Research on the Orientation Error of the Translational Cable-Driven Parallel Robots

Parallel cables are gradually widely used in cable-driven parallel robots (CDPR) to provide constraints to the end effector and to realize translational degrees of freedom. However, when there are dimensional errors, parallel cables become no longer parallel and will cause terminal attitude errors, which can’t be compensated by kinematic calibration. In this paper, the attitude assurance method is studied considering a three DOFs translational CDPR. Firstly, the kinematic model and error mapping model of the robot is established by using the closed-loop method, considering the pulley radius. Secondly, the influence of the dimensional parameter errors on the terminal error is analyzed with the sensitivity index, which establishes a theoretical basis for the simplification of the accuracy synthesis process. Thirdly, the design tolerances of the cable connection points are determined through accuracy synthesis, which is implemented with the genetic algorithm considering the optimal manufacturing cost and ensure the attitude accuracy of the end effector. Finally, to reduce the influence of cable length error, the method of adjusting the initial pose was proposed and studied, which is verified as an effective approach.

Automated Storey Separation and Door and Window Extraction for Building Models from Complete Laser Scans

Heritage buildings are often lost without being adequately documented. Significant research has gone into automated building modelling from point clouds, challenged by irregularities in building design and the presence of occlusion-causing clutter and non-Manhattan World features. Previous work has been largely focused on the extraction and representation of walls, floors, and ceilings from either interior or exterior single storey scans. Significantly less effort has been concentrated on the automated extraction of smaller features such as windows and doors from complete (interior and exterior) scans. In addition, the majority of the work done on automated building reconstruction pertains to the new-build and construction industries, rather than for heritage buildings. This work presents a novel multi-level storey separation technique as well as a novel door and window detection strategy within an end-to-end modelling software for the automated creation of 2D floor plans and 3D building models from complete terrestrial laser scans of heritage buildings. The methods are demonstrated on three heritage sites of varying size and complexity, achieving overall accuracies of 94.74% for multi-level storey separation and 92.75% for the building model creation. Additionally, the automated door and window detection methodology achieved absolute mean dimensional errors of 6.3 cm.

Analyzing the Effects of the Kinematic System on the Quality of Holes Drilled in 42CrMo4 + QT Steel

This article discusses the relationship between the kinematic system used in drilling and the quality of through-holes. The drilling was done on a CTX Alpha 500 universal turning center using a TiAlN-coated 6.0 mm drill bit with internal cooling, mounted in a driven tool holder. The holes were cut in cylindrical 42CrMo4 + QT steel samples measuring 30 mm in diameter and 30 mm in length. Three types of hole-drilling kinematic systems were considered. The first consisted of a fixed workpiece and a tool performing rotary (primary) and linear motions. In the second system, the workpiece rotated (primary motion) while the tool moved linearly. In the third system, the workpiece and the tool rotated in opposite directions; the tool also moved linearly. The analysis was carried out for four output parameters characterizing the hole quality (i.e., cylindricity, straightness, roundness, and diameter errors). The experiment was designed using the Taguchi approach (orthogonal array). ANOVA multi-factor statistical analysis was used to determine the influence of the input parameters (cutting speed, feed per revolution and type of kinematic system) on the geometrical and dimensional errors of the hole. From the analysis, it is evident that the kinematic system had a significant effect on the hole roundness error.

On-Line Compensation for Micromilling of High-Aspect-Ratio Straight Thin Walls

In order to improve the machining quality and reduce the dimensional errors of micro high-aspect-ratio straight thin walls, the on-line cutting parameter compensation device has been introduced and corresponding micromilling processes have been investigated. Layered milling strategies for the micromilling of thin walls have been modeled and simulated for thin walls with different thicknesses based on the finite element method. The radial cutting parameters compensation method is adopted to compensate the thin wall deformation by raising the radial cutting parameters since the thin wall deformation make the actual radial cutting parameters smaller than nominal ones. The experimental results show that the dimensional errors of the thin wall have been significantly reduced after the radial cutting parameter compensation. The average relative dimensional error is reduced from 6.9% to 2.0%. Moreover, the fabricated thin walls keep good shape formation. The reduction of the thin wall dimensional error shows that the simulation results are reliable, which has important guiding significance for the improvement of thin wall machining quality, especially the improvement of dimensional accuracy. The experimental results show that the developed device and the machining strategy can effectively improve the micromilling quality of thin walls.

Review on Quality Control Methods in Metal Additive Manufacturing

Metal additive manufacturing (AM) has several similarities to conventional metal manufacturing, such as welding and cladding. During the manufacturing process, both metal AM and welding experience repeated partial melting and cooling, referred to as deposition. Owing to deposition, metal AM and welded products often share common product quality issues, such as layer misalignment, dimensional errors, and residual stress generation. This paper comprehensively reviews the similarities in quality monitoring methods between metal AM and conventional metal manufacturing. It was observed that a number of quality monitoring methods applied to metal AM and welding are interrelated; therefore, they can be used complementarily with each other.

