errors for the MLA fabrication, and its form error would be measured. The theoretical and experimental results are found that the proposed tool setting method is effective with a high-precision accuracy and the tool setting errors would crucially induce periodical form error at the MLA of UPDT. Significantly, the study draws up a comprehensive understanding of the tool setting effect on form accuracy of MLA in UPDT with the further improvement. [ABSTRACT FROM AUTHOR]

X-ray computed tomography (XCT) provides a unique set of dimensional measurement capabilities suitable for assessing complex geometry. However, due to the origins of XCT as a medical imaging method and qualitative non-destructive examination technique, only recently has XCT been rigorously investigated as a dimensional metrology tool. Although the data produced via XCT may be leveraged with conventional coordinate metrology techniques, the instrument physics and volumetric reconstruction methods which govern the accuracy and precision of the data are complex, workpiece-specific, and non-negligible. In particular, there is minimal prior work which has studied complex multi-step metrology tasks such as datum reference frame (DRF) construction and feature position measurement. In this work, a qualified artifact was used to evaluate the fitness of XCT for such a task. Multiple XCT systems were used, and multiple instrument magnification levels compared. The form error of planar and cylindrical features was evaluated. Further, the influence of individual feature reconstruction on the development of datums and upstream position measurements was studied. It was found that negative, i.e., bore-like, and positive, i.e., pin-like configurations of certain features were subject to distinct XCT artifact effects which caused upstream measurement errors when these features were used to construct a DRF. High magnification and X-ray scatter produced high spatial frequency noise in surface reconstruction while beam hardening and beam penetration distance variation produced gross apparent form error. The latter was associated with greater measurement errors in feature position measurement within an DRF. • A qualified artifact was dimensionally inspected using XCT. • The position of an artifact feature within a datum reference frame was assessed. • Measurement errors were attributed to apparent feature form error in datum features. • Scanning artifacts caused by beam penetration distance variation limited accuracy. • Utilizing XCT for verification tasks as per GPS/GD&T requires expert implementation. [ABSTRACT FROM AUTHOR]

The article presents a literature review dealing with the effect of the honing parameters on the quality of the machined parts, as well as with the recent innovations in honing processes. First, an overview about the honing and the plateau-honing processes is presented, considering the main parameters that can be varied during machining. Then, the influence of the honing parameters on surface finish, shape deviation and material removal rate is presented. Finally, some special and innovative applications of the honing process are described. For example, honing with variable kinematics allows obtaining oil grooves that are not rectilinear but curvilinear, in order to reduce the temperature of the part during machining and thus achieving better surface finish and lower shape deviation. Automation of the honing machines is useful to improve both the production and the verification process. Another innovation consists of using 3D printed tools in honing processes, which will help to obtain abrasive tools with complex shapes, for example by means of powder bed fusion processes. [ABSTRACT FROM AUTHOR]

In the present paper the comparison of dimensional accuracy and form errors of FFF (Fused Filament Fabrication) 3D printed spur gears obtained in two different polymeric materials (PLA and Nylon-PA6) is presented. Two types of gears were designed and printed, having different module and teeth number. First, the gear modelling process is presented. The printing parameters were defined for both materials. Then, the measuring processes were described. Using the method of the sector span, the base circular thickness and the base pitch of the gears were determined. Additionally, the root and tip diameters were measured, and their roundness and concentricity errors were determined. The analysis of the results shows that, in general, PLA allows obtaining better dimensional accuracy than Nylon. Nylon parts, which were obtained with lower infill ratio than PLA parts showed lower from errors.

In ultra-precision machining (UPM), position-independent geometric errors (PIGEs), i.e., squareness errors, have a crucial impact upon the form accuracy of a machined surface. Accordingly, more research work has been conducted in PIGE identification, to improve the form accuracy. However, the general identification methods were developed without consideration of the specific squareness errors for crucial PIGEs under the form errors of the machining process. Therefore, a new method with featured structures was proposed, to identify crucial PIGEs in UPM. Firstly, a volumetric error model was developed for PIGEs, to discuss the relationship between squareness errors and their resulting machining form errors. Secondly, following the developed model, some featured structures have been proposed with their machining form errors, to significantly indicate crucial PIGEs. Finally, a series of UPM and measuring experiments were conducted for the featured structures, and then their machining form errors were measured and extracted with specific squareness errors for the identification of crucial PIGEs. The theoretical and experimental results revealed that the proposed method is simple and efficient with the featured structures to accurately identify crucial PIGEs in UPM. Significantly, the study offers a deep insight into high-quality fabrication in UPM.

Precision grinding is a key process for realizing the use of large-aperture aspherical optical elements in laser nuclear fusion devices, large-aperture astronomical telescopes, and high-resolution space cameras. In this study, the arc envelope grinding process of large-aperture aspherical optics is investigated using a CM1500 precision grinding machine with a maximum machinable diameter of Φ1500 mm. The form error of the aspherical workpiece induced by wheel setting errors is analytically modeled for both parallel and cross grinding. Results show that the form error is more sensitive to the wheel setting error along the feed direction than that along the lateral direction. It is a bilinear function of the feed-direction wheel setting error and the distance to the optical axis. Based on the error function above, a method to determine the wheel setting error is proposed. Subsequently, grinding tests are performed with the wheels aligned accurately. Using a newly proposed partial error compensation method with an appropriate compensation factor, a form error of 3.4 μm peak-to-valley (PV) for a Φ400 mm elliptical K9 glass surface is achieved. [ABSTRACT FROM AUTHOR]

Surface reconstruction is an essential operation in the evaluation of free-form surface form error. As a feasible technology in free-form surface sampling, touch-trigger probing has been widely used in on-machine measurement and coordinate measurement machine. However, surface reconstruction quality is influenced by limited sampling point size. This study proposes a surface reconstruction method based on surface position error and deformation error model. Surface form error is decomposed into surface position error and deformation error. Then, the design surface is taken as a rigid body, and a point-to-surface function-based iterative algorithm is conducted to adjust surface location and orientation to best match the sampling points. The advantage of this algorithm is that it considers the probe dimension, so further compensation of probe radius is not required. The geometry of the adjusted design surface is modified based on thin plate energy minimization and point-to-surface function. Due to the inherent feature of the proposed method, geometric features of the design surface are kept. Experiments are conducted to verify the effectiveness of the proposed method, and results show that the proposed method can achieve lower error compared with existing methods. • Surface location error and deformation error are defined and computed to evaluate the form error. • Geometry of the measured surface is modified based on thin plate energy minimization and point-to-surface function. • Experiment results show that the reconstruction accuracy is improved by 37.9%, compared with an existing method. [ABSTRACT FROM AUTHOR]

Evaluation of the deviation zone based on discrete measured points is crucial for quality control in manufacturing and metrology. However, deviation-zone evaluation is a highly nonlinear problem that is difficult to solve using traditional numerical optimization methods. Swarm intelligence has many advantages in solving this problem: it produces gradient-free, high-quality solutions and is characterized by its ease of implementation. Therefore, this study applies an improved Harris hawks algorithm (HHO) to tackle the problem. The average fitness is applied to replace the random operator in the exploration phase to solve the problem of conflicting exploration strategies due to randomness. In addition, the salp swarm algorithm (SSA) with a nonlinear inertia weight is embedded into the HHO, such that the superior explorative ability of SSA can fill the gap in the exploration of HHO. Finally, the optimal solution is greedily selected between SSA-based individuals and HHO-based individuals. The effectiveness of the proposed improved HHO optimizer is checked through a comparison with other swarm intelligence methods in typical benchmark problems. Moreover, the experimental results of form deviation-zone evaluation on primitive geometries show that the improved method can accurately solve various form deviations, providing an effective general solution for primitive geometries in the manufacturing and metrology fields.