Analysis and Experimental Verification of Mechanical Errors in Nine-Link Type Double-Toggle Mold/Die Clamping Mechanisms

Nine-link type double-toggle mold/die clamping mechanisms are widely used in modern injection molding machines and die casting machines in order to provide sufficient mold/die clamping force for counteracting the pressure occurred inside molds/dies. In this paper, the analysis and experimental evaluation of mechanical errors in nine-link type double-toggle mold/die clamping mechanisms are presented. The kinematic error equations of the output link (i.e., the moving platen) caused by dimensional errors (or tolerances) of link members are derived analytically through the concept of tolerance sensitivity analysis. Evaluation indices based on the asymmetry of the mold/die clamping mechanism caused by mechanical errors are established. A case study is then given to demonstrate the derived analytical equations and the established evaluation indices. Subsequently, a prototype for performing the experimental evaluation is conceptually designed and was actually constructed. Experiments were conducted for evaluating the quantitative influence of mechanical errors on the operating performance of the constructed mold/die clamping mechanism. According to the experimental results, response surface modelling for benefiting the constructed mold/die clamping mechanism with better operating performance could be performed. The presented research results will be helpful in the tolerance analysis and mechanical error detection of nine-link type double-toggle mold/die clamping mechanisms.

Determination of the errors first component in the tolerance field structure of the inter-transition size for the transformation of geometric elements in the structure of the initial blanks

To determine the errors first component in the tolerance field structure of the inter-transition size the knowledge base of the production technological preparation by seven levels of its basic objects of functionally different types is used. The task is solved in the working space of working machines, in the structure of which two technological schemes are built: for basing the initial blanks in working machines and for basing form elements in working machines and their geometric forming on working machines. Technological schemes for basing the initial blanks into working machines in the general case have a significant impact on the geometric and dimensional errors (the considered component) of the shape elements to be converted in the technological schemes for basing form elements into working machines and their geometric forming on working machines. It is shown that the determination of the errors first component in the tolerance field structure of the inter-junction size must be carried out by means of specialized intelligent control and measuring systems, embedding them in the structure of working machines. Determination of the first component in the tolerance field structure of the inter-transition size is relevant, has scientific novelty and practical significance. Keywords technological preparation of production; cutting processing; system analysis; information technology; modeling solutions; systems technology

Anthropometric Landmarks Extraction and Dimensions Measurement Based on ResNet

Anthropometric dimensions can be acquired in 2D images by landmarks. Body shape variance causes low accuracy and bad robustness of landmarks extracted, and it is difficult to determine the position of axis division point when dimensions are calculated by the ellipse model. In this paper, landmarks are extracted from images by convolutional neural network instead of the gradient of body outline. A general multi-ellipse model is proposed, the anthropometric dimensions are obtained from the length of different elliptical segments and the position of axis division point is determined by thickness–width ratio of body parts. Finally, an evaluation is completed based on 87 subjects, in which it turns out that the average accuracy of our method for identifying landmarks is 96.6%, when the number of rotation angles is 2, the three main dimensional errors calculated by our model are smaller than existing method, and the errors of other dimensions are also within the margin of error for garment measuring.

Novel 500-GHz Band Waveguide Stepped Septum-Type Circular Polarizer with a New High-Accuracy and Very Small Waveguide Flange

A new waveguide stepped septum-type circular polarizer (SST-CP) was developed to operate in the 500-GHz band for radio astronomical and planetary atmospheric observations. In a previous study, we developed a practical SST-CP for the 230-GHz band. However, several issues prevent this device being easily scaled down to the 500-GHz band, such as manufacturing dimensional errors and waveguide flange position errors. In this study, we developed a new waveguide flange with a high-accuracy position determination mechanism and a very small size of 10 × 10 mm. We also developed a new fabrication technique to obtain very good flatness for the device’s blank materials by high-accuracy polishing using a resin fixture. Using these new methods, the manufactured 500-GHz band SST-CP achieved a cross-polarization talk level of better than – 30 dB at 465–505 GHz, a device surface flatness of within 3 μm, and also the horizontal positioning error of ± 3 μm. These results indicate that the developed 500-GHz band SST-CP has high performance in the high-frequency band, and thus the new manufacturing methods are effective in the 500-GHz band.

Repeatability and Reproducibility Assessment of a PolyJet Technology Using X-ray Computed Tomography

From the very start of their use until today, processes in Additive Manufacturing (AM) have found a way to grow from prototype production to individual and small-series production. Improvements in machinery, materials and other challenges in AM development have improved product quality, its mechanical properties and dimensional accuracy. Research in the field of dimensional accuracy must be focused on achieving better tolerances. From the beginning of AM, there has been a big issue in assuring dimensional repeatability and reproducibility of a part being printed over the course of several days. In order to examine that, a test plate was designed and built repeatedly with PolyJet technology over the course of several weeks. Measurements of dimensional accuracy and shape deviations of several typical features were carried out using X-ray Computed Tomography. Measurement results were analysed and presented in order to indicate the repeatability and reproducibility of PolyJet AM technology. Results show that PolyJet technology consistently produces parts within ±100 μm, at a 95% confidence interval, under reproducibility conditions of over a 1-month period. Accuracy for measurands (distance) in the x and y axis was significantly better than it was for the z axis which was from 56 to 197 µm, i.e., in the x and y axis, it was from −8 to 76 µm. Shape errors (i.e., cylindricity) were larger than positional or dimensional errors; this can be attributed to relatively large surface roughness and small feature sizes on the test plate that was used.