[Display omitted] • Over smoothing of filtering is identified as one of the major sources of on-machine compensation in fabrication of structured surface. • A novel on-machine profile error evaluation and compensation strategy based on anisotropic diffusion filter is proposed. • The proposed method controlled the form error of high aspect ratio structured surface at the scale of submicron. Structured surfaces with high aspect ratio are promising in optical components, healthcare devices, and microelectronics. A preferable method to create precise structured surfaces is using single point diamond turning with on-machine surface measurement (OMSM). However, fabricating these surfaces often pose challenges due to steep gradients and discontinuous slopes, leading to significant form errors in machining. We propose an innovative solution by employing partial differential equation (PDE) filtration in a closed loop compensation process to enhance form accuracy and surface roughness compared to traditional methods. We tackle the problem of over-smoothing induced profile error encountered with traditional Gaussian filters. The proposed compensation strategy adapts to surface curvature and reduces instrument noise during on-machine measurements. Experimental of fabricating a segment spherical artefact, demonstrate improved precision. After adopting the proposed method, the form error is reduced from 1.2 µm to 0.5 µm and vibration ripples are mitigated, and a better surface finish is achieved. [ABSTRACT FROM AUTHOR]

This study investigated a novel methodology called equivalent-sphere swing grinding (ESSG) for the cup wheel grinding of large revolving aspheric and spherical surfaces. The method is proposed to improve the machining efficiency and reduce the complexity of machine tools. Different from the traditional single-point grinding of aspheric surfaces, the ESSG method developed a novel multipoint grinding process to increase the material removal rate (MRR) and reduce the wear of single abrasive grain. A structure with few axes and a wheel spindle with multi degrees of freedom simplifies the machine tools and improves the machine dynamic stiffness. The grinding process was modeled, and the feasibility for grinding aspheric and spherical surfaces was verified. The criteria for ESSG-based grinding method were established, and the wheel position and posture models were derived. The cup wheel posture was proved to have multiple options for grinding a revolving surface, in which the optimal posture can achieve the maximum number of abrasive particles involved in grinding and maximize MRR under the same wheel wear. The numerical trajectory control parameters were calculated, and a hierarchical grinding method is proposed. An experiment was conducted on a developed grinding machine prototype. The results indicate that the proposed methodology can efficiently grind paraboloid surfaces and can be extended to grinding other revolving aspheric and spherical surfaces. [ABSTRACT FROM AUTHOR]

The article presents a literature review dealing with the effect of the honing parameters on the quality of the machined parts, as well as with the recent innovations in honing processes. First, an overview about the honing and the plateau-honing processes is presented, considering the main parameters that can be varied during machining. Then, the influence of the honing parameters on surface finish, shape deviation and material removal rate is presented. Finally, some special and innovative applications of the honing process are described. For example, honing with variable kinematics allows obtaining oil grooves that are not rectilinear but curvilinear, in order to reduce the temperature of the part during machining and thus achieving better surface finish and lower shape deviation. Automation of the honing machines is useful to improve both the production and the verification process. Another innovation consists of using 3D printed tools in honing processes, which will help to obtain abrasive tools with complex shapes, for example by means of powder bed fusion processes.

This paper is concerned with the generation of numerical artefacts, that is, reference data sets, for assessing the accuracy and fitness of purpose of software for computing minimum zone (MZ, Chebyshev) associated features. We describe an algorithm for generating datasets corresponding to a pre-specified best-fit surface and form error. We use a Gaussian process model to generate form errors that are spatially correlated. The form errors can be drawn from multivariate Gaussian or rectangular distributions. For the latter case a Gaussian copula is used to construct a multivariate multivariate distribution with the pre-assigned correlation. We illustrate the data generation on MZ circle fitting problems. We also describe an approximate MZ circle fitting problem that can be solved using linear programming.

Form error is the departure of a manufactured part from its design or ideal shape, and is a key characteristic to be assessed in quality engineering in manufacturing. In practice, form errors are usually estimated from coordinate measurements involving only a finite number of measured points and the form error for the complete workpiece surface has to be inferred on the basis of these measurements. This paper is about determining whether a product meets its specifications based on its form error using a probabilistic model. Based on form error data and a product specification, the relationship between conformance testing and making decisions is established. In this paper, we define a form error model using a uniform distribution with unknown bounds, and then utilize a Bayesian approach to assign a distribution to the form error parameter and use this distribution in a conformity and risk assessment methodology to quantify the risk of incorrect decisions. The risk assessment is carried out using derived expressions of specific risks associated with product conformity. A slightly more extensive posterior model, taking into consideration the probable random effects of form errors, is discussed for the reader's interest. Numerical experiments illustrate the effectiveness of this approach by providing a decision framework to control the risks associated with making a wrong decision.

To accurately characterize the geometric form of key components in industrial products, many profile measuring instruments have been developed to date. However, there are some special components, such as the hemispherical resonators featuring thin curved transparent surfaces, which are difficult to be measured using general instruments. The chromatic confocal technology was introduced in this paper to conduct the bilateral form characterization of this type of surfaces. Based on the assumption of tilted plate approximation, a modified ray tracing model was presented to correct the errors produced by the curved surfaces. The experiment of measurement on tilted, fused silica plates was conducted to demonstrate the effectiveness of the proposed model. Results show that the developed model improves the measurement accuracy of plates with large tilt angle. A three-axis motion stage was built with self-developed chromatic confocal sensor to obtain the bilateral profiles of the resonator. By fitting the spheres with the scanning profiles, the form error between the measurement points and the fitted spheres can be calculated. Partial form errors along the circumferential and axial directions of the resonator are evaluated, and an intuitive assessment of its thickness variation along the circumferential direction was made. [ABSTRACT FROM AUTHOR]

The prospect of utilizing freeform optics to develop a more compact and smaller VLC receiver front-end is explored in this study for a multi-cell indoor environment. A novel freeform surface element (FSE) has been fabricated by an ultra-precision single-point diamond turning (SPDT) machine and characterized by the mechanical and optical profiler to investigate its potential use inside a freeform diversity receiver. A 9 dB increment in average signal-to-interference-plus-noise-ratio (SINR) is observed after third iteration while the form error reduces to 1.92 µm. The communication functionality of the fabricated FSE is also validated experimentally. The average SINR over the communication floor is computed as 109.29 dB. The fabricated freeform element is further modified to a freeform Fresnel profile for more compactness. The result shows, a substantial decrease in receiver height (2.314 mm) is possible using the proposed approach. Moreover, different fabrication challenges related with freeform Fresnel have been identified and discussed to set the future research pathway. [ABSTRACT FROM AUTHOR]

In the present paper the comparison of dimensional accuracy and form errors of FFF (Fused Filament Fabrication) 3D printed spur gears obtained in two different polymeric materials (PLA and Nylon-PA6) is presented. Two types of gears were designed and printed, having different module and teeth number. First, the gear modelling process is presented. The printing parameters were defined for both materials. Then, the measuring processes were described. Using the method of the sector span, the base circular thickness and the base pitch of the gears were determined. Additionally, the root and tip diameters were measured, and their roundness and concentricity errors were determined. The analysis of the results shows that, in general, PLA allows obtaining better dimensional accuracy than Nylon. Nylon parts, which were obtained with lower infill ratio than PLA parts showed lower from errors. • Spun gears having different modulus and teeth number are obtained with FFF. • Nylon gears have higher dimensional error than PLA gears. • PLA gears have higher roundness and concentricity errors than Nylon gears. [ABSTRACT FROM AUTHOR]

• A two-stage methodology for form error inspection of free-form surfaces is proposed. • This novel methodology is specific to CMM operated in discrete scanning mode. • The effective time complexity of the method is O(m log n). • The form-error estimate step is 8x times faster than the point-inversion method. • The accuracy of the method is on par with that of point-inversion method. Coordinate Measuring Machines (CMM) are widely used in form inspection of free-form surfaces. Generally, the form error at each measured point is estimated using the widely known and accurate point-inversion method. This method has relatively high time complexity and cannot be preferred for fast inspection. Hence in this work, an alternative two-stage methodology based on the concept of the Voronoi diagram is proposed. In the first stage, the poles data is extracted from the Voronoi diagram of the discretized surface. In the second stage, the form-error-estimate algorithm executing in O(m log n) time estimates the errors using the poles data and the discretized surface. Numerical and experimental implementations are executed using NURBS surfaces. The proposed method's accuracy is on par with the point-inversion method and is 94.97% faster than the latter. Hence this method can be used for fast and accurate CMM and CNC based (in-situ) free-form surface inspection. [ABSTRACT FROM AUTHOR]